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Collins-McIntyre, Liam James. "Transition-metal doped Bi2Se3 and Bi2Te3 topological insulator thin films." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:480ea55a-5cac-4bab-a992-a3201f10f4c5.
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Topological insulators (TIs) are recently predicted, and much studied, new quantum materials. These materials are characterised by their unique surface electronic properties; namely, behaving as band insulators within their bulk, but with spin-momentum locked surface or edge states at their interface. These surface/edge crossing states are protected by the underlying time-reversal symmetry (TRS) of the bulk band structure, leading to a robust topological surface state (TSS) that is resistant to scattering from impurities which do not break TRS. Their surface band dispersion has a characteristic crossing at time reversal invariant momenta (TRIM) called a Dirac cone. It has been predicted that the introduction of a TRS breaking effect, through ferromagnetic order for instance, will open a band-gap in this Dirac cone. It can be seen that magnetic fields are not time reversal invariant by considering a solenoid. If time is reversed, the current will also reverse in the solenoid and so the magnetic field will also be reversed. So it can be seen that magnetic fields transform as odd under time reversal, the same will be true of internal magnetisation. By manipulating this gapped surface state a wide range of new physical phenomena are predicted, or in some cases, already experimentally observed. Of particular interest is the recently observed quantum anomalous Hall effect (QAHE) as well as, e.g., topological magneto-electric effect, surface Majorana Fermions and image magnetic monopoles. Building on these novel physical effects, it is hoped to open new pathways and device applications within the emerging fields of spintronics and quantum computation. This thesis presents an investigation of the nature of magnetic doping of the chalcogenide TIs Bi<sub>2</sub>Se<sub>3</sub> and Bi<sub>2</sub>Te<sub>3</sub> using 3d transition-metal dopants (Mn and Cr). Samples were grown by molecular beam epitaxy (MBE), an ideal growth method for the creation of high-quality thin film TI samples with very low defect densities. The grown films were investigated using a range of complementary lab-based and synchrotron-based techniques to fully resolve their physical structure, as well as their magnetic and electronic properties. The ultimate aim being to form a ferromagnetic ground state in the insulating material, which may be expanded into device applications. Samples of bulk Mn-doped Bi<sub>2</sub>Te<sub>3</sub> are presented and it is shown that a ferromagnetic ground state is formed below a measured T<sub>C</sub> of 9-13 K as determined by a range of experimental methodologies. These samples are found to have significant inhomogeneities within the crystal, a problem that is reduced in MBE-grown crystals. Mn-doped Bi<sub>2</sub>Se<sub>3</sub> thin films were grown by MBE and their magnetic properties investigated by superconducting quantum interference device (SQUID) magnetometry and x-ray magnetic circular dichroism (XMCD). These reveal a saturation magnetisation of 5.1 μ<sub>B</sub>/Mn and show the formation of short-range magnetic order at 2.5 K (from XMCD) with indication of a ferromagnetic ground state forming below 1.5 K. Thin films of Cr-doped Bi<sub>2</sub>Se<sub>3</sub> were grown by MBE, driven by the recent observation of the QAHE in Cr-doped (Bi<sub>1−x</sub>Sb<sub>x</sub>)<sub>2</sub>Te<sub>3</sub>. Investigation by SQUID shows a ferromagnetic ground state below 8.5 K with a saturation magnetisation of 2.1 μ<sub>B</sub>/Cr. Polarised neutron reflectometry shows a uniform magnetisation profile with no indication of surface enhancement or of a magnetic dead layer. Further studies by extended x-ray absorption fine structure (EXAFS) and XMCD elucidate the electronic nature of the magnetic ground state of these materials. It is found that hybridisation between the Cr d and Se p orbitals leads to the Cr being divalent when doping on the Bi<sup>3+</sup> site. This covalent character to the electronic structure runs counter to the previously held belief that divalent Cr would originate from Cr clusters within the van der Waals gap of this material. The work overall demonstrates the formation of a ferromagnetic ground state for both Cr and Mn doped material. The transition temperature, below which ferromagnetic order is achieved, is currently too low for usable device applications. However, these materials provide a promising test bed for new physics and prototype devices.
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Wolf, Michael Scott. "Infrared and Optical Studies of Topological Insulators BI2TE3 BI2SE3 and SB2TE3." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1310675743.
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Ghasemi, Arsham. "Atomic structure of thin films and heterostructure of Bi2Te3 and Bi2Se3 topological insulators." Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/18907/.
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The atomic structure of transition metals doped three dimensional (3D) topological insulators (TIs) and the bonding nature of Bi2Te3 with FeSe layers and Ge(111) substrate were studied. Motivation behind transition metal doping of 3D TIs is driven by achieving long range ferromagnetism of Bi2Se3 and Bi2Te3, which is expected to give rise to different spintronic effects that can be utilise in device applications. The nature of this magnetisation depends on the location of the dopants in the Bi chalcogenide matrix. Dopants in Bi based TIs can substitute for Bi, Te, or incorporate between the quintuple layers in the van der Waals gap. Long range ferromagnetism is observed in both Cr doped Bi2Se3 and Mn doped Bi2Te3; however, the main goal of achieving room-temperature ferromagnetism in homogeneously doped TIs has proven to be difficult. In this thesis it is shown that 4.6 at-% of Cr is incorporated substitutionally on Bi sites with no phase segregation. The presences of grain boundaries can cause Cr segregation; hence by controlling the defect density a homogeneous Cr distribution could in principle be achieved even at higher concentrations. In case of Mn as a dopant, we show that the local environment of Mn in Bi2Te3 is heterogeneous. The first principal calculations revealed that the Mn dopants ferromagnetically couple in Bi2Te3 lattice. In addition, we have shown that doping of Bi2Te3 with Mn should be limited to low concentrations (< 6 at-%), higher dopants concentrations results in the formation of secondary phases. Next we have demonstrated that epitaxial growth of FexCu1-xSe on Bi2Te3 is possible regardless of their different lattice symmetries and large lattice mismatch of 19%. First-principles energy calculations revealed that this is realised through van der Waals-like bonding between the Se and Te atomic planes at the interface. Finally, we have shown that the weak van der Waals bonding between the Bi2Te3 and Ge(111) substrate can be strengthen by formation of a Te monolayer at the interface. The electronic band structure calculations revealed that this is due to the stronger atomic p-type orbital hybridization at the interface.
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Adhikari, Pan P. "Optical Study of Inter-band Transitions in Topological Insulators Bi2Se3, Bi2Te3, and Sb2Te3." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1497994862971012.
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Chitroub, Mohamed. "Etude des propriétés thermoélectriques de Bi2Te3 et des alliages Bi2Te3, Bi2Se3 en fonction des écarts à la stoéchiométrie." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37596703g.
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Ribeiro, Guilherme Almeida Silva. "Estudo por primeiros princípios das propriedades estruturais e eletrônicas dos compostos Bi2Te3 e Bi2Se3." Universidade Federal de Minas Gerais, 2013. http://hdl.handle.net/1843/BUBD-9FTHU5.
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The understanding of the physical properties of topological insulators has been a very active field in the past few years. These materials are strong candidates for spintronics applications due to their unusual electronic properties. In this text, we present a brief introduction to the theory concerning these materials, and an abinitio study of the electronic and structural properties of the compounds Bi2Te3 and Bi2Se3. First, we discuss the quantum spin-Hall effct and an effective model to describe the 2D and 3D topological insulators. After that, we present the methodology of the density functional theory, which was employed in our calculations, and we discuss two distinct problems. In the first one, we worked with the experimental group of Prof. Rogério Paniago (Physics department, UFMG) in order to investigate the surface termination of the topological insulator Bi2Te3 after cleavage, and after a thermal treatment. Our results suggest that a bismuth bilayer appears on the top of the surface. In the second work, carried out in collaboration with the surface physics group from UFMG, we studied the structural properties of the topological insulator Bi2Se3. We show that there is not a significant structural reconstruction between superficial layers, which interact by van der Waals forces, and, therefore, this fact should not be responsible for the presence of additional electronic states which are observed in these compounds after cleavage.<br>O entendimento das propriedades físicas de isolantes topológicos tem sido um campo muito ativo nos últimos anos. Esses materiais são fortes candidatos para aplicações em spintrônica, graças a suas propriedades eletrônicas não usuais. Neste texto, apresentamos uma breve introdução à teoria que permeia esses materiais, e um estudo por primeiros princípios das propriedades eletrônicas e estruturais dos compostos Bi2Te3 e Bi2Se3. Primeiramente, discutimos o efeito spin-Hall quântico e um modelo efetivo para descrever os isolantes topológicos 2D e 3D. Em seguida, apresentamos a metodologia da teoria do funcional da densidade empregada em nossos cálculos, e discutimos dois problemas distintos. No primeiro, trabalhamos em colaboração com o grupo do Prof. Rogério Paniago (Física, UFMG) para caracterizar a terminação de superfície do isolante topológico Bi2Te3 quando tratada termicamente após clivagem. Nossos resultados sugerem o aparecimento de uma bicamada de bismuto sobre a superfície do material. Em um segundo trabalho, feito em colaboração com o grupo de física de superfícies da UFMG, estudamos as propriedades estruturais do isolante topológico Bi2Se3. Mostramos que não há uma relaxação estrutural significativa entre camadas superficiais que interagem por forças de van der Waals, e que, portanto, tal fato não deve ser responsável por estados eletrônicos adicionais que foram observados nesses compostos após a clivagem de suas superfícies.
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Veyrat, Louis. "Quantum Transport Study in 3D Topological Insulators Nanostructures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-210217.
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In this thesis, we investigate the quantum transport properties of disordered three dimensional topological insulator (3DTI) nanostructures of BiSe and BiTe in detail. Despite their intrinsic bulk conductivity, we show the possibility to study the specific transport properties of the topological surface states (TSS), either with or without quantum confinement. Importantly, we demonstrate that unusual transport properties not only come from the Dirac nature of the quasi-particles, but also from their spin texture.
Without quantum confinement (wide ribbons), the transport properties of diffusive 2D spin-helical Dirac fermions are investigated. Using high magnetic fields allows us to measure and separate all contributions to charge transport. Band bending is investigated in BiSe nanostructures, revealing an inversion from upward to downward bending when decreasing the bulk doping. This result points out the need to control simultaneously both the bulk and surface residual doping in order to produce bulk-depleted nanostructures and to study TSS only. Moreover, Shubnikov-de-Haas oscillations and transconductance measurements are used to measure the ratio of the transport length to the electronic mean free path ltr/le. This ratio is measured to be close to one for bulk states, whereas it is close to 8 for TSS, which is a hallmark of the anisotropic scattering of spin-helical Dirac fermions.
With transverse quantum confinement (narrow wires or ribbons), the ballistic transport of quasi-1D surface modes is evidenced by mesoscopic transport measurements, and specific properties due to their topological nature are revealed at very low temperatures. The metallic surface states are directly evidenced by the measure of periodic Aharonov-Bohm oscillations (ABO) in 3DTI nanowires. Their exponential temperature dependence gives an unusual power-law temperature dependence of the phase coherence length, which is interpreted in terms of quasi-ballistic transport and decoherence in the weak-coupling regime. This remarkable finding is a consequence of the enhanced transport length, which is comparable to the perimeter. Besides, the ballistic transport of quasi-1D surface modes is further evidenced by the observation of non-universal conductance fluctuations in a BiSe nanowire, despite the long-length limit (L > ltr) and a high metallicity (many modes). We show that such an unusual property for a mesoscopic conductor is related to the limited mixing of the transverse modes by disorder, as confirmed by numerical calculations. Importantly, a model based on the modes' transmissions allows us to describe our experimental results, including the full temperature dependence of the ABO amplitude.
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Nowka, Christian. "Untersuchungen zu Gasphasentransporten in quasibinären Systemen von Bi2Se3 mit Bi2Te3, Sb2Se3, MnSe und FeSe zur Erzeugung von Nanokristallen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-216927.
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In Topologischen Isolatoren (TI) werden metallische Zustände an der Oberfläche beobachtet, während die entsprechenden Volumenzustände eine Bandlücke aufweisen. Der Volumenbeitrag zur Leitfähigkeit von TI-Materialien macht eine Synthese von Nanokristallen bzw. eine Dotierung nötig. Der Fokus der Untersuchungen dieser Arbeit liegt dabei auf der Erzeugung von Nanokristallen der TI-Materialien Bi2Te3- und Bi2Te2Se sowie dotierter Bi2Se3-Nanokristallen.
Die Synthese der Nanokristalle erfolgte durch den Gasphasentransport im geschlossenen System über den Mechanismus einer Zersetzungssublimation bzw. unter dem Einsatz eines Transportmittels. Für eine erfolgreiche Erzeugung der Nanokristalle sind im Vorfeld thermodynamische Modellierungen des Gasphasentransports sowie Versuche zum chemischen Transport für die quasibinären Systeme Bi2Se3-Bi2Te3, Bi2Se3-Sb2Se3 und Bi2Se3-FeSe sowie für das ternäre System Mn-Bi-Se durchgeführt worden.
Durch Versuche zum chemischen Transport konnten die Aussagen der Modellierung bestätigt und im Weiteren der Dotandengehalt in den abgeschiedenen Kristallen sowie der Einlagerungsmechanismus durch Ergebnisse aus XRD- und ICP-OES-Untersuchungen beschrieben werden. Die Synthese bzw. Dotierung der Nanokristalle wurde hauptsächlich durch die Transportrate und den Dampfdruck des Dotanden bestimmt.
In den Systemen Bi2Se3-Bi2Te3 und Bi2Se3-Sb2Se3 ist ein Gasphasentransport über eine Zersetzungssublimation durchführbar und resultierte in einer erfolgreichen Darstellung von Bi2Te3- und Bi2Te2Se-Nanokristallen sowie von dotierten (SbxBi1-x)2Se3-Nanokristallen. Entgegen dessen erfolgte der Gasphasentransport in den Systemen Bi2Se3-FeSe und Mn-Bi-Se unter Verwendung eines Transportmittels. Hierbei verringerten die gesteigerten Transportraten das Wachtum von Nanokristallen. Im Weiteren gelang es dotierte (Fe,Mn)xBi2-xSe3-Volumenkristalle sowie MnBi2Se4-Einkristalle darzustellen und mittels XRD, ICP-OES, magnetischer Messungen sowie elektrischem Transport zu charakterisieren.
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Sevriuk, Vasilii [Verfasser]. "Scanning tunneling microscopy study of Bi2Se3(0001) and of FeSe and Bi nanostructures on Bi2Se3(0001) / Vasilii Sevriuk." Halle, 2017. http://d-nb.info/1141177986/34.
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Wetzel, Duston. "ROOM TEMPERATURE MAGNETORESISTANCE IN LARGE AREA Co/Bi2Se3 BILAYERS." OpenSIUC, 2021. https://opensiuc.lib.siu.edu/theses/2841.
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The area of spintronics has witnessed tremendous progress in the 21st century. During the 1980s and 1990s, the Giant and Tunnel Magnetoresistance effect dominated spintronics research with room-temperature ferromagnets(FM), metals, and insulators. Since then, the observation of several spin-based phenomena in heavy non-magnetic materials such as the Spin Hall Effects and the discovery of topological insulators have broadened the scope of spintronics research. Strong spin-orbit coupling (SOC) in topological insulators is expected to induce strong spin-orbit torques on proximal magnetic moments. This has motivated much recent interest in FM/TI systems with applications in spintronic memory and sensing. In this work, magnetron sputtered large-area Co/Bi2Se3 thin films were investigated with a custom-built magnetotransport setup. When current is passed predominantly through the Co layer we observe typical Co anisotropic magnetoresistance, but by promoting higher current density through the interface, we observe unidirectional magnetoresistance with a much larger change in resistance than Co alone. We also observe an unusual inverse current dependence. To test the contributions of each constituent material, Co/Ta and Cr/Bi2Se3 were prepared as controls, and similar observations were made in both materials, but not Co/Cr, suggesting that high SOC in the overlayer may be the driving force. While a proper understanding of our magnetoresistance data is not available at this point, the results broadly highlight the exciting prospects of observing novel phenomena in bilayer spintronic systems at room temperature.
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Reis, Diogo Duarte dos. "Estudo das estruturas atômicas de superfície dos isolantes topológicos Bi2Se3 e Bi2Te3, e de filmes finos de La0.7Sr0.3MnO3." Universidade Federal de Minas Gerais, 2014. http://hdl.handle.net/1843/BUOS-9PXK5B.
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The physico-chemical, electrical, magnetic, and optical properties of a surface can be seen as a function of their electronic structure which is strongly related to its atomic structure. Furthermore, the creation of a surface represents a break in one direction of periodicity of the crystal, which can result in structural changes and consequently generates changes in the above mentioned properties. Thus it is of extremely significance the experimental determination of surface structure for a complete understanding of the properties of a material. In this thesis, the low-energy electrons diffraction technique (LEED) was applied to the investigation of the atomic structures of the (111) surfaces of two topological insulators Bi2Se3 and Bi2Te3, and also to study the crystallographic structure evolution with the thickness of doped manganate thin films La0:7Sr0:3MnO3 grown on a SrTiO3 as a substrate. The results for Bi2Te3 and Bi2Se3 show that these surfaces undergo slight relaxations, being almost bulk terminated. Among the details researched is the value of the van der Waals gap, due to assumptions about its influence on the electronic structure of these materials. The structural investigation of La0:7Sr0:3MnO3 thin films was carried out during the internship at the Department of Astronomy and Physics, Louisiana State University, United States of America, under the supervision of Prof. Ward Plummer. This study showed that the surface undergoes stoichiometric and also structural changes in relation to the bulk. Special attention was paid to the evolution of the bond angle O-Mn-O, representing a Jahn-Teller distortion as well the tolerance factor, which has a minimum value when the thickness reaches the critical value wherein the metal-insulator transition occurs.<br>As propriedades físico-químicas, elétricas, magnéticas e ópticas de uma superfície podem ser vistas como função de sua estrutura eletrônica que é fortemente relacionada à estrutura atômica. Além disso, a criação de uma superfície representa uma quebra da periodicidade em uma direção do cristal, o que pode acarretar em mudanças estruturais e por consequência gerar mudanças nas propriedades supracitadas. Assim é de extrema importância a determinação experimental das estruturas de superfícies para um completo entendimento das características de um material. Nesta tese, a técnica de difração de elétrons de baixa energia (LEED) foi aplicada à investigação das estruturas atômicas das superfícies (111) de dois isolantes topológicos Bi2Se3 e Bi2Te3, e também ao estudo da evolução da estrutura cristalográfica com a espessura de filmes finos do manganato dopado La0:7Sr0:3MnO3 crescidos sobre um substrato de SrTiO3. Os resultados encontrados para o Bi2Te3 e para o Bi2Se3 mostraram que estas superfícies sofrem pequenas relaxações, sendo quase do tipo bulk terminated. Dentre os detalhes investigados minuciosamente estão o valor do gap de Van der Waals, devido a suposições de sua influência na estrutura eletrônica desses materiais. A investigação estrutural dos filmes de La0:7Sr0:3MnO3 foi realizada durante o estágio sanduíche no Departamento de Astronomia e Física da Louisiana State University, Estados Unidos da América, sob supervisão do Prof. Ward Plummer. Esse estudo mostrou que a superfície sofre alterações estequiométricas e também estruturais em relação ao volume. Foi dada especial atenção à evolução do ângulo das ligações O-Mn-O, que representam uma distorção tipo Jahn-Teller e, ao fator de tolerância, que apresenta um mínnimo quando a espessura em que ocorre a transição metal-isolante é alcançada.
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Gao, Yibin. "Thermoelectric Properties of Bi2Se3 and Copper-Nickel Alloy." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420629394.
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Grauer, Stefan [Verfasser]. "Transport Phenomena in Bi2Se3 and Related Compounds / Stefan Grauer." München : Verlag Dr. Hut, 2018. http://d-nb.info/1155058925/34.
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Zhang, Renyan. "Intercalation induced superconductivity in MoS2, black phosphorus and Bi2Se3." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/intercalation-induced-superconductivity-in-mos2--black-phosphorus-and-bi2se3(bd6767e7-79b2-46ac-bdd8-d78322a54d7b).html.
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Intercalation is known to be an efficient method for tuning the band structure of layered materials to bring out superconductivity, without significantly altering the crystal structure of the host material. Graphite intercalation compounds and intercalated transitional metal dichalcogenides (TMDs) are two most studied representatives. This thesis presents an experimental study of several new superconductors obtained by intercalation of layered materials, including MoS2, black phosphorus and a topological insulator Bi2Se3. Polymorphism is an essential feature of MoS2. While, superconductivity in doped 2H-MoS2 has been extensively studied. Superconductivity in its 1T and 1T' counterparts has been neither observed, nor even predicted theoretically. In this thesis, we have investigated potassium (K)-intercalated MoS2 and found that doping with K induces both structural and superconducting phase transitions. We demonstrate that all three phases of MoS2 - 2H, 1T and 1T'- become superconducting as a result of intercalation, with critical temperature Tc of 6.9 K, 2.8 K and 4.6 K, respectively. Black phosphorus has been 'rediscovered' in the last few years due to its layered structure and unique electronic properties. This thesis describes successful intercalation of black phosphorus with several alkali metals (Li, K, Rb, Cs) and alkaline earth metal Ca, with all five compounds showing superconductivity. Importantly, and very unexpectedly, the found superconductivity of intercalated black phosphorus is independent of the intercalant, with all five compounds having exactly the same superconducting characteristics (Tc, critical fields, anisotropy). We suggest that the superconductivity is due to heavily doped phosphorene layers, with alkali metal atoms acting mainly as charge reservoirs. Superconducting topological insulators, such as Bi2Se3, are regarded as the most promising candidates for topological superconductivity. However, the nature of superconductivity in doped Bi2Se3, such as CuxBi2Se3, SrxBi2Se3 and NbxBi2Se3, remains controversial and so far no convincing evidence of topological superconductivity has been reported for these materials. In this thesis, we report superconductivity in a new family of superconductors derived from Bi2Se3, by intercalation with K, Rb and Cs metals. All three superconductors exhibit qualitatively identical but highly anomalous behaviour of magnetisation, with several new features consistent with the properties of topological superconductors. Specifically, the new materials exhibit a highly unusual extra diamagnetic screening in the Meissner state and two coexisting superconducting phase, including surface superconductivity that we attribute to heavily doped surface states of the original topological insulator (Bi2Se3). This work provides a new platform in the study of the interplay between the topological and superconducting orders. In conclusion, superconductivity has been induced in MoS2, black phosphorus and Bi2Se3 through alkali or alkaline earth metal intercalation. The study of these new superconducting materials has been summarised in the thesis.
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Kan, Xin, and 阚欣. "Growth of Bi2Se3 on Si substrate by molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B46474687.
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Wang, Ziyan, and 王子砚. "MBE growth of AlInN and Bi2Se3 thin films and hetero-structures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47163483.
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Molecular Beam Epitaxy is an advanced method for the synthesis of single-crystal thin-film structures. However, the growth behavior varies case by case due to the complicated kinetic process. In this thesis, the epitaxial growth processes of AlxIn1-xN alloy and Bi2Se3 thin-films are studied.
Heteroepitaxial growth of AlxIn1-xN alloy on GaN(0001) substrate is carried out in the Nitrogen-rich flux conditions. A series of transient growth stages are identified from the initiation of the deposition. A significant effect of source beam-flux on the incorporation rate of Indium atoms is observed and measured. A correlation between the incorporation rate and the growth conditions (flux ratio and growth temperature) is revealed by the dependence of the growth-rate of the film on beam fluxes. A mathematic model is then suggested to explain the effect, through which the measured results indicating a surface diffusing and trapping process is indicated. Unexpected behavior of the lattice-parameter evolution of the growth front during deposition is also observed, indicating a complex strain-relaxation process of the epilayers.
For three-dimensional (3D) topological insulator of Bi2Se3, growths are attempted on various substrate surfaces, including clean Si(111)-(7x7), Hydrogen terminated Si(111), Bismuth induced Si(111) reconstructed surfaces, GaN(0001), and some selenide “psudo-substrates”. The specific formation process of this quintuple-layered material in MBE is investigated, from which the Van der Waals epitaxy growth characteristics inherent to deposition of Bi2Se3 is determined, and the mechanism of the “two-step growth” technique for this material is further clarified. Among the various substrates, those that are inert to chemical reaction with Bi/Se are important for the growth. The epilayers’ lattice-misfit with the substrate is also a crucial factor to the structural quality of the Bi2Se3 epifilms, such as the defects density and the single-crystalline domain size. The effect of a vicinal substrate on suppressing the twin-defects in film is also addressed. Using a suitable substrate and adapting an optimal condition, ultra-thin films of Bi2Se3 with a superior structural quality have been achieved. Multilayered Bi2Se3 structures with ZnSe and In2Se3 spacers are attempted. Finally the high-quality superlattices of Bi2Se3/In2Se3 are successfully synthesized. The hetero-interfaces in the superlattice structure of Bi2Se3/In2Se3 are sharp, and the individual layers are uniform with thicknesses being strictly controlled.
The behaviors of strain evolution during the hetero-growth process are finally investigated. An exponential relaxation of misfit strain is observed. And the correlation between the residual strain and the starting surface in the initial growth stage is also identified.<br>published_or_final_version<br>Physics<br>Doctoral<br>Doctor of Philosophy
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Vasconcelos, Hugo Menezes do Nascimento. "Propriedades estruturais e magnéticas do isolante topológico Bi2Se3 com aglomerados de FexSey." Universidade Federal de São Carlos, 2016. https://repositorio.ufscar.br/handle/ufscar/8122.
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Previous issue date: 2016-03-29<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>In this work, we discuss the growth of Fe containing Bi2 Se3epilayers on the
GaAs(111) substrate by molecular beam epitaxy (MBE) with Fe contents of in the 8-
20% range. It is shown that Bi2 Se3 film thin are grown with quality and the Fe form a
phase segregation of Fe x Sey material that may have different stoichiometries possibity,
leading to magnetic and superconducting results. Despite the composite structure, the
surface state of Bi2 Se3 is preserved as shown with persistence of Dirac Cone of the Γ
point by Angle-Resolved Photoemission Spectroscopy (ARPES). It was observed that
higher Fe content deposited is increased formation of compound responsible for
ferrimagnetic layers together with the superconducting phase supposed. The Fe3Se 4
was the most abundant type of segregation in all samples, with the results ferrimagnetic
these samples at temperatures around 315 K.<br>Neste trabalho, abordamos o crescimento de Bi2 Se3 com adição de Fe em
substrato de GaAs(111) por meio de epitaxia de feixe molecular (MBE), variando o
teor de Fe depositado de 8% até 20%. É mostrado que os filmes de Bi2 Se3 são
crescidos com qualidade e o Fe juntamente com o Se formam uma segregação de fases
Fex Sey , material que pode ter diferentes estequiometrias levando a resultados
magnéticos e possivelmente supercondutor. Apesar da estrutura compósita, a estrutura
superficial do Bi2 Se3 é preservada como mostrado pela persistência do cone de Dirac
no ponto Γ nas medidas de espectroscopia de fotoemissão de resolução angular
(ARPES). Foi possível observar que quanto maior o teor de Fe depositado, ocorre uma
maior formação de compostos responsável pela fase ferrimagnética em conjunto com a
fase supostamente supercondutora. O Fe3Se 4 foi o tipo de segregação mais abundante
em todas as amostras, levando a resultados ferrimagnéticos nessas amostras em
temperaturas em torno de 315 K.
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Tumelero, Milton Andre. "Bi2Se3: eletrodeposição de filmes finos e cálculos Ab initio de defeitos pontuais." reponame:Repositório Institucional da UFSC, 2014. https://repositorio.ufsc.br/xmlui/handle/123456789/129335.
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Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2014.<br>Made available in DSpace on 2015-02-05T20:58:11Z (GMT). No. of bitstreams: 1
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Previous issue date: 2014<br>Neste trabalho foi realizado um estudo sistemático sobre a eletrodeposição do composto seleneto de bismuto (Bi2Se3) em substrato de Si(100). Em paralelo, foram realizados cálculos de primeiros princípios com o objetivo de encontrar as energias de formação e de transição para diferentes defeitos pontuais existentes em Bi2Se3. O trabalho foi dividido em duas partes, a primeira com resultados experimentais e a segunda com resultados teóricos. Na primeira parte é mostrado que as amostras obtidas com eletrodeposição em Si(100) apresentam majoritariamente a fase cristalina ortorrômbica. O crescimento dos filmes finos sobre substrato de Si(100) ocorre em duas etapas de nucleação, onde a segunda etapa gera filmes finos cristalinos e com crescimento preferencial dos planos (020). O gap de energia obtido para a fase ortorrômbica do Bi2Se3 foi 1,25 eV, que é maior que os valores previstos teoricamente. Filmes de Bi2Se3 puramente na fase hexagonal foram obtidos através de tratamentos térmicos. Foi mostrado que há um forte alinhamento do eixo basal da estrutura cristalina hexagonal com o eixo perpendicular ao plano do substrato. Amostras obtidas em diferentes substratos indicam que o crescimento não é epitaxial. A caracterização elétrica indica um comportamento condutivo ativado termicamente para as amostras de Bi2Se3 na fase ortorrômbica e comportamento elétrico degenerado para amostras em fase hexagonal. Os valores medidos de resistividade elétrica e coeficiente Seebeck estão de acordo com valores prévios relatados e confirmam a qualidade das amostras eletrodepositadas. Na segunda parte do trabalho foramrealizados cálculos teóricos com DFT, que mostram que os defeitos mais estáveis na fase hexagonal do Bi2Se3 são as vacâncias de Se1 e os Bi intersticiais. Para a fase ortorrômbica os mais estáveis são as vacâncias de Se e os antisítios de Bi e de Se, explicando o comportamento elétrico tipo-n.<br><br>Abstract : We present a study of electrodeposition of Bismuth Selenide (Bi2Se3) on Si(100) substrate. At same time, first principles calculation was performed in order to find the formations and transitions energies of some possible native point defects in Bi2Se3. The work was separated in two parts, the experimental one and the theoretical one. In the first part, we show that samples obtained by electrodeposition on Si(100) substrate present predominance of orthorhombic crystalline phase. The growth of thin films occurs in two nucleation steps and with preferential growth of (020) plane. The measured bandgap of 1.25 eV is larger than values expected from theoretical predictions. Thin films of hexagonal crystalline phase were obtained by thermal annealing of the samples. The electrical characterization of orthorhombic phase samples shows thermal activated behavior, with two activation energies. The hexagonal phase samples show degenerated semiconductive behavior. The measured electrical resistivity and Seebeck coefficient are in accordance with previous studies and confirm the quality of our samples. In the second part of the work, we perform DFT calculation that shows that the most stable defects of hexagonal Bi2Se3 are the selenium vacancies and bismuth interstitials. In the case of orthorhombic Bi2Se3 the most stable defects are the selenium vacancies and the Se and Bi antisites. These defects are enough to explain the n-type conduction found in both phases of Bi2Se3.
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Nowka, Christian [Verfasser], Bernd [Akademischer Betreuer] [Gutachter] Büchner, and Jörg [Gutachter] Feller. "Untersuchungen zu Gasphasentransporten in quasibinären Systemen von Bi2Se3 mit Bi2Te3, Sb2Se3, MnSe und FeSe zur Erzeugung von Nanokristallen / Christian Nowka ; Gutachter: Bernd Büchner, Jörg Feller ; Betreuer: Bernd Büchner." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/112393178X/34.
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Sapkota, Yub Raj. "PHYSICAL PROPERTIES OF TOPOLOGICAL INSULATOR: BISMUTH SELENIDE THIN FILMS." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2261.
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Topological Insulator (TI) is new classes of materials with gapless surface states and insulating bulk. The topological connection can be traced back to the discovery of Integer Quantum Hall Effect in 1980. In the last decade, new categories of topological insulators were predicted and later discovered, that have gained a lot of attraction for room-temperature applications. Since the experimental observation of single Dirac cone on the surface states of Bismuth selenide (Bi2Se3) in 2009, it has emerged as the prototype. Bismuth Selenide has one of the highest bulk band gaps of 0.3 eV among all TI materials. While its single crystal properties are well documented, thin films are producing equally exciting discoveries. In this work, Bi2Se3 thin films were synthesized using magnetron sputtering method and a diverse set of physical properties, such as structural, optical, and electronic, are investigated. In particular, properties of few-layer (ultra-thin) Bi2Se3 thin films are studied. Optical properties of Bi2Se3 was particularly revealing. We observed a sharp increase (blue shift) in the bulk band gap of Bi2Se3 by almost 0.5 eV as it approached the two-dimensional limit. Strong thickness-dependent structural and transport properties were also observed.
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Grauer, Stefan [Verfasser], Laurens W. [Gutachter] Molenkamp, and Christian [Gutachter] Schneider. "Transport Phenomena in Bi2Se3 and Related Compounds / Stefan Grauer ; Gutachter: Laurens W. Molenkamp, Christian Schneider." Würzburg : Universität Würzburg, 2018. http://d-nb.info/1154386643/34.
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Irfan, Bushra. "Transport magnetic and galvanomagnetic studies on grown 3D topological insulators of Bi2Se3 and Bi2Te2Se families." Thesis, IIT Delhi, 2016. http://localhost:8080/iit/handle/2074/7055.
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松尾, 貞茂. "Bi2Se3薄膜における量子干渉効果の研究". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188510.
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Riha, Christian. "Quantum transport investigations of low-dimensional electron gases in AlxGa1-xAs/GaAs- and Bi2Se3-based materials." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20352.
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Die Transporteigenschaften eines Elektronengases mit reduzierter Dimensionalität
werden von den Welleneigenschaften der Elektronen bestimmt. Dies ermöglicht es,
verschiedene Quanteneffekte, wie Quanteninterferenz, zu beobachten.
Im ersten Teil dieser Arbeit werden geätzte Quantenringe und eindimensionale
(1D) Verengungen, basierend auf AlxGa1-xAs/GaAs-Heterostrukturen, hinsichtlich
ihrer Transporteigenschaften untersucht. Messungen des thermischen Rauschens
im Gleichgewichtszustand zeigen, dass der Erwartungswert mit den Rauschspektren
aller 1D Verengungen übereinstimmt, jedoch um bis zu 60 % bei allen Quantenringen
überschritten wird.
Rauschmessungen im thermischen Nichtgleichgewicht ergeben, dass der Wärmefluss
in Quantenringen mithilfe einer globalen Steuerelektrode (Topgate) an- und
ausgeschaltet werden kann. Die magnetische Widerstandsänderung der Quantenringe
zeigt Oszillationen, die dem Aharonov-Bohm-Effekt zugeordnet werden. Die
Beobachtbarkeit dieser Oszillationen hängt stark von dem Abkühlvorgang der Probe
ab und die Oszillationen zeigen Hinweise auf ein Schwebungsmuster sowie auf Phasenstarre.
Im zweiten Teil der Arbeit werden die Oberflächenzustände von exfolierten Bi2Se3
Mikroflocken untersucht. Für Mikroflocken mit metallischen Temperaturabhängigkeiten
des Widerstandes wurde schwache Anti-Lokalisierung beobachtet. Diese
Beobachtung deutet darauf hin, dass sich die magnetische Widerstandsänderung
weniger ausschließlich aus den 2D Oberflächenkanälen als vielmehr aus einem geschichtetem
Transport von 2D Kanälen im Volumenkörper zusammensetzt. Eine
Mikroflocke mit halbleitenden Eigenschaften zeigt keine Hinweise auf solch einen
geschichteten 2D Transport und es wird angenommen, dass ihre magnetische Widerstandsänderung
ausschließlich von den 2D Oberflächenzuständen verursacht wird.<br>The transport properties of an electron gas with reduced dimensionality are dominated
by the electron’s wave nature. This allows to observe various quantum effects,
such as quantum interference.
In the first part of this thesis etched quantum rings and one-dimensional (1D)
constrictions, based on AlxGa1-xAs/GaAs heterostructures, are investigated with
respect to their transport properties. Thermal noise measurements in equilibrium
show that the expectation value agrees with the noise spectra of all 1D constrictions
but is exceeded by up to 60 % for the noise spectra of all quantum rings.
Noise measurements in thermal non-equilibrium reveal that the heat flow can
be switched on and off for a quantum ring by a global top-gate. The measured
magnetoresistance of the quantum rings shows oscillations that are attributed to
the Aharonov-Bohm effect. The observability of these oscillations strongly depends
on the cooling process of the sample and the oscillations show indications of a beating
as well as phase rigidity.
In the second part of the thesis the surface states of exfoliated Bi2Se3 microflakes
are studied. For microflakes that show a metallic temperature dependence of the
resistance weak anti-localization is observed. This observation suggests that the
magnetoresistance is a result of layered transport of 2D channels in the bulk rather
than just the surface 2D channels. A microflake with semiconducting characteristics
does not show indications of such a 2D layered transport and its magnetoresistance
is considered to be carried by the 2D surface states only.
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Al, Bayaz Asmaïl. "Elaboration et caractérisation de matériaux thermoélectriques Bi2Se3 et Bi2(Te1-xSex)3 déposés par MOCVD : réalisation de micromodules Peltier." Montpellier 2, 2003. http://www.theses.fr/2003MON20040.
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Sassi, Selma. "Synthèse, caractérisation physico-chimique et propriétés de transport des composés homologues (PbSe)5 (Bi2Se3)3m (m = 1, 2, 3)." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0135/document.
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Les composés homologues de formule chimique (PbSe)5(Bi2Se3)3m avec m = 1, 2 et 3 se caractérisent par une structure lamellaire où alternent des couches de PbSe avec m couches de Bi2Se3. Ces composés, que l’on retrouve à l’état naturel, ont récemment suscité un intérêt pour la thermoélectricité en raison de leur remarquable aptitude à ne conduire que très faiblement la chaleur. L’objectif des travaux de cette thèse est d’étudier en détail le transport électrique et thermique de ces matériaux et de sonder leurs performances pour la génération d’électricité. Pour atteindre ces objectifs, des techniques de synthèse par métallurgie de poudres ont été mises en œuvre. Les matériaux résultants ont été ensuite caractérisés finement. Les caractérisations ont porté sur des analyses physico-chimiques mais aussi sur des mesures de propriétés électriques et thermiques aussi bien à basses températures (2 – 300 K) pour identifier les mécanismes microscopiques qui gouvernent le transport qu’à hautes températures (300 – 723 K) pour déterminer leur domaine d’application optimal. Une étude détaillée de leur structure cristalline a été menée en combinant des mesures de diffraction des rayons X sur monocristal et des analyses de microscopie électronique à transmission à haute résolution. Les mesures des propriétés physiques de ces composés ont confirmé leur potentiel pour des applications en génération d’électricité à températures moyennes. De nombreuses substitutions ont été entreprises afin de tenter d’optimiser davantage les performances de ces composés. Les éléments en substitution ont été choisi pour soit augmenter (m = 1) ou au contraire diminuer (m = 2 et 3) la concentration en électrons. Ces travaux ont permis de démontrer pour la première fois la possibilité de doper ces matériaux avec de nombreux éléments tels que l’iode, le sodium, l’argent ou le tellure. D’autre part, une étude détaillée des propriétés thermiques de ces matériaux a été réalisée par diffusion inélastique des neutrons sur poudre afin de dévoiler l’origine microscopique des très faibles valeurs de conductivité thermique de réseau mesurées<br>The homologous series of compounds of general chemical formula (PbSe)5(Bi2Se3)3m with m = 1, 2 et 3 is characterized by a lamellar crystal structure where PbSe layers alternate with m Bi2Se3 layers. These compounds, that can be found as minerals, have recently focused attention for thermoelectric applications owing to their remarkable ability to poorly conduct heat. In order to evaluate their thermoelectric performances, the present work dealt with their synthesis by powder metallurgy techniques followed by measurements of their transport properties not only at low temperatures (2 – 300 K) with the aim to identify the basic mechanisms governing the transport but also at high temperatures (300 – 723 K) to determine their optimum temperature range. A detailed study of their crystalline structure has been carried out by a combination of X-ray diffraction on high-quality single crystals and high-resolution transmission electron microscopy. Measurements of their transport properties have confirmed the potential of these materials for power generation applications at mid temperatures. Numerous substitutions have been studied to optimize further their thermoelectric performances. The elements in substitution have been chosen to either increase (m = 1) or decrease (m= 2 and 3) the electron concentration. This work has demonstrated for the first time the possibility to dope these materials with various elements such as iodine, sodium, silver or tellurium. Moreover, a detailed study of the thermal properties of these compounds has been performed by means of powder inelastic neutron scattering in order to unveil the microscopic origin of the very low lattice thermal conductivity values measured
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Ivan, Kostylev. "Uniaxial-Strain Control of Nematic Superconductivity in SrxBi2Se3." Kyoto University, 2019. http://hdl.handle.net/2433/245307.
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Inhofer, Andreas. "Etude de la compressibilité AC des isolants topologiques 3D HgTe et Bi2Se3 : mise en évidence d'états massifs excités de surface." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE016/document.
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Dans cette thèse, j’étudie la compressibilité électronique de deux isolants topologiques tridimensionnels : Le tellurure de mercure (HgTe) sous contrainte et le séléniure de bismuth (Bi2Se3).Je présente des mesures d’admittance électronique à basse température résolues en phase sur une large gamme de fréquence. Cela permet d’extraire la capacité quantique associé à la densité d’états et la résistivité des matériaux étudiés.Nous montrons qu’un isolant topologique intrinsèque présente une réponse dominée par les états de surface topologiques sur une large gamme d’énergie qui s’étend au-delà du gap de transport du matériau massif. Ce régime, appelé « écrantage de Dirac », est caractérisé par une compressibilité électronique proportionnelle à l’énergie de surface et une haute mobilité.Dans la suite, nous nous intéressons à la limite de ce régime. Nous observons qu’à haute énergie et sous l’influence de forts champs électriques perpendiculaires, des états excités massifs de surface sont peuplés ce qui se manifeste expérimentalement de différentes façons : Une chute dans la constante de diffusion électronique, un pic de conductivité ainsi que l’apparition d’un deuxième type de porteurs en magnéto-transport et de métastabilité dans la relation charge-tension.Un modèle théorique basé sur un traitement quasi-relativiste du Hamiltonien de surface est présenté. Il permet d’identifier la dépendance en énergie et champ électrique des états massifs de surface.Cette thèse est complémenté par des résultats expérimentaux sur Bi2Se3 obtenu par croissance sur nitrure de bore mettent en évidence l’importance de la pureté des interfaces d’isolants topologiques<br>This thesis discusses the electronic compressibility of two representative three dimensional topological insulators: Strained mercury telluride (HgTe) and bismuth selenide (Bi2Se3).I present low temperature phase-sensitive electron admittance data over a broad frequency range. This allows to extract the quantum capacitance related to the density of states and the resistivity of the investigated materials.We show that the response of an intrinsic topological insulator is dominated by topological surface states over a large energy range exceeding the bulk material’s transport gap. This regime, named “Dirac screening” is characterized by an electron compressibility proportional to the surface Fermi level and a high mobility.Subsequently, we investigate the limits of this regime. At high energy and large perpendicular electric fields we observe the population of excited massive surface states. Experimentally, these manifest themselves in multiple signatures: A drop in the electronic diffusion constant, a peak in the conductivity, appearance of a second carrier type in magneto-transport and meta-stability in the charge-voltage relation.A theoretical model based on a quasi-relativistic treatment of the surface Hamiltonian is presented. It allows to identify the electric field and energy dependence of the massive surface states.This thesis is complemented by experimental results on Bi2Se3 grown on boron nitride, where we demonstrate the importance of clean surfaces for the study of electronic properties in topological insulators
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Yee, Michael Manchun. "Scanning Tunneling Spectroscopy of Topological Insulators and Cuprate Superconductors." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11584.
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Over the past twenty-five years, condensed matter physics has been developing materials with novel electronic characteristics for a wide range of future applications. Two research directions have shown particular promise: topological insulators, and high temperature copper based superconductors (cuprates). Topological insulators are a newly discovered class of materials that can be manipulated for spintronic or quantum computing devices. However there is a poor spectroscopic understanding of the current topological insulators and emerging topological insulator candidates. In cuprate superconductors, the challenge lies in raising the superconducting transition temperature to temperatures accessible in non-laboratory settings. This effort has been hampered by a poor understanding of the superconducting mechanism and its relationship with a mysterious pseudogap phase. In this thesis, I will describe experiments conducted on topological insulators and cuprate superconductors using scanning tunneling microscopy and spectroscopy, which provide nanoscale spectroscopic information in these materials.<br>Physics
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Riha, Christian [Verfasser], Saskia [Gutachter] Fischer, Hartmut [Gutachter] Buhmann, and Thomas [Gutachter] Schröder. "Quantum transport investigations of low-dimensional electron gases in AlxGa1-xAs/GaAs- and Bi2Se3-based materials / Christian Riha ; Gutachter: Saskia Fischer, Hartmut Buhmann, Thomas Schröder." Berlin : Humboldt-Universität zu Berlin, 2019. http://d-nb.info/1193989159/34.
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Pournia, Seyyedesadaf. "Exploring the Photoresponse and Optical Selection Rules in the Semiconductor Nanowires, Topological Quantum Materials and Ferromagnetic Semiconductor Nanoflakes using Polarized Photocurrent Spectroscopy." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627666632280473.
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Berntsen, Magnus H. "Consequences of a non-trivial band-structure topology in solids : Investigations of topological surface and interface states." Doctoral thesis, KTH, Material- och nanofysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121974.
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The development and characterization of experimental setups for angle-resolved photoelectron spectroscopy (ARPES) and spin- and angle-resolved photoelectron spectroscopy (SARPES) is described. Subsequently, the two techniques are applied to studies of the electronic band structure in topologically non-trivial materials. The laser-based ARPES setup works at a photon energy of 10.5 eV and a typical repetition rate in the range 200 kHz to 800 kHz. By using a time-of-flight electron energy analyzer electrons emitted from the sample within a solid angle of up to ±15 degrees can be collected and analyzed simultaneously. The SARPES setup is equipped with a traditional hemispherical electron energy analyzer in combination with a mini-Mott electron polarimeter. The system enables software-controlled switching between angle-resolved spin-integrated and spin-resolved measurements, thus providing the possibility to orient the sample by mapping out the electronic band structure using ARPES before performing spin-resolved measurements at selected points in the Brillouin zone. Thin films of the topological insulators (TIs) Bi2Se3, Bi2Te3 and Sb2Te3 are grown using e-beam evaporation and their surface states are observed by means of ARPES. By using a combination of low photon energies and cryogenic sample temperatures the topological states originating from both the vacuum interface (surface) and the substrate interface are observed in Bi2Se3 films and Bi2Se3/Bi2Te3 heterostructures, with total thicknesses in the ultra-thin limit (six to eight quintuple layers), grown on Bi-terminated Si(111) substrates. Band alignment between Si and Bi2Se3 at the interface creates a band bending through the films. The band bending is found to be independent of the Fermi level (EF) position in the bulk of the substrate, suggesting that the surface pinning of EF in the Si(111) substrate remains unaltered after deposition of the TI films. Therefore, the type and level of doping of the substrate does not show any large influence on the size of the band bending. Further, we provide experimental evidence for the realization of a topological crystalline insulator (TCI) phase in the narrow-band semiconductor Pb1−xSnxSe. The TCI phase exists for temperatures below the transition temperature Tc and is characterized by an inverted bulk band gap accompanied by the existence of non-gapped surface states crossing the band gap. Above Tc the material is in a topologically trivial phase where the surface states are gapped. Thus, when lowering the sample temperature across Tc a topological phase transition from a trivial insulator to a TCI is observed. SARPES studies indicate a helical spin structure of the surface states both in the topologically trivial and the TCI phase.<br><p>QC 20130507</p>
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Ameziane, Jamal. "Etude physico-chimique des conditions d'élaboration de jonctions de semi-conducteurs V2VI3. Application à la réalisation d'homojonctions Bi2Te3/Bi2Te3 et d'hétérojonctions Sb2Te3/Bi2Te3." Montpellier 2, 1993. http://www.theses.fr/1993MON20131.
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Le travail de these a pour but de mettre en evidence la faisabilite d'heterostructures de type bi#2te#3/sb#2te#3. Pour cela l'auteur utilise toutes les methodes qui sont a la disposition d'un laboratoire de chimie du solide. Le travail a ete effectue en collaboration avec le laboratoire de centre d'electronique de montpellier ce qui montre le souci de finalisation de ce travail. L'ouvrage peut se scinder en deux parties. Dans une premiere partie on etudie les caracteristiques des materiaux bi#2te#3 et sb#2te#3 sur le plan de leurs proprietes thermoelectriques ainsi que sur le plan des equilibres de phases heterogenes dont l'apport est utilise dans la deuxieme partie. Cette derniere partie concerne l'aspect experimental du probleme. On etudie par la technique des jets moleculaires. Les conditions de croissance des composes bi#2te#3 et sb#2te#3 sont definies. En particulier on a etudie la composition des couches qui ont ete determinees en fonction de la temperature et du rapport des flux incidents de matiere. Dans le domaine de stchiometrie correspondant aux materiaux etudies on a pu definir la transition amorphe cristallise
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Alves, Edvaldo de Oliveira. "Propriedades F?sicas do Semicondutor Bi2Te3." Universidade Federal do Rio Grande do Norte, 2007. http://repositorio.ufrn.br:8080/jspui/handle/123456789/16534.
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Previous issue date: 2007-12-13<br>Thermoelectric Refrigerators (TEC Thermoelectric Cooling) are solid-state heat pumps used in applications where stabilization of temperature cycles or cooling below the room temperature are required. TEC are based on thermoelectric devices, and these in turn, are based on the Peltier effect, which is the production of a difference in temperature when an electric current is applied to a junction formed by two non-similar materials. This is one of the three thermoelectric effects and is a typical semiconductor junction phenomenon. The thermoelectric efficiency, known as Z thermoelectric or merit figure is a parameter that measures the quality of a thermoelectric device. It depends directly on electrical conductivity and inversely on the thermal conductivity. Therefore, good thermoelectric devices have typically high values of electrical conductivity and low values of thermal conductivity. One of the most common materials in the composition of thermoelectric devices is the semiconductor bismuth telluride (Bi2Te3) and its alloys. Peltier plates made up by crystals of semiconductor P-type and N-type are commercially available for various applications in thermoelectric systems. In this work, we characterize the electrical properties of bismuth telluride through conductivity/resistivity of the material, and X-rays power diffraction and magnetoresistance measurements. The results were compared with values taken from specific literature. Moreover, two techniques of material preparation, and applications in refrigerators, are discussed<br>Refrigeradores Termoel?tricos (TEC Thermoelectric Cooling) s?o bombas de calor de estado s?lido usados em aplica??es onde estabiliza??o de ciclos de temperatura ou para resfriamentos abaixo da temperatura ambiente s?o requeridos. Os TEC s?o baseados em dispositivos termoel?tricos e, estes, por sua vez s?o baseados no efeito Peltier, que consiste na produ??o de um diferencial de temperatura quando uma corrente el?trica ? aplicada a uma jun??o formada por dois materiais diferentes. Este efeito ? um dos tr?s efeitos termoel?tricos e ? um fen?meno t?pico de jun??o. A efici?ncia termoel?trica, conhecida como Z termoel?trico ou a figura de m?rito ? um par?metro que mede a qualidade de um dispositivo termoel?trico. Ele depende diretamente da condutividade el?trica e do inverso da condutividade t?rmica. Assim, bons dispositivos termoel?tricos devem apresentar valores elevados de condutividade el?trica e baixa condutividade t?rmica. Um dos materiais mais comuns na composi??o de dispositivos termoel?tricos ? o semicondutor telureto de bismuto (Bi2Te3) e suas ligas. Placas Peltier composta por cristais tipo P e Tipo N deste semicondutor s?o dispon?veis comercialmente para diversas aplica??es em sistemas termoel?tricos. Neste trabalho buscou-se caracterizar propriedades f?sicas de amostras de telureto de bismuto, extra?das de placas Peltier, atrav?s das medidas de condutividade/resistividade do material, de medidas de raios X e de magnetoresist?ncia. Os resultados foram comparados com valores da literatura da ?rea. Al?m disso, descrevemos duas t?cnicas de prepara??o destes semicondutores e discutimos aplica??es em refrigeradores
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Mohelský, Ivan. "Infračervená magneto-spektroskopie topologického izolátoru Bi2Te3." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417169.
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Tato práce se zabývá charakterizací topologického izolátoru Bi2Te3, materiálu s nevodivými stavy v objemu, ale jedním vodivým pásem na povrchu. Tento materiál je zkoumán již přes 60 let, ale i přes to není jeho objemová pásová struktura úplně objasněna, obzvláště charakter zakázaného pásu je stále předmětem diskuze. V této práci jsou prezentovány výsledky infračervené spektroskopie na Landauových hladinách v magnetickém poli až do 34 T, doplněné elipsometrickým měřením mimo magnetické pole. Výsledky těchto měření by měli pomoci vyjasnit některé vlastnosti zakázaného pásu. Pozorovaná optická odezva odpovídá polovodiči s přímým zakázaným pásem, ve kterém se nosiče náboje chovají jako Diracovské hmotné fermiony. Šířka zakázaného pásu za nízkých teplot byla určena jako Eg = (175±5) meV a samotný zakázaný pás se nachází mimo trigonální osu, tím pádem se v první Brillouinově zoně vyskytuje 6 krát nebo 12 krát.
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Tan, Hong'En. "High pressure quantum oscillation study of BiTeI and Bi2Te3." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284884.
Full textAbstract:
The work presented in this thesis investigates the behaviour of the Rashba semi-conductor BiTeI and of the topological insulator $\text{Bi}_2\text{Te}_3\,$ under pressure. Using Shubnikov-de Haas quantum oscillation measurements, the evolution of the Fermi surface of both materials was tracked as a function of pressure. At ambient pressure, two distinct quantum oscillation frequencies in BiTeI, corresponding to inner and outer Fermi surface orbits as a result of spin-splitting caused by the Rashba effect, were observed. Using a model Hamiltonian with a Rashba interaction term to model this system, experimental results were fitted to determine model parameters. Based on this model, carrier densities for the samples were calculated and there was good agreement with Hall effect measurements. The phase of the oscillations showed that both Fermi surfaces have a Berry phase of $\pi$ associated with them, consistent with theoretical predictions for a Rashba system. As pressure is applied, it was observed that the inner Fermi surface expands while the outer Fermi surface shrinks. Phase analysis of the oscillations showed deviations from the ambient pressure value, hinting at a topological transition. For $\text{Bi}_2\text{Te}_3\,$, we report the observation of two oscillation frequencies ($\sim 40$ T and $\sim 340$ T) at ambient pressures. Based on the angular dependence of the oscillation frequencies, phase analysis, and comparison against band structure from published ARPES results, it is deduced that the higher frequency oscillation corresponds to the surface state of $\text{Bi}_2\text{Te}_3$. Non-linear behaviour in the Hall measurement also suggests the presence of multiple bands, and a two-band model with parameters derived from quantum oscillation measurements is used to fit the experimental data. Under pressure, a slight decrease in the low field Hall coefficient and a new frequency appearing at $\sim 20$ kbar was observed. These may be signatures of a change in the Fermi surface of $\text{Bi}_2\text{Te}_3\,$ caused by an electronic topological transition.
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Доброжан, Олександр Анатолійович, Александр Анатольевич Доброжан, Oleksandr Anatoliiovych Dobrozhan, et al. "Thermoelectric properties of the colloidal Bi2S3-based nanocomposites." Thesis, Jadavpur University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/65347.
Full textAbstract:
In this work we present the proof of the concept of the novel strategy to improve the thermoelectric
properties of Bi2S3based nanostructured bulk materials by blending the metallic nanoinclustions with
the semiconductor nanoparticles forming the nanocomposites (NCts). The obtained NCts were
composed of Bi2S3nanorods (length - 100 nm and width – 10 nm) and Ag nanoparticles (diameter - 2-
3 nm) synthesized by colloidal method. The morpohology, phase and chemical composition,
electrical conductivity and Seebeck coefficient of NCts were investigated by using transmission
electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray analysis (EDAX), 4-point probes
method and static dc-method. This strategy is the perspective way to improve the conversion
efficiency of others thermoelectric materials.
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Zimmer, Alexandre. "Caractérisations optiques et electrochimiques de films electrodéposés de type Bi2Te3." Metz, 2006. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/2006/Zimmer.Alexandre.SMZ0606.pdf.
Full textAbstract:
Ce travail concerne la caractérisation de films électrodéposés de tellurure de bismuth (-0,2x0,2), semi-conducteur thermoélectrique à faible gap. Les paramètres de transport ont été déterminés par ellipsométrie spectroscopique, spectroscopie d'impédance électrochimique (diagramme de Mott-Schottky) et par des mesures additionnelles d'effets Hall et Seebeck. Ces techniques ont nécessité l'optimisation des conditions de synthèse pour améliorer l'état de surface des couches électrodéposées. L'analyse des films par matrices de Mueller a démontré leur isotropie optique. Les fonctions diélectriques des films ont été déterminées dans le domaine spectral 0,03-3,1 eV. Une modélisation combinant les lois dispersives de Drude et de Tauc-Lorentz a été utilisée dans l'infrarouge. Le gap Eg apparaît constant (0,11 eV) quel que soit x. Cette analyse a été étendue avec succès à des films de Bi2(Te0,9Se0,1)3. Tous les résultats sont en accord avec un semi-conducteur de type n et ce quel que soit x. Les films présentent des concentrations en porteurs de l'ordre de 1020 cm-3, une résistivité de 15-50 . M et une mobilité de 4-14 cm2/(V. S) liées à leur nature polycristalline. Un banc de caractérisation original a été utilisé combinant simultanément des données de microbalance à cristal de quartz électrochimique, électrochimiques et une analyse par ellipsométrie spectroscopique temps réel dans le domaine du visible. Le système électrochimique est totalement réversible et la masse volumique apparente des films est de 7,34 g/cm3. La croissance de la couche a révélé une première période d'environ 30 secondes correspondant au recouvrement progressif du substrat d'or par les cristallites de Bi2Te3. Une épaisseur minimum de 35 nm est nécessaire pour obtenir des caractéristiques morphologiques et optiques identiques à celles d'échantillons épais<br>Optical and electrochemical characterizations of electroplated films of bismuth telluride compounds. This work concerns the characterization of electroplated films of bismuth telluride (-0. 2x0. 2) which is a semiconductor compound with narrow band-gap generally used for thermoelectric applications. Transport parameters were determined using Spectroscopic Ellipsometry, Electrochemical Impedance Spectroscopy (Mott-Schottky plot) and additional measurements (Hall & Seebeck effects) which required to optimize the synthesis conditions to improve surface quality of electroplated layers. Mueller Matrix analysis showed the optically isotropic behavior. The dielectric functions of the films were determined in the energy range of 0. 03 to 3. 10 eV. In the infrared range, Tauc–Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0. 11 eV independent of x. This analysis was successfully extended to Bi2(Te0. 9Se0. 1)3 films. All results showed that the films are described as n-type semiconductor independently of x. Carrier concentration of the order of 1020 cm-3, resistivity of 15-50 . M and mobility of 4-14 cm2/(V. S) were explained by polycrystalline material features. An original experimental setup was carried out including simultaneously electrochemical quartz crystal microbalance data, electrochemical data and real time ellipsometer analysis in the visible range. The electrochemical system was found to be fully reversible and the apparent volumic mass of the film is equal to 7. 34 g/cm3. The analysis of the layer growth revealed a first period around 30 seconds where the gold substrate is progressively covered by the crystallites of Bi2Te3. A minimum of 35 nm-thick film is necessary to obtain morphological and optical characteristics quite similar to thick samples
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Gühne, Robin. "Electronic properties of the topological insulators Bi2Se3 and Bi2Te3." 2019. https://ul.qucosa.de/id/qucosa%3A37768.
Full textAbstract:
Die drei-dimensionalen Topologische Isolatoren Bi2Se3 and Bi2Te3 sind Modell-Systeme einer neuen Klasse von Isolatoren mit metallischen Oberflächenzuständen. Ihre kleinen Bandlücken und die schweren Elemente sind essentiell für die topologisch nicht-triviale Bandstruktur, sind aber ebenso verantwortlich für andere bemerkenswerte Eigenschaften, wie etwa für ihre Leistungsfähigkeit als Thermoelektrika.
Diese Arbeit untersucht die elektronischen Eigenschaften der Topologischen Isolatoren Bi2Se3 und Bi2Te3 mittels zahlreicher experimenteller Methoden. Es wird
gezeigt, dass Ferromagnetismus in Mn gedoptem Bi2Te3 durch sintern unterdrückt
werden kann. Zudem werden ein überraschend großer Magnetoresistiver Effekt
und ein ladungsträgerunabhängiger Vorzeichenwechsel des Seebeck-Koeffizienten mit zunehmenden Mn Gehalt diskutiert. Kernmagnetische Resonanz (NMR) von 125Te Kernen in Bi2Te3 Einkristallen lässt auf eine ungewöhnliche elektronische SpinSuszeptibilität and komplexe NMR Verschiebungen schließen. Es wird gezeigt dass die Quadrupolwechselwirkung von 209Bi Kernen in Bi2Se3 Einkristallen eine Signatur der Bandinversion ist, in quantitativer Ubereinstimmung mit DFT Rechnungen. Weiterhin wird argumentiert dass die starke Spin-Bahn Kopplung der Leitungselektronen zu einer nicht-trivialen Orientierungsabh¨angigkeit der 209Bi Quadrupolaufspaltung führt.:Contents
List of Figures
List of Tables
List of abbreviations
Introduction
1 Topological insulators in three dimensions
2 Theoretical background
3 Methods I: structural, electronic and magnetic properties
4 Methods II: nuclear magnetic resonance
5 Sample preparation and basic characterisation6 Magnetic and electronic properties of Mn doped Bi2Te3
7 NMR of spin 1/2 nuclei: 125Te in Bi2Te3
8 NMR of quadrupole nuclei: 209Bi in Bi2Se3
Conclusions and outlook
Appendix
Bibliography<br>The three-dimensional topological insulators Bi2Se3 and Bi2Te3 are model systems
of a new class of materials with an insulating bulk and gapless surface states. Their
small band gaps and the heavy elements are essential for the topologically non-trivial band structure, but these features are similarly responsible for other remarkable properties, such as their high thermoelectric performance.
This thesis investigates the electronic properties of the topological insulators
Bi2Se3 and Bi2Te3 with a broad range of experimental methods. Ferromagnetism
in Mn doped Bi2Te3 is shown to disappear under sample sintering. A surprisingly
large magnetoresistance and a charge carrier independent change in the sign of
the thermopower with increasing Mn content are discussed.125Te nuclear magnetic
resonance (NMR) of Bi2Te3 single crystals suggest an unusual electronic spin susceptibility and complex NMR shifts. The quadrupole interaction of 209Bi nuclei in
Bi2Se3 single crystals is shown to be a signature of the band inversion in quantitative agreement with first-principle calculations. Furthermore, it is proposed that the strong spin-orbit coupling of conduction electrons causes a non-trivial orientation dependent quadrupole splitting of the 209Bi resonance.:Contents
List of Figures
List of Tables
List of abbreviations
Introduction
1 Topological insulators in three dimensions
2 Theoretical background
3 Methods I: structural, electronic and magnetic properties
4 Methods II: nuclear magnetic resonance
5 Sample preparation and basic characterisation6 Magnetic and electronic properties of Mn doped Bi2Te3
7 NMR of spin 1/2 nuclei: 125Te in Bi2Te3
8 NMR of quadrupole nuclei: 209Bi in Bi2Se3
Conclusions and outlook
Appendix
Bibliography
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Li-WeiHsu and 許立緯. "Hybrid CIGS solar cell using Bi2Se3/Bi2Te3 under layer." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/84526165918085614399.
Full textAbstract:
碩士<br>國立成功大學<br>物理學系碩博士班<br>101<br>In this report, Bi2Se3 and Bi2Te3 thin films were grown by molecular beam epitaxy(MBE) that applied to CIGS solar cell on the device base. On the other hand, the CIGS solar cell device assemble procedure and investigated the CIGS thin-film solar cell device characteristics and efficiency that we cooperate with NDLs (National Nano Device Laboratories). Currently, the solar cell efficiency were not breakthrough. Therefore, we analyze and discuss the CIGS thin-film solar cell device characteristics.
By using X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), scanning electron microscopy(SEM) to investigate the structure and morphology properties of CIGS. According to SIMS analysis, we observed Na concentration can be adjusted Bi2Se3/Bi2Te3 thin film growth parameters.
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Tz-ShiunHuang and 黃子勳. "Study of Bi2Te3/Bi2Se3 Multilayer and Alloy Grown on Glass." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/82577778474616701573.
Full textAbstract:
碩士<br>國立成功大學<br>物理學系碩博士班<br>101<br>Bi2Te3/Bi2Se3 multi-layers and alloys grow on non-crystal-phase glass by molecular beam epitaxy(MBE). X-ray diffraction tell us that multi-layers and alloys on glass still have C-orientation. Raman spectra show multi-layers' and alloy's vibrational modes. Then, we use Hall-effect to recognize major carrier, and obtain p-type Bi2Te3 and Bi2TexSe3-x alloy; n-type Bi2Se3 and multi-layers. Electrical resistivity variation is observed by Van der pauw method. We also observe Bi2TexSe3-x alloy have higher Seebeck coefficient in alloy and so do four-layer in multi-layer. Finally, measuring thermal conductivity is required, futher to get Figure of merit(ZT) for thermoelectic device. Bi2Te3 have best ZT in alloy; Four have best ZT in multilayer.
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Peng, Jing-Ting, and 彭靖婷. "Preparation and Thermoelectric Properties of (Bi2Se3)1-x/(Bi2Te3)x Composites." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/s3t23v.
Full textAbstract:
碩士<br>國立東華大學<br>材料科學與工程學系<br>102<br>In this study, Bi2Se3 was selected as a matrix material and a semiconductor material Bi2Te3 with lower melting point is incorporated to form microstructure in it. The (Bi2Te3)x/(Bi2Se3)1-x composites with x = 0, 0.1, 0.2 and 0.3 were prepared by powder metallurgy technique. As Bi2Te3 and Bi2Se3 powder were mixed homogeneously and sintered at the temperature between the melting point of Bi2Se3 and Bi2Te3. The liquidized Bi2Te3 may diffuse throughout the Bi2Se3 solid matrix and then form a microstructure in it.
However, according to the results of XRD and FE-SEM, the composites prepared by the method we used, the main structure of the most samples are single phase. These results is attributed that Te atoms may substitute for Se atoms and that form ternary compounds and Te precipitates. The thermoelectric measurements show that all samples are n-type in temperature range from 50 K to 400 K. With increasing temperature, the resistivity, Seebeck coefficient and thermal conductivity increased. The resistivity of the sample (Bi2Te3)x/(Bi2Se3)1-x with x = 0.1 is smaller than other samples. The Seebeck coefficient of the pure Bi2Se3 is the largest. The thermal conductivity of the sample (Bi2Te3)x/(Bi2Se3)1-x with x = 0.2 is smaller than other samples. The dimensionless thermoelectric figure of merit ZT for these composites was evaluated and discussed. This study demonstrated that the ZT value of Bi2Se3 was not enhanced by addition of Bi2Te3 particles.
Key words : thermoelectric materials, (Bi2Te3)x/(Bi2Se3)1-x composites, powder metallurgy.
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Pin-HuiChen and 陳品卉. "Epitaxial Growth and Structural Characterization of Single Crystalline Bi2Te3/Bi2Se3 Topological Insulator Multilayer." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/88022157468971825629.
Full textAbstract:
碩士<br>國立成功大學<br>物理學系碩博士班<br>101<br>Bi2Te3/Bi2Se3 topological insulator multilayers have been successfully established on Al2O3 (0001) substrates by molecular beam epitaxy (MBE). In-situ reflection high energy electron diffraction (RHEED) and ex-situ atomic force microscopy (AFM) indicate the smooth surface of the thin films. XRD reveals that the Bi2Te3/Bi2Se3 multilayers are single crystalline (000l) structure. Raman spectra of the multilayers show both the Bi2Te3 and Bi2Se3 phonon vibrational modes with obvious shift comparing to the single-layer films. The peak shift is mainly due to the diffusion between the Bi2Te3 and Bi2Se3 interface. Besides, the full width at half maximum (FWHM) broadens as the layer increases. This is due to the lattice distortion existing in the multilayers.
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Yu, Shih-Hsun, and 余世勛. "Characterization of Topological insulator Bi2Se3 and the study of superconductivity induced in Cu intercalation Bi2Se3." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/5xy32y.
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Lai, Zong-Yo, and 賴宗佑. "NMR Study of Topological Insulator Bi2Se3." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/27931167519329437248.
Full textAbstract:
碩士<br>國立交通大學<br>電子物理系所<br>100<br>Topological insulators are novel electric materials that have a bulk band gap like an ordinary insulator but have protected conducting states on the edge or surface. This thesis reports a nuclear magnetic resonance (NMR) study on the topological insulator Bi2Se3. We measured 209Bi NMR in five different Bi2Se3 single crystals prepared by different methods. All samples show different NMR spectra. We found that these crystals have different levels of defects. Though these defects are too small to be detected by x-ray diffraction, they can make significant difference in the charge carrier density, owing to the semiconductor nature of Bi2Se3. We were able to extract the charge carrier density information from the NMR frequency shift and nuclear spin lattice relaxation rate, and compare with resistivity measurement. There are 9 peaks in the 209Bi spectrum and their intensities do not look like the ones for the nuclear quadrupolar spectrum. However, by measuring spectra at different crystal orientation, we confirm that the 9 peaks are indeed from quadrupolar splitting and there is only one Bi site seen by NMR. Most NMR signals are from the Bi nuclei in the bulk states and the topological surface states could not be probed by NMR technique.
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Nowka, Christian. "Untersuchungen zu Gasphasentransporten in quasibinären Systemen von Bi2Se3 mit Bi2Te3, Sb2Se3, MnSe und FeSe zur Erzeugung von Nanokristallen." Doctoral thesis, 2016. https://tud.qucosa.de/id/qucosa%3A30095.
Full textAbstract:
In Topologischen Isolatoren (TI) werden metallische Zustände an der Oberfläche beobachtet, während die entsprechenden Volumenzustände eine Bandlücke aufweisen. Der Volumenbeitrag zur Leitfähigkeit von TI-Materialien macht eine Synthese von Nanokristallen bzw. eine Dotierung nötig. Der Fokus der Untersuchungen dieser Arbeit liegt dabei auf der Erzeugung von Nanokristallen der TI-Materialien Bi2Te3- und Bi2Te2Se sowie dotierter Bi2Se3-Nanokristallen.
Die Synthese der Nanokristalle erfolgte durch den Gasphasentransport im geschlossenen System über den Mechanismus einer Zersetzungssublimation bzw. unter dem Einsatz eines Transportmittels. Für eine erfolgreiche Erzeugung der Nanokristalle sind im Vorfeld thermodynamische Modellierungen des Gasphasentransports sowie Versuche zum chemischen Transport für die quasibinären Systeme Bi2Se3-Bi2Te3, Bi2Se3-Sb2Se3 und Bi2Se3-FeSe sowie für das ternäre System Mn-Bi-Se durchgeführt worden.
Durch Versuche zum chemischen Transport konnten die Aussagen der Modellierung bestätigt und im Weiteren der Dotandengehalt in den abgeschiedenen Kristallen sowie der Einlagerungsmechanismus durch Ergebnisse aus XRD- und ICP-OES-Untersuchungen beschrieben werden. Die Synthese bzw. Dotierung der Nanokristalle wurde hauptsächlich durch die Transportrate und den Dampfdruck des Dotanden bestimmt.
In den Systemen Bi2Se3-Bi2Te3 und Bi2Se3-Sb2Se3 ist ein Gasphasentransport über eine Zersetzungssublimation durchführbar und resultierte in einer erfolgreichen Darstellung von Bi2Te3- und Bi2Te2Se-Nanokristallen sowie von dotierten (SbxBi1-x)2Se3-Nanokristallen. Entgegen dessen erfolgte der Gasphasentransport in den Systemen Bi2Se3-FeSe und Mn-Bi-Se unter Verwendung eines Transportmittels. Hierbei verringerten die gesteigerten Transportraten das Wachtum von Nanokristallen. Im Weiteren gelang es dotierte (Fe,Mn)xBi2-xSe3-Volumenkristalle sowie MnBi2Se4-Einkristalle darzustellen und mittels XRD, ICP-OES, magnetischer Messungen sowie elektrischem Transport zu charakterisieren.
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Ya-ChenJhong and 鍾亞宸. "Characteristics of MBE-grown Sb2Se3-Bi2Se3 heterostructures." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/252264.
Full textAbstract:
碩士<br>國立成功大學<br>物理學系<br>105<br>Both Sb2Se3 and Bi2Se3 belong to the family of V(Bi, Sb)-VI(Se, Te) compounds. Among the four binary compounds in this family, three are predicted and confirmed to be three-dimensional topological insulators. The exception for Sb2Se3 to be an ordinary insulator is due to the weaker spin orbit coupling and its orthorhombic crystal structure at ambient pressure. However, the theoretical prediction of Sb2Se3-Bi2Se3 heterostructures systems has not been studied experimentally. In this work, we further explore the characteristics of this heterogeneous structure. Maybe Sb2Se3 can be utilized as a tunnel barrier and gate dielectric, which are essential components of many TI devices.
We have demonstrated a successful MBE growth of Bi2Se3-Sb2Se3 heterostructures on sapphire substrate, the analysis of reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and atomic force microscopy (AFM) has a significant difference in Sb2Se3 on Bi2Se3/sapphire and on sapphire.
On the other hand, our devices has nonlinear I-V curve by junction analysis, knowing that Sb2Se3 results in a Schottky-Type transport property. We also indicate that charge transfer results in higher carrier concentration are significant at Sb2Se3-Bi2Se3 systems. In addition, the transport properties can be improved and changed by doping and tri-layer structure.
Key word: topological insulator(TI), heterostructures, spin
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Janíček, Petr. "Termodynamické a transportní vlastnosti materiálů na bázi Bi2Se3." Master's thesis, 2008. http://www.nusl.cz/ntk/nusl-290356.
Full textAbstract:
Single crystals of Bi2Se3 doped with Mn (cMn=0 - 3,0.1019 atoms/cm3) atoms were grown using a modified Bridgman method. Prepared samples were characterized by X-ray diffraction analysis, reflectivity measurement in the plasma resonance frequency region, temperature and magnetic field dependences of the transport coefficients (electrical conductivity, Hall constant), by magnetization measurements (measurement of magnetization curves and temperature dependence of molar magnetic susceptibility) and by measurements of specific heat. The measuremens of above mentioned quantities revealed that the incorporation of Mn atoms to crystal structure leads to increase the free electrons concentration as well as mobility of free electrons. Valence of manganese atoms is according to the magnetic measurements Mn2+. These effects are explained on the point defect model, which is based on idea that the Mn impurity creates substitutional defects Mn'Bi and decreases concentration of antistructure defects Bi 'Se at the same time.
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Yu-HaoChang and 張彧豪. "Electron transport in Bi2Se3 surface and bulk states." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/emtdfk.
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Zhi-WeiWang and 王致惟. "The effect of spin pumping in epitaxial Bi2Se3 films." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/44727489595692584934.
Full textAbstract:
碩士<br>國立成功大學<br>物理學系<br>102<br>Bi2Se3 is one of the promising “second generation” topological insulator (TI) materials, which have both helical spin polarization and strong spin-orbit coupling. In this work, high quality Bi2Se3 thin films were grown on c-plane sapphire (Al2O3) substrates by molecular beam epitaxy (MBE). The central part of the Bi2Te3 layer was covered with a permalloy (Ni80Fe20) layer by IBS with a shadow mask. Through the spin-electricity conversion, and the spin injection into the topological insulator Bi2Se3 thin film can be observed at room temperature (RT) by a spin pumping method. The DC voltage VISHE were obtained and heating effect signals are hard to observed in a Py/Bi2Se3 bilayer system at RT. Our measurements reveal that Py/Bi2Se3 bilayer system could be used as spin-based devices or spintronic devices.