The origin of electrical property deterioration with increasing Mg concentration in ZnMgO:Ga

Transparent conductive Ga-doped Zn_1 − xMg_xO (ZnMgO:Ga) films were epitaxially grown via Pulsed Laser Deposition on sapphire by optimizing the substrate temperature and other parameters of deposition. Zn_0.68Mg_0.31Ga_0.01O/sapphire films deposited at 400 °C have a Hall mobility (μ) of 9.2 ± 0.5 cm² V^− 1 s^− 1 and a free electron density (n) of 1.79 × 10²⁰ ± 0.06 × 10²⁰ cm^− 3, yielding an electrical conductivity (σ) = 262 ± 22 S/cm. Zn_0.90Mg_0.09Ga_0.01O/sapphire films, deposited under the same growth conditions, have similar crystalline quality, but significantly better electrical properties (σ = 1450 ± 10 S/cm, μ = 24.5 ± 2.5 cm² V^− 1 s^− 1, n = 3.81 × 10²⁰ ± 0.20 × 10²⁰ cm^− 3). This comparison provides evidence of electrical property deterioration in doped ZnMgO bulk material with increasing Mg content, independent of crystalline quality. Electrical properties of ZnMgO:Ga are further deteriorated by the decrease of the crystalline quality. Polycrystalline Zn_0.90Mg_0.09Ga_0.01O/a-SiO₂ samples deposited under identical conditions on amorphous silica substrates had both inferior crystal quality and inferior transport properties (μ = 2.5 ± 0.2 cm² V^− 1 s^− 1, n = 2.04 × 10²⁰ ± 0.20 × 10²⁰ cm^− 3, σ = 80 ± 8 S/cm) compared to their epitaxial counterparts. Overall, the results of this study indicate that both bulk material properties and crystalline quality influence the electrical properties of single-phase ZnMgO:Ga thin films.     

Investigating variability of fatigue indicator parameters of two-phase nickel-based superalloy microstructures

Variability of fatigue properties of Nickel-based superalloys induced by microstructure feature uncertainties is investigated. The microstructure at one material point is described by its grain size and orientation features, as well as the volume fraction of the γ′ phase. Principal component analysis (PCA) is introduced to reduce the dimensionality of the microstructure feature space. PCA and kernel PCA (KPCA) techniques are presented and compared. Reduced representations of input features are mapped to uniform or standard Gaussian distributions through polynomial chaos expansion (PCE) so that the sampling of new microstructure realizations becomes feasible. A crystal plasticity constitutive model is adopted to evaluate fatigue properties of two-phase superalloy microstructures under cyclic loading. The fatigue properties are measured by strain-based fatigue indicator parameters (FIP). Adaptive sparse grid collocation (ASGC) and Monte Carlo (MC) methods are used to establish the relation between microstructure feature uncertainties and the variability of macroscopic properties. Convergence with increasing dimensionality of the reduced surrogate stochastic space is studied. Distributions of FIPs and the convex hulls describing the envelope of these parameters in the presence of microstructure uncertainties are shown.     

Junction like behavior in polycrystalline diamond films

We have successfully fabricated polycrystalline diamond rectifying junction devices on n-type (1 0 0) silicon substrates by Hot Filament Chemical Vapor Deposition (HFCVD) using methane/hydrogen process gas and trimethyl borate and trimethyl phosphite dissolved in acetone as p- and n-type dopants, respectively. Impedance spectroscopy and current-voltage analysis indicates that the conduction is vertical down the grains and facets and not due to surface effects. Electrical characteristics were analyzed with In and Ti/Au top metal contacts with Al as the substrate contact. Current-voltage characteristics as a function of temperature showed barrier potentials of 1.1 eV and 0.77 eV for the In and Ti/Au contacts, respectively. Barrier heights of 4.8 eV (In) and 4.4 eV (Ti/Au) were obtained from capacitance-voltage measurements.     

Modeling the gate bias dependence of contact resistance in staggered polycrystalline organic thin film transistors

We have modeled the dependence on the gate voltage of the bulk contact resistance and interface contact resistance in staggered polycrystalline organic thin film transistors. In the specific, we have investigated how traps, at the grain boundaries of an organic semiconductor thin film layer placed between the metal electrode and the active layer, can contribute to the bulk contact resistance. In order to the take into account this contribution, within the frame of the grain boundary trapping model (GBTM), a model of the energy barrier E_B, which emerges between the accumulation layer at the organic semiconductor/insulator interface and injecting contact, has been proposed. Moreover, the lowering of the energy barrier at the contacts interface region has been included by considering the influence of the electric field generated by the accumulation layer on the injection of carriers at the source and on the collection of charges from the accumulation layer to the drain contact. This work outlines both a Schottky barrier lowering, determined by the accumulation layer opposite the source electrode, as well as a Poole-Frenkel mechanism determined by the electric field of the accumulation layer active at the drain contact region. Finally it is provided and tested an analytical equation of our model for the contact resistance, summarizing the Poole-Frenkel and Schottky barrier lowering contribution with the grain boundary trapping model.     

The potential of zero total charge of Pt nanoparticles and polycrystalline electrodes with different surface structure: The role of anion adsorption in fundamental electrocatalysis

In the present paper anion effects are discussed on different shape-controlled Pt nanoparticles as well as on polycrystalline Pt electrodes of different surface structures. In particular, the potentials of zero total charge (pztc) were determined by using the CO displacement approach, both in sulphuric and perchloric media. The CO monolayer oxidative stripping was studied on the different samples. CO coverages were independent of the electrolyte provided that the true CO stripping charges, corrected for double layer contributions are compared to the charge involved only in the hydrogen adsorption region. The classical charge density normalization process is discussed and small changes are proposed. Then, criteria to evaluate the real surface area of platinum electrodes from charge measurements are proposed in both electrolytes.     

Preparation and characteristics of porous CuS microspheres consisted of polycrystalline nanoslices

This paper presents a facile method to fabricate CuS porous microspheres, which were formed by the intergrowth of CuS polycrystalline nanoslices. The obtained sample has been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electronic diffraction (SAED), X-ray diffraction (XRD), UV-vis diffusion reflection and Laser Raman. On the basis of the experimental results, we proposed a self-assemble mechanism to elucidate the formation of CuS nanoslice structure. The current-voltage characteristic under different gas atmospheres shows that the as prepared CuS polycrystalline nanoslices are sensitive to ammonia at ppm level and the electrical conductivity is found to be weaker in ammonia than that in air.     

In situ hydrogen plasma treatment for improved transport of (4 0 0) oriented polycrystalline silicon films

Polycrystalline silicon (poly-Si) films were deposited on glass by very high-frequency (100 MHz) plasma enhanced chemical vapor deposition from a gaseous mixture of SiF₄ and H₂ with small amounts of SiH₄. (2 2 0) oriented films prepared at small SiF₄/H₂ ratios (<30/40 sccm) showed intrinsic transport properties of poly-Si. However, the room temperature dark conductivity (σ_d) of the (4 0 0) oriented film was very high for intrinsic poly-Si, 7.2×10⁻⁴S/cm. This conductivity exhibited a T^−1/4 behavior, suggesting a high defect density at the grain boundaries. It was found that in situ hydrogen plasma treatment successfully produced (4 0 0) oriented poly-Si with a reasonably low σ_d of 4.5×10⁻⁷S/cm and a good photoconductivity of 1.3×10⁻⁴S/cm.     

Fractography of hardmetal dies used for the manufacture of polycrystalline diamond

Some WC/Co hardmetal dies used for the high-temperature, high-pressure fabrication of polycrystalline diamond have been subjected to fractographic investigation after service failure. In each die a number of flat plate-like fragments have been found showing an unusual fountain-like appearance to the fracture surface markings. Despite extensive probing, discrete fracture origins could not be found. Instead, from the evidence of the microcracking found in the die bore region and the recognised development of deformations during a campaign, it was concluded that microstructural damage was developed under the complex non-equitriaxial compression stresses which are developed during the duty cycles. When the propagation of this damage reached the axial tensile zone that exists in the cooler regions of the die, the plate-like, more-brittle failure pattern developed.     

Thermal damage mechanisms of Si-coated diamond powder based polycrystalline diamond

The polycrystalline diamond (PCD) composites were synthesized from Si-coated diamond or diamond powder mixtures with Si. The characterizations of phase structures, morphologies and thermal stability of PCD were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The thermal damage mechanisms of PCD were studied under air condition up to 750 ℃ by thermal weight loss, XRD, SEM and wear tester. The results showed that the PCD was successfully synthesized by the Si-coated diamond with a homogeneous structure. The thermal stability and wear resistance of PCD with Si-coated diamond were better than those of PCD with uncoated diamond. It was determined that the chemical thermal damage mechanism with oxidation reaction dominated the damage of the PCD after high temperature annealing and the physical thermal damage mechanism also took effect on the exfoliation of binder and fine diamond grains from PCD.