Organoselenium Precursors for Atomic Layer Deposition

Organoselenium compounds with perspective application as Se precursors for atomic layer deposition have been reviewed. The originally limited portfolio of available Se precursors such as H2Se and diethyl(di)selenide has recently been extended by bis trialkylsilyl)selenides, bis(trialkylstannyl)selenides, cyclic selenides, and tetrakis(N,N-dimethyldithiocarbamate)-selenium. Their structural aspects, property tuning, fundamental properties, and preparations are discussed. It turned out that symmetric four- and six-membered cyclic silyl selenides possess well-balanced reactivity/stability, facile and cost-effective synthesis starting from inexpensive and readily available chlorosilanes, improved resistance toward air and moisture, easy handling, sufficient volatility, thermal resistance, and complete gas-to-solid phase exchange reaction with MoCl5, affording MoSe2 nanostructures. These properties make them the most promising Se precursor developed for atomic layer deposition so far

Anodic TiO2 nanotube layers decorated by Pd nanoparticles using ALD: An efficient electrocatalyst for methanol oxidation

Herein, we report the performance of Pd nanoparticles (NPs) prepared by Atomic Layer Deposition (ALD) as a catalyst for methanol electro-oxidation. Pd NPs were decorated onto anodic TiO2 nanotube (TNT) layers as supporting material that possess a large available surface area and direct electrical contact via the underlying titanium foil. Different Pd loadings (150 - 300 - 450 - 600 ALD cycles) show different particles sizes ranging between 7 and 12 nm, as revealed by transmission electron microscopy. Coalescence dominated visibly from 450 ALD cycles, which led to a porous Pd layer all along the TNT walls rather than the growth of individual particles. Electrocatalytic performance was investigated by cyclic voltammetry (CV), where the catalytic activity increased proportional with Pd loading up to the highest values for 400 and 450 cycles, whereas a further increase in the number of ALD cycles (N-ALD) did not show any additional improvement in methanol oxidation current densities. TNT layers decorated with 400, 450 and 600 Pd ALD cycles show featureless curves suggesting complete anti-poisoning ability or possibly a proof of a direct conversion from CH3OH to CO2 (without any intermediate byproducts). The lack of an oxidation peak during the anodic scan and therefore a reduction peak during the cathodic scan, confirms Pd NPs (stabilized by TiO2) efficiently utilize OHads and chemisorbed CH3OH in a way that its CO poisoning was inhibited. As a result, the tuned high surface area TNT layers exhibited excellent performance as a supporting material for Pd NPs against formation of electrochemical poisoning species. Finally, the mechanism of the TNT layers interaction with Pd NPs, which led to the propelling methanol oxidation reaction without loss in performance over cycling is postulated

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing

The present work presents a strategy to stabilize amorphous anodic self-organized TiO2 nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO2 nanotube layers uniformly coated by thin TiO2 using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced.We investigated the soaking effects of ALD TiO2 coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO2 coatings (8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO2 nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment

ALD growth of MoS2 nanosheets on TiO2 nanotube supports

Two-dimensional MoS2 nanostructures are highly interesting and effective in a number of energy-related applications. In this work, the synthesis of ultra-thin MoS2 nanosheets produced by the thermal Atomic Layer Deposition (ALD) process is reported for the first time using a previously unpublished set of precursors, namely bis(t-butylimido)bis(dimethylamino)molybdenum and hydrogen sulfide. These nanosheets are homogenously deposited within one-dimensional anodic TiO2 nanotube layers that act as a high surface area conductive support for the MoS2 nanosheets. The decoration of high aspect ratio TiO2 nanotube layers with MoS2 nanosheets over the entire nanotube layer thickness is shown for the first time. The homogeneous distribution of the MoS2 nanosheets is proved by STEM/EDX. This resulting new composite is employed as anode for Li-ion microbatteries. The MoS2-decorated TiO2 nanotube layers show a superior performance compared to their counterparts without MoS2. Compared to electrochemical performance of pristine TiO2 nanotube, a more than 50% higher areal capacity and a coulombic efficiency of 98% are obtained on the MoS2 decorated TiO2 nanotube layers, demonstrating clear synergic benefits of the new composite structure

TiO2 Nanotube Layers Decorated with Al2O3/MoS2/Al2O3 as Anode for Li-ion Microbatteries with Enhanced Cycling Stability

TiO2 nanotube layers (TNTs) decorated with Al2O3/MoS2/Al2O3 are investigated as a negative electrode for 3D Li-ion microbatteries. Homogenous nanosheets decoration of MoS2, sandwiched between Al2O3 coatings within self-supporting TNTs was carried out using atomic layer deposition (ALD) process. The structure, morphology, and electrochemical performance of the Al2O3/MoS2/Al2O3-decorated TNTs were studied using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and chronopotentiometry. Al2O3/MoS2/Al2O3-decorated TNTs deliver an areal capacity almost three times higher than that obtained for MoS2-decorated TNTs and as-prepared TNTs after 100 cycles at 1C. Moreover, stable and high discharge capacity (414 mu Ah cm(-2)) has been obtained after 200 cycles even at very fast kinetics (3C)

ALD coating of centrifugally spun polymeric fibers and postannealing: case study for nanotubular TiO2 photocatalyst

This work describes the synthesis of highly photocatalytically active TiO2 tubes (TiTBs) by combining centrifugal spinning and atomic layer deposition (ALD). Poly(vinyl pyrrolidone) (PVP) fibers were first produced by centrifugal spinning and subsequently coated with TiO2 with various film thicknesses in a fluidized bed ALD reactor. After annealing of the TiO2 ALD coated PVP fibers, TiO2 tubes (TiTBs) with excellent textural properties and diameters in the range from approx. 170 to 430 nm were obtained. The morphology and structure of all TiTBs were investigated by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller analysis (BET). Liquid phase photocatalysis was conducted to determine the photocatalytic activity of the TiTBs. The photocatalytic activity of the TiTBs obtained after 50 TiO2 ALD cycles (degradation rate 0.123 min(-1)) was twice that of the reference TiO2 P25. The underlying reasons for the remarkable photocatalytic performance were textural properties of the resulting tubes along with suitable crystallinity, embedded within the 1D tubular morphology. The herein presented proof-of-concept approach paves a way for the processing of various polymeric fibers into various tubular nanostructures