Gallium Nitride (GaN) and other III-N semiconductors are rapidly gaining importance in high power and high frequency electronic applications. III-N material based devices are fabricated on heterostructures that are usually grown by high vacuum techniques such as metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). However, in many applications, it is necessary to regrow thin cap layers of III-N materials during device fabrication. One such application is regrowth of ohmic contacts to III-N devices. Heavily doped n+ GaN, or InGaN grown by MBE or MOCVD is used to obtain low resistance non-alloyed ohmic contacts to GaN based devices. However, from a commercial point of view, this becomes difficult because of the high cost and lack of availability of ultra high vacuum (∼1x10-10 Torr) techniques in most clean room facilities. Reactive sputtering provides a cheaper and more ubiquitous alternative for the growth of thin cap layers on parent MOCVD III-N heterostructures during device fabrication. In this work, we explore the possibility of using reactive sputtering as a method to grow III-N materials as ohmic contacts to GaN based devices.

Amorphous oxide semiconductors (AOS) are important candidates for next generation display transistors, but instability under illumination with month-long transients is a significant drawback and may limit broader use. Several models have been developed to fit transient photoconductivity observed in AOS and relate it to a spectrum of weighted time constants, equivalent to either a density of states distribution of deep traps within the activated energy model, or to a time-dependent relaxation time constant in other models. In this work, we classify fits of the time constant spectrum to the transient data as either “descriptive” if they make no presumption about the spectral shape, or “predictive” if they assume a spectral shape a priori characterized by a few simple parameters. By fitting both descriptive and predictive models to simulated transients, it is observed that the best fit converges for the descriptive model if the measurement duration exceeds the mode (“peak”) value of the time constant distribution. The predictive models can converge orders of magnitude faster, but rely on a proper identification of the correct lineshape a priori. Therefore, it is recommended that first an unbiased descriptive model of sufficient measurement duration be performed. Then the known lineshape can be applied as a predictive model for future measurements, reducing subsequent measurement durations by orders of magnitude.

Here we report on the effect of gamma radiation treatment on transport properties and single-trap kinetics in Si nanowire (NW) field effect transistor (FET) structures. We used noise spectroscopy as a powerful method for advanced physical characterization of nanoscale devices. Our results demonstrate that transport properties of NW FETs can be changed using small doses of gamma radiation treatment. We reveal an enhancement of the gate coupling effect, which is explained as a result of the reorganization of the native defect structure after treatment. The radiation treatment approach allows the single-trap dynamic to be changed, which opens up prospects for a number of fundamental studies and applications of Si NW FET device structures, including biosensors.

We investigated the fabrication of convex diamond-like carbon (DLC) based microgears in room-temperature curing nanoimprint lithography (RTC-NIL) using the ladder-type hydrogen silsesquioxane (HSQ), as an application for the medical micro electro mechanical system (MEMS). The HSQ which is an inorganic polymer of sol-gel system turns into a gel when exposed to air and has the siloxane bond. Therefore, the HSQ was used as RT-imprinting material, and also used as an oxide mask material in electron cyclotron resonance (ECR) oxygen (O2) ion shower etching. We fabricated the polydimethylsiloxane (PDMS) mold with concave microgear patterns which has 40, 50 and 60 μm-tip diameter and 300 nm-depth. We carried out the RTC-NIL process using the PDMS mold under the following optimum conditions of 0.10 MPa-imprinting pressure and 1.0 min-imprinting time. We found that the residual layer of imprinted HSQ microgear patterns was removed with ECR trifluoromethane (CHF3) ion shower under the following conditions of 300 eV-ion energy and 2.0 min-etching time, and then microgears of the HSQ on the DLC film were etched with ECR O2 ion shower under the following conditions of 400 eV-ion energy and 10 min-etching time. As a result, the convex DLC based microgears which have 40, 50 and 60 μm-tip diameter and 400 nm-height were fabricated with high accuracy in the new fabrication process of RTC-NIL.

Overall, autologous bone grafting continues to be the gold standard for the restoration of bone defects while other practices include metallic meshes and plates. These practices are not always suitable particularly when performing reconstructive surgery in the maxillofacial region as the defects tend to be complex in terms of size and shape. These bone defect usually occur due to trauma, infection or a result of oncologic surgeries and therefore the patient requires large amount of bone grafting material [1].

There is a need for alternative methods such as is artificial bone scaffolds with regenerative medicine approaches in order to enable original tissue regeneration. In order to stimulate tissue regeneration scaffolding materials are required to have certain properties such as biocompatibility, adequate mechanical properties and internal and surface topographical features in order to provide specific biological signals to promote cell attachment and proliferation. Ideally, it would also need to be biodegradable and provide sufficient support for both the particular defect area and cellular ingrowth to degrade over time as new bone tissue is formed [2]. This work analyses the mechanical and chemical properties of Hydroxyapatite (HA) - poly(ethylene glycol) dimethacrylate (PEGDMA) and Hydroxyapatite (HA) - poly(ethylene glycol) diacrylate (PEGDA) based composites used as artificial bone scaffold material with internal structures optimized using finite element analysis (FEA) using Hyperworks OptiStruct (Altair, USA) Topological Optimization and manufactured using commercially available additive manufacturing techniques in order to develop a product that can be introduced directly into the patient. The technique allows implants to be custom made, having the right dimensions and the right mechanical properties.

Testing of the ceramic-hydrogel composite include mechanical testing in compression, tension, bending, impact and hardness while chemical analysis include Fourier Transform Infrared spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC). Morphology was analyzed using Scanning Electron Microscopy (SEM) and Laser Scanning Confocal Microscopy.

The simple perovskite manganite Sr1-xSmxMnO3 (SSMO) has been reported to have a highly-correlated electronic system for eg-electrons in a Mn ion. According to the previous studies, the C-type orbital-ordered (COO) state with the I4/mcm symmetry was found to be formed from the disordered-cubic (DC) state on cooling. The feature of the COO state is that its crystal structure involves both the Jahn-Teller distortion to orbital ordering and the R25-type rotational displacement of oxygen octahedra. Because of the involvement of both the distortion and the displacement, their competition should be expected in the formation of the COO state. However, the detailed features of the competition have not been understood yet. Thus, the crystallographic features of the COO state in SSMO have been examined by x-ray powder diffraction and transmission electron microscopy. It was found that, when the Sm content increased from x = 0 at room temperature, the DC state changed into the COO state with the tetragonal symmetry around x = 0.13. The notable feature of the COO state is that the state is characterized by a nanometer-scaled banded structure consisting of an alternating array of two tetragonal bands. One tetragonal band consisted of the COO state involving both the Jahn-Teller distortion and the R25-type rotational displacement. But, there was only the latter displacement in the other, the state of which could be identified as a disordered tetragonal (DT) state. Based on this, it is understood that the COO-state formation from the DC state should take place via the appearance of the DT state, which may involve fluctuations of the C-type orbital ordering.

In this work, 3 simple, fast, labour and energy efficient methodologies were used to prepare carbon quantum dots (C-dots) using a red beetroot (Beta vulgaris subsp. vulgaris var. vulgaris) aqueous extract as the carbon source: alkali-assisted (AA), microwave-assisted (MA) and alkali-microwave-assisted (AMA) synthesis. TEM images shows nanoparticles with a nearly spherical morphology and diameters around 7.0 nm. FTIR spectra show characteristic peaks of C-H, C-O, O-H and C=C bonds for all the samples. The emission spectra show an interesting feature of the as-prepared samples: the emission band position can be tunable by changing the excitation wavelength. Comparing the 3 different methodologies in terms of photoluminescence properties, the one based only on the microwave-assisted heating has showed the most improved emission.

We present here a reactive ion etching recipe to fabricate germanium nanowires. We used a combination of Cl2, N2 and O2 and studied the influence of both the gas pressure and the O2 mass flow on the morphology of the nanowires. 5 µm long nanowires with an aspect ratio of 20 are demonstrated with smooth surfaces and a tapering below 20 nm/µm. We also show that both gold and aluminum can be used as hard mask; the latter achieving a selectivity with germanium above 100.

Having worked on several approaches to CO2 capture over the past decade, we have studied a great number of physical and chemical solvents as well as polymer and composite membranes. Initially, most of these materials were based upon ionic liquids (ILs), however due to challenges encountered in applying ILs to meet the demanding requirements in CO2 separation processes, there is a need to reconsider what role (if any) ILs might play in CO2 capture technologies. Ultimately, more promising and robust materials will not come from ILs themselves, but from retrosynthetic analysis and a reconsideration of which structural variables and properties are (and are not) important. The hybridization of the constituent parts into entirely new, yet seemingly familiar substances, can yield greatly improved properties and economics. This manuscript highlights recent work from our group based on lessons learned from ILs that have spurred the development of new amine solvents and polymer materials to better address the demanding process conditions and requirements of CO2 capture and related separations.

This study reports on the preparation of cobalt doped zinc oxide (Co:ZnO) films via pulsed electron beam ablation (PEBA) from a single target containing 20 w% Co on sapphire (0001) and silicon (100) substrates. The films have been deposited at various temperatures (350оC, 400оC, 450оC) and pulse frequencies (2 Hz, 4 Hz), under a background argon (Ar) pressure of about 3 mtorr, and an accelerating voltage of 14 kV. The surface morphology has been examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). According to SEM analysis, the films consist of nano-globules whose size is in the range of 80-178 nm. Energy dispersive x-ray spectroscopy (EDX) reveals that deposition is congruent and the prepared films contain ∼20±5 w% cobalt. It has been found that the nano-globules in the deposited films are cobalt-rich zones containing ∼70 w% Co. From x-ray photoelectron spectroscopy (XPS) analysis, Co 2p3/2 peaks indicate that the deposited films contain CoO (binding energy = 780.5 eV) as well as metallic Co (binding energy = 778.1-778.5 eV). X-ray diffraction (XRD) analysis supports the presence of metallic Co hcp phase (2ϴ = 44.47° and 47.43°) in the films.

A new device-first low-temperature bonded gallium nitride (GaN)-on-diamond high-electronic mobility transistor (HEMT) technology with state-of-the-art, radio frequency (RF) power performance is described. In this process, the devices were first fabricated on a GaN-on-silicon carbide (SiC) epitaxial wafer and were subsequently separated from the SiC and bonded onto a high-thermal-conductivity diamond substrate. Thermal measurements showed that the GaN-on-diamond devices maintained equivalent or lower junction temperatures than their GaN-on-SiC counterparts while delivering more than three-times higher RF power within the same active area. Such results demonstrate that the GaN device transfer process is capable of preserving intrinsic transistor electrical performance while taking advantage of the excellent thermal properties of diamond substrates. Preliminary step-stress and room-temperature, steady-state life testing shows that the low-temperature bonded GaN-on-diamond device has no inherently reliability limiting factor. GaN-on-diamond is ideally suited to wideband electronic warfare (EW) power amplifiers as they are the most thermally challenging due to continuous wave (CW) operation and the reduced power-added efficiency obtained with ultra-wide bandwidth circuit implementations.

A new approach for adjusting molecular dynamics results on UO2 thermal conductivity to include phonon-spin scattering has been used to improve calculations on U x Pu1−x O2 and U x Th1−x O2. We demonstrate that by including spin scattering a strong asymmetry as a function of uranium actinide fraction, x, is obtained. Greater degradation is shown for U x Th1−x O2 than U x Pu1−x O2. Minimum thermal conductivities are predicted at U0.97Pu0.03O2 and U0.58Th0.42O2, although the degradation in U x Pu1−x O2 is negligible relative to pure UO2.

The present report is dedicated to a study of possible ways of increasing the energy density of the supercapacitor and thus, bridging the gap between the supercapacitor and the battery. Chemical functionalization of carbon nanomaterials, such as carbon nanotubes, activated carbon cloth, and activated carbon powder used as supercapacitor electrodes as well as novel aqueous electrolytes with the electrochemical window of up to 2 V are described. The hybrid approaches to energy storage mechanism in electrochemical energy storage devices are discussed. The first experimental results on the discussed hybrid energy storage devices are presented.