States Of Impurity Atoms Research Articles

Charge State Of Impurity Atoms In Semiconductors Studyed By The Emission Mössbauer Spectroscopy Method

When studying the charge state and symmetry of the local environment of impurities, based on the data of nuclear gamma-resonance spectroscopy, it is concluded that the state of impurity atoms depends both on the type of conductivity and on whether these atoms are in the surface layer or in the bulk of semiconductors.

In English

The experimental results obtained in the study on the possibility of sensitizing titanium dioxide (polymorphic anatase phase) to the visible region of the spectrum by doping and co-doping with impurities of non-metals in order to create effective photocatalysts for the decomposition of organic compounds have been analyzed. The presence of impurity atoms appears to result in a change in the electronic structure of the titanium dioxide matrix, in the appearance of “impurity bands” and in the narrowing of the energy gap of titanium dioxide. Such a modification is accompanied by an extension of the spectral range of sensitivity of photoactive solids to the long-wavelength region of the spectrum and, therefore, can be used to improve the catalytic properties of these materials. Spectral manifestations of carbon impurities in titanium dioxide in the form of carbide and carbonate, as well as sulfur in the forms of sulfite, sulfide, and sulfate, have been studied by the density functional theory method. A Ti14H22O39 cluster model was chosen for the titanium dioxide matrix. The calculations were carried out in the framework of the cluster approximation, using functional B3LYP and basis set 6-31G (d, p). Comparison of the results of quantum chemical calculations with the available experimental data shows that the impurity sulfur and carbon atoms in titanium dioxide, which are in different coordination states and different oxidation states, appear in different spectral ranges. This circumstance makes it possible to elucidate the structure of the samples based on the experimental spectra. A change in the coordination and oxidation states of impurity atoms leads to spectral shifts and splitting of peaks, which can reach 1.5 eV (XPS). The presence of admixtures of non-metals leads to a change in color (deepening in the case of sulfide or carbide) of the samples, appearing in the corresponding UV spectra.

Doping and characterization of impurity atoms in Si and Ge nanowires

AbstractSi and Ge nanowires (SiNWs and GeNWs) are of great interest due to their novel physical properties. They are considered to be desirable materials for the next‐generation metal‐oxide semiconductor field‐effect transistors (MOSFETs) and solar cells. Impurity doping is one of the important techniques to functionalize SiNWs and GeNWs. The crucial point is how the states of impurity atoms can be clarified. In order to realize it, we applied Raman scattering, electron spin resonance, and x‐ray diffraction methods. These results showed that B and P atoms were doped and electrically activated in SiNWs and GeNWs, showing the formation of p‐type and n‐type NWs. Recently, Si/Ge and Ge/Si core‐shell NWs were grown and the site‐selective doping was demonstrated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Doping and Raman Characterization of Boron and Phosphorus Atoms in Germanium Nanowires

Impurity doping is the most important technique to functionalize semiconductor nanowires. The crucial point is how the states of impurity atoms can be detected. The chemical bonding states and electrical activity of boron (B) and phosphorus (P) atoms in germanium nanowires (GeNWs) are clarified by micro-Raman scattering measurements. The observation of B and P local vibrational peaks and the Fano effect clearly demonstrate that the B and P atoms are doped into the crystalline Ge region of GeNWs and electrically activated in the substitutional sites, resulting in the formation of p-type and n-type GeNWs. This method can be a useful technique for the characterization of semiconductor nanowire devices. The B-doped GeNWs showed an increasingly tapered structure with increasing B concentration. To avoid tapering and gain a uniform diameter along the growth direction of the GeNWs, a three step process was found to be useful, namely growth of GeNWs followed by the deposition of an amorphous Ge layer with high B concentration and then annealing.

Study of a hydrogenic atom near a rigid wall by using the finite element method

A direct numerical solution of the Schrodinger equation for a hydrogenic atom near a rigid wall, and the corresponding graphics of some of the energies and wave functions are presented. The solution is obtained by using the finite-element method (FEM) with the appropriate boundary conditions. In particular, crossings of the von Neumann–Wigner type are observed and a classification is suggested of different eigenenergy sets, according to symmetries of the system. The limit with the nucleus being on the wall and the 3D bulk limit are also studied. A discussion of a possible role of the model for the treatment of atom–surface interactions is presented. This system can also be used as a model for 2D and 3D quantum devices, such as shallow state of impurity atoms or Wannier exciton near interfaces.

Effect of Pressure on Dislocation Damping in Aluminum Crystals

Attenuation of megahertz ultrasound has been measured in an aluminum crystal under hydrostatic pressure at room temperature. From the pressure dependence of attenuation at various sound frequencies, the pressure dependence of damping constant for dislocation motion was determined by an analysis based on the overdamped resonance theory of dislocation. Specimen used was primarily zone-refined 99.9999% Al single crystal containing 1 ppm of Si as impurities. The specimen was irradiated by neutrons and 2–4 ppm of Si atoms were further introduced by a nuclear reaction. The specimen was also heat-treated in various ways. Thus the amount and state of impurity atoms were altered, and the high pressure experiments were made for the specimen in different states. The pressure dependence of damping constant was found to be very sensitive to the state of impurities. The order of magnitude and even the sign of the dependence were different for different impurity states. A qualitative discussion was given to interpret th...

Electronic states of impurity atoms in noble-metal lattices

Electronic states of impurity atoms in noble-metal lattices