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Alternating current polarization (ACP) has been demonstrated to enhance the performance of 1-3 piezoelectric single crystal composites (PSCCs), compared to direct current polarization (DCP). However, the scaling effect and temperature stability of PSCCs under different polarization modes, which are of significance to practical applications, have rarely been studied. Here, we compared and analyzed the thickness and temperature-dependent properties of PSCCs under ACP and DCP. The results indicated that ACP PSCCs have improved piezoelectric, electromechanical coupling, and dielectric properties. There were scaling effects for PSCCs with thickness below 400 μm. Compared to high-thickness PSCCs, the piezoelectric coefficient (d33), free dielectric constant ( ε 33 T ε 0 ) as well as thickness electromechanical coupling factor (kt) of low-thickness samples were inferior and the corresponding performance enhancements under ACP were also relatively low. In contrast, the clamped dielectric constant ( ε 33 S ε 0 ) did not show significant thickness correlation. As for temperature stability, all performances of PSCCs improved with increase in temperature and the performance enhancement with temperature change was not dependent on the polarization conditions. This work provides reference significance of selecting appropriate polarization for PSCCs, thus benefiting the design and preparation for transducers. [ABSTRACT FROM AUTHOR]

We report on van der Waals epitaxy of single-crystalline α-MoO3 sheets with single-unit-cell thickness on the mica substrate. The crystalline lattice structure, growth habits, and Raman spectra of the grown α-MoO3 sheets are analyzed. The anisotropic growth of α-MoO3 sheets can be understood by period bond chains theory. Unlike monolayer MoS2 or graphene, Raman spectra of α-MoO3 do not possess frequency shift from bulk crystal to single-unit-cell layer. The relative intensities of two Raman modes (Ag) at 159 and 818 cm-1 are sensitive to the polarization of incident light. This scenario provides a quick approach to determine the lattice orientation of α-MoO3 crystals. Our studies indicate that van der Waals epitaxial growth is a simple and effective way to fabricate high-quality ultrathin α-MoO3 sheets for physical property investigations and potential applications. [ABSTRACT FROM AUTHOR]

A supersaturation of nitrogen atoms is found in the surface layer of microstructured silicon after femtosecond (fs) laser irradiation in NF3. The average nitrogen concentration in the uppermost 50 nm is about 0.5 ± 0.2 at.%, several orders of magnitude higher than the solid solubility of nitrogen atoms in silicon. The nitrogen-hyperdoped silicon shows high crystallinity in the doped layer, which is due to the repairing effect of nitrogen on defects in silicon lattices. Nitrogen atoms and vacancies can be combined into thermal stable complexes after fs laser irradiation, which makes the nitrogen-hyperdoped silicon exhibit good thermal stability of optical properties. [ABSTRACT FROM AUTHOR]

We demonstrate small molecule bulk heterojunction organic photovoltaic cells using oblique angle vacuum deposition. Obliquely deposited donor chloroaluminum phthalocyanine (ClAlPc) films on indium tin oxide have surface feature sizes of ∼30 nm, resulting in ClAlPc/C60 donor-acceptor heterojunctions (HJs) with approximately twice the interface area of HJs grown at normal incidence. This results in nearly twice the external quantum efficiency in the ClAlPc absorption band compared with analogous, planar HJs. The efficiency increase is attributed to the increased surface area presented by the donor-acceptor junction to the incident illumination by ClAlPc protrusions lying obliquely to the substrate plane formed during deposition. The power conversion efficiency improves from (2.0±0.1)% to (2.8±0.1)% under 1 sun, AM 1.5G simulated solar illumination. Similarly, the power efficiency of copper phthalocyanine/C60 organic photovoltaic cells is increased from (1.3±0.1)% to (1.7±0.1)%. [ABSTRACT FROM AUTHOR]

InAs is very attractive as a channel material for high-speed metal-oxide-semiconductor (MOS) field-effect transistors due to its very high electron mobility and saturation velocity. We investigated the processing conditions and the interface properties of an InAs metal-oxide-semiconductor structure with Al2O3 dielectric deposited by atomic-layer deposition. The MOS capacitor I-V and C-V characteristics were studied and discussed. Simple field-effect transistors fabricated on an InAs bulk material without source/drain implantation were measured and analyzed. [ABSTRACT FROM AUTHOR]

Studies the fine structures in the photoresponse spectra of GaAs/AlGaAs quantum well infrared photodetectors. Monolayer change in the quantum well reflected in the photocurrents; Absorption coefficients for different well widths; Postgrowth processes.

Pb-based relaxor piezoelectric single crystal composites (PSCCs) have attracted widespread attention for improving the bandwidth and sensitivity performance of acoustic transducers due to their excellent electromechanical and piezoelectric properties. Alternating current polarization (ACP) has been proven as an effective method for enhancing the dielectric and piezoelectric properties of relaxor-PbTiO3 single crystals. Herein, we investigated the effects of the amplitude, frequency, and cycle number of the poling electric field on the piezoelectric and dielectric performances of PSCCs and obtained the optimum poling condition of ACP. Compared with the traditional direct current poling method, both the dielectric permittivity ( ε 33 T / ε 0 ) and piezoelectric coefficient ( d 33 ) of the AC-poled PSCCs were both increased by up to 20%. Notably, the ACP PSCC with a volume fraction of 60% exhibited a high d 33 of 1610 pC/N, which is superior to values previously reported for PSCCs. This work provides an alternative strategy for enhancing the properties of PSCCs and may contribute to the further development of piezoelectric applications. [ABSTRACT FROM AUTHOR]

Using a free-electron laser(FEL) source, we have studied the two-photon-absorption (TPA) effect in GaAs/AlGaAs quantum-well infrared photodetector (QWIP). The TPA-induced photoresponse in QWIPs has been measured under different FEL excitation power by the photoconductivity method. The effective-mass approximation theory is used for the QWIP structure to explain the photoresponse behavior. It is demonstrated that the TPA-induced photocarrier density is proportional to the square of the excitation power. Based on the experimental results, the TPA coefficients of QWIPs were obtained to be 0.0045, 0.0030, 0.0103, and 0.0061 cm/MW for the excitation lines of 10.6, 10.7, 11.9 and 13.2 μm, respectively. The dependence the TPA coefficients on the excitation wavelength is explained by our theoretical model. [ABSTRACT FROM AUTHOR]

A coupled three-dimensional optoelectrical simulation was used to evaluate the optical and electrical designs requirements for improving the efficiency of Si nanowire array (NWA)/Poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) solar cells. Due to the addition of organic coating layers, better light absorptions are observed for the Si NWA/P3HT:PCBM structure at the wavelengths both below and above the absorption cutoff wavelengths of P3HT:PCBM. Optimized optical designs are obtained by maximizing the ultimate photocurrent under AM1.5G illumination. Furthermore, from the electrical simulation of the solar cell at optimized photo-absorption structure, the proposed Si NWA/P3HT:PCBM hybrid cell exhibits a promising character that is insensitive to exciton recombination at the optimized coating thickness of 80 nm. An efficiency of 9.4% can still be obtained even at high bimolecular recombination rates. [ABSTRACT FROM AUTHOR]

Continuous-wave optical orientation spectroscopy and the Hanle effect are used to investigate the optical spin polarization and spin dephasing time (gTs) in GaAsSb with a Sb concentration of ~6% as a function of temperature. Optical and spin polarizations up to ~21% were achieved at ~120K, and the scaled spin lifetime gTs decreased monotonously from ~1.5ns at 5 K to ~20 ps at 200 K. We demonstrate that the spin properties of GaAs could be modified by incorporating a small percentage of Sb into it, as a result of an increase in the spin-orbit interactions. [ABSTRACT FROM AUTHOR]

Confocal micro-Raman spectroscopy is employed to characterize various grades of human cataracts. Results show that the intensity ratio of the tyrosine doublet (I855/I833) changes from 1:1.07?±?0.03 to 1:1.17?±?0.05 with the aggravation of cataracts, which indicates that there are more tyrosine residues bound to strong H acceptors instead of bounding to water. The decrease of relative intensity at 880?cm-1 band suggests that the "buried" tryptophan residues become "exposed" during the course of lens opacification. A three-dimensional principal component analysis is used to classify the Raman spectra of opacity tissues, which show a one-to-one correspondence with different grades of cataracts. [ABSTRACT FROM AUTHOR]

The nonequilibrium carrier distribution in an InGaAs/InP avalanche photodiode under light illumination is obtained by cross-sectional scanning capacitance microscopy combined with numerical simulation. The sheet density of negative surface charge is determined to be 1.85×1010 cm-2 on the native-oxidized InGaAs (110) face. This surface charge is found responsible for the accumulation of minority holes, which leads to an inversion layer at the sidewall surface of device in the absorption region under illumination exceeding 0.1 mW/cm2. The inversion depth increases up to 200 nm along with the enhancement of excitation intensity. This work suggests that a surface leakage channel may form in semiconductor photodetectors through detection light excitation. [ABSTRACT FROM AUTHOR]