Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films

Ge_2Sb_2Te_5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge_2Sb_2Te_5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge_2Sb_2Te_5 film is due to the amorphous －Te－-Te－ stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe_4 and the Sb－Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb－Sb (Te_2) and (Sb_2) Sb－Sb (Te_2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge_2Sb_2Te_5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te_2) Sb－Sb (Te_2).     

Landau quantization and the thickness limit of topological insulator thin films of Sb2Te3

We report the experimental observation of Landau quantization of molecular beam epitaxy grown Sb{2}Te{3} thin films by a low-temperature scanning tunneling microscope. Different from all the reported systems, the Landau quantization in a Sb{2}Te{3} topological insulator is not sensitive to the intrinsic substitutional defects in the films. As a result, a nearly perfect linear energy dispersion of surface states as a 2D massless Dirac fermion system is achieved. We demonstrate that four quintuple layers are the thickness limit for a Sb{2}Te{3} thin film being a 3D topological insulator. The mechanism of the Landau-level broadening is discussed in terms of enhanced quasiparticle lifetime.     

Optical and Short- wavelength Recording Properties of Ag_8In_( 14) Sb_( 55) Te_(23) Phase-change Films

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Optical and Short-wavelength Recording Properties of Ag8In14Sb55Te23 Phase-change Films

The Ag-In-Sb-Te phase-change films were deposited on K9 glass substrates by RF magnetron sputtering technology with an Ag-In-Sb-Te alloy target. The spectral properties and short-wavelength optical storage properties of Ag8In13Sb55Te23 films were studied. X-ray diffraction results have indicated that the crystallization compounds include mainly AgSbTe2 with small amounts of Sb and AgInTe2. A comparatively large absorption has been observed in the visible wavelength range. The optical storage characteristics of Ag8In13Sb55Te23 thin films indicated that larger reflectivity contrast can be obtained at lower writing power and shorter writing pulse width.     

Superconductivity of A1-type SnSb,SbTe and TeI alloys

Superconducting A1-type Sn, SnSb, Sb, SbTe, Te, Te I and I films were vapour-quenched on glass substrates quench-coated with CaO. The highest transition temperature is exhibited by 100 Å thick 20Sn–80Sb films, which become superconducting at 21.6 K.     

Thermal phase change and activation energy of crystallization of Ge-Sb-Te-Sn thin films

To improve the optical storage performance, Sn was doped into Ge2Sb2Te5 phase change thin films. The optical and thermal properties of Sn-doped Ge2Sb2Te5 film were investigated. The crystal structures of the as-sputtered and the annealed films were identified by the X-ray diffraction (XRD) method. The differential scanning calorimeter (DSC) method is used to get the crystallization temperature and crystallization energy (Ea). It was found that proper Sn-doping could highly improve storage performance of the Ge2Sb2Te5 media.     

Optical Recording Performance of In_（47）Sb_（14）Te_（39）Phase Change Thin Films using 514．5nm Wavelength Laser Beam

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Thermal effect of Ge_2Sb_2Te_5 in phase change memory device

The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm-1in In film composed of In/InOx core–shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.     

溅射气压对Ge2Sb2Te5薄膜光学常数的影响

实验研究了氩气气压对溅射制备的Ge2 Sb2 Te5 薄膜的光学常数随波长变化的影响 ,结果表明 :随薄膜制备时氩气气压的增加 ,Ge2 Sb2 Te5 薄膜的折射率n先增大后减小 ,而消光系数k先减小后增大。二者都随波长的变化而变化 ,且在长波长范围变化较大 ,短波长范围变化较小 ,解释了溅射气压对Ge2 Sb2 Te5 薄膜的光学常数影响的机理     

Theoretical and experimental investigations of the properties of Ge2Sb2Te5 and indium-doped Ge2Sb2Te5 phase change material

We have carried out comprehensive computational and experimental study on the face-centered cubic Ge₂Sb₂Te₅ (GST) and indium (In)-doped GST phase change materials. Structural calculations, total density of states and crystal orbital Hamilton population have been calculated using first-principle calculation. 5 at.% doping of In weakens the Ge–Te, Sb–Te and Te–Te bond lengths. In element substitutes Sb to form In–Te-like structure in the GST system. In–Te has a weaker bond strength compared with the Sb–Te bond. However, both GST and doped alloy remain in rock salt structure. It is more favorable to replace Sb with In than with any other atomic position. X-ray diffraction (XRD) analysis has been carried out on thin film of In-doped GST phase change materials. XRD graph reveals that In-doped phase change materials have rock salt structure with the formation of In₂Te₃ crystallites in the material. Temperature dependence of impedance spectra has been calculated for thin films of GST and doped material. Thickness of the as-deposited films is calculated from Swanepoel method. Absorption coefficient (α) has been calculated for amorphous and crystalline thin films of the alloys. The optical gap (indirect band gap) energy of the amorphous and crystalline thin films has also been calculated by the equation \( \alpha h\nu = \beta (h\nu - E_{\text{g }} )^{2} \) . Optical contrast (C) of pure and doped phase change materials have also been calculated. Sufficient optical contrast has been found for pure and doped phase change materials.     

激光致晶态Ag11In12Te26Sb51相变介质光学常数的研究

研究了结晶度对Ag11In12 Te2 6Sb51相变薄膜光学常数的影响。用初始化仪使相变薄膜晶化 ,改变晶化参量得到不同的结晶度 ,当转速固定时 ,随激光功率的增加 ,折射率基本随之减小 ,消光系数先是增大 ,而后减小 ;当激光功率固定时 ,随转速的增大 ,折射率也随之增大 ,消光系数也是先增大后减小。非晶态与晶态间的变换、薄膜微结构的变化 (包括晶型的转变和原子间键合状态的变化 )以及薄膜内残余应力是影响Ag11In12 Te2 6Sb51相变薄膜复数折射率的主要原因。测量了单层膜的透过率和CD RW相变光盘中Ag11In12 Te2 6Sb51薄膜非晶态和晶态的反射率     

Local structure of AlSb2Te3 thin film studied by experimental and theoretical methods

Local structure of AlSb₂Te₃ thin film was studied by experiments and theoretical calculations. Results show that both Sb and Te atoms are likely to be replaced by Al to form Al–Sb and Al–Te covalent bonds. At a smaller dopant concentration, Al atoms presumably incorporate into Sb₂Te₃ matrix by substitute Sb or Te atoms without spoiling its structural unit. Compared together with other reported data, for Al doping Sb₂Te₃ PCM material, optimizing Al content is a key criteria for its phase stability and electric performance.     

Photoconductivity in amorphous chalcogenide thin films: Effect of incorporation of Bi,Sb and Te IN Ge22Se78 binary alloy

Temperature and intensity dependence of steady state photoconductivity is studied in amorphous thin films of various chalcogenide glasses with a view to see the effect of incorporation of Bi, Sb and Te in Ge-Se system. Our results show that the photosensitivity decreases as 10 at % of Bi, Sb and Te are incorporated in Ge₂₂Se₇₈.Transient photoconductivity measurements have also been made on the same samples. These results show that the decay of photoconductivity becomes slower when Bi, Sb and Te are incorporated. The results have been explained in terms of the defect states which are introduced after incorporation of these elements in the binary system.     

SiO2/Si衬底上石墨烯的制备与结构表征

在分子束外延(MBE)设备中,利用直接沉积C原子的方法在覆盖有SiO₂的Si衬底(SiO₂/Si)上生长石墨烯,并通过Raman光谱和近边X射线吸收精细结构谱等实验技术对不同衬底温度(500℃,600℃,700℃,900℃,1100℃,1200℃)生长的薄膜进行结构表征.实验结果表明,在衬底温度较低时生长的薄膜是无定形碳,在衬底温度高于700℃时薄膜具有石墨烯的特征,而且石墨烯的结晶质量随着衬底温度的升高而改善,但过高的衬底温度会使石墨烯质量降低.衬底温度为1100℃时结晶质量最好.衬底温度较低时C原子活性较低,难以形成有序的C-sp²六方环.而衬底温度过高时(1200℃),衬底表面部分SiO₂分解,C原子与表面的Si原子或者O原子结合而阻止石墨烯的形成,并产生表面缺陷导致石墨烯结晶变差.     

Voltage and response-time measurements by thin-single-film laser pulse detectors

Previously, voltage and response-time measurements have been made in refractory materials. We have tried to observe such effects in some low-melting-point materials. For this purpose Sb-, Bi- and Te-film detectors were developed and studied using pulsed Nd-glass and CO₂ lasers. Te films show the highest responsivity and Sb detectors give the fastest response time (12.5 ns). We have also measured voltages in obliquely-deposited Te films, with varying angles of deposition from 0° to 60°. An Ar⁺ laser was also used to irradiate the Te films.     

Study of aluminium-modified Ge2Sb2Te5 thin films for the applicability as phase-change storage device material

Electrical and optical studies have been carried out on aluminium-modified Ge₂Sb₂Te₅ thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Al_x(Ge₂Sb₂Te₅)_1?x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge–Sb–Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge–Sb–Te alloy films.     

化学气相沉积石墨烯薄膜的洁净转移

石墨烯因其优异的性能在很多领域具有广阔的应用前景.目前石墨烯薄膜主要是以铜作为催化基底,通过化学气相沉积法制备.这种方法制备的石墨烯薄膜需要被转移到目标基底上进行后续应用,而转移过程则会对石墨烯造成污染,进而影响石墨烯的性质及器件的性能.如何减少或避免污染,实现石墨烯的洁净转移,是石墨烯薄膜转移技术研究的重要课题,也是本综述的主题.本综述首先简单介绍了石墨烯的转移方法;进而重点讨论由于转移而引入的各种污染物及其对石墨烯性质的影响,以及如何抑制污染物的引入或如何将其有效地去除;最后总结了石墨烯洁净转移所存在的挑战,展望了未来的研究方向和机遇.本综述不仅有助于石墨烯薄膜转移技术的研究,对整个二维材料器件的洁净制备也将有重要参考价值.     

On RF magnetron-sputtering preparation of Ag–Sb–S thin films

One important application area of chalcogenide materials is rewritable optical data storage. This technology is based on a reversible phase transition between the crystalline and the amorphous state and vice versa. Currently dominant materials for rewritable optical recording are Ge–Sb–Te and Ag–In–Sb–Te alloys. Material research still continues due to the need for increasing storage capacity and data rates. Polycrystalline bulks of AgSbS₂ were prepared by melt-quench technique. Composition and homogeneity of these bulks were checked by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), crystallinity was studied by X-ray diffraction (XRD). Targets for RF magnetron sputtering were prepared from pulverized bulks by hot-pressing technique. Targets were characterized the same way as bulks. Thin Ag–Sb–S films were prepared by RF magnetron sputtering as potential candidates for rewritable optical data storage films. Composition and homogeneity of prepared thin films were characterized by SEM-EDX, Rutherford Back Scattering (RBS) and Elastic Recoil Detection Analysis (ERDA); character (amorphous/crystalline) was traced by XRD. Optical properties (spectral dependence of refractive index) were evaluated on the basis of UV–Vis–NIR spectroscopy and variable angle spectral ellipsometry (VASE). Crystallization abilities were studied by the measurement of thermal dependence of the prepared thin films optical transmission.     

Sb_2Te_3热电薄膜的离子束溅射制备与表征

采用离子束溅射技术交替沉积Sb-Te-Sb多层薄膜后进行高真空热处理,直接制备Sb2Te3薄膜.利用X射线衍射(XRD)仪、霍尔系数测试仪、薄膜Seebeck系数测量系统对所制备的薄膜特性进行表征.XRD测量结果显示,薄膜的主要衍射峰与Sb2Te3标准衍射峰相同,在[101]/[012]晶向取向明显,存在较多的Te杂质峰;霍尔系数测试结果表明,薄膜为p型半导体薄膜,薄膜电阻率较低,其电导率接近于金属电导率,载流子浓度量级为1023cm-3,具有良好的电学性能;Seebeck系数测量结果显示,薄膜具有良好的热电性能,在不同条件下制备的薄膜的Seebeck系数在7.8—62μV/K范围;在所制备的薄膜中,退火时间为6h、退火温度为200℃的薄膜其Seebeck系数达到最大,约为62μV/K,且电阻率最小.     

Field emissions of graphene films deposited on different substrates by CVD system

<正>Graphene films are deposited on copper(Cu) and aluminum(Al) substrates,respectively,by using a microwave plasma chemical vapour deposition technique.Furthermore,these graphene films are characterized by a field emission type scanning electron microscope(FE-SEM),Raman spectra,and field emission(FE) I-V measurements.It is found that the surface morphologies of the films deposited on Cu and Al substrates are different:the field emission property of graphene film deposited on the Cu substrate is better than that on the Al substrate,and the lowest turn-on field of 2.4 V/μm is obtained for graphene film deposited on the Cu substrate.The macroscopic areas of the graphene samples are all above 400 mm~2.