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 1 H 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 assynthesized dispersion of colloidal copper nanocrystals into a nano-ink that can be formulated to produce metallic copper strips by screen or inkjet printing.

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Colloidal quantum dots (QDs) are a promising material for optoelectronic applications. Typically, device integration requires QDs to be embedded in a host material. Atomic layer deposition (ALD) is often considered as a deposition technique for such purposes. However, it is known that ALD and vacuum processes often influence the optical properties of QDs in a negative way. Here, we describe an in situ photoluminescence (PL) measurement setup and use it to monitor the PL of QDs under vacuum and during ALD. For CdSe-based core/shell QDs, a reduction in the QD PL was observed upon exposure to vacuum. Water was identified as crucial for maintaining a high PL as evidenced by re-exposure to different gases. Furthermore, we addressed the influence of vacuum, different plasmas (O 2 , H 2 O, H 2 , H 2 S/Ar, and Ar), precursors (trimethylaluminum, diethylzinc, tetrakis(dimethylamido)titanium, and tetrakis(ethylmethylamido)hafnium), reactants (H 2 O, H 2 S, and O 3 ), and ALD processes (Al 2 O 3 , TiO 2 , HfO 2 , and ZnS) on QDs. We observed a PL reduction by up to 90% upon plasma treatments. Furthermore, we found that trimethylaluminum and diethylzinc reduced the PL efficiency by more than 70% while exposure to tetrakis(dimethylamido)titanium and tetrakis(ethylmethylamido)hafnium lowered the PL by only 10−20%. Surprisingly, tetrakis(dimethylamido)titanium and H 2 O, which by themselves had only a minor influence on the QD PL, still caused an 80% drop of the PL efficiency when combined as an ALD process. On the other hand, ALD growth of HfO 2 by combining tetrakis(ethylmethylamido)hafnium and O 3 preserved 80% of the initial PL quantum yield, making it a promising process for QD embedding. These results put forward in situ PL measurements as a versatile technique to identify suitable precursors, reactants and ALD processes for QD embedding and investigate the interaction between QDs and reactive gaseous species in general.

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 Å/cycle at 90 °C. Self-saturated growth could be achieved in a temperature window ranging from 90 to 350 °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.

Zinc sulfide thin films were deposited by plasma enhanced atomic layer deposition (PE-ALD) using diethylzinc and H 2 S/Ar plasma. The growth characteristics were studied in situ with spectroscopic ellipsometry and ex situ with x-ray reflectometry. The growth was linear and selflimited. Furthermore, it was demonstrated that the growth per cycle was less temperature dependent for the PE-ALD process compared to the thermal process. ZnS thin film properties were investigated ex situ using x-ray photoelectron spectroscopy, x-ray diffraction, ultraviolet/visible optical spectroscopy, and atomic force microscopy. The as-deposited films were crystalline with a transmittance of >90% and a band gap of 3.49 eV. ZnS films deposited by PE-ALD were smoother than films deposited by thermal ALD. The plasma enhanced ALD process may have an advantage for ALD of ternary compounds where different temperature windows have to be matched or for applications where a smooth interface is required. V