Non-magnetic hexagonal nanocrystalline ni films grown by radio frequency magnetron sputtering

Nanoscale Ni films in the thickness range 15-500 nm were grown on various substrates, such as amorphous glass, single crystalline silicon and sapphire, and polycrystalline alumina, at a temperature of about 350 K by radio frequency magnetron sputtering. It is demonstrated, via X-ray diffraction and high-resolution transmission electron microscopy, that there is an Ar-gas pressure window that favors the growth of stable single-phase hexagonal nanocrystalline Ni films regardless of the film thickness and the kind of the substrate. At lower or higher Ar pressures the films grow in the regular face centered cubic phase of Ni. The structural habits are attributed to differences in the kinetic energy of the Ni atoms impinging on the substrates. Superconducting quantum interference device magnetometry measurements reveal that the hexagonal films show zero magnetic response down to liquid Helium temperature. This result is discussed with respect to earlier first principle calculations and to experimental results on Ni nanoparticles.     

Characterization of crystalline structure and morphology of NiO thin films

We investigated the relation of sputtering powers with structural and morphological properties of nickel oxide (NiO) thin films. NiO thin films were fabricated by using an rf-reactive sputtering method on Si(100) substrates with a Ni target in a partial pressure of oxygen and argon. The films were deposited by various rf-sputtering powers from 100 to 200 W at room temperature. The phases and crystalline structures of the deposited films were investigated by using grazing incident X-ray diffraction (XRD). The thickness and surface morphology of the films were investigated by using a field emission-scanning electron microscopy (FE-SEM). The different sputtering conditions drastically affected the crystallinity and the surface morphology of NiO thin films. A combined analysis of the data obtained from X-ray diffraction and SEM images demonstrates that the preferred orientation of NiO films tends to grow from (111) to (200) direction as increasing the sputtering power, which can be explained by in terms of the surface energy along the indexing plane in an fcc structure. As increasing the rf power, lattice constants decreased from 4.26 to 4.20 angstroms and samples became high-quality crystals. Under our experimental condition, NiO films prepared at 150 W with 20% partial pressure of oxygen and 7 cm distance from the sample to the target show the best quality of the crystal.     

fcc titanium in Ti-Al multilayers

Thin titanium films deposited on aluminum, in a multilayered form, were found to transform from a hexagonal close-packed (hcp, P63/MMC) structure to the face-centered cubic structure (fcc, FM3M) upon thinning of cross sections for TEM study. The transformation results in twinned Al and Ti layers with noncoherent Σ = 3 boundaries separating the twin related crystals in each layer. The as-deposited Ti is hcp and the Al fcc. The Ti layers studied varied in thickness between 30 and 500 nm. They were deposited by electron beam evaporation in vacuum, using 30 nm thick layers of Al to form multilayered films which contained between 10 and 100 bilayers. The study was conducted by TEM and X-ray diffraction and the hcp to fcc transformation of the Ti layers was observed in all the multilayers.     

Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure

We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.     

Controllable synthesis of hexagonal close-packed nickel nanoparticles under high nickel concentration and its catalytic properties

The hexagonal close-packed (hcp) Ni nanoparticles have been synthesized successfully in triethylene glycol with high ionic Ni concentration under the presence of protective agent (PVP or PEG). The protective agent (PVP or PEG) played an important role in the formation of hcp Ni. The crystal structure of nickel can be tuned by changing the concentration of Ni ions, reaction temperature, and amount of protectors. The X-ray diffraction and magnetic studies revealed the formation of pure hcp Ni. The VSM study showed that the magnetic properties of hcp Ni is quite different from that of face-centered cubic (fcc) Ni. The hcp Ni nanoparticle had a low saturation magnetization, while the coercivity value of hcp Ni was nearly the same as that of fcc Ni. A stable hcp Ni supported on γ-Al₂O₃ catalyst was also prepared successfully for the first time and its catalytic activity was investigated in the aqueous-phase reforming of glycerol. The achieved conversion of glycerol and selectivity to hydrogen was high up to 52 and 64%, while the selectivity to methane was only 5%, indicating the preventing of methanation on hcp Ni.     

直流反应溅射TiO2薄膜的制备及其性能研究

采用直流反应磁控溅射的方法,溅射高纯钛靶在ITO石英衬底上制备了TiO2薄膜.用XRD、Raman光谱、AFM和紫外-可见光分光光度计分别测试了TiO2薄膜的结构、表面形貌和紫外-可见光透射谱,研究了工艺因素中溅射气压、氧氩比和退火温度对薄膜结构的影响.采用C(胶)/TiO2/ITO三层结构研究了锐钛矿TiO2薄膜的紫外光响应.实验结果表明较低的溅射气压、合适的氧氩比和较高的退火温度有利于锐钛矿TiO2薄膜的结晶.在2 V的偏压下,锐钛矿TiO2薄膜的紫外光响应上升迟豫时间约为3 s,稳定光电流可达到2.1 mA,对紫外光的灵敏性和稳定的光响应表明TiO2薄膜有可能成为一种新的紫外光探测器材料.     

Magnetic force microscopy on nanocrystalline Co films

Pioneer works in ultrathin magnetic films have shown perpendicular magnetic domains in the demagnetized state. The source of this perpendicular anisotropy is the interface anisotropy developed at the interface. Similar domains could be observed in tetragonally distorted ultrathin films due to the magnetoelastic anisotropy. On the other hand, single-crystalline hexagonal close packed (hcp) Co films when grown epitaxially with the c-axis oriented perpendicular to the film plane may show perpendicular stripe magnetic domains even up to a thickness of about 500 nm. In that case the source of perpendicular anisotropy was the magnetocrystalline anisotropy of bulk Co, which favors the c-axis. In this work, we have grown by radio frequency magnetron sputtering Co films in the thickness range 15-4500 nm. We have used various substrates, such as Corning glass, silicon and Al-foil. The substrate temperature was about 350 K. The films have been found by X-ray diffraction experiments to present various structures and textures depending on the preparation conditions, mainly the Ar-pressure and deposition rate. Stripe- and labyrinth-like domain configurations are observed in films textured along the c-axis, and in films with a mixture of hcp and fcc grains, repectively. Films which show mainly fcc or amorphous structure do not form perpendicular domains. The results are discussed with respect to magnetization loops.     

超薄Ni81Fe19薄膜的各向异性磁电阻及磁性能

利用磁控溅射方法制备了一系列超薄Ta(5nm)/Ni81Fe19(20nm)/Ta(3nm)磁性薄膜。着重研究了基片温度、缓冲层厚度对Ni81Fe19薄膜各相异性磁电阻(AMR)及磁性能的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针技术测量了薄膜的电阻率和各向异性磁电阻;用FD-SMOKE-A表面磁光克尔效应试验系统测量了薄膜的磁滞回线。结果表明:在基片温度为400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻效应和较低的磁化饱和场,薄膜最大各向异性磁电阻为3.5%,最低磁化饱和场为739.67A/m。基片温度为500℃制备的薄膜,饱和磁化强度Ms值最大。随着缓冲层厚度x的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

Magnetic properties of Er-Ta granular thin films

The magnetic and structural properties of granular Er-Ta films have been studied with SQUID magnetometry and transmission electron microscopy (TEM). The films have been fabricated by co-sputtering using DC magnetron sputtering. The particle size of granular films was found to be affected by both the composition and annealing temperature. Electron diffraction patterns showed that the as-sputtered Er-Ta films have an amorphous structure. After annealing at different temperatures, the amorphous phase transforms first into an intermediate fcc structure and finally into an Er hcp phase and Ta phase, in which granular particles are clearly observed by TEM. The intermediate fcc structure shows only one magnetic transition whereas the hcp Er granular solids show a superparamagnetic and a modulated magnetic phase transitions. The modulated phase is not as obvious as in hcp Er films and this may be due to finite size effects.     

Carbon occupancy of interstitial sites in vanadium carbide films deposited by direct current reactive magnetron sputtering

Vanadium carbide thin films were deposited on Si substrates by direct current reactive magnetron sputtering from a V target in Ar/CH₄ plasma, varying the Ar/CH₄ partial pressure ratio and substrate temperature. The films were characterized by glancing angle X-ray diffraction and Rutherford backscattering spectrometry. Well defined crystalline structures were obtained for CH₄ content higher than 13%. The increase of substrate temperature during deposition diminishes the film thickness slightly while diminishing substantially the C/V atomic ratio. The intensity ratio of the Bragg peaks (111)/(200) decreases for increasing substrate temperature. This result is discussed in terms of a proposed mechanism for interstitial diffusion of carbon atoms in vanadium carbide thin films with fcc-like crystalline structure and the temperature dependence of carbon occupancy of tetrahedral or octahedral interstitial sites.     

Study of magnetic properties of thin cobalt films deposited by chemical vapour deposition

Chemical Vapour Deposition (CVD) of cobalt was deposited from a liquid source precursor of cobalt tricarbonyl nitrosyl (Co(CO)₃NO) on to oxidised < 100 > silicon wafers. The cobalt layers were deposited at 450∘C at 1.5 torr chamber pressure of hydrogen for 15 min processing time with various precursor flow rates. X-ray diffraction studies of the cobalt films reveal both hcp and fcc peaks. The vibrating sample magnetometer (VSM) yields coercivity (Hc) 167 Oe and 364 Oe for 46 nm and 30 nm thickness layers respectively at room temperature and squareness (S) M_r/M_s (remanence/saturation of magnetisation) value of ∼ 1. The study of magnetic properties of the cobalt suggests that magnetisation is dependent on grain size and therefore thickness. The grain size was observed by atomic force microscopy (AFM). Magnetic images were observed by magnetic force microscopy (MFM) and analyzed in terms of domain structure. The surface domain structure was recorded with the tip lift height 100 nm so that the magnetic interactions arising produced the topography effect. Where there is repulsive interaction the intensity is recorded as a bright region and where the interaction is attractive the intensity is recorded as a dark region.     

Ar工作压强对磁控溅射Ni-Mn-Ga铁磁形状记忆薄膜成分的影响

采用直流磁控溅射技术在单晶硅衬底上沉积Ni-Mn-Ga铁磁性形状记忆薄膜.试验结果表明,Ar工作压强对Ni-Mn-Ga薄膜化学成分有显著影响.Ni含量随Ar工作压强的升高呈先增加后减少的趋势,Mn含量呈先减少后增加的趋势,Ga含量几乎呈线性减少的趋势.随Ar工作压强的升高,薄膜的e/a值逐渐增大,薄膜的相变温度逐渐升高,室温下可以获得具有四方结构马氏体相的Ni-Mn-Ga薄膜.     

Effects of oxygen pressure on the structure and photoluminescence of ZnO thin films

A series of ZnO thin films were deposited on silicon (100) substrate at 473 K by using facing target RF magnetron sputtering system at different oxygen pressure in this paper. The structure, surface morphology and photoluminescence of the ZnO thin films were characterized by X-ray diffraction, atomic force microscopy (AFM), and photoluminescence spectra (PL), respectively. The results showed that only a (002) peak of hexagonal wurtzite appeared in all ZnO thin films, indicating that ZnO films exhibited strong texture. With increasing the oxygen pressure, the results indicated that the ZnO film deposited at 1.2 Pa Ar pressure and 0.6 Pa oxygen pressure had the best preferential C-axis orientation and the weakest compressive stress. Meanwhile, AFM observation showed that ZnO film deposited at pure Ar had the highest surface roughness. With the increment of oxygen pressure, the surface roughness decreased gradually. In addition, PL measurement showed that the ZnO film deposited at 1.2 Pa Ar pressure and 0.6 Pa oxygen pressure had the strongest ultraviolet emission and the weakest blue emission.     

溅射工艺对BST薄膜取向行为的影响

采用射频磁控溅射法在Si(100)衬底上沉积了Ba0.65Sr0.35TiO3薄膜.借助XRD、AFM和SEM研究了衬底温度、退火温度、溅射气压等不同的溅射参数对Ba0.65Sr0.35TiO3薄膜的晶化行为和显微结构的影响.在室温下沉积并未经退火处理的Ba0.65Sr0.35TiO3 薄膜是无定形态,在较高温度下沉积的薄膜晶化相对较好;随着在氧气气氛中退火温度的升高,X射线衍射峰的半峰宽变窄,衍射峰强度增强;在0.37～1.2Pa气压下沉积的Ba0.65Sr0.35TiO3薄膜有(110)和(200)主衍射峰,且其强度随溅射气压的增加而增强;当溅射气压继续升到3.9Pa,(110)和(200)衍射峰明显增强,说明Ba0.65Sr0.35TiO3 薄膜具有(110) (200)择优取向.AFM和SEM结果显示薄膜晶粒细小均匀、结构致密、表面平整,且无裂纹、无孔洞.分析结果显示优化工艺参数制备的Ba0.65Sr0.35TiO3 薄膜是用以制备非致冷红外探测器的优质材料.     

磁控溅射TiAlVN薄膜中V含量对其结构和抗腐蚀性能的影响

向TiAlN薄膜中添加V可改善薄膜性能.采用磁控溅射技术沉积了不同V含量的TiAlVN薄膜,通过能谱仪、台阶仪、X射线衍射仪(XRD)和原子力显微镜(AFM)分析薄膜的成分、厚度、相结构和表面形貌,用动电位极化的方法研究薄膜的抗腐蚀性能.结果表明:TiAlVN薄膜属于面心立方(fcc)和六方密排(hcp)二重结构,晶格...     

Influence of deposition parameters on preferred orientation of RF magnetron sputtered BST thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films have been deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and field emission scanning electron microscopy, respectively. The crystallization behavior of these films was apparently affected by the substrate temperature, annealing temperature and sputtering pressure. The as-deposited thin films at room temperature were amorphous. However, the improved crystallization is observed for BST thin films deposited at higher temperature. As the annealing temperature increased, the dominant X-ray diffraction peaks became sharper and more intense. The dominant diffraction peaks increased with the sputtering pressures increasing as the films deposited at 0.37–1.2 Pa. With increasing the sputtering pressure up to 3.9 Pa, BST thin films had the (110) + (200) preferred orientation. Possible correlations of the crystallization with changes in the sputtering pressure were discussed. The SEM morphologies indicated the film was small grains, smooth, and the interface between the film and the substrate was sharp and clear.     

Influence of ion-beam sputtering deposition parameters on highly photosensitive and transparent CdZnO thin films

CdZnO thin films with a nominal thickness of ~200 nm were grown on c-plane sapphire substrates by dual ion-beam sputtering deposition technique. The effect of substrate temperature (300–600 °C) and gas ambience on structural, morphological, compositional and opto-electronic properties was studied. X-ray diffraction patterns confirmed that all the films were polycrystalline in nature and were preferentially oriented along the c-axis. It was revealed that the films grown at Ar/O₂ ratio of 4:1 were structurally more ordered and the film quality was found to be the best at 500 °C. The compositional studies specify that approximately 11.8 at.% of cadmium were present in the film deposited at 300 °C in Ar–O₂ mixture. Investigations on optical properties by photoluminescence and absorption studies indicate band gap shrinkage with the increase in argon partial pressure and substrate temperature. It was found that photosensitivity of the deposited films was highly dependent on growth conditions. The photosensitivity was found to be 5000-fold higher for CdZnO film grown at 600 °C in Ar–O₂ ambience compared to the best reported result, and this was promising to realize high-performance opto-electronic devices on such CdZnO films.     

Study of annealing effects in In-Sb bilayer thin films

The thin films of In-Sb having different thicknesses of antimony keeping constant thickness of indium was deposited by thermal evaporation method on ITO coated conducting glass substrates at room temperature and a pressure of 10⁻⁵ torr. The samples were annealed for 1 h at 433 K at a pressure of 10⁻⁵ torr. The optical transmission spectra of as deposited and annealed films have been carried out at room temperature. The variation in optical band gap with thickness was also observed. Rutherford back scattering and X-ray diffraction analysis confirms mixing of bilayer system. The transverse I-V characteristic shows mixing effect after annealing at 433 K for 1 h. This study confirms mixing of bilayer structure of semiconductor thin films.     

Electroless deposition of CoPtWP magnetic thin films

CoPtWP magnetic thin films were prepared by electroless deposition. The influence of bath pH, deposition temperature and bath composition on the deposition speed, alloy content, microstructure, and magnetic properties of CoPtWP thin films were investigated. It was found that deposition speed increased gradually with the bath pH and deposition temperature. The cobalt content in the CoPtWP thin films varied from 77 at.% to 85 at.% by controlling the bath pH. The microstructure of CoPtWP thin films was dependent on bath pH and deposition temperature: two mixed structures, face centered cubic (fcc) and hexagonal close packed (hcp), were observed at low pH values and low deposition temperature. With the increase of pH values and deposition temperature, the intensity of fcc (111) peak suppressed gradually. The surface morphology was markedly influenced by bath pH, deposition temperature and bath composition. VSM and MFM measurements revealed that perpendicular coercivity had been increased with the bath pH. Unique hard magnetic properties of CoPtWP thin films with large perpendicular magnetic anisotropy were obtained at 90 °C and bath pH 13.0.     

Origin on amorphization of Co-Mo magnetic thin films: Experiments and thermodynamic calculation

Amorphisation of Co-Mo magnetic thin films has been studied by using X-ray diffraction technique, and thermodynamic calculation based on Miedema's semi-empirical model has been used to clarify the nature of amorphisation in this binary alloy system. The transition composition from the hexagonal cubic packed structure to the amorphous (H/A) is about 19 at.%Mo when the Co-Mo thin films are deposited at room temperature (RT) under a working Ar pressure of 0.2 Pa and a deposition rate of about 0.7 Å/s, but increases up to about 23 at.%Mo when deposited at 300 °C. The calculated transition composition at RT based on the Miedema's model or the thermodynamically assessed parameters is 18.7 at.%Mo or 16.1 at.%Mo, respectively, well consistent with the experimental value of ~ 19.0 at.%Mo. Higher deposition rate and lower pressure shift the H/A transition composition to a higher Mo content.