Surface properties of diamond-like carbon films prepared by CVD and PVD methods

Diamond-like carbon (DLC) films have been deposited using three different techniques: (a) electron cyclotron resonance---plasma source ion implantation, (b) low-pressure dielectric barrier discharge, (c) filtered---pulsed cathodic arc discharge. The surface and mechanical properties of these films are compared using atomic force microscope-based tests. The experimental results show that hydrogenated DLC films are covered with soft surface layers enriched with hydrogen and sp$^{3}$ hybridized carbon while the soft surface layers of tetrahedral amorphous carbon (ta-C) films have graphite-like structure. The formation of soft surface layers can be associated with the surface diffusion and growth induced by the low-energy deposition process. For typical CVD methods, the atomic hydrogen in the plasmas can contribute to the formation of hydrogen and sp$^{3}$ hybridized carbon enriched surface layers. The high-energy ion implantation causes the rearrangement of atoms beneath the surface layer and leads to an increase in film density. The ta-C films can be deposited using the medium energy carbon ions in the highly-ionized plasma.     

Raman Spectrum of Epitaxial Graphene Grown on Ion Beam Illuminated 6H-SiC （0001）

Patterning SiC substrates with focused ion beam for growth of confined graphene nanostructures is interesting for fabrication of graphene devices. However, by imposing an ion beam, the morphology of illuminated SiC substrate surface is inevitably damaged, which imposes significant effects on the subsequent growth of graphene. By using confocal Raman spectroscopy, we investigate the effects of ion beam illumination on the quality of graphene layers that are grown on 6H-SiC （0001） substrates with two different growth methods. With the first method, the 6H-SiC （0001） substrate is flash annealed in ultra-high vacuum. Prominent defects in graphene grown on illuminated areas are revealed by the emergence of Raman D peak. Significant changes in D peak intensity are observed with Ga＋ ion fluence as low as 10^5 μm^-2. To eliminate the damage from the ion beam illumination, hydrogen etching is employed in the second growth method, with which prominent improvement in the quality of crystalline graphene is revealed by its Raman features. The defect density is significantly reduced as inferred from the disappearance of D peak. The Raman shift of G peak and 2D peak indicates strain-released graphene layers as grown in such a method. Such results provide essential information for patterning graphene nano-devices.     

Wettability of Si and Al–12Si alloy on Pd-implanted 6H–SiC

Si C monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences,and the effects of Pd ion implantation on wettability of Si/Si C and Al–12 Si/Si C systems are investigated by the sessile drop technique.The decreases of contact angles of the two systems are disclosed after the ion implantation,which can be attributed to the increase of surface energy(σ_(SV)) of Si C substrate derived from high concentration of defects induced by the ionimplantation and to the decrease of solid–liquid surface energy(σ_(SL)) resulting from the increasing interfacial interactions.This study can provide guidance in improving the wettability of metals on Si C and the electronic packaging process of Si C substrate.     

Deuterium Retention in the Co-Deposition Carbon Layers Deposited by Radio-Frequency Magnetron Sputtering in D2 Atmosphere

Carbon is deposited on C and Si substrates by rf magnetron plasma sputtering in a D2 atmosphere. The deposited layers are examined with ion beam analysis and thermal desorption spectroscopy （TDS）. The growth rates of the layers deposited on Si decrease with increasing substrate temperature, while increase significantly with the increase of D2 pressure. Meanwhile, the deuterium concentrations in the layers deposited on the Si substrates decrease front 30% to 2% and front 31% to 1% on the C substrates, respectively, when the substratc temperature varies from 350K to 90OK. Similarly, the D concentration in the layer on the Si substrates increases from 3.4% to 47%, and from 8% to 35% on the C substrates when the D2 pressure increases from 0.3Pa to 8.OPa. D desorption characterized by TDS is mainly in the forms of D2, HD, HDO, CD4, and C2D4, and a similar release peak occm% at 645K. The release peak olD2 molecules at 960K can be attributed to the escaped gas from the thin co-deposited deuterium-rich carbon layer in the form of C D bonding.     

Conditions for formation and trapping of the two-ion Coulomb cluster in the dissipative optical superlattice

Conditions have been studied under which a polychromatic optical superlattice can form and trap the Coulomb cluster of two strongly interacting ions.In our previous work(Krasnov I V and Kamenshchikov L P 2014 Opt.Comm.312 192)this new all-optical method of obtaining and confining the Coulomb clusters was demonstrated by numerical simulations for special values of the optical superlattice parameters and in the case of Yb ions.In the present paper the conditions are explicitly formulated,under which the long-lived two-ion cluster in the superlattice cell is formed.The peculiarity of these conditions is the renormalization of the ion–ion Coulomb interaction.Notably,the renormalized Coulomb force is determined by the effective charge which depends on the light field parameters and can strongly differ from the "bare"ion charge.This result can be accounted for by the combined manifestation of the quantum fluctuations of optical forces,nonlinear dependence of these forces on the velocity,and non-Maxwellian(Tsallis type) velocity distribution of the ions in the optical superlattice.Explicit analytical formulas are also obtained for the parameters of the optical two-ion cluster.     

Raman spectrum study of graphite irradiated by swift heavy ions

Highly oriented pyrolytic graphites are irradiated with 40.5-Me V and 67.7-Me V ^112Sn-ions in a wide range of fluences： 1×10^11 ions/cm^2–1×10^14ions/cm^2. Raman spectra in the region between 1200 cm^-1 and 3500cm^-1 show that the disorder induced by Sn-ions increases with ion fluence increasing. However, for the same fluence, the amount of disorder is greater for 40.5-Me V Sn-ions than that observed for 67.7-Me V Sn-ions, even though the latter has a slightly higher value for electronic energy loss. This is explained by the ion velocity effect. Importantly, ～ 3-cm^-1frequency shift toward lower wavenumber for the D band and ～ 6-cm^-1 shift toward lower wavenumber for the 2D band are observed at a fluence of 1×10^14 ions/cm^2, which is consistent with the scenario of radiation-induced strain. The strain formation is interpreted in the context of inelastic thermal spike model, and the change of the 2D band shape at high ion fluence is explained by the accumulation of stacking faults of the graphene layers activated by radiation-induced strain around ion tracks. Moreover,the hexagonal structure around the ion tracks is observed by scanning tunneling microscopy, which confirms that the strains near the ion tracks locally cause electronic decoupling of neighboring graphene layers.     

Unidirectional expansion of lattice parameters in GaN induced by ion implantation

This paper reports that the 150-keV Mn ions are implanted into GaN thin film grown on Al2O3 by metal-organic chemical vapour deposition.The X-ray diffraction reciprocal spacing mapping is applied to study the lattice parameter variation upon implantation and post-annealing.After implantation,a significant expansion is observed in the perpendicular direction.The lattice strain in perpendicular direction strongly depends on ion fluence and implantation geometry and can be partially relaxed by post-annealing.While in the parallel direction,the lattice parameter approximately keeps the same as the unimplanted GaN,which is independent of ion fluence,implantation geometry and post-annealing temperature.     

Optical Planar Waveguides in KTiOPO4 Crystals by MeV Oxygen Ion Implantation

We report on the optical planar waveguide formation in KTiOPO4 crystals by single or double oxygen ion implantation at energies of 2.4-3.0 MeV and doses of 1015 ions/cm^2. The dark-line spectroscopy properties are investigated by a prism-coupling method. With an effective refractive index method, the refractive index profiles of the waveguides are reconstructed. The program code TRIM＇98 （transport of ions in matter） is used to simulate the implantation process of oxygen ions into the KTiOPO4 crystal. It is found that an inherent relationship exists between the nuclear damage and the refractive index changes induced by the ion-beam implantation.     

Effects of high-dose Ge ion implantation and post-implantation annealing on ZnO thin films

This paper reports that ion implantation to a dose of 1×10¹⁷ ions/cm² was performed on c-axis-orientated ZnO thin films deposited on (0001) sapphire substrates by the sol-gel technique. After ion implantation, the as-implanted ZnO films were annealed in argon ambient at different temperatures from 600-900℃. The effects of ion implantation and post-implantation annealing on the structural and optical properties of the ZnO films were investigated by x-ray diffraction (XRD), photoluminescence (PL). It was found that the intensities of (002) peak and near band edge (NBE) exitonic ultraviolet emission increased with increasing annealing temperature from 600-900℃. The defect related deep level emission (DLE) firstly increased with increasing annealing temperature from 600- 750℃, and then decreased quickly with increasing annealing temperature. The recovery of the intensities of NBE and DLE occurs at \sim 850℃ and \sim 750℃ respectively. The relative PL intensity ratio of NBE to DLE showed that the quality of ZnO films increased continuously with increasing annealing temperature from 600 - 900℃.     

Generation of Very Energetic Ions from Intense Femtosecond Laser Interactions with Rare Gas Clusters in a Dense Jet

Very energetic ions, which are detected by time-of-flight spectrometry with maximum energy up to 1.3 MeV and an average energy of 68keV, are generated in the explosion of large Xe clusters in a dense jet irradiated with a high-intensity (～10^16 W/cm2) 50fs laser pulse from a Ti:sapphire TW laser at 79Ohm wavelength. The interaction of intense laser pulses with a jet of argon clusters is also performed and high average ion energies are observed. The dependence of energy of the ions on the gas backing pressure is examined, suggesting that the results are consistent with the absorption efficiency of the laser energy by the cluster plasmas.     

Characterization of a hybrid Li-ion anode system from pulsed laser deposited silicon on CVD-grown multilayer graphene

A hybrid anode system for lithium (Li) ion battery applications based on pulsed laser deposited silicon films on chemical vapor deposited multilayer graphene (MLG) layers on a nickel foam substrate was electrochemically characterized. The as-grown material was directly fabricated into an anode without a binder, and tested in a half-cell configuration. There is evidence of the participation of both the multilayer graphene and the Si in the transport of Li ions. Even when cycled under stressful voltage limits that accelerate degradation, the MLG–Si films displayed higher stability than Si-only anodes, especially at higher cycling rates. Unlike the Si cells that display capacity fade even within the first few cycles, the MLG–Si cells show a very narrow spread in capacity, indicative of the role of the graphene layers in improving adhesion of the Si and acting as a compliant buffer for its volume expansion. Stable average specific capacities of ~1,200 mAh/g per total weight of MLG + Si, over 80 cycles at C/5 rate, were obtained for the MLG–Si anode. Pre- and post-cycling characterization of the anode materials revealed the differences between the two systems.     

One-step synthesis of TiC/multilayer graphene composite by thermal plasma

Graphene hybrid materials have been attracting a great deal of attention due to their superior properties. Nevertheless, problems such as expensive and complicated production processes have limited their application to industrial fields. Here, we introduce a one-step synthesis of titanium carbide (TiC) nanoparticles on multilayer graphene nanosheet (TiC/multilayer graphene) composites using thermal plasma. Although there are three types of titanium alkoxides (titanium ethoxide, titanium isopropoxide and titanium n-butoxide), the TiC/multilayer graphene was synthesized from only titanium isopropoxide. The injection temperature of the precursor was varied to investigate the effects of the precursor concentration in the plasma region. A TiC/multilayer graphene hybrid material with crystalline TiC nanoparticles below 50 nm on graphene nanosheets was observed. The number of graphene nanosheet layers varied from one to over 10 according to the injection temperature. When titanium ethoxide and titanium butoxide were injected, TiC with amorphous carbon and graphite were synthesized. The formation of graphene is considered to be affected by the structure of the carbon chain in the precursors and the concentration in the plasma region.     

On the correction of errors in quantum cryptography systems

The Raman and photoluminescence spectra of short-period C/SiC superlattices produced by RF magnetron sputtering are investigated. The Raman data indicate that, in 35-period Sitall/Ni/[C/SiC] superlattices with the C and SiC effective thicknesses of 3.5 and 3 Å, respectively, subjected to postgrowth avalanche annealing, the carbon layers assume the structure of multilayer graphene with 3–5 graphene sheets per superlattice period. A method for the fabrication of graphene-like carbon structures on the basis of short-period superlattices grown by RF sputtering is suggested and implemented.     

调幅W(Mo)/Cu纳米多层膜He+离子辐照响应行为

用磁控溅射技术制备不同调幅波长 (L) 的W(Mo)/Cu纳米多层膜,所制膜系在60 keV氦离子 (He⁺) 辐照条件下注入不同剂量: 0, 1×10¹⁷ He⁺/cm², 5×10¹⁷ He⁺/cm². 用X射线衍射仪 (XRD) 和高分辨透射电子显微镜(TEM)表征W(Mo)/Cu纳米多层膜辐照前后微观结构. 研究结果表明: 1) He⁺离子轰击引起温升效应是导致沉积态亚稳相β-W 转变成稳态 α-W相的主因, 而与调幅波长无明确关联; 2) 纳米多层结构中W(Mo) 和Cu膜显现出的辐照耐受性与调幅波长相关, 调幅波长越小, 抗He⁺的辐照性能越强; 3) 在5×10¹⁷ He⁺/cm²注入条件下, 观察到He团簇/泡在纳米结构W(Mo) 和Cu膜中的积聚行为存在明显差异: 在W (Mo) 膜中He团簇/泡的分布与晶粒取向相关, He团簇/泡倾向于沿W (211) 晶面分布; 而Cu膜非晶化且He团簇/泡在其体内呈均匀分布. 关键词： W(Mo)/Cu纳米多层膜 +辐照')" href="#">He⁺辐照 He团簇/泡 相转变     

Estimation of the sizes of disordered surface regions of Cu and Ag thin films using the ion transmission method

The dimensions of cluster phases that form on the surfaces of free Cu and Ag films in the case of different irradiation doses are estimated for the first time. It is shown that ion implantation leads to a significant decrease in the number of ions passed through a free film. Under the same conditions of the ion implantation, the concentration of impurity atoms on the surface and their depth-distribution profile for the free film differ noticeably from those for a bulk crystal.     

The simulation of two-beam high-dose ion implantation into solid targets

A physicomathematical model and a BEAM2HD program for the dynamic simulation of one-and two-beam high-dose ion implantation into multilayer and multicomponent targets are developed. The number of target layers is no more than three, and the number of sorts of atoms in each of the layers is no more than seven. The simulation is performed by the Monte Carlo method. Numerical results for the formation of C _x→3N _y→4 superhard layers by two-beam high-dose implantation of nitrogen ions into the Si₃N₄/C/Si₃N₄/Si system are presented.     

Difference in formation of carbon cluster cations by laser ablation of graphene and graphene oxide

The distributions of positive carbon cluster ions produced by laser ablation of graphene (G) and graphene oxide (GO) are found to be quite different. Under a typical experimental condition, narrow distributions of even-numbered clusters from C60+ to C162+ were observed for G, and broad distributions including even-numbered clusters from C100+ to C400+ and odd-numbered clusters from C189+ to C395+ were observed for GO. The threshold of laser energy for G is lower than that of GO. Further results of collision-activated dissociation mass spectrometry indicate that the cluster ions generated from G are structurally similar but are different with those generated from GO or nanodiamonds. It is proposed that the experimentally observed difference can be attributed to the different mechanisms behind the process. A top-down mechanism including both direct transformation of G to fullerene and fragmentation of large-sized fullerenes is suggested for the generation of carbon cluster cations in the process of laser ablation of G. For GO, the experimental results are close to those of nanodiamonds and other materials reported previously and can be explained by the generally accepted bottom-up mechanism.     

铜表面抗氧化性能与其覆盖石墨烯的层数依赖关系研究

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di-minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indi-cates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.     

Chemical- or radiation-assisted selective dealloying in bimetallic nanoclusters

A selective dealloying in bimetallic nanoclusters prepared by ion implantation has been found upon thermal annealing in oxidizing atmosphere or irradiation with light ions. In the first process, the incoming oxygen interacts preferentially with copper promoting Cu2O formation, therefore extracting copper from the alloy. In the second process the irradiation with Ne ions promotes a preferential extraction of Au from the alloy, resulting in the formation of Au-enriched "satellite" nanoparticles around the original AuxCu1-x cluster.     

Structural characteristics of nanocrystalline copper after carbon ion implantation

A gradient structure was produced in a pure copper plate by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer was reduced to nanoscale and the grain size increased gradually along the depth of the treated sample. In situ transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) observation was performed on the nanocrystalline copper after implantation of carbon. Carbon atoms first precipitated along the edges of the copper substrate or at the surface, then formed amorphous carbon layers. Subsequently, onion-like fullerenes were formed under electron-beam irradiation. The effects of ion implantation, electron beam irradiation, nanostructure of the substrate and interaction of C and Cu atoms on the formation of the onion-like fullerenes are discussed.