What controls deposition rate in electron-beam chemical vapor deposition?

The key physical processes governing electron-beam-assisted chemical vapor deposition are analyzed via a combination of theoretical modeling and supporting experiments. The scaling laws that define growth of the nanoscale deposits are developed and verified using carefully designed experiments of carbon deposition from methane onto a silicon substrate. The results suggest that the chamber-scale continuous transport of the precursor gas is the rate controlling process in electron-beam chemical vapor deposition.     

Energy storage and heat deposition in Cr,Yb,Er co-doped phosphate glass

Energy storage and heat deposition in Cr,Yb,Er co-doped phosphate glass were reported. A model based on rate equations was used to determine the energy storage from the free-oscillating output energy characteristics. The heat deposition was calculated by measuring the temperature rise of the glass rod. The results provided important information for the glass operating in Q-switched mode, and also for calculating the temperature profiles and cooling requirements of the glass under single shot and repetitive pulsed conditions.     

Pulsed laser deposition—UV laser sources and applications

Progress in material research and processing industry is fueled by the technique of pulsed laser deposition (PLD). High energy excimer lasers enable this technique since every material is amenable to their high photon energies. Spectral properties, temporal pulse and laser beam parameters of state of the art excimer lasers will be compared with frequency converted Nd:YAG lasers. Both quality and longevity of the deposited layers strongly depend on the degree of accuracy achieved in the thin film ablation and subsequent deposition process.     

The penetration, diffusion and energy deposition of high-energy photon

This paper presents a new theory for calculating the transport of high-energy photons and their secondary charged particles. We call this new algorithm characteristic line method, which is completely analytic. Using this new method we cannot only accurately calculate the transport behaviour of energetic photons, but also precisely describes the transport behaviour and energy deposition of secondary electrons, photoelectrons, Compton recoil electrons and positron-electron pairs. Its calculation efficiency is much higher than that of the Monte Carlo method. The theory can be directly applied to layered media situation and obtain a pencil-beam-modelled solution. Therefore, it may be applied to clinical applications for radiation therapy.     

Energy deposition and GDR emission in the reaction 209Bi(α,α′) at 240 MeV

Neutron fold distributions measured for the reaction ²⁰⁹Bi(α,α′) at 240 MeV have been analyzed with the help of Statistical Model calculations to determine the distribution of excitation energy, E_x, in the primary target fragments as a function of the projectile energy loss, EL. The reconstructed distributions in excitation energy feature a plateau which extends from the kinematical limit E_x = EL to very small excitations, indicating a variety of interactions of the beam particles with the target nucleus. The requirement of an additional coincidence with a light charged particle leads to the selection of a significant higher average excitation energy. Those results are extrapolated to explore the effects of including the excitation energy distributions in the analysis of previous GDR measurements in ²⁰⁸Pb. Corrections of the derived GDR parameters due to the partial transfer of excitation energy are suggested.     

Measurement of cluster–cluster interaction in liquids by deposition and AFM of silicon clusters onto HOPG surfaces

Experimental studies have been performed on unisize tungsten clusters constructed on a graphite surface by means of the scanning tunneling microscopy. It was found that the geometry of the clusters changes instantaneously from a monatomic-layer tungsten disk to a diatomic-layer structure between the cluster size of 10 and 11. We concluded that this transition is driven by a change in the dominant interaction from the attractive electrostatic interaction between the cluster and the surface to intracluster cohesive metallic interaction.     

Classical simulation of atomic beam focusing and deposition for atom lithography

We start from the intensity distribution of a standing wave (SW) laser field and deduce the classical equation of atomic motion.The image distortion is analyzed using transfer function approach. Atomic flux density distribution as a function of propagation distance is calculated based on Monte-Carlo scheme and trajectory tracing method.Simulation results have shown that source imperfection,especially beam spread, plays an important role in broadening the feature width,and the focus depth of atom lens for real atomic source is longer than that for perfect source.The ideal focal plane can be easily determined by the variation of atomic density at the minimal potential of the laser field as a function of traveling distance.     

Electron behaviour in CH4／H2 gas mixture in electron-assisted chemical vapour deposition

The behaviour of electrons in CH_{4}/H_{2} gas mixture in electron-assisted chemical vapour deposition of diamond is investigated using Monte Carlo simulation. The electron drift velocity in gas mixture is obtained over a wide range of E/P (the ratio of the electric field to gas pressure) from 1500 to 300000 (V/m kPa^{-1}). The electron energy distribution and average energy under different gas pressure (0.1－20kPa) and CH_{4} concentration (0.5%－10.0%) are calculated. Their effects on the diamond growth are also discussed. It is believed that these results will be helpful to the selection of optimum experimental conditions for high quality diamond film deposition.     

Sub-10 nm writing: focused electron beam-induced deposition in perspective

Over the past decade, focused electron beam-induced deposition has become a mature necessary part of the tool box engineers and scientists. This review presents the current state of the art in sub-10 nm focused electron beam deposition and describes the dominant mechanisms that have been found so far for this regime. Several questions regarding patterning at the highest resolution are addressed. What do our findings mean for using sub-10 nm focused electron beam deposition for industrial applications? And which fundamental issues remain to be solved? The overview shows that low-energy secondary electrons dominate the deposition process. As a result, the highest obtainable spatial resolution (averaged over many deposits) is limited by the mean free path of those electrons. Therefore, the only route to improve the resolution beyond the current appears to be using complexes that are sensitive to the high-energy electrons in the incident beam, rather than to the secondaries. Focused electron beam-induced deposition is compared to related techniques. It is on par with resist-based sub-10 nm electron beam lithography, showing similar spatial resolutions at similar electron doses. Regarding ion beam lithography, there are several distinguishing issues. Sub-10 nm writing has yet to be demonstrated for ion deposition, and although the deposition rate is relatively low when writing with electrons, electrons do not induce damage to the sample. The latter is a crucial advantage for focused electron beam-induced deposition. Finally, the main challenges regarding the applicability of sub-10 nm focused electron beam-induced deposition are discussed.     

Effect of chemical and magnetic interactions on fractal growth under deposition–diffusion–aggregation in some binary metal systems

We have investigated fractal growth phenomena in three binary metal systems; the Sc-Co, Sc-Cr and Sc-Ni systems. For the Sc-Co and Sc-Cr systems, we describe the observed evolution process of the fractals based on the deposition–diffusion–aggregation model and find that the magnetic interaction can play an important role in influencing the fractal dimension, i.e. the stronger the magnetic moment of the aggregating particles, the smaller the dimension of the resultant fractal. Comparing the observations in the three systems studied, it was found that the chemical interaction between two dissimilar atoms might prevent the formation of the fractal pattern during deposition, for example in the Ni-Sc system . PACS 61.43. Hv; 68.55. -a; 66.30. Ny; 75.50. -y     

Microstructure and photoluminescence of Er-doped SiOx films synthesized by ion beam assisted deposition

Er-doped SiO_x films were synthesized at 500℃ by ion beam assisted deposition technique and annealed at 800 and 1100℃ for 2h in the air atmosphere. The analysis by using energy dispersive x-ray spectroscopy showed that the ratio of Si to O decreased from 3 in the as-deposited films to about 1 in the annealed films. The investigation by using transmission electron microscopy and x-ray diffraction indicated that annealing induces a microstructure change from amorphous to crystalline. The grain sizes in the films were about 10 and 40nm when annealed at 800 and 1100℃, respectively. The films annealed at temperatures of 800 and 1100℃ exhibited a sharp photoluminescence (PL) at 1.533μm from the Er centres when pumped by 980nm laser. The influence of microstructure and grain size on the PL from Er-doped SiO_x films has been studied and discussed.     

The penetration, diffusion and energy deposition of high—energy photon＊

This paper presents a new theory for calculating the transport of high-energy photons and their secondary charged particles. We call this new algorithm characteristic line method, which is completely analytic. Using this new method we cannot only accurately calculate the transport behaviour of energetic photons, but also precisely describes the transport behaviour and energy deposition of secondary electrons, photoelectrons, Compton recoil electrons and positron－electron pairs. Its calculation efficiency is much higher than that of the Monte Carlo method. The theory can be directly applied to layered media situation and obtain a pencil-beam-modelled solution. Therefore, it may be applied to clinical applications for radiation therapy.     

X-ray diffraction study of effect of deposition conditions on α--β phase transition and stress evolution in sputter-deposited W coatings

Pure W and W-Cu-W trilayer coatings were deposited on an Fe substrate by d.c. magnetron sputtering. The α-β phase evolution, intragranular stress evolution in sputter-deposited W layer were investigated by x-ray diffraction. They are directly related to the film microstructure, density and adhesion. Therefore, control of the film stress and phase component transition is essential for its applications. The phase component transition from β-W to α-W and intragranular stress evolution from tensile to compressive strongly depend on the deposition parameters and can be induced by lowering Ar pressure and rising target power. The compressively stressed films with α-W phase have a dense microstructure and high adhesion to Fe substrate.     

Direct detonation initiation with thermal deposition due to pore collapse in energetic materials – towards the coupling between micro- and macroscale

In this work we investigate the initiation of detonations in energetic materials through thermal power deposition due to pore collapse. We solve the reactive Euler equations, with the energy equation augmented by a power deposition term. The deposition term is partially based on previous results of simulations of pore collapse at the microscale, modelled at the macroscale as hotspots. It is found that a critical size of the hotspots exists. If the hotspots exceed the critical size, direct initiation of detonation can be achieved even with a low power input, in contrast to the common assumption that a sufficient power is necessary to initiate detonation. We show that sufficient power is necessary only when the size of the hotspots is below the critical size. In this scenario, the so-called ‘explosion in the explosion’, the initial ignition does not lead to a detonation directly, but detonation occurs later as a result of shock-to-detonation transition in the region processed by the shock wave generated by the initial ignition.     

Fabrication and strain investigation of ZnO nanorods on Si composing sol–gel and chemical bath deposition method

High density vertically aligned ZnO nanorods arrays were prepared on Si substrate by the simple and facile sol–gel and chemical bath deposition combination technology. ZnO nanorods, preferentially oriented along the c-axis, were of the hexagonal wurzite structure. The lattice constants of ZnO nanorods a was shrunken by about 0.004 nm, which can result in about 1.29% mismatch between ZnO nanorods and Si substrate. The Raman spectrum was also analyzed in detail, and the result indicates that the stress between ZnO nanorods and Si substrate was about 0.227 GPa, which can be ascribed to the stress relaxation effect of the ZnO nanorods. The room temperature photoluminescence (PL) measurement result has shown a main deep level emission. The forming mechanism for ZnO nanorods was further analyzed.     

Post‐deposition annealing and crystallisation of Y-Ba-Cu-O thin films deposited on polycrystalline substrates

Superconducting thin films of Y-Ba-Cu-O have been prepared by 50 Hz ac sputtering on polycrystalline SrTiO₃, yttria-stabilized-ZrO₂, and MgO substrates. Films deposited on different substrate materials are required to be annealed at different temperatures to induce superconductivity. The optimum annealing temperature for a film depends on the reaction between the film and its substrate material. It appears that a correlation exists between the process of crystallisation and substrate-film reaction.     

Investigation of optical emission spectroscopy in diamond chemical vapor deposition by Monte Carlo simulation

The optical emission spectra(atomic hydrogen(H_α,H_β,H_γ),atomic carbon C(2p3s→2p~2:λ=165.7 nm)and radical CH(A~2Δ→X~2Π:λ=420-440 nm))in the gas phase process of the diamond film growth from a gas mixture of CH4 and H_2 by the technology of electron-assisted chemical vapor deposition (EACVD)have been investigated by using Monte Carlo simulation.The results show that the growth rate may be enhanced by the substrate bias due to the increase of atomic hydrogen concentration and the mean temperature of electrons.And a method of determining the mean temperature of electrons in the plasma in-situ is given.The strong dependence on substrate temperature of the quality of diamond film mainly attributes to the change of gas phase process near the substrate surface.     

Magnetic anisotropy in Ni–Si nanoparticle films produced by ultrashort pulsed laser deposition

Pulsed laser deposition (uPLD) in vacuum by means of subpicosecond laser pulses is a powerful, versatile technique for the production of films constituted by nanoparticles. On impact with the deposition substrate, the nanodrops ejected from the target assume an oblate ellipsoidal shape, solidifying with the major cross-section parallel to the substrate plane. These features and the difficult coalescence among the deposited nanoparticles are peculiar characteristics specific to the films obtained by uPLD. In the case of magnetic nanoparticle films obtained by means of this technique, a magnetization isotropy in the film plane and a hard magnetization axis orthogonal to the film plane are expected. This simple assumption, generated by the specific shape and orientation of the deposited nanoparticles, was not experimentally verified up to now. The present investigation represents the first experimental validation of magnetic anisotropy, determined by the peculiar morphology and topology of the constituent particles, in the uPLD Ni_xSi_100−x nanoparticle films. The in-plane isotropic magnetization behaviour, as well as the presence of a hard magnetization axis perpendicular to the sample surface were demonstrated for all investigated films. The difficult coalescence among the magnetic nanoparticles, even at high Ni volume fractions, is confirmed by the behaviour of the initial magnetization curve, typical for single-domain nanoparticles systems.     

Substrate and pretreatment dependence of Cu nucleation by metal–organic chemical vapor deposition

The nucleation of copper (Cu) with (hfac)Cu(VTMS) organometallic precursor is investigated for Si, SiO₂, TiN, and W₂N substrates. As the deposition temperature is increased, the dominant growth mechanism is observed to change from the nucleation of Cu particles to the clustering of Cu nuclei around 180 °C independent of the employed substrates. It is also observed that the cleaning of substrate surfaces with the diluted HF solution improves the selectivity of Cu nucleation between TiN and SiO₂ substrates. Dimethyldichlorosilane treatment is found to passivate the surface of TiN substrate, contrary to the generally accepted belief, when the TiN substrate is cleaned by H₂O₂ solution before the treatment.     

Nanoparticulate-induced toxicity and related mechanism in vitro and in vivo

In urban areas, the quantity of exhaust particles from vehicle emissions is tremendous and has been regarded as the main contributor to particulate matter (PM) pollution. Recently, the nano-sized PM on public health has begun to raise the attention. The increased toxicity of nanoparticulate can be largely explained by their small size, high airborne concentration, extensive surface area and high content of organic carbon and transition metals. We have attempted to address the toxicity of nano sized-particlulate matter by comparing various particulates including micro-SiO₂ (mSiO₂), nano-SiO₂ (nSiO₂), micro-TiO₂ (mTiO₂), and nano-TiO₂ (nTiO₂) in RAW264.7 cells and in vivo. The cell viability of all particulates decreased dose dependently. 24-h incubation with nSiO2 demonstrated apoptosis in RAW264.7 using Annexin-V binding immunofluorescent microscopy, but not in any other particulates. In vivo, cytotoxicity of nanosized was higher than micro-sized particulates. As higher the concentration of particulates, the more pulmonary injury and neutrophilic infiltration were observed in nano-sized than micro-sized particulates, respectively. Particularly, 5.0 mg/kg of mTiO₂ never shows any increase of neutrophile even with high cellularity of total cells and macrophages. From these results, we suggested that particulate-induced respiratory toxicity be influenced by component, size, and dose of particulates including the characteristic nature of the target cells in vitro and in vivo.