Like Driving a Car: Acquiring Quality SEM/FESEM Images in Different Situations

This video presentation provided by the Nanotechnology Applications and Career Knowledge (NACK) Center explores scanning electron microscopy and field emission scanning electron microscopy (SEM/FESEM) image best practices. In the video, Liu Bangzhi simplifies SEM/FESEM imaging by drawing analogies to common things in everyday life such as writing with a pencil and driving a car. Bangzhi also explores imaging parameters, such as working distance (WD), beam voltage, and detectors; provides examples of FESEMs; and highlights how professionals can achieve an ideal electron beam. The video recording runs 54:42 minutes in length.Presentation slides are also provided

Observation of two different temperature-dependent behaviors of the defects in III-nitride micro-LEDs

As micro-LED pixel sizes shrink, the volume-to-surface ratio increases, so defect-assisted non-radiative recombination becomes more important for LED pixel efficiency degradation. The donor-type defects on the pixel sidewalls are induced by inductively coupled plasma etching, and the carrier leakage through the sidewalls is determined by the density of surface traps. The defects in quantum wells provide places for the non-radiative recombination of electron–hole pairs, and the recombination rate is related to the thermal velocity of carriers and the trapping cross section of defects. The experimental results indicate that the significant improvement of quantum efficiency from sidewall passivation happens at current densities higher than 400 A/cm2 at an environmental temperature of 300 K. When the temperature decreases to 150 K, the sample with sidewall passivation has 10% higher quantum efficiency at all current ranges. Numerical modeling is applied to evaluate the behaviors of two types of defects at different temperatures. Our observation from modeling reveals that the efficiency drop caused by surface defects is hardly affected by temperature changes, whereas results show that the Shockley–Read–Hall nonradiative recombination rate decreases rapidly at low temperature due to longer carrier lifetime and increased difficulty of electron and hole recombination in traps. Therefore, the significant increase in the efficiency at 150 K, especially in the low current density range, is due to the defects within the quantum well

Cr/Pt Ohmic contacts to B₁₂As₂

Palladium, Pt, and Cr/Pt contacts to the wide band gap icosahedral boride semiconductor B₁₂As₂ have been studied. All Pd and Pt contacts exhibited nonlinear I-V characteristics, while Cr/Pt contacts were Ohmic. The specific contact resistance was reduced from 6Ω cm² as-deposited to 3x10[superscript]-⁴ Ω cm² after the Cr/Pt contacts were annealed at 750 °C for 30 s in Ar. Annealing at 600 °C or higher drastically reduced the semiconductor sheet resistance, whether annealing was performed before or after metallization. This apparent activation of the semiconductor is a likely cause for the improvement in the Ohmic contacts with annealing

Catalytic Asymmetric [3 + 2] Cyclization Reactions of 3‑Isothiocyanato Oxindoles and Alkynyl Ketones Via an in Situ Generated Magnesium Catalyst

A highly enantioselective formal [3 + 2] cycloaddition reaction between 3-isothiocyanato oxindoles and alkynyl ketones is reported for the first time. An oxazoline–OH type chiral ligand derived from <i>o</i>-hydroxy-phenylacetic acid is employed to generate an effective magnesium catalyst in the current cyclization reaction and give serials of chiral spirooxindoles with good chemical yields and enantioselectivities