Formation and crystal structure of metallic inclusions in a HPHT as-grown diamond single crystal

One of the most important characteristics associated with crystal growth technology is the entrapment of inclusions by the growing crystal. Diamond single crystals prepared under high temperature-high pressure (HPHT) usually contain metallic inclusions. In the present paper, metallic inclusions in a diamond grown from a Fe-Ni-C system using the HPHT method have been, for the first time, systematically examined by transmission electron microscopy (TEM). Energy dispersive X-ray spectrometry (EDS) , combined with selected area electron diffraction (SAD) patterns, has been used to identify the chemical composition and crystal structure of the metallic inclusions. The metallic inclusions were found to be composed mainly of cubic γ-(FeNi), face-centered cubic (FeNi)₂₃C₆, ortho-rhombic Fe₃C and hexagonal Ni₃C, which may have been formed through the entrapment of molten catalyst by the growth front or through reaction of the trapped melt with contaminants in the diamond. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 16 August 2000     

Effects of Fe additive on diamond crystallization from carbonyl nickel powders-C system under HPHT condition

In this paper, diamond crystallization from carbonyl nickel powders-C and carbonyl nickel powders + Fe–C systems are investigated in detail at a pressure of 6.0 GPa and temperatures ranging from 1410°C–to 1435°C by temperature gradient growth. The effects of Fe additive on the crystal morphology are discussed in the diamond crystallization process.Furthermore, Fourier infrared measurement results indicate that the spectrum of the diamond obtained from Ni + Fe–C system after annealing treatment is nearly consistent with that of natural diamond crystal. We believe that this study is of benefit to a further understanding of the growth mechanism of natural diamond.     

Inclusions in large diamond single crystals at different temperatures of synthesis

The inclusions in large diamond single crystals have effects on its ultimate performance, which restricts its industrial applications to a great extent. Therefore, it is necessary to study the inclusions systematically. In this paper, large diamond single crystals with different content values of inclusions are synthesized along the(100) surface by the temperature gradient method(TGM) under 5.6 GPa at different temperatures. With the synthetic temperature changing from 1200?C to 1270?C,the shapes of diamonds change from plate to low tower, to high tower, even to steeple. From the microscopic photographs of the diamond samples, it can be observed that with the shapes of the samples changing at different temperatures, the content values of inclusions in diamonds become zero, a little, much and most, correspondingly. Consequently, with the temperature growing from low to high, the content values of inclusions in crystals increase. The origin of inclusions is explained by the difference in growth rate between diamond crystal and its surface. The content values of inclusions in diamond samples are quantitatively calculated by testing the densities of diamond samples. And the composition and inclusion content are analyzed by energy dispersive spectroscopy(EDS) and x-ray diffraction(XRD). From contrasting scanning electron microscopy(SEM) photographs, it can be found that the more the inclusions in diamond, the more imperfect the diamond surface is.     

UV detectors based on epitaxial diamond films grown on single-crystal diamond substrates by vapor-phase synthesis

The prospects for use of CVD-technology for epitaxial growth of single-crystal diamond films of instrumental quality in UHF plasma for the production of optoelectronic devices are discussed. A technology for processing diamond single crystals that provides a perfect surface crystal structure with roughness less than 0.5 nm was developed. It was demonstrated that selective UV detectors based on synthetic single-crystal diamond substrates coated with single-crystal films can be produced. A criterion for selecting clean and structurally perfect single crystals of synthetic diamond was developed for the epitaxial growth technology.     

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     

Nanostructuring of single crystal diamond by reactive and non-reactive accelerated cluster erosion

Reactive accelerated cluster erosion (RACE) of single crystal artificial diamond has been used to fabricate various nano- and microstructures. Carbondioxide clusters of about 1000 molecules are accelerated to 100 keV to act as the eroding agent. Using movable shadow masks, the accelerated cluster beam may erode staircase structures acting as an optical grating. A cycloid gear has been generated via a stationary nickel mask. Non-reactive accelerated cluster erosion using argon clusters will be considered for comparison. Received 30 November 2000     

高温超导衬底大尺寸LaAlO_3单晶体生长研究

铝酸镧(LaAlO3)单晶是超导研究领域使用最普遍的单晶体之一,详细介绍了采用下称重,CZ法(Czo-chralski)生长大尺寸(Φ80mm)LaAlO3单晶的工艺条件,并对影响晶体质量的主要因素进行了分析、讨论,给出了解决晶体质量问题的手段和有效途径。     

Nanofriction studies of reactively or non-reactively cluster-eroded single crystal diamond

Friction properties of cluster-eroded surfaces of synthetic single crystal diamond (Monodite) are compared after erosion with high-speed CO₂ cluster beams as well as with corresponding Ar cluster beams, the cluster impact kinetic energy being 100 keV in both cases. The respective friction values are determined by atomic force microscope measurements. Using CO₂ clusters, the reactive accelerated cluster erosion (RACE) of the single crystal diamond substrates leads to more than seven times higher friction values than those observed after erosion with non-reactive accelerated Ar clusters. Molecular dynamics calculations reveal related differences in the simulations of respective single cluster impacts already at 2 ps after impact.     

Spectral studies on erbium doped potassium lithium tantalate niobate single crystal grown by the step-cooling technique

An erbium doped K_0.603Li_0.397Ta_0.428Nb_0.572O₃ single crystal was grown by the step-cooling technique. The crystal has a tetragonal tungsten bronze-type structure at room temperature with a Curie temperature of 303°C. There are Er ions characteristic absorption bands around 449, 485, 521, 550, and 652 nm in the visible absorption spectrum. Upconversion fluorescence spectra and power dependence centered at 527 nm, 548 nm, and 660 nm under 975 nm excitation were measured at room temperature. Decay lifetimes of the 548 nm and 660 nm emission bands are 281 μs and 420 μs, respectively. The lifetime of the 548 nm emission corresponding to the transition of ?⁴ S _3/2→⁴ I _15/2 is ten times the lifetime of the same transition of Er³⁺ in LiNbO₃ crystal and twice in KYb(WO₄)₂ crystal. The crystal might become a promising upconversion laser material. The upconversion mechanism of Er³⁺ in the sample was discussed based on decay curves and pump power dependence analyses in this work.     

Effect of FeS doping on large diamond synthesis in FeNi-C system

The large single-crystal diamond with FeS doping along the(111) face is synthesized from the FeNi–C system by the temperature gradient method(TGM) under high-pressure and high-temperature(HPHT). The effects of different FeS additive content on the shape, color, and quality of diamond are investigated. It is found that the(111) face of diamond is dominated and the(100) face of diamond disappears gradually with the increase of the FeS content. At the same time, the color of the diamond crystal changes from light yellow to gray-green and even gray-yellow. The stripes and pits corrosion on the diamond surface are observed to turn worse. The effects of FeS doping on the shape and surface morphology of diamond crystal are explained by the number of hang bonds in different surfaces of diamond. It can be shown from the test results of the Fourier transform infrared(FTIR) spectrum that there exists an S element in the obtained diamond. The N element content values in different additive amounts of diamond are calculated. The XPS spectrum results demonstrate that our obtained diamond contains S elements that exist in S–C and S–C–O forms in a diamond lattice. This work contributes to the further understanding and research of FeS-doped large single-crystal diamond characterization.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)     

Optical and dielectric studies of solution grown glycinium maleate single crystal

Bulk single crystals of glycinium maleate have been grown from aqueous solution by slow evaporation method by optimizing the growth parameters within a period of 15 days. From X-ray diffraction analysis, the crystal was found to crystallize in monoclinic structure (space group C_2/c) with a = 17.866 Å, b = 5.684 Å, c = 17.408 Å and β = 112.65°. Presence of characteristic functional groups was confirmed in FTIR analysis. UV–Vis spectral analysis has revealed the absence of any high absorbance region between the wavelengths ranging from 300 to 900 nm. The optical band gap was calculated and found to be 3.91 eV. The activation energy for conduction at different frequencies was calculated and found to decrease from 0.54 eV to 0.41 eV as frequency increased from 100 Hz to 2 MHz. The dielectric behavior, conduction mechanism and the optical characterization of the glycinium maleate single crystals are being reported for the first time.     

Transmission electron microscopy studies on structure and defects in crystalline yttria and lanthanum oxide thin films grown on single crystal sapphire by molecular beam synthesis

The Molecular beam synthesis and characterization are reported for Y₂O₃ thin films grown on Al₂O₃ (0001) substrate. The Y₂O₃ layer was highly oriented in the [111] direction with predominant orientation relations (111) Y₂O₃ ‖ (0001) Al₂O₃ and [110] Y₂O₃ ‖ [2110] Al₂O₃, corresponding to a lattice mismatch of ～20% at the interface. No significant interfacial layers were found at the Y₂O₃/Al₂O₃ interface and the large lattice misfit was accommodated by formation of stacking faults, dislocations and secondary orientation in the Y₂O₃ layer. A La₂O₃ interlayer improved the quality of the Y₂O₃ films. Full width at half maximum (FWHM) of the Y₂O₃ (222) peak decreased from 3.12° to 1.43° and the defect density in the Y₂O₃ layer was significantly reduced. These results may be relevant in the broader context of designing oxide heterolayers with controlled microstructures.     

Improved structural ordering in sexithiophene thick films grown on single crystal oxide substrates

We report on sexithiophene films, about 150-nm thick, grown by thermal evaporation on single-crystal oxides and, as comparison, on Si/SiO₂. By heating the entire deposition chamber at 100°C we obtain standing-up oriented molecules all over the bulk thickness. Surface morphology shows step-like islands, each step being only one monolayer in height. The constant and uniform warming of the molecules obtained by heating the entire deposition chamber allows a stable diffusion-limited growth process. Therefore, the regular growth kinetics is preserved when increasing the thickness of the film. Electrical measurements on differently structured films evidence the impact of the inter-island separation region size on the main charge-transport parameters.     

Structure of diamond nanoparticles grown by chemical vapor deposition

We studied the structure of diamond nanoparticles grown by chemical vapor deposition. SEM images show that the material contains cubic, hexagonal, and possibly icosahedral structures ranging in size from 10 to 200 nm. Raman spectroscopy shows bands, which are characteristic of crystalline diamond, E_2g mode of hexagonal diamond, a-C, and graphite.     

Magnetic phase transitions and large mass enhancement in single crystal CaFe4As3

High quality single crystal CaFe₄ As₃ was grown by using the Sn flux method. Unlike layered CaFe₂ As₂ , CaFe₄ As₃ crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed at ～ 90 K and ～ 27 K, respectively. The high temperature transition is an antiferromagnetic（AF） ordering transition. However, the low temperature transition shows complex properties. It shows a ferromagnetic-like transition when a field is applied along b-axis, while antiferromagnetism-like transition when a field is applied perpendicular to b-axis. These results suggest that the low temperature transition at 27 K is a first-order transition from an AF state to a canted AF state. In addition, the low temperature electron specific heat coefficient reaches as high as 143 mJ/mol·K 2 , showing a heavy fermion behavior.     

Electrons diffusion study on the nitrogen-doped nanocrystalline diamond film grown by MPECVD method

Nitrogen-doped nanocrystalline diamond (NNCD) films were deposited onto p-type silicon substrates with three different layer structures: (i) directly onto the silicon substrate (NNCD/Si), (ii) silicon with undoped nanocrystalline diamond layer which was deposited in the same way as the above mentioned NNCD by the recipe Ar/CH₄/H₂ with a ratio of 98%/1%/1% (NNCD/NCD/Si), and (iii) silicon wafer with 100 nm thickness SiO₂ layer (NNCD/SiO₂/Si). Atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman spectroscopy were employed to characterize the morphology and microstructure of the as-grown nitrogen-doped diamond films. Silver colloid/silver contacts were made at to measure the current-voltage (I-V) characteristics for the three different structures. Electrons from a CVD reactor hydrogen plasma diffuse toward the p-type silicon substrate during a deposition process under the high temperature (∼800 °C). The study concluded that the SiO₂ layer could effectively prevents the diffusion of electrons.     

Photoconductivity study of a single crystal of GuGaS2 grown by iodine transport

Photoconductivity spectrum of a single crystal of CuGaS₂ has been resolved into various distincts peaks in the range from 0.5 to 0.7 micro. The peaks are explained on the basis of creation of electron-hole pairs and transitions caused by deep centers. The characteristic absorption in the green region is also reflected in the photoconductivity spectrum.