Metal nanostructures fabricated by selective metal nanoscale etch method

A new method for fabricating metal nanostructures, called ‘the selective metal nanoscale etch method (SMNEM)’, was developed. The SMNEM consists of a galvanic displacement and selective etching process. The process was found to be simple and produced a uniform surface with a self-controlled etch rate of 32.2 ± 2.1 nm per cycle at a temperature and immersion time of 75°C and 3 min, respectively. Since it is a wet chemical process, SMNEM provides high throughput and low temperature etching which is compatible with conventional semiconductor processes. Various metal nanostructures, such as nanostairs, nanogratings, and nanowires were produced using SMNEM.     

Microstructural evaluation of molybdenum-containing stainless steel weld metals by a potentiostatic etching technique

Microstructure of austenitic stainless steel weld metals is complicated by the presence of delta-ferrite and microsegregated regions rich in chromium and molybdenum, as well as other minor alloying elements such as sulphur and phosphorus at the / interphase boundaries. Detailed microstructural studies are required in order to establish correlation between various metallurgical as well as electrochemical corrosion properties with the weld metal microstructure. The conventional chemical etching technique was found to be inadequate in revealing different microconstituents. A powerful potentiostatic etching technique was used to reveal not only ferrite but also different microconstituents that had different specific electrochemical potentials at which they dissolved. This paper describes the weld metal microstructure developed by the addition of molybdenum (4.16–5.83 wt%) to type 316 stainless steel weld metals during Tungsten Inert Gas (TIG) welding with different heat inputs. © 1998 Chapman & Hall     

Improvement of microstructural and mechanical properties of plasma sprayed Mo coatings deposited on Al-Si substrates by pre-mixing of Mo with TiN powder

The present work embodies development of a new class of mechanically improved Mo-TiN coating material using plasma spray technique. The coatings are developed on Al-Si alloy at different torch input power levels ranging from 15 kW to 30 kW. Pre-mixing of TiN with molybdenum enhances adhesion strength and hardness of the coatings. Maximum adhesion strength of 22 MPa (±0.75) and hardness of 748 HV (±30) are found for the coating when molybdenum is pre-mixed with 10% TiN. FESEM micrographs of the as-sprayed coatings showed formation of plate-like structures of splats which indicates TiN sites as reinforcement in Mo matrix. X-ray diffraction study reveals the formation of both MoO2 and TiN as minor phases in the coating microstructure. The significant enhancement of mechanical properties like adhesion strength and hardness is attributed towards the presence of these phases.     

Effect of conductor crossings on propagation margins

The effects of conductor delineation technique on magnetic bubble propagation across the conductor edge are described. Propagation margins are obtained for bubble circulation around 18-μm diameter Permalloy discs which cross four edges of an Al-Cu feature. Specifically investigated are isotropic wet etching, anisottopic wet etching to achieve a uniform taper, ion beam milling, and metal lift-off to provide a planar structure. Margins are obtained at ± 40°C, with the most significant degradation observed at the lower temperature. Permalloy magnetic continuity in the crossings can be inferred from hysteresis loop measurements of a Permalloy sheet deposited over a grating pattern formed by the above processing techniques. Although the least anisotropic loops are invariably obtained with smoothly tapered Al-Cu edges under the Permalloy, propagation margins are not maximized with such structures, but rather favor a planar crossing. The results suggest that although patterned stress is still an important concern in functional operation, other geometric effects can be more significant. In particular, poor magnetic step coverage as inferred from loop measurements leads to spurious pole formation from the drive field, while even with adequate step coverage, static bias-field distortions can result because of the component of the field along the step.     

On improving the track development properties of soda glass detectors

A detailed study of track development properties of soda glass detectors is carried out by varying the etching parameters, i.e. etching time, etchant temperature and the composition of the etching solution. The etch product layer (EPL) which mainly limits the sensitivity of these detectors is dissolved chemically as soon as it is formed. The largest observable etch pit diameter by the use of this method is almost double the one obtained using HF. Room temperature (39 ± 1)°C appears to be the optimum temperature for etching of soda glasses in this solution. The spectrometric response of soda glasses to fission fragments of ²⁵²Cf has also been studied, using this solution. The energy resolution of soda glass detectors is seen to improve and become comparable with the energy resolution of phosphate glass detectors.     

Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS2

Here, the hydrogen evolution reaction (HER) activities at the edge and basal‐plane sites of monolayer molybdenum disulfide (MoS₂) synthesized by chemical vapor deposition (CVD) are studied using a local probe method enabled by selected‐area lithography. Reaction windows are opened by e‐beam lithography at sites of interest on poly(methyl methacrylate) (PMMA)‐covered monolayer MoS₂ triangles. The HER properties of MoS₂ edge sites are obtained by subtraction of the activity of the basal‐plane sites from results containing both basal‐plane and edge sites. The catalytic performances in terms of turnover frequencies (TOFs) are calculated based on the estimated number of active sites on the selected areas. The TOFs follow a descending order of 3.8 ± 1.6, 1.6 ± 1.2, 0.008 ± 0.002, and 1.9 ± 0.8 × 10^?4 s^?1, found for 1T′‐, 2H‐MoS₂ edges, and 1T′‐, 2H‐MoS₂ basal planes, respectively. Edge sites of both 2H‐ and 1T′‐MoS₂ are proved to have comparable activities to platinum (≈1–10 s^?1). When fitted into the HER volcano plot, the MoS₂ active sites follow a trend distinct from conventional metals, implying a possible difference in the reaction mechanism between transition‐metal dichalcogenides (TMDs) and metal catalysts.     

Crystal growth and magnetic anisotropy of YTiO3

Single crystals of YTiO₃ were grown from the melt by the Czochralski technique from molybdenum crucibles under purified argon. YTiO₃ melts congruently at about 1965 ± 30°C. The largest crystals were a few mm on a side. Measurements of the magnetic moment of oriented single crystals at 4.2K reveal that the b- and c-axes are easy axes of magnetization while the a-axis is hard. The saturation magnetization in either of the easy directions is 0.84 ± .01 μ_B mole^?1.     

The fabrication of ferromagnetic nanocontact structure

In this paper, we report the fabrication of permalloy nanocontact structures with greatly improved surface and edge smoothness. Magnetic sputtering and thermal evaporation were used for metal film deposition, and lift-off and dry etching techniques were employed for nanocontact structure patterning. The compositional properties of the resulting nanocontacts were investigated using energy dispersive analysis of X-ray (EDAX). Atom force microscope and scanning electron microscope were used for morphological characterisation. We found that high quality permalloy nanocontact structures can be obtained by using the combination of thermal evaporation and lift-off with optimised processing parameters; meanwhile, in the case of depositing metal films using magnetic sputtering, dry etching technique rather than lift-off was used for improved surface morphology of the nanostructures.     

Formation and mechanism of silicon nanostructures by Ni-assisted etching

Instead of noble metal like Pt, Au and Ag, cheap Ni nanoparticles (Ni NPs) were used to fabricate silicon nanostructures. Ni was found to be etched off during the etching process, while forming silicon nanostructures with very low reflectance of 1.59 % from 400 to 900 nm. The formation mechanism of silicon nanostructures by Ni-assisted etching was presented from the point of view of the low electronegativity of Ni. The Ni NPs were found being etched off during the assisted etching process, which implies that the transfer rate of electrons from Si to Ni is slower than that from Ni to O^? in the case of using Ni as assisted metal. The reason of sparser and deeper silicon nanostructures etched in lower H₂O₂ concentration solution is that the Ni NPs can be lasted for longer time in the etching solution with lower H₂O₂ concentration so that more silicon atoms will be oxidized and then removed for those under Ni NPs due to the hole transfer and those where uncovered by Ni NPs due to the hole diffusion.     

Thermomechanical Nanocutting of 2D Materials

Atomically thin materials, such as graphene and transition metal dichalcogenides, are promising candidates for future applications in micro/nanodevices and systems. For most applications, functional nanostructures have to be patterned by lithography. Developing lithography techniques for 2D materials is essential for system integration and wafer-scale manufacturing. Here, a thermomechanical indentation technique is demonstrated, which allows for the direct cutting of 2D materials using a heated scanning nanotip. Arbitrarily shaped cuts with a resolution of 20 nm are obtained in monolayer 2D materials, i.e., molybdenum ditelluride (MoTe₂), molybdenum disulfide (MoS₂), and molybdenum diselenide (MoSe₂), by thermomechanically cleaving the chemical bonds and by rapid sublimation of the polymer layer underneath the 2D material layer. Several micro/nanoribbon structures are fabricated and electrically characterized to demonstrate the process for device fabrication. The proposed direct nanocutting technique allows for precisely tailoring nanostructures of 2D materials with foreseen applications in the fabrication of electronic and photonic nanodevices.     

X-ray photoelectron study of the MoCl2C30H30 composite

The surface of a MoCl₂C₃₀H₃₀ composite in the form of molybdenum nanoclusters in a polyacetylene matrix, produced by reacting MoCl₅ with C₂H₂ in benzene and toluene, has been studied by X-ray photoelectron spectroscopy before and after Ar⁺ ion milling. The composite actively reacts with atmospheric oxygen and moisture. As a result, the molybdenum clusters on its surface oxidize to molybdenum(V) or molybdenum(VI) oxides or oxychlorides (E _b(Mo 3d _5/2) = 232.3–232.5 eV) during the sample preparation process. The electron binding energy of molybdenum affter surface etching (E _b(Mo 3d _5/2) = 228.5 eV) suggests that the oxidation state of the molybdenum in the composite is 2⁺ or 3⁺. Analysis of the structure of the spectrum of the C 2s electrons of the inner valence molecular orbitals using the energy level diagram of the C₂ molecule suggests that the hydrocarbon matrix of the composite contains, in addition to-CH=CH-CH=CH- conjugate bonds, linear carbyne fragments: -HC=C=CH- or -C≡C-. After etching, the surface layer of the composite contained argon, which might be due to adsorption because of the small particle size of the composite or chemisorption on the surface of the polyacetylene matrix. The composite is stable in a high vacuum of 1.3 × 10⁻⁵ Pa up to 350°C and does not experience charging when exposed to X-rays, which indicates that it has weak dielectric properties.     

The triple point of pure normal-deuterium

The triple point temperature of pure normal-deuterium was determined on IPTS-68 using a calorimetric technique in an adiabatic cryostat and samples of about 0.2 mol of deuterium, 99.86% pure, permanently sealed in small metal cells. The temperature value was found to be 18.729 ± 0.002 K. Two thirds of the quoted uncertainty was due to the differences in IPTS-68 calibrations from NBS, NPL and PRM); differences in a range of 4.2 mK were observed using five calibrated thermometers. Natural para-ortho conversion rate was observed to be 7 ± 2h^?1 at 18.7 K; the rate of conversion back to normal composition for the gas at 20 MPa and ambient temperature was 3 ± 1h¹. The enthalpy of melting was 199 ± 1 Jmol^?1.     

Sub‐Micron Anisotropic InP‐based III–V Semiconductor Material Deep Etching for On‐Chip Laser Photonics Devices

Two InP‐based III–V semiconductor etching recipes are presented for fabrication of on‐chip laser photonic devices. Using inductively coupled plasma system with a methane free gas chemistry of chlorine and nitrogen at a high substrate temperature of 250 °C, high aspect ratio, anisotropic InP‐based nano‐structures are etched. Scanning electron microscopy images show vertical sidewall profile of 90° ± 3°, with aspect ratio as high as 10. Atomic Force microscopy measures a smooth sidewall roughness root‐mean‐square of 2.60 nm over a 3 × 3 μm scan area. The smallest feature size etched in this work is a nano‐ring with inner diameter of 240 nm. The etching recipe and critical factors such as chamber pressure and the carrier plate effect are discussed. The second recipe is of low temperature (?10 °C) using Cl₂ and BCl₃ chemistry. This recipe is useful for etching large areas of III–V to reveal the underlying substrate. The availability of these two recipes has created a flexible III–V etching platform for fabrication of on‐chip laser photonic devices. As an application example, anisotropic InP‐based waveguides of 3 μm width are fabricated using the Cl₂ and N₂ etch recipe and waveguide loss of 4.5 dB mm^?1 is obtained.

     

Tailored Height Gradients in Vertical Nanowire Arrays via Mechanical and Electronic Modulation of Metal‐Assisted Chemical Etching

In current top‐down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask‐dependent material deposition or etching techniques, is usually uniform, and on‐chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect‐ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal‐assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20‐fold on‐chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano‐assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics.     

A microcylindrical lens array made of silver-halide-sensitized gelatin etched by an enzyme with a real-time mask

Abstract

A novel method has been developed to fabricate microcylindrical lenses by etching silver-halide-sensitized gelatin (SHSG) with an enzyme solution, and the exposure pattern is produced on SHSG through a real-time mask technique. In this paper the principle of etching SHSG with an enzyme solution is given in detail and the optimum technique parameters of this process are presented; furthermore the theoretical analysis and solving scheme for the nonlinearities which arise from the absorption of light energy by film are given. A good linear relationship is experimentally obtained between the etching depth and time in depth a range up to 4 μm. Finally, the microcylindrical lens is achieved by experiment. The results are evaluated for experiments with a stylus profiling instrument and scanning electron microscope. This method does not require the use of expensive equipment, and it is not sophisticated and time consuming. So it is a practical method to fabricate excellent micro-optical elements.     

Reactive etching mechanism of tungsten silicide in CF4-O2 plasma

The WSi₂ etch rate contains contributions from the directional ion-enhanced etching mechanism which follows the nth power of the d.c. self-bias voltage across the plasma sheath (n = 1.7±0.5) and from the isotropic chemical etching mechanism linearly proportional to the number density of fluorine atoms in the CF₄-O₂ r.f. plasma. The “apparent” reaction probability of chemical etching, defined as the chemical etching rate per fluorine atom, increases with the r.f. power because of additional heating by the eddy current induced by the r.f. magnetic field. The r.f. inductive heating in the silicide film makes the temperature of the underlying polycrystalline silicon (poly-Si) film increase, resulting in a poly-Si chemical etching rate higher than that of a blanket poly-Si film. Etch rates due to the chemical etching are proportional to the silicon content in the silicide film for a given plasma condition. At a fixed silicon content (x = 2.6), a film prepared by the chemical vapor deposition technique exhibits a chemical etching rate higher by a factor of 2 than that of films prepared by either electron beam co-evaporation or co-sputter deposition.     

Growth of LiNaSO4 single crystals from a solution of stoichiometric pH value

Single crystals of LiNaSO₄ were grown without adjusting the pH value of equimolar aqueous solution containing Li₂SO₄·H₂O and NaHSO₄ at 30°C. As-grown crystals were characterized using X-ray, IR, Raman and other crystal perfection studies such as chemical etching, scanning electron micrograph and microhardness measurements. Atomic absorption technique was adopted to verify the composition of Li⁺ and Na⁺ ion content and these were found to be consistent with the desired composition to within ± 6 mol%.     

Molybdenum Carbide‐Decorated Metallic Cobalt@Nitrogen‐Doped Carbon Polyhedrons for Enhanced Electrocatalytic Hydrogen Evolution

Electrocatalytic hydrogen evolution reaction (HER) based on water splitting holds great promise for clean energy technologies, in which the key issue is exploring cost‐effective materials to replace noble metal catalysts. Here, a sequential chemical etching and pyrolysis strategy are developed to prepare molybdenum carbide‐decorated metallic cobalt@nitrogen‐doped porous carbon polyhedrons (denoted as Mo/Co@N–C) hybrids for enhanced electrocatalytic hydrogen evolution. The obtained metallic Co nanoparticles are coated by N‐doped carbon thin layers while the formed molybdenum carbide nanoparticles are well‐dispersed in the whole Co@N–C frames. Benefiting from the additionally implanted molybdenum carbide active sites, the HER performance of Mo/Co@N–C hybrids is significantly promoted compared with the single Co@N–C that is derived from the pristine ZIF‐67 both in alkaline and acidic media. As a result, the as‐synthesized Mo/Co@N–C hybrids exhibit superior HER electrocatalytic activity, and only very low overpotentials of 157 and 187 mV are needed at 10 mA cm^?2 in 1 m KOH and 0.5 m H₂SO₄, respectively, opening a door for rational design and fabrication of novel low‐cost electrocatalysts with hierarchical structures toward electrochemical energy storage and conversion.     

Thermal conductivity of helium in the eange 400–1500°K as determined by a molybdenum measurement cell

The apparatus described uses a heated wire (filament) to heat a molybdenum measurement cell by passage of electric current. The thermal conductivity of helium is measured in the range 400–1500°K with maximum experimental error of ±4%.     

Etching technique for revelation of plastic deformation zone in low carbon steel

Abstract

In this study, an etching technique to detect the localised plastic deformation behaviour in a low carbon steel was developed. With this technique, etching with Fry solution under ultrasonic vibration was carried out on samples plastically deformed and then heated at 550°C for a certain period of time. The plastic zone was revealed by different degrees of etching in the plastically deformed and non-deformed regions; the plastic zone was found to be only slightly etched, whereas the other region was deeply etched. From the surface offset after etching, the deformation zone was found to be observable even at low magnification, such as 10 times. As the heating duration increased, the plastic zone became clearer. The mechanism for such an etching reaction is discussed on the basis of electrochemical analysis.