Dependence of Atomic-Scale Si(110) Surface Roughness on Hydrogen Introduction Temperature after High-Temperature Ar Annealing

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&#176C during the cooling to 100&#176C 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&#176C, 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.

The effect of high-temperature annealing on LaFe_(11.5)Si_(1.5) and the magneto-caloric properties of La_(1-x)Ce_xFe_(11.5)Si_(1.5) compounds

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.

High-Temperature Annealing Induced He Bubble Evolution in Low Energy He Ion Implanted 6H-SiC

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.

Influences of high-temperature annealing on atomic layer deposited Al_2O_3/4H-SiC

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.

Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

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.

Effect of High-Temperature Annealing on Yellow and Blue Luminescence of Undoped GaN

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℃.

Introducing voids around the interlayer of AlN by high temperature annealing

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.

Comparison study on the annealing behaviors of dispersion strengthened copper alloys with different nanoparticles

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.

Multilayered Ti-Al intermetallic sheets fabricated by cold rolling and annealing of titanium and aluminum foils

Multilayered Ti-Al based intermetallic sheets were fabricated by sintering alternately layered titanium and aluminum foils.The microstructure and phase formation of the obtained sheets under different sintering conditions were evaluated by various techniques.The results reveal that when the sintering temperature is above the melting point of aluminum,the self-propagating high-temperature synthesis reaction occurs between Ti and Al,and forms various phases of Ti-based solid solutions including α-Ti Ti3Al,TiAl,TiAl2 and α-Ti including TiAl3,etc.When the sintering time increased,Ti-based solid solution,TiAl2 and TiAl3 disappeared gradually,and the sheet containing Ti3Al and TiAl phases in a multilayered structure formed finally.A lot of voids were also observed in the sintered structures,which were caused by the melting Al,Kirkendall effect and the difference of molar volumes between reactants and products.The voids were eliminated and a dense sample was obtained by the following hot press.

Precipitation behavior of 14H LPSO structure in single 18R phase Mg-Y-Zn alloy during annealing at 773K

The microstructural evolution of a 18R single phase （S 18） alloy during annealing at 773 K for 100 h was investigated in order to reveal the formation mechanism of 14H phase. The results showed that the as-cast S 18 alloy was composed of 18R phase （its volume fraction exceeds 93%）, W particles and α-Mg phase. The 18R phase in S18 alloy was thermally stable and was not transformed into 14H long period stacking ordered （LPSO） phase during annealing. However, 14H lamellas formed within tiny α-Mg slices, and their average size and volume fraction increased with prolonging annealing time. Moreover, the 14H phase is nucleated within α-Mg independently on the basis of basal stacking faults （SFs）. The broadening growth of 14H lamellas is an interface-controlled process which involves ledges on basal planes, while the lengthening growth is a diffusion-controlled process and is associated with diffusion of solute atoms. The formation mechanism of 14H phase in this alloy could be explained as α-Mg＇→α-Mg＋14H.

Ar气氛退火对LRE-Ba-Cu-O单畴熔融织构样品超导性能的影响

采用顶部热籽晶技术和"二步冷却"生长工艺,在空气中制备了Gd-Ba-Cu-O、(SmGd)-Ba-Cu-O和(SmEuGd)-Ba-Cu-O三种体系的单畴熔融织构样品,并研究了Ar气氛退火(ArPA)对所制备的单畴样品超导性能的影响.结果表明,三种体系的单畴样品77K下的俘获场分布均呈中心对称的圆锥形,其中SEG样品的冻结场达到0.34T(φ18mm),与OCMG工艺制备的相同尺寸的样品处在同一水平.Ar气氛退火对三种体系单畴样品超导性能的影响不同:对Gd-Ba-Cu-O体系,ArPA不能进一步提高单畴样品的临界电流密度;而对(SmGd)-Ba-Cu-O和(SmEuGd)-Ba-Cu-O体系,合适温度下的ArPA可以大幅度提高样品的超导性能.

95%Ar+5%H2气氛退火对Ag/MoS2和Ag/BN/MoS2薄膜形貌和结构的影响

采用射频(RF)磁控溅射在室温下连续逐层沉积,然后在95%Ar+5%H 2混合气氛中进行500℃低温退火制备了Ag/MoS2和Ag/BN/MoS2纳米薄膜,采用拉曼光谱(Raman)、X射线光电子能谱(XPS)和原子力显微镜(AFM)对其结构、组成和表面形貌进行了研究。结果表明:所制备的纳米膜均匀连续,界面紧密且清洁。95%Ar+5%H 2混合气氛中退火能强烈影响顶部MoS2层的形貌并有效去除MoS2中的杂质氧改善其结晶性、稳定性和结构完整性;顶部MoS2层在沉积态时呈细小颗粒状,退火后呈片层状和颗粒状混合形态,特别是引入BN层后促进了其向更大更薄的片状转变,且MoS2薄膜由块状变成类层状结构。另外,电性能表征显示Ag/MoS2具有良好的欧姆接触且电阻率低,引入BN层使得Ag与BN以及BN与MoS2的界面处产生肖特基势垒从而使Ag/BN/MoS2具有整流特性。

Improved performance of UVC-LEDs by combination of high-temperature annealing and epitaxially laterally overgrown AlN/sapphire

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.

High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

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.

Phase structure of the CPD prepared CdS films before and after Ar^+ ion irradiation

CdS films prepared with chemical pyrolysis deposition (CPD) at differ- ent temperature during film growth were characterized by XRD. Hexagon-like struc- ture appeared at the temperature of 350-500℃, while wurtzite phase was observed at temperature of 540℃ during film growth. Also CdS films prepared by CPD at 400℃ were undergone post annealing at different temperature of 200-600℃ or post Ar+ ion irradiation. It is found that wurtzite phase happened when the annealing temperature rose to 600℃. And hexagon-like structure existed at the annealing temperature from 25℃ to near 500℃. Ar+ ion irradiation could not cause phase transformation. but induce some preferred orientations and an increase in grain size for the CdS films.

Effect of Ce,Co,B on formation of LaCo_(13)-structure phase in La(Fe,Si)_(13) alloys

The effect of Ce, Co, and B on the formation of 1：13 phase in La（Fe, Si）13 alloys was investigated by XRD, SEM and EDS. The results show that Co can improve the formation of 1：13 phase in as-cast LaFe11.6-xCoxSi1.4 alloys, but in as-cast and annealed LaFe11.6Si1.4-xCox alloys, it will hamper the formation of 1：13 phase and help the formation of a-Fe（Co, Si） solid solution. Ce2Fel7 phases will form when x reaches a certain value in as-cast and annealed La1-xCexFe11.5Si1.5 alloys. B can improve the formation of 1：13 phase accompanied with Fe2B phase in as-cast LaFe11.6-xBxSi1.4 alloys. B improves the formation of a-Fe solid solution in LaFe11.6Si1.4-xBx alloys, and there is almost only a-Fe in as-cast and annealed LaFe11.6Si0.9B0.5 alloy. In all, the introduction of Co, B, and Ce cannot eliminate the a-Fe phases in corresponding alloys prepared by the high-temperature and short-time annealing process.

硅基底和金刚石基底上沉积ZnO薄膜工艺研究

采用射频磁控溅射方法分别在硅基底和金刚石基底上制备ZnO薄膜,研究了硅和金刚石衬底的不同对ZnO薄膜生长机理的影响,同时分析了氩氧比和退火温度这两个工艺参数对薄膜的晶格取向和表面形貌的影响。利用XRD和AFM对ZnO压电薄膜的性能进行了测试。结果显示,金刚石基片上制备的薄膜表面状态远优于硅基片上的薄膜表面状态;在同类型基底上生长的ZnO薄膜,薄膜的晶格取向随着氩氧比的升高而增强;对于硅基底上生长的ZnO薄膜,适当的退火能够成倍地提高薄膜的c轴取向性。

直流磁控溅射工艺对ZnO薄膜结构影响的研究

ZnO是一种新型的Ⅱ Ⅵ族直接带隙化合物材料,是一种很有潜力的短波长光电器件材料。当ZnO薄膜具有良好的c轴取向和晶格结构时,可得到优良的光电性能比如紫外光受激发射。本实验用XRD和SEM研究了工艺条件如基片温度、氩氧比及退火工艺对ZnO薄膜结构特性的影响。结果表明在基片温度250℃、氩氧比为1∶4的条件下,可得到结晶质量良好的ZnO薄膜;通过退火可以使薄膜应力得到驰豫,降低缺陷浓度,改善薄膜的结构特性。本实验采用直流磁控溅射的方法,最终在(100)硅衬底基片上制备出了高c轴取向、晶粒尺寸约70nm的ZnO薄膜。

加权复合分位数自回归模型在隧道围岩变形预测中的应用

提出加权复合分位数自回归模型对隧道围岩变形进行预测的新方法,并给出其原理和实现算法。以昆明市阳宗隧道为例,对加权复合分位数自回归预测模型进行计算,并与其他模型进行对比分析。结果表明,新方法预测效果优于非加权复合分位数估值的AR(2)模型、基于最小二乘参数估计的自回归预测、经遗传算法优化的支持向量机等预测方法。

Study on WC dispersion-strengthened copper

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.