Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

High Real-Space Resolution Measurement of the Local Structure of Ga 1-x In x As Using X-Ray Diffraction

Abstract: High real-space resolution atomic pair distribution functions PDFs from the alloy series $\mathrm{Ga}{}_{1\ensuremath{-}x}{ln}_{x}\mathrm{As}$ have been obtained using high-energy x-ray diffraction. The first peak in the PDF is resolved as a doublet due to the presence of two nearest neighbor bond lengths, Ga-As and In-As, as previously observed using x-ray absorption fine structure. The widths of nearest, and higher, neighbor PDF peaks are analyzed by separating the broadening due to static atom displacements from the thermal motion. The PDF peak width is 5 times larger for distant atomic neighbors than for nearest neighbors. The results are in agreement with model calculations.

Critical investigation of the infrared-transmission-data analysis of hydrogenated amorphous silicon alloys.

Abstract: Infrared-transmission spectroscopy is widely used to obtain quantitative information about hydrogen bonding in hydrogenated amorphous silicon (a-Si:H), silicon-germanium (a-SiGe:H), and silicon-carbon (a-SiC:H) alloys. To simplify the conversion of transmission spectra to absorption spectra the most commonly used methods, suggested by Brodsky, Cardona, and Cuomo (BCC) [Phys. Rev. B 16, 3556 (1977)] and Connell and Lewis (CL) [Phys. Status Solidi B 60, 291 (1973)], assume incoherent multiple reflections in the film as well as the substrate. We show that the absorption in a-Si:H alloy films on c-Si substrates is different for coherent and incoherent reflections in the film. This difference causes the BCC and CL methods to overestimate or underestimate the absorption coefficient (\ensuremath{\alpha}) in many experimental situations. The most notable feature is an overestimate of \ensuremath{\alpha} if the film thickness d is below a critical value (${\mathit{d}}_{\mathrm{min}}$). For dg${\mathit{d}}_{\mathrm{min}}$, the error in absorption coefficient is usually less than 10%. Below ${\mathit{d}}_{\mathrm{min}}$, the error in \ensuremath{\alpha} increases as d decreases. The maximum error, which occurs in the limit d\ensuremath{\rightarrow}0, increases with the refractive index of the film and is \ensuremath{\ge}30% for a-SiC:H alloys, \ensuremath{\sim}70% for a-Si:H, and \ensuremath{\le}90% for a-SiGe:H alloys. The value of ${\mathit{d}}_{\mathrm{min}}$ decreases as the refractive index of the film and the frequency of the vibrational mode increase. For a-Si:H, for example, the hydrogen content determined from the 640-${\mathrm{cm}}^{1}$ Si-H wagging-mode absorption is overestimated if d is less than \ensuremath{\sim}1 \ensuremath{\mu}m. We show that experimental data are consistent with the predictions of this analysis. In most cases it is possible to correct the results from the BCC and CL methods so that they are accurate to within 10%. For greater accuracy, infrared-transmission data should be analyzed by taking the effects of optical interference into account.

Dopant location identification in Nd 3 + -doped Ti O 2 nanoparticles

Abstract: Large band gap semiconductors are typically doped in order to enhance their photocatalytic, photovoltaic, and other chemical and optoelectronic properties The identification of dopant position and its local environment are essential to explore the effect of doping X ray techniques, including extended x ray absorption fine structure, x ray photoelectron spectroscopy, and x ray diffraction, were performed to analyze the Nd $(0\phantom{\rule{03em}{0ex}}\text{to}\phantom{\rule{03em}{0ex}}15\phantom{\rule{03em}{0ex}}\mathrm{at}\phantom{\rule{03em}{0ex}}%)$ dopant location and the structural changes associated with the doping in anatase $\mathrm{Ti}{\mathrm{O}}_{2}$ nanoparticles, which were synthesized by metalorganic chemical vapor deposition Nd ions were determined to have a trivalent chemical state and substitute for ${\mathrm{Ti}}^{4+}$ in the $\mathrm{Ti}{\mathrm{O}}_{2}$ structure The substitutional ${\mathrm{Nd}}^{3+}$ ions cause anatase lattice expansion along $c$ direction with a maximum value of $015\phantom{\rule{03em}{0ex}}\mathrm{\AA{}}$ at 15 % Nd doping level and the local structure of the dopants changes towards rutile like configuration The lengths of the nearest neighbor $\mathrm{Nd}\text{\ensuremath{-}}\mathrm{O}$ and $\mathrm{Nd}\text{\ensuremath{-}}\mathrm{Ti}$ bonds increase by $05--08\phantom{\rule{03em}{0ex}}\mathrm{\AA{}}$ compared to their counterparts in the pure $\mathrm{Ti}{\mathrm{O}}_{2}$ host structure The substitutional nature of ${\mathrm{Nd}}^{3+}$ dopants explains why they are efficient not only for charge carrier separation but also for visible light absorption in $\mathrm{Ti}{\mathrm{O}}_{2}$

Temperature Dependence of the Optical Response of Small, Open Shell Sodium Clusters.

Abstract: The optical absorption of small, open sodium cluster ions (Na{sup +}{sub {ital n}},{ital n}=4, 7, and 11) exhibit an unexpectedly large temperature dependence. Clearly separated absorption lines observed for cold clusters ({ital T}{similar_to}35 K) are interpreted as transitions between electronic states of the Na{sup +}{sub {ital n}} molecule. At the highest temperature ({ital T}{gt}380 K), however, the clusters are liquid, and broad absorption peaks are observed whose energy positions can be explained for {ital n}{gt}7 by the model of nearly free electrons oscillating in a spheroidal container.

Surface chemistry and bonding configuration of ultrananocrystalline diamond surfaces and their effects on nanotribological properties

Abstract: We present a comprehensive study of surface composition and nanotribology for ultrananocrystalline diamond (UNCD) surfaces, including the influence of film nucleation on these properties. We describe a methodology to characterize the underside of the films as revealed by sacrificial etching of the underlying substrate. This enables the study of the morphology and composition resulting from the nucleation and initial growth of the films, as well as the characterization of nanotribological properties which are relevant for applications including micro-/nanoelectromechanical systems. We study the surface chemistry, bonding configuration, and nanotribological properties of both the topside and the underside of the film with synchrotron-based x-ray absorption near-edge structure spectroscopy to identify the bonding state of the carbon atoms, x-ray photoelectron spectroscopy to determine the surface chemical composition, Auger electron spectroscopy to further verify the composition and bonding configuration, and quantitative atomic force microscopy to study the nanoscale topography and nanotribological properties. The films were grown on $\mathrm{Si}{\mathrm{O}}_{2}$ after mechanically polishing the surface with detonation synthesized nanodiamond powder, followed by ultrasonication in a methanol solution containing additional nanodiamond powder. The $s{p}^{2}$ fraction, morphology, and chemistry of the as-etched underside are distinct from the topside, exhibiting a higher $s{p}^{2}$ fraction, some oxidized carbon, and a smoother morphology. The nanoscale single-asperity work of adhesion between a diamond nanotip and the as-etched UNCD underside is far lower than for a silicon-silicon interface ($59.2\ifmmode\pm\else\textpm\fi{}2$ vs $826\ifmmode\pm\else\textpm\fi{}186\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕{\mathrm{m}}^{2}$, respectively). Exposure to atomic hydrogen dramatically reduces nanoscale adhesion to $10.2\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕{\mathrm{m}}^{2}$, at the level of van der Waals' interactions and consistent with recent ab initio calculations. Friction is substantially reduced as well, demonstrating a direct link between the surface chemistry and nanoscale friction. The proposed mechanism, supported by the detailed surface spectroscopic analysis, is the elimination of reactive (e.g., ${\mathrm{C}}^{*}$), polar (e.g., $\mathrm{C}\mathrm{O}$), and $\ensuremath{\pi}$-bonded $(\mathrm{C}\mathrm{C})$ surface groups, which are replaced by fully saturated, hydrogen-terminated surface bonds to produce an inert surface that interacts minimally with the contacting counterface.