First‐principles study on the concentrations of native point defects in high‐dielectric‐constant binary oxide materials

The intrinsic concentrations of point defects in high‐k binary oxide materials of HfO₂, ZrO₂, Y₂O₃ and La₂O₃ are evaluated on the basis of first‐principles calculations. Oxygen defects are found to dominate over a wide range of the oxygen chemical potential. Neutral oxygen vacancies are likely to be responsible for electron trapping in the investigated materials. In HfO₂ and ZrO₂, oxygen Frenkel pairs are likely to form. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correction of small imperfections on white glazed china surfaces by laser radiation

A laser-assisted technique has been developed for correction of small diameter (1 mm) and shallow (0.5 mm) imperfections on the surface of gloss fired porcelain. To study the physics and establish the important parameters, artificially made holes in a porcelain sample have been first filled with correction material, then covered with raw glaze and treated by a pulsed, 7 kHz repetition rate CO₂ laser at 10.6 μm. The modification of the surface and the surrounding area have been quantified and studied with a large range of parameters of incident laser power (1-10 W), width of the laser pulses (10-125 μs) and duration of laser heating (60-480 s). Although the shine of the treated area, defined as the distribution of micro-droplets on the surface, is very similar to the untreated surfaces, the surroundings of the treated area usually show cracks. The measurement of both the spatial temperature distribution and the temporal cooling rate of the treated surface has revealed that a simple melting process always results in high gradient temperature distribution within the irradiated zone. Its inhomogeneous and fast cooling always generate at least micro-cracks on the surface within a few seconds after the laser was turned off. The duration and intensity of the laser irradiation have been then optimized in order to achieve the fastest possible melting of the surface, but without producing such high temperature gradients. To eliminate the cracks, more elaborated pre-heating and slowed-cooling-rate processes have been tried with prosperous results. These achievements complete our previous study, making possible to repair the most common surface imperfections and holes of gloss fired china samples.     

Collisions between linear polar molecules trapped in a microwave field

The collisions between linear polar molecules, trapped in a microwave field with circular polarization, are theoretically analyzed. We demonstrate that the collisional dynamics is mostly controlled by two ratios ν/B and x=μ₀E₀/ħ B (ν is the microwave frequency, B is the molecular rotational constant, μ₀ is the dipole moment, and E₀ is the electric field amplitude). We discuss the dependence of collision cross sections on these ratios in order to find an advantageous condition for evaporative cooling.     

Natural variability in the surface roughness of combinatorial libraries of materials

Using a conventional method for the fabrication of solid-state combinatorial libraries, we have produced the binary libraries Fe_1−xCr_x and Mo_1−xSn_x (0 < x < 1) and found that their surface roughness is highly dependent on chemical composition. Roughness enhancements of up to 20-fold have been observed on the nanometer scale and were manifested in the boundaries between structurally dissimilar phases. It is anticipated that this is a common occurrence in thin-film libraries of metals and an obstacle in separating the influence of roughness and composition on the performance of library materials in biomaterial studies.     

Patterning of indium-tin oxide on glass with picosecond lasers

The results of patterning of the indium-tin oxide (ITO) film on the glass substrate with high repetition rate picosecond lasers at various wavelengths are presented. Laser radiation initiated the ablation of the material, forming grooves in ITO. Profile of the grooves was analyzed with a phase contrast optical microscope, a stylus type profiler, scanning electron microscope (SEM) and atomic force microscope (AFM). Clean removal of the ITO film was achieved with the 266 nm radiation when laser fluence was above the threshold at 0.20 J/cm², while for the 355 nm radiation, the threshold was higher, above 0.46 J/cm². The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm². The 532 nm radiation allowed getting well defined grooves, but a lot of residues in the form of dust were generated on the surface. UV radiation with the 266 nm wavelength provided the widest working window for ITO ablation without damage of the substrate. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize surface contamination and the recast ridge formation during the process.     

First-Principles Studies on Electronic Structures and Absorption Spectra of PbWO4 Crystals with Defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-c

Electronic structures and absorption spectra for perfect PbW04 （PWO） crystals and the crystal containing aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-exhibit two absorption bands peaking at 1.90eV （65Onto） and 3.02eV （41Onto）. It is predicted that the 420 and fiSOnm absorption bands are related to the existence of the aggregated defect [V^2- Pb-V^2＋ o-V^2- Pb]^2-in the PWO crystal.     

Naphtho-Gamma-Pyrones (NγPs) with Obvious Cholesterol Absorption Inhibitory Activity from the Marine-Derived Fungus Aspergillus niger S-48

Eight naphtho-gamma-pyrones (NγPs) (1–8), together with four known biosynthetically related coumarin derivatives (9–12), were isolated from the potato dextrose agar media of a marine-derived fungus Aspergillus niger S-48. Among them, natural compounds 1 and 2 were tentatively subjected to benzohydrazide reaction to evaluate the importance of pyran rings in NγPs. Their structures were elucidated by extensive 1D and 2D NMR spectroscopic data and MS spectra. Compounds 1–4 showed obvious activity for reducing cholesterol absorption verging on ezetimibe. This work highlighted the potential of natural NγPs as NPC1L1 inhibitors.     

Effect of Chemicals on Chemical Mechanical Polishing of Glass Substrates

We investigate the effect of chemicals on chemical mechanical polishing （CMP） of glass substrates. Ceria slurry in an ultra-low concentration of 0.25 wt. % is used and characterized by scanning electron microscopy. Three typical molecules, i.e. acetic acid, citric acid and sodium acrylic polymer, are adopted to investigate the effect on CMP performance in terms of material removal rate （MRR） and surface quality. The addition of sodium acrylic polymer shows the highest MRR as well as the best surface by atomic force microscopy after CMP, while the addition of citric acid shows the worst performance. These results reveal a mechanism that a long-chain molecule without any branches rather than small molecules and common molecules with ramose abundant-electron groups is better for the dispersion of the slurry and thus better for the CMP process.     

Thermal stability of SiGe films on an ultra thin Ge buffer layer on Si grown at low temperature

The thermal stability of SiGe films on an ultra thin Ge buffer layer on Si fabricated at low temperature has been studied. The microstructure and morphology of the samples were investigated by high-resolution X-ray diffraction, Raman spectra and atomic force microscopy, and using a diluted Secco etchant to reveal dislocation content. After thermal annealing processing, it is observed that undulated surface, threading dislocations (TDs) and stacking faults (SFs) appeared at the strained SiGe layer, which developed from the propagation of a misfit dislocation (MD) during thermal annealing, and no SFs but only TDs formed in strain-relaxed sample. And it is found that the SiGe films on the Ge layer grown at 300 °C has crosshatch-free surface and is more stable than others, with a root mean square surface roughness of less than 2 nm and the threading dislocation densities as low as ∼10⁵ cm⁻². The results show that the thermal stability of the SiGe films is associated with the Ge buffer layer, the relaxation extent and morphology of the SiGe layer.     

Calculated influence of work function on SE escape probability and Secondary Electron Emission yield

The influence of changes of the work function, ?, or electron affinity, χ, on the escape probability, A, of Secondary Electrons, SE, is derived from their angular and energy distributions, respectively ∂δ/∂α and ∂δ/∂E_k. Based on the evaluation of the spectral distribution of inner SEs, the present approach quantifies the dominant role of potential barrier on the SE emission and its change with surface treatments or thin film deposits. For instance it is shown that a 1 eV-increase of ? for Au leads to a decrease of A, and then of SE emission yield, δ, of about 50% while a 0.4 eV-increase of χ for potassium chloride induces a decrease of a factor 4 for A and then for the SEE yield δ. These results are summarized by empirical expressions of form A/A° = (?/?°)⁻³ for Au and A/A° =(χ/χ°)^−3/2 for KCl. Applied here to an insulating sample and to a metal, the present approach may be easily transposed to any kind of material of known Fermi energy and work function, metals, or known affinity, semiconducting and insulating samples. The large SEE yield values of inorganic insulators relative to that of metals are explained by larger values of their escape probability A - KCl: A° ∼ 25% for χ° = 0.6 eV; Au: A° ∼ 4% for ?° = 3.5 eV - combined to larger SE attenuation lengths and despite a less SE generation factor. This approach underlines the significant role of A on the large deviations between SEEY data as reported in literature and a strategy combining in situ δ and ? measurements is suggested to partly compensate the corresponding dispersion of experimental results. The present approach may be transposed to other energetic projectiles such as X-rays or ions and some practical consequences related to Scanning Electron Microscopy, mechanisms of contamination and crystalline contrasts, are pointed out.