IR spectroscopy of copper-intercalated graphite nanoclusters in amorphous carbon

We measured optical absorption coefficients of the metal-induced quasi-Raman absorption bands in hydrogenated carbon films. Parameters of the copper-induced quasi-Raman bands were used to estimate the size of the graphite-like nanoclusters in a-C:H(Cu) with various copper concentrations. Preliminary comparative data on Cu-, Er-, and Co-modified a-C:H are reported.     

Organization of copper nanoclusters in Langmuir-Blodgett films

Stable nanoclusters of Cu were synthesized using Langmuir-Blodgett films of octadecylsuccinic acid (ODSA) as template. The Langmuir-Blodgett films of ODSA formed from subphase containing copper ions were first subjected to sulphidation (S) using sodium sulphide and then hydrogenated (H) using hydrogen gas. Diffuse reflectance UV-visible spectroscopy (DIR-UV-vis), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) used to characterize these films indicated the formation of Cu(0) metallic clusters ranging in size from 3 ∼ 10 nm.     

Two-dimensional distribution of carbon nanotubes in copper flake powders

We report an approach of flake powder metallurgy to the uniform, two-dimensional (2D) distribution of carbon nanotubes (CNTs) in Cu flake powders. It consists of the preparation of Cu flakes by ball milling in an imidazoline derivative (IMD) aqueous solution, surface modification of Cu flakes with polyvinyl alcohol (PVA) hydrosol and adsorption of CNTs from a CNT aqueous suspension. During ball milling, a hydrophobic monolayer of IMD is adsorbed on the surface of the Cu flakes, on top of which a hydrophilic PVA film is adsorbed subsequently. This PVA film could further interact with the carboxyl-group functionalized CNTs and act to lock the CNTs onto the surfaces of the Cu flakes. The CNT volume fraction is controlled easily by adjusting the concentration/volume of CNT aqueous suspension and Cu flake thickness. The as-prepared CNT/Cu composite flakes will serve as suitable building blocks for the self-assembly of CNT/Cu laminated composites that enable the full potential of 2D distributed CNTs to achieve high thermal conductivity.     

改良电沉积法制备硝酸根高敏传感铜簇

溶液中硝酸根的检测是生态环境保护中亟待解决的首要问题。用氢气泡模板法通过调节沉积时间制备出了系列对硝酸根具有良好电化学传感作用的高密度纳米铜簇材料。通过能谱分析、扫描电镜观察和电化学性能测试对该系列纳米铜簇的成分、相结构、形貌和催化性能进行了测定。研究结果表明,沉积时间是影响纳米铜簇材料传感性能的重要因素。通过优化沉积时间,可以获得纳米枝晶和大量纳米颗粒复合的结构,该结构对硝酸根具有较强的传感信号,且在0.03~1.5mmol/L的NO-13浓度范围内还原峰电流密度与硝酸根离子浓度成线性关系。     

Size and shape of nanoclusters: single-shot imaging approach

A method of single-shot imaging via aberration-corrected scanning transmission electron microscopy equipped with high angle annular dark-field detector (STEM-HAADF) has been applied to size-selected gold model catalysts (Au(25) and Au(39) ) on hydroxyapatite. Through quantitative intensity analysis, the size, in terms of number of atoms as well as 3D shape of the clusters are obtained.     

Growth and characterization of copper nanoclusters embedded in SiC matrix

Nanocrystalline copper clusters embedded in silicon carbide were made by island growth during sputter deposition. The distribution and morphology of metal clusters were observed by high-resolution transmission electron microscopy. To investigate chemical bonding at the copper-silicon carbide interface, we studied the electronic states of copper and silicon using X-ray photoelectron spectroscopy (XPS). It was found that the formation of copper silicide was suppressed in this system and that small shifts in binding energy were observed for different sizes of clusters, which was different from the chemical shift for copper silicide formation.     

Diamond-like amorphous carbon

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp³ bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).     

二元A1-Ni纳米团簇结合能的尺寸和成分依赖性研究

利用分子动力学的方法研究了二元A1-Ni团簇结合能的尺寸和成分依赖性。研究表明，低于300K时，团簇的结构不依赖于成分，仍然保持面心立方结构。成分一定时，团簇的结合能随着尺寸的增大而增大；尺寸一定时，A1-Ni团簇的结合能先随着Ni含量的增大而增大，当Ni含量为O．75时，达到极值，而后随着Ni含量的增大而减小，说明Al0.25Ni0.75为最稳定的结构。对于A1-Ni团簇进一步研究表明，Al有表面聚集的趋势。     

阴极电弧法定向生长的铜纳米线上沉积非晶碳膜及其场发射特性

以阴极电弧法,分别于硅基材与铜纳米线(CuNWs)/硅基材(其中铜纳米线系阳极氧化铝(AAO)模板技术成长于硅基材上)沉积非晶碳膜,,分别以扫描电子显微镜(SEM)、原子力电子显微镜(AFM)和X光电子光谱仪(XPS)表征了非晶碳膜/铜纳米线/硅基材与非品碳膜/硅基材两者之表面形貌、粗糙度、结构及键结等物理特性.并比较两者之电子场发射特性.研究结果显示:两者都拥有低起始电场及高电流密度,其中非品碳膜/铜纳米线/硅基材的场发射起始电压为3.75 V/μm优于非品碳膜/硅基材的15 V/μm,因此非晶碳膜/铜纳米线/硅基材更适用于场发射平面显示器(FED)之发射子,可应用于高稳定性及低成本之场发射平面显示器之研发.     

Developing a millifluidic platform for the synthesis of ultrasmall nanoclusters: ultrasmall copper nanoclusters as a case study

The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs).     

Piezoresistive effect in amorphous carbon thin films

Abstract

In this contribution amorphous carbon (a-C) films are integrated as strain gauges in micromachined silicon boss membranes. Sputter deposited a-C films have high hardness and <2 % hydrogen content in it. The tribological properties of the a-C films are comparable with diamond and can be used for hard coatings. The films have very low resistivity which decreases with the temperature. Current voltage characteristics of a-C/oxide Si shows Ohmic behaviour. Variable range hopping mechanism is dominant at low temperatures and is thermally activated at room temperature and at higher temperatures. Piezoresistive gauge factor are measured in the temperature range 23–50°C.     

Raman spectra of iron-modified amorphous carbon

Raman spectra of amorphous carbon films containing encapsulated iron (a-C:Fe) have been measured in the frequency range 200–1000 cm⁻¹. The concentration of encapsulated iron atoms (3, 26, 38, and 54 at. %) was controlled by changing the relative areas of iron and graphite targets during the film deposition by RF magnetron sputtering and checked by Rutherford backscattering. The Raman spectra of a-C:Fe films display a series of almost equidistant bands spaced by approximately 110 cm⁻¹. This character of the spectrum is explained in terms of the atomic vibrations in short carbon nanotubes formed during the introduction of iron into an amorphous carbon matrix.     

Spectroscopic ellipsometry characterization of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride thin films

Carbon nitride (CN_x) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV-VIS-NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C-N or C-C modes. This feature is generally associated with sp³ C-N or sp³ C-C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp² hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The π→π? electronic transition associated with sp² C bonds in carbon films and with sp² N bonds (as N bonded in pyridine-like manner) in CN_x films is also present, but not as strong. Another feature present in all CN_x films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.     

非晶炭包裹铜纳米粒子在导热流体中的应用

采用氩电弧等离子体法制备不同粒径的炭包铜纳米粒子,研究其抗氧化性能、在水介质中的分散性能和导热性能.结果表明:炭层的保护作用赋予铜晶体更高的抗氧化性能;非晶炭层的特殊结构可通过双氧水化学处理使其表面产生羧基和羟基,提高其在水介质中的分散性能;炭包铜粒径越小,纳米流体导热性能越好.     

Possible n-type dopants in diamond and amorphous carbon

It has been extremely difficult to produce n-type conducting diamond, whereas it seems that n-type conducting tetrahedrally bonded amorphous carbon (ta-C) can be obtained using phosphorous or nitrogen as dopant. In this work we have studied substitutional group V–VII impurities (N, O and Cl) in diamond and ta-C using first-principles electronic structure methods. Electronic structure calculations reveal the differences between ta-C and diamond in the microscopic level and ease, therefore, the experimental search for producing n-type conducting diamond-like materials.     

Structural morphology of amorphous conducting carbon film

Amorphous conducting carbon films deposited over quartz substrates were analysed using X-ray diffraction and AFM technique. X-ray diffraction data reveal disorder and roughness in the plane of graphene sheet as compared to that of graphite. This roughness increases with decrease in preparation temperature. The AFM data shows surface roughness of carbon films depending on preparation temperatures. The surface roughness increases with decrease in preparation temperature. Also some nucleating islands were seen on the samples prepared at 900°C, which are not present on the films prepared at 700°C. Detailed analysis of these islands reveals distorted graphitic lattice arrangement. So we believe these islands to be nucleating graphitic. Power spectrum density (PSD) analysis of the carbon surface indicates a transition from the nonlinear growth mode to linear surface-diffusion dominated growth mode resulting in a relatively smoother surface as one moves from low preparation temperature to high preparation temperature. The amorphous carbon films deposited over a rough quartz substrate reveal nucleating diamond like structures. The density of these nucleating diamond like structures was found to be independent of substrate temperature (700–900° C).     

The electron paramagnetic resonance in copper-modified amorphous carbon

Room-temperature EPR spectra of copper-modified α-C:H films exhibit signals due to the isolated paramagnetic copper centers and dangling carbon bonds. An analysis of variation of the EPR signal intensity depending of the annealing temperature (T _a≤300°C) and relaxation of the EPR and IR absorption signals upon annealing indicates that the annealing-induced modification of the α-C:H films involves hydrogen and oxygen impurities in the amorphous carbon matrix.     

Chemical bond analysis of amorphous carbon films

Hydrogen-free carbon films with the various sp³ bond fractions between 83% and 40% were prepared by mass-separated ion beam deposition (MSIBD). These sp³ bond fractions were obtained by electron energy loss spectroscopy (EELS). Chemical bond analysis of these carbon films was performed by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Raman spectroscopy, and the comparison of these methods was examined. XPS C1s spectra of carbon films show two contributions at the energies of 284.5 and 285.5 eV, which are originated from sp²-bonds and sp³ bonds, respectively. The sp³ bond fractions obtained by XPS are in good agreement with the values given by EELS. The fine structure of AES spectra at the kinetic energy region between 245 and 265 eV reflects the sp³ bond fraction. AES spectra are changed from the diamond-like feature to the graphite-like one with decreasing the sp³ bond fraction. Raman spectra show two broad peaks of G band and D band, the ratio of two peak intensities is independent on the sp³ bond fraction of films. The shift of G peak position has a correlation with the sp³ bond fraction in the sp³ bond rich region.