Supported iridium catalysts prepared by atomic layer deposition: effect of reduction and calcination on activity in toluene hydrogenation

Ligand removal from supported iridium catalysts prepared by atomic layer deposition from Ir(acac)₃ was studied by direct reduction in hydrogen flow and by calcination in oxygen flow followed by reduction in hydrogen flow, as well as by thermogravimetric analysis. Thermal decomposition of acac ligand residuals required high temperatures, and in samples containing no iridium the removal of carbonaceous species was not complete. Metallic iridium particles less than 2 nm in size were formed during direct reduction and larger particles upon calcination followed by reduction. The activity of the catalysts in toluene hydrogenation in most cases depended on particle size.     

Electrodeposition of Ru by atomic layer deposition (ALD)

Studies are presented describing attempts to form a cycle for the growth of Ru nanofilms using the electrochemical form of atomic layer deposition (ALD). Au substrates have been used to form Ru nanofilms, based on layer by layer growth of deposits, using surface limited reactions. These deposits were formed using surface limited redox replacement (SLRR), where an atomic layer of a sacrificial element is first deposited by underpotential deposition (UPD), and is then exchanged for the element of interest. The use of the UPD atomic layer limits subsequent growth by limiting the number of electrons available for deposition. In the present study, Pb atomic layers were used, and exposed to solutions of Ru³⁺ ions at open circuit. This process can then be repeated to grow films of the desired thickness. It was shown that less than an at.% of Pb was evident in the deposits, using electron probe microanalysis (EPMA), and even that could be removed if a stripping step was added to the ALD cycle. The deposits displayed the expected Ru voltammetry, as well as the Ru hcp XRD pattern. There were some differences in the first 20 cycles, compared with subsequent, suggesting some nucleation process that must be investigated. However, after 20 cycles, the deposit showed the linear growth with the number of cycles expected for an ALD process. The morphology of Ru films, deposited on template-stripped Au was studied using ex situ scanning tunneling microscopy (STM), and showed no evidence of 3D growth.     

Beta Zeolite-Supported Iridium Catalysts by Gas Phase Deposition

In this study, H-beta zeolite-supported iridium catalysts were prepared by atomic layer deposition (ALD) and characterized as such and after different activation treatments. A reference catalyst was prepared by wet impregnation. The samples were tested in decalin ring opening reaction. ALD samples were clearly more active and selective in decalin ring opening compared to impregnated sample. The differences observed in characteristics and activities between ALD samples and impregnated sample are discussed.     

原子层沉积技术在银工艺饰品抗变色中的应用

分析了电镀贵金属、无机钝化膜、有机保护膜等几类常见银合金表面处理方法的特点及存在的问题,概述了原子层沉积技术的发展背景、基本原理、工艺特点、研究及应用状况,介绍了该技术应用于银工艺饰品抗变色上的效果.     

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.     

Synthesis and microstructure of iridium coatings on carbon fibers

Uniform, adherent, and non-bridging iridium coatings were applied to polyacrylonitrile-derived (ex-PAN) carbon fibers using low temperature metal organic chemical vapor deposition (MOCVD) from iridium (III) acetylacetonate. Composition, morphology, texture and topography of the iridium coated carbon fibers depending on MOCVD parameters have been studied by scanning electron microscopy/energy dispersive spectroscopy, atomic force microscopy, X-ray diffraction and extended X-ray absorption fine structure (EXAFS). For the MOCVD parameters studied, metallic iridium is the main phase of the coating. Together with iridium, a carbon-containing phase can be also present in the coating. The interatomic distances, corresponded coordination numbers and structural/microstructural parameters were established. The dependence of the microstructure of the Ir-coated carbon fibers on MOCVD parameters and possible structural models are discussed in detail. EXAFS showed that the Ir–O chemical bond on the boundary between the carbon fiber and the iridium coating is either absent or its contribution is too small to be detected by this method. Iridium appears to be bound to carbon fiber only by van der Waals forces. The data obtained by all methods are in a good agreement.     

Comparative study of self-assembling of multilayers using reactive sputter deposition and mass selective ion beam deposition

While experimenting with the growth of metal-containing amorphous carbon (a-c:Me) thin films using two different growth processes, self-assembled multilayered structures were observed. One of the processes is a reactive magnetron sputter deposition process. The other process is a mass selective ion beam deposition process. Despite of the differences in the growth method and the growth condition, self-assembled multilayered thin films, consisting of alternating dark layer and bright layer, were obtained in both processes. Based on the consideration of energy for atomic diffusion in the thin films, the growth mechanism is discussed.     

Epitaxial lateral overgrowth (ELO) of homoepitaxial diamond through an iridium mesh

In the present work iridium layers forming a mesh on diamond have been studied as potential candidates for buried electrodes or stopping layers in an ELO process for heteroepitaxial diamond. Thin iridium layers (∼ 15 nm) were deposited by e-beam evaporation at ∼ 700 °C on the facets of individual (001)-oriented CVD diamond crystallites and macroscopic Ib HPHT substrates with off-axis angles of several degrees. The heteroepitaxial iridium films formed a mesh with 10–200 nm large holes. These were penetrated by homoepitaxial diamond in a microwave plasma chemical vapour deposition process (MWPCVD) burying the iridium layer completely after 15 min of diamond growth. High resolution X-ray diffraction including reciprocal space mapping and Raman spectroscopy was used to characterize the structural properties of the diamond overlayer on the Ib HPHT substrate. It was monocrystalline with an FWHM of 0.03–0.05° of the X-ray rocking curve. Its lattice planes were tilted by ∼ 0.01° with respect to the substrate and showed a macroscopic strain of − 10^− 4 perpendicular to the surface. Besides the smaller lattice constant due to the lack of nitrogen the strain is mostly attributed to a tensile in-plane stress state. Strain and tilt can be attributed to the lateral overgrowth and the off-axis angle of the substrate.     

Directed inorganic modification of bi-component polymer fibers by selective vapor reaction and atomic layer deposition

Nanocomposite organic/inorganic materials with spatially-controlled composition can be formed using vapor-phase atomic layer deposition (ALD) on bi-component polymer fibers. The ALD process promotes selective precursor infusion into the inner core of a core/shell polymer fiber, yielding nanoparticles encapsulated within the core. Likewise, choosing alternate precursors or reaction conditions yield particles or films on the outer polymer shell. In-situ infrared spectroscopy and transmission electron microscopy show that infusion yields selective dispersion of aluminum oxide in different polymer regions, forming fine nanoparticle dispersions or films. Selective inclusion of metal oxide materials during atomic layer deposition on polymers can create unique organic/inorganic composite structures for many advanced uses.     

Electrochemical Formation of CdSe Monolayers on the Low Index Planes of Au

The electrochemical analog of atomic layer epitaxy (ALE) is being studied. ALE is a method for growing thin films of materials using a cycle of surface limited reactions. The surface limited reactions control the deposition by limiting the growth to an atomic layer at a time. In electrochemistry, a surface limited deposition is generally referred to as underpotential deposition (UPD), and UPD is used to form the atomic layers in electrochemical ALE (ECALE). The work presented here is an atomic level study of the deposition of the first few monolayers of CdSe via ECALE: by the alternated UPD of atomic layers of Se and Cd on the low index planes of Au. UPD of Se resulted in the formation of ordered structures on each of the low index planes of Au, as observed by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The subsequent UPD of Cd resulted in CdSe deposits which exhibited 1:1 stoichiometry, as determined by coulometry and Auger electron spectroscopy (AES). The following LEED patterns were observed for the CdSe monolayers: Au(111)(√7×√7)R19.1°, Au(111)(3×3), Au(110)(2×3), and the Au(100)(√2×2√2)R45°. Similar LEED patterns were observed on each surface for deposits formed using up to three ECALE cycles. In situ STM studies of Cd deposition on Se-covered Au(111) indicated the formation of a (3×3) structure, consistent with LEED results, and with previous TEM studies. The same LEED patterns were also observed for CdSe monolayers where Cd was deposited as the first atomic layer. AES indicated that the element deposited first remained on the bottom, and that deposited second remained on top.     

Large scale metal-free synthesis of graphene on sapphire and transfer-free device fabrication

Metal catalyst-free growth of large scale single layer graphene film on a sapphire substrate by a chemical vapor deposition (CVD) process at 950 °C is demonstrated. A top-gated graphene field effect transistor (FET) device is successfully fabricated without any transfer process. The detailed growth process is investigated by the atomic force microscopy (AFM) studies.     

High-performance bilayer flexible resistive random access memory based on low-temperature thermal atomic layer deposition

We demonstrated a flexible resistive random access memory device through a low-temperature atomic layer deposition process. The device is composed of an HfO₂/Al₂O₃-based functional stack on an indium tin oxide-coated polyethylene terephthalate substrate. After the initial reset operation, the device exhibits a typical bipolar, reliable, and reproducible resistive switching behavior. After a 10⁴-s retention time, the memory window of the device is still in accordance with excellent thermal stability, and a 10-year usage is still possible with the resistance ratio larger than 10 at room temperature and at 85°C. In addition, the operation speed of the device was estimated to be 500 ns for the reset operation and 800 ns for the set operation, which is fast enough for the usage of the memories in flexible circuits. Considering the excellent performance of the device fabricated by low-temperature atomic layer deposition, the process may promote the potential applications of oxide-based resistive random access memory in flexible integrated circuits.     

Synthesis and characterization of iridium oxide thin film via a pre-coordination step for bio-stimulating electrode application

An effective solution-based process is developed for the fabrication of iridium oxide thin film in application of bio-stimulating electrode. The chemical bath employs a pre-coordination scheme in which the IrCl₆³⁻ precursor undergoes a ligand exchange step to form stable Ir(OH)₆³⁻, followed by an oxidative electroless deposition to render iridium oxide thin film with desirable surface morphologies. Relevant processing parameters have been optimized to increase the utilization rate of Ir precursor for a thicker deposit without any noticeable defect. The iridium oxide thin film is mechanically robust and exhibits superior performances in both charge storage capacity and charge injection capacity. In particular, the normalized charge storage capacity is recorded at 0.367 mC/(cm2˙nm), a value that is five times greater than comparable iridium oxide thin films. In addition, in cell viability test, the iridium oxide thin film demonstrates impressive biocompatibility with desirable growth of neuronal cells.     

Design of High Efficient Mid‐Wavelength Infrared Polarizer on ORMOCHALC Polymer

While an organically modified chalcogenide (ORMOCHALC) can be used to fabricate a polymeric mid‐wavelength infrared (MWIR) polarizer with competitive extinction ratio compared to the commercial wire‐grid polarizers, which are composed of fragile inorganic materials, there is still a knowledge gap regarding the systematic design process to obtain high transmission efficiency and extinction ratio. To this end, a computational parameter study for design optimization is conducted with the geometric parameters of the bilayer grating ORMOCHALC polarizer. The computational study shows that the Fabry–Pérot cavity is the primary mechanism that determines the transmission behaviors and the extinction ratio. A bilayer grating design, guided by the parameter study, is realized through the thermal nanoimprint and metal deposition processes. The extinction ratios measured with the Fourier‐transform infrared are 245, 304, and 351 at the wavelength of 3, 4, and 5 µm, respectively. Compared to the state‐of‐the‐art of the polymeric MWIR linear polarizers, the extinction ratio is improved by 1.4 times, and the transmission efficiency is increased by 2.5 times. Theoretical analysis with the multiple‐layer model based on the transfer matrix method predicts a matched transmission behavior with the experiment and a full‐wave electromagnetic simulation.     

Combined AFM–SEM study of the diamond nucleation layer on Ir(001)

During bias enhanced nucleation (BEN) of diamond on iridium the nucleation centres are gathered in discrete islands — the so called “domains”. The topographic signature of these domains has been clarified in the present study by two different concepts. First scanning electron microscopy (SEM) and atomic force microscopy (AFM) were combined to take images with both techniques of a small identical area on a standard BEN sample. In spite of the 2–3 nm deep roughening of the iridium it turned clearly out that the surface shows a 1 nm deep depression within the domains compared with the surface of the surrounding layer. On a second sample which did not show the normal roughening the domains could be identified directly from AFM images. The topographic signature of the domains was the same. Conductive AFM measurements showed that inside and outside the domains the carbon nucleation layer behaves like a high resistivity dielectric sustaining fields up to 10⁷ V/cm. Finally, the temporal development of the domain patterns was studied by consecutive biasing steps on one sample. Depending on the local ion bombardment conditions we observed lateral growth or shrinkage on the same sample. This result suggests that domain formation is a continuous process during the whole BEN procedure starting from a local nucleation event and subsequent lateral expansion.     

Nanopatterning by direct-write atomic layer deposition

A novel direct-write approach is presented, which relies on area-selective atomic layer deposition on seed layer patterns deposited by electron beam induced deposition. The method enables the nanopatterning of high-quality material with a lateral resolution of only ～10 nm. Direct-write ALD is a viable alternative to lithography-based patterning with a better compatibility with sensitive nanomaterials.     

Chemistry of SiNx thin film deposited by plasma-enhanced atomic layer deposition using di-isopropylaminosilane (DIPAS) and N2 plasma

Silicon nitride (Si₃N₄) films have received great attention not only as dielectric materials for the gate dielectric of transistors and the insulator of capacitors, but also as a buffer layer and etch-stop layer for the semiconductor industry. As the applications of Si₃N₄ film increase, the necessity of investigating a novel deposition process applicable at low temperature has emerged. In this regard, the plasma-enhanced atomic layer deposition (PEALD) technique is attractive as a promising process; however, the Si₃N₄ film deposition process at growth temperatures less than 150?°C using PEALD has not been investigated. In this work, the growth behavior and chemistry of SiN_x (x?<?1.33) film deposited by the PEALD process at various growth temperatures were developed. Insufficient thermal energy from low growth temperature induces an unstable chemical state of deposited film due to the remaining unreacted ligand of adsorbed precursors. This state results in a further chemical reaction to SiO₂ formation by air exposure. Other chemical effects depending on chemical composition and electrical property were also examined in detail.     

Plasma-enhanced atomic layer deposition of gallium nitride thin films on fluorine-doped tin oxide glass substrate for future photovoltaic application

To serve as an electron transport layer (ETL) or a buffer layer for the third-generation solar cells, a compact and uniform gallium nitride (GaN) thin layer with suitable energy level is needed. Meanwhile, it is also meaningful to explore its low-temperature deposition especially on transparent electrodes. In this work, GaN thin films have been deposited on fluorine-doped tin oxide (FTO) glass substrate for the first time by plasma-enhanced atomic layer deposition (PEALD) technology. 280–300 °C is identified as the optimized deposition temperature for forming a compact and uniform n-type GaN layer on FTO substrate. The 50–200 PEALD cycles of GaN layers show an amorphous structure, and their bandgap values ranging from 3.95 eV to 3.58 eV have been displayed. Interestingly, as the GaN thickness increases, Fermi level moves upward obviously along with a reduction of conduction band minimum (CBM) value as well as an increase of valence band maximum (VBM) value. The thickness-dependent band structure is preliminarily explained as the relaxation of compressive stress and increased carrier concentration for a thicker GaN layer. The above situation enables us to regulate the energy level of GaN layer via thickness control, and thus accelerates its future application in new generation solar cells.     

Formation of PbTe nanofilms by electrochemical atomic layer deposition (ALD)

This article describes optimization of a cycle for the deposition of lead telluride (PbTe) nanofilms using electrochemical atomic layer deposition (ALD). PbTe is of interest for the formation of thermoelectric device structures. Deposits were formed using an ALD cycle on Au substrates, one atomic layer at a time, from separate solutions, containing Pb²⁺ or HTeO₂⁺ ions. Single atomic layers were formed using surface limited reactions, referred to as underpotential deposition (UPD), so the deposition cycle consisted of alternating UPD of Te and Pb. The Pb deposition potential was maintained at −0.35 V throughout the 100 cycle-runs, while the Te deposition potential was ramped up from −0.55 V to −0.40 V over the first 20 cycles and then held constant for the remaining ALD cycles. Coulometry for the reduction of both Te and Pb indicated coverages near one monolayer, each cycle. Electron probe microanalysis (EPMA) indicated a uniform and stoichiometric deposit, with a Te/Pb ratio of 1.01. X-ray diffraction measurement showed that the thin films had the rock salt structure, with a preferential (2 0 0) orientation for the as formed deposits. No annealing was used. Infrared reflection absorption measurements of PbTe films formed with 50, 65, and 100 cycles indicated strong quantum confinement.     

Plasmonic energy transformation in the photocatalytic oxidation of ammonium

The plasmonic transformation of light into energy for a chemical reaction is demonstrated in the endothermic oxidation of ammonium ions. The plasmonic heating effect physically triggers a platinum thin film, which becomes an active catalyst for the plasmonic catalytic reaction. The amount of chemical energy consumed in the plasmonic photocatalytic reaction was less than that in the normal chemical process. A homogeneous, condensed, pinhole-less 8 nm platinum thin film fabricated via plasma-enhanced atomic layer deposition served as a medium that transformed the energy in two steps.