We present a study of mechanical, electronic and magnetic properties of two-dimensional (2D), monolayer of silicon carbide (SiC) in honeycomb structure and its quasi-one-dimensional (quasi-1D) armchair nanoribbons using first-principles plane-wave method. In order to reveal dimensionality effects, a brief study of three-dimensional (3D) bulk and 1D atomic chain of SiC are also included. Calculated bond-lengths, cohesive energies, charge transfers and band gaps display a clear dimensionality effect. The stability analysis based on the calculation of phonon frequencies indicates that 2D SiC monolayer is stable in planar geometry. We found that 2D SiC monolayer in honeycomb structure and its bare and hydrogen passivated nanoribbons are ionic, nonmagnetic, wide band gap semiconductors. The band gap is further increased upon self-energy corrections. The mechanical properties are investigated using the strain energy calculations. The effect of various vacancy defects, adatoms, and substitutional impurities on electronic and magnetic properties in 2D SiC monolayer and in its armchair nanoribbons is also investigated. Some of these vacancy defects and impurities, which are found to influence physical properties and attain magnetic moments, can be used to functionalize SiC honeycomb structures.

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First-principles study of defects and adatoms in silicon carbide honeycomb structures

We propose a mixed-space approach using the accurate force constants calculated by the direct approach in real space and the dipole–dipole interactions calculated by linear response theory in reciprocal space, making the accurate prediction of phonon frequencies for polar materials possible using the direct approach as well as linear response theory. As examples, by using the present approach, we predict the first-principles phonon properties of the polar materials α-Al2O3, MgO, c-SiC, and h-BN, which are in excellent agreement with available experimental data. (Some figures in this article are in colour only in the electronic version)

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A mixed-space approach to first-principles calculations of phonon frequencies for polar materials.

Crystal defects affect the thermal and heat-transport properties of materials by scattering phonons and modifying phonon spectra1–8. To appreciate how imperfections in solids influence thermal conductivity and diffusivity, it is thus essential to understand phonon–defect interactions. Sophisticated theories are available to explore such interactions, but experimental validation is limited because most phonon-detecting spectroscopic methods do not reach the high spatial resolution needed to resolve local vibrational spectra near individual defects. Here we demonstrate that space- and angle-resolved vibrational spectroscopy in a transmission electron microscope makes it possible to map the vibrational spectra of individual crystal defects. We detect a red shift of several millielectronvolts in the energy of acoustic vibration modes near a single stacking fault in cubic silicon carbide, together with substantial changes in their intensity, and find that these changes are confined to within a few nanometres of the stacking fault. These observations illustrate that the capabilities of a state-of-the-art transmission electron microscope open the door to the direct mapping of phonon propagation around defects, which is expected to provide useful guidance for engineering the thermal properties of materials. State-of-the-art electron energy-loss spectroscopy in a transmission electron microscope maps the detailed phonon spectra of single defects in silicon carbide

Single-defect phonons imaged by electron microscopy.

This Chapter presents the current status of phonon-dispersion studies using very high energy resolution inelastic X-ray scattering. The theoretical back- ground and the instrumental principles are briefly summarized. This is followed by a representative selection of studies on single crystals and polycrystalline materials, including high-pressure work. The Chapter concludes with novel applications of the technique.

Inelastic X-Ray Scattering from Phonons

Fundamental band edge absorption is investigated in nominally undoped (n<1014cm−3) and heavily doped (n∼8×1018cm−3) 4H‐SiC by a spectroscopy technique based on spatially and time-resolved free-carrier absorption. The spectra are extracted over a wide absorption range (0.02–500cm−1) at temperatures from 75to450K. The experimental results are supported by an indirect transition theory with a unique set of dominating momentum-conserving phonons, showing good correlation with earlier findings of differential absorption measurements at 2K. Exciton binding energy of 30±10meV is derived from fitting the data at 75K. The detected polarization anisotropy of absorption with respect to c axis is shown to be consistent with the selection rules for the corresponding phonon branches. An analytical model related to constant degree of involved phonons describes well the obtained energy gap variation with temperature. Finally, doping induced band gap narrowing is characterized above the impurity-Mott transition and compar...

Fundamental band edge absorption in nominally undoped and doped 4H‐SiC

We present an experimental and theoretical investigation of the phonon dispersion relations in zinc blende (3C) SiC. The experimental data were obtained for the entire Brillouin zone by inelastic x-ray scattering (IXS) using a synchrotron radiation source. Eigenvector analysis is performed with the aid of state-of-the-art linear response first principles calculations based on density functional theory. The theoretical predictions reproduce the experimental phonon dispersion remarkably well. These results are compared with data obtained previously for the 〈111〉 direction by Raman spectroscopy using several SiC polytypes and the backfolding technique. IXS data for 4H modification along the c axis are also reported.

Determination of the phonon dispersion of zinc blende (3C) silicon carbide by inelastic x-ray scattering

A description is given of the profiling of CVD grown 3C SiC on undulant (001) Si using low temperature photoluminescence (LTPL). Inelastic neutron scattering (INS) and X-ray Raman scattering (XRS) are compared for acoustical modes of 4H SiC. Schottky barrier heights are obtained for 4H and 6H SiC on different crystal faces using three different measuring techniques. Scanning electron microscopy (SEM) is used to display a variety of porous SiC morphologies achieved in n-type and p-type SiC. This paper is intended to be the introduction to the “CHARACTERIZATION” section of this volume. To serve this purpose we illustrate the subject matter with new results using four distinct experimental techniques.

Four Current Examples of Characterization of Silicon Carbide

A B C D E F B G H I D J G K L M L N L O P N Q R S K L I P T Q U S Q O T Q K H V N G W X Y S M K S G Z S Q W K L Q [ \\ X ] ^ _ ` a b L N L L W B Q L X c S Q d B G e 1 f g h B G H S g E V T L T G b T N Q H S i f E b j X f Q W T G G S k B L M T G B F l B Z T Q B L T Q e X f Q W T G G S X J F F M G T M K ` ^ m n a D m o \\ m 6 p N Q T U S B G b e G H V Q T L Q T G q B g M B L M T G R B H M F M L e i p b q R j X r [ E [ s s ^ X n o ^ m n c Q S G T Z F S X R Q B G H S : J G K L M L N L O P N Q t V S T Q S L M K H V S E V e K M I X u G M h S Q K M L P B L q S W S G K Z N Q W X a n ^ m ^ q S W S G K Z N Q W X c S Q d B G e @ v S U B Q L B d S G L T O E V e K M H K X u G M h S Q K M L e T O E M L L K Z N Q W V X E M L L K Z N Q W V E f \\ _ s ` ^

Lattice Dynamics of 4H-SiC by Inelastic X-Ray Scattering

Preliminary results for the phonon dispersion curves of hexagonal 4H-SiC from experimental inelastic neutron (INS) and X-ray scattering (IXS) are reported and contrasted with those of cubic 3C-SiC and silicon. The experimental frequencies and scattering intensities are in excellent agreement with those from first-principles calculations using density-functional methods. The relative merits of the two experimental techniques and aspects of the density functional perturbation theory and the so-called frozen phonon method for the determination of the basic phonon properties are briefly outlined.

B. Stojetz

Papers

Determination of the phonon dispersion of zinc blende (3C) silicon carbide by inelastic x-ray scattering

Four Current Examples of Characterization of Silicon Carbide

Lattice Dynamics of 4H-SiC by Inelastic X-Ray Scattering

Phonons in SiC from INS, IXS, and Ab-Initio Calculations