Plasma enhanced atomic layer deposition of gallium sulfide thin films

Gallium sulfide has a great potential for optoelectronic and energy storage applications. Since most of these applications require a high control over the layer thickness or a high conformality, atomic layer deposition is a promising deposition technique. In this work, the authors present a novel plasma enhanced atomic layer deposition process for gallium sulfide based on trimethylgallium and H2S/Ar plasma. The growth was characterized using in situ spectroscopic ellipsometry. It was found that the process grew linearly at a rate of 0.65 angstrom/cycle and was self-limited in the temperature range from 70 to 350 degrees C. The process relied on a combustion reaction, which was shown by the presence of CS2 during in situ mass spectrometry measurements. Furthermore, the material properties were investigated by x-ray photoelectron spectroscopy, x-ray diffraction, and optical transmission measurements. The as-deposited films were amorphous and pinhole free. The GaSx thin films had a transmittance of >90% and a band gap of 3.1-3.3 eV

Ligand binding to copper nanocrystals : amines and carboxylic acids and the role of surface oxides

Dispersions and inks based on copper nanoparticles have raised extensive interest for printed electronics as copper holds promise for attaining high electric conductivity at low cost. Here, we use the decomposition of copper formate in oleylamine to produce a nanocolloid consisting of∼4 nm copper nanocrystals, a size that is ideal to study the binding of ligands to nanocopper. Using solution 1H NMR spectroscopy, we demonstrate that oleylamine binds to the surface of as-synthesized copper nanocrystals, thus stabilizing the dispersion by steric hindrance. We find that addition of a carboxylic acid to a purified nanocolloid induces an exchange between the originally bound oleylamine and the carboxylic acid as the surface-bound ligand.We provide evidence that the carboxylic acid dissociates upon binding to the copper nanocrystals. As such a process requires an amphoteric surface, a characteristic of a metal oxide but not of an elementary metal, we argue that ligand binding is determined by residual surface oxides and not by the pristine copper surface. Finally, we demonstrate that stable copper nanocolloids can be obtained in a variety of polar solvents by replacing oleylamine as a ligand by 2-[2-(2-methoxyethoxy)ethoxy]acetic acid(MEEAA). The inevitable oxidation of the small copper nanocrystals used here can be undone by mild thermal annealing,which especially in the case of MEEAA-stabilized nanocopper leads to significant grain growth. In this way, we turn an as-synthesized dispersion of colloidal copper nanocrystals into a nano-ink that can be formulated to produce metallic copper strips by screen or inkjet printing

Recommended reading list of early publications on atomic layer deposition-Outcome of the "Virtual Project on the History of ALD"

Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency. (C) 2016 Author(s).Peer reviewe

Plasma enhanced atomic layer deposition of gallium sulfide thin films

Gallium sulfide has a great potential for optoelectronic and energy storage applications. Since most of these applications require a high control over the layer thickness or a high conformality, atomic layer deposition is a promising deposition technique. In this work, the authors present a novel plasma enhanced atomic layer deposition process for gallium sulfide based on trimethylgallium and H2S/Ar plasma. The growth was characterized using in situ spectroscopic ellipsometry. It was found that the process grew linearly at a rate of 0.65 angstrom/cycle and was self-limited in the temperature range from 70 to 350 degrees C. The process relied on a combustion reaction, which was shown by the presence of CS2 during in situ mass spectrometry measurements. Furthermore, the material properties were investigated by x-ray photoelectron spectroscopy, x-ray diffraction, and optical transmission measurements. The as-deposited films were amorphous and pinhole free. The GaSx thin films had a transmittance of >90% and a band gap of 3.1-3.3 eV

Plasma enhanced atomic layer deposition of aluminum sulfide thin films

Aluminum sulfide is a promising material for energy storage, photonics, and microelectronics applications. Most of these applications require thin films with a high control over layer thickness and composition making atomic layer deposition an ideal deposition technique. The authors report a plasma enhanced process for aluminum sulfide based on trimethylaluminum and H2S-plasma. The growth characteristics were studied using in situ spectroscopic ellipsometry, indicating linear growth at a rate of 1.2 angstrom/cycle at 90 degrees C. Self-saturated growth could be achieved in a temperature window ranging from 90 to 350 degrees C. The process relies on combustion reactions during the plasma step, as confirmed by the observation of CS2 using in situ mass spectrometry measurements. Ex situ x-ray photoelectron spectroscopy, x-ray diffraction, and scanning electron microscopy/energy-dispersive x-ray spectroscopy measurements showed that the deposited layers are amorphous and pinhole free