The powder X-ray diffraction patterns of LaFell.sSil.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFell.sSiL5 com...The powder X-ray diffraction patterns of LaFell.sSil.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFell.sSiL5 compound annealed at 1423 K (5 h). In the temperature range from 1423 to 1523 K, ^-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed, and the most amount of 1:13 phase is obtained in the compound annealed at 1523 K (5 h). With the annealing temperature increasing to 1573 and 1623 K, LaFeSi is detected again in the LaFell.sSil.s compound. According to the results of annealing at different high-temperatures, the Lal-xCexFelt.sSit.5 compounds are annealed at high temperatures of 1373 K (2 h) + 1523 K (5 h). The main phase is NaZn13-type phase, and the impurity is a small amount of et-Fe in Lal-xCexFexx.sSil.5 compounds with 0 〈 x 〈 0.35, and there is a large amount of CeaFe17 phase in Lao.sCeo.sFela.sSil.s. It indicates that the substitution of cerium atoms for La in LaFelLsSil.5 compounds has limit. At the same time, the substitution of Ce for La has large effect on magnetocaloric properties. With increasing Ce content from x = 0 to x = 0.35, the Curie temperature decreases linearly from 196 to 168 K, the magnetic entropy change increases from 16.5 to 57.3 J-kg-kK-1 in a low magnetic field change of 0-2 T, and the thermal hysteresis also increases from 3 K to 8 K.展开更多
Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The (0001)-oriented 6H-SiC wafers are implanted with 15keV helium ions at a dose of 1×10^17 cm^-2 at room temp...Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The (0001)-oriented 6H-SiC wafers are implanted with 15keV helium ions at a dose of 1×10^17 cm^-2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473K for 30rain. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealingabides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120-135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236eV.展开更多
High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O 2 atmosphere is studied with temperature ranging from 800℃ to 1000℃. It is observed that the surface morphology of Al2O...High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O 2 atmosphere is studied with temperature ranging from 800℃ to 1000℃. It is observed that the surface morphology of Al2O3 films annealed at 800℃ and 900℃ is pretty good, while the surface of the sample annealed at 1000℃ becomes bumpy. Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900℃. Furthermore, C–V measurements exhibit improved interface characterization after annealing, especially for samples annealed at 900℃ and 1000℃. It is indicated that high-temperature annealing in O2 atmosphere can improve the interface of Al2O3 /SiC and annealing at 900℃ would be an optimum condition for surface morphology, dielectric quality, and interface states.展开更多
The effect of high-temperature annealing on A1N thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence (P...The effect of high-temperature annealing on A1N thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence (PL) with the excitation wavelength as short as ~ 177 nm. Annealing experiments were carded out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200 ℃ to 1600 ℃. It is found that surface roughness reduced and compres- sive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL--ON complex in the A1N material.展开更多
The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during ...The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000°C during the cooling to 100°C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200°C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.展开更多
The effect of high-temperature annealing on the yellow and blue luminescence of the undoped GaN is investi- gated by photoluminescenee (PL) and x-ray photoelectron spectroscopy (XPS). It is found that the band-edg...The effect of high-temperature annealing on the yellow and blue luminescence of the undoped GaN is investi- gated by photoluminescenee (PL) and x-ray photoelectron spectroscopy (XPS). It is found that the band-edge emission in the GaN apparently increases, and the yellow luminescence (YL) and blue luminescence (BL) bands dramatically decrease after annealing at 700℃. At the annealing temperature higher than 900℃, the YL and BL intensities show an enhancement for the nitrogen annealed GaN. This fact should be attributed to the increment of the Ga and N vacancies in the GaN decomposition. However, the integrated PL intensity of the oxygen an- nealed GaN decreases at the temperature ranging from 900℃ to 1000℃. This results from the capture of many photo-generated holes by high-density surface states. XPS characterization confirms that the high-density surface states mainly originate from the incorporation of oxygen atoms into GaN at the high annealing temperature, and even induces the 0.34eV increment of the upward band bending for the oxygen annealed GaN at 1000℃.展开更多
The LaFe11.4Si1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h). The powder X-ray diffraction (XRD) and microstructure observations show...The LaFe11.4Si1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h). The powder X-ray diffraction (XRD) and microstructure observations show that large amount of 1:13 phase begins to appear in the LaFe11.4Si1.6 compound annealed at 1423 K (5 h). In the temperature range from 1423 K to 1523 K, the α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. The LaFeSi phase is rarely observed by XRD when the as-cast compound is annealed at 1523 K (5 h). With annealing temperature increasing to 1573 K, LaFeSi phase is detected again in LaFe11.4Si1.6 compound. In LaFe11.4Si1.6 compounds annealed at 1523 K (5 h), at 1373 K (2 h)+1523 K (5 h), and 1523 K (7 h)+1373 K (2 h), the impurity phases including small amount of α-Fe and LaFeSi phase reduce in turn. The magnetic measurement shows that LaFe11.4Si1.6 compounds annealed by above three processes keep the first-order of magnetic transition behavior, and Tc are both at about 200 K. But the values of the maximal ASM(T, H) of has large difference, they are 9.94, 12.66, and 13.96 J/(kg.K) under a magnetic field of 0- 2 T, respectively.展开更多
Introducing voids into AlN layer at a certain height using a simple method is meaningful but challenging.In this work,the AlN/sapphire template with AlN interlayer structure was designed and grown by metal-organic che...Introducing voids into AlN layer at a certain height using a simple method is meaningful but challenging.In this work,the AlN/sapphire template with AlN interlayer structure was designed and grown by metal-organic chemical vapor deposition.Then,the AlN template was annealed at 1700℃for an hour to introduce the voids.It was found that voids were formed in the AlN layer after high-temperature annealing and they were mainly distributed around the AlN interlayer.Meanwhile,the dislocation density of the AlN template decreased from 5.26×10^(9)cm^(-2)to 5.10×10^(8)cm^(-2).This work provides a possible method to introduce voids into AlN layer at a designated height,which will benefit the design of AlN-based devices.展开更多
The hardness measurement,optical microscopy (OM),and transmission electron microscopy (TEM) microstructure observation on the annealing behaviors of Cu-Al2O3 (2.25 vol.% and 0.54 vol.% Al2O3) and Cu-0.52vol.%Nb ...The hardness measurement,optical microscopy (OM),and transmission electron microscopy (TEM) microstructure observation on the annealing behaviors of Cu-Al2O3 (2.25 vol.% and 0.54 vol.% Al2O3) and Cu-0.52vol.%Nb alloys were carried out. The results show that with the increase of annealing temperature,the hardness of Cu-Al2O3 alloys decreases slowly. No change of the fiber structure formed by cold rolling in the Cu-2.25vol.%Al2O3 alloy is observed even after annealing at 900℃and the higher dislocation density can still be observed by TEM. Less combination of fiber formed by cold rolling and subgrains are observed in the Cu-0.54vol.%Al2O3 alloy annealed at 900℃. With the increase of annealing temperature,the hardness of the Cu-0.52vol.%Nb alloy exhibits a general decreasing trend,and its falling rate is higher than that of the Cu-Al2O3 alloys,indicating that its ability of resistance to softening at elevated temperature is weaker than that of the Cu-Al2O3 alloys. However,when annealed at a temperature of 300-400℃,probably owing to the precipitation strengthening of niobium,the hardness of the Cu-0.52vol.%Nb alloy arises slightly. The fibers formed by cold rolling be-come un-clear and un-straight and have less combination,and considerably more subgrains are observed by TEM.展开更多
We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes(UV-LEDs)emitting at 265 nm grown on stripe-patterned high-temperature annealed(HTA)epitaxially laterally overgrown(ELO)aluminium nitri...We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes(UV-LEDs)emitting at 265 nm grown on stripe-patterned high-temperature annealed(HTA)epitaxially laterally overgrown(ELO)aluminium nitride(AIN)/sapphire templates.For this purpose,the structural and electro-optical properties of ultraviolet-c light-emitting diodes(UVC-LEDs)on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared.Cathodoluminescence measurements reveal dark spot densities of 3.5×10^9 cm^-2,1.1×10^9 cm^-2,1.4×10^9 cm^-2,and 0.9×10^9 cm^-2 in multiple quantum well samples on as-grown planar AIN/sapphire,HTA planar AlN/sapphire,ELO AlN/sapphire,and HTA ELO AlN/sapphire,respectively,and are consistent with the threading dislocation densities determined by transmission electron microscopy(TEM)and high-resolution X-ray diffraction rocking curve.The UVC-LED performance improves with the reduction of the threading dislocation densities(TDDs).The output powers(measured on-wafer in cw operation at 20 mA)of the UV-LEDs emitting at 265 nm were 0.03 mW(planar AlN/sapphire),0.8 mW(planar HTA AlN/sapphire),0.9 mW(ELO AlN/sapphire),and 1.1 mW(HTA ELO AlN/sapphire),respectively.Furthermore,Monte Carlo ray-tracing simulations showed a 15%increase in light-extraction efficiency due to the voids formed in the ELO process.These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs,improving both the internal quantum efficiency and the light-extraction efficiency.展开更多
Dispersion-strengthened copper (DSC) with WC as dispersoid was prepared bymeans of mechanical alloying (MA) following the traditional powder metallurgy (P/M) route. Influenceof WC content on the properties of material...Dispersion-strengthened copper (DSC) with WC as dispersoid was prepared bymeans of mechanical alloying (MA) following the traditional powder metallurgy (P/M) route. Influenceof WC content on the properties of material was discussed in detail, and result shows that when thevolume fraction of WC is 1.6%, the material achieves the best overall property, and a little moreparticle addition led to a less superior property owing to occurrence of particle agglomeration. Theas-sintered composite was designed to undergo a deformation of 75%. It is proved that appropriatedeformation is helpful to attain a higher density and consequently better properties. Deformedmaterial was then exposed to elevated temperature to test its effect on material. Annealing for 1 hat 1173K caused material to recover quite completely, but no obvious recrystallization was observed.It's supposed the particles handicaps motion of dislocations and material demonstrates goodretention of strength with substantial improvement in elongation.展开更多
4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state re...4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm^2 with a total active area of 2.46× 10 ^-3 cm^2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250 ℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9× 10^-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.展开更多
The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed th...The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope (SEM) showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.展开更多
The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbi...The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbides in different positions of ESR ingot.The results show that the two-dimensional morphology of primary carbides is blocky,fibrous,and spherulitic.The three-dimensional morphology of primary carbides is blocky,spherulitic,fibrous,and short rods.X-ray diffraction results show that primary carbides are M_(7)C_(3) carbides.Electron backscattered diffraction results indicate that large-sized primary carbides consist of blocky,fibrous,and spherulitic carbides with different orientations.High-tem-perature diffusion annealing experiments show that as the temperature increases,the continuity between primary carbides decreases,and the precipitated secondary carbides disappear.The area fraction of primary carbides is reduced,but the morphology of primary carbide is unchanged.The effect of high-temperature diffusion annealing on the dissolution of M_(7)C_(3) primary carbon compounds in ESR ingot was limited.展开更多
The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),...The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and vibrating-sample magnetometer (VSM), respectively. The results showed that the excess Fe would make the 1:13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFelL6*xSil.4 alloys. The LaFel 1.6.xSil.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFel 1.6,xSil.4 alloys with x=1.05 and 1.1, respectively.展开更多
In this paper, high density of dislocations, grain boundaries and nanometer-scale α precipitates were intro- duced to a metastable Ti-36Nb-5Zr alloy (wt%) through a thermo-mechanical approach including severe cold ...In this paper, high density of dislocations, grain boundaries and nanometer-scale α precipitates were intro- duced to a metastable Ti-36Nb-5Zr alloy (wt%) through a thermo-mechanical approach including severe cold rolling and short-time annealing treatment. The martensitic trans- formation was retarded, and the β phase with low content of β stabilizers was retained at room temperature after the thermo-mechanical treatment. As a result, both low mod- ulus (57 GPa) and high strength (950 MPa) are obtained. The results indicate that it is a feasible strategy to control martensitic transformation start temperature through microstructure optimization instead of composition design, with the aim of fabricating low modulus β-type Ti alloy.展开更多
The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex*11.6Si1.4 (x=0.96, 0.98, 1.0, and 1.02) compounds prepared by arc-melting and then annealed at 1423 K (1.5 h...The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex*11.6Si1.4 (x=0.96, 0.98, 1.0, and 1.02) compounds prepared by arc-melting and then annealed at 1423 K (1.5 h)+1523 K (4.5 h) were investigated. The main phase was NaZn13-type phase, the impurity phases included a small amount of α-Fe and LaFeSi phase in four samples. The crystal cell parameters of 1:13 phase increased from 1.1433(5) to 1.1454(4) nm with x increasing from 0.96 to 1.02, respectively. All samples kept the typical first-order magnetic transition. The increase of Fe strengthened IEM behavior, and led to the remarkable enhancement of MCE effect and negative slopes in Arrott plots around TC. The maximum ΔSM (T, H) under a low magnetic field (0–2 T) was 15.3, 16.8, 17.9, and 24.7 J/kg K with increasing of Fe content from x=0.96 to 1.02, respectively.展开更多
The large disc LaFe11.6Si1.4 alloy, which was prepared by medium-frequency induction furnace, was annealed at 1503 K for different time. The main phases were 1:13 phase in the edge parts of the large discs alloy; the...The large disc LaFe11.6Si1.4 alloy, which was prepared by medium-frequency induction furnace, was annealed at 1503 K for different time. The main phases were 1:13 phase in the edge parts of the large discs alloy; the impurity phases included α-Fe phase, LaFeSi phase, and even very small amount of La5Si3 phase. The amounts of impurity phases reduced with increasing in annealing time. The magnetic properties in the edge parts of the large discs LaFe11.6Si1.4 alloy were investigated. The magnetic susceptibility had an abrupt change at Curie temperature(TC) as the magnetization in M-T curves. The alloys had almost the same TC(191 K), the magnetocaloric effect(MCE) and relative cooling power(RCP) increased with increasing in annealing time. In addition, for the same alloy, the magnetic hysteresis decreased with the increase in temperature.展开更多
The effects of the introduction of Ce to La(1-x)CexFe(11.5)Si(1.5) alloys on 1:13 phase formation mechanism,the first-order magnetic phase transition strengthening characteristics,and magnetocaloric property we...The effects of the introduction of Ce to La(1-x)CexFe(11.5)Si(1.5) alloys on 1:13 phase formation mechanism,the first-order magnetic phase transition strengthening characteristics,and magnetocaloric property were studied,respectively.The results show that the formation mechanisms of 1:13 and La Fe Si phases in La(1-x)CexFe(11.5)Si(1.5) alloys are the same as those of Ce2Fe(17) and CeFe2 phases in Ce–Fe binary system,respectively.The substitution of Ce in 1:13 phase which is limited can make the first-order magnetic phase transition characteristics strengthen,which can make thermal and magnetic hysteresis increase,the temperature interval of temperatureinduced phase transition decrease,and the critical magnetic field of field-induced magnetic phase transition(HC)increase,respectively.Owing to the lattice shrink of 1:13phase with the increase in Ce content,the Curie temperatures(TC) show a linear decrease.The maximum change in magnetic entropy gradually increases due to the decrease in temperature interval of temperature-induced phase transition,but the relative cooling capacities are all about80 Jákg-1at magnetic field of 2 T.展开更多
基金supported by the Key Project of National Natural Science Foundation of China (No. 50731007)the National High-Tech Research and Development Program of China (No. 2007AA03Z440)
文摘The powder X-ray diffraction patterns of LaFell.sSil.5 compounds annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h) show that a large amount of 1:13 phase begins to form in LaFell.sSiL5 compound annealed at 1423 K (5 h). In the temperature range from 1423 to 1523 K, ^-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed, and the most amount of 1:13 phase is obtained in the compound annealed at 1523 K (5 h). With the annealing temperature increasing to 1573 and 1623 K, LaFeSi is detected again in the LaFell.sSil.s compound. According to the results of annealing at different high-temperatures, the Lal-xCexFelt.sSit.5 compounds are annealed at high temperatures of 1373 K (2 h) + 1523 K (5 h). The main phase is NaZn13-type phase, and the impurity is a small amount of et-Fe in Lal-xCexFexx.sSil.5 compounds with 0 〈 x 〈 0.35, and there is a large amount of CeaFe17 phase in Lao.sCeo.sFela.sSil.s. It indicates that the substitution of cerium atoms for La in LaFelLsSil.5 compounds has limit. At the same time, the substitution of Ce for La has large effect on magnetocaloric properties. With increasing Ce content from x = 0 to x = 0.35, the Curie temperature decreases linearly from 196 to 168 K, the magnetic entropy change increases from 16.5 to 57.3 J-kg-kK-1 in a low magnetic field change of 0-2 T, and the thermal hysteresis also increases from 3 K to 8 K.
基金Supported by the National Natural Science Foundation of China under Grant No 11475229
文摘Bubble evolution in low energy and high dose He-implanted 6H-SiC upon thermal annealing is studied. The (0001)-oriented 6H-SiC wafers are implanted with 15keV helium ions at a dose of 1×10^17 cm^-2 at room temperature. The samples with post-implantation are annealed at temperatures of 1073, 1173, 1273, and 1473K for 30rain. He bubbles in the wafers are examined via cross-sectional transmission electron microscopy (XTEM) analysis. The results present that nanoscale bubbles are almost homogeneously distributed in the damaged layer of the as-implanted sample, and no significant change is observed in the He-implanted sample after 1073 K annealing. Upon 1193 K annealing, almost full recrystallization of He-implantation-induced amorphization in 6H-SiC is observed. In addition, the diameters of He bubbles increase obviously. With continually increasing temperatures to 1273K and 1473 K, the diameters of He bubbles increase and the number density of lattice defects decreases. The growth of He bubbles after high temperature annealingabides by the Ostwald ripening mechanism. The mean diameter of He bubbles located at depths of 120-135 nm as a function of annealing temperature is fitted in terms of a thermal activated process which yields an activation energy of 1.914+0.236eV.
基金the National Natural Science Foundation of China(Grant No.61106080)the Major Program of the National Natural Science Foundation of China(Grant No.2013ZX02305)
文摘High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O 2 atmosphere is studied with temperature ranging from 800℃ to 1000℃. It is observed that the surface morphology of Al2O3 films annealed at 800℃ and 900℃ is pretty good, while the surface of the sample annealed at 1000℃ becomes bumpy. Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900℃. Furthermore, C–V measurements exhibit improved interface characterization after annealing, especially for samples annealed at 900℃ and 1000℃. It is indicated that high-temperature annealing in O2 atmosphere can improve the interface of Al2O3 /SiC and annealing at 900℃ would be an optimum condition for surface morphology, dielectric quality, and interface states.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB619306)863 Program of China(Grant No.2011AA03A101)
文摘The effect of high-temperature annealing on A1N thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence (PL) with the excitation wavelength as short as ~ 177 nm. Annealing experiments were carded out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200 ℃ to 1600 ℃. It is found that surface roughness reduced and compres- sive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL--ON complex in the A1N material.
文摘The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000°C during the cooling to 100°C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200°C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB301900,2012CB619200 and 2012CB619304the High-Technology Research and Development Program of China under Grant Nos 2014AA032605 and 2015AA033305+4 种基金the National Natural Science Foundation of China under Grant Nos 60990311,61274003,61422401,51461135002,60936004,61176063 and 61334009the Natural Science Foundation of Jiangsu Province under Grant Nos BK2011010 and BK20141320the Scientific Innovation Research of College Graduate in Jiangsu Province under Grant No CXLX12.0049a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Solid State Lighting and Energy-saving Electronics Collaborative Innovation Center
文摘The effect of high-temperature annealing on the yellow and blue luminescence of the undoped GaN is investi- gated by photoluminescenee (PL) and x-ray photoelectron spectroscopy (XPS). It is found that the band-edge emission in the GaN apparently increases, and the yellow luminescence (YL) and blue luminescence (BL) bands dramatically decrease after annealing at 700℃. At the annealing temperature higher than 900℃, the YL and BL intensities show an enhancement for the nitrogen annealed GaN. This fact should be attributed to the increment of the Ga and N vacancies in the GaN decomposition. However, the integrated PL intensity of the oxygen an- nealed GaN decreases at the temperature ranging from 900℃ to 1000℃. This results from the capture of many photo-generated holes by high-density surface states. XPS characterization confirms that the high-density surface states mainly originate from the incorporation of oxygen atoms into GaN at the high annealing temperature, and even induces the 0.34eV increment of the upward band bending for the oxygen annealed GaN at 1000℃.
基金supported by the Key Project of National Natural Science Foundation of China (Nos.50731007 and 51176050)the National High Technical Research and Development Programme of China (No.2007AA03Z440)
文摘The LaFe11.4Si1.6 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K (5 h) to 1623 K (2 h). The powder X-ray diffraction (XRD) and microstructure observations show that large amount of 1:13 phase begins to appear in the LaFe11.4Si1.6 compound annealed at 1423 K (5 h). In the temperature range from 1423 K to 1523 K, the α-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. The LaFeSi phase is rarely observed by XRD when the as-cast compound is annealed at 1523 K (5 h). With annealing temperature increasing to 1573 K, LaFeSi phase is detected again in LaFe11.4Si1.6 compound. In LaFe11.4Si1.6 compounds annealed at 1523 K (5 h), at 1373 K (2 h)+1523 K (5 h), and 1523 K (7 h)+1373 K (2 h), the impurity phases including small amount of α-Fe and LaFeSi phase reduce in turn. The magnetic measurement shows that LaFe11.4Si1.6 compounds annealed by above three processes keep the first-order of magnetic transition behavior, and Tc are both at about 200 K. But the values of the maximal ASM(T, H) of has large difference, they are 9.94, 12.66, and 13.96 J/(kg.K) under a magnetic field of 0- 2 T, respectively.
基金the National Key Research and Development Program of China(Grant No.2017YFB0404100)the National Natural Science Foundation of China(Grant Nos.61827813,61974144,and 62004127)+2 种基金the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB22)the Key-Area Research and Development Program of Guangdong Province,China(Grant Nos.2020B010169001 and 2020B010174003)the Science and Technology Foundation of Shenzhen(Grant No.JSGG20191129114216474)。
文摘Introducing voids into AlN layer at a certain height using a simple method is meaningful but challenging.In this work,the AlN/sapphire template with AlN interlayer structure was designed and grown by metal-organic chemical vapor deposition.Then,the AlN template was annealed at 1700℃for an hour to introduce the voids.It was found that voids were formed in the AlN layer after high-temperature annealing and they were mainly distributed around the AlN interlayer.Meanwhile,the dislocation density of the AlN template decreased from 5.26×10^(9)cm^(-2)to 5.10×10^(8)cm^(-2).This work provides a possible method to introduce voids into AlN layer at a designated height,which will benefit the design of AlN-based devices.
文摘The hardness measurement,optical microscopy (OM),and transmission electron microscopy (TEM) microstructure observation on the annealing behaviors of Cu-Al2O3 (2.25 vol.% and 0.54 vol.% Al2O3) and Cu-0.52vol.%Nb alloys were carried out. The results show that with the increase of annealing temperature,the hardness of Cu-Al2O3 alloys decreases slowly. No change of the fiber structure formed by cold rolling in the Cu-2.25vol.%Al2O3 alloy is observed even after annealing at 900℃and the higher dislocation density can still be observed by TEM. Less combination of fiber formed by cold rolling and subgrains are observed in the Cu-0.54vol.%Al2O3 alloy annealed at 900℃. With the increase of annealing temperature,the hardness of the Cu-0.52vol.%Nb alloy exhibits a general decreasing trend,and its falling rate is higher than that of the Cu-Al2O3 alloys,indicating that its ability of resistance to softening at elevated temperature is weaker than that of the Cu-Al2O3 alloys. However,when annealed at a temperature of 300-400℃,probably owing to the precipitation strengthening of niobium,the hardness of the Cu-0.52vol.%Nb alloy arises slightly. The fibers formed by cold rolling be-come un-clear and un-straight and have less combination,and considerably more subgrains are observed by TEM.
基金Bundesministerium für Bildung und Forschung(03ZZ0134C,Advanced UV for Life)Deutsche Forschungsgemeinschaft(Semiconductor Nanophotonics,Collaborative Research Centre,CRC7879315)。
文摘We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes(UV-LEDs)emitting at 265 nm grown on stripe-patterned high-temperature annealed(HTA)epitaxially laterally overgrown(ELO)aluminium nitride(AIN)/sapphire templates.For this purpose,the structural and electro-optical properties of ultraviolet-c light-emitting diodes(UVC-LEDs)on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared.Cathodoluminescence measurements reveal dark spot densities of 3.5×10^9 cm^-2,1.1×10^9 cm^-2,1.4×10^9 cm^-2,and 0.9×10^9 cm^-2 in multiple quantum well samples on as-grown planar AIN/sapphire,HTA planar AlN/sapphire,ELO AlN/sapphire,and HTA ELO AlN/sapphire,respectively,and are consistent with the threading dislocation densities determined by transmission electron microscopy(TEM)and high-resolution X-ray diffraction rocking curve.The UVC-LED performance improves with the reduction of the threading dislocation densities(TDDs).The output powers(measured on-wafer in cw operation at 20 mA)of the UV-LEDs emitting at 265 nm were 0.03 mW(planar AlN/sapphire),0.8 mW(planar HTA AlN/sapphire),0.9 mW(ELO AlN/sapphire),and 1.1 mW(HTA ELO AlN/sapphire),respectively.Furthermore,Monte Carlo ray-tracing simulations showed a 15%increase in light-extraction efficiency due to the voids formed in the ELO process.These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs,improving both the internal quantum efficiency and the light-extraction efficiency.
文摘Dispersion-strengthened copper (DSC) with WC as dispersoid was prepared bymeans of mechanical alloying (MA) following the traditional powder metallurgy (P/M) route. Influenceof WC content on the properties of material was discussed in detail, and result shows that when thevolume fraction of WC is 1.6%, the material achieves the best overall property, and a little moreparticle addition led to a less superior property owing to occurrence of particle agglomeration. Theas-sintered composite was designed to undergo a deformation of 75%. It is proved that appropriatedeformation is helpful to attain a higher density and consequently better properties. Deformedmaterial was then exposed to elevated temperature to test its effect on material. Annealing for 1 hat 1173K caused material to recover quite completely, but no obvious recrystallization was observed.It's supposed the particles handicaps motion of dislocations and material demonstrates goodretention of strength with substantial improvement in elongation.
基金supported by the National Natural Science Foundation of China (Grant No. 51102225)the Natural Science Foundation of Beijing City, China (Grant No. 4132076)the Youth Innovation Promotion Association, Chinese Academy of Sciences
文摘4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm^2 with a total active area of 2.46× 10 ^-3 cm^2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250 ℃ in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9× 10^-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.
基金Project supported by the National Natural Science Foundation of China (50701011)the National High Technology Research and Develop-ment Program of China (2007AA03Z230, 2009AA03Z230)
文摘The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope (SEM) showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.
基金the funding support from the National Natural Science Foundation of China (22325903,22221003,and 22071225)the National Key Research and Development Program of China (2018YFA0702001)+1 种基金the Plan for Anhui Major Provincial Science&Technology Project (202203a0520013 and 2021d05050006)the USTC Research Funds of the Double First-Class Initiative (YD2060002032)。
基金This work was supported by the Guangdong YangFan Innovative&Entrepreneurial Research Team Program(No.2016YT03C071)the Guangdong Science and Technology Special Fund Project(No.SDZX202005)the National Natural Science Foundation of China(Nos.51874030 and 51904022).
文摘The micro structure of 10Cr15MoVCo electroslag remelting(ESR)ingot was observed using an optical microscope and a scanning electron microscope.There are differences in the number,size,and distribution of primary carbides in different positions of ESR ingot.The results show that the two-dimensional morphology of primary carbides is blocky,fibrous,and spherulitic.The three-dimensional morphology of primary carbides is blocky,spherulitic,fibrous,and short rods.X-ray diffraction results show that primary carbides are M_(7)C_(3) carbides.Electron backscattered diffraction results indicate that large-sized primary carbides consist of blocky,fibrous,and spherulitic carbides with different orientations.High-tem-perature diffusion annealing experiments show that as the temperature increases,the continuity between primary carbides decreases,and the precipitated secondary carbides disappear.The area fraction of primary carbides is reduced,but the morphology of primary carbide is unchanged.The effect of high-temperature diffusion annealing on the dissolution of M_(7)C_(3) primary carbon compounds in ESR ingot was limited.
基金supported by China Postdoctoral Science Foundation(2013M542274)
文摘The effect of Fe on microstructure and magnetic thermal performance of LaFel 1.6.xSil.4 alloys were studied by X-ray dif- fraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and vibrating-sample magnetometer (VSM), respectively. The results showed that the excess Fe would make the 1:13 phase reduce in proportion and the easy corrosion phase LaFeSi phase disappear in LaFelL6*xSil.4 alloys. The LaFel 1.6.xSil.4 alloys kept the first order magnetic phase transition, and the maximum isothermal magnetic entropy changed and the relative cooling power reached the maximum in LaFel 1.6,xSil.4 alloys with x=1.05 and 1.1, respectively.
基金financially supported by the National Natural Science Foundation of China (No.51601217)the Natural Science Foundation of Jiangsu Province (No.BK20160255)the Fundamental Research Funds for the Central Universities (No.2017QNA04)
文摘In this paper, high density of dislocations, grain boundaries and nanometer-scale α precipitates were intro- duced to a metastable Ti-36Nb-5Zr alloy (wt%) through a thermo-mechanical approach including severe cold rolling and short-time annealing treatment. The martensitic trans- formation was retarded, and the β phase with low content of β stabilizers was retained at room temperature after the thermo-mechanical treatment. As a result, both low mod- ulus (57 GPa) and high strength (950 MPa) are obtained. The results indicate that it is a feasible strategy to control martensitic transformation start temperature through microstructure optimization instead of composition design, with the aim of fabricating low modulus β-type Ti alloy.
基金supported by the Key Project of National Natural Science Foundation of China (50731007)the National High Technology Research and Development Program of China (2007AA03Z440)
文摘The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex*11.6Si1.4 (x=0.96, 0.98, 1.0, and 1.02) compounds prepared by arc-melting and then annealed at 1423 K (1.5 h)+1523 K (4.5 h) were investigated. The main phase was NaZn13-type phase, the impurity phases included a small amount of α-Fe and LaFeSi phase in four samples. The crystal cell parameters of 1:13 phase increased from 1.1433(5) to 1.1454(4) nm with x increasing from 0.96 to 1.02, respectively. All samples kept the typical first-order magnetic transition. The increase of Fe strengthened IEM behavior, and led to the remarkable enhancement of MCE effect and negative slopes in Arrott plots around TC. The maximum ΔSM (T, H) under a low magnetic field (0–2 T) was 15.3, 16.8, 17.9, and 24.7 J/kg K with increasing of Fe content from x=0.96 to 1.02, respectively.
基金Project supported by the National Natural Science Foundation of China(51176050)China Postdoctoral Science Foundation(2013M542274)
文摘The large disc LaFe11.6Si1.4 alloy, which was prepared by medium-frequency induction furnace, was annealed at 1503 K for different time. The main phases were 1:13 phase in the edge parts of the large discs alloy; the impurity phases included α-Fe phase, LaFeSi phase, and even very small amount of La5Si3 phase. The amounts of impurity phases reduced with increasing in annealing time. The magnetic properties in the edge parts of the large discs LaFe11.6Si1.4 alloy were investigated. The magnetic susceptibility had an abrupt change at Curie temperature(TC) as the magnetization in M-T curves. The alloys had almost the same TC(191 K), the magnetocaloric effect(MCE) and relative cooling power(RCP) increased with increasing in annealing time. In addition, for the same alloy, the magnetic hysteresis decreased with the increase in temperature.
基金financially supported by the National Natural Science Foundation of China(No.51176050)the Research Projects in Sichuan Province Education Office(No.12ZB073)
文摘The effects of the introduction of Ce to La(1-x)CexFe(11.5)Si(1.5) alloys on 1:13 phase formation mechanism,the first-order magnetic phase transition strengthening characteristics,and magnetocaloric property were studied,respectively.The results show that the formation mechanisms of 1:13 and La Fe Si phases in La(1-x)CexFe(11.5)Si(1.5) alloys are the same as those of Ce2Fe(17) and CeFe2 phases in Ce–Fe binary system,respectively.The substitution of Ce in 1:13 phase which is limited can make the first-order magnetic phase transition characteristics strengthen,which can make thermal and magnetic hysteresis increase,the temperature interval of temperatureinduced phase transition decrease,and the critical magnetic field of field-induced magnetic phase transition(HC)increase,respectively.Owing to the lattice shrink of 1:13phase with the increase in Ce content,the Curie temperatures(TC) show a linear decrease.The maximum change in magnetic entropy gradually increases due to the decrease in temperature interval of temperature-induced phase transition,but the relative cooling capacities are all about80 Jákg-1at magnetic field of 2 T.