Ultrathin SiC Research Articles

Non-equilibrium electronic properties of ultra-thin SiC NWs influenced by the tensile strain

The effect of the tensile strain on non-equilibrium electronic properties are studied for the ultra-thin SiC NWs (NWs) with different diameters. Results show that the equilibrium conductance fluctuates with the strain, and the maximum decreases with the increase of the size. Essentially, strong conductance originates from large electron transmission and delocalized electronic states. For I–V characteristics, the tensile strain affects significantly the growth rate and intensity of the current. Under any biases, the strongest current appears in late strain (0.7136) for the single-atom chain, while in the starting strains (e.g. 0.1584, 0.2504) for thicker NWs. The tensile strain would weaken the current of thicker NWs. The mechanical stretching contributes to valuable negative differential resistance (NDR) effect, which appears in middle and late stretching stages such as 5408, 0.7136 and 0.8472 for these three SiC NWs, respectively. Furthermore, NDR effect occurs at more strains and presents multistage features as the diameter of NW increases. The conductance waves with voltage. Such fluctuation deepens and show a more concentrated range with the increased size of NWs. The conductance at closer strains changes with the bias in a relatively close range. From structural evolution, when the NWs are fully extended under tensile strain without structural damage, the necking or the formation of single atom chains, the corresponding conductance and current are stronger, deriving from delocalized electronic states. This work provides an approach to get access to valuable NDR effect and strong backing in promising applications of nano piezoelectric electronics for ultra-thin SiC NWs.

Mechanical tensile behavior-induced multi-level electronic transport of ultra-thin SiC NWs

Mechanical tensile behavior and its influence on electron transport are especially appealing for ultra-thin SiC Nanowires (NWs). Our studies theoretically show that ultra-thin SiC-[100] NWs in different diameters possess much better plasticity than SiC NWs in large scales and exhibit non-traditionally multiple-fluctuating stress-strain curves due to the chain-by-chain fracture of NWs. Noticeably, NWs possesses almost the same fracture stain and the corresponding stress decreases with diameter. Influenced by the strain, ultra-high transmission coefficients appear (exceed 1) and stable electron transmission can be kept in some strain range for all sizes of SiC NWs. An obvious increase of transmission peaks occurs in the thinnest SiC atomic chain at larger strains while the strain has almost no effect on the number of transmission peaks for other thicker SiC NWs. The generation of monatomic chains would weaken the electron transport of thicker SiC NWs. Internally, C elements and p-orbital contribute more in electron transport and stretching strains have almost no effect on such contribution assignments. This work provides stronger support for applications of ultra-thin SiC-[100] NWs in nano-piezoelectric devices and nanoelectronics in mechanically disturbed environments, and an effective way to strengthen electron transport of NWs.

Synthesis of Ultra-Thin Two-Dimensional SiC Using the CVD Method

Two-dimensional materials have shown great potential for applications in many research areas because of their unique structures, and many 2D materials have been investigated since graphene was discovered. Ultra-thin SiC layers with thicknesses of 8–10 nm and multi-layer SiC films were designed and fabricated in this study. First, the multi-layer SiC films were obtained by the chemical vapor deposition (CVD) method with the addition of boron elements. We found that boron additives showed novel effects in the CVD process. Boron can promote the formation and crystallization of SiC films at low temperatures (1100 °C), resulting in the separation of SiC films into multi-layers with thicknesses of several nanometers. In addition, a formation mechanism for the 2D SiC layers is proposed. The boron mostly aggregated spontaneously between the thin SiC layers. Photoluminescence spectroscopy results showed that the SiC films with multi-layer structures had different bandgaps to normal SiC films. The present work proposes a potential method for fabricating 2D SiC materials with convenient experimental parameters and shows the potential of 2D SiC materials for use in electronics.

Superior electron transport of ultra-thin SiC nanowires with one impending tensile monatomic chain

The effect of the tensile strain on the electron transport are studied theoretically for ultra-thin SiC Nanowires (NWs) with different diameters. Results show that these NWs exhibit distinctive and non-traditional stress-strain curves, characterized by multistage fluctuations. The tension greatly affects the electron transport. The strongest transmission appears when the wire is stretched to the near-emergence of the monatomic chain in the necking place (especially for thicker SiC NWs) which suppresses the electron transport, essentially originating from localized transmission eigenstates and pathways. This work provides an approach to enhance the electron transport and strong backing in promising applications of nanoelectronics and nano-piezoelectric devices for ultra-thin SiC NWs.

Interface Characterization and Analysis of 4H-SiC Direct Bonding Structure Based on Plasma Processing

A plasma-assisted direct bonding method for 4H-SiC is put forward to prepare all-SiC vacuum-sealed cavity in this paper. This method takes three significant steps of bonding surface treatment, hydrophilic pre-bonding and hot pressing bonding. The SiC bonded sample with a cylindrical sealing cavity structure was prepared under a pressure of 2 MPa for a period of 1 h at 1000 °C using the direct bonding method. The bonded sample’s airtightness is approximately 0.1 × 10−9 pa·m3 s−1, and the bonding strength reaches 24.9 MPa, meeting the requirements of most pressure sensors. The cavity structure of the bonded sample is unbroken and the bonding interface is smooth without stress concentration under a scanning electron microscope (SEM). Transmission electron microscope (TEM) observation results reveal that bonding interface is amorphous with a thickness of less than 1 nm. The bonding interface is mainly composed of carbon and silicon which is analyzed through energy dispersive X-ray (EDX). It is speculated that the transition layer of ultrathin amorphous SiC is formed during bonding process. Finally, the SiC bonding mechanism is discussed in detail based on the experimental results. All-SiC bonding structures with a vacuum-sealed cavity can be applied to fabricate mechanical quantity sensors for use in severe environment.

Tunable fabrication and photoluminescence property of SiC nanowires with different microstructures

SiC nanowires including ultra-thin, hierarchical, bamboo-like, beaded-like and core-shell nanowires were successfully synthesized via carbothermal reduction method without using catalyst. The microstructures and diameter were controlled by reaction temperature ranging from 1500 to 1600 °C, holding time from 2 to 4 h and different raw materials. Notably, the diameter of ultra-thin SiC nanowires was ranging from 8 to 20 nm. Photoluminescence properties of obtained nanowires with unique microstructures were investigated at room temperature. It indicates that the primary emission peaks locate in the blue/violet band range of 350–500 nm with obvious blue shifts. Meanwhile, the luminescence mechanism of SiC nanowires is discussed in detail. The ultra-thin SiC nanowires exhibit the highest intensity because of the strong quantum confinement effect and the quasi-direct band gap. Due to the strong defects effect of twin segments, hierarchical and bamboo-like nanowires with high stacking faults and rough surface show higher intensity under 263 nm excitation. While beaded-like and core-shell nanowires with SiO2 shell and smooth surface exhibit a noticeable increase in the intensity under 318 nm excitation. This might be ascribed to the neutral oxygen vacancies and oxygen atoms.

Porous SiC/melamine-derived carbon foam frameworks with excellent electromagnetic wave absorbing capacity

Porous three-dimensional SiC/melamine-derived carbon foam (3D-SiC/MDCF) composite with an original open pore structure was fabricated by the heat treatment of the commercial melamine foam (MF), carbonization of the stable MF, and chemical vapor deposition of the ultra-thin SiC coating. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to detect the microstructure and morphology of the as-prepared composites. The results indicated that the 3D-SiC/MDCF composites with the coating structure were prepared successfully. The obtained minimum reflection loss was -29.50 dB when the frequency and absorption thickness were 11.36 GHz and 1.75 mm, respectively. Further, a novel strategy was put forward to state that the best microwave absorption property with a thin thickness of 1.65 mm was gained, where the minimum reflection loss was -24.51 dB and the frequency bandwidth was 3.08 GHz. The excellent electromagnetic wave absorption ability resulted from the specific cladding structure, which could change the raw dielectric property to acquire excellent impedance matching. This present work had a certain extend reference meaning for the potential applications of the lightweight wave absorption materials with target functionalities.

Direction-independent dual-band perfect absorption induced by fundamental magnetic polaritons.

In this paper, we designed a single sized Metal-Insulator Pair-Metal hybrid grating for dual-band perfect absorption from 8 μm to 14 μm utilizing both nondispersive insulators and dispersive phonic insulators. The hybrid grating was composed of Al/ZnTe-SiC pair/Al, which incorporated an ultrathin phononic SiC layer between the nondispersive ZnTe dielectric spacer and Al substrate. The physical mechanisms responsible for the dual-band perfect absorption were elucidated by the resonance of fundamental magnetic polaritons (MPs). Dual-band perfect absorption with incident angle insensitive feature was enabled. An equivalent LC circuit model predicting the dual-band resonant absorption peaks wavelengths was proposed and verified. Furthermore, the effects of grating period, strip width, nondispersive dielectric spacer thickness and polar phononic dielectric spacer thickness on the absorption were explored.

Al-DTPA microfiber assisted formwork construction technology for high-performance SiC membrane preparation

High gas permeance and particle interception efficiency are critical for the performance of dust filtration membrane, which requires the membrane to have higher porosity support and ultrathin separation layer. In this work, Al-DTPA (aluminium-diethylenetriamine pentaacetic acid) microfibers were prepared as the sacrificial intermediate layer to bridge the gaps between the large pore support for ameliorating the infiltration of the suspension in the membrane preparation process. The temporary Al-DTPA constructed layer was subsequently removed via calcination, which has few effects on decreasing the combine force of support and separation layer. An ultrathin SiC membrane with its thick of ~100 μm and pore size of 2–5 μm was successfully prepared on the SiC support with a pore size of 30 μm. The preparation and defect formation mechanism were analyzed by investigating the formula and the preparation process. The resulting asymmetric, transition layer-free, defect-free SiC membrane exhibited excellent gas permeance (240–277 m3 m−2 h−1·kPa−1) and dust interception efficiency (99.8%) for particles less than 0.5 μm. The successful fabrication of this transition layer-free and defect-free asymmetric membrane enable the use of mismatched particle size between the support and separation layer, which may provide a new route for the preparation of high-performance gas-solid separation ceramic membranes.

Graphene and silicene nanodomains in a ultra-thin SiC layer for water splitting and hydrogen storage. A first principle study

First-principles calculations within the density functional theory (DFT) have been addressed to investigate the energetic stability, electronic and optical properties of graphene and silicene nanodomains in a SiC single layer (h-SiC). We observe that graphene domains form a planar structure and give rise to an occupied and an empty electronic levels inside the h-SiC band gap, leading the h-SiC to present a strong optical absorption peak in the visible region. On the other hand, when a silicene nanodomain is present the system is no longer planar and present a corrugated structure similar to the silicene structure. The silicene nanodomain introduce three empty electronic levels within the band gap, leading the h-SiC with optical absorption in the visible region. These results show that a graphene nanodomain in h-SiC is appropriate for optical devices, while silicene nanodomains form almost sp3 quantum dots. This finding suggest that the graphene and silicene nanodomains in a SiC single layer increase the possibility to use h-SiC to produce new electronic and optical devices as well for energy storage by hydrogen adsorption. In fact, we study the H2 and O2 adsorption on the pristine system and on the nanodomains, we observe that the presence of the nanodomais increase the binding energies of the adsorbed molecules.

Synthesis and microwave absorption properties of novel reticulation SiC/Porous melamine-derived carbon foam

The ultrathin SiC coating/melamine-derived porous carbon foam composite (SiC/PCF) was synthesized for the first time by the stable treatment of the commercial melamine foam (MF), carbonization stage of the steady MF, and chemical vapor deposition of the SiC thin films. The microstructure analysis demonstrated that the SiC/PCF composites with layered structures and altered dielectric response were fabricated eventually. The minimum reflection loss of −25.93 dB was obtained when the thickness was 1.05 mm and the measured frequency was 17.20 GHz. Meanwhile, the reflection loss could drop below −10 dB in the whole thickness with the frequency ranging from 3.00 to 18.00 GHz, which showed a more excellent microwave absorbing performance compared with PCF. Furthermore, the influencing mechanism of both the impedance matching ratio and attenuation constant was discussed to provide actual guidances in designing excellent microwave absorbing materials for functional applications.

Ultrathin SiC Nanosheets with High Reduction Potential for Improved CH4 Generation from Photocatalytic Reduction of CO2

AbstractExploitation of low‐cost and efficient photocatalysts for selective reduction of CO2 into fuels such as methane or methanol is highly desired in the field of solar‐to‐fuel conversion. Herein, ultrathin SiC nanosheets (NSs) with high crystallinity are prepared using two‐dimensional reduced graphene oxide as sacrificial template. The ultrathin feature of SiC NSs readily shortens the migration distance of photoexcited carriers, thereby reducing the recombination probability and providing more energetic electrons to participate in CO2 reduction. Consequently, both the yield (3.11 μmol h−1 g−1) and selectivity (90.6%) of CH4 over SiC NSs demonstrate dramatic improvements in comparison with that of micro‐size SiC (0.76 μmol h−1 g−1, 77.9%) and commercial TiO2 (1.46 μmol h−1 g−1, 61.0%). The initial absorption and activation of CO2 molecules on the surface of SiC NSs is confirmed by the in situ diffuse reflectance infrared Fourier transform spectroscopy. The SiC NSs can promote the deep reduction of carbon intermediate into CH4 thanks to the strong reduction potential of photoexcited electrons. This work not only proves ultrathin SiC NSs to be a promising photocatalyst for CO2 reduction, but also provides novel insights into deep photoreduction of CO2 to CH4.

Novel Three-Dimensional SiC/Melamine-Derived Carbon Foam-Reinforced SiO2 Aerogel Composite with Low Dielectric Loss and High Impedance Matching Ratio

Novel three-dimensional SiC/melamine-derived carbon foam composite filled by silica aerogel (SiC/MDCF–Aerogel) was first fabricated by the pyrolysis process of commercial melamine foam, chemical vapor deposition of ultrathin SiC films, and the sol–gel method of silica aerogel. The results indicated that the SiC/MDCF–Aerogel composite consisted of the SiC three-dimensional open-celled network structure and the pregnant silica aerogel in the pores. Tiny cracks on the interface of skeletons and clumps were induced during the aging process, which was drastically beneficial to the microwave-absorbing properties. A minimum reflection loss could be obtained as low as −18.41 dB at the measured frequency of 16.92 GHz when the thickness of the absorber was 3.65 mm, and the reflection loss could drop below −10 dB when the selected frequencies ranged from 15.80 to 17.52 GHz, along with the thickness ranging from 2.75 to 5.0 mm, which possessed a relatively better microwave absorption performance especially at a highe...

In Situ-Fabricated 2D/2D Heterojunctions of Ultrathin SiC/Reduced Graphene Oxide Nanosheets for Efficient CO2 Photoreduction with High CH4 Selectivity.

Photoreduction of CO2 into fuel molecules such as CH4 represents a promising route to simultaneously explore renewable energy and alleviate global warming. However, the implementation of such a process is hampered by low product yields and poor selectivity. A 2D/2D heterojunction of ultrathin SiC and reduced graphene oxide (RGO) nanosheets was fabricated in situ for efficient and selective photoreduction of CO2 . Ultrathin SiC suppresses significant charge recombination in the bulk phase, thus providing more energetic electrons. The robust 2D/2D heterojunction allows fast transfer of energetic electrons from SiC to RGO. Combining the vital role of RGO in facilitating CO2 activation, the optimized SiC/RGO exhibits an electron-transfer rate of 58.17 μmol h-1 g-1 towards CO2 reduction, 2.7 times that of pure SiC (20.25 μmol h-1 g-1 ). About 92 % of the transferred electrons from SiC are devoted to generating CH4 (6.72 μmol h-1 g-1 ). Such high efficiency and selectivity are mainly a result of the densely accumulated energetic electrons within RGO, which facilitate the eight-electron process to produce CH4 . This work will inspire the design of catalyst/cocatalyst systems for efficient and selective photoreduction of CO2 .

Effect of thickness of SiC films on compression and thermal properties of SiC/CF composites

Commonly, carbon foam derived from commercially available melamine foam showed brittle characteristics. In this paper, the carbon foam was prepared via the direct carbonization of the melamine foam, and chemical vapor deposition was employed to deposit ultra-thin SiC films on the CF skeleton. The evolution, microstructure, mechanical strength, and thermal properties of the as-prepared SiC/CF composites were investigated. Test results showed that a novel SiC skeleton with a three-dimensional interconnected network was prepared successfully. The thickness of the SiC filmes had a significant influence on the compression and thermal properties of the composites. The SiC/CF-II possessed a higher compression performance than that of SiC/CF-I, while the thermal insulation was relatively much poorer. This present work had some reference meaning to the correlation studies of the thermal insulation material for the potential applications while bearing live loads.

Freestanding ultrathin single-crystalline SiC substrate by MeV H ion-slicing

SiC is a widely used wide-bandgap semiconductor, and the freestanding ultrathin single-crystalline SiC substrate provides the material platform for advanced devices. Here, we demonstrate the fabrication of a freestanding ultrathin single-crystalline SiC substrate with a thickness of 22 μm by ion slicing using 1.6 MeV H ion implantation. The ion-slicing process performed in the MeV energy range was compared to the conventional case using low-energy H ion implantation in the keV energy range. The blistering behavior of the implanted SiC surface layer depends on both the implantation temperature and the annealing temperature. Due to the different straggling parameter for two implant energies, the distribution of implantation-induced damage is significantly different. The impact of implantation temperature on the high-energy and low-energy slicing was opposite, and the ion-slicing SiC in the MeV range initiates at a much higher temperature.

Elimination of Voids at Interface of β-SiC Films and Si Substrate by Laser CVD

Void-free β-SiC films were deposited on Si(001) substrates by laser chemical vapor deposition using hexamethyldisilane (HMDS) as the precursor. The effect of the time of introducing HMDS, i e, the substrate temperature when HMDS introduced (Tin), on the preferred orientation, surface microstructure and void was investigated. The orientation of the deposited SiC films changed from to random to with increasing Tin. The surface showed a layer-by-layer microstructure with voids above Tin ⩾ 773 K, and then transformed into mosaic structure without voids at Tin= 298 K. The mechanism of the elimination of voids was discussed. At Tin =298 K, Si surface can be covered by an ultrathin SiC film, which inhibits the out-diffusion of Si atoms from substrate and prohibites the formation of the voids.

Photoluminescent two-dimensional SiC quantum dots for cellular imaging and transport

Two-dimensional (2D) ultrathin SiC has received intense attention due to its broad band gap and resistance to large mechanical deformation and external chemical corrosion. However, the synthesis and application of ultrasmall 2D SiC quantum dots (QDs) has not been explored. Herein, we synthesize a type of monolayered 2D SiC QDs with advanced photoluminescence (PL) properties via a facile hydrothermal route. Their average size and thickness can be easily adjusted by altering the reaction time. The ultrasmall 2D SiC QDs exhibit a long fluorescence lifetime of 2.59 μs due to efficient quantum confinement. The applications of SiC QDs are demonstrated through labeling A549, HeLa, and NHDF cells and delivering agents for intracellular low-abundant microRNA (miRNA) detection. This advance in preparing photoluminescent SiC QDs is of great significance for broadening their potential in biomedical and optical applications.

Robust Free‐Standing Nano‐Thin SiC Membranes Enable Direct Photolithography for MEMS Sensing Applications

This work presents fabrication of micro structures on sub–100 nm SiC membranes with a large aspect ratio up to 1:3200. Unlike conventional processes, this approach starts with Si wet etching to form suspended SiC membranes, followed by micro‐machined processes to pattern free‐standing microstructures such as cantilevers and micro bridges. This technique eliminates the sticking or the under‐etching effects on free‐standing structures, enhancing mechanical performance which is favorable for MEMS applications. In addition, post‐Si‐etching photography also enables the formation of metal electrodes on free standing SiC membranes to develop electrically‐measurable devices. To proof this concept, the authors demonstrate a SiC pressure sensor by applying lithography and plasma etching on released ultrathin SiC films. The sensors exhibit excellent linear response to the applied pressure, as well as good repeatability. The proposed method opens a pathway for the development of self‐sensing free‐standing SiC sensors.

From graphene to silicon carbide: ultrathin silicon carbide flakes

This study presents a new ultrathin SiC structure prepared by a catalyst free carbothermal method and post-sonication process. We have found that merging ultra-light 3D graphene foam and SiO together at high temperature leads to the formation of a complex SiC structure consisting of 3D SiC foam covered with traditional 1D nanowires. Upon breaking off, the 3D SiC was confirmed to be made from 2D nanosheets. The resulting novel 2D SiC nanosheets/nanoflakes were thoroughly investigated by using optical microscope, SEM, EDS, TEM, STEM, AFM, and Raman, which verified the highly crystallised structure feature. AFM results revealed an average thickness of 2–3 nm and average size of 2 μm for the flakes. This new SiC structure could not only actualise SiC usage for nano-electronic devices but is also expected to open new applications as well.