Graphene on SiC(0001) and SiC(0001̅) surfaces grown via Ni-silicidation reactions

This paper presents the structure and electronic properties of graphene grown on 6H-SiC(0001) and SiC(0001?) surfaces via Ni-silicidation reactions at temperatures around 800 °C. Silicidation reactions take place at temperature higher than 400 °C for Ni(10 ML)/SiC and a single-phase θ-Ni₂Si(0001)-layer grows epitaxially on SiC(0001?) at 500 °C, whereas a mixed phase silicide-layer is formed on the SiC(0001) substrate. Annealing at 800 °C leads to growth of ordered graphite layers on both SiC(0001?) and SiC(0001) surfaces with an areal occupation ratio of ～ 65%, which surround the Ni-silicide islands. High-resolution ion scattering analysis reveals that single- and double-layer of graphite grow on the SiC(0001?) and SiC(0001), respectively. The dispersion curve of the π band for the double-layer graphite (DG) on the Si-face lies about 1 eV above that of the single-layer graphite (SG) on the C-face around the Γ-point. The work functions of the SG/SiC(0001?) and DG/SiC(0001) are derived to be 5.15 ± 0.05 and 4.25 ± 0.05 eV, respectively, which coincide well with the theoretical prediction based on the ab initio calculations. The present results indicate that the electronic states of graphene are influenced by the interaction with supports.     

Uniformity study of wafer-scale InP-to-silicon hybrid integration

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.     

Research on adhesion strength and optical properties of SiC films obtained via RF magnetron sputtering

SiC is widely used in various mechanical applications as a protective film because of its strength, thermal stability and good mechanical hardness. Here, amorphous SiC thin films with AlN as a buffer layer were deposited on glass and Si substrates through RF magnetron sputtering at different RF powers. The influence of the AlN buffer layer thickness on the morphological and the mechanical properties of the composite films was investigated. Results demonstrate that the AlN buffer layer can effectively improve the adhesion strength of SiC thin films, which has increased gradually from 26.78 N to 37.66 N. The transmittance of SiC thin films was measured using a UV–Vis–NIR spectrophotometer over a spectral range of 300–1200 nm. The average transmittance of SiC films decreases with increasing RF power, and their optical band gap values have varied from 3.31 eV to 3.50 eV.     

Fabrication of two types of one-dimensional Si–C nanostructures by laser ablation

Two types of one-dimensional (1D) nanostructures—amorphous silicon carbide (SiC) nanowires, 5–30 nm thick and 0.5–2 μm long, and carbon nanotubes (CNTs) filled completely with crystalline SiC nanowires, 10–60 nm thick and 2–20 μm long—were synthesized by the laser ablation of carbon-silicon targets in the presence of high-pressure Ar gas up to 0.9 MPa. All the CNTs checked by transmission electron microscopy contained SiC, and no unfilled CNTs were produced. We discuss the growth of the two nanostructures based on the formation of molten Si–C composite particles and their instabilities leading to the precipitation of Si and C.     

Oxidation behaviour of SiC coatings

Amorphous silicon carbide (SiC) films were deposited on silicon substrates by radio-frequency magnetron sputtering. The films were oxidized in air in the temperature range 400–900 °C and for times from 1 to 16 h. Neutron reflectivity measurements provided information on the thickness, density and roughness of the SiC and on the formed SiO₂ layers. Fourier transform infrared spectroscopy was used to determine the bond structure of the formed SiO₂ and changes in the bonding of SiC after exposure at the oxidation temperature. The surface morphology of the oxidized films was characterized by atomic force microscopy measurements. The oxidation kinetics is initially fast and as the SiO₂ layer is formed it slows down. The SiC consumption varies linearly with time at all oxidation temperatures. Exposure of the SiC at the oxidation temperature affects its density and to some degree its bond structure, while the formed SiO₂ has density and bond structure as that formed by oxidation of Si under the same conditions. PACS  66.30.Ny; 68.47.Gh; 68.55.J-     

Comparative PEEM and AES study of surface morphology and composition of Cu films on Si and 3C–SiC substrates

We have conducted photoemission electron microscope (PEEM) and Auger electron spectroscopy (AES) studies on the Cu(30 nm)/3C–SiC(1 0 0) and Cu(30 nm)/Si(1 0 0) samples annealed successively up to 850 °C. With PEEM, lateral diffusion of Cu atoms on the 3C–SiC substrate was observed at 400 °C while no lateral diffusion was seen for the Cu/Si(1 0 0) samples up to 850 °C. The 30 nm Cu thin film on 3C–SiC began to agglomerate at 550 °C, similar to the case for the Cu/Si(1 0 0) system. No further spread of the lateral diffusion region was found in subsequent annealing up to 850 °C for Cu/3C–SiC while separated regular-sized dot structures were found at 850 °C for Cu/Si(1 0 0). AES studies of Cu/Si(1 0 0) system showed partial interface reaction during Cu deposition onto the Si(1 0 0) substrate and oxidation of the resultant Cu₃Si to form SiO₂ on the specimen surface at room temperature in air. Surface segregation of Si and C was observed after annealing at 300 °C for Cu/Si(1 0 0) and at 850 °C for the Cu/3C–SiC system. We have successfully elucidated the observed phenomena by combining PEEM and AES considering diffusion of the constituent elements and/or reaction at interfaces.     

Soliton propagation optimization and dynamic modulation in photonic crystal waveguide with polystyrene background

Bright optical soliton propagation properties near the left band edge of photonic crystal waveguide (PCW) are numerically investigated. Compared with the normal PCW with air background, by employing polystyrene as PCW background and adjusting the structure parameters simultaneously, the required soliton peak power sharply decreases from 8.63 × 10⁶ W/m to 9.98 × 10² W/m. The influence of optical loss on soliton propagation is numerically investigated. The dynamic modulation of the soliton propagation in PCW is realized, and a modulation range of 459 nm wavelength for the soliton transmission has been achieved. Simulation results show that the transmission wavelength, required soliton peak power and delay time decrease almost linearly as the external modulated voltage increases; the modulation sensitivities are 8.316 nm/V, 3.416 W/m/V and 16.6 ps/V, respectively.     

Investigation of the SiC thin films synthetized by Thermionic Vacuum Arc method (TVA)

Thermionic Vacuum Arc method (TVA) was used for the first time to prepare SiC thin films. This method is very suitable for deposition of high purity thin films with compact structure and extremely smooth in vacuum conditions. The nanocomposites were investigated using Transmission Electron Microscopy (TEM) analyses provided with HR-TEM and SAED facilities. The structure of the films can be indexed as following three forms: cubic structure of SiC (F4-3m) a = 0.4348 nm, cubic Si (Fd3m) a = 0.54307 nm and graphite (P63/mmc) a = 0.2456 nm; c = 0.6696 nm. The morphology, topography, wettability and wear properties were also performed by SEE system and by Raman Spectroscopy, increasing the interest for emerging applications.     

Analysis and optimization of propagation losses in LiNbO3 optical waveguides produced by swift heavy-ion irradiation

The propagation losses (PL) of lithium niobate optical planar waveguides fabricated by swift heavy-ion irradiation (SHI), an alternative to conventional ion implantation, have been investigated and optimized. For waveguide fabrication, congruently melting LiNbO₃ substrates were irradiated with F ions at 20 MeV or 30 MeV and fluences in the range 10¹³–10¹⁴ cm⁻². The influence of the temperature and time of post-irradiation annealing treatments has been systematically studied. Optimum propagation losses lower than 0.5 dB/cm have been obtained for both TE and TM modes, after a two-stage annealing treatment at 350 and 375^∘C. Possible loss mechanisms are discussed.     

First principles study of <Emphasis Type="Italic">p</Emphasis>-type doping in SiC nanowires: role of quantum effect

Using first principles density functional theory calculations, we investigated the X and X–N–X (X = Al and Ga) doped 3C–SiC nanowires grown along the [111] crystal direction with diameter of 1.00 and 1.33 nm. We found that the ionization energy of acceptor state is much larger in nanowires than that in the bulk SiC as a result of quantum confinement effect. Simulation results show that the reduced dimensionality in p-type SiC nanowires strongly reduces the capability of the materials to generate free carriers. It is also found that X–N–X (X = Al and Ga) complexes are energetically favored to form in the materials and have lower ionization energy than single doping. It is confirm that codoping is more suitable method for achieving low-resistivity semiconductors either in nano materials or bulk material.     

AFM study of a SiC film grown on Si(1 0 0) surface using a C2H4 beam

A 3C-silicon carbide (SiC) thin film grown on a Si(1 0 0) surface using an ethylene (C₂H₄) molecular beam has been studied by atomic force microscopy. At the center of the irradiation area of the ethylene beam, the shape of the SiC islands was rectangular, the average length of which was 74.5 nm and the average height was 13.1 nm. Each SiC island consists of the SiC particles with the average diameter of 17 nm. Just inside of the boundary region of the beam irradiation, the average size and height of the islands decreased to 50.1 and 8.2 nm, respectively. Just outside of the boundary region, the average size and height decreased to 17.7 and 5.1 nm, respectively. The average reaction probabilities at the above three points were estimated to be 0.14, 0.27 and 2.7%, respectively. New growth mode of the crystal growth is proposed (particles gathering island mode).     

Design and fabrication of electro-optic waveguides with self-assembled superlattice films

This paper presents a strategy for fabricating low loss waveguide devices based on high electro-optic (EO) coefficient self-assembled superlattice (SAS) films, a new sort of polymeric films grown on SiO₂ film and coated with other polymeric films to form multi-layer EO waveguides structure without electric field poling. Firstly, the optical propagation loss induced by the absorption of electrodes is simulated and optimized to obtain both the low optical loss and the low drive voltage. Then this paper gives the scanned electron microscopic (SEM) images of the fabricated devices, the simulated and experimental images of the single guided mode, and the measured optical propagation loss of the EO waveguide devices of 1.0 dB/cm. Finally, the very great agreement between the simulated and measured results of propagation loss of devices is observed.     

TEOS-based low-pressure chemical vapor deposition for gate oxides in 4H–SiC MOSFETs using nitric oxide post-deposition annealing

The use of SiO₂/4H–SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) can be problematic due to high interface state density (D_it) and low field-effect mobility (μ_fe). Here, we present a tetra-ethyl-ortho-silicate (TEOS)-based low-pressure chemical vapor deposition (LPCVD) method for fabricating the gate oxide of 4H–SiC MOSFETs using nitric oxide post-deposition annealing. SiO₂/4H–SiC MOS capacitors and MOSFETs were fabricated using conventional wet and TEOS oxides. The measured effective oxide charge density (Q_eff) and D_it of the TEOS-based LPCVD SiO₂/4H–SiC MOS capacitor with nitridation were 4.27 × 10¹¹ cm⁻² and 2.99 × 10¹¹ cm⁻²eV⁻¹, respectively. We propose that the oxide breakdown field and barrier height were dependent on the effective Q_eff. The measured μ_fe values of the SiO₂/4H–SiC MOSFETs with wet and TEOS oxides after nitridation were, respectively, 11.0 and 17.8 cm²/V due to the stable nitrided interface between SiO₂ and 4H–SiC. The proposed gate stack is suitable for 4H–SiC power MOSFETs.     

DC-conductivity of thin films of 1,4-cis-polybutadiene doped with SiC

In this paper the results of DC-conductivity investigation of 1,4-cis-polybutadiene thin films doped with 5% weight of silicon carbonate (SiC) of nanocrystalline form with the size of grains being about 20 nm are presented. The aim of the study was to receive a knowledge about the electrical properties and DC-conductivity mechanisms depending on film thickness, temperature and electric field magnitude. The investigated films thickness ranged from 1 to 12 μm. The investigations were carried out for both undoped and doped with nanocrystalline SiC polymers. The current flow through the material bulk changed from 10⁻¹² to 10⁻⁴ A with applied electric fields of 0 to 3 × 10⁷ V/m and temperature of the film varying from 15 to 325 K. It was observed that the magnitude of the current flow through the investigated material bulk is governed by a phase state of the polymer and the presence of SiC in the bulk. The charge transport through the material bulk is controlled by the Poole-Frenkel phenomenon as well as by hopping. The determined activation energies were between kT and 0.36 eV.     

Plasmonic Newton's cradle for low-loss subwavelength energy transport: Homogeneous or heterogeneous nanoparticle chains?

Five closely spaced Au or Ag NPs are linearly arranged in analogy with Newton's cradle, forming various homogeneous and heterogeneous NP chains. Using small NPs, the Au–Ag–Ag–Ag–Au heterochain has the lowest propagation loss (17.6%) at short resonance wavelengths. When the NP diameter is increased to 80 nm, the dominant resonance is shifted to longer wavelengths. As low as 6% of the total energy dissipates in the intermediate NP component, and there seems to be little difference between the Au–Ag–Ag–Ag–Au heterochain and the Ag–Ag–Ag–Ag–Ag homochain. Besides the wavelength-dependent intrinsic loss (i.e., the imaginary part of the permittivity) in metals, the real part of the permittivity also plays a critical role in determining the propagation loss. Considering the high fabrication cost of the heterochain, the homochain composed of moderately large Ag NPs (<100 nm) may be an optimal choice for low-loss subwavelength energy transport in practice.     

Propagation of nonlocal optical solitons in lossy media with exponential-decay response

Propagation of optical solitons in lossy nonlocal media with exponential-decay response was investigated theoretically. The analytical solutions of nonlocal solitons and breathers are obtained by variational approach which is applied to a (1 + 1)D nonlocal nonlinear Schrödinger equation. The critical power of soliton and period of breathers are also obtained in the absence of the loss. When the loss is relatively small, the average beam width of breathers has a trend to expand during propagation. The analytical results are confirmed by numerical simulation.     

A long-range hybrid THz plasmonic waveguide with low attenuation loss

Numerical solutions are obtained for the proposed novel hybrid terahertz plasmonic waveguide structure, namely the silicon metal silicon (SMS) waveguide. It is shown that the SMS waveguide can overcome the diffraction limit while still maintaining a sizeable propagation length. The geometric dependence of the mode characteristics of this structure is analyzed in detail, showing strong confinement and low loss with propagation lengths exceeding 14 mm at normalized mode areas of 1.72 × 10⁻². By using the FEM method (Comsol), the guiding properties of the hybrid terahertz surface plasmon polariton (HTSPP) waveguide are numerically analyzed at the THz frequency, and a combination of double-structured comparisons of the best features of the terahertz plasmonic waveguide is made. Depending on the height used and how the mode confinement is measured, various modal designs, such as double microwire structures, are developed. The structures indicate that we verified the possibility of low attenuation loss of hybrid THz plasmonics propagation. The effective mode area A_eff, energy distribution, and propagation length L_p versus height for waveguides with Si microwire and SiO₂ are shown. The numerical calculation results reveal a potential for use in applications such as optical force in trapping and transporting biomolecules, and in high-density integrated circuits.     

Demonstration of temperature resilient properties of 2D silicon carbide photonic crystal structures and cavity modes

In this paper, photonic crystal (PhC) based on two dimensional (2D) square and hexagonal lattice periodic arrays of Silicon Carbide (SiC) rods in air structure have been investigated using plane wave expansion (PWE) method. The PhC designs have been optimized for telecommunication wavelength (λ = 1.55 μm) by varying the radius of the rods and lattice constant. The result obtained shows that a photonic band gap (PBG) exists for TE-mode propagation. First, the effect of temperature on the width of the photonic band gap in the 2D SiC PhC structure has been investigated and compared with Silicon (Si) PhC. Further, a cavity has been created in the proposed SiC PhC and carried out temperature resiliency study of the defect modes. The dispersion relation for the TE mode of a point defect A1 cavity for both SiC and Si PhC has been plotted. Quality factor (Q) for both these structures have been calculated using finite difference time domain (FDTD) method and found a maximum Q value of 224 for SiC and 213 for Si PhC cavity structures. These analyses are important for fabricating novel PhC cavity designs that may find application in temperature resilient devices.     

Magnetism in nanocrystalline SiC films

Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °С and 1200 °С. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral V_SiV_C divacancies in separate nanocrystals. The estimated concentration of neutral V_SiV_C divacancies in nanocrystalline SiC films is ~10²⁰ сm⁻³.     

Stress-induced depolarization loss in a YAG zigzag slab

The stress-induced depolarization loss in a [1 1 1] orientated YAG zigzag slab was studied. The process to get correct piezo-optic tensor was given in detail. The results indicated that the relationships between losses and cut angles varied with the change in the bounce numbers of light in zigzag propagation through the slab. The loss mainly occurred in the area near the edges in width and the mean depolarization loss was less than 3%. The coupling of a laser beam with adequate bounce number and aspect ratio less than 1 on the entrance plane was found to reduce the depolarization loss.