Epitaxial growth mechanism of La2Zr2O7 thin film on metal substrate

We have studied the growth behavior of pyrochlore structure La₂Zr₂O₇ (LZO) thin films with different thickness on biaxial texture NiW substrates prepared by metal?Corganic deposition (MOD) method. The structure and morphology of LZO films were investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Our results show that the surface morphology of LZO films varies with changes in the surface coverage ratio of the metal substrates after crystallization in argon?Chydrogen atmosphere. The degree of texture of the LZO films reaches a maximum when the film thickness increases to 37 nm, where the NiW substrate surface is just fully covered. The complete coverage of the substrate surface together with the enhanced texture suggests that there exists a possible connection between the surface morphology and the texture development of the films prepared by MOD. Information on the nucleation and growth of oxide thin films on metal substrates with biaxial texture is important for understanding the mechanism of buffer layer formation and also for optimizing the preparation conditions for high-temperature superconducting coated conductors.     

Epitaxial growth and properties of (CO3) stabilised BaCuO2 superconducting thin films

We report on the epitaxial growth of BaCuO₂ infinite layer (stabilised with CO₃ groups) thin films by rf magnetron sputtering on (100) SrTiO₃ and (100) LaAlO₃. Excellent (001) films with c4Å are obtained at 540 °C in a sputtering atmosphere of 1–10 mTorr of Ar+O₂ with some addition of CO₂. Off axis x-ray analysis reveal perfect in plane ordering and a tetragonal structure with a=b3.96 Å. For these deposition conditions the resistivity at room temperature is of the order of several cm and exhibits a strong semiconductor-like behaviour. When the deposition temperature is increased to 660 °C, a supercell along the c axis appears with a period of about 8Å. After an in-situ annealing of these films in 7 Torr of oxygen at 500 °C, (300K) falls to 800cm. The resistance versus temperature curve reveals then a metallic behaviour and a superconducting transitions with onsets between 10–40K.     

外延SCNN电光薄膜生长及研究

用激光脉冲沉积(PLD)法在MgO(001)衬底上成功地生长、制备出了外延铌酸锶钡钠(SCNN)电光薄膜.对生长制备出的SCNN电光薄膜用X射线衍射对其微观结构进行了测量研究;X射线衍射结果显示生长在MgO(001)衬底上的SCNN电光薄膜是外延膜;对生长在MgO(001)衬底上的外延SCNN电光薄膜在200～900nm光谱范围的透射光谱进行了测量研究,通过对薄膜透射光谱的振荡曲线分析计算得到了SCNN电光薄膜的光学常数,结果发现外延SCNN电光薄膜的折射率符合单电子模型.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

Epitaxial growth of Fe nanodots on SrF2/Si (111)

Fe nanodots were grown on SrF₂ (111) surfaces deposited on Si (111) substrates in a molecular beam epitaxy (MBE) system. The crystallographic and surface morphological characters were studied by reflection high-energy electron diffractometry (RHEED) and atomic force microscopy (AFM). The triangular terraces and step edges of SrF₂ were formed at 600 °C, and its crystallinity was high in quality. Fe (111) layers with thicknesses between 0.5 and 5 nm were grown epitaxially on this SrF₂ layer at room temperature (RT) with the help of electron beam exposure. In 1-nm thick Fe layers deposited at RT, the number density was about 2 × 10¹² cm^− 2. At the end of this report, an epitaxial growth of the SrF₂/Fe/SrF₂ tri-layer on Si (111) is briefly described.     

Epitaxial growth of Cu(100) and Pt(100) thin films on perovskite substrates

Pulsed laser deposition has been used to grow epitaxially oriented thin films of Cu and Pt on (100)-oriented SrTiO₃ and LaAlO₃ substrates. X-ray diffraction results illustrated that purely epitaxial Cu(100) films could be obtained at temperatures as low as 100 °C on SrTiO₃ and 300 °C on LaAlO₃. In contrast, epitaxial (100)-oriented Pt films were attained on LaAlO₃(100) only when deposited at 600 °C. Atomic force microscopy images showed that films deposited at higher temperatures consisted of 3D islands and that flat, layered films were obtained at the lowest deposition temperatures. Importantly, Cu films deposited at 100 °C on SrTiO₃(100) were both purely (100)-oriented and morphologically flat. Pt and Cu films displaying both epitaxial growth and smooth surfaces could be obtained on LaAlO₃(100) only by using a three-step deposition process. High-resolution transmission electron microscopy demonstrated an atomically sharp Cu/SrTiO₃ interface. The crystalline and morphological features of Cu and Pt films are interpreted in terms of the thermodynamic and kinetic properties of these metals.     

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.     

Epitaxial growth of thin films of V2VI3 semiconductors

Epitaxial growth conditions of V₂VI₃ semiconductors have been studied using the molecular beam epitaxy technique, which was applied to the growth of Sb₂Te₃ on Bi₂Te₃ substrates. These substrates were prepared by gradient freeze method in a Bridgman apparatus. Ingots were cleaved along the (0001) plane. The deposition conditions have been studied as a function of two parameters: substrate temperature and flux ratios of the two elements. The quality of these epilayers was controlled by SEM and X-ray diffraction. Epilayers of good quality have been obtained for the first time.     

Strain evolution in heteroepitaxial ZnO/sapphire(0001) thin films grown by radio frequency magnetron sputtering

We present the strain evolution of ZnO/sapphire(0001) thin films studied by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The effect of input radio frequency (rf) sputtering power and growth temperature was examined. Initially the highly strained flat ZnO layers were grown. At samples deposited at higher temperatures than ∼ 500 °C, the strain was fully relaxed by nucleating the ZnO nano-grains as the film thickness increased. However, we found that the strain was partially relaxed at the samples grown at lower temperatures, which was attributed to the insufficient surface undulations. For the effect of rf input power, a consistent behavior of strain relaxation independent of the rf input power was observed. The ZnO nano-grains were enlarged and transformed to well-defined hexagonal nano-discs with film thickness.     

(111)-Oriented Pb(Zr0.52Ti0.48)O3 thin film on Pt(111)/Si substrate using CoFe2O4 nano-seed layer by pulsed laser deposition

Perovskite Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film with perfect (111)-orientation was achieved on CoFe₂O₄ seeded-Pt(111)/Ti/SiO₂/Si substrate by pulsed laser deposition technique using target with limited excess Pb. Pyrochlore phase formation was suppressed on Pt by CoFe₂O₄ nano-seed layer (~7 nm), and perovskite PZT was achieved at temperature as low as 550 °C. CoFe₂O₄ seed layer that has perfect (111)-orientation acts as a promoter for perfectly (111)-orientated growth of PZT. PZT film grown at 600 °C has higher degree of crystalline orientation, lower surface roughness, and compacted microstructure in comparison to the film grown at 550 °C. The PZT film has a nano-size grain-feature structure with grain size of about 40–60 nm. Perovskite formation was also confirmed by ferroelectric measurement. The ferroelectric properties of PZT film grown at 600 °C is higher than that grown at 550 °C which could be attributed to the enhancement of the crystalline orientation, crystallinity, and microstructure of the film.     

Deformation behavior during nanoindentation of epitaxial ZnO thin films on sapphire substrate

Nanoindentation studies were carried out on epitaxial ZnO thin films on (0001) sapphire substrates grown by radio frequency magnetron sputtering. A single discontinuity (‘pop-in’) in the load–displacement curve was observed at a specific depth (13−16 nm) irrespective of the film thickness. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the nucleation, propagation and interaction behavior of the glissile threading dislocations during mechanical deformation. Indentation well below the critical depth was found to be plastic deformation behavior (residual impression of 4 nm).     

Epitaxial growth of cadmium sulphide on (111) germanium substrates

Single-crystal expitaxial layers of CdS on (111) Ge substrates, 8 to 60 μm thick, have been grown from the vapour phase in a closed-tube system. Hydrogen was used as a transport agent. The experimental conditions (source and deposit temperatures, and initial pressure of hydrogen) have been defined where the growth of single-crystal expitaxial layers is feasible. Observations on the morphology of the layers are reported, which suggest that at least two different growth mechanisms should be active in the system. Finally, the composition of the gaseous phase was calculated by assuming a non-reactivity of the Ge substrate with the vapour phase.     

Epitaxial growth of anatase TiO2 thin films on LaAlO3(100) prepared using pulsed laser deposition

Titanium dioxide thin films were grown on a lattice-matched LaAlO₃(100) surfaces using pulsed laser deposition (PLD) in oxygen atmosphere. The films were characterized using X-ray diffraction (XRD), reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The crystal structure of all the films was anatase. Preferred oriented films with a c-axis normal to the substrate surface were obtained. RHEED analysis also revealed that the films had the preferential in-plane orientation, demonstrating that anatase films were epitaxially grown on the substrate. The flatness of the films depended on their growth conditions and thickness.     

蓝宝石衬底上制备SiO2薄膜的研究

采用射频磁控反应溅射法,以高纯Si为靶材,高纯O2为反应气体,成功地在蓝宝石基片上制备出了二氧化硅(SiO2)薄膜,并对薄膜的沉积速率、成分、结构及红外光学性能进行了研究.结果表明,制备的SiO2薄膜与蓝宝石衬底结合牢固;和其它镀膜技术相比,射频磁控反应溅射法可以在较低的温度下制备出SiO2薄膜;制备出的SiO2薄膜在3～5μm波段对蓝宝石衬底有明显的增透效果.     

Study of the growth of CuAlS2 thin films on oriented silicon (111)

Within the chalcopyrite family the sulphur based compounds CuMS₂ (M = In, Ga, Al) have attracted much interest in recent years because they show a direct wide band-gap covering from E_gap = 1.53 eV (CuInS₂) over E_gap = 2.43 eV (CuGaS₂) to E_gap = 3.49 eV (CuAlS₂). Therefore they are particularly suitable for optoelectronic as well as photovoltaic applications. The CuAlS₂ semiconductor is one of these compounds and has good luminescent properties and a wide direct gap of 3.5 eV making it suitable for the use as material for light-emitting devices in the blue region of the spectrum. To dig up fully its potential a better understanding of the fundamental properties of the CuAlS₂ film itself is essential, which could be achieved from high-quality single-crystalline materials. So, the aim of this work has been to study the growth of multilayer CuAlS₂ thin films on Si(111) substrates at a substrate temperature of 723 K. One, two and three layers with 60, 120 and 180 nm thicknesses, respectively, were deposited on Si(111) substrate. The effect of the CuAlS₂ layer numbers on the structure, morphology and optical properties of the samples was investigated. The X-ray diffraction studies revealed that all the samples are polycrystalline in nature, single CuAlS₂ phase and exhibiting chalcopyrite structure with a preferred orientation along the (112) direction. However, the sample with three CuAlS₂ layers exhibit the highly oriented (112) plane with grain sizes of 80 nm. So we show that this experimental process affects significantly the structural properties of the CuAlS₂ films. Raman spectroscopic measurements indicated five prominent peaks at 193, 205, 325, 335 and 370 cm^− 1. The possible origin of the 370 cm^− 1 peak was investigated and was found to be some local vibration in the structure. The peaks at 193-205 and 335 cm^− 1 were ascribed to A₁ and B₂ modes, respectively.     

Molecular beam epitaxy of InGaN thin films on Si(111): Effect of substrate nitridation

The effect of silicon nitridation on structural quality, indium incorporation, and electrical properties of the InGaN/Si heterojunctions is investigated. A series of In_xGa_1 − xN (x = 0-0.32) thin films are grown directly on Si(111) substrates, with and without a Si_xN_y surface layer, by plasma-assisted molecular beam epitaxy. The crystalline quality is higher and the indium incorporation is increased when the In_xGa_1 − xN thin films are grown with the intentional Si_xN_y buffer. These observations are explained by the reduced local elastic stress at the interface and N-polarity of the surface, both of which promote the incorporation of In. The obtained n-In_xGa_1 − xN/p-Si (x = 0.2-0.3) heterojunctions exhibit a nearly ohmic behavior, and the series resistance is higher for the Si_xN_y-containing junctions. Our results suggest that unlike the amorphous Si_xN_y region spontaneously formed during direct deposition of III-nitrides on Si, the Si_xN_y layer obtained by high-temperature annealing of Si(111) in nitrogen atmosphere is beneficial to the In_xGa_1 − xN deposition.