208 research outputs found
Heteroepitaxial Growth of 3C-SiC Films on Maskless Patterned Silicon Substrates
No full textHeteroepitaxial growth of 3C-SiC on patterned Si substrates by low pressure chemical vapor deposition (LPCVD) has been investigated to improve the crystal quality of 3C-SiC films. Si substrates were patterned with parallel lines, 1 to 10μm wide and spaced 1 to 10μm apart, which was carried out by photolithography and reactive ion etching. Growth behavior on the patterned substrates was systematically studied by scanning electron microscopy (SEM). An air gap structure and a spherical shape were formed on the patterned Si substrates with different dimensions. The air gap formed after coalescence reduced the stress in the 3C-SiC films, solving the wafer warp and making it possible to grow thicker films. XRD patterns indicated that the films grown on the maskless patterned Si substrates were mainly composed of crystal planes with (111) orientation
Epitaxial growth on 4H-SiC by TCS as a silicon precursor
No full textEpitaxial growth on n-type 4H-SiC 8°off-oriented substrates with a size of 10 × 10 mm~2 at different tem-peratures with various gas flow rates has been performed in a horizontal hot wall CVD reactor, using trichlorosilane (TCS) as a silicon precursor source together with ethylene as a carbon precursor source. The growth rate reached 23 μm/h and the optimal epilayer was obtained at 1600 ℃ with a TCS flow rate of 12 sccm in C/Si of 0.42, which has a good surface morphology with a low RMS of 0.64 nm in an area of 10 × 10μm~2. The homoepitaxial layer was oh-tained at 1500 ℃ with low growth rate (< 5μm/h) and the 3C-SiC epilayers were obtained at 1650 ℃ with a growth rate of 60-70μm/h. It is estimated that the structural properties of the epilayers have a relationship with the growth temperature and growth rate. Silicon droplets with different sizes are observed on the surface of the homoepitaxial layer in a low C/Si ratio of 0.32
AMS measurements of Be-10 and C-14 in loess profile at Donglingshan, Beijing
No full textA loess profile in Donglingshan site (40 degrees 02'N, 115 degrees 27'E) near Beijing was chosen to study the loess formation process and paleo-climate variation. Thirty eight samples were collected and analyzed for C-14, Be-10 as well as MS. TOC and delta C-13. Based on C-14 measurements, we established a time scale for this loess profile during Holocene. The averaged Be-10 deposition flux was found to be 4.87 x 10(6) atoms/cm(2) year. This is similar to the flux of 4.2 x 10(6) atoms/cm(2) year estimated for Chinese Loess Plateau in central China. High Be-10 concentrations of 3.85-5.66 x 10(8) atoms/g for the samples in layer 23-39 cm from 2965 to 528 years BP suggest a warm and humid weather during this period. MS values have similar variation with Be-10 and reflect the similar paleo-climate information. TOC and delta C-13 suggest that the vegetation around Donlingshan area was C-3 type plants during entire Holocene. (C) 2009 Elsevier B.V. All rights reserved.Instruments & InstrumentationNuclear Science & TechnologyPhysics, Atomic, Molecular & ChemicalPhysics, NuclearSCI(E)EICPCI-S(ISTP)
Carbon isotopic composition and its implications on paleoclimate of the underground ancient forest ecosystem in Sihui, Guangdong
No full textWe present the carbon isotopic composition of the total organic carbon (TOC) and fine roots in the sedimentary profile from the underground ancient forest in Sihui to study the climatic and environmental changes from 4.5 ka BP to 0.6 ka BP. Results show that C(3) plant was the main vegetation from 4.5 ka BP to 0.6 ka BP in this region. The ancient forest began to develop in the wetland at around 4 ka BP and disappeared together with the wetland at about 3.0 ka BP, implying that the climate had changed greatly at around 3.0 ka BP. As indicated by the simulation results, the content of atmospheric CO(2) increased slightly during 3.5 ka BP to 3.0 ka BP, implying climate warming during that period. The interval of radiocarbon age between 3.0 ka BP to 1.2 ka BP was possibly caused by the strong erosion when the block was lifted in the neotectonic movement. From 1.2 ka BP to 0.6 ka BP, the region remained in terrestrial sedimentary environment, and the surface plant biomass declined gradually. Drought caused by the climate change was the likely cause for the disappearance of the ancient forest. South transition of Intertropical Convergence Zone (ITCZ) was probably the main mechanism for the climate change.Geosciences, MultidisciplinarySCI(E)EI3ARTICLE5638-6465
Effect of annealing process on the surface roughness in multiple Al implanted4H-SiC
No full textA P-layer can be formed on a SiC wafer surface by using multiple Al ion implantations and post-implantation annealing in a low pressure CVD reactor. The Al depth profile was almost box shaped with a height of1×1019cm-3 and a depth of550 nm. Three different annealing processes were developed to protect the wafer surface. Variations in RMS roughness have been measured and compared with each other. The implanted SiC, annealed with a carbon cap, maintains a high-quality surface with an RMS roughness as low as3.8 nm. Macrosteps and terraces were found in the SiC surface, which annealed by the other two processes(protect in Ar/protect with SiC capped wafer in Ar). The RMS roughness is12.2 nm and6.6 nm, respectively.?2011 Chinese Institute of Electronics
Multi-wafer3C-SiC thin films grown on Si(100) in a vertical HWLPCVD reactor
No full textWe report the latest results of the3C-SiC layer growth on Si(100) substrates by employing a novel home-made horizontal hot wall low pressure chemical vapour deposition(HWLPCVD) system with a rotating susceptor that was designed to support up to three50 mm-diameter wafers.3C-SiC film properties of the intra-wafer and the wafer-to-wafer, including crystalline morphologies and electronics, are characterized systematically. Intra-wafer layer thickness and sheet resistance uniformity(σ/mean) of～3.40% and～5.37% have been achieved in the3×50 mm configuration. Within a run, the deviations of wafer-to-wafer thickness and sheet resistance are less than4% and4.24%, respectively.?2011 Chinese Institute of Electronics
Carbon isotopic composition, turnover and origins of soil CO2 in a monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir, South China
No full textCarbon isotopic compositions of soil CO2 in rainy season (July) from two natural soil profiles (DHLS & DHS) in the monsoon evergreen broadleaf forest in the Dinghushan Biosphere Reservoir (DBR), South China, are presented. Turnover and origins of soil CO2 are preliminarily discussed in this paper. Results show that the content of soil CO2 varies between 6120 and 18718 ppmv, and increases with increasing depth until 75 cm, and then it declines. In DHLS, soil CO2 delta C-13 ranges from -24.71aEuro degrees to -24.03aEuro degrees, showing a significant inverse correlation (R (2)=0.91) with the soil CO2 content in the same layer. According to a model related to soil CO2 delta C-13, the soil CO2 is mainly derived from the root respiration (> 80%) in DHLS. While in DHS, where soil CO2 delta C-13 ranges from -25.19aEuro degrees to -22.82aEuro degrees, soil CO2 is primarily originated from the decomposition of organic matter (51%-94%), excluding the surface layer (20 cm, 90%). Radiocarbon data suggest that the carbon in soil CO2 is modern carbon in both DHLS and DHS. Differences in C-14 ages between the "oldest" and "youngest" soil CO2 in DHLS and DHS are 8 months and 14 months, respectively, indicating that soil CO2 in DHLS has a faster turnover rate than that in DHS. The Delta C-14 values of soil CO2, which range between 100.0aEuro degrees and 107.2aEuro degrees and between 102.5aEuro degrees and 112.1aEuro degrees in DHLS and DHS, respectively, are obviously higher than those of current atmospheric CO2 and SOC in the same layer, suggesting that soil CO2 is likely an important reservoir for Bomb-C-14 in the atmosphere.Multidisciplinary SciencesSCI(E)1ARTICLE232548-25565
Laterally Electrostatically Driven Poly 3C-SiC Folded-Beam Resonant Microstructures
No full textMicromachined comb-drive electrostatic resonators with folded-cantilever beams were designed and fabricated. A combination of Rayleigh＇s method and finite-element analysis was used to calculate the resonant frequency drift as we adjusted the device geometry and material parameters. Three micromachined lateral resonant resonators with different beam widths were fabricated. Their resonant frequencies were experimentally measured to be 64.5,147.2, and 255.5kHz, respectively, which are in good agreement with the simulated resonant frequency. It is shown that an improved frequency performance could be obtained on the poly 3C-SiC based device structural material systems with high Young＇s modulus
Influences of organic–inorganic interfacial properties on the performance of a hybrid near-infrared optical upconverter
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