Effects of current density on the structure of Ni and Ni–Mn electrodeposits

Grain size and texture of Ni electrodeposited from sulfamate baths depend greatly on current density. Increasing grain size is observed with increasing current density and the deposit texture changes from 〈110〉 at current densities lower than 5 mA cm⁻² to 〈100〉 for higher current densities. Co-deposition of Mn modifies the deposit structure by favoring the growth of the 〈110〉 texture and decreasing the average grain size even as the current density increases. While the average Mn film content increases with increasing current density, local Mn concentrations are a more complex function of deposition parameters, as indicated by atom probe tomography measurements. In both direct-current plated and pulse plated films, large variations on a nanometer scale in local Mn concentration are observed.     

Control of composition and size for Pd–Ni alloy nanowires electrodeposited on highly oriented pyrolytic graphite

In order to fabricate effective Pd–Ni alloy nanowire arrays with given compositions and size, the process of nucleation and growth and the dependence of alloy composition on deposition potential were investigated. The results reveal that the compositions and sizes of Pd–Ni alloy nanowires can be controlled within a desired range through adjusting suitable nucleation and growth potentials as well as the time. The Ni content in the alloy nanowires was found to vary from 6 to 28% when the deposition potential was changed from −0.3 to −1.9 V. A growth potential of −0.35 to − 0.50 V was applied to fabricate Pd–Ni alloy nanowires with 8–15% Ni content. Continuous and parallel nanowire arrays can be successfully fabricated when nucleation is performed at a potential of −1.2 V for 50 ms with further growth at −0.45 V for 800 s. Pd–Ni crystal phases exist in the alloy structure forms of 〈111〉, 〈200〉, 〈220〉, 〈311〉. The nanowires have an average diameter of 150 nm and a length of 100–450 μm.     

Lonsdaleite diamond growth on reconstructed Si (100) by hot-filament chemical vapor deposition (HFCVD)

In this paper, the growth of Lonsdaleite diamond using hot-filament chemical vapor deposition (HFCVD) on flashed and reconstructed Si (100) is reported. Surface morphology studies using scanning electron microscopy (SEM) show that the film is composed of decahedron and icosahedron diamond particles. The X-ray diffraction (XRD) pattern has a strongest peak at 47° and a peak at 41°, which is indicative of Lonsdaleite nature of the grown diamond film. The Raman spectrum of the film shows a broadened diamond peak at wave number of 1,329 cm⁻¹, which has shifted towards the peak position corresponding to Lonsdaleite nature of the diamond (1,326 cm⁻¹).     

Dry etching of diamond nanowires using self-organized metal droplet masks

In a top-down approach diamond nanowires (DNW) were fabricated by anisotropic oxygen plasma etching of undoped or boron doped polycrystalline diamond layers. Dewetting an evaporated metal film, resulting in randomly distributed metal droplets of 5-50 nm in diameter, created the etching mask. This study focused on the investigation of the effect of the metal layer type, i.e., Al, Ti, Co, Ni, Cu, Pd, Pt and Au, and thickness on surface density, shape and size of the resulting droplets. Two dry etching techniques were studied: (1) Capacitively Coupled Plasma Reactive Ion Etching (CCP-RIE) and (2) Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Using CCP-RIE diamond etch rates were between 10 nm/min and 50 nm/min; however, diamond/Ni selectivity was not high enough to fabricate nanowires > longer than 250 nm. ICP-RIE etching created tapered, high aspect diamond nanostructures at 1000 W plasma power, 10 W platen power for ion acceleration and long etching times (> 40 min) while preserving the mask. Anisotropy can be improved by the addition of Ar in the plasma and the reduction of the pressure. So far, vertically aligned diamond nanowires of 800 nm in length were obtained by ICP-RIE etching in appropriate conditions.     

A direct-write,resistless hard mask for rapid nanoscale patterning of diamond

We introduce a simple, resist-free dry etch mask for producing patterns in diamond, both bulk and thin deposited films. Direct gallium ion beam exposure of the native diamond surface to doses as low as 10¹⁶ cm^?2 forms a top surface hard mask resistant to both oxygen plasma chemical dry etching and, unexpectedly, argon plasma physical dry etching. Gallium implant hard masks of nominal 50 nm thickness demonstrate oxygen plasma etch resistance to over 450 nm depth, or 9:1 selectivity. The process offers significant advantages over direct ion milling of diamond including increased throughput due to separation of patterning and material removal steps, allowing both nanoscale patterning resolution as well as rapid masking of areas approaching millimeter scales. Retention of diamond properties in nanostructures formed by the technique is demonstrated by fabrication of specially shaped nanoindenter tips that can perform imprint pattern transfer at over 14 GPa pressure into gold and silicon surfaces. This resistless technique can be applied to curved and non-planar surfaces for a variety of potential applications requiring high resolution structuring of diamond coatings.     

Formation of Nanopits in Si Capping Layers on SiGe Quantum Dots

In-situ annealing at a high temperature of 640°C was performed for a low temperature grown Si capping layer, which was grown at 300°C on SiGe self-assembled quantum dots with a thickness of 50 nm. Square nanopits, with a depth of about 8 nm and boundaries along 〈110〉, are formed in the Si capping layer after annealing. Cross-sectional transmission electron microscopy observation shows that each nanopit is located right over one dot with one to one correspondence. The detailed migration of Si atoms for the nanopit formation is revealed by in-situ annealing at a low temperature of 540°C. The final well-defined profiles of the nanopits indicate that both strain energy and surface energy play roles during the nanopit formation, and the nanopits are stable at 640°C. A subsequent growth of Ge on the nanopit-patterned surface results in the formation of SiGe quantum dot molecules around the nanopits.     

Recovery treatments for ion-induced defects in high-quality homoepitaxial CVD diamond

Effects of vacuum annealing and hydrogen plasma exposure on ion-implantation-induced defects have been investigated in case of high-quality chemical-vapor deposited (CVD) diamond mainly using cathodoluminescence (CL) measurements. The well-focused 30-keV Ga ions were implanted into regions with different ion doses from 1×10¹² to 1×10¹⁵ ions/cm². The free-exciton emission and the N–V center were observed at 235 and 575 nm, respectively, in room temperature CL spectra for as-grown homoepitaxial CVD diamond. The former vanished completely after all the implantation processes examined while the latter was destroyed more strongly with increasing ion doses. On one hand, the band edge emissions at 235 nm were hardly recovered even after any treatments examined. On the other hand, the CL peak at 575 nm reappeared either after a 30-min vacuum annealing at 900°C for the Ga dose of 1×10¹² ions/cm² or after a suitable hydrogen plasma treatment for all the Ga ion dosages examined. Thus, it is found that the band edge emission signal is required to investigate the beam damages to ‘high’ crystalline quality diamond. A removal of the damaged surface layer by the plasma etching is also discussed in relation to the recovery process mainly for the 575-nm peak at heavier ion doses.     

Formation of nanometer-size high-density pits on epitaxial diamond (100) films

We report the formation of pits having widths of approximately 10 nm and a density of 2.5 × 10¹¹/cm² on epitaxial diamond (100) films. The pits are formed by etching the films using atomic hydrogen at a substrate temperature of approximately 500 °C. Exposure to oxygen followed by etching with atomic hydrogen forms additional pits. We propose that the high-density pits are formed due to etching that occurs both perpendicular and parallel to the surface.     

Characterization of the performance and failure mechanisms of boron-doped ultrananocrystalline diamond electrodes

This research investigated the anodic stability of boron-doped ultrananocrystalline diamond (BD-UNCD) film electrodes on a variety of substrates (Si, Ta, Nb, W, and Ti) at a current density of 1 A cm⁻². At an applied charge of 100 A h cm⁻², measurable BD-UNCD film wear was not observed using SEM cross-sectional measurements. However, anodic treatment of the electrodes resulted in surface oxidation and film delamination, which caused substantial changes to the electrochemical properties of the electrodes. The substrate roughness, substrate electroactivity, and compactness of the substrate oxide were key parameters that affected film adhesion, and the primary mechanism of electrode failure was delamination of the BD-UNCD film. Substrate materials whose oxides had a larger coefficient of thermal expansion relative to the reduced metal substrates resulted in film delamination. The approximate substrate stability followed the order of: Ta > Si > Nb > W ≫ Ti.     

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to −14000 C cm⁻² in steps of −600 C cm⁻² using −1 A cm⁻² caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: −9 C cm⁻², passed at −1 A cm⁻². This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.     

Synthesis of a novel amphiphilic polymer containing nucleobases in the self-organized nanospheres

A simple strategy to achieve molecular recognition in water is to make the polymers self-organized into nanospheres which could incorporate the functional groups containing hydrogen bonding sites into hydrophobic-lipophilic regions. A novel amphiphilic polymer, Poly(polyoxyethylene-600)-oxy-5-(6-(1-thymine)hexyl)) isophthaloyl (PPETHI), has been synthesized. The PPETHI polymer could self-organize into nanospheres in dilute aqueous solution, which were 150–300 nm in diameter as estimated by SEM. The isophthaloyl with side hexyl thymine of the polymer self-organized into hydrophobic regions and the PEG surrounded it. Molecular recognition between thymine in PPETHI polymer and adenine substrate has been studied by FT-IR. The FT-IR studies demonstrate that C₄=O of thymine has recognized with N-H of adenine through complementary nucleobases. It shows that the typical characteristic band at 3,352 cm⁻¹ of N-H stretching vibration of adenine shifted to 3,373 cm⁻¹ and the band at 1,685 cm⁻¹ of C₄=O of thymine shifted to 1,680 cm⁻¹. To confirm the formation of hydrogen bonds, the N-H band at 3,373 cm⁻¹ and C₄=O band at 1,680 cm⁻¹ have retrieved to 3,312 cm⁻¹ and 1,685 cm⁻¹ respectively upon heating to 115 °C or higher by means of variable temperature FT-IR. The formations of hydrogen-bonds between thymine in the polymer and adenine substrate in nanospheres were confirmed. It could enhance their interaction and loading capacity.     

Unusual morphology of CVD diamond surfaces after RIE

Reactive ion etching of (100) CVD diamond films in O₂ has been performed using a 13.56 MHz capacitively coupled reactor at pressures of 20 mTorr–100 mTorr and r.f. powers of 100 W–300 W. The formation of columnar structures was observed at the grain boundaries whereas the (100) facets were etched to yield a smooth surface under optimum conditions. For comparison, the RIE of single, isolated cubo-octahedral crystallites produced smooth (100) facets and roughened (111) surfaces reminiscent of the micro-columnar structures evident in the films.     

Preparation of phenolic resin derived 3-D ordered macroporous carbon

Three-dimensionally ordered long-range macroporous carbon structures were prepared using commercially available phenolic resin by utilizing sacrificial colloidal silica crystalline arrays as templates that were subsequently removed by HF etching after pyrolysis in an argon atmosphere. SEM, TEM, and BET were employed to characterize the morphology and the surface area of the porous carbon structures. The pore size (150–1000 nm) and BET surface area, which reflect pore volume (298.6 m²/g (1.32 cm³/g) ∼ 93.7 m²/g (0.12 cm³/g)), of the macroporous carbon structures produced were approximately proportional to the size (150–1000 nm) of the sacrificial silica sphere templates used (annealing temp. 550°C). The achieved 550 nm porous carbon structures were examined to function as potential catalyst carriers and were successfully impregnated with Ag or Pt-Ru on their inner walls after borohydride reduction at room temperature. In addition, porous carbon patterns were fabricated using the ‘micromolding in capillary’ technique, which has potential applications in the microreaction technology.     

Structural and optical properties of diamond and nano-diamond films grown by microwave plasma chemical vapor deposition

We compare structural and optical properties of microcrystalline and nanocrystalline diamond (MCD and NCD, respectively) films grown on mirror polished Si(100) substrates by microwave plasma chemical vapor deposition. The films were characterized by SEM, Raman spectroscopy, XRD, and AFM. Optical properties were obtained from transmittance and reflectance measurements of the samples in the wavelength range of 200–2000 nm. Raman spectrum of the MCD film exhibits a strong and sharp peak near 1335 cm⁻¹, an unambiguous signature of cubic crystalline diamond with weak non-diamond carbon bands. Along with broad non-diamond carbon bands, Raman spectra of NCD films show features near 1140 cm⁻¹, the intensity of which is significantly higher in the film grown at 600°C compared to the NCD film grown at higher temperature. The Raman feature near 1140 cm⁻¹ is related to the calculated phonon density of states of diamond and has been assigned to nanocrystalline or amorphous phase of diamond. XRD patterns of the MCD film show sharp peaks and NCD films show broad features, corresponding to cubic diamond. The rms surface roughness of the films was observed to be approximately 60 nm for MCD film that reduced substantially to 17 and 34 nm in the NCD films grown at 600 and 700°C, respectively. Tauc's optical gap for the diamond film is found to be approximately 5.5 eV. NCD grown at 700°C has a high optical absorption coefficient in the whole spectral region and the NCD film grown at 600°C shows very high transmittance (∼78%) in the near IR region, which is close to that of diamond. This indicates that the NCD film grown at 600°C has the potential for applications as optical windows since its surface roughness is significantly low as compared to the MCD film.     

Properties of boron-doped epitaxial diamond layers grown on (110) oriented single crystal substrates

Boron doped diamond layers have been grown on (110) single crystal diamond substrates with B/C ratios up to 20 ppm in the gas phase. The surface of the diamond layers observed by scanning electron microscopy consists of (100) and (113) micro-facets. Fourier Transform Photocurrent Spectroscopy indicates substitutional boron incorporation. Electrical properties were measured using Hall effect from 150 to 1000 K. Secondary ion mass spectrometry analyses are consistent with the high incorporation of boron determined by electrical measurements. A maximum mobility of 528 cm² V^− 1 s^− 1 was measured at room temperature for a charge carrier concentration of 1.1 10¹³ cm^− 3. Finally, properties of boron doped (110) diamond layers are compared with layers on (100) and (111) orientated substrates.     

Growth of diamond films with high surface smoothness

Diamond films with highly smooth backside surface have been deposited by positively biasing the substrate during diamond growth in a hot-filament chemical vapor deposition (HFCVD) system. By bonding the diamond film on the glass and wet etching to remove silicon, the highly smooth diamond surface can be exposed and used directly for the fabrication of diamond devices.Silicon substrate was first treated by diamond powder of 625 nm in an ultrasonic bath. By positively biasing the substrate, electron bombardment during diamond growth increases the nucleation density from 10⁸ ∼ 10⁹ cm^− 2 to 4 × 10¹¹ cm^− 2. The surface smoothness on the backside of diamond film has thus been improved significantly, inducing root-mean-square roughness of 5 nm. Owing to the extremely high surface smoothness and the high crystalline quality on the backside of diamond film and the high diamond growth rate, the backside surface of the diamond film grown under electron bombardment is particularly suitable for device fabrication.     

Preparation of diamond whiskers using Ar/O2 plasma etching

Radio frequency (RF) plasma etching of chemical vapor deposition (CVD) diamond film has been investigated in Ar/O₂ plasmas, with an emphasis to elucidate the effects of reacting gas on the fabrication of diamond whiskers. Diamond whiskers were formed on diamond films pre-coated with Al. It was found that diamond whiskers preferentially formed at the diamond grain boundaries. The densities of diamond whiskers increased with O₂ / Ar ratio. Whiskers obtained in pure O₂ plasma etching were 50 nm in diameter and 1 μm in height. The etching rate was increased by mixing Ar with appropriate volume of O₂. Al coated on the diamond surface reacted with O₂ to form Al₂O₃, serving as mask to restrain the etching underneath. Raman spectroscopy measurement confirmed that the whiskers kept sp³ diamond bonding structure after RF plasma etching. The field emission characteristics of the whiskers were also inspected.     

Fabrication and application of nano–microcrystalline composite diamond films on the interior hole surfaces of Co cemented tungsten carbide substrates

Nano–microcrystalline composite diamond films are deposited on the interior hole surface of Co cemented tungsten (WC–6%Co) drawing using a squirrel-cage hot filament passing through the interior hole with large aperture by the bias-enhanced hot filament CVD. A new process is used to deposit nano–microcrystalline composite diamond coatings by a two-step hot filament chemical vapor deposition (HFCVD) procedure. Research results show that the as-deposited composite diamond films exhibit nanocrystalline diamond crystallites with grain sizes ranging from 60 to 90 nm and their surface roughness is measured as approximately Ra 220 nm with 4 mm scanning length. The Raman spectrum mainly exhibits three features near 1332, 1560 cm^? 1 (G peak), and a weak peak at approximately 1150 cm^? 1, which is attributed to the transpolyacetylene. XRD pattern indicates good crystallite quality of the composite films. The as-fabricated diamond coated dies show obvious performance enhancement in the practical application. Comparing with the WC–Co drawing die, the working lifetime of the diamond coated drawing die increases by a factor of above 15. Furthermore, the surface quality of the drawn copper pipes is greatly improved.     

Fabrication of submicron scale vertically aligned diamond rods by mask-free oxygen plasma etching

A mask-free plasma etching process is described to fabricate 6 μm long submicron diamond rods (SDRs) in long conical shape. Polished polycrystalline diamond is etched in oxygen plasma ignited at a pressure of 10 mTorr by radio-frequency power of 100 W at 13.56 MHz. Each SDR is a bi-crystal, consisting of two diamond crystallites of micron size. The SDR is coated with a Fe₂O₃ layer, as characterized by Auger electron spectroscopy, X-ray photoemission microscopy, and transmission electron microscopy. We propose that a “self-forming” mask of Fe₂O₃ is generated during the etching process in which iron atoms sputtered from the substrate holder are deposited and oxidized on the diamond surface forming “micromask” that protects the underlying diamond and promotes the formation of SDRs.     

Purity Assessment of Commercial Zein Products After Purification

Successful utilization of commercial zein products for certain food, pharmaceutical, cosmetic and medical applications requires a decolorized/deodorized zein of high purity that can be achieved by column filtration of commercial yellow zein solutions through Zeolite 5A and activated carbon. The objective of this investigation was to devise a combination of methodologies to assess purity and degree of deodorization and decolorization. Off-odor removal is defined by a UV spectroscopic ratio of 280:325 nm where diferuloylputrescine is the major contributor. Removal of yellow color, attributed to xanthophylls in zein, was followed by visible spectroscopic assays of a series of dilutions at 448 nm. SDS-PAGE analysis demonstrated removal of β-zein in combination with diminished sulfur content by sulfur analysis. Zein purity was assessed by Dumas nitrogen and FTIR of commercial zein before and after column filtration. Spectral differences were observed in the amide I (1,650 cm⁻¹) peak, amide II region (1,530 and 1,550 cm⁻¹) and the amide III peak at 1,240 cm⁻¹, where ratio of the dominant peaks were strongly dependent on purity of sample. Circular dichroism (CD) analyses validated the FTIR results by showing increased α-helical content for the column purified zeins. Combinations of these methodologies can be used to define zein products as a quality control measure for a commercial operation.