Indentation studies on 〈1 0 0〉, 〈0 0 1〉 and 〈1 0 1〉 face of ammonium dihydrogen phosphate (ADP) single crystals: A novel nonlinear optical material

In the present work, Vickers microhardness measurements were carried out on different faces i.e. (1 0 0), (0 0 1) and (1 0 1) of ammonium dihydrogen phosphate (ADP) single crystals grown by slow evaporation solution technique at room temperature in the load ranging from 0.2 to 2 N. The obtained results show that the load independent hardness values are 0.8, 0.7 and 0.66 GPa, respectively at different faces of ADP crystal. From the crack length measurements, the fracture toughness values (K_c) was estimated using Evans and Anstis model and the present studies suggest that Evans model is more relevant when compared to Anstis model. The load variation of some mechanical properties viz. brittle index number (B_i) and yield strength (σ_y) for ADP have also been calculated for the first time.     

Influence of cold-rolling texture and heating rate on {1 1 0}〈0 0 1〉 development in inhibitor-free 3%Si–Fe sheets

This paper presents cold-rolling and annealing methods to obtain a high-magnetic induction in inhibitor-free 0.1-mm-thick 3% silicon–iron sheets containing 18 or 150 ppm sulfur. In case of the two-step cold-rolling, the sheets containing 150 ppm sulfur showed a strong {1 0 0} final texture at 400 °C/h, and some fraction of {1 1 0} component was observed at 25 °C/h. However, three-step cold-rolling resulted in a sharp {1 1 0}〈0 0 1〉 final texture at 25 °C/h. This is due to the difference in intensity ratio of {1 0 0}〈0 1 1〉 to {1 1 1}〈1 1 2〉 in the cold-rolling texture which influences the nucleation of {1 1 0}〈0 0 1〉 component and the selective growth kinetics of various grains. In case of 18 ppm sulfur, the final texture was mainly composed of a sharp {1 1 0}〈0 0 1〉 component even at 400 °C/h, due to the relatively low segregation concentration.     

Growth of 〈1 0 0〉 directed ADP crystal with slotted ampoule

Good quality ammonium dihydrogen phosphate single crystals have been grown by: (i) Sankaranarayanan–Ramasamy (SR) method and (ii) SR method with slotted ampoule. The grown crystals were subjected to UV–Vis spectroscopy, high-resolution X-ray diffractometer, dielectric, piezoelectric and laser damage threshold studies. Compared to the (1 0 0) plane of the conventional method grown ADP crystal and 〈1 0 0〉 directed SR method grown ADP crystal, the crystal grown by SR method with slotted ampoule has higher growth rate, higher optical transparency, high crystalline perfection, low dielectric loss, high piezoelectric charge coefficient and high laser damage threshold due to diffusion of segregated impurities away from the growing crystal in the slotted ampoule growth.     

Thermal evolution of surface blistering and exfoliation due to ion-implanted hydrogen monomers into Si〈1 1 1〉

This study investigated the dependence of surface blistering and exfoliation phenomena on post-annealing time in H⁺-implanted Si〈1 1 1〉. Czochralski-grown n-type Si〈1 1 1〉 wafers were room-temperature ion-implanted with 40 keV hydrogen monomers to a fluence of 5×10¹⁶ cm⁻², and followed by furnace annealing treatments at 400 and 500 °C for various durations ranging from 0.25 to 3 h. The corresponding analysis results for Si〈1 0 0〉 [1] (Liang et al., 2008); [2] (Bai, 2007) were adopted in order to make comparisons. The evolution of blister formation and growth for Si〈1 1 1〉 at 400 °C has a shorter characteristic time compared to Si〈1 0 0〉. However, there is a longer characteristic time when annealing takes place at 500 °C. In addition, no craters were observed for Si〈1 1 1〉 annealed at 400 °C while the opposite is true for Si〈1 0 0〉. The evolution of crater development for Si〈1 1 1〉 annealed at 500 °C has a longer characteristic time compared to Si〈1 0 0〉. These results are attributed to the fact that compared to Si〈1 0 0〉, Si〈1 1 1〉 has a smaller surface binding energy of silicon atoms and a larger areal number density of silicon atoms on the plane perpendicular to the incident-ion axis. Furthermore, Si〈1 1 1〉 has a greater areal number density, smaller diameter, and a similar covered-area fraction of optically-detectable blisters compared to Si〈1 0 0〉. However, Si〈1 1 1〉 has a lower areal number density and a smaller covered-area fraction of craters than does Si〈1 0 0〉. Increasing post-annealing temperature from low (e.g. 400 °C) to high (e.g. 500 °C) revealed that Si〈1 1 1〉 tends to create more blisters while Si〈1 0 0〉 tends to develop larger blisters as well as create more craters.     

Effect of magnetic annealing on magnetostrictive performance of a 〈1 1 0〉 oriented crystal Tb0.3Dy0.7Fe1.95

A 〈1 1 0〉 oriented rod of the alloy Tb_0.3Dy_0.7Fe_1.95 was subjected to a magnetic heat treatment, cooling through its Curie temperature under 240 kA/m. Besides the improved magnetostriction under free conditions, the magnetically annealed rod still exhibited an obvious magnetostriction “jump” effect when subjected to a uniaxial compressive pre-stress. A giant magnetostriction of 2680×10⁻⁶ was achieved under 640 kA/m and 30 MPa, which became 67% larger than before magnetic annealing. The optimum magnetostrictive strain coefficient d₃₃ was also dramatically enhanced. Magnetic force microscopy images show magnetic domain configurations that contribute to the improved magnetostrictive performance. The effect of induced additional anisotropy by magnetic annealing on the improvement of the magnetostriction is also discussed.     

Effect of growth parameters on the structure and magnetic properties of thin polycrystalline Fe films fabricated on Si〈1 0 0〉 substrates

This paper deals with the experimental investigation of the structure and magnetic properties of thin polycrystalline Fe films. Two sets of 50 ± 2 nm thick Fe films were fabricated on Si〈1 0 0〉 substrates with native oxides in place by varying (i) the sputter pressure p_Ar and (ii) the Fe sputter power P_Fe. X-ray diffraction (XRD) study revealed that all films grew with strong 〈1 1 0〉 texture normal to the film plane. No higher order peaks were observed in any of the films studied. For both film sets, the lattice constant (a) was less than the bulk Fe lattice constant (a₀ = 2.866 Å), which suggested the existence of compressive strain in all films. Two regions of homogeneous strain were observed over the range of p_Ar studied. Magneto-optical Kerr effect (MOKE) measurements showed that all films exhibited magnetically isotropic behaviour. The magnetic properties were observed to be influenced strongly by p_Ar. The film grown at p_Ar = 4 μbar was the most softest (H_s = 100 ± 8 kA m⁻¹, M_r/M_s = 0.87 ± 0.02) film among all the films studied. The magnetic properties were found to be independent of P_Fe. The effective saturation magnetostriction constant λ_eff determined (using the Villari method) was positive (4 ± 1 ppm) and observed to vary within the calculated error.     

Photoemission from α and β phases of the GaAs(0 0 1)-c(4 × 4) surface

We prepared α- and β surface phases of GaAs(0 0 1)-c(4 × 4) reconstruction by molecular beam epitaxy (MBE) using As₄ and As₂ molecular beams, respectively, and examined them by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation as an excitation source. The UPS valence band spectra and the XPS 3d core level data show pronounced differences corresponding to the surface composition and the atomic structure of the two phases, as proposed in the literature. In UPS, the β phase is characterized by an intensive surface state 0.5 eV below the top of the valence band at low photon energy, while an analogous peak in the α phase spectra is missing. The surface state is interpreted in terms of dangling bonds on As dimers. The As3d and Ga3d core level photoelectron lines exhibit phase-specific shapes as well as differences in the number, position and intensity of their deconvoluted components. The location of various atoms in the surface and subsurface layers is discussed; our photoemission results support models of the β phase and the α phase with As-As dimers and Ga-As heterodimers, respectively.     

A selective [4 + 2]-like cycloaddition of α, β-unsaturated ketone on Si(1 1 1)-7 × 7

The interaction of ethyl vinyl ketone (EVK) with Si(1 1 1)-7 × 7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH₂ (3099 cm⁻¹) and CO (1684 cm⁻¹) coupled with the appearance of new CC stretching mode (1660 cm⁻¹) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC¹H₂C²HC³(C⁴H₂C⁵H₃)OSi surface species via [4 + 2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C¹/C² and C³ upon chemisorption display chemical downshifts of 0.8 eV and 2.2 eV, respectively, further confirming the proposed [4 + 2]-like cycloaddition reaction for the EVK/Si(1 1 1)-7 × 7 system. DFT theoretical calculations suggest that the proposed [4 + 2]-like cycloadduct is thermodynamically most favorable.     

Growth process and structure of Fe/Si(1 1 1) ultrathin film: Transition from single-domain Fe(1 1 1)/Si(1 1 1) to β-FeSi2

The growth processes and structures of Fe/Si(1 1 1) ultrathin films grown by solid-phase reactive epitaxy were investigated by coaxial impact-collision ion scattering spectroscopy (CAICISS). It has been revealed that the Fe(1 1 1) thin films with a bcc-type structure were epitaxially grown on a Si(1 1 1) crystal, even at room temperature, and formed a single-domain structure: Fe(1 1 1)∥Si(1 1 1). After annealing at above 600 °C, the Fe(1 1 1) films were transformed into β-FeSi₂ via the collapse of the bcc-type structure to an amorphous or polycrystalline structure. On the basis of the thickness dependences of the growth processes, this phenomenon was discussed in terms of the diffusion of Si into Fe thin films.     

Adsorption and decomposition of γ-butyrolactone on Pd(1 1 1) and Pt(1 1 1)

The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO₂ are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO₂, and H₂. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism.     

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.     

Synthesis of azo benzothiazole polymer and its application of 1 × 2 Y-branched and 2 × 2 Mach–Zehnder interferometer switch

The azo benzothiazole polyurethane–urea (ABPUU) was synthesized from chromophore molecule 4-[(6-nitrobenzothiazole-2-yl)diazenyl]phenyl-1,3-diamine NBDPD, polyether polyol (NJ-210) and isophorone diisocyanate (IPDI). The structure, thermal property, mechanical property and physical property were characterized and investigated. The refractive index (n) and thermo-optic coefficient (dn/dT) of ABPUU was determined at different temperature and wavelength (532 nm, 650 nm and 850 nm) using attenuated total reflection (ATR) technique. Using the CCD digital imaging devices, transmission loss of ABPUU was measured. A 1 × 2 Y-branched and 2 × 2 Mach–Zehnder interferometer (MZI) switch with two rib waveguides, dual driving electrodes and two critical 3-dB couplers polymeric thermo-optic switches based on thermo-optic effect of prepared ABPUU were designed and simulation. The power consumption of the Y-branched switch is less than 0.84 mW. The Y-branched and MZI switching rising and falling times obtained are 0.8 ms and 0.2 ms, respectively.     

The γ-Fe formation in epitaxial Cu(0 0 1)/Fe(0 0 1) thin films by the solid-state synthesis: Structural and magnetic features

The γ-Fe formation in epitaxial Cu(0 0 1)/Fe(0 0 1) bilayers with the annealing temperature increasing has been studied. Using Mössbauer spectroscopy, X-ray diffraction, and magnetic analysis, structural and chemical characterization of the interface between cooper and iron layers has been performed. After annealing at 850 °C and subsequent cooling to room temperature, paramagnetic γ-Fe(0 0 1) precipitates with an average size of 30 nm coherent to a Cu(0 0 1) matrix form. Conditions of intermixing and the γ-Fe formation at the Cu/Fe interface are explained in terms of the solid-state synthesis in thin films. Specific features of the martensitic transition γ↔α are discussed.     

Distribution of doped Mn at the Σ3 (1 1 2) grain boundary in Ge

Using first-principles density functional theory method, we have investigated the distribution and magnetism of doped Mn atoms in the vicinity of the Σ3 (1 1 2) grain boundary in Ge. We find that at low concentration, the substitutional sites are energetically favorable over the interstitial ones for Mn. The binding energy of Mn varies with lattice sites in the boundary region, and hence a non-uniform distribution of Mn nears the boundary. However, the average of their segregation energy is quite small, thus no remarkable grain boundary segregation of Mn is predicted. Due to volume expansion at the grain boundary, the spin polarization of Mn is slightly enhanced. Overall, we find that the magnetism of Mn-doped Ge is not sensitively dependent on the grain structure.     

Adsorption of molecular oxygen on the reconstructed β2(2 × 4)-GaAs(0 0 1) surface: A first-principles study

In this work, first-principles modeling techniques are used to investigate the mechanism(s) of adsorption of molecular oxygen on the GaAs(0 0 1)-(2 × 4) surface. The reaction of adsorption was modeled using ab-initio molecular dynamics at constant temperature for two thermal regimes, i.e. 300 K and 680 K, respectively. The resulting adsorbate configurations were relaxed using density functional theory and the adsorption energies were subsequently computed. Our results suggest a dominant mechanism of adsorption described by molecular dissociation, followed by oxygen insertion in the Ga-As bonds, bridging Ga-O-As chemical bonds. The electronic properties of the clean reconstructed GaAs(0 0 1) surface and the ones obtained after O₂ adsorption were computed. It is found that for the most stable adsorbate configuration, where oxygen is incorporated in a Ga-O-As unit, the associated density of electronic states is free of defect levels within the GaAs band gap region.     

Local bond rupture of Si atoms on Si(1 1 1)-(2 × 1) induced by the surface π-π∗ excitation

A scanning tunneling microscopy study has revealed that threefold-coordinated Si atoms at intrinsic sites of reconstructed (2 × 1) structure on the Si(1 1 1) surface are removed to form a surface monovacancy by an electronic mechanism under surface-specific optical transitions at 0.45 eV. This result provides direct evidence for the relaxation of excited surface electronic states as the origin of excitation-induced structural instability on semiconductor surfaces.     

First-principles study of thiophene on β-SiC (0 0 1)-(2×1) surface

In this work, we performed density functional calculations to examine the molecular adsorption states of thiophene on β-SiC(0 0 1)-2×1 surface. A number of possible adsorption geometries are considered into two groups as the polymeric thiophene chain and the individual molecules covalently bonded onto the surface. The results show that the polymeric chain on the surface is the less stable adsorption case and individual arch like adsorption case structure is more stable than others. In all adsorption cases, the adsorbed SiC surfaces are characterized as different semiconductors.     

Catalysis of the hydrogen oxidation reactions by Sr-doped LaMn1 − yCryO3 ± δ oxides

Sr-doped and Sr-free La_1 − xSr_xMn_1 − yCr_yO_3 ± δ (LSMC, x(Sr) = 0-0.2, y(Cr) = 0.4-0.6) perovskite-type oxides were synthesized and evaluated as single phase anodes for use in intermediate temperature solid oxide fuel cell applications. Their thermo-chemical and chemical stabilities were investigated in hydrogen at high temperatures and correlated with their oxygen non-stoichiometry (3 ± δ), determined by permanganate titration. The catalytic activity towards hydrogen oxidation was examined as a function of oxide sintering time, operating temperature, and the Sr and Cr contents, using a Pt mesh current collector. While all of the perovskite oxides studied here showed some irreversible performance degradation with time under both open circuit and anodically polarized conditions, La_0.9Sr_0.1Mn_0.6Cr_0.4O_3.03 (LSMC9164), sintered at 1200 °C for 10 h, was found to be the most catalytically active and also the most stable.     

Current–voltage temperature characteristics of Au/n-Ge (1 0 0) Schottky diodes

The variation in electrical characteristics of Au/n-Ge (1 0 0) Schottky contacts have been systematically investigated as a function of temperature using current–voltage (I−V) measurements in the temperature range 140–300 K. The I–V characteristics of the diodes indicate very strong temperature dependence. While the ideality factor n decreases, the zero-bias Schottky barrier height (SBH) (Φ_B) increases with the increasing temperature. The I–V characteristics are analyzed using the thermionic emission (TE) model and the assumption of a Gaussian distribution of the barrier heights due to barrier inhomogeneities at the metal–semiconductor interface. The zero-bias barrier height Φ_B vs. 1/2 kT plot has been used to show the evidence of a Gaussian distribution of barrier heights and values of Φ_B=0.615 eV and standard deviation σ_s0=0.0858 eV for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively. The Richardson constant and the mean barrier height from the modified Richardson plot were obtained as 1.37 A cm⁻² K⁻² and 0.639 eV, respectively. This Richardson constant is much smaller than the reported of 50 A cm⁻² K⁻². This may be due to greater inhomogeneities at the interface.     

The first π*←π transition of the benzene single crystal in polarized light

The first π*←π transition in the benzene single crystal is investigated at 82 K. Intensities and polarization ratios for both true and false origins in crystal planes (100) and (010) have been measured and rationalized in terms of crystal field perturbation. At liquid nitrogen temperature the origin of the transition is located at 37865 cm^-1 (b), 37817 cm^-1 (c) and 37807 cm^-1(a).