Laser carbon nitrides

Up to the present, a number of conventional film preparation methods like PVD, CVD, electro-chemical deposition, etc., have been reported to be used in synthesis of CNx films. Muhl et al. [57] reviewed the works performed worldwide, before the year 1998, on the methods and results of preparing carbon nitride hlms. They divided the preparation techniques into several sections including atmospheric-pressure chemical processes, ion-beam deposition, laser techniques, chemical vapor deposition, and reactive sputtering [57]. The methods used in succeeding research work basically did not... 

HP-HT techniques have been used to synthesize and recover metastable forms of carbon nitrides. A mixmre of Ceo and N2, laser-heated up to 2000-2500 K at about 30 GPa, gives rise to a chemical reaction, visually indicated by... 

Ling, H. Wu, J.D. Sun, J. Shi, W. Ying, Z.F. Li, F.M. Electron cyclotron resonance plasma-assisted pulsed laser deposition of boron carbon nitride films. Diamond Relat. Mater. 2002, 11, 1623-1628. 

Klotzbucher et al. [92] deposited thin carbon nitride films on Si(lOO) substrates by a hybrid RF-pulsed laser deposition, a technique significantly different from that of Chowd-... 

The lone pair is produced intrinsically by the sp-orbit hybridization of O and N. The number of lone pairs in a tetrahedron follows the rule of 4-n , where n is the valence value of the electronegative additive. Vibration of the dipole induced by the lone pairs should be detectable by Raman spectroscopy in the frequency range below 1,000 cm . A Raman experimental survey (HeNe laser, normal incidence) from the following specimens confirmed this expectation [12]. Figure 6.2 shows Raman spectra of (1) AI2O3 and Ti02 powders (2) thin films of Ti nitride (TiN) and amorphous carbon nitride and, (3) films of amorphous carbon (a-C) and Ti carbide (TiC). As anticipated, the lone-pair features of the oxides (n = 2) are stronger than those of the nitrides (n = 3) while no such features can be resolved from carbides (n = 4). The appearance and the relative intensity of these low-frequency Raman features support the prediction and the rules of 4-n for lone-pair formation as well. 

Soto R, Gonzalez P, Redondas X, Parada EG, Pou J, Leon B, Perez-Amor M, da Silva MF, Soares JC. Growth and characterization of carbon nitride films prepared by laser ablation. Nucl Instrum Methods B 136-138 236, 1998. 

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. 

Figure 6.9 Part of laser mass spectrum of boron nitride contaminated with carbon, iron and chromium. (I. S. Becker and H. ). Dietze, Fresenius /. Anal. Chem., 344, 69 (1992). Reproduced by permission of Springer Science and Business Media.)...

Part of a mass spectrum for the determination of Fe and Cr contamination in boron nitride contaminated with carbon measured by LIMS is shown in Figure 6.9. The analyte ions 53Cr+ and 54Fe+ due to different masses of isobaric atomic and cluster ions are clearly separated from boron and boron carbide cluster ions as demonstrated in Figure 6.9. Cluster ion formation has been studied by laser ionization mass spectrometry (LIMS) on a boron nitride target.10... 

There is mass spectroscopic evidence for clusters C59B, C68B2,. ..C54 B6 in the products of laser ablation of boron nitride/graphite composites (Guo et al. 1991). It is proposed that these may be versions of the fullerene cage in which heteroatoms have occupied carbon sites with little disturbance of the framework. This is a plausible hypothesis for low doping ratios, in view of the ability of carbon to substitute for boron in carboranes. Bond-energy considerations suggest that... 

Bando and co-workers271 have prepared BN nanolubes by the reaction of MgO, FeO and B in the presence of NH, at 1400 °C. Reaction of boric acid or B20, with N2 or NH, at high temperatures in the presence of carbon or catalytic metal particles has been employed in the preparation of BN nanotubes.2 2 Boron nitride nanotubes can be grown directly on substrates at 873 K by a plasma-enhanced laser-deposition technique.172 Recently, GaN nanotube brushes have been prepared using amorphous carbon nanotubes templates obtained using AAO membranes.274... 

Atomic Force Microscopy Atomic force microscopy is a direct descendant of STM and was first described in 1986 [254], The basic principle behind AFM is straightforward. An atomically sharp tip extending down from the end of a cantilever is scanned over the sample surface using a piezoelectric scanner. Built-in feedback mechanisms enable the tip to be maintained above the sample surface either at constant force (which allows height information to be obtained) or at constant height (to enable force information to be obtained). The detection system is usually optical whereby the upper surface of the cantilever is reflective, upon which a laser is focused which then reflects off into a dual-element photodiode, according to the motion of the cantilever as the tip is scanned across the sample surface. The tip is usually constructed from silicon or silicon nitride, and more recently carbon nanotubes have been used as very effective and highly sensitive tips. 

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