Results 1 - 10 of 16510
Results 1 - 10 of 16510. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] Due to technical constraints this article was published in volume 240:1 with erroneous article citation ID number 6 whereas this should have been 76 which is corrected as such. Springer Nature sincerely apologizes towards the author(s) for the inconvenience caused.
[en] Terahertz generation has been achieved from a photoconductive switch based on hydrogenated nanocrystalline silicon (nc-Si:H), gated by a femtosecond laser. The nc-Si:H samples were produced by a hot wire chemical vapour deposition process, a process with low production costs owing to its higher growth rate and manufacturing simplicity. Although promising ultrafast carrier dynamics of nc-Si have been previously demonstrated, this is the first report on THz generation from a nc-Si:H material
[en] We report on thermopower (TEP) and resistance measurements of inhomogeneous graphene grown by chemical vapor deposition (CVD). Unlike the conventional resistance of pristine graphene, the gate-dependent TEP shows a large electron-hole asymmetry. This can be accounted for by inhomogeneity of the CVD-graphene where individual graphene regions contribute with different TEPs. At the high magnetic field and low temperature, the TEP has large fluctuations near the Dirac point associated with the disorder in the CVD-graphene. TEP measurements reveal additional characteristics of CVD-graphene, which are difficult to obtain from the measurement of resistance alone
[en] This thesis is concerned with the study of fundamental and defect induced optical properties of synthetic diamond grown using high pressure, high temperature (HPHT) synthesis or chemical vapour deposition (CVD). The primary technique used for investigation is cathodoluminescence (including imaging and decay-time measurements) in addition to other forms of optical spectroscopy. This thesis is timely in that the crystallinity and purity of synthetic diamond has increased ten fold over the last few years. The diamond exciton emission, which is easily quenched by the presence of defects, is studied in high quality samples in detail. In addition the ability now exists to engineer the isotopic content of synthetic diamond to a high degree of accuracy. The experimental chapters are divided as follows: Chapter 2: High resolution, low temperature spectra reveal a splitting of the free-exciton phonon recombination emission peaks and the bound-exciton zero phonon line. Included are measurements of the variation in intensity and decay-time as a function of temperature. Chapter 3: The shift in energy of the phonon-assisted free-exciton phonon replicas with isotopic content has been measured. The shift is in agreement with the results of interatomic force model for phonon scattering due to isotope disorder. Chapter 4: A study of the shift in energy with isotopic content of the diamond of the GR1 band due to the neutral vacancy has allowed a verification of the theoretical predictions due to the Jahn Teller effect. Chapter 5: The spatial distribution of the free-exciton luminescence is studied in HPHT synthetic and CVD diamond. A variation in intensity with distance from the surface is interpreted as a significant non-radiative loss of excitons to the surface. Chapter 6: The decay-times of all known self-interstitial related centres have been measured in order to calculate the concentration of these centres present in electron irradiated diamond. (author)
[en] Previously, we demonstrated the principal possibility to synthesize arsenic telluride films of different chemical and phase composition by PECVD when we directly use elemental arsenic and tellurium as the precursors. This paper presents the results of systematic study of physicochemical properties of As-Te films prepared in low-temperature non-equilibrium RF (40 MHz) argon plasma discharge at low pressure (0.1 Torr) as well. The surface morphology, structure and thermal crystallization behavior of the films obtained were studied in dependence on the plasma parameters of the deposition process. The characteristics of stationary and transitional photoconductivity of the films have been studied as well. (paper)
[en] Silicon dioxide (SiO2) and silicon oxynitride (SiON) thick films used for cladding and core layer of silica based waveguides were fabricated by plasma enhance chemical vapor deposition (PECVD) method, at a low temperature (320 .deg. C) and from (SiH4+N2O+N2) gas mixtures. The effects of deposition parameters on properties of SiO2 and SiON thick films were investigated by variations of SiH4, N2, N2O flow ratio and RF power. The obtained SiO2 films had a high thickness and refractive index of 1.460±0.001 with the annealing process. FTIR and XPS revealed that deposited films were nearly stoichiometric composition with no presence of hydrogen content. SiON films had a 0.75 % higher refractive index than the cladding layer and a high thickness (>5 μm)
[en] The authors report on the growth of Be-doped p-type GaN epilayers by metal-organic chmical vapor deposition (MOCVD). The electrical and optical properties of the Be-doped GaN epilayers were studied by Hall-effect measurements and photoluminescence (PL) spectroscopy. The PL spectra of Be-doped GaN epilayers ethibited two emission lines at 3.36 and 2.71 eV, which were obsent in undoped epilayers. The transition at 3.36 eV was at 3.36 and 2.71eV, which were absent in undoped epilayers. The transition at 3.36 eV was assigned to the transition of free electrons to the neutral Be acceptor Bedeg.. The transition at 2.71 eV was assigned to the transition of electrons bound to deep level donors to the Bedeg. acceptors. Three independent measurements: (a) resistivity vs. temperature, (b) PL peak positions between Be doped and undoped GaN and (c) activation energy of 2.71 eV transition all indicate that the Be energy level is between 120 and 140 meV above the valence band. This is about 20-40 meV shallower than the Mg energy level (160 meV) in GaN. It is thus concluded that Be could be an excellent acceptor dopant in nitride materials. (authors).
[en] This paper is about refractory metal coatings, particularly as made by atmospheric pressure CVD. APCVD does not have a good reputation for semiconductor coatings. It is widely believed to be a technique capable, at best, of only second rate coatings and only oxide coatings at that. The authors' experience is that this is a myth which is simply the result of many disappointing experiences with inadequate equipment. As our proficiency with advanced APCVD has progressed, it has become increasingly evident that there are inherent advantages, not disadvantages, to an atmospheric process. In general, if the desired result can be obtained at atmospheric pressure, it is not clear that any advantage can be gained by going above or below atmospheric. The advantages available from advanced APCVD are quite substantial. The inherent simplicity tends to improve cost effectiveness, but there are also productivity and process advantages. Wafers receive individual processing which helps insure that they are all alike; that dopants have been uniformly distributed. A precise relationship between gas source and substrate helps control gas phase reaction and depletion. Particle generation (contrary to what would be expected for a conveyorized system) is the lowest in the industry