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We have investigated the effects of silicon (Si) doping on the chemical bonding states and the electrical, optical, and mechanical properties of nitrogen-doped diamond-like carbon (N−DLC) films prepared via plasma-enhanced chemical vapor deposition using hydrogen as a dilution gas. N doping accelerated the formation of clustered sp2 C in N−DLC films, whereas the clustering was almost suppressed in Si and N doped DLC (Si−N−DLC) films. Sp3 C sites in the Si–N–DLC films were higher than those in the N–DLC films. For the Si−N−DLC films, sp3 C-N bonds were preferentially formed compared with the sp2 C=N bonds. The internal stress on the Si−N−DLC films was lower than that on the N−DLC films. The Si−N−DLC films exhibited higher optical bandgaps than the N−DLC films. As the N2 flow ratio increased, the optical bandgap of the Si−N−DLC films showed an increasing trend, whereas that of the N−DLC films showed an opposite trend. The current−voltage characteristics of Si−N−DLC/p-type Si heterojunctions were not rectifying; however, after postdeposition annealing, the heterojunctions exhibited rectifying characteristics.

In this paper, we report on the fabrication of multi-layer bismuth selenide (Bi2Se3) devices by lithography process and their electrical transport characteristics studied at room temperature. The observation of a non-linear current-voltage characteristic is analyzed with various current transport mechanisms such as Schottky barrier, space-charge limited conduction (SCLC), Fowler-Nordheim (F-N) tunneling and Poole-Frenkel (P-F) conduction. The F-N tunneling via field emission current induced in high-voltage was found to be the dominant conduction mechanism which could responsible for the nonlinear behavior as compared to SCLC and P-F conduction phenomena. The charge traps present in the Bi2Se3 bulk causes SCLC and P-F conduction. A carrier mobility in Bi2Se3 is extracted as ~ 1220 cm2 V−1 s−1. Our study further advances the understanding of the fundamental charge transport mechanisms appeared in Bi2Se3 which will be an essential parameter in the development of various electronic applications such as resistive memory switching and sensing devices.

The adsorption of CO2 molecules on monolayer epitaxial graphene on a SiC(0001) surface at 30 K was investigated by temperature-programmed desorption and X-ray photoelectron spectroscopy. The desorption energy of CO2 on graphene was determined to be (30.1–25.1) ± 1.5 kJ/mol at low coverages and approached the sublimation energy of dry ice (27–25 kJ/mol) with increasing the coverage. The adsorption of CO2 on graphene was thus categorized into physisorption, which was further supported by the binding energies of CO2 in core-level spectra. The adsorption states of CO2 on graphene were theoretically examined by means of the van der Waals density functional (vdW-DF) method that includes nonlocal correlation. The experimental desorption energy was successfully reproduced with high accuracy using vdW-DF calculations; the optB86b-vdW functional was found to be most appropriate to reproduce the desorption energy in the present system.

The growth of graphene on 3C-SiC/Si heterostructure is a promising approach, which provides low production cost, high scalability and easiness of nanoelectromechanical system fabrication. However, the quality of graphene is still insufficient for device applications due to mediocre morphological and structural quality of the 3C-SiC epilayers compared to bulk SiC crystals and to excessive Si out-diffusion from the Si substrate. Here, we propose a solution of inserting a 4H-AlN layer between 3C-SiC and Si, which allows us to polish the 3C-SiC film without worrying about enhancement of the Si out-diffusion despite the thinning after the polishing. With this insertion, a considerable quality improvement is achieved in our graphene on silicon.

Results of investigations of the SiC/Si growth from monomethylsilane are reported. Growth conditions favoring the rotated epitaxy of 3C-SiC(111) films on Si(110) are determined experimentally. Surface energies of clean and hydrogen covered 3C-SiC(110) and 3C-SiC(111) surfaces are calculated with the density functional theory approach. It is shown that the change of the 3C-SiC film orientation with decreasing surface temperature and increasing monomethylsilane pressure may be induced by a reduction of the surface energy anisotropy due to the surface passivation by hydrogen.

The fusion of graphene with silicon may provide an effective solution to the problem of scale in electronic devices. This approach will allow the excellent electronic properties of graphene to be combined with known Si device technologies. We review the epitaxial growth of graphene on Si substrates (GOS) for fabricating transistors. GOS has been multifunctionalized by controlling the orientation of the Si substrate. The site-selective epitaxy of GOS has also been developed by controlling the base SiC thin films. These results demonstrate that GOS is suitable for integrated devices.

3C-SiC is the only polytype that grows heteroepitaxially on Si substrates and, therefore, it is of high interest for various potentail applications. However, the large (~20 %) lattice mismatch of SiC with the Si substrate causes a serious problem. In this respect, rotated epitaxy of 3C-SiC(111) on the Si(110) substrate is highly promising because it allows reduction of the lattice mismatch down to a few percent. We have systematically searched the growth conditions for the onset of this rotated epitaxy, and have found that the rotaed epitaxy occurrs at higher growth temperatures and at lower source-gas pressures. This result indicates that the rotated epitaxy occurs under growth conditions that are close to the equilibrium and is thefore thermodynamically, rather than kinetically, driven.

In the formation of epitaxial graphene on Si substrates, the growth of high-quality 3C-SiC thin films on Si substrates is a key to success. As a solution to the large mismatch between the Si substrate and the 3C-SiC film, rotated epitaxy in which 3C-SiC(111) films are grown on Si(110) substrates is quite attractive. In some applications, on the other hand, a certatin thickness (~100 nm or more) is required for this 3C-SiC films as well. A two-step growth method has been thus developed to realize a high-rate, qualified rotated epitaxy. A qualified graphene is found to be formed on this rotated epi-film, as typified by the increase of the grain size by a factor of 1.6 from the non-rotated epitaxy.

A method to realize a novel hybrid orientations of Si surfaces, Si(111) on Si(110), has been developed by use of a Si(111)/3C-SiC(111)/Si(110) trilayer structure. This technology allows us to use the Si(111) portion for the n-type and the Si(110) portion for the p-type channels, providing a solution to the current drive imbalance between the two channels confronted in Si(100)-based complementary metal oxide semiconductor (CMOS) technology. The central idea is to use a rotated heteroepitaxy of 3C-SiC(111) on Si(110) substrate, which occurs when a 3C-SiC film is grown under certain growth conditions. Monomethylsilane (SiH 3 –CH 3 ) gas-source molecular beam epitaxy (GSMBE) is used for this 3C-SiC interlayer formation while disilane (Si 2 H 6 ) is used for the top Si(111) layer formation. Though the film quality of the Si epilayer leaves a lot of room for betterment, the present results may suffice to prove its potential as a new technology to be used in the next generation CMOS devices.

We have deposited unhydrogenated and hydrogenated Si-incorporated DLC (Si-DLC) films by pulsed laser deposition using KrF excimer laser, and systematically examined the structure and the mechanical and tribological properties of the films. Hydrogenated Si-DLC films were prepared by atomic-hydrogen irradiation during deposition. The Si/(Si+C) ratio in DLC films increased by atomic-hydrogen irradiation during deposition, indicating that the hydrogen etching is more effective for C atoms compared with Si atoms. The formation of Si–C bonds in the films and silicon oxides only at the surfaces was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was found that the atomic-hydrogen irradiation led to the formation of Si–H bonds to prevent the surface oxidation of the Si-DLC films. The scratch tests revealed that the critical loads of the films deposited with hydrogen were higher than those of the films deposited without hydrogen. We found that the moderately hydrogen-irradiated Si-DLC films tended to have higher wear resistance than the unhydrogenated Si-DLC films.

Kinetics of the step flow growth on the (16 × 2) reconstructed Si(110) surface has been studied experimentally and with computer simulations. It is shown that during Si growth under DC heating vicinal steps on the (16 × 2) reconstructed Si(110) surfaces undergo a kinetic step bunching and develop extended segments preferentially oriented along the (16 × 2) reconstruction domains. The final step configuration depends crucially on the direction of the applied electric field. In particular, when DC is applied in the [ 1 1 ¯ 2 ] direction, an array of straight multisteps parallel to the current direction and rotated in respect to the original orientation of the vicinal steps can be fabricated. Surprisingly, the observed step transformations are not affected by the polarity of the applied electrical field. Using a simple model of the Si/Si(110)-(16 × 2) growth and kinetic Monte Carlo simulations we show that the step bunching and step rotation on Si(110)-(16 × 2) might be induced by an incoherent matching of the (16 × 2) reconstruction domains across the vicinal steps on the surface.

We have deposited unhydrogenated diamond-like carbon (DLC) films on Si substrate by pulsed laser deposition using KrF excimer laser, and investigated the effects of atomic-hydrogen exposure on the structure and chemical bonding of the DLC films by photoelectron spectroscopy (PES) using synchrotron radiation and Raman spectroscopy. The fraction of sp 3 bonds at the film surface, as evaluated from C1s spectra, increased at a substrate temperature of 400 °C by atomic-hydrogen exposure, whereas the sp 3 fraction decreased at 700 °C with increasing exposure time. It was found that the sp 3 fraction was higher at the surfaces than the subsurfaces of the films exposed to atomic hydrogen at both the temperatures. The Raman spectrum of the film exposed to atomic hydrogen at 400 °C showed that the clustering of sp 2 carbon atoms progressed inside the film near the surface even at such a low temperature as 400 °C.

Since the pioneering work by Novoselov and Geim in 2004 [1], graphene has attracted skyrocketing attention as a new electronic material. Behind this enthusiasm are the fundamental limitations that silicon is facing, which impede further scaling of Si devices down into sub-10 nm regions. In this respect, the expectation for graphene is two-fold: medium term and long term. As for the former, the expectation as a new channel material in field-effect transistors (FET) is at its center (More Moore strategy). As for the latter, graphene’s novel quantum properties are expected to bring about new paradigm of information processing (Beyond CMOS strategy). The fact that many quantum phenomena, such as quantized Hall effect [2] and spin-polization of the current [3], can be observed at room temperatures in graphene, which is not usual in other materials, fuels the trend.

This paper reports preparation of top-gate epitaxial graphene FETs (EGFETs) on silicon substrates. Epitaxial graphene is obtained from a thermal decomposition at the surface of a 3C–SiC layer grown on Si substrates. We provide the first demonstration and comparison of the EGFETs fabricated on Si(1 1 0) and Si(1 1 1) substrates. For all EGFETs, an n-type transistor operation is observed by the gate voltage modulation. We find that the Si(1 1 1) substrates give better flatness at the surface of the 3C–SiC layer. As a result, the EGFETs fabricated on Si(1 1 1) substrates exhibit higher channel currents than those on Si(1 1 0) substrates.

We have fabricated and characterized the field effect transistors having an epitaxial-graphene channel grown on Si substrates. Epitaxial graphene is usually formed on SiC substrates by ultrahigh-vacuum (UHV) annealing. We used an approach to grow 3C–SiC layer on Si substrates and subsequently to anneal them in UHV to make few layers of graphene on the sample surface. Backgate transistors were able to be formed by using the SiC layer as a gate insulator. Although the gate-leakage current is not negligible, the drain current modulation by means of the gate voltage is confirmed by extracting the channel current from the total drain current. A new evaluation method of the area contact resistance between graphene and metal is also proposed.

We have deposited boron- and/or nitrogen-incorporated DLC films by radio-frequency magnetron sputtering, and systematically investigated the structure and the mechanical and tribological properties. The N content in DLC films increased with increasing N2 flow ratio [N2/(Ar + N2)], and it tended to be saturated at higher N2 flow ratios. The N content further increased with an increase in the B content of the targets. The B/C ratios of the films were almost the same as those of the B-containing targets regardless of the N content. Scratch tests revealed that the adhesion strength of N-incorporated DLC films decreased with increasing N2 flow ratio and the critical loads of B-incorporated films were lower than that of an unincorporated film. It was found that for B, N-coincorporated films there was an optimum N2 flow ratio at which the critical load became a maximum value, which was higher than that of the unincorporated film. The optimum N2 flow ratio increased with an increase in the B composition of the targets. The N-incorporated films peeled off during ball-on-plate friction tests. On the other hand, the B, N-coincorporated films showed good wear-resistant properties that the specific wear rates were lower than those of the unincorporated and B-incorporated films.

We have deposited Si-DLC films by pulsed laser deposition using KrF excimer laser, and have investigated etching of the Si-DLC films by atomic hydrogen. We have examined the structure and chemical bonding of the films by Raman spectroscopy, X-ray photoelectron spectroscopy and photoelectron spectroscopy using synchrotron radiation. Photoelectron spectra of Si 2p with 135 eV photons showed two distinguishing components. The main components were identified with Si–C and silicon oxides. The intensity of the oxide component increased when the detection angle to the surface normal was increased from 0 to 60°, indicating that thin oxide layers were formed at the surface. The oxide component decreased by annealing at a substrate temperature above 850 °C in an ultra-high vacuum and it disappeared at 1050 °C. We found that the etching rate of the films drastically decreased by the incorporation of Si. It was also found that the etching rate of the Si-DLC films markedly increased after dipping in a HF solution, indicating that the hydrogen etching of the Si-DLC films is suppressed by thin oxide layers formed at the surfaces. When the HF-treated Si-DLC films were annealed at a temperature above 400 °C in a high vacuum chamber, the etching rate decreased, suggesting that oxide layers were formed again at the surfaces.

Gallium nitride (GaN) films and Aluminium nitride (AlN) layers were deposited on SiC/Si (111) substrates by an alternating source gas supply or an intermittent supply of a source gas such as ammonia (NH3), trimethylgallium (TMG) or trimethylaluminum (TMA) in a hot-mesh chemical vapor deposition (CVD) apparatus. The AlN layer was deposited as a buffer layer using NH3 and TMA on a SiC layer grown by carbonization on Si substrates using propane (C3H8). GaN films were grown on an AlN layer by a reaction between NHx radicals generated on a ruthenium (Ru) coated tungsten (W)-mesh and TMG molecules. An alternating source gas supply or an intermittent supply of one of the source gases during the film growth are expected to be effective for the suppression of gas phase reactions and for the enhancement of precursor migration on the substrate surface. By the intermittent supply of alkylmetal gas only during the growth of the AlN layer, the defect generation in the GaN films was reduced. GaN film growth by intermittent supply on an AlN buffer layer, however, did not lead to the improvement of the film quality.

MoO2 nanotube with rectangular cross sections can be prepared on Mo substrates by using an O2-C2H2 combustion-flame method [Jpn. J. Appl. Phys. 44 (2005) L449]. We have investigated the growth behavior of the nanotube in detail by using scanning electron microscopy and energy dispersive x-ray microanalysis. The precursor of the growth is produced onsite at the Mo substrate, through reactions with oxygen radicals supplied from the combustion flame. The precursor is then transferred, in the flow of the combustion flame, to the backside of the substrate to form the rectangular nanotube. The growth is accompanied by oxidation, which is crucial in determining the shape of the nanostructure. A two-stage growth model, consisting of initial bulk-cluster growth and subsequent growth of nanotube, is proposed based on the observations. [DOI: 10.1380/ejssnt.2009.307]

We have deposited Si-incorporated diamond-like carbon (DLC) films by radio-frequency plasma-enhanced chemical vapor deposition using methane, argon, and monomethylsilane (MMS; CH3SiH3) as a silicon source, and have investigated the structural and mechanical properties of the films. The deposition rate and Si atomic fraction [Si/(Si+C)] in the DLC films increased with increasing MMS flow ratio. The Si fraction was approximately 13% at a MMS flow ratio [MMS/(MMS+CH4)] of 3%, showing that the deposition using a combination of CH4 and MMS produces films with high Si content compared with those deposited using conventional C and Si sources. The Si fraction was also found to increase with a decrease in Ar flow rate under a constant MMS flow ratio. Many particles composed mainly of Si, whose size was 0.3–1 µm in diameter, were observed on the surface when deposition was carried out at MMS flow ratios of 15 and 30%. Compressive internal stress in the films decreased with the MMS flow ratio and/or with the Ar flow rate. The decrease in internal stress is probably due to the relaxation of a three-dimensional rigid network by the formation of Si–C and Si–H bonds in the films as well as Ar+ ion bombardment.

High quality polycrystalline Si films deposited on polyethylene terephthalate (PET) substrates without incubation layers have been achieved with high growth rate (40 nm/min) using plasma-enhanced chemical vapor deposition (PECVD) operated at near atmospheric pressures. A short-pulse based power system was employed to maintain a stable discharge H 2 -diluted SiH 4 in the near atmospheric pressures without the use of any inert gases such as He. Highly crystallized features were observed using Raman scattering spectroscopy and X-ray diffraction (XRD). Observations by cross-sectional transmission electron microscopy (X-TEM) suggested that the Si polycrystallites were generated directly on the PET substrates without forming the incubation layers.

The abstraction reaction of D adatoms by H atoms have been investigated on the Si(1 1 0) surfaces. The direct abstraction to form HD molecules obeys a second-order rate law in D coverage θ D . On the other hand, the indirect abstraction to form D 2 molecules obeys a fourth-order rate law in θ D . In addition to the direct abstraction, indirect abstraction to form HD molecules is also included due to piled H adatoms during H exposure. It is found that the indirect abstraction is promoted on the surfaces saturated with dideuterides, suggesting that dideuterides (dihydrides) play a significant role in the indirect abstraction paths. The kinetics of the abstraction reactions on the Si(1 1 0) surfaces look similar to those on the Si(1 0 0) surface. However, the delayed D 2 desorption exhibits time profiles different from those on the Si(1 0 0) surfaces.

GaN films were grown on AlN/SiC/Si substrates by hot-mesh chemical vapor deposition (CVD) using ruthenium (Ru)-coated tungsten (W)-mesh. When using the Ru-coated mesh, the crystallinity of the GaN films did not degrade until a mesh temperature of 1000 °C, while the crystallinity markedly degraded at lower than 1100 °C when using the W-mesh. From the photoluminescence (PL) spectra of GaN films grown using the Ru-coated W-mesh, strong near-band-edge emission without yellow luminescence can be observed. In order to elucidate the difference in the decomposition efficiency of ammonia gas, the hydrogen radical density generated by the heated W-mesh and Ru-coated mesh was also evaluated using tungsten phosphate glass plates.

GaN films were grown on SiC/Si (111) substrates by hot-mesh chemical vapor deposition (CVD) using ammonia (NH 3 ) and trimetylgallium (TMG) under low V/III source gas ratio (NH 3 /TMG = 80). The SiC layer was grown by a carbonization process on the Si substrates using propane (C 3 H 8 ). The AlN layer was deposited as a buffer layer using NH 3 and trimetylaluminum (TMA). GaN films were formed and grown by the reaction between NH x radicals, generated on a tungsten hot mesh, and the TMG molecules. The GaN films with the AlN buffer layer showed better crystallinity and stronger near-band-edge emission compared to those without the AlN layer.

Initial oxidation of HF-acid treated Si(1 0 0) surfaces with air exposure has been studied by using synchrotron radiation X-ray photoelectron spectroscopy. We demonstrate that the initial oxidation is explained not by a layer-by-layer process, but by a non-uniform mechanism. Just after dipping a Si substrate in HF-acid and spin-drying, the Si surface is immediately oxidized partly with a coverage of 0.2. It is considered that the non-uniform oxidation takes place at surface defects on H passivated Si surfaces. With increasing the air exposure up to 1 week, we have found that the non-oxidized part is oxidized uniformly at slower rates compared to the beginning. IR absorption spectroscopy with a multiple-internal-reflection geometry clearly indicates the backbond oxidation of surface Si takes place despite the H passivation produced by the HF-acid treatment.

The initial oxidation of a Si(110)-16×2 clean surface, both at room temperature (RT) and elevated temperatures (635, 660 °C), was investigated by scanning tunneling microscopy (STM). The effects of annealing (300 °C, 15 min) on an RT-oxidized surface were also investigated. On the RT-oxidized surface, a BN site, detected as a bright (B) spot in the filled-state image but as a normal (N) 16×2 adatom in the empty-state image, was observed. After annealing, DD, BD, and BB sites were found to exist in addition to the BN site. Here, DD (BD, BB) is a site that appears dark (bright, bright) in its filled-state image and appears dark (dark, bright) in its empty-state image. The relative population is DD>BD≈BN>BB. For oxidation at 635 °C, DD, BD, and BN sites were observed. For oxidation at 660 °C, only the BD site was observed. On the basis of these results, an atomistic process during the initial oxidation of the Si(110)-16×2 surface is discussed.

Growth of highly crystalline poly-Si films on polyethylene terephthalate (PET) substrates at 150 {degree sign}C has been achieved with practical growth rates by using pulsed-plasma CVD under near-atmospheric pressure. The precursor is SiH4 diluted in H2, and no inert gases such as He were used. A short-pulse based power system has been employed to maintain a stable discharge in the near-atmospheric pressures. By using this technique we have succeeded in growth of poly-Si thin film on the glass substrate at 180 {degree sign}C with virtually no incubation layers. Good crystallinity of the poly-Si thin films were observed by Raman scattering spectroscopy and cross-sectional transmission electron microscopy.

Because of the interplay among various surface processes, an integrated description of 2D film growth is usually a very difficult task. As far as adsorption–migration–desorption of precursors and the resultant nucleation, growth, and coalescence of 2D islands up to 1 monolayer are concerned, however, the autocatalytic-reaction (ACR) model [Phys. Rev. Lett. 82 (1999) 2334] can be a rare exception, which satisfactorily models the oxide film uptake curve during Si dry oxidation from a Langmuir to sigmoidal behaviors. A kinetic Monte Carlo (KMC) simulation, conducted to mimic the 2D growth of thin films, shows a similar shift from a Langmuir to sigmoidal uptake behavior by varying the parameters corresponding to adsorption, migration, and desorption. A comparison between ACR and KMC clarifies that the success of the ACR model lies in its effective inclusion of adsorption of species as well as of nucleation, growth, and coalescence of islands. A recipe is presented to translate the ACR parameters to KMC ones, which allows one to discuss the surface morphology based on the ACR analysis on the film uptake curve.

Coverage and adsorption state of hydrogen atoms on the growing surface of Si1−yCy film using monomethylsilane has been investigated by using temperature-programmed desorption (TPD) and multiple-internal-reflection Fourier-transform infrared spectroscopy (MIR-FT-IR). The surface hydrogen coverage decreases with the growth temperature Tg until it disappears at 800 °C. All the H2-TPD spectra are well resolved into six SiH-related and one CHn-related hydrogen desorption peaks. The SiH-related FT-IR peak showed a blue shift with increasing Tg, which, in conjunction with the TPD, is related to enhanced C incorporation at backbonds of SiH.

Gallium nitride (GaN) films were grown on SiC/Si(111) substrates by hot-mesh chemical vapor deposition (CVD) using trimethylgallium (TMG) and ammonia (NH3). A SiC buffer layer was formed by carbonization on the Si(111) substrates using propane (C3H8). GaN epitaxial films were grown on the SiC layer by the reaction between NHx radicals generated on a tungsten hot-mesh surface and TMG molecules. From the X-ray diffraction pattern, the GaN epitaxial films grown by the two- or three-step growth technique at the substrate temperatures of 600°C and 800°C to 1000°C and the hot-mesh temperature of 1200°C showed good crystallinity. Photoluminescence spectra of GaN films grown by the three step growth technique showed a strong near-band-edge emission and a weak yellow luminescence.

Photo-thermal reflection microscopy has been used for investigating semiconductor materials to evaluate carrier diffusivity, lifetime and surface recombination velocity. We developed this technique to obtain carrier recombination velocities at the interface between SiO2 oxide film and Si substrate. Two samples with different oxide film thickness of 92 and 45 nm were prepared. Since the oxide film layer does not absorb the pump and probe laser light, carrier recombination velocity at the SiO2/Si interface can be estimated. Curve fitting procedures with the theoretical prediction results in an estimation of the interface recombination velocity of 100 cm/s for thick oxide sample. When the sample was chemically etched, the recombination velocity increases to 2500 cm/s. The chemical etching results in the drastic increase of the recombination velocity. The etching solution may soak through the SiO2 oxide film layer and attack the Si surface during the chemical etching. Increase of the number of the interface traps induces the increase of the carrier recombination velocity at the interface. We, therefore, found that the present photo-thermal reflection (PTR) microscopy is a useful technique for investigating the carrier dynamics at SiO2/Si interface.

Temperature-programmed desorption (TPD) has been used to study the initial adsorption and C-incorporation of organosilanes [monomethylsilane (MMS), dimethylsilane (DMS) and trimethylsilane (TMS)] at Si(0 0 1) surfaces. Hydrogen was the only desorbing species observed in the TPD spectra from organosilanes. Organosilane molecules adsorb dissociatively on the Si(0 0 1) surfaces at room temperature. TPD spectra from DMS- and TMS-adsorbed Si surfaces present carbon-related hydrogen (H2) desorption peaks from the initial adsorption. The carbon-incorporation ratio was found to be larger in the order of TMS > DMS > MMS, with the sticking probability of molecules being almost identical for the three organosilane molecules.

Germane (GeH4) adsorption at Si (001) at room temperature has been investigated through observations of surface hydrides by means of temperature-programmed desorption and multiple-internal-reflection Fourier-transformed infrared spectroscopy. For surfaces with considerable concentration of dimer vacancies, prepared by in-situ thermal cleaning followed by rapid cooling, saturation with germane presented almost full coverage of SiH without any Ge or Si-higher hydrides, which strongly suggests site exchange between ad-Ge and substrate Si atoms. For a smoother surface prepared by forming a Si epilayer, the Ge dihydride is much populated at higher doses of germane. From measurements using (1 × 2) single domain surface and polarized lights in FTIR, the Ge dihydrides are found to be at their “in-dimer” position rather than the “intra-row” position.

We have deposited diamond-like carbon (DLC) films by pulsed laser deposition using a KrF excimer laser (248 nm), and have investigated the thermal effects on the structural properties of the DLC films by visible Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The Raman spectra show the G and D peaks near 1580 and 1370 cm−1, respectively. It has been clarified that the intensity of the D peak increases with the deposition temperature, indicating ordering of the a-C films. Fraction of the sp3 bonds in the deposited films, as evaluated from the C1s-XPS peak, decreases with the deposition temperature. The Raman spectra for the films deposited at 150 °C show ordering of a-C by annealing, while the structure of the films deposited at room temperature does not change. When a laser repetition rate is decreased from 20 to 10 Hz, ordering of a-C was observed.

To suppress inclusion of fine particles in amorphous silicon films, a negatively-charged fine particle (NFP) collector has been successfully installed in a silane plasma. Two modes of operation of the NFP collector biasing were examined: (i) turning on after the appearance of fine particles; and (ii) turning on from the very beginning of the plasma operation. While the former proved the effectiveness of the NFP collector in the removal of fine particles, apparently very small particles (

Si(0 0 1) surfaces exposed to various doses of germane (GeH 4 ) at room temperature (RT) have been investigated by using temperature-programmed desorption (TPD) and multiple internal reflection Fourier transform infrared spectroscopy (MIR-FTIR). It is found that all H atoms from GeH 4 molecules are transferred to surface Si atoms on adsorption, and form mainly doubly occupied Si dimers. Ge hydrides and Si higher hydrides rarely exist. These features persist beyond 1 monolayer of the hydrogen coverage. These findings strongly suggest atomic exchange between Ge adatoms and surface Si atoms even at RT. Through analysis of H uptake curve, the number of necessary surface dangling bonds for a GeH 4 molecule adsorption is obtained to be unity at low coverage.

Adsorption kinetics of dimethylsilane (DMS) at Si(0 0 1) surface has been investigated by using temperature-programmed desorption (TPD). The saturated hydrogen coverage of two monolayer was identical with that from monomethylsilane (MMS)-saturated surface. By being combined with the C/H ratios within a molecule (1/6 for MMS and 1/4 for DMS), this fact suggests enhanced C incorporation by DMS as compared with MMS by a factor of 1.5. The TPD spectra are deconvoluted into β1 (∼510 °C), β1′ (∼550 °C), γ (∼615 °C) and δ (∼910 °C) peaks. The appearance of the bulk C-related γ peak from the very initial adsorption, in contrast to MMS, is consistent with the enhanced C incorporation. Although the hydrogen uptake (H-uptake) curve is quantitatively fitted with the four-site adsorption model, discussions on the sub-peak assignments suggest presence of further decompositions of ad-species at initial adsorptions.

Adsorption and desorption kinetics of organosilanes [dimethylsilane (DMS) and monomethylsilane (MMS)] at Si(001) surfaces have been investigated by using temperature-programmed desorption (TPD), and compared with those of acetylene (C2H2)- and atomic hydrogen (H)-adsorbed Si surfaces. TPD spectra from DMS/Si(001) present β1 (~510°C), β1' (~550°C), γ (~615°C) and δ (~910°C) peaks while MMS/Si(001) shows only β1 (~510°C) and δ (~870°C) peaks. C2H2/Si(001) presents β1 (~510°C) and γ (~615°C) peaks as well but showed no β1' and δ peaks. The β1' peak, observed for DMS, is currently understood to be due to hydrogen desorption from the Si–H at a Si–C hetero-dimer. Unlike MMS, the appearance of the bulk-carbon related γ peak from the initial DMS adsorption suggests enhanced C incorporation with the use of DMS. The analysis of the hydrogen uptake curve also implies that DMS and MMS have different adsorption kinetics.

We have deposited diamond-like carbon (DLC) films using RF magnetron sputtering techniques, and investigated structure, chemical bonding of deposited films and these thermal stabilities by Raman spectroscopy and photoelectron spectroscopy. It has been found that the film deposited under typical conditions is amorphous carbon (a-C) with 62% sp2 and 38% sp3 bonds. Ordering of a-C has been observed with an increase in substrate temperature during deposition and similarly observed after postannealing, although the sp3/sp2 ratio in a film does not change even at 900°C. The absence of conversion between sp3 and sp2 bonds indicates that the DLC films have high thermal stabilities.

In many thin film growth systems, the surface morphology develops via nucleation of two-dimensional clusters, their growth and coalescence. When desorption of surface adsorbate is thermally activated, time evolution of the film's coverage becomes a delicate function of both the temperature and pressure of the growth. The autocatalytic reaction (ACR) model, a rate equation known in chemical kinetics, is a powerful tool to describe such complicated temporal behaviors, and is successfully applied to analysis of dry oxidation at Si(001)-2×1 surfaces. Monte Carlo simulation indicates that the physics behind the ACR model lies in its effective inclusion of nucleation, growth, and coalescence processes.

We have grown extremely thin, single-domain 3C-SiC films by forming a low-temperature interfacial buffer layer using monomethylsilane (H3C-SiH3) on nominally on-axis Si(001) substrate, whose miscut is estimated to be less than 0.1−0.2o. We have clarified that single-domain 3C-SiC(001) 3×2 films can be grown on both Si(001) 2×1 single-domain and Si(001) 2×1 + 1×2 double-domain surfaces. The film is as thin as 45−200 nm, which is compared to the film as required in a previous study (> 5 μm) to achieve the single-domain 3C-SiC films on a nominally on-axis Si(001) substrate. The development of the single domain observed is understood in terms of electromigration during dc-resistive heating and unique adsorption nature of the monomethylsilane.

Low-temperature (~1073 K) formation of graphene was performed on Si substrates by using an ultrathin (2 nm) Ni layer deposited on a 3C-SiC thin film heteroepitaxially grown on a Si substrate. Angle-resolved, synchrotron-radiation X-ray photoemission spectroscopy (SR-XPS) results show that the stacking order is, from the surface to the bulk, Ni carbides(Ni3C/NiCx)/graphene/Ni/Ni silicides (Ni2Si/NiSi)/3C-SiC/Si. In situ SR-XPS during the graphitization annealing clarified that graphene is formed during the cooling stage. We conclude that Ni silicide and Ni carbide formation play an essential role in the formation of graphene.

Effects of electron temperature ( T e ) on the quality of deposited silicon thin film were investigated using a modified magnetron typed plasma source equipped with a T e control system. Two kinds of Si films were prepared; amorphous silicon (a-Si:H) and micro-crystalline silicon (μc-Si). In the a-Si:H deposition, T e reduction from 4.75 eV to 0.4 eV increased the ratio of photo to dark conductivity, σ p /σ d , by a factor of 30 and decreased the SiH 2 concentration by a factor of two. In the μc-Si deposition, the crystallinity was also improved by a slight reduction of T e . However, we found a presence of an optimum T e (=3.9 eV) at which the crystal fraction becomes maximum.

Autocatalytic-reaction model, a chemical-kinetics model that provides an integrated description of various dynamical processes in the very initial oxidation of Si(100) surface, is illustrated. The nonlinear rate equation of this model has an analytical solution. With only two fitting parameters as it is, the solution quantitatively reproduces the experimental time-evolution of the surface oxide coverage in various oxidation modes, which range from the Langmuir-type in the low-temperature/high-pressure regime to the two-dimensional-island-growth-type in the high-temperature/low-pressure regime, or even to the one in the etching regime containing simultaneous decomposition of grown oxides in addition to their growth. Microscopic background behind the model is discussed in comparison with existing oxidation models and thin-film-growth models.

Graphene exhibits unusual electronic properties, caused by a linear band structure near the Dirac point. This band structure is determined by the stacking sequence in graphene multilayers. Here we present a novel method of microscopically controlling the band structure. This is achieved by epitaxy of graphene on 3C-SiC(111) and 3C-SiC(100) thin films grown on a 3D microfabricated Si(100) substrate (3D-GOS (graphene on silicon)) by anisotropic etching, which produces Si(111) microfacets as well as major Si(100) microterraces. We show that tuning of the interface between the graphene and the 3C-SiC microfacets enables microscopic control of stacking and ultimately of the band structure of 3D-GOS, which is typified by the selective emergence of semiconducting and metallic behaviours on the (111) and (100) portions, respectively. The use of 3D-GOS is thus effective in microscopically unlocking various potentials of graphene depending on the application target, such as electronic or photonic devices.

The surface chemistry of Si during gas-source molecular beam epitaxy (GSMBE) doped with phosphorus (P) has been investigated in detail, by obtaining the hydrogen (H) and P coverages on the growing surface by silane (SiH4) and phosphine (PH3). The low temperature region of doped epitaxy was found to consist of two domains: domain I (550 650°C) increased with mild P dopings, which is related to enhanced sticking probability at Si sites in the presence of surface P. The P coverage on the growing surface was some three orders of magnitude greater than that in the bulk, suggesting rapid surface segregation as a major cause for doping limitation.