Copper Nanorod Arrays Research Articles

Copper Nanoflower Assembled by Sub-2 nm Rough Nanowires for Efficient Oxygen Reduction Reaction: High Stability and Poison Resistance and Density Functional Calculations.

The copper nanoflowers, assembled by sub-2 nm rough nanowires with high catalytic active (200) facets, are prepared by a prompt and simple method with cetyltrimethylammonium bromide (CTAB) as a capping agent. The CTAB plays a vital role in the synthesis process, whereas the copper nanorod arrays assembled by copper nanoparticles are obtained without CTAB. The copper nanoflowers are used as catalysts in oxygen reduction reactions and exhibit excellent electrocatalytic activity, which shows nearly the same activity compared with the commercial Pt/C catalyst, attributing to the nanoflower-exposed higher catalytic active (200) facets. Furthermore, the nanoflowers can avoid methanol-poison effect and show better long-term operation stability. The density functional theory was used to calculate the atom energy of Cu(100) facets and Cu(111) facets. Both of O2 dissociation and H2O activation on the facets are very easy. However, the difference between Cu(100) facets and Cu(111) facets is the adsorption and dissociation energy of O2, and the adsorption and activation of oxygen molecule is much easier on Cu(100) facets than on Cu(111) facets because of the more open nature of (100) facets.

Cu Nanostructures for Enhanced Heat Transferin Micro Systems

Vertically aligned copper (Cu) nanorod arrays fabricated by glancing angle deposition (GLAD) technique was used to study the heat transfer by natural convection in micro systems. These nanorods were deposited on Cu thin film surface, which was coated on Si (100) wafer substrates. For comparison, planar Cu thin film samples were also produced by normal incidence deposition. This study focuses on investigating experimentally the heat transfer by natural convection from the sample(nanostructured plate) to the surrounding air. Newton's law of cooling has been utilized to calculate the free-convection heat transfer coefficient for Cu nanorods as well as Cu thin film. Compered to Cu thin film samples, it has been found that the heat transfer coefficient values of Cu nanorods are higher due to the enhanced heat transfer-surface area, which causes a significant reduction in thermal resistance. These nanostructured surfaces offer an effective method of device cooling such as for small electronic devices, micro-reactors and air conditioning.

Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

The Effect of Nanostructure Distribution on Subcooled Boiling Heat Transfer Enhancement over Nanostructured Plates Integrated Into a Rectangular Channel

In this study, subcooled flow boiling is investigated over nanostructured plates at flow rates ranging from 69 mL/min to 145 mL/min. The first configuration of the nanostructured plate includes ˜600-nm-long, closely packed copper nanorod arrays distributed randomly upon the surface with an average nanorod diameter of ˜150 nm, and the second configuration consists of a periodic structure having ˜600-nm-long copper (Cu) nanorods with an average nanorod diameter of ˜550 nm and a center-to-center nanorod separation of ˜1 μm. The nanorod arrays are deposited utilizing glancing angle deposition (GLAD) technique on the copper thin film (˜50 nm thick) coated on silicon wafer substrates. Dimensions of the test section, heat flux values, and flow rates are chosen to ensure that nanostructured plates remain intact along with their nanorods in their original shape and position, so that the nanostructured plates could be used for many experiments. A consistent increase (up to 30%) in heat transfer coefficients is observed on nanostructured plates compared to the Cu thin film, which is used as the control sample. However, no significant difference in the boiling heat transfer performance between the random and periodic nanorods was observed, which indicates that the distribution of nanostructures may not be very critical in achieving enhanced heat transfer. In light of the obtained promising results, channels with nanostructured surfaces are proven to be useful, particularly in applications such as cooling of small electronic devices, where conventional surface modification techniques are not applicable.

Copper nanorod array assisted silicon waveguide polarization beam splitter.

We present the design of a three-dimensional (3D) polarization beam splitter (PBS) with a copper nanorod array placed between two silicon waveguides. The localized surface plasmon resonance (LSPR) of a metal nanorod array selectively cross-couples transverse electric (TE) mode to the coupler waveguide, while transverse magnetic (TM) mode passes through the original input waveguide without coupling. An ultra-compact and broadband PBS compared to all-dielectric devices is achieved with the LSPR. The output ports of waveguides are designed to support either TM or TE mode only to enhance the extinction ratios. Compared to silver, copper is fully compatible with complementary metal-oxide-semiconductor (CMOS) technology.

Ordered Silver and Copper Nanorod Arrays for Enhanced Raman Scattering Created via Guided Oblique Angle Deposition on Polymer

We report the manufacture of ordered silver and copper nanorod arrays for surface-enhanced Raman scattering using oblique angle deposition (OAD) on prepatterned polymer sheets. It was found that the patterned polymer substrate defined nucleation sites which guided subsequent growth of nanorods. Enhanced surface-enhanced Raman spectroscopy (SERS) intensities of the Raman probe molecule trans-1,2-bis(4-pyridyl)ethylene (BPE) were found for Ag arrays on polymer, up to about 10 times that of the Ag–silica control. The SERS response of Ag nanorod arrays of different structures was investigated alongside results obtained from discrete dipole approximation simulations. This revealed that narrow gaps between nanorods, formed by guided nucleation during OAD, were responsible for this dramatic enhancement. Ordered Cu nanorod arrays were also successfully fabricated, producing a SERS intensity about 3 times that of Cu on silicon for both BPE and another Raman probe—rhodamine B isothiocyanate (RBITC)—highlighting the potential of this large-scale, low-cost, SERS-active substrate.

Submerged jet impingement cooling using nanostructured plates

In this paper, the results of a series of heat transfer experiments conducted on a compact electronics cooling device based on single and two phase jet impingement technique are reported. Deionized and degassed water is propelled into four microchannels. The generated jet impingement is targeted through these channels towards the surface of two nanostructured plates with different surface morphologies placed inside a liquid pool filled with deionized-water. These nanostructured plates are composed of copper nanorods grown on top of a silicon wafer substrate of thickness 350μm coated with a 50nm thick copper thin film layer (i.e. Cu-nanorod/Cu-film/Silicon-wafer). Nanorods were grown using the sputter glancing angle deposition (GLAD) technique. First type of nanostructured plates incorporates ∼600nm long vertically aligned copper nanorod arrays. The second type incorporates ∼600nm long tilted copper nanorod arrays. Heat removal characteristics induced through jet impingement are investigated using the nanostructured plates and compared to the results obtained from a plain surface plate of copper thin film coated on silicon wafer surface. Surface temperatures are recorded by a data acquisition system with four thermocouples integrated on the surface at various prescribed locations. Volumetric flow rate and heat flux values are varied between 107.5–181.5ml/min and 1–40W/cm2. A single phase average heat transfer enhancement of 22.4% and a two phase average heat transfer enhancement of 85.3% has been realized using the nanostructured plate with vertical nanorods compared to flat plate. This enhancement is attributed to the increased heat transfer surface area and the single crystal property of the vertical Cu nanorods. On the other hand, nanostructured plate with tilted nanorods has shown poorer heat transfer performance compared to both the nanostructured plate with vertical nanorods and plain surface plate in the performed experiments. The lower heat transfer rate of the tilted Cu nanorods is believed to be due to the decreased supply of liquid jets to the base of the plate caused by their tilted orientation and closely spaced dense array structure. This leads to formation of air gaps that ultimately become trapped among the tilted nanorods, which results in reduced heat transfer surface area and increased resistance to heat transfer.

A PASSIVE WIRELESS GAS SENSOR BASED ON MICROSTRIP ANTENNA WITH COPPER NANORODS

Applications of copper (Cu) nanorod arrays, produced by glancing angle deposition (GLAD) technique, which extends the function of conventional microstrip antennas to encompass passive wireless gas sensors at microwave frequencies are presented. The proposed microstrip antenna consists of Cu nanorod arrays grown on silicon wafers which were coated with thin fllms of Cu of 50nm in thickness. To study the efiect of the length of Cu nanorods on antenna performance, Cu nanorods of difierent lengths (400, 700, and 1000nm) were fabricated. The efiects of Cu nanorods morphologies (Cu thin fllm, closely-spaced Cu nanorods, and well-separated Cu nanorods), were investigated too. Conventional microstrip antennas based on sputtered Cu thin fllm were prepared for comparison. It was found that as the length of Cu nanorods increases, the antennas exhibit a wider bandwidth and lower frequency resonance than those of the conventional antennas based on Cu thin fllm. Furthermore, moving from ∞at surface to well-separated nanorods results in a decrease in the resonant frequency, while there was no observable efiect on the bandwidth. These enhancements are attributed to the mutual coupling occurring among Cu nanorods. Based on the antenna characterization, the 1000nm long Cu nanorods sample was selected for gas detection measurements due to its observed sharp resonance and narrow bandwidth. The detection mechanism is based on the change of in the magnitude of the re∞ection coe-cient as well as the resonant frequency due to the introductions of difierent gases. The proposed sensor based on Cu nanorods shows a signiflcant response in

Clustered copper nanorod arrays: a new class of adhesive hydrophobic materials

Clustered copper nanorod arrays constitute single-component, two-level hierarchical structures that mimic rose petals by showing high contact angles as well as considerable contact angle hysteresis (CAH). The cluster morphology of the nanorod arrays – electrochemically grown within porous alumina templates – is determined by the template geometry and the drying conditions. The CAH (a measure of the adhesion) is a function of the nanorod length and the cluster size to inter-cluster separation ratio. The measured pinning force was 176 μN, among the highest reported. The first level of the hierarchical nano-microstructure consists of the nanorod clusters and the air trapped between them – leading to a Cassie–Baxter type hydrophobicity. The second level comprises the tips of the clustered copper nanorods which pin the water droplets due to the inherently hydrophilic nature of metals. This conjecture is supported by fluorescence imaging and surface polymerization experiments. Thus, a clustered metal nanorod array provides a simple model system for studying the coexistence and complex interplay of hydrophobicity and adhesion, while also providing some degree of control over these mutually contradictory properties.

Highly enhanced hard x-ray emission from oriented metal nanorod arrays excited by intense femtosecond laser pulses

We report a 43-fold enhancement in the hard x-ray emission (in the 150--300 keV range) from copper nanorod arrays (compared to a polished Cu surface) when excited by 30-fs, 800-nm laser pulses with an intensity of ${10}^{16}$ W/cm${}^{2}$. The temperature of the hot electrons that emit the x rays is 11 times higher. Significantly, the x-ray yield enhancement is found to depend on both the aspect ratio as well as the cluster size of the nanorods. We show that the higher yield arises from enhanced laser absorption owing to the extremely high local electric fields around the nanorod tips. Particle-in-cell plasma simulations reproduce these observations and provide pointers to further optimization of the x-ray emission.

Low Temperature Wafer Bonding by Copper Nanorod Array

A vast array of Cu nanorods with a diameter of grown by an oblique angle deposition technique was utilized as an adhesive layer for bonding Si wafers at low temperatures. The focus ion beam∕scanning electron microscope images illustrate that the Cu nanorod array underwent coalescence readily upon a bonding temperature at . Upon , a dense Cu bonding layer with homogeneous structure was achieved. A fully dense bonding structure was also obtained upon a lower bonding temperature at followed by a postannealing at in a reducing ambient.

ELECTROCHEMICALLY SYNTHESIZED COPPER NANOTUBES AND NANOROD ARRAYS IN POLYCARBONATE MEMBRANES

The large area, highly uniform copper nanorod arrays with cylindrical morphology in polycarbonate membranes (PC) have been successfully prepared by electrochemical deposition. The copper nanorod arrays have the length of 3 μm, the diameter of 400 nm, approximately, which correspond closely to the pore diameter and thickness of membranes. The copper nanotubes were also obtained by controlling initial voltage and polycarbonate membranes treatment process. The possible growing mechanisms of copper nanostructures in membrane pores were discussed.

Low Temperature Copper-Nanorod Bonding for 3D Integration

ABSTRACTWafer bonding is an emerging technology for fabrication of complex three-dimensional (3D) structures; particularly it enables monolithic wafer-level 3D integration of high performance, multi-function microelectronic systems. For such a 3D integrated circuits, low-temperature wafer bonding is required to be compatible with the back-end-of-the-line processing conditions. Recently our investigation on surface melting characteristics of copper nanorod arrays showed that the threshold of the morphological changes of the nano-rod arrays occurs at a temperature significantly below the copper bulk melting point. With this unique property of the copper nanorod arrays, wafer bonding using copper nanorod arrays as a bonding intermediate layer was investigated at low temperatures (400 °C and lower). 200 mm Wafers, each with a copper nanorod array layer, were bonded at 200 – 400 °C and with a bonding down-force of 10 kN in a vacuum chamber. Bonding results were evaluated by razor blade test, mechanical grinding and polishing, and cross-section imaging using a focus ion beam/scanning electron microscope (FIB/SEM). The FIB/SEM images show that the copper nanorod arrays fused together accompanying by a grain growth at a bonding temperature of as low as 200 °C. A dense copper bonding layer was achieved at 400 °C where copper grains grew throughout the copper structure and the original bonding interface was eliminated. The sintering of such nanostructures depends not only on their feature size, but also significantly influenced by the bonding pressure. These two factors both contribute to the mass transport in the nanostructure, leading to the formation of a dense bonding layer.

Fabrication of Nanorod Arrays for Organic Solar Cell Applications

ABSTRACTWe report on a novel use of nanorod arrays for organic based solar cell devices. A metal foil with copper nanorods attached to the surface was developed by electrodepositing copper from a copper sulfate solution into an anodic alumina oxide (AAO) template that had been coated with a metal on one side. The AAO membrane was dissolved in NaOH leaving behind an aligned array of copper nanorods. This nanorod array was evaluated to explore the possibility of increasing the power conversion efficiency of organic solar cells. Nanorod array characteristics were investigated by focus ion beam, scanning electron microscopy, and x-ray diffraction spectroscopy. A solar cell device was made by applying a polymer layer of poly(2-methoxy-5-(3', 7'-dimethyloctyloxy)-1, 4-phenylene-vinylene) (MDMO-PPV) mixed with 6, 6 phentl-C61-butyl acid-methylester (PCBM) onto the copper nanorod array and sandwiching it with a film of poly(3, 4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS) applied onto a indium tin oxide coated glass substrate.