Aharonov–Bohm oscillations observed in nanoscale open-dot structures fabricated in an InAs surface inversion layer

We fabricated nanoscale open-dot structures in an InAs surface inversion layer using an atomic-force-microscope oxidation process. Due to its superior nanofabrication capability, small open-dot structures with the feature size ranging between 100 and 300 nm were successfully fabricated. The magnetoresistance signal measured at 4.2 K showed reproducible fluctuations and a periodic oscillation component that varies in both amplitude and periodicity depending on the dot size. We show that the period of the oscillations corresponds to that of the Aharonov–Bohm effect and propose that the possible mechanism for the oscillations is due to the formation of a one-dimensional electron channel enclosing the open-dot structure as a result of the electron transfer from the InAs oxide to InAs.     

Quantum mechanical study of the potential energy surface of the ClO + NO2 reaction

In the study of the reaction pathways of the ClO + NO2 reaction including reliable structures of the reactants, products, intermediates, and transition states as well as energies the MP2/6-311G(d), B3LYP/6-311G(d), and G2(MP2) methods have been employed. Chlorine nitrate, ClONO2, is formed by N-O association without an entrance barrier and is stabilized by 29.8 kcal mol(-1). It can undergo either a direct 1,3 migration of Cl or OCl rotation to yield an indistinguishable isomer. The corresponding barriers are 45.8 and 7.1 kcal mol(-1), respectively. ClONO2 can further decompose into NO3 + Cl with an endothermicity of 46.4 kcal mol(-1). The overall endothermicity of the NO2 + ClO --> NO3 + Cl reaction is calculated to be 16.6 kcal mol(-1). The formation of cis-perp and trans-perp conformer of chlorine preoxynitrite, ClOONO(cp) and ClOONO(tp), are exothermic by 5.4 and 3.8 kcal mol(-1), respectively. Calculations on the possible reaction pathways for the isomerization of ClOONO to ClONO2 showed that the activation barriers are too high to account for appreciable nitrate formation from peroxynitrite isomerization. All quoted relative energies are related to G2(MP2) calculations.     

Reduction of ion thermal diffusivity associated with the transition of the radial electric field in neutral-beam-heated plasmas in the large helical device

Recent large helical device experiments revealed that the transition from ion root to electron root occurred for the first time in neutral-beam-heated discharges, where no nonthermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. A clear reduction of ion thermal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory when the neoclassical ion loss is more dominant than the anomalous ion loss.     

Soil stress and compaction effects for four tractor tyres

Compaction effects and soil stresses were examined for four tractor tyres under three inflation pressures: 67, 100 and 150% of the recommended pressure. The four tyres were 18.4 R 38, 520/70 R 38, 600/65 R 38 and 650/60-38 and they carried a wheel load of 2590 kg. The 650/60-38 was a bias-ply tyre while the other three were radial tyres. Increased inflation pressure significantly increased all measured parameters: rut depth, penetration resistance and soil stress at 20 and 40 cm depth. The 18.4 R 38 caused a greater rut depth and penetration resistance than the other tyres, which did not differ significantly from each other. The soil stress was highest for the 18.4 R 38, followed by the 650/60-38. The low-profile tyres decreased compaction compared with the 18.4–38 tyre, mainly by allowing a lower inflation pressure. The use of low-profile tyres did not reduce compaction if not used at a lower inflation pressure. The bias-ply tyre caused a higher stress in the soil than the radial tyres when used with the same inflation pressure, but the compaction effects in terms of rut depth and penetration resistance were not greater for this tyre than for the radial low-profile tyres.     

Automated data reduction for hydrogen/deuterium exchange experiments,enabled by high-resolution fourier transform ion cyclotron resonance mass spectrometry

Mass analysis of proteolytic fragment peptides following hydrogen/deuterium exchange offers a general measure of solvent accessibility/hydrogen bonding (and thus conformation) of solution-phase proteins and their complexes. The primary problem in such mass analyses is reliable and rapid assignment of mass spectral peaks to the correct charge state and degree of deuteration of each fragment peptide, in the presence of substantial overlap between isotopic distributions of target peptides, autolysis products, and other interferant species. Here, we show that at sufficiently high mass resolving power (m/Δm_50% ≥ 100,000), it becomes possible to resolve enough of those overlaps so that automated data reduction becomes possible, based on the actual elemental composition of each peptide without the need to deconvolve isotopic distributions. We demonstrate automated, rapid, reliable assignment of peptide masses from H/D exchange experiments, based on electrospray ionization FT-ICR mass spectra from H/D exchange of solution-phase myoglobin. Combined with previously demonstrated automated data acquisition for such experiments, the present data reduction algorithm enhances automation (and thus expands generality and applicability) for high-resolution mass spectrometry-based analysis of H/D exchange of solution-phase proteins.     

Growth mechanisms involved in the synthesis of smooth and microtextured films by acetylene magnetron discharges

The growth of hydrogenated amorphous carbons (a-C:H) produced by continuous or pulsed discharges of acetylene (C(2)H(2)) in an unbalanced magnetron setup was investigated. At 5 × 10(-3) Torr, only smooth films are obtained, whereas at 5 × 10(-1) Torr using a pulsed discharge some microtextured films are formed if the duty cycle is low. The morphology of these microtextured films consists of nanoparticles, filamentary particles, and particular agglomerates ("microflowers"). This paper presents a study of acetylene gas phase polymerization by mass spectrometry, and a detailed analysis of bulk structure of films by combining three techniques which include IR spectroscopy, Raman spectroscopy, and laser desorption/ionization Fourier transform mass spectrometry (LDI-FTMS). Finally, based on the study of gas phase and film structure, we propose a model for the growth of both smooth and microtextured films.     

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm²/V s. By using the ZnO thin film grown by two-step PLD and a HfO₂ high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×10⁶ and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.     

Characterization of [ZnO]m[ZnMgO]n multiple quantum wells grown by molecular beam epitaxy

Thermal stability of single-crystalline [ZnO]_m[Zn_0.7Mg_0.3O]_n multiple quantum wells (MQWs) grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy is reported. X-ray diffraction analysis revealed that these MQWs were grown as designed with a fixed Zn_0.7Mg_0.3O barrier width of and a series of ZnO well widths of . Cathodoluminescence spectra from these MQWs consisted of two major peaks; one was the emission from the bound excitons in Zn_0.7Mg_0.3O barrier layers, and the other was that from the confined excitons in ZnO well layers. These structural and optical properties were found to be dramatically changed by the ex situ annealing treatments over 700 °C. These changes were presumably due to the onset of phase separation of the Zn_0.7Mg_0.3O barrier layers with pronounced Mg diffusion toward the ZnO wells.     

Alloying n‐Butylamine into CsPbBr3 To Give a Two‐Dimensional Bilayered Perovskite Ferroelectric Material

Cesium‐lead halide perovskites (e.g. CsPbBr₃) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr₃, we design the first cesium‐based two‐dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C₄H₉NH₃)₂CsPb₂Br₇ ( 1 ). Strikingly, 1 shows a high Curie temperature (T_c=412 K) above that of BaTiO₃ (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm^?2), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs⁺ ions. To our knowledge, such a 2D bilayered Cs⁺‐based metal–halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large “on/off” ratios of photoconductivity (>10³).     

Optical properties of ultrashort semiconducting single-walled carbon nanotube capsules down to sub-10 nm

Single-walled carbon nanotubes (SWNTs) are typically long (greater than or approximately equal 100 nm) and have been well established as novel quasi one-dimensional systems with interesting electrical, mechanical, and optical properties. Here, quasi zero-dimensional SWNTs with finite lengths down to the molecular scale (7.5 nm in average) were obtained by length separation using a density gradient ultracentrifugation method. Different sedimentation rates of nanotubes with different lengths in a density gradient were taken advantage of to sort SWNTs according to length. Optical experiments on the SWNT fractions revealed that the UV-vis-NIR absorption and photoluminescence peaks of the ultrashort SWNTs blue-shift up to approximately 30 meV compared to long nanotubes, owing to quantum confinement effects along the length of ultrashort SWNTs. These nanotube capsules essentially correspond to SWNT quantum dots.