Debye temperature of metallic nanowires--an experimental determination from the resistance of metallic nanowires in the temperature range 4.2 K-300 K

We have studied the resistance of metallic nanowires (silver and copper) as a function of the wire diameter in the temperature range 4.2 K-300 K. The nanowires with an average diameter of 15 nm-200 nm and length 6 microm were electrochemically deposited using polycarbonate membranes as template from AgNO3 and CuSO4, respectively. The wires after growth were removed from the membranes by dissolving the polymer in dichloromethane and their crystalline nature confirmed by XRD and TEM studies. The TEM study establishes that the nanowires are single crystalline and can have twin in them. The resistivity data was fitted to Bloch-Gruneisen theorem with the values of Debye temperature and the electron-acoustic phonon coupling constant as the two fit variables. The value of the Debye temperature obtained for the Ag wires was seen to match well with that of the bulk while for Cu wires a significant reduction was observed. The observed increase in resistivity with a decrease in the wire diameter could be explained as due to diffuse surface scattering of the conduction electrons.     

Metallic nanowires by full wafer stencil lithography

Aluminum and gold nanowires were fabricated using 100 mm stencil wafers containing nanoslits fabricated with a focused ion beam. The stencils were aligned and the nanowires deposited on a substrate with predefined electrical pads. The morphology and resistivity of the wires were studied. Nanowires down to 70 nm wide and 5 mum long have been achieved showing a resistivity of 10 microOmegacm for Al and 5 microOmegacm for Au and maximum current density of approximately 10(8) A/cm(2). This proves the capability of stencil lithography for the fabrication of metallic nanowires on a full wafer scale.     

Optimized Sol–Gel Chemical Route Using Vacuum Suction for Fabrication of Densely Packed NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanowires

Highly ordered nanowire arrays of NiFe₂O₄ spinel with a high aspect ratio were fabricated by sol–gel method associated with anodic aluminum oxide (AAO) templates. The preparation of nanowires was carried out by sol–gel method using nickel nitrate, ferric nitrate and citric acid. The molar proportion of nickel nitrate to ferric nitrate and citric acid was 1:2:3. The suction with 0.1 mbar vacuum was used to draw the gel into the AAO nanochannels. The results showed that the lowest annealing temperature is around 600?°C to obtain the single-phase nanostructured NiFe₂O₄. The NiFe₂O₄ nanowires were also uniform and parallel. TEM pictures determined the diameter size of the nanowires of about 100 nm. The magnetic results also showed that the wires have an easy axis of magnetization along their length and they are fully saturated in a field of 7 kOe. It seems that this material could be a good candidate for high perpendicular magnetic storage devices.     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

High-precision measurements of magnetostriction in nickel structures for magnetoresistive nanocontacts

Variations as small as 2 nm in the dimensions of a nickel microwire exposed to a magnetic field have been detected using an atomic force microscope specially made of nonmagnetic materials. Based on the results of these high-precision measurements, it is established that the ballistic magnetoresistance of nanocontacts formed by nickel electrodeposition between nickel nanowires is related to a considerable extent to the mutual displacement of nanowires caused by magnetostriction. Analogous measurements for nickel nanofilms did not reveal such displacements to within the experimental sensitivity. Therefore, film nanostructures are more suitable for the formation of nanocontacts with a minimum magnetostriction contribution.     

Self-assembled tungsten oxide nanowires by electron beam assisted rapid thermal annealing

We report on the fabrication of WO₃ nanowires on Si (100) substrate using nickel catalyzed electron beam assisted rapid thermal annealing process. A 7 nm thick W layer deposited on the nickel coated substrate was annealed under high vacuum using electron beam (3 keV) for 30, 60 and 90 s. The nickel activates the growth of tungsten nanowires with a high aspect ratio and subsequently is oxidized due to the high refractory nature of tungsten under exposure to oxygen gas. The resulting changes in surface morphology, oxidization state and elemental composition of WO₃ nanowires were investigated systematically. The oxidization of metallic tungsten nanowire was found to depend on the annealing time.     

A structural comparison of electroless and electroplated nickel

Nickel that has been electrolessly deposited from a low temperature hypophosphite bath undergoes severe cracking when heat treated. The cracks, which are of two different types, can weaken the nickel deposit and can lead to leak paths in composite structures. In the study reported here the characteristics of thin nickel films were studied by several methods, all of which can be applied to any crystalline thin film: an X-ray method for stress and precipitation sequences; electron microscopy; cross-sectional analysis; kinetic studies. The electroless nickel was compared with a low stress electroplated nickel which does not crack with heat treatment. The electroplated nickel was found not only to have lower stress than the electroless nickel but also to have no significant secondary phase precipitation.     

An investigation on corrosion resistance of as-applied and heat treated Ni–P/nanoSiC coatings

EN–SiC coatings are recognized for their hardness and wear resistance. In this work electroless Ni–P coatings containing nano SiC particles were co-deposited on St37 tool steel substrate. Scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD), polarization and electrochemical impedance spectroscopy (EIS) were used to analyze morphology, structure and corrosion resistance of the coatings. The results showed that SiC nano-particles co-deposited homogeneously, and the structure of Ni–P–SiC nano-composite coatings as deposited was amorphous. Heat-treatment at 400 °C for 1 h induced crystallization of the electroless Ni–P coatings. Microhardness of electroless Ni–P–SiC composite coatings increased due to the existence of nano-particles, and reached to a maximum value after heat-treatment. Corrosion tests showed that both electroless nickel and electroless nickel composite coatings demonstrated significant improvement of corrosion resistance in salty atmosphere. Proper post heat-treatment significantly improved the coating density and structure, giving rise to enhanced corrosion resistance.     

Adsorption characteristic of copper ions and its application in electroless nickel plating on a hydrogel-functionalized poly(vinyl chloride) plastic

A facile and palladium-free process for the electroless plating on poly(vinyl chloride) (PVC) plastic has been demonstrated. The process is based on the Cu adsorption capacity of semi-interpenetrating polymer network (semi-IPN) hydrogel chemically bonded to PVC surface via a simple and one-step approach that applying a chitosan/polyethylene glycol/glutaraldehyde system under mild stirring at room temperature. Therefore, electroless plating can be achieved in the following three steps, namely: (1) the functionalization of PVC by the semi-IPN hydrogel film (2) the adsorption and formation of the catalyst Cu⁰ on the PVC surface, and (3) the electroless nickel plating in plating bath. Batch adsorption experiments are conducted to determine the effects of pH, initial Cu²⁺ ions concentration and the dosage of crosslinking agent glutaraldehyde on copper adsorption and the surface resistance of the corresponding plated-PVC. The activated reaction progress and resulting nickel–phosphorus (Ni–P) layer were characterized by attenuated total reflection Fourier transform infrared, scanning electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The results show that the Cu nanoparticles chemisorbed on the functionalized PVC substrate, could effectively initial the subsequent electroless nickel plating; and a compact and continuous Ni–P layer with amorphous phase was successfully deposited on PVC by this process. Besides, the surface resistance of the plated-PVC as low as 0.5 Ω sq^?1 showed an excellent adhesion with the PVC substrate proved by Scotch-tape test.     

锅炉炉管Ni—P—PTFE化学复合镀层研究

锅炉炉管的水垢或磨损不利于锅炉的安全节能,在炉管内外表面制备不同的Ni—P化学镀层和Ni—P—PTFE化学复合镀层,具有耐磨且低表面自由能性能,防水垢防磨损,安全节能效果明显。在化学镀Ni—P合金基础上加入PT—FE粒子,采用镍盐和还原剂在同一溶液中进行的自催化氧化-还原反应,从而在工件表面沉积出的Ni—P—PTFE化学复合镀层,具有低表面自由能,且具有高的硬度、耐磨性、润滑性、优异的耐蚀性。PTFE浓度、表面活性剂、温度和pH值,对Ni—P—PTFE化学复合镀层PTFE含量和PTFE粒子分散性有影响。     

Effects of annealing process on microstructure and electrical properties of cold-drawn thin layer copper cladding steel wire

The microstructure, mechanical and electrical properties of cold-drawn thin layer copper cladding steel (CCS) wires annealed after different processes were studied by optical microscopy, electron omnipotent material experiment machine, micro hardness machine, SEM and electrical resistivity measurement system. The results indicated that the recovery and recrystallization of steel-core happened in the temperature range 550–750 °C for the holding period of 120 min. When the annealing temperature was higher than 750 °C, grains begun to grow and grain sizes increased gradually with increasing the annealing temperature. The tensile strength and micro hardness were declined with increasing annealing temperature and holding time. The distance of Cu–Fe atoms interfacial diffusion of thin layer CCS wires ranged from 4 µm of cold-drawn wire to 7.5 µm of annealed wire at 850 °C for 120 min. The higher the annealing temperature become, the larger the distance of Cu–Fe atoms interfacial diffusion is. When the annealing temperature was lower than 650 °C, the resistivity was slightly less than 71 × 10^?3 Ω mm² m^?1 which was the resistivity of cold-drawn wire. When the annealing temperature was higher than 650 °C, the resistivity increased with increasing the annealing temperature. Meanwhile, the variation of electrical property of thin layer CCS wires was analyzed and discussed based on microstructure and interfacial diffusion.     

Effect of processing conditions on the nucleation and growth of indium-tin-oxide nanowires made by pulsed laser ablation

Indium–tin oxide nanowires were deposited by excimer laser ablation onto catalyst-free oxidized silicon substrates at a low temperature of 500 °C in a nitrogen atmosphere. The nanowires have branches with spheres at the tips, indicating a vapor–liquid–solid (VLS) growth. The deposition time and pressure have a strong influence on the areal density and length of the nanowires. At the earlier stages of growth, lower pressures promote a larger number of nucleation centers. With the increase in deposition time, both the number and length of the wires increase up to an areal density of about 70 wires/μm². After this point all the material arriving at the substrate is used for lengthening the existing wires and their branches. The nanowires present the single-crystalline cubic bixbyite structure of indium oxide, oriented in the 〈100〉 direction. These structures have potential applications in electrical and optical nanoscale devices.     

Thermal stability of Ti/Mo and Ti/MoN nanostructures for barrier applications in Cu interconnects

This work focuses on the barrier capabilities of sputter deposited Ti/Mo and Ti/MoN nanofilms against diffusion of Cu into Si substrates. The thermal stability of the corresponding bi-layer barrier structures is investigated after annealing Cu/barrier layer/Si samples at different temperatures in N(2) for 5?min. The drastic increase in sheet resistance of Cu and the probing of Cu(3)Si with x-ray diffraction after high temperature annealing indicate the failure of these barrier structures. The formation of Cu(3)Si at the barrier breakdown temperature is also confirmed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Cu?diffusion barrier performance analyses show that a Ti(5?nm)/MoN(5?nm) bi-layer nanostructure fails only after annealing at 800?°C; on the other hand, a Ti(5?nm)/Mo(5?nm) barrier stack is found to break down at 700?°C.     

Rapid thermal annealing of in situ p-doped polycrystalline silicon thin-films

Polycrystalline silicon thin films deposited via low-pressure chemical vapour deposition (LPCVD) have a rough surface and a resistance which is too high for use within microelectronic devices. However, both of these problems may be overcome by in situ doping of the polycrystalline silicon films with phosphorus by introducing PH₃/N₂ and SiH₄/N₂ mixtures simultaneously into a LPCVD reactor but, such doping requires a high temperature furnace step (950°C) to bring the resistivity down to the required level. In general, prolonged exposure to high temperature is undesirable since it not only reduces the resistivity of the polycrystalline silicon film but also disturbs the existing dopant profiles and alters the structure of the films deposited. This ultimately makes the devices fabricated unreliable, difficult to reproduce and thus a broad device specification in batch production. The solution is to decrease the furnace temperature or reduce the time the devices are kept at high temperature. The latter may be achieved by using a technique known as rapid thermal annealing (RTA). In this paper we examine rapid thermal annealing as a quick method of redistributing the dopants in order to achieve a lower sheet resistance. The results obtained are compared with conventional furnace annealing. It will be shown that rapid thermal annealing is an attractive and often better alternative to conventional annealing.     

稀土Nd掺杂纳米SnO2薄膜特性

对采用真空气相沉积法在玻璃衬底上制备的稀土Nd掺杂的SnO2薄膜,进行结构、电学及光学特性的测试分析.实验表明:氧化、热处理条件为500 ℃、45 min时样品性能好.采用一步成膜工艺法制备的SnO2薄膜晶粒度较小,随掺Nd浓度的增大,从31.516 nm减小到25.927 nm;两步成膜工艺法制备的SnO2薄膜晶粒度随掺Nd浓度的增大,从45.692 nm增至66.256 nm.XRD分析,掺Nd(5 at%)薄膜沿[110]、[101]晶向的衍射峰加强,薄膜呈多晶结构.掺Nd可使薄膜透光率下降,而薄膜的薄层电阻随热处理温度升高和掺Nd浓度的增大,呈先降后升趋势.     

Enhanced photoluminescence in Au-embedded ITO nanowires

Gold (Au)-embedded indium tin oxide (ITO) nanowires were synthesized by thermal evaporation of a mixture of In(2)O(3,) SnO(2) and graphite powders on Si (100) substrates coated with Au thin films followed by annealing. At the initial stages of annealing, Au formed a continuous linear core located along the long axis of each ITO nanowire. The morphology of the Au core changed from a continuous line to a discrete line, and then to a droplet-like chain, finally evolving into a peapod in which crystalline Au nanoparticles were encapsulated in crystalline ITO with increasing annealing temperature. The ITO nanowires with the Au core showed an emission band at ~380 nm in the ultraviolet region. The ultraviolet emission intensity increased rapidly with increasing annealing temperature. The intensity of emission from the Au-peapod ITO nanowires (annealed at 750 °C) was approximately 20 times higher than that of the emission from the Au-core/ITO-shell ITO nanowires with a continuous linear shaped-Au core (annealed at 550 °C). This ultraintense ultraviolet emission might have originated mainly from the enhanced crystalline quality of the annealed ITO nanowires.     

Effects of annealing temperature on the structural,morphology, optical properties and resistivity of sputtered CCTO thin film

CaCu₃Ti₄O₁₂ (CCTO) thin films with a thickness of 200 nm were deposited on ITO substrates by RF magnetron sputtering using a pure CCTO target. After the deposition, thin films were annealed at 400, 450, 500 and 550?°C, respectively, for 1 h. The effects of annealing temperature on the structural, surface morphology, optical properties and resistivity of (CCTO) thin films were investigated. The X-ray diffractometer results show that the thin films are polycrystalline in nature and are assigned to body-centered cubic perovskite configuration with a space group of Im-3. The intensity of the peaks and crystallinity gradually increased with the increase in annealing temperature. Microstructural investigation through FESEM showed that the grain size increased with increase in annealing temperature from 32 to 85 nm. The root mean square and roughness (Ra) were also enhanced with higher annealing temperatures, from 3.8 to 6.2 nm and from 4.7 to 7.7 nm, respectively, as confirmed by AFM. Increase in annealing temperature also affected the optical transmittance values which decreased to almost 60% at the visible range (550–850), as well as the optical energy band gap which decreased from 3.86 to 3.39 eV. The relevance between resistance behaviors and film microstructure is discussed. Therefore, it can be concluded that the desirable crystallinity, surface roughness, energy band gap and resistivity for 200 nm thick CCTO thin films deposited by RF magnetron sputtering can be achieved through the annealing process.     

Low temperature annealing behavior of electroplated nickel

The low temperature annealing characteristics of electroplated nickel containing an occluded brightener, fuchsin, have been studied in the temperature range 25–250°C. Supportive annealing experiments were also conducted between the temperatures 250°C and 700°C to assist in evaluating the lower temperature behavior. The effect of annealing was monitored by measuring resistivity changes at liquid nitrogen temperatures and by viewing selected samples by transmission electron microscopy. In addition, various chemical analysis techniques were employed to follow the variations in impurity content.A detailed comparison was made between deposits from a standard “watts” nickel electrolyte and those from a “watts” nickel solution containing the fuchsin additive. Isochronal anneals of fuchsin-containing deposits were characterized by a large decrease in resistivity up to a temperature of 175°C. Higher temperature annealing from 175°C to 275°C demonstrated an increase in resistivity with increasing temperature. This increase was then followed by a general decrease in resistivity at temperatures greater than 350°C. The first two minima at 175°C and 300°C on the Δ?°/Δ? versus temperature curve were found to coincide with temperatures where partial decomposition of the fuchsin reagent occured.The low temperature resistivity decrease from 28°C to 125°C was attributed to the diffusion of divacancies to fixed sinks such as grain boundaries. A high non-equilibrium vacancy concentration is believed to be present owing to the accommodation of fuchsin molecules in the nickel lattice. The resistivity decay is described by an Arrhenius-type equation:

$\text{dp}\text{dt}\text{=K exp}\text{?}\text{19.4 kcal}\text{RT}$

The experimentally determined activation energy agrees favorably with literature values for divacancy diffusion in nickel. During this interval no visual change in structure was noted, and fuchsin could be extracted from the deposit unaltered.     

Electroless Ni‐P coating on Cu substrate with strike nickel activation and its corrosion resistance

Electroless Ni‐P coating was successfully deposited on Cu substrate by strike nickel activation process. The specific pretreatment steps were discussed. The surface and cross‐section morphologies, phosphorus content, adhesive force, and corrosion resistance were characterized for electroless Ni‐P coating. Scanning electron microscopy shows the compact surface. Energy dispersed X‐ray shows the 11.4% phosphorus content. Adhesive test shows the qualified adhesion of electroless Ni‐P coating to substrate. Porosity test shows pores free of the coating, and immersion test in 10% HCl solution indicates the better corrosion resistance of electroless Ni‐P coating in protecting Cu substrate from the corrosion of Cl ions. Thus, strike nickel activation pretreatment is suitable for electroless Ni‐P coating on Cu substrate.     

Large-scale solution-phase growth of Cu-doped ZnO nanowire networks

Film-like networks of Cu-doped (0.8-2.5 at.%) ZnO nanowires were successfully synthesized through a facile solution process at a low temperature (<100 degrees C). The pH value of solution plays a key role in controlling the density and quality of the Cu-doped ZnO nanowires and the dopant concentration of ZnO nanowires was controlled by adjusting the Cu2+/Zn2+ concentration ratio during the synthesis. The structural study showed that the as-prepared Cu-doped ZnO nanowires with a narrow diameter range of 20-30 nm were single crystal and grew along [0001] direction. Photoluminescence and electrical conductivity measurements showed that Cu doping can lead to a redshift in bandgap energy and an increase in the resistivity of ZnO. The thermal annealing of the as-grown nanowires at a low temperature (300 degrees C) decreased the defect-related emission within the visible range and increased the electrical conductivity. The high-quality ZnO nanowire network with controlled doping will enable further application to flexible and transparent electronics.