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The mechanical strength of pure aluminum matrix can be greatly enhanced by adding a small amount of nickel-coated carbon nanotubes (NiCNTs), where the nickel coating helps to the uniform dispersion...

Aluminum powder compaction was studied using both test and simulation. Cold compaction, hot compaction, and vibration-assisted (cold) compaction tests were conducted to achieve different density ratios. First, the hot compaction test (at 300 °C, compression pressure 140 MPa) improved about 6% compared with cold compaction under the same compression pressure. Second, although the relative density ratio does not obviously improve at a vibration-assisted (cold) compaction, the strength of the specimens made under vibration loading is much better than those of cold compaction. Additionally, finite element models with well-calibrated Drucker–Prager Cap (DPC) material constitutive model were built in abaqus/standard to simulate the powder compaction process. The results of the finite element model have very good correlations with test results up to the tested range, and this finite element model further predicts the loading conditions needed to achieve the higher density ratios. Two exponential equations of the predicted density ratio were obtained by combining the test data and the simulation results. A new analytical solution was developed to predict the axial pressure versus the density ratio for the powder compaction according to DPC material model. The results between the analytical solution and the simulation model have a very good match.

Nanostructures tin (IV) oxides have been synthesized by chemical vapor deposition (CVD) and sol-gel methods and their composites incorporated with multi-wall carbon nanotubes have also been obtained. The characterization of oxidized carbon nanotubes (CNTs) by Raman spectroscopy revealed more defects in CNTs with larger diameters. The tin (IV) oxide nanostructures have been investigated by X-ray diffraction methods, electron spectroscopy and Ramani spectroscopy and results have been showed that SnO2, synthesized by CVD method, characterized by more crystalline structure comparatively to the tin (IV) oxide sample, obtained by sol-gel technology. Sensitivity measurements of SnO2, CNTs and SnO2/CNTs samples towards hydrogen have been carried out. It was found that synthesis method affects not only on physical properties of tin (IV) oxide, but also on the sensing properties. In the case of CNTs samples sensitivity significantly depends on the diameter of carbon nanotubes and oxidation conditions imperc...

Carbon nanotubes (CNTs) are regarded as a desirable filler to develop advanced composites including advanced solders due to their exceptional mechanical properties. However, some issues remain unsolved for metallic composites owing to “wetting” and nonuniform dispersion of CNTs. In this study, electroless nickel coating onto CNTs was used to overcome these issues. Multiwalled carbon nanotubes (MWCNTs) were used for this study, and Ni-coated MWCNTs were dispersed in molten Sn assisted by sonication and compared with MWCNTs without Ni coating. Adding 3 wt.% Ni-coated MWCNTs, which corresponds to 0.6 wt.% pure CNTs, resulted in an increase in tensile strength by 95% and hardness by 123%. Nickel coating also prevented separation of the CNTs from the molten metal due to buoyancy effects, leading to more uniform dispersion.

The high thermal conductivity of thermal interface material (TIM) is essential since the heat dissipation of electronic chips in an integrated circuit is solely achieved through TIM, which forms the bottleneck of the heat conduction. In the current study, the efficiency of utilizing multi-walled carbon nanotubes (MWCNTs) to increase the thermal conductivity of a typical TIM 70Sn-30Bi alloy has been investigated. Encapsulation of carbon nanotubes (CNTs) with nickel by electroless deposition was used to prevent aggregation of CNTs and to enhance the interfacial bonding between CNTs and the metal matrix. The nickel encapsulation also allows avoiding the separation of CNTs from the molten metal due to the buoyancy effect. The dispersion of Ni-encapsulated CNTs was assisted by sonication. The thermal conductivity of 3 wt % Ni/MWCNTs reinforced 70Sn-30Bi alloy was found to be more than 170% greater than that of the base alloy.

Dispersion of carbon nanotubes (CNTs) in metal matrix composites has been an unsolved issue since the discovery of CNTs. This paper presents a newly developed fabrication process of bulk Cu/CNT composite with uniformly distributed CNTs. That is, copper encapsulated CNTs powders were firstly fabricated by an electrochemical deposition where CNTs can be completely dispersed in the copper electrolyte assisted by sonication, and then the fabricated composite powders were used to make bulk Cu/CNT composite by a powder metallurgy process. The increment in microhardness of Cu/CNT composite after compaction and sintering was observed to be ~47.6% per 1% CNTs. The developed fabrication process of Cu/CNT composite powders by electrochemical co-deposition can be scaled up to meet specific application needs, and a similar process is expected to be applicable for other metals.

In this study, aluminium–carbon nanotube–nickel (Al–CNT–Ni) composite was prepared by powder metallurgy from pure Al powder and Ni-encapsulated CNT. Previously, carbon nanotubes were coated with nickel following ultraviolet-assisted electroless deposition method. Tensile strength and hardness of the composites were found to increase in proportion to the CNTs addition. For an addition of 7 wt.% Ni-coated CNTs containing 2.5 wt.% nanotubes of 8–15 nm diameter (Ni to CNT ratio was 1–0.357), resultant tensile and yield strength were increased by 129.26% and 157.48% respectively compared to pure aluminium. Hardness was also increased by 171.39%. These results were obtained while conventional sintering was followed by further consolidation by Hot Isostatic Pressing (HIP). Enhanced mechanical properties are attributed to the well dispersion of CNTs in aluminium matrix and strong interfacial bonding between CNT and aluminium. Well dispersion of CNTs and strong interfacial bonding was resulted from the uniform Ni-encapsulation as verified by red shift in Raman Spectroscopy.

Recent experimental studies by Chen et al. [1] , [3] showed that copper (Cu) matrix reinforced by a small amount of carbon nanotubes (CNT, about 4% volume fraction) will increase material strength by about 300% while sacrificing some material ductility. The strengthening mechanisms of Cu/CNT nano-composites were firstly studied numerically using 2D axial symmetric unit cell finite element (FE) models in Ls-Dyna, which consist of both copper matrix and CNTs. The simulation results were verified by existing experimental data. A round of parametric studies was performed to investigate the effects of several modeling parameters in the FE simulations. These parameters include the volume fraction of CNTs, aspect ratio of CNTs, size of hardening zone, and the “equivalent” hardened plastic strain in the hardened zone. Two main strengthening mechanisms are found that affect CNTs reinforcement prediction. The first one is the load-bearing effect resulting from boundary condition imposed in the models. The CNTs significantly affect the plastic flow of copper around CNTs during plastic deformation, which is one important reinforcement mechanism because of high aspect ratio ( H / D ) of CNTs. The second strengthening mechanism is found to be the hardened zone of Cu matrix around CNTs, which is introduced by manufacturing processes and/or the Orowan effect. The Orowan effect plays a key role in reinforcement especially in the nano-scale, which results in a very small inter-particle spacing. The Orowan effect was also studied using analytical methods. Both analytical solution and unit cell FE modeling well correlated with the experimental results for various Cu/CNT composites with different CNT outside diameters.

Carbon nanotubes (CNTs) encapsulated with copper chains have been investigated with quantum mechanics calculations, with an emphasis on the effects of copper on CNTs electronic structure and the resultant conductance. Density functional theory frames in conjunction with nonequilibrium Green’s function were used for the study. The results have shown that due to the interaction between copper and CNTs, the conductance of the metallic CNTs-Cu system can be significantly increased.

The authors have studied the electronic structure and transport properties of hybrid nanowires made of a copper chain adsorbed on a single-wall carbon nanotube (CNT) using first principle methods. Results have shown that after the adsorption of the Cu chain, the density of states and the transmission coefficients of the CNT (5, 5)/Cu nanowire have been increased, while the band gap of CNT (10, 0)/Cu have been significantly reduced. These results imply that the conductivity of CNTs, either metallic or semiconducting, have been enhanced by the adsorption of a copper chain. These hybrid nanowires with enhanced conductivity may be suitable for nanoelectronics.

The electric resistance and transport properties of a carbon nanotube (5,5) adsorbed with a copper chain connected with two copper electrodes have been calculated by employing nonequilibrium Green’s functions and Density Functional Theory. The properties of the pure carbon nanotube (5,5) with the Cu junction electrodes have also been calculated as a reference. Both the equilibrium and nonequilibrium conditions have been investigated. The results show that the resistance of the metallic carbon nanotube (5,5) has been reduced by the adsorption of a Cu chain due to the interaction between the Cu and the carbon nanotube. The change of the current–voltage curve slope is also explained in terms of transmission spectrum.

The electric resistance and the transport properties of a carbon nanotube (5,5) adsorbed with a copper chain connected with two copper end electrodes have been calculated by employing the nonequilibrium Green’s function and the Density Function Theory. The properties of the pure carbon nanotube (5,5) with the Cu electrodes have also been calculated as a reference. Both the equilibrium and the nonequilibrium conditions have been investigated. The results have shown that the electrical resistance of the metallic CNT (5,5) has been reduced by the adsorption of the Cu chain due to the interaction between the Cu and the CNT. The change of the I-V curve slope is also explained in terms of the transmission spectrum.

Importance of the activation site density on final encapsulation of multi-walled carbon nanotubes (MWCNTs) with copper was investigated in this study. MWCNTs, sensitized with tin and activated with silver, were used as precursors to prepare copper-decorated nanotubes. The effect of activation bath pH was found to be critical to control the density of silver-activation sites and to produce uniform encapsulation of carbon nanotubes (CNTs) with copper in the subsequent electroless deposition method. The morphology of the copper decorated nanotubes was studied using Field Emission Gun Scanning Electron Microscope (FEG SEM) and Energy Dispersive Spectroscopy (EDS).

In this study, thermal conductivity measurements of carbon nanotube (CNT) copper nanocomposite fabricated with a novel electrochemical co-deposition method were carried out. The measured thermal conductivity of a Cu-CNT nanocomposite is about 180% greater than that of pure copper. The resultant thermal conductivity of Cu-CNT composite is found to be proportional to the CNT addition.

Highly dispersed copper/multi-walled carbon nanotube (MWCNT) nanowires have been fabricated using ultrasonic-assisted electroless copper plating. The structures of the Cu/MWCNT nanowires were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). The study clearly demonstrates the advantages of the ultrasonic technique on electroless copper plating on MWCNT, including an enhanced electroless copper deposition rate, improved interfacial bonding as well as preventing Cu/MWCNT nanowires from aggregating.

A novel micromachined single wall carbon nanotube (SWCNT) reinforced nanocrystalline tin dioxide gas sensor has been developed. The presence of SWCNT in SnO 2 matrix was realized by a spin-on sol–gel process. The SWCNT/SnO 2 sensor's sensitivity for hydrogen detection has greatly increased by a factor of three, in comparison to that of pure SnO 2 sensor. The novel sensor also lowers the working temperature, response time and recovery time. The greatly improved performances are mainly attributed to the effective gas accessing nano passes through SWCNT plus the smaller distance between adjacent gas accessing boundaries formed by the distribution of tiny SWCNTs. Therefore, both the spatial requirement ( D ≤ 2 L , D is the distance between adjacent gas accessing boundaries and L is the space charge layer thickness) and surficial requirement (adequate gas activation area) are met and the maximum inherent sensitivity of SnO 2 is achieved.

In situ UV-LIGA assembled robust micro check valves with large flow rates (>10 ml/s, displacement related), high-pressure support ability (>10 MPa) and high operational frequencies (>10 kHz) made of nano-structured nickel were presented in this paper. The microvalve consists of an array of 80 single micro valves to achieve the required flow rates. Test results show that the forward flow rate is about 19 ml/s under pressure of 90Psi. The backward flow rate is negligible. The reliability of the valve is ensured by the valve design and nanostructured nickel realized. The tested tensile strength of a nano structured nickel is about 1GPa. The strength of SU-8 is 50MPa, which is more than 50% higher that fabricated with a standard process.

In situ UV-LIGA assembled robust microcheck valves with large flow rates (>10 ml/s, displacement related), high-pressure support ability (>10 MPa) and high operational frequencies (>10 kHz) made of nano-structured nickel were presented in this paper. The microvalve consists of an array of 80 single microvalves to achieve the required flow rates. A novel in situ UV-LIGA process was developed for the fabrication. Test results show that the forward flow rate is about 19 ml/s under pressure of 90 psi. The backward flow rate is negligible. The loading/unloading test results show that the flow rates were repeated very well over a large range of tested pressure differences. The reliability of the valve is ensured by the low stress valve design and the robust nano-structured nickel material fabricated.

Carbon nanotubes (CNTs) are excellent multifunctional materials in terms of mechanical robustness, thermal, and electrical conductivities. These multifunctional properties, as well as the small size of the structures, make CNTs ideal building blocks in developing nanocomposites. However, the matrix materials and the fabrication processes are critical in achieving the expected multifunctional properties of a CNT-reinforced nanocomposite. This paper has proved that electrochemical co-deposition of a metallic nanocomposite is a good approach for achieving good interfacial bonding between CNTs and a metallic matrix. Good interfacial bonding between a single-walled carbon nanotube (SWCNT) and a copper matrix has been verified by enhanced fracture toughness (increased stickiness) and a shift in the Raman scattering spectra. For the Cu/SWCNT nanocomposite, the radial breath mode (RBM) has disappeared and the tangential or G-band has shifted and widened, which is an indication of better energy transport.

A robust passive high frequency high pressure micro check valve was developed for piezoelectrically actuated pumps. A novel cross-patterned microvalve flap is used to increase the valve’s structural stiffness with pressures up to 10 MPa. A mechanical valve stopper prevents valve-flap failure under extreme high pressure. The valve-flap is also designed to work at frequency larger than 10,000 Hz. The valve-flap was fabricated with electroformed nickel on silicon substrate. Deep RIE etching was used to fabricate the valve channels in the silicon substrate. The whole valve weighs 0.2 g including packaging. The microvalve flow rate (water) is measured to be 18 cm3/s under a pressure difference of 50 psi. The microvalve was integrated with a compact piezoelectric pump and produced pressure of 350 psi when operated at 10 kHz frequency.

MEMS-based batch fabrication compatible sol–gel synthesized mesoporous nanocrystalline SnO2 gas sensor has been developed. The SnO2 nanofilm is fabricated with the combination of polymeric sol–gel chemistry and block copolymers used as structure directing agents. The novel hydrogen sensor has a fast response time (2 s) and quick recovery time (10 s), as well as good sensitivity (up to 90), in comparing to other hydrogen sensors developed. The working temperature of the sensor developed can be reduced as low as 100 ◦ C. The low working temperature poses advantages such as lower power consumption; lower thermal induced signal shift as well as safe detection in certain environments where temperature is strictly limited. The nanocrystalline SnO2 sensor has a broad sensitivity. The developed sensor cell will be used to develop a high sensitivity and high selectivity electronic nose for harmful chemical gas detection by combining different catalysts doped SnO2 gas sensor array with fuzzy neural network. © 2004 Elsevier B.V. All rights reserved.

A summary of the influence of microfabrication processes (wet and dry etching) and crystal orientation on the effective shear strength of microridges is addressed in this paper. Test results indicate that both crystal orientation and geometry plays an important role in determining the strength. The largest shear strengths obtained were for triangular and rectangular ridges fabricated with wet etching and deep RIE respectively. Both of these structures had similar crystal orientations. These strength values were approximately 3.5 times larger than the lowest strengths measured for wet etching structures. Using Chlorine RIE, we were able to demonstrate the influence of crystal orientation on strength, with microridges of {110} sidewall made on a (100) wafer the largest. For wet etching, we found that the strength was concentration dependent. For example, a 45% KOH fabricated structure produced strength values 65% higher than 30% KOH fabricated ones (note crystal orientation the same). This was attributed to a geometric effect, that is the 45% KOH solution had a “V” shaped bottom while the 30% KOH had a flat bottom. EDP and TMAH values had similar strengths to the 30% KOH solution (note similar crystal orientation). Therefore, microcomponent strength is strongly dependent upon fabrication process as well as crystal orientation.

Carbon nanotubes (CNTs) have attracted broad attentions for developing innovative nanocomposites due to their exceptional properties. However, the success of developing nanocomposites is largely dependent on material processing. Authors' group has developed an innovative electrochemical co-deposition form synthesis of CNT reinforced metallic (Ni). Results indicate that the yield and ultimate strength of the as-deposited pure nickel are found to be about 350MPa and 625MPa, respectively, which are comparable to the reported data. However, it demonstrates that the yield strength and ultimate strength of Ni/MWCNT composite are about 1,290MPa and 1,700MPa, respectively. In other word, the ultimate strength of Ni/MWCNT nanocomposite is about 270% higher than that of pure nickel. Authors believe the largely increased mechanical strength of Ni/CNT nanocomposite is attributed to the novel fabrication that high temperature associated degradation problems in metallic composite processing such as diffusion, chemical reaction and mismatch of coefficient of thermal expansion (CTE) are eliminated.

MEMS based SnO 2 gas sensor with sol gel synthesized mesoporous nanocrystalline ( 2 nano film is fabricated with the combination of polymeric sol gel chemistry with block copolymers used for structure directing agents. The novel hydrogen sensor has a fast response time (1s) and quick recovery time (3s), as well as good sensitivity (about 90%), comparing to other hydrogen sensors developed. The improved capabilities are credited to the large surface to volume ratio of gas sensing thin film with nano sized porous surface topology, which can greatly increase the sensitivity even at relatively low working temperature. The gas sensing film is deposited onto a thin dielectric membrane of low thermal conductivity, which provides good thermal isolation between substrate and the gas-sensitive heated area on the membrane. In this way the power consumption can be kept very low. Since the fabrication process is completely compatible with IC industry, it makes mass production possible and greatly reduces the cost. The working temperature of the new sensor can be reduced as low as 100°C. The low working temperature posse advantages such as lower power consumption, lower thermal induced signal shift as well as safe detection in certain environments where temperature is strictly limited.

Experimental results of carbon nanotube (CNT) reinforced copper composites (Cu/CNT) have shown that the resultant tensile strength of Cu/CNT composite is CNT diameter dependent, in a form of parabolic relationship that the smaller the CNT diameters the greater the resultant strength of the Cu/CNT composites. The largely increased strength of Cu/CNT composited is attributed to the good CNT dispersion in both the electrolyte and in composite after electrochemical deposition, as well as to the good interfacial bonding formed by the electrochemical deposition process. Smaller CNT diameters result in greater total interfacial bonding area thus the greater resultant strength of the composite.

Metallic nanowires are promising as components in nanoscale systems including nanoelectronics. However, the application of nanowires made of a single material is limited by the properties of the material used. We report here an effort to fabricate a hybrid copper-coated carbon nanotube (CNT)-Cu/CNT nanowire, using a microfluidic reactor. The fabrication of copper/multi-walled carbon nanotube (MWCNT) hybrid nanowires was realized by an electroless copper deposition technique in which MWCNT templates and an electrolyte were introduced separately into the microfluidic reactor. The morphology and structure of the Cu/MWCNT hybrid nanowire were studied by means of transmission electron microscopy (TEM), selected-area electron diffraction (SAED), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX), as well as XRD. Results reveal that the fabricated Cu/MWCNT hybrid nanowires are continuously covered by crystallized copper with a preferred crystal orientation along the (111) planes in the radial direction of the MWCNTs. These structural properties are attributed to the unique reaction environment including laminar flow and diffusion-controlled reaction.

The authors have characterized the mechanical properties of carbon nanotube (CNT) reinforced copper nanocomposites which were fabricated with an innovative electrochemical co-deposition process. The mechanical strength of Cu/CNT nanocomposites is found to be more than three times greater than that of pure copper. The increased strength is attributed to the good distribution of CNTs and good interfacial bonding between CNT and copper realized by the fabrication method.

Carbon nanotubes (CNTs), including single-walled CNT (SWCNT) and multi-walled CNT (MWCNT), have been regarded as the stiffest and strongest materials ever developed and are promising reinforcement fillers for developing nanocomposites. However, the scientific community has been puzzled about the reinforcement efficiency. Here we report CNT-reinforced nickel nanocomposites fabricated with an innovative electrochemical co-deposition process for achieving good interfacial bonding between CNT and metallic matrices. Test results show that Ni/SWCNT composite produces a tensile strength as high as 2 GPa, which is more than three times stronger than that of pure nickel. The mechanical strength of Ni/CNT nanocomposites is dependent on CNT addition, while the fracture strain remains similar or better than that of pure nickel. The good reinforcement of CNT/metal nanocomposites is attributed to the good interfacial bonding as well as the stiffer matrix nature.

Copper nanowires were fabricated by electrochemical deposition inside anodic alumina template anodized on aluminum substrate. The morphology, composition and structure of the copper nanowires were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive (EDS) and X-ray diffraction spectroscopy (XRD). The results revealed that copper nanowires were dense, continuous, highly-crystalline and uniform with diameters. The electrical properties of copper nanowires wrer characterized with two-terminal electrical measurements. Different current-voltage (I-V) characteristics of single copper nanowire were observed and possible conductive mechanisms were discussed. The crystalline copper nanowires are promising in application of future nanoelectronic devices and circuits.