Isao Kusunoki

XPS study of a SiC film produced on Si(100) by reaction with a C2H2 beam

A Si(100) surface reacted with a well-collimated C2H2 beam was studied by XPS after storing it in air for about one year. The SiC film formation was confirmed by the characteristic XPS peaks of Si2p (101.3 eV) and Cls (283.3 eV) for SiC. The chemical maps on the surface were obtained by imaging XPS. The ≈ 1 mm diameter SiC region was clearly identified on the Si substrate by the method. In the SiC and the non-reacted Si regions the Si2p XPS peak for SiO2 (103.6 eV) and the O 1s peak were also observed. The intensities of the O 1s and Si 2p (SiO2) peaks in the SiC region were smaller by a factor of 0.75 than in the surrounding Si region. This indicates that the carbide (SiC) film was less reactive to O2 than the Si surface. There was very little evidence of any SiOx (x < 2) products which may be transients in the formation of SiO2 or complexes like CSiO.

XPS study of nitridation of diamond and graphite with a nitrogen ion beam

Diamond (CVD) and graphite (HOPG) samples were nitrided at room temperature by irradiation with 300–700 eV N2+ ion beams. X-ray photoelectron spectra (XPS) were recorded in situ during the nitridation. The XPS spectra of C1s and N1s core levels are divided into three (A, B, C) and four (D, E, F, G) components, respectively. The A component at ∼284.8 eV is assigned to the non-damaged substrate below the ion penetration depth. The B component at ∼286.0 eV originates in the damaged phase and the sub-nitride phase (CNx: x<1). The C component at ∼287.3 eV is attributed to genuine nitrides such as C3N4. The broad N1s XPS peak at ∼400 eV splits clearly into the D (∼398.4 eV) and F (∼401.2 eV) components upon annealing at 600°C in vacuum. The splitting is caused by evaporation of the volatile E component (∼399.7 eV). The intensity of the D component was always comparable to that of the F component in both diamond and graphite cases. The origins of these components are discussed. The G component may be due to nitrogen trapped at defects.

SiC film formation on Si(001) by reaction with C2H2 beams

Abstract β-SiC films on Si(001) have been formed by direct reaction of Si crystal with C 2 H 2 molecular beams in ultra-high vacuum. Depth profiles of the C/Si composition ratio of the films have been measured by an Auger electron spectrometer combined with an Ar + ion sputtering gun. The structures and topographies of the films were observed by SEM and TEM. The growth rate of the film has been found to be proportional to the reaction time and the beam flux under low beam flux condition. However, the growth rate decreased at high temperatures. In this case, the surface under reaction was covered with a Si-rich layer and the epitaxial growth of SiC crystals was observed on the substrate. In the substrate pyramidally shaped corrosion along the (111) face was observed by TEM. In the etched parts SiC was also formed by reaction with C-containing reactants. Under high beam flux condition, the surface of the growing film was covered with a C-rich layer and the growth rate decreased. In this case, the grown film consisted of polycrystals and was covered with hillocks.

Potential energy surfaces of the reaction C++H2 → CH++H

Potential energy surfaces of six low lying states for the reaction C++H2 have been calculated with an ab initio MCSCF–POLCI method. An emphasis has been placed on the reaction channel leading to the chemiluminescent product CH+(A 1Π)+H(2S). Based on the characteristics of the surfaces, a mechanism for this reaction has been proposed which involves a nonadiabatic transition from 2 2A′ to 3 2A′ in the vicinity of the C2v symmetry. An alternative path involving a 1 2A″ → 2 2A″ transition cannot be denied.

Chemiluminescent ion–molecule reactions: Rotational–vibrational population distributions of CH+(A 1Π) and CD+(A 1Π) from C++H2 and C++D2 collisions

Optical emission in the 3000–5000 A range was observed as a result of low‐energy (3–8 eVCM) ion–molecule reactions of C+ ions with H2 and D2 molecules. Most of the emission is due to (A 1Π→X 1Σ+) transitions of CH+ and CD+, which were each studied with 6 A and 20 A FWHM optical resolution. Rotational lines of much higher J were observed than are present in spectra from conventional CH+ light sources. The observed spectra were simulated on a computer, taking into account the strong dependence of the electronic transition moment on the internuclear distance, as given by ab initio calculations. Relative band oscillator strengths fv′v″(J) were calculated for each rotational line J and were found to depend strongly on J as result of centrifugal stretching. These calculations were done using the R centroid approximation as well as the exact band oscillator strength formula. From the spectrum simulations, accurate rotational and vibrational population distributions were derived. A simple model is proposed which ...

Observation of c(4 × 4) LEED pattern induced by reaction of Si(100) surface with C2H4

The initial stage of carbide layer formation on a Si(100) surface by reaction with C2H4 gas was studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). A c(4 × 4) LEED pattern was clearly observed after an exposure of C2H4 of 5 × 10−6 Torr for 5 min at a sample temperature of 600°C to the Si(100) surface. Some factors which induce the c(4 × 4) pattern are discussed.

Reaction of Si surfaces with a C2H4 beam

Abstract The reactions of Si(100) and (111) surfaces with a C 2 H 4 beam in ultrahigh vacuum were studied using high resolution X-ray photoelectron spectroscopy (XPS) at temperatures of 600–900°C. These reactions produce silicon carbide (SiC) layers on the silicon surfaces, the growth rates of which increase with surface temperature up to about 675°C, but decrease at higher temperatures. The observed behavior is explained by the balance between the carbon supply rate from the C 2 H 4 beam and the silicon out-diffusion rate from the substrate to the carbide surface. The carbon supply rate is limited by the surface residence time of chemisorbed C 2 H 4 and the beam flux. At the temperature of maximal growth the composition ratio of carbon to silicon in the carbide layer is close to unity, but decreases with increasing temperature. Below the optimal temperature the FWHM of the C 1s XPS peak is broader than that of the stoichiometric compound SiC, implying that the chemical bonding in the carbide layer is distributed. The SiC bulk plasmon-loss peaks accompanying the Si 2s and C 1s XPS peaks appear in carbide films thicker than about 13A.

Nitridation of a Si(100) surface by 100–1000 eV N+2 ion beams

The nitridation mechanism of silicon at room temperature under exposure to 100–1000 eV N+2 ion beams has been studied in situ in an ultrahigh vacuum apparatus using x‐ray photoelectron spectroscopy. The increase of the nitrogen content in a surface layer as a function of the ion dose was described by a simple formula which was derived by assuming random occupation of the reaction sites in the penetration zone of the nitrogen atoms. A change of the binding energy and the width of the N1s x‐ray photoelectron spectrum during the reaction was observed and discussed with the component ratio N/Sireacted. The Si2p x‐ray photoelectron spectra were deconvoluted into five components of Si(0), Si(1), Si(2), Si(3), and Si(4) by curve fitting, where Si(n) represents the component of Si bonded to n nitrogen atoms. Their populations were dependent on the ion dose and the ion energy. The nitride layers formed in the Si surface with low energy beams of 100–200 eV had near‐stoichiometric composition of Si3N4. With beams of...

Spectroscopy and dynamics of the chemiluminescent reactions N+(1D)+H2→NH+(B 2Δ)+H and N+(1D)+D2→ND+(B 2Δ)+D

Optical emission in the 3500–5000 A range has been observed resulting from N++H2(D2) collisions at 1–9 eVCM. It is due to the B 2Δ→X 2Π transition of NH+ (ND+) formed in an exchange reaction. Numerous previously unobserved bands were resolved and the vibrational molecular constants determined. Vibrational and rotational product level populations were obtained through spectrum simulation. A comparison with other chemiluminescent ion–molecule reactions indicates a very high degree of internal excitation. From the measured reaction threshold, metastable N+ (1D) ions were identified as the reactants, and the product B 2Δ state formation is discussed in terms of electronic structure. Surprisingly no product is observed in the closely related A 2Σ− state, and reasons for this are suggested.

Scanning Auger microscopy study of heterogeneous growth of SiC film on Si(100) by reaction with a C2H2 beam

A Si(100) surface which was reacted with a well-collimated C2H2 beam was studied using scanning Auger electron microscopy (SAM) after storage in air for a long period of time. Formation of a SiC film was confirmed by the chemical shifts of the C KLL, Si LVV, and Si KLL peaks in the AES integral mode. Chemical maps of the surface were obtained using SAM. A sharp boundary of the region of SiC formed by the C2H2 beam irradiation was observed. The grains with bright tones in the SEM image observed at high magnification were identified as SiC crystals using SAM. The dark areas among the grains were the elemental Si regions. It is clear that the SiC film on the Si surface was not uniformly formed on a µm scale. This suggests that the SiC film grows via nuclear growth.