Temperature dependent photoluminescence of composition tunable ZnxAgInSe quantum dots and temperature sensor application.

Quantum dots (QDs) exhibit not only wide tunability of luminescence but also complex optical properties because of the large degree of freedom in their structure and chemical composition. Quaternary ZnxAgInSe QDs with different Zn/Ag ratios were synthesized and examined as temperature sensors. The relationship among the luminescence energy, emission intensity, and full-width at half-maximum (FWHM) of the emission band at different temperatures was investigated. To understand the photoluminescence mechanism, time-resolved photoluminescence spectra were recorded. Moreover, the dependence of the luminescence peak energy and FWHM on temperature was investigated, and a small deviation from the actual temperature was observed, indicative of the use of ZnxAgInSe QDs as high sensitivity temperature sensors.

Epitaxial Growth of MgxCa1-xO on GaN by Atomic Layer Deposition.

We demonstrate for the first time that a single-crystalline epitaxial MgxCa1-xO film can be deposited on gallium nitride (GaN) by atomic layer deposition (ALD). By adjusting the ratio between the amounts of Mg and Ca in the film, a lattice matched MgxCa1-xO/GaN(0001) interface can be achieved with low interfacial defect density. High-resolution X-ray diffraction (XRD) shows that the lattice parameter of this ternary oxide nearly obeys Vegard's law. An atomically sharp interface from cross-sectional transmission electron microscopy (TEM) confirmed the high quality of the epitaxy. High-temperature capacitance-voltage characterization showed that the film with composition Mg0.25Ca0.75O has the lowest interfacial defect density. With this optimal oxide composition, a Mg0.25Ca0.75O/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility (MOS-HEMT) device was fabricated. An ultrahigh on/off ratio of 1012 and a near ideal SS of 62 mV/dec were achieved with this device.

Synthesis of Calcium(II) Amidinate Precursors for Atomic Layer Deposition through a Redox Reaction between Calcium and Amidines.

We have prepared two new Ca(II) amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N'-diisopropylformamidinato)calcium(II) (1) and bis(N,N'-diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X-ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η(2) -L)Ca(µ-η(2) :η(2) -L)(µ-η(2) :η(1) -L)Ca(η(2) -L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available Ca(II) precursor, [Ca3 (tmhd)6 ]. In CaS ALD with 1 and H2 S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3 (tmhd)6 ] and H2 S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic Ca(II) amidinates suitable for use as ALD precursors.

Band-Offset Analysis of Atomic Layer Deposition La2O3 on GaAs(111), (110), and (100) Surfaces for Epitaxial Growth.

In this paper, we measured band offsets for La2O3 prepared by atomic layer deposition on GaAs(111), (110), and (100) surfaces. La2O3 grows epitaxially on GaAs(111) with very low interfacial defect density and exhibits a band offset that is predicted for defect-free interfaces by the metal-induced gap state theory. On the other hand, the polycrystalline La2O3 deposited on GaAs(110) and (100) shows band offsets close to the values predicted for Fermi-level pinning. In this way, band offsets can qualitatively estimate interfacial defect levels.

Direct-Liquid-Evaporation Chemical Vapor Deposition of Nanocrystalline Cobalt Metal for Nanoscale Copper Interconnect Encapsulation.

In advanced microelectronics, precise design of liner and capping layers become critical, especially when it comes to the fabrication of Cu interconnects with dimensions lower than its mean free path. Herein, we demonstrate that direct-liquid-evaporation chemical vapor deposition (DLE-CVD) of Co is a promising method to make liner and capping layers for nanoscale Cu interconnects. DLE-CVD makes pure, smooth, nanocrystalline, and highly conformal Co films with highly controllable growth characteristics. This process allows full Co encapsulation of nanoscale Cu interconnects, thus stabilizing Cu against diffusion and electromigration. Electrical measurements and high-resolution elemental imaging studies show that the DLE-CVD Co encapsulation layer can improve the reliability and thermal stability of Cu interconnects. Also, with the high conductivity of Co, the DLE-CVD Co encapsulation layer have the potential to further decrease the power consumption of nanoscale Cu interconnects, paving the way for Cu interconnects with higher efficiency in future high-end microelectronics.

A novel gold-catalyzed chemoselective reduction of alpha,beta-unsaturated aldehydes using CO and H2O as the hydrogen source.

Chemoselective reduction of alpha,beta-unsaturated aldehydes in the presence of CO and H(2)O proceeds effectively over a ceria-supported gold catalyst system, providing a novel, efficient and clean approach to produce useful primary allyl alcohols with excellent activity and selectivity.