Search

Recently, the studies on ZnO nanostructure characteristics and their fabrication methods have been increased significantly in order to be able to use its magnificent properties by reaching the desired optimum features. Very high growth rate and high quality growth have always been the center of attention. In this study, a sequential microwave-assisted ZnO nanorod (NR) growth as an ultra-fast, highly efficient method for vertical growth of high quality ZnO NRs on different substrates is proposed. A NRs׳ growth rate of 4.2 μm/h was obtained which led to uniformly distributed, high aspect ratio and vertically-aligned NRs. Furthermore, the influences of spinner׳s speed as an important parameter on the quality of ZnO seed and annealing treatment have been studied. The sol–gel casting approach is optimized for the layer. Different seed layers were used to grow the nanostructures and the optimum spinner speed is found to be 2000 rpm. In order to diminish the dependency of the uniformity of ZnO NRs on the quality of seed layers, a remedy is suggested. [ABSTRACT FROM AUTHOR]

An ultra-violet (UV) phototransistor with 700 × 200 μm² gate area decorated with vertically aligned Zinc Oxide (ZnO) nanorods to enhance UV responsivity is designed and manufactured. Spectral responsivity of the device was measured for wavelengths ranged from 200 to 1100 nm of the electromagnetic spectrum in different transistor working regions. The best responsivity was achieved at sub-threshold and very weak inversion region. In order to enhance UV range selectivity, oxygen plasma has been employed on the nanorods, and consequently, nearly 3-fold improvement in its relative sensitivity at 375 nm was achieved. The final manufactured phototransistor shows a highly selective response of 24 kA/W in the UV range. [ABSTRACT FROM AUTHOR]

Wide-band-gap technologies enable ultra-high efficiencies in the high-frequency power conversion. However, inadequate accuracies in electrical measurements could lead to spurious efficiency measurements, even above 100%. Furthermore, bandwidth limitations, particularly of current probing, delay mismatches between current and voltage probes, loading effects, and electromagnetic interferences, make electrical techniques inappropriate for measuring extremely-low losses in switches with high dv/dt and di/dt values and magnetic components under high-frequency excitations. Calorimetric methods overcome this issue by a direct loss measurement through the generated heat. Nevertheless, limited ranges and accuracies of the existing systems hinder their application in sensitive measurements. Moreover, time-consuming calibrations with extensive data processing impede rapid design assessments. In this work, we propose a closed-type double-chamber calorimeter based on a real-time calibration between two identical chambers to eliminate extra compensation for ambient variations or changes within the system itself. By streaming the same coolant in both chambers, our system removes the need for flow measurements, enabling extremely low flow rates, which improves sensitivity and reduces complexity and system cost. The system provides an adjustable cooling and can measure losses down to 500 mW, enabling the evaluation of high-performance power converters and their components with no dependence on the geometry of the evaluated devices or systems. [ABSTRACT FROM AUTHOR]

Soft-switching power converters based on wide-band-gap (WBG) transistors offer superior efficiency and power density advantages. However, at high frequencies, loss behavior varies significantly between different WBG technologies. This includes losses related to conduction and dynamic on-state resistance (RDS(ON)) degradation, also charging/discharging of input capacitance (CISS) and output capacitance (COSS). As datasheets lack such important information, we present measurement techniques and evaluation methods for soft-switching losses in WBG transistors which enable a detailed loss-breakdown analysis. We estimate the gate loss under soft-switching conditions using a simple small-signal measurement. Next, we use Sawyer–Tower and nonlinear resonance (NR) methods to measure large-signal COSS energy losses up to 40 MHz. Finally, we investigate the dependence of dynamic RDS(ON) degradation on off-state voltage using pulsed-IV measurements. We demonstrate an insightful comparison of soft-switching losses for various normally off gallium nitride (GaN) and silicon carbide (SiC) devices. A p-GaN-gated device exhibits the most severe RDS(ON) degradation and the lowest gate loss. Cascode arrangement increases threshold voltage for GaN devices and reduces gate losses in SiC transistors; however, it leads to higher C{OSS losses. The study facilitates the evaluation of system losses and selection of efficient WBG devices based on the trade-offs between various sources of losses at high frequencies. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) nanostructures as amazing piezoelectric materials have been recently extensively investigated in order to harvest energy. ZnO nanorods with hexagonal wurtzite structure oriented along c -axis were grown on the glass substrate by combining the facile sol–gel and chemical bath deposition techniques. Zinc acetate dihydrate as a Zn 2+ source, ethanol and acetone as solvents were used in the sol preparation without using any organic stabilizer additive. ZnO sol's structure was characterized by FTIR spectroscopy. Particles forming the sol were analyzed to be zinc (hydroxo and/or oxo) acetate, according to the characterization results. The influence of the binary solvent system on the stability and optical properties of the particles as well as morphological properties of ZnO grains were studied. The positive effect of an optimum percentage of acetone in the precursor sol which reduced the zinc (hydroxo and/or oxo) acetate dissolution and ensured the particles stabilization could subsequently be understood. Dense ZnO grains with high aspect ratio on the seed layer which led to vertically aligned ZnO nanorods were obtained using the sol with 1:1 ratio of EtOH and acetone. To increase the piezoresponse of the nanorods, their crystal structure needed to be modified. Therefore, they were subjected to oxygen plasma in order to reduce oxygen vacancies and repair the crystal structure (defects) of the as-grown n-type ZnO nanorods. Photoluminescence analysis was used to analyze the crystal before and after the plasma treatment. Piezoresponse Force Microscopy (PFM) has also been employed to evaluate the reverse piezoelectric response of the nanorods as an actuator before and after plasma treatment. The magnitude and phase RMS value increase of 27% and 143% was observed after plasma treatment. [ABSTRACT FROM AUTHOR]

Presents corrections to the above named paper. [ABSTRACT FROM AUTHOR]