Effects of temperature and pressure on CVD diamond growth from the C-H-O system

Received: 28 August 1997/Accepted: 18 November 1997     

Thermodynamics of diamond film deposition at low pressure from chlorinated precursors

3 and C₂H₂ concentrations at growth surface and accelerating abstraction of surface-terminating atoms. The effects of Cl addition on diamond film quality are also discussed. Received: 1 May 1998 / Accepted: 15 October 1998     

Novel technique for hetero-epitaxial diamond film growth on cubic boron nitride from iron carbide at high temperature and high pressure

Cubic boron nitride (c-BN) crystals about 0.1–0.3 mmin dimension were treated with iron carbide powders (high purity 99%) with size of 80–100 mesh at a high temperature of 1620 K and a high pressure of 5.2 GPa. It was found that hetero-epitaxial diamond films have been grown on the c-BN from iron carbide. The formation of dia-mond films on the cubic boron nitride can be confirmed by laser Raman spectra, face scan of elements and reflective high-energy electron diffraction. It was suggested that diamond films could be epitaxially formed on the c-BN through decomposition of iron carbide. This approach provides a possible and very effective way to realize hetero-epitaxial growth of homogeneous and large-area diamond films on c-BN, which is different from the conventional technique using a chemical vapor deposition method. Received: 20 December 2000 / Accepted: 9 January 2001 / Published online: 28 February 2001     

Laser diagnostics of NO reburning in fuel-rich propene flames

Absolute NO concentrations were measured by laser-induced fluorescence (LIF) in three different fuel-rich non-sooting propene flames (φ=1.5, 1.8 and 2.3). The experiments were performed in low-pressure premixed propene flames with 0.2%-1% NO added. Laser diagnostics was applied as a tool for investigating reburn chemistry. The Q₂(25.5) line in the A-X(0,0) band was excited because of the small temperature dependence of its ground state population. The NO fluorescence lifetimes were measured directly and compared to theoretical values. The initial NO levels are strongly reduced in all three flames. According to modeling results, the HCN mole fraction increases strongly with stoichiometry. As guidelines for laser diagnostics applications in such systems, the modeling results were analyzed with respect to the main reaction channels and reaction partners in fuel-rich flames. Received: 1 March 2000 / Revised version: 20 April 2000 / Published online: 20 September 2000     

A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals

One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond, through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)₂₃C₆, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic theory during quenching from HPHT to room temperature and ambient pressure. Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn     

Phase diagram and LPE growth of strongly Sn- and Te-doped InGaAs

Sn and Te are used as n-type dopants in LPE In_0.53Ga_0.47 As contact layers, and carrier concentrations up to 2.2·10¹⁹ cm^–3 are obtained for both dopants. The distribution coefficients are k_Sn=(1.55±0.10)·10^–3 and k_Te0.11, respectively. With Sn a better control of the doping level is achieved than with Te, but the large amount of Sn necessary strongly affects the phase diagram. In order to facilitate the growth of InGaAs:Sn, the phase equilibria in the system In-Ga-As-Sn near 600° C are established. The liquid interaction parameters (Ga-Sn) and (As-Sn) are determined as 700 and -2050 cal/mole, respectively.     

Spatially resolved absolute concentration and fluorescence-lifetime determination of H2CO in atmospheric-pressure CH4/air flames

Using laser-induced fluorescence (LIF), spatially resolved concentration profiles of formaldehyde (H₂CO) were obtained in the preheating zone of atmospheric-pressure premixed CH₄/air flames stabilized on the central slot of a multiple-slot burner similar in construction to domestic boilers. The isolated pQ₁(6) rotational line (339.23 nm) in the 2¹ ₀4¹ ₀ vibronic combination transition in the ?¹A₂- ¹A₁ electronic band system around 339 nm was excited in the linear LIF intensity regime. For a quantification of quenching effects on the measured LIF signal intensities, relative fluorescence quantum yields were determined from direct fluorescence lifetime as a function of height above the slot exit. Absolute H₂CO number densities in the flames were evaluated from a calibration of measured LIF signal intensities versus those obtained in a low-pressure sample with a known H₂CO vapor pressure. Peak concentrations in the slightly lean and rich flames reached (994±298) and (174±52) ppm, respectively. Received: 25 September 2000 / Published online: 30 November 2000     

Pulsed-laser-induced transformation path of graphite to diamond via an intermediate rhombohedral graphite

The new phase transformation of hexagonal graphite to cubic diamond was experimentally produced without catalyst, using a high-power pulsed laser. Interestingly, by the X-ray diffraction spectra, it was proved that this transition was not direct, but through an intermediate rhombohedral phase. Furthermore, it is important that the rhombohedral phase, as the theoretical transformation path of hexagonal graphite to cubic diamond, was first truly substantiated by our experimental results. The transformation mechanism was suggested that diamond with hexagonal structure was obtained by the direct transforming of hexagonal graphite to hexagonal diamond, and diamond with cubic structure was formed by the indirect transforming, i.e., hexagonal graphite to rhombohedral graphite to cubic diamond. Received: 7 February 2000 / Accepted: 28 March 2000 / Published online: 9 November 2000     

Simulation of polycrystalline 3D film growth: An investigation of the evolution of grain size and texture in diamond films

An analytical method for simulating gas phase film growth has been developed and used to study the growth of diamond films during prolonged deposition, i.e. the film thickness is much larger than the lateral grain size. From a model system composed of 10⁴ grains, reliable results can be evaluated for the growth of diamond films by (111) and (001) deposition under different initial conditions and with varying growth parameters. It is demonstrated that the rate of structure evolution is sensitively influenced by the aspect ratio of diamond crystal. A near-linear proportionality between the average grain size and the thickness of films can be approximately yielded for a large film thickness which is about 10 times of the average distance of the nuclei. The proportionality constant varies for a statistical nucleation from 0.0056 to 0.43 by changing the aspect ratio. Furthermore, the orientational distribution is drastically narrowed down so that the probability of coalescence of grains with a slight orientational difference is considerably increased. Received: 28 September 2000 / Accepted: 19 February 2001 / Published online: 3 May 2001     

2-D absolute OH concentration profiles in atmospheric flames using planar LIF in a bi-directional laser beam configuration

1 (6) rotational line in the A²Σ⁺(v^′=0)←X²Π(v^′′=0) band of OH at 309 nm. The requirements for obtaining a good signal-to-noise ratio for the technique are discussed and the possibilities of single-shot measurements are investigated. Received: 31 October 1996/Revised version: 3 December 1996     

Raman-Rayleigh-LIF measurements of temperature and species concentrations in the Delft piloted turbulent jet diffusion flame

We report a series of Raman-Rayleigh-LIF measurements in two turbulent natural-gas jet diffusion flames produced by the Delft piloted jet diffusion flame burner. The main objective of the Raman-Rayleigh-LIF measurements was to obtain detailed information on the major species concentrations in the flames. The measurements provide simultaneous data on temperature, the concentrations of the major species and the radicals OH and NO and mixture fraction. The application of the Raman technique in the undiluted natural-gas flames proves to be very challenging because of the high fluorescence interference levels. The interference contributions to the recorded Raman signals are identified and subtracted using empirical correlations between the Raman signals and the signals on fluorescence interference monitor channels. The calibration and data reduction of the Raman-Rayleigh and LIF signals are discussed in detail. The resulting dataset compares excellently with data from previous experiments. Because the Raman-Rayleigh-LIF data provide quantitative concentrations and accordingly quantitative mixture fractions, they form a valuable and useful extension of the existing database for the Delft piloted jet diffusion flame burner. Received: 19 October 1999 / Revised version: 31 January 2000 / Published online: 7 June 2000     

The analysis of the precision of single shot 2λ-CARS temperature measurements in hydrogen

Received: 16 October 1996/Revised version: 17 March 1997     

Interaction of laser radiation with TNT with respect to the laser neutralisation of AP mines

According to UN estimations there are between 80 and 115 million activated landmines worldwide. These mines, or other unexploded ordnance (UXO), can be triggered accidentally and kill or injure more than 2000 civilians per month. The most common explosive in these mines is trinitrotoluene (TNT). In this paper, the potential of some of the most promising lasers for mine neutralisation is investigated, namely an ArF laser, a KrF excimer laser and a Nd:YAG solid-state laser. We have studied the interaction between laser beams emitting at λ=193 nm, 248 nm and 1060 nm and a bare solid sample of TNT of approximately 15 mg. Using pulsed excimer radiation at λ=193 nm, with an energy density up to 1 J/mm², ablation of the TNT without any deflagration has been achieved. At λ=248 nm, using the KrF excimer laser with a pulse duration of 30 ns and a repetition rate of 5 Hz, the TNT sample started melting and burning after an irradiation of 10 s. Preliminary results with the Nd:YAG solid-state laser operating in cw emission have shown that the irradiated sample exhibits the desired burning behaviour even after the exposure is stopped. Received: 14 December 2000 / Accepted: 18 December 2000 / Published online: 20 June 2001     

Electrochemical growth of copper single crystals in pores of polymer ion-track membranes

Copper single-crystals are grown by a galvanic method, using etched ion tracks in a polymer foil as templates. The copper deposition is carried out by reversible pulse electrolysis in an ultrasonic field. The method applied for this purpose permits fabrication of stable standing cylindrical single crystals with diameters in the nanometer and micrometer range with high aspect ratio and density of 10⁵–10⁷ per cm² on a large area. The experimental results obtained in this way are compared with the results obtained by direct current plating under ultrasonic treatment and sole reversible electrolysis. The effects of all these deposition processes on the structure of copper claddings are shown. Received: 12 May 1999 / Accepted: 14 May 1999 / Published online: 24 June 1999     

Time-, wavelength-, and polarization-resolved measurements of OH (A 2Σ+ ) picosecond laser-induced fluorescence in atmospheric- pressure flames

Laser-induced fluorescence of OH (A ²Σ⁺, v’=1) was measured in hydrogen/oxygen and hydrogen/air/nitrogen flames using laser pulses of 80 psec duration. A 2D signal acquisition scheme simultaneously employed wavelength, temporal, and polarization resolution. The signals emitted in different rotational branches exhibit polarization-dependent intensities, depending on the rotational branch of the absorption line used. It is possible to select experimental conditions such that rotational and vibrational relaxation as well as electronic quenching can be monitored simultaneously. Advantages and limitations of the experimental approach are discussed. Numerical simulations are presented of the LIF spectra affected by energy transfer. Received: 29 March 1999 / Revised version: 14 June 1999 / Published online: 27 October 1999     

Epitaxial growth of metals with high Ehrlich–Schwoebel barriers and the effect of surfactants

Interlayer diffusion in epitaxial systems with a high energy barrier at the atomic steps – the so-called Ehrlich–Schwoebel (ES) barrier – is strongly reduced. As a consequence of this, a continuous accumulation of roughness takes place during growth. This undesirable effect can be corrected by using surfactant agents. We have studied the influence of the ES barrier on the preparation of epitaxial films on Cu(111), and the surfactant effect of a monolayer of Pb. Received: 21 April 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999     

Two-dimensional imaging of glyoxal (C2H2O2) in acetylene flames using laser-induced fluorescence

2 H₂O₂). Laser-induced fluorescence spectra from glyoxal vapor using the same excitation wavelength of 428 nm showed the same strongest lines as the signal from the flame. Glyoxal was visualized in two different modes; two-dimensional imaging and a spatial-spectral mode where spectra were obtained at different spatial positions in the flame simultaneously. For the premixed laminar rich flame it is shown that glyoxal is produced early in the flame, before the signals for C₂ and CH appear. For the turbulent non-premixed flames it is shown that glyoxal is produced in a layer on the fuel rich side of the flames. Here the fuel is premixed with ambient air. This layer is thin and has a high spatial resolution. The general trend was that the glyoxal signal appeared in regions with a lower temperature compared with the emission from C₂ and CH. The imaging of glyoxal in turbulent acetylene flames is a promising tool for achieving new insight into flame phenomena, as it gives very good structural information on the flame front. Tests so far do not indicate that the detected glyoxal is a result of photo-production. To our knowledge, this is the first detection of glyoxal in flames using laser-induced fluorescence. Received: 19 December 1996/Revised version: 26 May 1997     

Nitrogen atom detection in low-pressure flames by two-photon laser-excited fluorescence

Nitrogen atoms have been detected in stoichiometric flat premixed H₂/O₂/N₂ flames at 33 and 96 mbar doped with small amounts of NH₃, HCN, and (CN)₂ using two-photon laser excitation at 211 nm and fluorescence detection around 870 nm. The shape of the fluorescence intensity profiles versus height above the burner surface is markedly different for the different additives. Using measured quenching rate coefficients and calibrating with the aid of known N-atom concentrations in a discharge flow reactor, peak N-atom concentrations in these flames are estimated to be on the order of 10¹²–5×10¹³ cm^–3; the detection limit is about 1×10¹¹ cm^–3.