A.P. Dementjev

X-ray photoelectron spectroscopy reference data for identification of the C3N4 phase in carbon-nitrogen films

The β-C3N4 phase should have a tetrahedral (sp3-bonded) structure resulting in C1s and N1s XPS peaks with only one feature at a position defined by the electronegativity of four CN bonds. In this work we determined the binding energy of the C1s and N1s XPS peaks in melamine (C3N6H6). In this compound the carbon atoms have four bonds with nitrogen atoms (double and two single); the nitrogen atoms have two chemical states: CNC and CNH2. Since the total number of chemical bonds in this compound is the same as in the hypothetical β-C3N4 compound, this compound is more suitable as a C1s XPS reference for the β-C3N4 phase. The binding energy of the C1s and N1s XPS peaks in melamine was determined to be equal to 287.9 and 399.1 eV, respectively. The binding energies were determined relative to the C1s XPS peak for carbon contamination (adventitious carbon).

Wettability and surface energy of oxidized and hydrogen plasma-treated diamond films

Abstract The wettability of CVD diamond films with liquids of different physico-chemical natures (water, glycerin, tin melt) was investigated by measuring the contact angles using the sessile drop method. The translucent diamond films of 0.5-mm thickness were grown in a microwave plasma CVD using CH4–H2 mixtures as the source gas, and separated from Si substrates. The growth surfaces have been polished to a roughness of Ra≤10 nm, and then exposed to microwave hydrogen plasma or thermal oxidation in air at 500 °C. Raman and Auger/XPS spectroscopies, optical and atomic force microscopies have been used to characterize the diamond films. Based on the wettability data, the variations in surface energy induced by hydrogenation and oxidation of polycrystalline diamond have been evaluated by the Fowkes equation. The hydrogenation of the films in the plasma essentially increases hydrophobic properties (contact angle for water increases up to θ=93°) as compared to oxidation (θ=32°). This is attributable to a reduction in a polar component of the surface energy due to hydrogen adsorption-induced reconstruction of the film surface. For comparison, the wettability of HPHT diamond single crystal, diamond ceramics and pyrolytic graphite have been measured and the differences observed will be discussed in this paper.

The roles of H and O atoms in diamond growth

Abstract A chemical interaction of hydrogen and oxygen atoms with a surface of sp2-hybridized carbon solids (graphite, soot and C60) has been studied by XPS and X-ray-excited AES methods. The transition of carbon atoms from the sp2 state to the sp3-hybridized state has been observed. The measured concentration of the sp3-hybridized carbon atoms on the surface is in excess of the CO bonds concentration. On the basis of these data, the following model of a carbon film growth is proposed: decay of double carbon bonds by H and O atoms and formation of the sp3-hybridized CC, CH and CO bonds. It is suggested that one of the key roles of hydrogen and oxygen atoms in the diamond film growth is sp2→sp3 conversion of CC bonds on a surface under deposition.

Multilayer structures induced by plasma and laser beam treatments on a-Si:H and a-SiC:H thin films

Si/SiH/CN x and Si/SiC/CN x film structures have been obtained in a two step procedure: a-Si:H and a-SiC:H thin films have been deposited by PECVD from CH 4 /SiH 4 precursors; CN x films have been prepared by exposing the previous obtained samples to a RF plasma beam discharge generated in nitrogen with graphite electrodes. Several samples were submitted to KrF laser irradiation and treated at various incident laser fluences. The samples have been investigated by in depth X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Chemical and structural modifications are induced by the treatments. The promotion of Si-C bonds and the build-up of an intermediate SiCN layer at the a-Si:H/CN x and a-SiC:H/CN x interfaces are proven.

Comparison of X-ray-excited Auger lineshapes of graphite, polyethylene and diamond

The experimental x-ray-excited Auger lineshapes for graphite, diamond and polyethylene have been obtained. The comparison of N(E) C KVV spectral features of graphite, diamond and polyethylene has also been carried out. The coincidence of C KVV Auger lineshape and energy position between diamond and polyethylene spectra is observed and the reasons discussed. The features of the CKVV Auger lineshapes for graphite, polyethylene and diamond provide a useful identification of sp 2 and sp 3 states in carbon solids.

Study of carbon nitride films deposited using a Hall-type ion source

The Hall-type ion source operated with nitrogen has been used in two ways in the synthesis of carbon nitride films: by ion beam nitridation of a graphite target and by simultaneous deposition on a collector (silicon wafer and nickel foil) of sputtered carbon atoms and nitrogen atoms from the surrounding nitrogen plasma. We present Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy results on the carbon and nitrogen atom fraction and chemical bonding state in carbon nitride films. The C 1s XPS peak of a sample deposited on silicon wafer was deconvoluted into three peaks at 284.7, 286.7 and 288.8 eV. The peak at 286.7 eV by analogy with polymethacrylonitrile (C≡N, 286.74 eV) can be identified as C≡N, the peaks at 284.7 and 288.8 eV as C-C and O=C-N, respectively. The N 1s peaks were also deconvoluted into three peaks at approximately 398.3, 400.5 and 402.6 eV. According to the N(E) CKVV spectra the surface samples contain an equal number of sp2 and sp3 bonds of carbon atoms.

Nanodiamond Seeding for Nucleation and Growth of CVD Diamond Films

Detonation nanodiamonds are shown to be effective seeds for growth of CVD diamond films as they provide high nucleation density on a substrate and can be placed on shaped surfaces and even into porous materials. XPS, AES and TEM analyses give useful information on the early stage of diamond growth. The transfer molding technique for manufacturing various diamond shapes is described. As the nucleation side of free-standing films produced by molding is the “working” surface, emphasis is placed on the study of its properties, such as topography, impurity contamination, thermal conductivity, and wettability. Diamond items grown directly on patterned Si templates are illustrated.

Chemical State of Carbon Atoms on a Nanodiamond Surface: Growth Mechanism of Detonation Nanodiamond

Identification of intermediate and final products of the chemical reaction that produces nanodiamond particles is a key factor in understanding its mechanism. In this work different nanodiamond samples were studied before and after chemical cleaning by X-ray photoelectron and Auger spectroscopy. It was found that the chemical state of carbon atoms is the same before and after chemical cleaning. We find that the carbon atoms are sp3-bonded inside nanodiamond particles and have a new, unique chemical state on the surfaces. The latter differs significantly from sp2- and sp3-bonded carbon and can be figured as the valence band near the Fermi level being occupied by three electrons.

Oxidized porous diamond/pyrocarbon nanocomposites as improved field electron emitters

Porous diamond/sp2-bonded carbon nanocomposites were studied for field electron emission properties and electroconductivity depending on composition and post-growth oxidation. It is found that the oxidation in nitric acid can sufficiently improve the field emission from the diamond samples. The oxidized composites exhibit lower emission threshold fields Eth=1–2 V/μm compared to Eth=4–6 V/μm for non-oxidized samples, and the emission uniformity (the number of emission sites per unit area) is also improved. More porous composites typically show better results. A possible reason of the emission improvement by oxidation in this two-phase carbon system is the lowering of the tunneling barrier due to formation of the dipole layers on the oxidized carbon surfaces.

Interaction of Carbon Atoms with Nanodiamond Surface

A combination of N(E) Auger spectroscopy, X-ray excitation (XAES), electron energy loss spectroscopy (EELS), and valence band (VB) XPS have been used to study nanodiamond (ND) particles. These methods have different information depths of 1–2, 5–7, and 10–12 monolayers (ML), respectively, and an inherent spectral structure in the identification of sp2–sp3 -bonds. Our data show that the upper 1–2 ML of a ND particle consists of carbon atoms with sp2-bonds, which differ from those in well- known carbon compounds. The ND core is made up of diamond. Chemical reactions of the carbon atoms with the particle have been studied in-situ and ex-situ. The crutial role of the upper monolayer in the diamond growth has been established for both cases.