Aerosol assisted fabrication of metallic film/carbon fiber and heat treatment to form crystalline alloy film

Carbon fiber (CF) was catalytically activated with spark generated Pd aerosol nanoparticles. Metal (Ag, Au, Cu, and Pd) and alloy (Ni-P, Ni-Cu-P) electroless films were deposited on Pd aerosol activated CF using a range of deposition parameters including deposition rate in an electroless deposition bath. Sintering was applied to the alloy films on the CF to examine the crystallization behavior at 400 °C in a nitrogen atmosphere. Ni-Cu-P had a higher crystallinity than Ni-P after the treatment.     

Interfacial reaction and elemental redistribution in Sn3.0Ag0.5Cu-xPd/immersion Au/electroless Ni solder joints after aging

Sn3.0Ag0.5Cu solder doped with 0, 100, and 500 ppm Pd was reflowed with electroless Ni/immersion Au substrate. As Pd concentration increased in the solder, formation and growth of (Cu,Ni)₆Sn₅ were suppressed. After thermal aging, Cu₄Ni₂Sn₅ and Cu₅NiSn₅ were observed at interface of Sn3.0Ag0.5Cu-xPd/Au/Ni systems. As compared to Cu₄Ni₂Sn₅, more Pd dissolved in Cu₅NiSn₅. In addition, Pd doping enhanced the growth of Cu₄Ni₂Sn₅ and slowed the formation of Cu₅NiSn₅, which would stabilize the intermetallic compound. Based on quantitative analysis by field emission electron probe microanalyzer, the correlation between Pd doping and elemental redistribution in solder joints was probed and discussed. This study described a possible mechanism of the formation of different intermetallic compounds in Pd-doped lead-free solder.     

Effects of preparation temperature on optical and electrical characteristics of (111)-oriented Cu2O films electrodeposited on (111)-Au film

The (111)-oriented Cu₂O films with a 2.0-eV-bandgap energy were prepared by electrodeposition on a (111)-oriented Au/Si wafer substrate at the preparation temperatures from 298 to 323 K, and the structural, optical, and electrical characterizations were carried out by X-ray absorption spectra measurements, X-ray diffraction, scanning electron microscopic observations, optical absorption spectra, photoluminescence spectra measurements, and Hall effect measurements. The photoluminescence spectra and electrical characteristics changed depending on the temperature. The 1.52-eV-visible light that originated from the copper vacancies weakened with a decrease in the preparation temperature, and the emission of the slight 2.0-eV-visible light due to the recombination of excitons was observed for the Cu₂O film prepared at 298 K. The hole density related to the copper vacancies decreased and the mobility increased with a decrease in the preparation temperature, and the maximum mobility of 21 cm² V⁻¹ s⁻¹ could be obtained at 303 K.     

Effect of phosphorus on the copper diffusion barrier properties of electroless CoWP films

The properties of electroless CoWP barrier films with different phosphorus contents in Cu/CoWP/Si stacked samples were explored. The Cu/CoWP/Si stacked samples with 30 nm CoWP films, contained about 5.7, 8.2 and 10.8 at.% P, were prepared by electroless deposition, and then annealed in a rapid thermal annealer at a temperature between 300 and 700 °C. The effect of phosphorus content in CoWP film on the barrier properties in preventing copper diffusion and the failure of the Cu/CoWP/Si stacked samples after thermal annealing were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES), and sheet resistance measurement. Increasing the phosphorus content in the electroless CoWP film markedly improves the barrier properties. The failure temperature of Cu/CoWP/Si increased from 500 to 600 °C with the phosphorus content in CoWP film increasing from 5.7 to 10.8 at.%, and the failure of the Cu/CoWP/Si has mainly arisen from the interdiffusion of copper and cobalt during thermal annealing.     

硅基体表面无钯活化化学镀镍工艺

硅材化学镀镍的活化是为了获取金属原子沉积中心,但现有的活化工艺存在种种不足。金纳米粒子具有小尺寸效应、表面与界面效应,呈现出良好的催化活性。采用金纳米粒子对硅基体进行活化后化学镀镍,并采用浸泡腐蚀试验,SEM及EDS测试将其与传统的钯活化法对比,研究了活化后的沉积速度及镀层形貌、结构、耐腐蚀性能,结果表明：金纳米粒子活...     

Effect of annealing temperature on electrical properties of Au/polyvinyl alcohol/n-InP Schottky barrier structure

In the present work, thin film of polyvinyl alcohol (PVA) is fabricated on n-type InP substrate as an interfacial layer for electronic modification of Au/n-InP Schottky contact. The electrical characteristics of Au/PVA/n-InP Schottky diode are determined at annealing temperature in the range of 100-300 °C by current-voltage (I-V) and capacitance-voltage (C-V) methods. The Schottky barrier height and ideality factor (n) values of the as-deposited Au/PVA/n-InP diode are obtained at room temperature as 0.66 eV (I-V), 0.82 eV (C-V) and 1.32, respectively. Upon annealing at 200 °C in nitrogen atmosphere for 1 min, the barrier height value increases to 0.81 eV (I-V), 0.99 eV (C-V) and ideality factor decreases to 1.18. When the contact is annealed at 300 °C, the barrier height value decreases to 0.77 eV (I-V), 0.96 eV (C-V) and ideality factor increases to 1.22. It is observed that the interfacial layer of PVA increases the barrier height by the influence of the space charge region of the Au/n-InP Schottky junction. The discrepancy between Schottky barrier heights calculated from I-V and C-V measurements is also explained. Further, Cheung's functions are used to extract the series resistance of Au/PVA/n-InP Schottky diode. The interface state density as determined by Terman's method is found to be 1.04 × 10¹² and 0.59 × 10¹² cm^− 2 eV^− 1 for the as-deposited and 200 °C annealed Au/PVA/n-InP Schottky diodes. Finally, it is seen that the Schottky diode parameters changed with increase in the annealing temperature.     

High-sensitivity non-enzymatic glucose biosensor based on Cu(OH)2 nanoflower electrode covered with boron-doped nanocrystalline diamond layer

A non-enzymatic biosensor was developed using boron-doped nanocrystalline diamond (BDND) based on a Cu electrode with Cu(OH)₂ dendritic architecture. The Cu(OH)₂ nanoflower electrode was covered with a BDND layer using an electrostatic self-assembly seeding method with nanodiamond particles and hot-filament chemical vapor deposition. X-ray diffraction and Raman spectral analysis confirmed that the BDND nanoflower electrode was synthesized onto Cu(OH)₂ nanoflowers. Field-emission scanning electron microscope images showed that the fabricated electrodes were nanoflowers possessing large surface areas. From cyclic voltammetry, the peak currents of an BDND/Cu(OH)₂/Cu electrode was about 7, 6.2, and 5.9 times higher than that of the Cu foil, Cu(OH)₂/Cu, and BDND/Cu electrodes, respectively. A biosensor based on BDND/Cu(OH)₂/Cu exhibited excellent performance for glucose detection, and it had a linear detection range of 0 to 6 mM, a correlation coefficient of 0.9994, a low detection limit of 9 μM, and a high sensitivity of 2.1592 mA mM^− 1 cm^− 1.     

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4‐Nitrophenol in Solution

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4‐nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy‐dispersive X‐ray spectroscopy coupled with aberration‐corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au‐rich or Cu‐rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25‐fold higher activity than an Au/Cu reference sample made by chemical impregnation.     

Magneto-optical Kerr-effect studies on copper oxide thin films produced by atomic layer deposition on SiO2

This work demonstrates the sensitivity of magneto-optical Kerr-effect (MOKE) spectroscopy to ultra-thin nonmagnetic films using the example of copper oxide. The films with an effective thickness between 0.6 nm and 6 nm are produced by atomic layer deposition (ALD) on silicon oxide substrates based on the Cu(I) β-diketonate precursor [(ⁿBu₃P)₂Cu(acac)] (acac = acetylacetonate) at a process temperature of 120 °C. The copper oxide films exhibit magneto-optical activity in the spectral ranges around 2.6 eV and above 4 eV. The evolution of the spectral features as a function of the number of ALD cycles is simulated numerically using the dielectric function and the Voigt constant of Cu₂O as input parameters. The comparison between experimental and simulated MOKE spectra strengthens the conclusion drawn from spectroscopic ellipsometry studies that the thin film optical constants differ markedly from the bulk ones.     

Aerosol based fabrication of a Cu/polymer and its application for electromagnetic interference shielding

The effect of a catalytic surface activation on the electromagnetic interference shielding of Cu deposited polymer substrates was investigated. The surface of polymer substrates was catalytically activated by different methods respectively adopted Pd aerosol nanoparticles and Sn-Pd wet chemical processes. Although both activations initiated the deposition of Cu on the substrates, differences such as morphology (Pd aerosol: ~80 nm vs Sn-Pd: ~ 140 nm, in Cu grain size) and composition (Pd aerosol: Cu and Pd vs Sn-Pd: Cu, Pd, Sn, and Cl) of Cu deposits were presented. Specimens activated using Pd aerosol nanoparticles showed a higher range of shielding effectiveness by about 4-10 dB than those activated by Sn-Pd processes in 2-18 Ghz frequencies.     

Influence of Au underlayer thickness on the electro-optical properties of ITO/Au layered films deposited by magnetron sputtering on unheated polycarbonate substrates

Transparent and conducting tin-doped indium oxide (ITO) and ITO/Au multilayered films were prepared on polycarbonate (PC) substrates by magnetron sputtering without intentional substrate heating. In order to consider the influence of the Au thickness on the optoelectrical properties and structure of ITO/Au films, the thickness of the Au underlayer was varied from 5 to 20 nm. The optoelectrical properties of the films were quite dependent on the Au film thickness. The lowest sheet resistance of 11 Ω/sq. and an optical transmittance of 61% with respect to air was obtained from ITO (95 nm)/Au (5 nm) films. Thin film crystallinity was also affected by the presence of the Au underlayer and varied with the thickness of the Au films. In X-ray diffraction (XRD) spectra, ITO films did not show any characteristic diffraction peak, while ITO/Au films with a 5-nm Au underlayer showed a characteristic diffraction peak. From the figure of merit, it can be concluded that the most effective Au thickness in ITO/Au films is 5 nm.     

Thermomechanical properties of copper–carbon nanofibre composites prepared by spark plasma sintering and hot pressing

Several types of carbon nanofibres (CNF) were coated with a uniform and dense copper layer by electroless copper deposition. The coated fibres were then sintered by two different methods, spark plasma sintering (SPS) and hot pressing (HP). The Cu coating thickness was varied so that different volume fraction of fibres was achieved in the produced composites. In some cases, the CNF were pre-coated with Cr for the improvement the Cu adhesion on CNF. The results show that the dispersion of the CNF into the Cu matrix is independent of the sintering method used. On the contrary, the dispersion is directly related to the efficiency of the Cu coating, which is tightly connected to the CNF type. Overall, strong variations of the thermal conductivity (TC) of the composites were observed (20–200 W/mK) as a function of CNF type, CNF volume fraction and Cr content, while the coefficient of thermal expansion (CTE) in all cases was found to be considerably lower than Cu (9.9–11.3 ppm/K). The results show a good potential for SPS to be used to process this type of materials, since the SPS samples show better properties than HP samples even though they have a higher porosity, in applications where moderate TC and low CTE are required.     

Effect of thermal annealing on Ni/Au contact to a-InGaZnO films deposited by dc sputtering

We deposited Ni (15 nm)/Au (30 nm) layers on a-InGaZnO in order to produce low-resistance ohmic contacts by using a dc sputtering method. The samples were annealed at various temperatures for 5 min in Ar ambient. The electrical and the structural properties of the Ni/Au contact to a-InGaZnO were investigated. According to the current-voltage measurements, both the as-deposited and low-temperature annealed samples showed an ohmic behavior. The specific contact resistance of the as-deposited sample was 4.1 × 10^− 5 Ω cm², which was the lowest value. Further increasing the temperature above 400 °C led to an increase in the specific contact resistance. This is due to the chemical intermixing and formation of the oxide in the contact interface caused by the post-growth thermal annealing.     

Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry

We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesize bimetallic gold (Au)–palladium (Pd) nanoparticles (NPs) with a core/shell configuration. The ability of Escherichia coli cells supplied with H₂ as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd–Au(III) mixture rapidly turned purple, indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction (XRD) analysis. However, surface analysis of cleaned NPs by cyclic voltammetry revealed large Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterization of the bimetallic particles using X-ray absorption spectroscopy confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90°C).     

Structural, compositional, and optoelectronic properties of thin-film CdS on p-GaAs prepared by pulsed-laser deposition

Thin-film CdS (300-400 nm) was deposited onto p-GaAs with low-temperature pulsed-laser deposition (PLD) using 532 nm emission of a Nd:YAG laser (6 ns, 10 Hz). The ablation threshold takes place at a fluence of 0.64 J/cm² and the deposition rate reaches its maximum at 2.68 J/cm², while further fluence increase caused a deposition rate drop due to plume shielding. X-ray investigations illustrated that the CdS film texture is composed of nano-sized crystallites (10-30 nm) embedded in an amorphous matrix. Energy dispersive analysis of X-ray and electron probe microanalysis revealed almost stoichiometric composition. Alternating photocurrent spectroscopy showed that the CdS/GaAs sample exhibits intrinsic room-temperature responsivity, which might be useful for specific optoelectronic interconnects. The work emphasizes versatility and straightforwardness of PLD to form operative devices based on hetero-pairing.     

Effect of various single metallic seed-layers on the magnetic properties of Co/Pd multilayers

We studied the effects of Pd, Ru, and Ta seed-layers on the perpendicular magnetic properties of Co/Pd multilayers, promising materials for high-density magnetic recording media. Among the various seeds, the Ta seed-layer demonstrated a large coercivity and most highly promoted fcc (111) preferred orientation of the Co/Pd multilayer. We also patterned films into island arrays with sizes of 2 × 2 μm², 5 × 5 μm², and 10 × 10 μm² to investigate the effect of size on the magnetic properties. The coercivity increased as the island size decreased. The 2 × 2 μm² patterned Co/Pd multilayer with the Ta seed-layer showed a coercivity about six times greater than that of the un-patterned film. This increase can be explained by a change in the magnetization reversal mechanism from domain wall propagation to domain rotation.     

The effect of nickel on the strain evolution in chemical copper films

Chemical (or electroless) copper films are deposited from an electrolyte on palladium-activated insulating substrates in order to construct electrical interconnects for electronic components. These films provide the electrical contacts that are required for subsequent galvanic copper plating. As smoother substrates are required for advanced applications, achieving sufficient film adhesion becomes more difficult. Nickel, initially added to the electrolytes in order to improve deposition speed, has increasingly become important to promote good film adhesion. Film stress strongly affects film adhesion. Here we studied the effect of nickel addition on the internal strain of the film during and after electroless deposition by monitoring the strain of the Cu crystals with X-ray diffraction. Films without nickel tend to have exponential relaxation of the film strain after the deposition. For a 2000 wt. ppm Cu electrolyte, about 30 wt. ppm Ni was required in order to prevent this from occurring. Films with higher nickel content have a columnar structure with reliable and constant tensile strain during and after the electroless deposition.     

Study on the solid state reaction between bilayered Pd/Au films and silicon substrates

Bilayers of pure palladium and gold films were evaporated alternatively on (1 0 0) and (1 1 1) monocrystalline silicon substrates. After annealing, in a vacuum furnace from 100 to 650 °C during 30 min, the growth sequence of the Pd₂Si and PdSi phases that evolved as the result of the diffusion reaction was examined by means of Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), whereas the surface morphology was investigated by scanning electron microscopy (SEM) technique. The effect of the intermediate gold layer is investigated in order to test its effectiveness as barrier for Cu and Si atoms interdiffusion and its influence on the morphology of the formed palladium silicides. The effect of substrate orientation on the palladium silicides growth and formation was also explored.     

Preparation of super-hydrophobic Cu/Ni coating with micro-nano hierarchical structure

Micro-nano hierarchical structured Cu/Ni multilayer coating was prepared by a simple two-step method combined with electroless and electro deposition. Structure and morphology of the as-prepared Cu/Ni multilayer coating were analyzed by X-ray diffractometer and field emission scanning electron microscopy. Results show that micro-nano Cu/Ni coating is well-crystallized and exhibits sea cucumber-like microstructure with Ni nanocone arrays uniformly dispersed perpendicular to the circular conical surface of Cu cone. Static contact angles were measured to investigate the surfaces' wettability. The result reveals that the Cu/Ni multilayer coating is super-hydrophobic, of which the static contact angle with test liquid (water) was 156°(> 150°).Due to its super-hydrophobic property and unique shape, Cu/Ni multilayer coating is expected to have extensive practical applications.