We study the use of a BGaN back-barrier layer in the GaN buffer of AlyGa1−yN/GaN highelectron mobility transistors to improve confinement of carriers in the 2D electron gas region. Unlike InGaN back-barrier designs, whose polarization-induced sheet charges form an electrostatic barrier at the backbarrier/ buffer interface, BGaN back-barrier designs create an electrostatic barrier at the channel/backbarrier interface. This can result in carrier confinement to sub-15 nm thickness, even when the channel is 30 nm wide. Although polarization sheet charges due to the BGaN back-barrier form a secondary well at the back-barrier/buffer interface, increasing the thickness of the back-barrier may move the secondary well so that it no longer interacts with the primary channel.

n-Si/p-PEDOT-PSS heterojunction diode was fabricated by deposition of poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) onto n-type Si wafer using spin coating. Its electrical properties of the diode were investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The field emission scanning electron microscopy (FE-SEM) was used to determine the surface quality. SEM result indicates that the surface morphology of the PEDOT-PSS film spin coated on n-Si substrate is almost homogeneous. Diode parameters such as the ideality factor, barrier height and series resistance were calculated using Cheung’s method and C-V measurements. I-V characteristics under dark and illumination conditions were performed to characterize the photovoltaic behavior of the diode.

A one-dimensional (1D) position sensitive detector (PSD) with the active layer imbedded in resonant cavity is proposed. The lateral photovoltaic effect (LPE) on the surface of active layer is related to the lifetime of photo-generated carriers-electrons and holes pairs. Theoretically, by improving the transmittance of multiple layered systems, the lifetime of carriers can be lengthened. For a photodetector in near infrared, we design the multiple layered system stacked by alternating layers with MgF2 and InP. The calculated result of electric field distribution in the proposed PSD is maximized in active layer with appropriate thickness. By this means, our aim is theoretically accomplished to enhance LPE in PSD based on resonant cavity structure.

The dielectric response of the liquid crystal (LC) and LC doped with graphene was studied by using dielectric spectroscopy technique in the frequency range of 100 kHz to 10 MHz at room temperature. The LC material used in this experiment was E7 and the concentration of doping material graphene was acquired as 0.05 wt.% in E7. Dielectric constant (ε'), dielectric loss (ε"), dielectric loss tangent (tan δ) and AC conductivity of pure LC and graphene-doped LC mixture were also calculated. Results showed that all dielectric parameters are strong functions of frequency and applied bias voltage. Also, it was found that doping LC with graphene strongly influenced threshold voltage.

The multilayered films-based charge trap flash memory cells were fabricated by incorporating high-k ZrO2/Al2O3 nanolaminates as charge trapping layer and amorphous Al2O3 as tunneling and blocking layers. The thickness of high-k ZrO2 or Al2O3 film in charge trapping layer after annealing treatment was about 1.5 nm for each layer. The charge storage characteristics of such memory cells were measured, and the results demonstrated that they had a large hysteresis memory window of 3.85 V at a sweeping gate voltage of ±8 V, an excellent endurance up to 105 write/erase cycles and a small charge loss of 9.6% after 10 years.

A sintered Ti13Cu87 bi-component target was sputtered by reactive DC magnetron sputtering in nitrogen ambient under various sputtering powers. Ti included Cu3N (Ti:Cu3N) thin films were deposited on Si (1 1 1), KBr (potassium bromide), quartz and glass slide substrates. Crystalline phases of the films were identified by X-ray diffraction (XRD) technique. Crystalline quality and phase stability are strongly dependent on sputtering power. Formation of copper vacancies in Cu3N cell substituted by Ti atoms and subsequent excess of interstitial nitrogen (N-rich) result in lattice constant expansion. Bonding environment in these films was obtained from fourier transform infrared (FTIR) spectroscopy. Surface morphology of the films that were studied by a scanning electron microscope (SEM) indicates a granular structure. Atomic Ti:Cu ratio of Ti:Cu3N films, determined by energy dispersive X-ray (EDX) spectroscopy, is less than that of original target. Optical study was performed by Vis-near IR transmittance spectroscopy. Film thickness, refractive index and extinction coefficient were extracted from the measured transmittance using pointwise unconstrained minimization approach. The TiCu3N films are direct semiconductor with bandgap energy with the range of 2.79–3.34 eV. Ti incorporation and subsequent N-rich have a significant role in bandgap widening and lattice constant expansion. The films electrically show quasi-metallic behavior.

Au/SiO2/Si interdigital electrodes with thickness of 1 μm were created on silicon substrate. Graphene oxide (GO) sheets hanging from these electrodes were obtained by spin coating of chemically synthesized GO dispersed in water. We used UV-light-induced photo-catalytic activity of titanium oxide nanoparticles to reduce the GO layer. Effects of the photo-induced chemical reduction on the conductivity of the GO were investigated. Also, low power DC plasma was used for oxidation of the sheets. Oxygen bombardment leads to sheets with low electrical conductivity. Measurements show that graphene and GO sheets with the controlled electrical conductivity were obtained by these processes. Scanning electron and atomic force microscopy were used to study the morphology of the TiO2/GO and graphene structures. X-ray diffraction and Raman scattering analysis were used to verify the structural characteristics of the prepared sheets. Analysis showed a gradual increase in the number of C-O bonds on the surface of the graphene layer as a result of increasing the time of plasma bombardment. Based on the Raman spectroscopy, the photo-catalytic activity of TiO2 nanoparticles resulted in a decrease in the number of C-O bonds.

Fast linear transformer driver (FLTD) has some advantages in repetitive operation compared with traditional pulsed power generators. However, different types of gas switches applied in the field of pulsed power technology in recent years cannot reach the requirements of repetitive operation of FLTD. Therefore, the capability of repetitive operation of a multigap gas switch has been investigated in a circuit similar to the basic discharge loop named as brick in this paper. The switch has been triggered more than 2000 times and the distribution of delay time and switch jitter are analyzed and reported. Also, the self-breakdown voltages of the switch during different segments of the triggered breakdown experiment have been tested. The experimental results indicate that the delay time obeys the Gauss distribution and the jitter of 2000 times of discharge is about 2.3 ns.

The split Hopkinson pressure bar (SHPB) was used to study the compressibility of shear thickening fluid (STF) at high deformation rate. In this study, a steel bulk was introduced into the SHPB system to confine and load the STF. A series of STFs with different particle types (SiO2 and PSt-EA) and volume fractions (63 vol.% and 65 vol.%) were tested and the results were compared. The reliability of the results was proved by repeating the tests and the force balance in suspension. The bulk modulus was used to evaluate the compressibility of STF, which indicated that the SiO2-based STF exhibited a larger compressibility than the PSt-EA-based STF. It was found that the bulk modulus increases with increasing of the strain rate and the volume fraction shows little effect on the bulk modulus. The structure-dependent mechanical property was analyzed and the loading effect of bulk modulus was considered to be originated from the interparticle clustering.

An all-electron scalar relativistic (AER) calculation on AunPtCO (n = 1–12) clusters had been performed using density functional theory (DFT) with the generalized gradient approximation (GGA) at Perdew-Wang 91 (PW91) exchange-correlation functional level. The CO molecule prefers to be adsorbed on Pt in AunPt (n = 1–12) clusters. The introduction of impurity Pt strengthens the adsorption toward CO molecule and then promotes the reactivity enhancement of CO molecule. The CO molecule is also more favorable to be adsorbed by the even-numbered AunPt clusters with closed-shell electronic structure.

An oligothiophene having a donor-acceptor-donor chromophore with hydrogen bonding groups is used as electron donor in planar heterojunction organic photovoltaic cells. We focus on the contact between the anode and the oligothiophene. Different anode buffer layers (ABLs) have been used, MoO3 and CuI, alone or coupled with MoO3. The thicknesses were 4 nm and 3 nm for MoO3 and CuI respectively. It is shown that the ABL improves the cells performances. The best results are achieved with the couple MoO3/CuI through an increase of the open circuit voltage and short circuit current. The optical absorption, the surface roughness and the organic film conductivity depend on the ABL. The conductivity of the oligothiophene film is one order of magnitude higher when the ABL is a CuI film. The influence of the ABL can be explained partly by the fact that it raises the anode work function. Nevertheless, the study of the structures ITO/ABL/oligothiophene shows that each ABL exhibits specific advantages and disadvantages. Therefore the couple MoO3/CuI allows summing up the advantages of both ABLs, MoO3 allows a very good band matching and avoids too high leakage current, while CuI allows achieving high Jsc thanks to its effect on the TTB conductivity.

Sliding friction at nanometer scale has become an important factor in the miniaturization of moving components in which the empirical laws of friction do not always hold. This paper carries out large-scale parallel molecular dynamics simulation on sliding friction at atomic scale to uncover the special physical essence. The simulation result shows that both of the elastic deformation normal to the sliding direction at the local area and the edge dislocation are generated in the bulk materials. The successive generation and fracture of the molecular junction between a friction pair ought to be the key reason for the variation of friction force. Furthermore, end failure is observed under both larger or smaller sliding velocity although it does not increase linearly by increasing velocity, that is to say, the end failure decreased if the velocity was larger than some critical value. Different kinds of materials transfer mode is observed in the friction process under different sliding velocity because of the different cross-section of the interaction surfaces. The stick-slip feature of this nanoscale sliding friction with zero separation is different from what was observed at a microscale and should be the integral effect of different control mechanism and the corresponding dynamic behavior.