Quantitative measurements of the CH radical in sooting diffusion flames at atmospheric pressure

The potential of Laser Induced Fluorescence detection of the CH radical using C–X (0–0) excitation is investigated in a sooting methane/air diffusion flame at atmospheric pressure. Fluorescence is detected using the very narrow (<0.4 nm) Q-branch of the C–X (0–0) band, which enables the measurement of CH in sooting flames without interference from PAH fluorescence and soot emissions. Absolute concentrations are obtained using Cavity Ring Down Spectroscopy. 1D CH profiles in the sooting zone are recorded using a CCD camera with an excellent signal-to-noise ratio. The C–X (0–0) excitation associated with Q-branch detection is shown to be three times more efficient than the B–X scheme. Received: 4 March 2002 / Revised version: 5 November 2002 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +33-3/2033-6463, E-mail: eric.therssen@univ-lille1.fr     

Growth of a textured quasicrystalline phase in Ti-Ni-Zr films prepared by pulsed laser deposition

The preparation in thin film form of the known icosahedral phase in Ti-Ni-Zr bulk alloys has been investigated as a function of substrate temperature. Films were deposited by pulsed laser deposition on sapphire substrates at temperatures ranging from room temperature to 350 °C. Morphological and structural modifications have been followed by grazing-incidence and θ–2θ X-ray diffraction, transmission electron diffraction and imaging. Chemical composition has been analyzed by electron probe microanalysis. The in-depth variation of composition has been studied by secondary neutral mass spectroscopy. We show that pulsed laser deposition at 275 °C makes the formation of a 1-μm-thick film of Ti-Ni-Zr quasicrystalline textured nanocrystallites possible. Received: 7 June 2001 / Accepted: 18 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +33-3/8357-6300, E-mail: brien@mines.u-nancy.fr     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Femtosecond study of surface structure and composition and time-resolved spectroscopy in metals

Surface structuring and compositioning in aluminum alloy 2024-T3 were demonstrated using a femtosecond pulse laser. Surface nanostructuring was developed as a function of laser parameters and the surface micrographs of the scanning electron microscopy were characterized as a function of incident laser fluence. Surface compositioning was performed by selectively removing the elements on the surface of the sample. Femtosecond studies of highly excited electrons were performed by a pump–probe technique, and the thermalization time was found to be in a range of 1.5–3 ps, increasing with incident fluence. The time-resolved measurement is well matched to the numerical calculation. Received: 6 September 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +1-405/744-6811, E-mail: dou@okstate.edu     

Strong blue photoluminescence from aligned silica nanofibers

Photoluminescence (PL) and infrared spectra of aligned silica nanofibers are investigated. Two striking strong blue luminescence emissions have been found at room temperature. This suggests that the silica nanofibers could be a candidate material for a blue-light emitter. The intensity of the PL emission decreases after annealing, which can be interpreted as the decrease of the oxygen deficiency resulting in the reduction of radiative recombination centers. Infrared spectra provide further evidence of this conclusion, where the enhancement of Si–O absorption is observed in annealed samples. Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-10/8264-9531, E-mail: ldai@vip.sina.com     

The characteristics of surface acoustic waves on AlN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO₃, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO₃ substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO₃ substrate. The TCF of a SAW on an AlN/LiNbO₃ device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO₃ substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO₃ substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V_p) of the SAW on an AlN/LiNbO₃ substrate was significantly increased by the increase of AlN thickness (h/λ). Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +886-7/525-4199, E-mail: ycc@ee.nsysu.edu.tw     

Preparation of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowires by calcining the precursor powders synthesized in a novel inverse microemulsion

Manganese oxide (hausmannite) nanowires were prepared by annealing precursor powders at a temperature of 800 °C for 3 h, which were produced in a novel inverse microemulsion (IμE) system. The microstructures of the as-prepared Mn₃O₄ nanowires were investigated by means of X-ray diffraction, transmission electron microscopy, and Raman spectra. It has been found that the Mn₃O₄ nanowires were relatively straight and their surfaces were smooth with a typical diameter of 75–150 nm. The formation mechanism of the Mn₃O₄ nanowires is discussed. Received: 30 May 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn     

Stress anisotropy in circular planar magnetron sputter deposited molybdenum films and its annealing effect

As part of the program to develop a free-standing thin-film filter for soft X-ray optics application, stress anisotropy in the molybdenum films deposited by dc circular planar magnetron sputtering were studied by X-ray diffraction (XRD) as a function of sputtering argon gas pressure over a range of 0.8–1.5 Pa. Surface morphology of the films has been investigated by optical microscopy and scanning tunneling microscopy (STM). It is found that, for the film deposited at 0.8 Pa pressure, the stresses are more compressive in the tangential than in the radial direction; the highest compressive stress exists in the center area. The film deposited at 1.5 Pa pressure has the highest stress anisotropy, and the stresses are less tensile in the tangential than in the radial direction. Annealing in vacuum is more effective in reducing tensile stress and stress anisotropy in the tensile stressed film than in the compressively stressed film. Received: 14 September 2001 / Accepted: 21 January 2002 / Published online: 5 July 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6598-6323, E-mail: ygwu@mail.tongji.edu.cn     

Production of biologically inert Teflon thin layers on the surface of allergenic metal objects by pulsed laser deposition technology

Allergic-type diseases are current nowadays, and they are frequently caused by certain metals. We demonstrated that the metal objects can be covered by Teflon protective thin layers using a pulsed laser deposition procedure. An ArF excimer laser beam was focused onto the surface of pressed PTFE powder pellets; the applied fluences were 7.5–7.7 J/cm². Teflon films were deposited on fourteen-carat gold, silver and titanium plates. The number of ablating pulses was 10000. Post-annealing of the films was carried out in atmospheric air at oven temperatures between 320 and 500 °C. The thickness of the thin layers was around 5 μm. The prepared films were granular without heat treatment or after annealing at a temperature below 340 °C. At 360 °C a crystalline, contiguous, smooth, very compact and pinhole-free thin layer was produced; a melted and re-solidified morphology was observed above 420 °C. The adhesion strength between the Teflon films and the metal substrates was determined. This could exceed 1–4 MPa depending on the treatment temperature. It was proved that the prepared Teflon layers can be suitable for prevention of contact between the human body and allergen metals and so for avoidance of metal allergy. Received: 12 June 2002 / Accepted: 13 June 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. E-mail: bhopp@physx.u-szeged.hu     

Early stages of laser graphitization of diamond

A mechanism for photographitization of a free diamond surface is proposed. The quantum-kinetic rate of this process is determined. The graphitization rate is close to zero if the activation energy of the graphitization process is taken as being equal to the binding energy of a carbon atom with the surface (i.e. equal to the sublimation energy of a carbon atom). On the contrary, if the activation energy is close to the energy of C–C bonds, the graphitization process may occur at a noticeable rate and be observed under ‘relatively smooth’ experimental conditions. The temperature rise leads to a considerable increase in the graphitization rates. Preliminary experimental data on the low-rate laser ablation of diamond are presented to support the proposed model of photographitization. An early stage of laser-induced graphitization in the bulk of diamond is also considered. It is found that the nucleation of a ‘tiny graphite drop’ is possible in the bulk of the diamond inside the focal area of a laser beam; the ‘graphite drop’ growth causing the appearance of mechanical stresses in the surrounding regions. The maximum size of the graphite drop is determined, which, when exceeded, leads to mechanical damage of the sample and to a change in the mechanism of laser graphitization. An evident mechanical criterion for laser-induced damage of diamond is proposed. Received: 2 October 2002 / Accepted: 5 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail: stvn@stankin.ru     

Effect of exposure to air on sheet resistance and phase composition of Co silicides annealed at a low temperature of 470 °C

Attention has been attracted to Co silicides due to their superior properties in deep-submicron integrated circuit technology. In this paper, the effect of exposure to air on the properties of Co silicides has been studied. Co films of 20-nm thickness were deposited onto polysilicon layers using Ar sputtering. After deposition, the samples were exposed to air at room temperature for different times, ranging from 0 to 48 h, before a rapid thermal annealing (RTA) at 470 °C. It is found that exposure to air significantly changes the sheet resistance (R_s) and the phase composition of the silicides. The sample exposed to air for 48 h has R_sof∼71 Ω/sq, which is about 10% lower than that for the sample annealed immediately. This is due to the fact that more Co₂Si phase and less CoSi phase are formed in the former sample. The mechanism can be attributed to the gases in air (e.g. O₂), which contaminate the Co/Si interface and act as a kinetic barrier during the subsequent RTA. It has been demonstrated that gaseous contamination from air strongly influences the CoSi_x phase transformation. Received: 3 June 2002 / Accepted: 29 June 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. E-mail: qiang.huang@philips.com     

High-resolution electron microscopy of individual metallofullerene molecules on the dipole orientations in peapods

Electron microscopy with atomic sensitivity enables us to obtain a direct image of the intra-molecular structure of metallofullerenes encapsulated inside single-walled carbon nanotubes. By a comparison of high-resolution images with a simulation to extract the relative atom positions for encaged metal atoms in each molecule, the distribution of the molecular orientations and interactions between adjacent molecules in metallofullerene peapods have been statistically analyzed. The results are suggestive of strong interactions between fullerene–fullerene and fullerene–tube in peapods at room temperature. Received: 10 October 2002 / Accepted: 25 October 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/61-6310, E-mail: suenaga-kazu@aist.go.jp     

Filling boron nitride nanotubes with metals

The authors’ endeavors over the last few years with respect to boron nitride (BN) nanotube metal filling are reviewed. Mo clusters of 1–2 nm in size and FeNi Invar alloy (Fe ∼60 at. %; Ni ∼40 at. %) or Co nanorods of 20–70 nm in diameter were embedded into BN nanotube channels via a newly developed two-stage process, in which multi-walled C nanotubes served as templates for the BN multi-walled nanotube synthesis. During cluster filling, low-surface-tension and melting-point Mo oxide first filled a C nanotube through the open tube ends, followed by fragmentation of this filling into discrete clusters via O₂ outflow and C→BN conversion within tubular shells at high temperature. During nanorod filling, C nanotubes containing FeNi or Co nanoparticles at the tube tips were first synthesized by plasma-assisted chemical vapor deposition on FeNi Invar alloy or Co substrates, respectively, and, then, the nanomaterial was heated to the melting points of the corresponding metals in a flow of B₂O₃ and N₂ gases. During this second stage, simultaneous filling of nanotubes with a FeNi or Co melt through capillarity and chemical modification of C tubular shells to form BN nanotubes occurred. The synthesized nanocomposites were analyzed by scanning and high-resolution transmission electron microscopy, electron diffraction, electron-energy-loss spectroscopy and energy-dispersive X-ray spectroscopy. The nanostructures are presumed to function as ‘nanocables’ having conducting metallic cores (FeNi, Co, Mo) and insulating nanotubular shields (BN) with the additional benefit of excellent environmental stability. Received: 10 October 2002 / Accepted: 25 October 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp     

Experimental validation of a mass- efficiency model for an indium liquid-metal ion source

A model is derived linking microdroplet emission of a liquid-metal ion source (LMIS) to the actual current–voltage characteristic and operating temperature. All parameters were experimentally investigated using an indium LMIS, confirming the relationships found. The model allows for the first time the optimisation of a LMIS for low droplet emission at high emission currents. This is very important for application as a thruster, which has been developed at ARC Seibersdorf research. It can be also used to extrapolate droplet emission values along the current–voltage characteristic. Received: 29 January 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +43-50550/3366, E-mail: martin.tajmar@arcs.ac.at     

Carbon nanotubes formed in graphite after mechanical grinding and thermal annealing

Multi-walled carbon nanotubes with cylindrical and bamboo-type structures are produced in a graphite sample after mechanical milling at ambient temperature and subsequent thermal annealing up to 1400 °C. The ball milling produces a precursor structure and the thermal annealing activates the nanotube growth. Different nanotubular structures indicate different formation mechanisms: multi-wall cylindrical carbon nanotubes are probably formed upon micropores and the bamboo tubes are produced because of the metal catalysts. A two-dimensional growth governed by surface diffusion is believed to be one important factor for the nanotube growth. A potential industrial production method is demonstrated with advantages of large production quantity and low cost. Received: 17 May 2002 / Accepted: 12 September 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +61-2/6125-8338, E-mail: ying.chen@anu.edu.au     

Line width of an atom laser

We describe the measurement of the line width of an atom laser beam extracted from a Bose–Einstein condensate. Using a novel magnetic resonance imaging technique, we find that the energy width of the atom laser beam is Fourier-limited by the duration of the output-coupling process. Received: 25 July 2002 / Revised version: 28 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +41-1/633-1254, E-mail: koehl@iqe.phys.ethz.ch     

A simple wet-chemical synthesis and characterization of CuO nanorods

Using a simple wet-chemical route, we synthesized CuO nanorods with diameters of ca. 5–15 nm and lengths of up to 400 nm. The purity, crystallinity, morphology, structure features, and chemical composition of the as-prepared CuO nanorods were investigated by powder X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Received: 22 March 2002 / Accepted: 12 June 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn     

Transient-diffusion effects

Transient effects on diffusion and activation during post-implantation anneals are a major obstacle for the further miniaturization of ultra-large-scale integrated semiconductor devices. The article reviews recent developments in the simulation of such phenomena with particular emphasis on models for the kinetics of self-interstitial agglomerates and boron–interstitial clusters. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-9131/761-212, E-mail: pichler@iis-bfhg.de     

Growth mechanism of carbon nanotubes produced by pyrolysis of a composite film of poly (vinyl alcohol) and fly ash

We produced carbon nanotubes (CNTs) by pyrolysis of a composite film of poly (vinyl alcohol) (PVA) with fly ash (FA) at 500°C for 10 min under nitrogen. The composite films were prepared by a suspension of PVA and FA in deionized water and cast onto glass petri dishes. The morphologies of the CNTs were observed in the images of scanning and transmission electron microscopy, showing different types of structures, e.g. whiskers, branches, ropes and graphene sheets. The widths of the CNTs measured varied in the range 18–80 nm. X-ray photoelectron spectroscopy analysis showed five types of carbon binding peaks, C–C/C–H (∼77%), C–O–H (∼9%), –C–O–C (∼5%), C=O (∼5%) and –O–C=O (∼3%). From an image of a broken CNT, a mechanism was proposed for the formation of CNTs. The CNTs grown on FA surfaces have potential for the fabrication of high-strength composite materials with polymer and metal.     

Ion-beam synthesis and growth mechanism of diamond-like materials

Opposite to most other deposition methods, the dominating nucleation and growth mechanism during ion-beam deposition of energetic ions in the range between 10 eV and 10 keV occurs in a region of a few nanometers below the surface of the growing film. This process is called ‘subplantation’ – emphasizing the implantation of ions into a subsurface region. Ordering and phase formation is a result of the interaction of the deposited ions with the solid state that takes place within the short time scale of femto- and picoseconds. This extreme non-equilibrium process can result in metastable amorphous or crystalline structures. This review will present several examples of the influence of the deposition parameters on the properties of diamond-like materials synthesized using mass-selected ion-beam deposition. Furthermore, several existing models of the deposition process will be presented and critically discussed. Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003 RID="*" ID="*"Corresponding author. Fax: +49-551/39-4493, E-mail: carsten.ronning@phys.uni-goettingen.de