Transformation properties and microstructure of sputter-deposited Ni-Ti shape memory alloy thin films

The influence of annealing parameters on the martensitic phase transformation in sputter-deposited Ti rich Ni-Ti films is systematically studied by differential scanning calorimetry and by transmission electron microscopy. The annealing temperature range extends from the crystallization temperature of the films up to 900°C. For increasing temperature, multiple phase transformations, transformations via an R-phase or direct martensite/austenite transformations are observed. A similar behavior is found for increasing annealing time. Related changes of the film microstructure, such as the strongly varying distribution of round Ti2Ni precipitates in the grains, are analyzed. Transformation temperatures could be shifted over a wide range by adjusting the film composition from 48 to 54 at.% Ti. The corresponding transformation curves, grain structure as well as nature and amount of precipitates were investigated. No subsequent annealing process is required for films deposited on substrates heated above about 500°C. In this case, the as-deposited films have a very fine-grained and homogeneous microstructure.     

Sol-Gel工艺Si基Bi4 Ti3 O12铁电薄膜制备与晶相结构研究

采用Sol-Gel工艺制备了Si基Bi4TiO12铁电薄膜.研究了退火温度、退火时间、薄膜厚度等对薄膜晶相结构的影响.研究表明,退火温度对Si基Bi4Ti3O12铁电薄膜晶相结构的影响最为显著,而且随退火温度升高,Bi4Ti3O12薄膜更趋向于沿c-轴取向的生长;退火时间在30分钟内对薄膜晶相结构的影响比较明显;薄膜厚度及30分钟以上的退火处理对薄膜晶相结构的影响不大.     

自组装单层膜表面的Bi2Ti2O7薄膜制备与表征

以硝酸铋和钛酸四丁酯为原料,以三氯十八烷基硅烷(OTS)为模板,采用自组装单层膜(self-as-sembled monolayers,SAMs)技术,在玻璃基板上成功制备了Bi2Ti2O7晶态薄膜。借助X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)、X射线能谱(EDS)及原子力显微镜(AFM)等测试手段对Bi2Ti2O7薄膜进行了表征。结果表明,以OTS为模板利用自组装技术,经540℃煅烧2h可成功制得立方相Bi2Ti2O7晶态薄膜,且薄膜表面平整光滑,均匀致密。     

Ti靶及TiO2靶溅射TiO2薄膜微观形貌、结构及光学性质研究

利用射频磁控溅射技术通过Ti靶及TiO2靶在氩氧气氛中同时溅射制备TiO2薄膜,并对所得的样品进行不同温度的退火处理。采用X射线衍射、扫描电子显微镜、拉曼光谱和吸收谱研究了不同的靶材及退火温度对TiO2薄膜晶体结构、微观形貌及光学性质的影响。结果表明:由于靶材的不同,Ti靶溅射时氧分压较低,造成薄膜中存在大量的氧缺陷,晶相发育不完善,颗粒相比TiO2靶溅射时较小,从XRD和拉曼光谱来看,Ti靶溅射得到的TiO2薄膜更有利于金红石相的形成。薄膜的透过率随退火温度的升高而降低,TiO2靶材溅射的薄膜的光学带隙随温度升高而明显降低,而Ti靶得到的薄膜的光学带隙对退火温度的依赖关系不明显。     

Effect of microwave annealing temperatures on lead zirconate titanate thin films

Lead zirconate titanate (Pb(1.1)(Zr(0.52)Ti(0.48))O(3)) thin films of thickness 260?nm on Pt/Ti/SiO(2)/Si substrates were densified by 2.45?GHz microwave annealing. The PZT thin films were annealed at various annealing temperatures from 400 to 700?°C for 30?min. X-ray diffraction showed that the pyrochlore phase was transformed to the perovskite phase at 450?°C and the film was fully crystallized. The secondary (again pyrochlore) phase was observed in the PZT thin films, which were annealed above 550?°C. The surface morphologies were changed above 550?°C of the PZT thin films due to the secondary phase. Higher dielectric constant (ε(r)) and lower dielectric loss coercive field (E(c)) were achieved for the 450?°C film than for the other annealed films.     

Pt／Ti电极的扩散行为及其对铁电薄膜的影响

采用直流磁控溅射方法制备Ｐｔ／Ｔｉ电极，用ＲＢＳ、ＸＲＤ、ＳＥＭ方法研究了Ｐｔ和Ｔｉ的扩散行为，发现在氧气氛中进行热处理造成Ｔｉ层的快速氧化，Ｔｉ厚度对Ｐｔ／Ｔｉ的扩散有很大影响。Ｐｔ／Ｔｉ的扩散造成其上的铁我差的显微结构和性能。     

Structure Evolution of Bulk Metallic Glass Zr52.5Ni14.6Al10Cu17.9Ti5 during Annealing

To whom correspondence should be addressedE-mail: heguo@bj.col.com.cn1. IDtroductionBulk metallic glasses["2] with size of more than micrometers in three dimensions can be produced evenby conventional technological methods such as metallic mold casting[3] ) high pressure die casting[4], waterquenching('l, melt injection casting[6], unidirectionalzone melting['] etc., because they have very lowercritical cooling rate for glass transformation duringcooling from liquid. Such large glass--forming…     

Sputter alloying of Ni,Ti and Hf for fabrication of high temperature shape memory thin films

Abstract

In the present paper, the fabrication and characterisation of typical high temperature Ni(Ti+Hf) alloyed thin films produced by simultaneous sputter deposition from separate elemental Ni, Ti and Hf targets are presented. Film composition, determined by energy dispersive X-ray spectroscopy, was controlled by adjusting the ratio of powers applied to each target. Films deposited at room temperature had an amorphous structure and subsequent annealing at 550°C was carried out in a high vacuum environment, based on crystallisation temperature evaluation by differential scanning calorimetry (DSC). High temperature martensitic transformation, confirmed by DSC and variable temperature X-ray diffraction (XRD), was achieved by deposition of (Ti+Hf) rich Ni–Ti–Hf films. Any slight change of composition towards Ni rich reduced the transformation temperature. Atomic force microscopy and XRD illustrated that the films had a fine grain structure (～100 nm). One way shape memory effect was observed at ～200°C in a film with composition of 15·6 at.-%Hf.     

Growth and characterization of shape memory alloy thin films for Si microactuator technologies

NiTi thin film alloys have been grown on Si (1 0 0) substrates by sequential multilayer deposition of Ni and Ti layers followed by metal interdiffusion via annealing. Short-time (5 min) annealing of the deposited layers at 500 °C leads to alloying of Ni and Ti, provided that preferential oxidation of Ti is avoided. This has been achieved by capping the layers with AlN, which constitutes a very efficient barrier preventing oxygen contamination of the film. For uncapped films, annealing has to be performed under high vacuum conditions. The structure of the processed films strongly depends on the temperature and time of the thermal process, obtaining Ni- and Ti-rich phases when the films are annealed at higher temperatures and/or during longer times. As-grown and processed films are analyzed by X-ray diffraction, in-depth Auger electron spectroscopy and X-ray photoelectron spectroscopy techniques. Finally, resistivity measurements show the existence of a phase transition in the films annealed at 600 °C without the capping layers (vacuum furnace). This contrasts with the behavior observed for AlN capped films, where cracking of the film occurs during cooling, which has been attributed to generation of stress in the buried film during the phase transition.     

Superelasticity of free‐standing NiTi films depending on the oxygen impurity of the used targets

Off‐stoichiometric NiTi sputter targets were manufactured by ingot metallurgy in order to produce Ni‐rich NiTi thin films. Crystalline samples, which undergo a martensitic transformation, were fabricated by magnetron sputtering and subsequent thermal treatment. The sacrificial layer technique was applied to obtain free‐standing NiTi films. The stoichiometry of the sputtered film is different to the stoichiometry of the target material. Sputtering targets with a Ti content higher than 49.5 at.% have a typical Ti‐loss rate in the order of 4.3 at.%, whereas at more Ni‐rich targets a Ti loss rate of only 0.5–1.5 at.% is observed. Due to this Ti loss rate target composites of Ti‐53.1Ni‐46.9 at.% and Ti‐53.2Ni‐46.8 at.% were taken. The NiTi films obtained from these two targets were compared. The main difference between the two targets is the impurity content of oxygen and carbon. Auger electron spectroscopy measurements were performed to determine qualitatively the content of oxygen in the free‐standing NiTi films. Transformation temperatures and hysteresis properties of the martensitic transformation were characterised by differential scanning calorimetry. Free‐standing films obtained from the Ti‐53.1Ni‐46.9 at.% and Ti‐53.2Ni‐46.8 at.% sputtering targets revealed superelastic properties at 45 °C as demonstrated by tensile testing. Tensile tests were taken at various temperatures of 40 °C, 45 °C, 50 °C, 55 °C and 60 °C, revealing e.g. a maximum superelastic strain of approximately 5 % at 45 °C.     

The influences of rapid-thermal annealing on the characteristics of Sr0.6Ba0.4Nb2O6 thin film

The Sr0.6Ba0.4Nb2O6 (SBN) thin films were successfully prepared on Pt/Ti/Si and SiO2/Si/Al substrates and crystallized subsequently using rapid thermal annealing (RTA) process in ambient atmosphere for 1 min. The surface morphologies and thicknesses of as-deposited and annealed SBN thin films were characterized by field emission scanning electron microscopy, and the thickness was about 246 nm. As compared with the as-deposited SBN thin films, the RTA-treated process had improved the crystalline structures and also had large influence on the crystalline orientation. When the annealing temperatures increased from 700 degrees C to 900 degrees C, the diffraction intensities of (410) and (001) peaks apparently increased. Annealed at 900 degrees C, the (001) peak had the maximum texture coefficient and SBN thin films showed a highly c-axis (001) orientation. The influences of different RTA-treated temperatures on the polarization-applied electric field (P-E) curves and the capacitance-voltage (C-V) curves were also investigated.     

Superelasticity of TiPdNi Alloys with and without Rare Earth Ce Addition

Ti50.6Pd30Ni19.4 and Ti51Pd28Ni21 (Ce) alloys have been prepared under various temperatures for long time annealing. Differential scanning calorimetery (DSC), X-ray diffraction (XRD) and tensile test were employed to investigate the phase transformation behavior and superelasticity of the alloys. It has been found that the phase transformation temperature of Ti50.6Pd30Ni19.4 is about 40C higher than that of Ti51Pd28Ni21(Ce), and do not change much with different annealed temperature. Obvious superelasticity is retained in Ti50.6Pd30Ni19.4 alloy annealed at 400C for 18 h, and annealing at higher temperature shows a deterioration of this property. The Ce addition in TisiPd28Ni2i alloy significantly delays recrystallization, increases yied strength and elastic modulus, but the superelasticity is poor.     

Oxidation behavior of sputter-deposited Ti–Ni thin films at elevated temperatures

The isothermal oxidation kinetics of sputter-deposited equiatomic Ti–Ni thin films in pure oxygen from 823 to 923 K is studied using thermo-gravimetric analysis. The structure, composition-depth distribution and surface morphology of oxidized Ti–Ni thin films are investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and atomic force microscope (AFM), respectively. The results show that the oxidation kinetics of Ti–Ni thin films obeys a near-parabolic law. TiO₂, TiNi₃ and parent B2 phase are the compositions of oxidized Ti–Ni thin films. A double-layered scale including the outermost layer and the Ni-rich layer is formed outside the B2 matrix of oxidized Ti–Ni thin films. Moreover, thermal oxidation induces a surface smoothening of Ti–Ni thin films and surface roughness of oxidized Ti–Ni films decreases with the increasing oxidation temperature.     

Crystallization and electrical characteristics of 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 thin films under different annealing temperature and atmosphere

0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 +1 wt% Bi2O3 (NBT-BT3) ceramic is used as target to deposit the NBT-BT3 thin films. The excess 1wt% Bi2O3 is used to compensate the vaporization of Bi2O3 during the sintering and annealing processes. NBT-BT3 thin films are successfully deposited using radio frequency (RF) magnetron sputter method and crystallized subsequently using a conventional furnace annealing (CFA) process. The annealed process is conducted in air and in oxygen atmosphere at temperatures ranging from 600-800 degrees C for 60 min. As compared with the as-deposited NBT-BT3 thin films, the CFA-treated process has improved the grain growth and crystallization. We will show that the annealing atmosphere is the more important parameter to influence the grain growth and crystallization of NBT-BT3 thin films than the annealing temperature. The influences of CFA-treated temperature and atmosphere on the electrical characteristics of NBT-BT3 thin films, including the polarization characteristics (Pr, Ps, and Ec values), the capacitance-voltage (C-V) curves, and the leakage current density-electric field (J-E) curves, are also investigated in this study.     

Interfacial reaction and adhesion between SiC and thin sputtered nickel films

Thin sputtered nickel films grown on SiC were annealed in an Ar/4 vol % H2 atmosphere at temperatures between 550 to 1450 °C for various times. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The reaction with the formation of silicides and carbon was observed to first occur above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted to Ni2Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to 1050 °C the relatively higher critical load values of 20–33 N for SiC/Ni couples are formed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of stress on the interfacial reactions of metal thin films on (0 0 1)Si

The influences of stress on the interfacial reactions of Ti and Ni metal thin films on (0 0 1)Si have been investigated. Compressive stress present in the silicon substrate was found to retard significantly the growth of Ti and Ni silicide thin films. On the other hand, the tensile stress present in the silicon substrate was found to enhance the formation of Ti and Ni silicides. For Ti and Ni on stressed (0 0 1)Si substrates after rapid thermal annealing, the thicknesses of TiSi₂ and NiSi films were found to decrease and increase with the compressive and tensile stress level, respectively. The results clearly indicated that the compressive stress hinders the interdiffusion of atoms through the metal/Si interface, so that the formation of metal silicide films was retarded. In contrast, tensile stress facilitates the interdiffusion of atoms. As a result, the growth of Ti and Ni silicide is promoted.     

N掺杂Cu2O薄膜的低温沉积及快速热退火研究

采用氧化亚铜(Cu_2O)陶瓷靶,利用射频磁控溅射沉积法在氮气和氩气的混合气氛下制备了N掺杂Cu_2O(Cu_2O∶N)薄膜,并在N_2气氛下对薄膜进行了快速热退火处理,研究了N_2流量和退火温度对Cu_2O∶N薄膜的生长行为、物相结构、表面形貌及光电性能的影响。结果显示,在衬底温度300℃、N_2流量12sccm条件下生长的薄膜为纯相Cu_2O薄膜;在N_2气氛下对预沉积薄膜进行快速热退火处理不影响薄膜的物相结构,薄膜的结晶质量随退火温度(450℃)的升高而显著改善;快速热退火处理能改善薄膜的结晶质量和缺陷,降低光生载流子的散射,增强载流子的传输,预沉积Cu_2O∶N薄膜经400℃退火处理后展示出较好的电性能,薄膜的霍尔迁移率(μ)为27.8cm~2·V~(-1)·s~(-1)、电阻率(ρ)为2.47×10~3Ω·cm。研究表明低温溅射沉积和快速热退火处理能有效改善Cu_2O∶N薄膜的光电性能。     

Ag/Bi4Ti3O12/p-Si异质结的制备及其C-V特性研究

为制备符合铁电存储器件要求的高质量铁电薄膜,采用溶胶-凝胶(Sol-Gel)工艺,制备了Si基Bi4Ti3O12铁电薄膜及MFS结构的Ag/Bi4Ti3O12/P-Si异质结,对Bi4Ti3O12薄膜的相结构特征及异质结的C-V特性进行了测试与分析.XRD图谱显示,Si基Bi4Ti3O12薄膜具有沿c-轴择优取向生长的趋势,而Ag/Bi4Ti3O12/p-Si异质结顺时针回滞的C-V特性曲线则表明,该异质结可实现电极化存储.此外,对该异质结C-V特性曲线的非对称及向负偏压方向偏移的产生原因也进行了分析.在此基础上,为提高铁电薄膜的铁电性能及改善其C-V特性提出了合理的结构设想.     

Influence of annealing on the structure and stoichiometry of europium-doped titanium dioxide thin films

This work presents the influence of annealing on the structure and stoichiometry of europium (Eu)-doped titanium dioxide (TiO₂). Thin films were fabricated by magnetron sputtering from a metallic Ti-Eu target in oxygen atmosphere and deposited on silicon and SiO₂ substrates. After deposition the selected samples were additionally annealed in air up to 1070 K.Film properties were examined by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) and the results were analyzed together with the undoped TiO₂ thin films prepared under similar technological conditions.XRD results showed that depending on the Eu content, as-deposited thin films consisted of the TiO₂-anatase or TiO₂-rutile.An additional annealing will result in the growth of anatase crystals up to 35 nm, but anatase to rutile phase transformation has not been recorded. AFM images display high quality and a dense nanocrystalline structure. From the XPS Ti2p spectra the 4+oxidation state of Ti was confirmed. The O1s XPS spectra displayed the presence of an O²⁻ photoelectron peak accompanied by an additional broader peak that originates from hydroxyl species chemisorbed at the sample surface. It has been found that Eu dopant increases the OH⁻ content on the surface of prepared TiO₂:Eu thin films. The calculated O/Ti ratio was in the range of 1.85-2.04 depending on the sample.     

热处理温度对铁电薄膜底电极Pt和Pt／Ti物相与形貌的影响

随着热处理温度上升，在ＳｉＯ２／Ｓｉ衬底上溅射的Ｐｔ、Ｐｔ／Ｔｉ电极中，构成Ｐｔ薄膜的晶粒由小变大，由分布均匀到晶粒局部聚集，最后分离成小岛。Ｔｉ层可提高Ｐｔ薄膜与基片间的粘附性和高温下的稳定性。快速热处理可提高Ｐｔ薄膜在高温下的连续性。并研究了Ｐｔ薄膜对ＰＬＴ铁电薄膜的成品率和分散性的影响。