Effect of a Cr Underlayer on the Magnetic Properties of TbCo Amorphous FIlms with Perpendicular Anisotropy

The effect of the Cr underlayer on the magnetic properties of TbCo amorphous films with perpendicular anisotropy has been investigated.It was found that the Cr underlayer thickness can influence the coercivity of TbCo films.A coercivity as high as 6.3kOe was obtained in 120nm Tb31Co69 films with a 180nm Cr underlayer.This was only 4.4kOe for the same thickness Tb31 CO69 films without the Cr underlayer.Cross-sectional scanning electron microscopy indicated that the TbCo film with the Cr underlayer consisted of a Column structure.It is considered that this heterogeneous structure gives rise to the coercity enhancement of TbCo films in the presence of the Cr underlayer.     

Improved crystal quality of GaN film with the in-plane lattice-matched Ino.17Alo.s3N interlayer grown on sapphire substrate using pulsed metal-organic chemical vapor deposition

We report on an improvement in the crystal quality of GaN film with an Ino.17Alo.83N interlayer grown by pulsed metal-organic chemical vapor deposition, which is in-plane lattice-matched to GaN films. The indium composition of about 17% and the reductions of both screw and edge threading dislocations （TDs） in GaN film with the InA1N interlayer are estimated by high resolution X-ray diffraction. Transmission electron microscopy （TEM） measurements are employed to understand the mechanism of reduction in TD density. Raman and photoluminescence measurements indicate that the InA1N interlayer can improve the crystal quality of GaN film, and verify that there is no additional residual stress induced into the GaN film with InA1N interlayer. Atomic force microscopy measurement shows that the InA1N interlayer brings in a smooth surface morphology of GaN film. All the results show that the insertion of the InA1N interlayer is a convenient method to achieve excellent crystal quality in GaN epitaxy.     

Raman Spectrum of Epitaxial Graphene on SiC （0001） by Pulsed Electron Irradiation

We report new Raman features of epitaxial graphene （EG） on Si-face 4H-SiC prepared by pulsed electron irradiation （PEI）. With increasing graphene layers, frequencies of G and 2D peaks show blue-shifts and approach those of bulk highly-oriented pyrolytic graphite. It is indicated that the EG is slightly tension strained and tends to be strain-free. Meanwhile, single Lorentzian line shapes are well fitted to the 2D peaks of EG on SiC（O001） and their full widths at half maximum decrease with the increasing graphene layers, which indicates that the multilayer EG on Si-face can also contain turbostratic stacking by our PEI route instead of only AB Bernal stacking by a traditional thermal annealing method. It is worth noting that the stacking style plays an important role on the charge carrier mobility. Therefore our findings will be a candidate for growing quality graphene with high carrier mobility both on the Si- and C-terminated SiC substrate. Mechanisms behind the features are studied and discussed.     

大口径碳化硅反射镜数控抛光工艺北大核心CSCD

研究了针对600mm口径方形轻质碳化硅元件的数控抛光工艺过程,采用国产OP1000数控研磨抛光机床对一块600mm×480mm的方形碳化硅元件进行数控抛光加工。在经过两周的加工时间,碳化硅光学元件的通光口径均方根(RMS)值收敛到了35nm(大约为λ/18,λ=632.8nm)。在加工过程中针对大口径椭圆形碳化硅反射镜采用了合适的加工参数优化,例如在加工过程中的不同阶段选择了不同颗粒度的金刚石微粉作为特定阶段的抛光辅料以保证光学元件的表面粗糙度。对计算机控制数控加工技术的快速收敛过程也进行了阐释。     

Formation of the intermediate semiconductor larger for the Ohmic contact to silicon carbide using Germanium implantation

By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P⁺ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρ_c as low as 4.23× 10^-5~Ωega \cdotcm² is achieved after annealing in N₂ at 800~°C for 3~min, which is much lower than that (>900~°C) in the typical SiC metallisation process. The sheet resistance R_sh of the implanted layers is 1.5~kΩega /\Box. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge⁺ ion implantations.     

SiO2图形化蓝宝石衬底对GaN生长及LED发光性能的影响

为了提高氮化镓(GaN)基发光二极管(LEDs)的发光性能,采用等离子体增强化学气相沉积(PECVD)在蓝宝石衬底上沉积SiO2薄膜,经过光刻和干法刻蚀技术制备了SiO2图形化蓝宝石衬底(SiO2 patterned sap-phire substrate,SPSS),利用LED器件的外延生长和微纳加工技术获得了基于S...     

Al2O3添加量对超高压烧结SiC的影响

碳化硅陶瓷具有高温强度大、抗氧化性强、耐磨损性好、热膨胀系数小、硬度高以及抗热震和耐化学腐蚀等优良特性，已经在很多领域获得应用。文中探索采用超高压烧结工艺烧结低Al2O3助剂添加量（质量分数O%-7％）的纳米SiC粉末，研究了烧结体的物相组成、化学成分、显微结构及显微硬度等。     

MgB2超导多层膜的制备方案

简要叙述了MgB2的发展和制备历史,通过对不同衬底材料上MgB2的反应情况的总结概括以及对不同衬底材料和MgB2的晶体结构和晶格常量的比较,提出一种MgB2超导多层膜的制备方案.     

柔性ITO衬底电化学沉积制备Cu/Cu2O薄膜

研究了使用电化学沉积法于碱性条件下在柔性ITO衬底上制备Cu/Cu₂O薄膜的方法。循环伏安曲线表明Cu₂O与Cu的阴极峰分别位于-500 mV(vs Ag/AgCl)和-800 mV(vs Ag/AgCl)附近。利用循环伏安法考察了生长温度和电解液pH值等对Cu₂O与Cu阴极峰电位的影响,阴极峰随生长温度的升高以及pH值的降低而略向阳极移动,沉积电流也随之相应增大。与弱酸性条件相比,上述两个阴极峰随pH值升高而移动的程度明显减小,这可能与碱性条件下C₃H₆O电离程度增大以及C₃H₆O根作为配体的过量程度有关。通过X射线衍射光谱和扫描电子显微镜的表征证实,在所研究的生长温度区间和pH值内可利用电化学沉积法在柔性ITO衬底上制备Cu/Cu₂O纳米混晶薄膜。在相同的生长温度和pH条件下,电化学沉积电位对样品表面形貌和晶体性质具有较大影响。     

高性能MgB2长线材制备及性能表征

采用原位粉末装管工艺,分别以Mg粉(99.5%),无定形B粉(99.9%)为原料,以纳米SiC(10-30 nm)作为掺杂材料制备铁基MgB2线.首先将已混合的原料在丙酮介质中球磨,真空干燥后,将粉末填入铁管内,然后通过孔型轧制、旋锻和拉拔等冷加工工艺得到11 m长外径Ф1.75 mm铁基MgB2超导线.用扫描电镜,电子能谱,X射线衍射仪和超导量子干涉仪测试发现,样品微观结构整齐,晶粒大小均匀,内部仅含微量MgO,TC(onset)= 35.1 K,ΔTC＝5.3 K.纳米SiC掺杂后,其中C造成MgB2晶格畸变,形成有效磁通钉扎中心,C元素在MgB2中分布均匀.标准四引线测试结果表明,11 m线均分10段后,各点的Jc(4.2 K,10 T)均超过1.0×104 A/cm2,最高值达到1.2×104 A/cm2.在10-18T范围各点临界电流值分布均匀,变化率小于10%.