Academic literature on the topic 'Absorpční spektroskopie'

The thesis presents design, development and realization of laser system with stabilized optical frequency which could become the basis of an etalon of wavelength for the telecommunication band of the near-infrared spectral region. Semiconductor DFB laser diode is used as a tunable source of radiation with narrow linewidth. Its optimum operation is ensured by especially designed current and temperature controller. The laser is prestabilized using FM spectroscopy technique to the passive Fabry-Perot cavity. This fast feed-back loop is able to improve spectral characteristics of the laser. The center frequency of the F.-P. cavity - the laser optical frequency is locked by a slow second feed-back loop to the absorption spectral line of acetylene 13C2H2 gas. The slow control loop is based on the third derivative spectroscopy technique. Relative stability at the level of 10E-12 was achieved.

The aim of this thesis is the actual elaboration literature search concerning the issue of platinum group metals in the environment, determination of platinum and palladium in great urban agglomerations. It includes chemical and physical properties, occurrence and platinum and palladium cycle in the environment. It also contains methods for extraction and determination of platinum and palladium.

Diploma thesis treat of effect of direct, alternate and pulse electrical stress on the properties surveyed electrical insulating material. Object of this experiment is crystalline high-density polystyrene QUINN PS. To monitor the stress is used the method of dielectric relaxation spectroscopy. Under examinations are the resultant dielectric spectra, which constitute the frequency dependencies of components of complex permitivity. Samples of the selected material are exposed to effects of alternate and pulse electrical stress on the different intensities of the electric field. In the direct field are then monitored absorption characteristics and specific volume resistance of the samples.

Hlavním předmětem této diplomové práce jsou elektromagnetické simulace pomocí metody konečných prvků (FEM) k vyšetření vlivu grafenu na hrotem zesílenou Ramanovu spektroskopii (TERS) a povrchem zesílenou infračervenou absorpční spektroskopii (SEIRA) a k prozkoumání citlivosti sondy skenovacího optického mikroskopu blízkého pole (SNOM) ke složkám elektromagnetického pole v závislosti na parametrech sondy (průměru apertury v pokovení). Nejprve je proveden výpočet TERS systému složeného ze stříbrného hrotu nacházejícího se nad zlatým substrátem s tenkou vrstvou molekul, jehož účelem je porozumění principů TERS. Poté je na molekuly přidána grafenová vrstva, aby se prozkoumal její vliv ve viditelné (TERS) a infračervené (SEIRA) oblasti spektra. Druhá část práce se zabývá výpočty energiového toku SNOM hrotem složeným z pokoveného skleněného vlákna interagujícím s blízkým polem povrchových plasmonových polaritonů. Zde uvažujeme zlatou vrstvu se čtyřmi štěrbinami uspořádanými do čtverce na skleněném substrátu sloužícími jako zdroj stojatého vlnění povrchových plasmonů s prostorově oddělenými maximy složek elektrického pole orientovanými rovnoběžně či kolmo na vzorek. Ve výpočtech hrotem zesílené spektroskopie zjišťujeme, že grafen přispívá pouze malým dílem k zesílení pole ve viditelné oblasti spektra, ovšem v infračervené oblasti má grafen vliv pro záření s energií menší než dvojnásobek Fermiho energie grafenu, pro kterou je hodnota zesílení pole větší než v případě výpočtu bez grafenu. Avšak pro velmi vysoké vlnové délky zesílení pole v přítomnosti grafenu klesá pod (konstantní) hodnotu pro případ bez grafenu. Při studiu citlivosti SNOM hrotu k jednotlivým složkám pole shledáváme, že pro hrot se zlatým pokovením je energiový tok skleněným jádrem hrotu kombinací příspěvků energie prošlé aperturou a periodické výměny energie mezi povrchovým plasmonem šířícím se po vnějším okraji pokovení a mody propagujícími se v jádře. Dále zjišťujeme, že hroty s malou aperturou (či bez apertury) jsou více citlivé na složku elektrického pole orientovanou kolmo ke vzorku (rovnoběžně s osou hrotu), zatímco hroty s velkou aperturou sbírají spíše signál ze složky rovnoběžné s povrchem vzorku. V případě hrotu s hliníkovým pokovením jsou hroty citlivější ke složce pole rovnoběžné s povrchem, což je způsobeno slabším průnikem pole skrze pokovení.

Surface-enhanced Raman scattering (SERS)-active systems based on macroscopic Ag nanosponge aggregates as well as the conditions of SERS spectral measurements were optimized for selective and sensitive detection of a biomedically important, amphiphilic bile pigment bilirubin (BR) in alkaline aqueous solutions and in its solutions in a selected water miscible solvent, namely dimethylsulfoxide (DMSO) and/or water-immiscible solvent, namely CH2Cl2. Ag nanosponges assembled by using HCl as a pre-aggregation agent were found to be the optimal SERS-active systems for a reliable detection of BR in all the above-mentioned solvents. In all cases, the protonated form of adsorbed BR has been detected upon BR incorporation into Ag nanosponges, and its marker bands have been established by SERS spectral probing at excitation wavelengths in the 445-780 nm range. The sensitivity of SERS spectral detection was evaluated in terms of the concentration values of SERS spectral detection limits (SERS LODs) of BR incorporated into Ag nanosponges. In particular, the SERS LOD for BR incorporated from its alkaline aqueous solution is 1 x 10-8 M (at 532 nm excitation), for BR incorporated from its solution in DMSO, its value is also 1 x 10-8 M (at 532 and/or 633 nm excitations), and for incorporation from the solution of BR...

Title: Model systems with the use of CeO2 for bioapplication Author: Sofiia Bercha Department: Department of Surface and Plasma Science Supervisor: Ing. Nataliya Tsud Ph.D., Department of Surface and Plasma Science Abstract: This thesis is focused on the investigation of model systems for bioapplications. Interfaces between biomolecules and inorganic materials were studied by means of advanced surface science techniques with emphasis on the molecular electronic structure and bonding geometry as a function of material morphology and/or molecular deposition method. For the histidine/cerium oxide system it is demonstrated that the morphology of the oxide determines the mechanism of the molecular adsorption. The presence of an aqueous medium does not alter the histidine interaction with the nanostructured cerium oxide. For the adenine/cerium oxide system we have shown that the adenine molecule chemisorbs on CeO2 intact via nitrogen atoms, independent of the oxide morphology and deposition technique. The adenine molecule was found to decompose on a reduced surface of the cerium oxide. Combining experimental and theoretical methods two distinct phases of adenine on CeO2 were found. For adenine/Cu(111) system it was shown that the strong interaction with the surface keeps the molecule intact on the surface till...

Chlorophyll molecules in their triplet excited state can react with the ground state oxygen, producing oxygen in a singlet excited state, which is very reactive and thus very harmful to the light-harvesting complex. Photosynthetic organisms employ carotenoids to prevent the damage by quenching both excited (singlet) states of oxygen and excited triplet states of chlorophyll. In this work, we use ns transient absorption spectroscopy and global analysis to study the dynamics of carotenoid and chlorophyll triplet states in two light-harvesting complexes of Amphidinium carterae, the Peridinin-Chlorophyll a-Protein complex (PCP) and the main light-harvesting complex (LHCP). It appears that at room temperature all triplets are transferred from chlorophylls to carotenoids within ~ 5 ns, providing a very efficient protection against formation of singlet oxygen. One carotenoid triplet with a lifetime of ~ 10.2 µs participating in the chlorophyll triplet quenching was observed in the PCP sample, while results from LHCP suggest that two carotenoid triplets with a similar lifetime of ~ 2.5 µs contribute to quenching of chlorophyll triplet states. The two carotenoid triplets are attributed to peridinin placed in a polar environment and peridinin placed in a non-polar environment in the LHCP complex.

Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...

In this Diploma Thesis, an interaction of genotoxic environmental pollutant 2-nitrofluorene with a double-stranded calf thymus DNA has been studied using a hanging mercury drop electrode (HMDE) as an electrochemical sensor. Two types of DNA damage were investigated and electrochemically detected (using cyclic voltammetry and differential pulse voltammetry): (i) The DNA damage caused by the direct interaction with 2-nitrofluorene and (ii) the DNA damage caused by short-lived radicals generated by the electrochemical reduction of the nitro group in 2-nitrofluorene. For the study of direct interaction, HMDE was modified by DNA and the interaction of DNA with 2-nitrofluorene was studied, after their incubation, right at the HMDE surface (adsorptive transfer stripping technique) or the DNA was preincubated with 2-nitrofluorene and, subsequently, the interaction was studied voltammetrically (DNA titration technique). Using both detection techniques, the formation of DNA - 2-nitrofluorene complex was observed and the mutual interaction was interpreted as an intercalation between the DNA base pairs, although such interaction was not clearly confirmed by UV-visible absorption spectroscopy. An electrostatic binding of 2-nitrofluorene on DNA sugar-phosphate backbone was partially formed at low concentrations of...