A novel method for the synthesis of Au nanoparticles incorporated amorphous hydrogenated carbon films

In this communication we report a novel electrochemical route for the preparation of Au nanoparticles incorporated a-C:H films on single crystal silicon substrates by choosing methanol as carbon source and Au nanoparticles as dopant. The morphology, composition and structure of the film have been investigated and the results show that the film obtained in our method is a hydrogenated diamond-like carbon film and zero-valence Au nanoparticles are stable and well-dispersed into the amorphous carbon matrix with unchanged size. It is simplified to achieve the co-deposition of carbon and metal by using metal nanoparticles rather than the metal salt solution as the dopant. The incorporation of Au nanoparticles in the carbon matrix can drastically decrease the resistivity and convert a-C:H films from insulator to semiconductor easily. The growth mechanisms of the Au-DLC films are also discussed.     

Approach to excellent superhydrophobicity and corrosion resistance of carbon-based films by graphene and cobalt synergism

A new series of carbon-based films doped with graphene oxide and cobalt (G-Co/a-C:H films) were successfully prepared on Si substrate via one-step electrochemical deposition of methanol as the carbon source and graphene oxide/cobalt as the dopant. G-Co/a-C:H films were fabricated at various graphene oxide concentration for comparative experiments. It can be found that the graphene oxide and cobalt were well embedded in amorphous carbon matrix to form superhydrophobic G-Co/a-C:H film at the doping GO concentration of 0.007 mg/mL, which was confirmed by transmission electron microscopy (TEM). It was noted that the superhydrophobicity of the resulting surface derives from its rough surface with hierarchical micro-nanostructures and the presence of the low-surface-energy GO components on it. The hierarchical micro-nanostructures are attributed to the corporate joint of GO and cobalt to form the multilevel nanoscale composite interface. Specially, the as-fabricated superhydrophobic G-Co/a-C:H film could exhibit excellent self-cleaning ability and corrosion resistance, revealed by the self-cleaning and corrosion tests.     

石墨烯/类金刚石碳复合薄膜的电化学沉积及其场发射性能

采用液相电化学方法在硅基底上制备了石墨烯掺杂的类金刚石碳复合薄膜,探讨了电化学沉积复合薄膜的机理。利用扫描电子显微镜（SEM）、拉曼光谱（Raman）、透射电子显微镜（TEM）和傅里叶变换红外（FTIR）光谱技术对薄膜表面形貌和微观结构进行了分析表征。结果表明,石墨烯片均匀分散沉积在含氢类金刚石碳（a-C：H）基体中,沉积的石墨烯/类金刚石（G/a-C：H）复合薄膜表面相对均匀平整。场发射测试显示石墨烯掺杂使开启电场从4.7 V·μm^-1增加至5.8 V·μm^-1,场发射电流密度从384 μA·cm^-2显著增加至876 μA·cm^-2。     

Electrochemical properties of amorphous nitrogen-containing hydrogenated diamondlike-carbon films

The electrochemical impedance of thin-film electrodes made of amorphous nitrogen-containing diamondlike carbon (a-C:N:H) in H₂SO₄ solutions and the kinetics of redox reactions on these electrodes in the Fe(CN) ₆ ^3-/4- system are studied. The amorphous diamondlike carbon films with an admixture of nitrogen are grown by a directed deposition from inductively coupled methane-nitrogen plasma. The films’ resistivity values determined from the ac impedance of a-C:N:H/electrolyte contact practically coincided with those determined from the current-vol.tage curves taken at the a-C:N:H/metal contact. With an increase in the nitrogen : methane ratio in the gas phase, both the electrical resistance and optical bandgap decrease from 3 x 10¹⁰ to 5 x 10⁶ ohm cm and from 1.3 to 0.6 eV, respectively. Simultaneously, the concentration of electrically active point-defect centers in a-C:N:H increases significantly and the reaction in the Fe(CN) ₆ ^3-/4- system is facilitated.     

Synthesis of silver and copper nanoparticle containing a-C:Hby ion irradiation of polymers

One of the many applications of diamond like carbon (DLC) is the biocompatible coating of medical tools and implants. The most recent field of interest concerns the generation of antimicrobial activity in combination with the excellent wear resistance and biocompatibility of DLC. As has already been shown for polymers, nanoparticles of silver or copper within a carbonacious matrix have a bactericidal effect.In this work we describe a new technique to produce amorphous hydrogenated carbon films (a-C:H), which contain nanometer sized clusters of silver or copper. The hybrid deposition process is based on sol–gel synthesis of polymer films and subsequent ion-induced densification and cross-linking to form a-C:H. By thermal or UV-induced reduction of metal salts in polymer solution, colloidal metal particles are produced. In this way polymer films, already containing noble metal nanoclusters, can be deposited in a wet chemical step. Upon sol–gel deposition, the polymer is subjected to ion irradiation. Based on earlier results, the influence of ion energy on chemical and mechanical properties, as well as bonding structure is investigated. Special attention is also dedicated to ion-induced diffusion and growth as well as oxidation effects.     

Effect of nitrogen and ammonia on transfer and deposition of hydrocarbon radicals in different regions of hollow-cathode glow discharge

The effect of addition of nitrogen or ammonia in an amount equal to the flow of methane entering as a 7: 1 H₂/CH₄ mixture into a hollow-cathode dc glow flow discharge on the rate of deposition/erosion of amorphous hydrocarbon (a-C:H) films at 300 K has been studied. The introduction N₂ or NH₃ into the mixture facilitates the transition from deposition to erosion of a-C(N):H films in the hollow cathode, but has a little effect on the growth rate of a-C(N):H films in the positive column and in the afterglow of the discharge. It has been suggested that the changes in the a-C:H film deposition/erosion rate are due to the formation of hydrogen cyanide, mainly, on the hollow-cathode surface.     

Self-ion irradiation on hydrogenated amorphous carbon films at depth of adhesion interlayer: Radiation-induced atomic intermixing and degraded film properties

Hydrogenated amorphous carbon (a-C:H) films consisting of a top a-C:H layer, a gradient transient a-C:H:Ti layer, and a bottom Ti layer were irradiated by 1.1-MeV C⁺ ions, resulting in a maximum displacement damage of 1.0 dpa and a projected range inside the Ti layer. Time-of-flight secondary ion mass spectrometry, electron energy loss spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy analyses were performed to investigate the compositional and structural transitions of a-C:H films after self-ion irradiation. The results revealed that C⁺ ions passing through the top a-C:H layer induced C–H fracture and hydrogen diffusion in this layer and then resulted in atomic intermixing in the multilayered adhesion interlayer. After local energy deposition of C⁺ ions, the initial sharp interfaces in the a-C:H:Ti layer became ambiguous due to interfacial mixing. In addition, titanium carbides formed in the Ti layer, with a gradual phase transition from TiCx to TiC with a diffusion depth of 200 nm. The broken compositional gradients of the adhesion interlayer resulted in a significant decrease in the adhesion strength of the films, which eventually resulted in degraded antiwear properties of the irradiated film in dry sliding tribotests.     

Nickel containing diamond like carbon thin films

Diamond like carbon (DLC) coatings are well established for multiple applications. The electrical conductivity of DLC or amorphous carbon can be influenced by several orders of magnitude via doping with different metals. Depending on the deposition process hydrogen may be incorporated as well, thereby decreasing the conductivity. Recent investigations of DLC disclose nice piezoresistive properties.Our work was focused on Ni:a-C:H thin films on different substrates by reactive sputtering from a nickel target. Several carbon precursors were added to the sputtering gas to create an amorphous carbon hydrogen network with embedded crystal clusters. In order to optimize the piezoresistive properties we varied various process parameters. The piezoresistive response was monitored by measuring the resistance change during bending. Our Ni:a-C:H films develop gauge factors of approx. 12 in a wide range of process parameters.For sensor applications the temperature coefficient of resistance (TCR) is important as well. It depends on the metal concentration in the thin film and can be adjusted by the concentration of the incorporated nickel. It can be set to approximately zero in a wide temperature range of 80–400 K. The combination of a high gauge factor and a very small TCR is achieved and described in this paper.XRD measurements reveal nickel or nickel carbide clusters with diameters of approx. 8–30 nm depending on the metal concentration. The clusters crystallize in the hexagonal hcp structure which could be transformed into the cubic fcc structure of nickel by thermal annealing in a vacuum.     

Achieving ultra-low friction of a-C:H film grown on 9Cr18Mo steel for industrial application via programmable high power pulse magnetron sputtering

Owing to the high hardness and hydrogen passivation of carbon bonds, hydrogenated diamond-like carbon (a-C:H) film has shown promising potential to achieve ultra-low friction and wear on steel surfaces. Here, a-C:H film was successfully deposited on 9Cr18Mo steel via programmable high power pulse magnetron sputtering and potential application for industrial was evaluated. The a-C:H films against different mating materials of GCr15 steel balls, Al₂O₃, Si₃N₄, ZrO₂, and a-C:H-coated GCr15 balls all showed ultra-low friction under a normal load of 5 N in a dry ambient air environment. Among them, self-mating tribo-system a-C:H films on steel surfaces and a-C:H-coated steel balls achieve best friction performance; the principal reason is that both contacting surfaces coated with a-C:H film have the lower electron affinities compared with other tribo-systems. However, the differences of coefficient of friction (COF) for uncoated-GCr15, Al₂O₃, ZrO₂, Si₃N₄, and a-C:H(GCr15) balls can be attributed to different sizes of clustering in wear debris. This work provides new insights on synthesis and industry application of the a-C:H films with ultra-low friction properties.     

Detailed TIMS study of Ar/C(2)H(2) expanding thermal plasma: identification of a-C:H film growth precursors

Acetylene chemistry is studied by means of threshold ionization mass spectrometry (TIMS) in remote Ar/C(2)H(2) expanding thermal plasma to identify the growth precursors of hydrogenated amorphous carbon (a-C:H) films. More than 20 hydrocarbon species are measured, enabling a comprehensive study of acetylene chemistry in the plasma environment. It is shown that the plasma composition is controlled by the initial ratio between the acetylene flow into the reactor and argon ion and electron fluence emanating from the remote plasma source. Complete decomposition of acetylene to C, CH, CH(2), C(2), and C(2)H radicals is achieved in subsequent charge transfer and dissociative recombination reactions under low acetylene flow conditions. The formation of soft polymer-like a-C:H films can be attributed to C, C(2), and also partially to CH and C(2)H deposition. At acetylene flows higher than argon ion and electron fluence, reactions of C, CH, C(2), and C(2)H radicals with acetylene lead to the formation of various hydrocarbon species, whose behavior is dependent on whether the number of carbon atoms is even or odd. The detected resonantly stabilized C(3), C(3)H, and probably also C(5) and C(5)H radicals are unreactive with acetylene in the gas phase and are, therefore, abundantly present close to the substrate. The C(3) radical has among them the highest density, and it is identified as the significant growth precursor of Ar/C(2)H(2) expanding thermal plasma deposited hard a-C:H films.     

Stability of carbon-supported palladium nanoparticles in alkaline media: A case study of graphitized and more amorphous supports

The stability and degradation mechanism of graphitized (Graphene nanosheets) and more amorphous (Vulcan XC-72R) carbon-supported palladium nanoparticles was investigated. Coupling identical-location transmission electron microscopy (ILTEM) and electrochemistry enabled to correlate the distribution of the Pd nanoparticles under accelerated stress test (up to 1000 cycles between 0.1 and 1.23 V vs. RHE, in a 0.1 M NaOH solution at 25 °C) with changes in electrochemical accessible surface area (ECSA). The carbon-supported Pd nanoparticles undergo similar rates of degradation in terms of electrochemical surface areas on both supports. However, their mechanisms of degradation differ: on amorphous carbon, the primary mode of degradation is Pd nanoparticles detachment (and minor agglomeration), whereas on graphitized supports it is more likely their coalescence and dissolution/redeposition. “Bulk” carbon-corrosion is negligible in both cases, as proven by ex situ Raman spectroscopy. So, using a graphitized carbon support (Graphene nanosheets) versus a more amorphous one (Vulcan XC-72R) does not enable to significantly depreciate the Pd/C catalyst degradation in alkaline media.     

大功率激光制备a-C和a-C∶H类金刚石膜的光学性能研究

采用大功率高重复频率准分子激光溅射热解石墨靶制备了类金刚石碳膜, 研究了实验条件对类金刚石膜光学性能的影响, 发现氢可以提高膜中sp3键的含量和膜的光学透过率. 在实验参数范围内, 膜的光学性能随着氢压的增加而提高. 根据类金刚石膜的反应沉积机理对上述结果进行了分析、解释.     

Effect of methane on magnetron sputtering graphite target deposited films and tribological properties of a-C:H:Ti/a-C:H friction pairs

In this study, we prepared a-C:H films with different nanostructures at different methane flow rates. The effect of the methane flow rate on the tribological properties of 440 steel/a-C:H friction pairs and a-C:H:Ti/a-C:H friction pairs in an atmospheric environment was studied by a reciprocating friction machine. The results show that there is no relationship between the tribological properties of 440 steel/a-C:H friction pair and methane flow rate. The tribological performance of the a-C:H:Ti/a-C:H friction pair was greatly improved. In particular, in the friction pair of a-C:H:Ti/a-C:H with a methane flow rate of 20 sccm, superlubricity is shown, and the wear rate is only 4.04 × 10⁻⁹ mm³/Nm. After tribological experiments, Raman spectroscopy, XPS, and other characterization methods were used to study the relationship between the nanostructure and tribological properties of a-C:H:Ti films and a-C:H prepared with different methane flow rates. This study is great significance to the application of a-C:H:Ti/a-C:H friction pair in mechanical parts under atmospheric environment.     

Characteristics of Ti–Nb,Ti–Zr and Ti–Al containing hydrogenated carbon nitride films

Nanocomposite Me–C–N:H coatings (Me is TiNb, TiZr or TiAl), with relatively high non-metal/metal ratios, were prepared by cathodic arc method using TiNb, TiZr and TiAl alloy cathodes in a CH₄ + N₂ atmosphere. For comparison purposes, a-C–N:H films were also produced through evaporating a graphite cathode in a similar atmosphere. The films were characterized in terms of elemental and phase compositions, chemical bonds, texture, hardness, adhesion and friction behavior by GDOES, XPS, Raman spectroscopy and XRD techniques, surface profilometry, hardness and scratch adhesion measurements, and tribological tests. The nanocomposite films consisted of a mixture of crystalline metal carbonitride and amorphous carbon nitride. The non-metal/metal ratio in the films composition was found to range between 1.8 and 1.9. For the metal containing nanocomposites, grain size in the range 7–23 nm, depending on the metal nature, were determined. As compared with the a-C–N:H, the Me–C–N:H films exhibited a much higher hardness (up to about 39 GPa for Ti–Zr–C–N:H) and a better adhesion strength, while the coefficients of friction were somewhat higher (0.2–0.3 for Me–C–N:H and 0.1 for a-C–N:H).     

X-ray absorption of nitrogen-doped amorphous carbon films for determining sp2/sp3 bonding concentrations

A method of analyzing X-ray absorption spectra of nitrogen-doped amorphous carbon (a-C) samples was developed to determine their sp² bonding concentrations. The films under consideration are simultaneously deposited onto polytetrafluoroethylene (PTFE) polymer or silicon wafer substrates by hot wire plasma sputtering of graphite. sp² bonding concentrations of a-C films deposited on PTFE increase from 74% to 93% with growing nitrogen doping. Silicon substrate films yield the same general trend, but show that the near surface electronic structure of a-C films depends on the substrate.     

Growth mechanisms involved in the synthesis of smooth and microtextured films by acetylene magnetron discharges

The growth of hydrogenated amorphous carbons (a-C:H) produced by continuous or pulsed discharges of acetylene (C(2)H(2)) in an unbalanced magnetron setup was investigated. At 5 × 10(-3) Torr, only smooth films are obtained, whereas at 5 × 10(-1) Torr using a pulsed discharge some microtextured films are formed if the duty cycle is low. The morphology of these microtextured films consists of nanoparticles, filamentary particles, and particular agglomerates ("microflowers"). This paper presents a study of acetylene gas phase polymerization by mass spectrometry, and a detailed analysis of bulk structure of films by combining three techniques which include IR spectroscopy, Raman spectroscopy, and laser desorption/ionization Fourier transform mass spectrometry (LDI-FTMS). Finally, based on the study of gas phase and film structure, we propose a model for the growth of both smooth and microtextured films.     

Fabrication of hydrophobic fluorinated amorphous carbon thin films by an electrochemical route

A novel electrochemical route for the preparation of hydrophobic fluorinated amorphous carbon (a-C:F) films with nanostructured surfaces on single crystal silicon substrate was reported. The films were investigated in terms of the surface morphology, chemical composition, microstructure and hydrophobic behavior. The results showed that a highly uniform and densely packed bamboo shoot-like nanostructure was obtained without any use of template. The incorporation of fluorine presented mainly in the forms of CF₂ chains and CCF_x (x = 1, 2) in the films. Sessile drop water contact angle measurements showed that the contact angle of a-C:F films deposited by electrochemical route was about 145°, which can be attributed to the lower surface energy of CF_x groups and higher diffusion resistance of the special nanostructured surface to water. Moreover, the related growth mechanism of the resulting films in liquid-phase electrodeposition is discussed as well.     

热辅助存储磁盘硅掺杂非晶碳薄膜氧化的ReaxFF反应力场分子动力学模拟

Heat-assisted magnetic recording (HAMR) is one of the promising ways to extend the magnetic recording area density to 1 Tb·in^-2 in hard disk drives (HDDs).High temperature induced by laser heating can cause carbon overcoat (COC) oxidation.Reactive molecular dynamics (MD) simulations are performed to investigate the oxidation process of silicon-doped amorphous carbon (a-C:Si) films for HAMR application.The atomic details of the structure evolution and oxidation process are investigated, and, the oxidation mechanism of the a-C:Si film is clarified.The effect of the duration of laser irradiation on the oxidation of the a-C:Si film is investigated.The oxidation occurs during heating and the beginning of cooling process.Both volume expansion during heating process and cluster of carbon atoms during cooling process increase the rate of sp² carbon.Because of the decrease in the amount of unsaturated silicon atoms and low diffusion coefficient of atomic oxygen, the oxidation rate of the a-C:Si film decreases with laser irradiation cycles.The molecular oxygen is the oxidant due to surface defect of a-C:Si film.The atomic strains break the O-O bonds in Si-O-O-Si linkages and rearrange the surface oxide layers, and process the oxidation of the a-C:Si film.     

Up-scaling the production of modified a-C:H coatings in the framework of plasma polymerization processes

Hydrogenated amorphous carbon (a-C:H) films with silicon and oxygen additions, which exhibit mechanical, tribological and wetting properties adequate for protective coating performance, have been synthesized at room temperature in a small- (0.1 m³) and a large-scale (1 m³) coaters by low-pressure Plasma-Activated Chemical Vapour Deposition (PACVD). Hence, a-C:H:Si and a-C:H:Si:O coatings were produced in atmospheres of tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO), respectively, excited either by radiofrequency (RF – small scale) or by pulsed-DC power (large scale). Argon was employed as a carrier gas to stabilize the glow discharge. Several series of 2–5 μm thick coatings have been prepared at different mass deposition rates, R_m, by varying total gas flow, F, and input power, W. Arrhenius-type plots of R_m/F vs. (W/F)^?1 show linear behaviours for both plasma reactors, as expected for plasma polymerization processes at moderated energies. The calculation of apparent activation energy, E_a, in each series permitted us to define the regimes of energy-deficient and monomer-deficient PACVD processes as a function of the key parameter W/F. Moreover, surface properties of the modified a-C:H coatings, such as contact angle, abrasive wear rate and hardness, appear also correlated to this parameter. This work shows an efficient methodology to scale up PACVD processes from small, lab-scale plasma machines to industrial plants by the unique evaluation of macroscopic parameters of deposition.     

Reactivity of hydrogen with solid-state films of alkylamine- and tetraoctylammonium bromide-stabilized Pd, PdAg, and PdAu nanoparticles for sensing and catalysis applications

Hydrogen gas spontaneously adsorbs to Pd metal as atomic hydrogen and diffuses into the lattice to form PdHx. We previously showed that films of hexanethiolate-coated Pd monolayer-protected clusters (MPCs) do not readily react with H2 due to the strong chemical bonding of the thiolate to the Pd, which inhibits the reaction. Consequently, these films require ozone or heat treatment for reactivity to occur, which is inconvenient for sensing or catalysis applications. In this report, we describe the reactivity between H2 and solid-state films of alkylamine-coated Pd, PdAg (10:1), and PdAu (10:1) MPCs and films of tetraoctylammonium bromide (TOABr)-stabilized Pd and PdAg (10:1) nanoparticles as determined by changes in film conductivity. Our data show that Pd nanoparticles coated with these more weakly coordinated amine or ammonium groups readily react with H2 without any need for ozone or heat treatment. The conductivity of films of octylamine (C8NH2)- or dodecylamine (C12NH2)-coated Pd, PdAg, and PdAu MPCs increases irreversibly upon initial exposure to 100% H2 to varying degrees and with different reaction kinetics and then exhibits stable, reversible changes in the presence of H2 concentrations ranging from 9.6 to 0.08%. The behavior upon initial exposure to H2 (conditioning) and the direction and magnitude of the reversible conductivity changes depend on the alkyl chainlength and alloy composition. Films of TOABr-coated Pd and PdAg nanoparticles show stable, reversible increases in conductivity in the presence of H2 concentrations from 9.6 down to 0.11% without conditioning. Surface FTIR spectroscopy and atomic force microscopy (AFM) provide information about the organic monolayer and film morphology, respectively, following reactivity with H2. This work demonstrates a simple approach toward preparing films of chemically synthesized Pd-containing nanoparticles with controlled reactivity to H2 for sensing and catalysis applications.