We have investigated on a relation between C-related deep-level defects and turn-on recovery characteristics in bulk regions of AlGaN/GaN hetero-structures containing various C concentrations, employing their Schottky barrier diodes. With decreasing the growth temperature of the GaN buffer layer, three specific deep-level defects located at ∼2.07, ∼2.75, and ∼3.23 eV below the conduction band were significantly enhanced probably due to the C impurity incorporation into the GaN buffer layer. Among them, the ∼2.75 and ∼3.23 eV levels are considered to be strongly responsible for the two-dimensional electron gas (2DEG) carrier trapping in the bulk regions of the hetero-structures, from their turn-on current recovery characteristics under various optical illuminations.

InP membranes have been bonded both oxide free and oxide mediated onto a Si substrate. The mechanical responses of the obtained thin (0.4 µm) membranes could be tested by nanoindentation and compared. Delamination of the membrane was observed to occur when the indenting load reached 55 mN for an oxide mediated bonded structure and 80 mN for an oxide free bonded one. Weibull analysis of these events yielded a modulus m of magnitude 6 to 10, indicating that delamination fracture is relatively predictable with a stronger interface obtained in oxide free approach. Delamination of the membrane is the result of constraint of plastic flow by the InP/Si interface. Membrane rotation is induced and increases with the indentation load, until it is sufficient to induce and propagate an interfacial crack.

Chemical Vapor Deposition of graphene on metallic substrates is one of the most attracting techniques for large area graphene production. The technique widely employed for transferring graphene to other substrates involves deposition of a polymer support with subsequent etching of the metal substrate. Here we report a safer transfer process, which requires a two-step PMMA deposition and bonding under pressure. Sheets of graphene before and after transfer have been both characterized by Raman spectroscopy, and show comparable quality, indicating that the proposed technique does not introduce additional defects in graphene.

As a promising transition metal dichalcogenide (TMDC), molybdenum disulfide (MoS2) has recently attracted a lot of attention due to its graphene-liked two dimensional layer structure, which leads to potential applications in electronic and optoelectronic devices. However, the fabrication of mono- or few-layer MoS2 is limited to ether liquid exfoliation or CVD, and the chemical solution deposition is limited to ammonium thiomolybdate-based precursor. In this paper, hydrazine-based dimensional reduction technique is applied in the chemical solution deposition of MoS2 thin-film, and a larger area uniform thin-film is obtained from bulk powder MoS2. This solution-based process could be applied with a variety coating techniques and lead to wafer level MoS2 thin film production.

The effect of Y dopant incorporated into ZTO with different Y ratios in Y-ZTO system on the performances of ZTO-based TFTs is investigated by using sol-gel process. The proper Y doped ZTO present both high film crystallization temperature and superior electrical properties as an active channel layer of TFTs. The fabricated YZTO-based TFTs with 11% Y show the excellent devices performance such as the channel field effect mobility of 1.756 cm2/Vs, SS of 2.13 V/dec, threshold voltage of 0.8V and on/off ratio of 3.12×106.

Monolayers of arrays of periodic polystyrene (PS) spheres are designed to couple onto the surface of cerium-doped lutetium-yttrium oxyorthosilicate scintillator to improve the light extraction efficiency. The enhancement of extraction efficiency up to 38% relative to the reference case without polystyrene spheres is achieved. Combining with the simulation for the transmission as well as its dispersion relation, detailed analysis of the effect of whispering gallery modes and diffraction on the extraction mechanism are given. As a result, the optimal diameter of 414 nm is obtained based on a trade-off between the transmission loss and the diffraction enhancement.

Thready stripe-patterned thermo-responsive surfaces were prepared and their surface properties were characterized. Prepared 3 μm wide stripe-patterned surfaces were evaluated by observing the adhesions and detachments of three types of cells: HeLa cells (HeLas), human umbilical vein endothelial cells (HUVECs), and NIH-3T3 cells (3T3s). Although cell adhesion and detachment in response to temperature were observed on all cells on a conventional thermo-responsive surface without patterns, the thermo-responsive surface with a 3 μm striped-pattern exhibited various cell adhesion properties. HeLas hardly adhered to the patterned surface even at 37 °C. On the other hand, although HUVECs adhered on the patterned surface at 12 h after incubation at 37 °C, the adhered HUVECs detached themselves after another 12 h incubation at 37 °C. 3T3s adhered to the patterned surface at 37 °C and detached themselves after reducing temperature to 20 °C. A mixture of HeLa, HUVEC and 3T3 was separated using their different specific cell-adhesion properties, and the composition of cells was analyzed by a flow-cytometry. As a result, the conventional thermo-responsive surface with a stripe-pattern was found to function as a cell-separating interface by using specific cell adhesion properties.

SiC power devices can handle large power and high frequency switching beyond the Si power devices. Typical full-SiC power modules are composed of both SiC-MOSFETs and SiC-SBDs to suppress the degradation of Ron of SiC-MOSFET during the bipolar reverse-current flow while there will be unfavorable consequences such as increased material cost, larger area, and larger wiring inductances. Panasonic has proposed the SiC-DioMOS which successfully integrates the unipolar reverse diode without any increase of chip size from the original DIMOS transistor. The SiC-DioMOS utilizes the highly-doped n-type epitaxial channel under the MOS gate for the FET channel and also for the reverse conduction path of the diode. Thickness and concentration of the highly-doped n-typed channel are carefully designed to achieve reasonable Vth of the MOSFET and Vf0 barrier constituting the diode current. The MOSFET and also the MOS-channel diode completely operate under unipolar mode. The SiC-DioMOS with BVds=1700V, Ron=20mΩ、Vth=4.5V, Vf0=0.8V is successively fabricated using the state-of-the-art epitaxial-growth technique. Fast switching of tr=58ns and tf=13ns is confirmed. The SiC-DioMOS meets practical standards for safety operation of high-power fast switching without SiC-SBD.

Reconfigurable nanowire transistors provide the operation of unipolar p-type and n-type FETs freely selectable within a single device. The enhanced functionality is enabled by controlling the currents through two individually gated Schottky junctions. Here we analyze the impact of the Schottky barrier height on the symmetry of Silicon nanowire RFET transfer characteristics and their performance within circuits. Prospective simulations are carried out, indicating that germanium nanowire based RFETs of the same dimensions will show a distinctly increased performance, making them a promising material solution for future reconfigurable electronics.

Neuromodulation devices such as deep brain stimulators (DBS), spinal cordstimulators (SCS) and cochlear implants (CIs) use electrodes in contact withtissue to deliver electrical pulses to targeted cells. In general, theneuromodulation industry has been evolving towards smaller, less invasivedevices. Improving power efficiency of these devices can reduce battery storagerequirements. Neuromodulation devices can realize significant power savings ifthe impedance to charge transfer at the electrode-tissue interface can bereduced. High electrochemical impedance at the surface of stimulationmicroelectrodes results in larger polarization voltages. Decreasing thispolarization voltage response can reduce power required to deliver the currentpulse. One approach to doing this is to reduce the electrochemical impedance atthe electrode surface. Previously we have reported on a novel electrochemicallydeposited 60:40% platinum-iridium (Pt-Ir) electrode material that lowered theelectrode impedance by two orders of magnitude or more.

This study compares power consumption of an electrochemically deposited Pt-Irstimulating microelectrode to that of standard Pt-Ir probe microelectrodeproduced using conventional techniques. Both electrodes were tested usingin-vitro in phosphate buffered saline (PBS) solution andin-vivo (live rat) models.

Nitinol was coated with biocompatible calcium phosphate materials by pulsed electrolytic deposition (ELD) to reduce toxic metal-ions elution. The pulse ELD for the stents was carried out with changing the current off-periods (t off) of the pulse wave. The pulse ELD suppressed the generation of H2 gas due to the electrolysis of water on a calcium phosphate layer and improved the adhesiveness of the coating layer on nitinol compared with a conventional DC-ELD. The coating layers were identified to be octacalcium phosphate (OCP) at lower t off, while they were transformed to dicalcium phosphate anhydraous (DCPA) with an increase of t off. The layers of OCP or DCPA on the nitinol surface were subjected to a NaOH treatment at 60°C for 3days to transform them into hydroxyapatite (HAp). From results of a metal-ions elution test, the deposited calcium phosphates suppressed nickel ions elution at one quarter compared with the bare nitinol stent. These results indicate that the pulse ELD of biocompatible calcium phosphate materials on the nitinol stent was one of the best techniques to create firmly attached coating on it and reduce toxic nickel ions elution.

Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinctive advantage over conventional silanes in terms of maintaining the integrity of surface coatings, adhesive primers and composites in aqueous and aggressive environments. The improved durability of such dipodal silanes is associated with an increased crosslink density of the interphase and the inherent resistance to hydrolysis, as they can form six, rather than three, Si-O bonds to the substrate. This study examines dipodal silanes with hydrophobic alkyl functionality and compares them with similar functionality on conventional silane coupling agents. It also introduces new structural dipodal silanes containing “pendant” and “bridged” functionality and then examines their stability in aqueous environments. In strongly acidic and brine environments, dipodal silanes clearly demonstrate improved resistance to hydrolysis compared to conventional silane coupling agents.

Iron oxide nanoparticles (NPs) have attracted a lot of interest due to their many potential applications in areas including optoelectronics, magneto-optics, high density data storage, etc. In particular, iron oxides (Fe3O4 and γ –Fe2O3) are also well suited for biomedical applications [1]. We have investigated Faraday Rotation (FR) response for two types of Fe2O3 NPs (in aqueous suspension) that are of the same average diameter (10 nm) but differ in one important respect; one group consists of uncoated particles whereas the other group is functionalized with caffeic acid. This system is being investigated and characterized for use in tumor imaging applications. Faraday rotation (FR) refers to the rotation of the polarization vector of a light beam as it passes through a sample in the presence of a magnetic field. FR can reveal interesting material properties such as saturation magnetization and wavelength dependent Verdet constant of the material under investigation. The latter is a measure of the magnetically induced birefringence of the material. Typically FR setups rely on AC or DC magnetic fields. While these are valuable techniques with their own advantages, this work focuses on a pulsed field setup that can reveal dynamic information about the resulting magnetization, as the magnetic response of the sample is measured in the presence of short intense fields on the order of 0.6 Tesla and lasting approximately 100 milliseconds. All experiments are carried out at excitation wavelength of 633 nm (He-Ne wavelength).

The two NP samples show very different response to the field pulses. The NP systems investigated in this work show very unique short term and long term behavior revealing various time scales of interest. These unique characteristic times for the functionalized vs. uncoated particles provide valuable clues about the magnetization response of the NP and its relationship to the detailed structure of the NPs (core vs. shell). Magnetic response from these systems persists long after the magnetic field pulse has subsided. This can be related to the relaxation modes (Néel vs. Brownian) and as possible evidence of NP size dispersion. Additionally, the possibility of agglomeration is also discussed. While more detailed quantitative analysis will be dealt with in a more comprehensive publication that is under preparation, we hope to show in this preliminary report both that the AC and pulsed FR measurements can reveal complimentary information and that FR in general can be a reliable technique, which can be used to develop a detailed picture of the magnetic response of these NP systems.

The electrical conductivity of insulating polymer matrix composites undergoes radical increase at a certain concentration of conductive filler, which is known as the percolation threshold. Polymer matrix conductive nanocomposites were fabricated by compression molding the mechanically mixed poly (methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles, as has been done with other polymer composites before. The electrical conductivity of PMMA/ATO nanocomposites increased by several orders of magnitude at a small concentration of ATO (∼ 0.27 vol %). The continuous 3D network like distribution of ATO nanoparticles contributed to this percolation at subcritical filler concentrations. The effects of processing parameters on these unique microstructures and electrical properties were investigated. The tetrakaidecahedron-like microstructure was observed by scanning electron microscopy (SEM) and was found to be affected by the molding pressure, temperature and amount of nanoparticles. The viscoelastic flow of matrix under the optimum processing conditions allowed the shape transformation of PMMA into space filling polyhedra and an ordered distribution of ATO nanoparticles along the sharp edges of the PMMA. Parametric finite element analysis was performed to model this unique microstructure-driven percolation. The 2D simplified model was generated in AC/DC frequency domain mode in COMSOL Multiphysics® to solve the effects of ordered distribution of conductive nanoparticles on the electrical properties of the composite. There was excellent agreement between experimental and simulated values of electrical conductivity and percolation concentration. This model can be used to predict percolation threshold and electrical properties for any types of composite systems containing insulating matrix and conductive fillers that can form this unique microstructure.

In order to make use of the waste heat caused by the unabsorbed light based on photovoltaic(PV) effect, a novel hybrid dye-sensitized solar cells (DSSC) with the synergies of PV and thermoelectric(TE) effect has been proposed in present work. The main idea is to prepare a composite hybrid DSSC photoanode which can simultaneously achieve PV and TE conversion by incorporating the excellent TE Bi-Te alloys into TiO2 nanomaterial. In this paper, Bi2Te3 nanoplates with different size were doped in the TiO2 nanoparticle photoanode and the effect of the Bi2Te3 size on the properties of DSSCs was analyzed. It is found that with the decrease of the size of the Bi2Te3 nanoplates, the TE performance became better and the dye absorption and the conversion efficiency of DSSCs were improved. Preliminary results show that the efficiency of DSSC with Bi2Te3 increased atleast 15.3% compared to the undoped. By further optimizing the parameters, the performance of DSSC is estimated to have a much more enhancement. Therefore, the way of combination PV and TE provides an alternative way to improve the performance of DSSC.

As a result of archaeological investigations carried out in the pre-Hispanic city of Izamal, Yucatan, Mexico a large number of fragments of pottery vessels were recovered from the period known as maya protoclassic. The most important of this collection was its similarity to ceramic style representative recognized as Holmul, whose production has been identified mostly in the region of the Central Maya Lowlands. This style includes Ixcanrio Orange Polychrome ceramic type as diagnostic type more easily distinguished by its orange slip and tetrapods supports. Izamal, is the only place in the Northern Maya Lowlands has reported a large amount of pottery of this ceramic type. In this study we try to identify the origin of manufacture using X-ray diffraction technique. This will allow us to understand the social and political behavior of this ceramic tradition and their presence in this region of the Maya area.

Recently, much attention has been devoted to trilayer graphene because it displays stacking and electric field dependent electronic properties well-suited for electronic and photonic applications [1-8]. Several theoretical studies have predicted the electronic dispersion of Bernal (ABA) and rhombohedral (ABC) stacked trilayers. However, a direct experimental visualization of a well-resolved band structure has not yet been reported. In this work, we obtain large area highly homogenous quasi-free trilayer graphene (TLG) on 6H-SiC(0001) and measure its electronic bands via angle resolved photoemission spectroscopy (ARPES). We demonstrate by low energy electron microscopy measurements that that trilayer domains on SiC extend over areas of tens of square micrometers. By fitting tight-binding bands to the experimental data we extract the interatomic hopping parameters for Bernal and rhombohedral stacked trilayers. For ABC stacks and in the presence of an electrostatic asymmetry, we detect the existence of a band-gap of about 120 meV. Notably our results suggest that on SiC substrates the occurrence of ABC-stacked TLG is significantly higher than in natural bulk graphite. Hence, growing TLG on SiC might be the answer to the challenge of controllably synthesizing ABC-stacked trilayer – an ideal material for the fabrication of a new class of gap-tunable devices.

Dirac materials are characterized by exceptional mobility, orders of magnitude higher than any semiconductor, due to the massless pseudorelativistic nature of the Dirac fermions. These systems being semimetallic, the lack of a genuine band-gap poses a serious limitation to their possible applications in electronics. We recently demonstrated that thin TiO2 nanowires can exhibit 1D Dirac states similar to metallic carbon nanotubes, with the crucial difference that these states lie inside the conduction band in proximity of a wide band gap. We analyze the robustness of the Dirac states respect to an Anderson disorder model and substitutional impurity and compare to different one dimensional systems. The results suggest that thin anatase TiO2 nanowires can be a promising candidate material for switching devices.

The correlation of stress in Silicon Carbide (SiC) crystal and frequency shift in micro- Raman spectroscopy was determined by an experimental method. We applied uniaxial stress to 4H- and 6H-SiC single crystal square bar specimen shaped with (0001) and (11-20) faces by four point bending test, under measuring the frequency shift in micro-Raman spectroscopy. The results revealed that the linearity coefficients between stress and Raman shift were -1.96 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (0001) face, -2.08 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (11-20) face and -2.70 cm-1/GPa for FTO(2/6)E2 on 6H-SiC (0001) face. Determination of these coefficients has made it possible to evaluate the residual stress in SiC crystal quantitatively by micro-Raman spectroscopy. We evaluated the residual stress in SiC substrate that was grown in our laboratory by utilizing the results obtained in this study. The result of estimation indicated that the SiC substrate with a diameter of 6 inch remained residual stress as low as ±15 MPa.