The age-related deterioration in bone quality and consequent increase in fracture incidence is an obvious health concern that is becoming increasingly significant as the population ages. Raman spectroscopy with deep-ultraviolet excitation (244 nm) is used to measure vibrational spectra from human cortical bone obtained from donors over a wide age range (34–99 years). The UV Raman technique avoids the fluorescence background usually found with visible and near-infrared excitation and, due to resonance Raman effects, is particularly sensitive to the organic component of bone. Spectral changes in the amide I band at 1640 cm–1 are found to correlate with both donor age and with previously reported fracture toughness data obtained from the same specimens. These results are discussed in the context of possible changes in collagen cross-linking chemistry as a function of age, and are deemed important to further our understanding of the changes in the organic component of the bone matrix with aging.
The direct gap of the In1-xGaxN alloy system extends continuously from InN (0.7 eV, in the near IR) to GaN (3.4 eV, in the mid-ultraviolet). This opens the intriguing possibility of using this single ternary alloy system in single or multi-junction (MJ) solar cells. A number of measurements of the intrinsic properties of InN and In-rich In1-xGaxN alloys (0 < x < 0.63) are presented and discussed here. To evaluate the suitability of In1-xGaxN as a material for space applications, extensive radiation damage testing with electron, proton, and alpha particle radiation has been performed. Using the room temperature photoluminescence intensity as a indirect measure of minority carrier lifetime, it is shown that In1-xGaxN retains its optoelectronic properties at radiation damage doses at least 2 orders of magnitude higher than the damage thresholds of the materials (GaAs and GaInP) currently used in high efficiency MJ cells. Results are evaluated in terms of the positions of the valence and conduction band edges with respect to the average energy level of broken-bond defects (Fermi level stabilization energy EFS). Measurements of the surface electron concentration as a function of x are also discussed in terms of the relative position of EFS. The main outstanding challenges in the photovoltaic applications of In1-xGaxN alloys, which include developing methods to achieve p-type doping and improving the structural quality of heteroepitaxial films, are also discussed.
KEYWORDS: Oxygen, Solar energy, Solids, Semiconductors, Optoelectronics, Photovoltaics, Chemical elements, Chemical species, Signal detection, Data modeling
We have studied the effects of composition and hydrostatic pressure on the direct optical transitions at the Γ point of the Brillouin zone in MBE-grown ZnOxSe1-x and ion-implantation-synthesized Zn1-yMnyOxTe1-x alloys. We observe a large O-induced band-gap reduction and a change in the pressure dependence of the fundamental band gap of the II-O-VI alloys. The effects are similar to those previously observed and extensively studied in highly mismatched III-N-V alloys. Our results are well explained in terms of the band anticrossing model that considers an anticrossing interaction between the highly localized oxygen states and the extended states of the conduction band of II-VI compounds. The O-induced modification of the conduction band structure offers an interesting possibility of using small amounts of O to engineer the optoelectronics properties of group II-O-VI alloys.
Incorporation of a few percent of nitrogen into conventional III-V compounds to form III-N-V alloys such as GaNAs and GaNP leads to a large reduction of the fundamental band gap. We show experimentally and theoretically that the effect originates from an anti-crossing interaction between the extended conduction-band states and a narrow resonant band formed by localized N states. The interaction significantly alters the electronic band structure by splitting the conduction band into two nonparabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy.
Wayne McKinney, Michael Martin, John Byrd, R. Miller, Mike Chin, G. Portman, Edward Moler, Ted Lauritzen, J. McKean, Mark West, N. Kellogg, V. Zhuang, P. Ross, Joel Ager, Wei Shan, Eugene Haller
The design and initial commissioning of the first IR beamline at the ALS has been described previously. We report the final commissioning and first results of the mid-IR spectromicroscopy beamline 1.4.3. In addition, several improvements and two new branchlines are presented. Beamline 1.4.2 is connected to the front end under vacuum and consists of a Bruker Rapid- and Step-Scan vacuum FTIR bench. The modulated light is then coupled into a UHV surface science chamber for grazing incidence reflection studies. Several more external ports are available from the Bruker bench. Beamline 1.4.1 receives light from a separate port on the beamline 1.4 front end and connects to an optical table for photoluminescence and other experiments using photons with energies up to 6 eV.
This paper describes a methodology that has been incorporated into a fully integrated measurement system, the n&k Analyzer, that determines simultaneously the thickness, energy band gap, and n and k spectra (from 190 to 900 nm) of various forms of silicon, i.e., a-Si, poly-Si films, and mixtures of a-Si and poly-Si films. Additionally, the system also measures the average surface roughness. In turn, the n and k spectra of such films can be correlated to processing conditions, temperature being the most important one in LPCVD method. The n&k Analyzer can be used to identify the amorphous-polycrystalline transition regime and characterization of films produced in this regime.
Amorphous 'hard carbon' and microcrystalline diamond films are being investigated and characterized using high-sensitivity and spatial-profiling Raman spectroscopy. The 'hard carbon' films have broad Raman spectra with no diamond line while higher quality diamond films show only a single sharp diamond line. Features in the Raman spectra of the amorphous 'hard carbon' films correlate with the rates of specific types of wear. Changes in the relative intensity of the Raman band near 1570 cm-1 (G-band) compared to the band near 1360 cm-1 (D-band) are related to the rate of abrasive wear. Shifts in the frequency of the G-band are related to the rate of tribochemical wear. The results are consistent with a structural model of amorphous carbon films in which small (< 20 angstrom) graphitic microcrystals comprised of sp2 bonded domains are cross-linked by sp3 carbon atoms. Profiles of Raman frequency and linewidth obtained from spatially resolved Raman spectroscopy across CVD-grown diamond thin films show that the Raman frequency and position are correlated in these films and that both change in regions of poorer film quality.
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