Growth of C60 single crystal films on metal substrates

High-quality C₆₀(111) single crystal films have been grown on Ni₃Fe(111), Ni₃Co(111) and Ni₃Fe(110) surfaces using hot-wall diffusion method. X-ray diffraction results show that well-ordered films can be obtained near 150°C on these substrates. The high quality of the films could be attributed to the perfect lattice match between C₆₀ film and substrates, low growth rate of C₆₀, and the suitable substrate temperature.     

Growth and structure of epitaxial CeO2 films on yttria-stabilized ZrO2

Thirty to a hundred-nm thick epitaxial CeO₂ layers are grown on YSZ (100), (110) and (111) surfaces of yttria-stabilized ZrO₂ (YSZ) by electron beam evaporation of Ce in oxygen at reduced pressure. Their growth, structure and thermal stability are studied with several bulk and surface sensitive techniques including Rutherford backscattering spectrometry, cross-sectional high resolution electron microscopy, low energy electron diffraction and low energy reflection electron microscopy. Excellent epitaxy is obtained on all YSZ surfaces at a growth temperature of 750 K. The surfaces of films grown on (111)-oriented substrates are flat, whereas those on the other substrates are faceted into small (111) planes. The grain sizes in the films are in the 10 nm range and smaller.     

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.     

The Rectification Studies on the P -Ion Implanted C60/Si Films

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^-2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

Heteroepitaxy of CuInSe2 on {111}-oriented germanium

Thin films of CuInSe₂ were deposited onto {111}-oriented germanium substrates by flash evaporation and were investigated by reflection high energy electron diffraction. Epitaxial growth was found in the substrate temperature range 720–820 K. In all cases the epitaxial layers had the chalcopyrite structure except at growth temperatures higher than 795 K where the layers were cubic. Deposition of CuInSe₂ onto {111}-oriented germanium is characterized by one-dimensional epitaxy, and the epitaxial relationship for the chalcopyrite phase is given by {111}_Ge{112}_CuInSe2     

Study of microstructure of epitaxial fullerenes films

A comprehensive study was made on the structure of epitaxial thin films of C₆₀ and C₇₀ by means of transmission electron microscopy. Both the films show similar face-centered cubic structure and are epitaxial on (001) mica with close-packed plane parallel to the substrate surface. Two main kinds of defects-stacking faults and twins-were observed and are discussed. The effect of the remaining C₇₀ impurity on the crystal orientation of C₆₀ films was studied by comparing different samples made from high-purity fullerene and C₆₀/C₇₀ mixtures. The results show that there is a higher density of planar defects in the films containing larger amounts of impurities: moreover, some faint anomalous reflections located at so-called 2a₀ fcc reciprocal lattice points were also detected, probably as a result of C₇₀ contamination. Finally, it is found that stacking disorders can be easily increased by keeping the high-quality pure C₆₀ film in air at room temperature for a few weeks, implying the instability of the crystal orientation of the epitaxial fullerene films.     

Effects of p(O2) and p(CO2) on epitaxial growth of BaTiO3 thin films on MgO(100) substrates by using metal organic acid salts

BaTiO₃ thin films were prepared by using metal organic acid salts on MgO(100) substrates, which have large lattice-misfit with BaTiO₃. Amorphous films prefired at 470°C were crystallized to BaTiO₃ phase by heat treatment at higher temperature. Crystallinity and in-plane alignment of the prepared films were found to depend on the heat-treatment conditions. BaTiO₃ films with high crystallinity but poor (100)-orientation were obtained in air at higher than 1200°C. Whereas, (100)-oriented epitaxial BaTiO₃ film was fabricated by annealing at 900°C under low oxygen partial pressure (p(O₂)). Low carbon dioxide partial pressure (p(CO₂)) is also found to be essential for preparation of epitaxial BaTiO₃ films on MgO substrates by using metal organic acid salts.     

Comparative study of the elastic properties of polycrystalline aluminum nitride films on silicon by Brillouin light scattering

Brillouin light scattering (BLS) has been used to investigate the elastic properties of polycrystalline AIN films, about 1 μm thick, grown by DC-reactive magnetron sputtering on Si₃N₄ coated (100)-Si substrates. Taking advantage from the detection of a number of different acoustic modes, a complete elastic characterization of the films has been achieved. The elastic constants c₁₁ and c₆₆ have been selectively determined from detection of the longitudinal and of the shear horizontal bulk modes, respectively, travelling parallel to the film surface. The three remaining elastic constants, namely c₄₄, c₃₃ and c₁₃, have been obtained from detection of the Rayleigh surface wave and of the longitudinal bulk wave propagating at different angles from the surface normal. The values of the elastic constants of these sputtered AIN films depend on the deposition conditions and on the microstructural properties of the films, especially oxygen contamination and quality of texture. In the case of the films with the best degree of texture and the lowest oxygen content, the values of the elastic constants are rather close to those previously determined in epitaxial A1N films grown at high temperature by MOCVD. This demonstrates that sputter deposition at relatively low temperature can be used to grow high quality A1N films on Si and is of great importance in view of the integration of these films in the technology of IC semiconductors.     

Preparation and characterization of C60S16 and C70S48 thin films

In this study, we have investigated different methods for preparation of thin films of C₆₀ and C₇₀-sulfur compounds. Films of good quality were obtained by reaction of amorphous C₆₀ and C₇₀ films with a saturated sulfur solution in toluene at 40°C or with saturated sulfur vapour at a temperature of 140°C for several hours. The quality of the fullerene-sulfur films were strongly dependent on the microstructure of the initially deposited fullerene film and the synthesis temperature. X-ray diffraction analyses showed that both methods lead to the formation of films consisting of C₆₀S₁₆ and C₇₀S₄₈ (space groups C 2/c and Amm2, respectively). C₆₀S₁₆ films synthesised on Al₂O₃(012) and Si(100) substrates were texture-free while C₇₀S₄₈ films typically exhibited a preferential (100) orientation. The films were also characterised by Raman and IR- spectroscopy, which confirmed that the interactions between the fullerene molecules and the S₈ rings are weak. The fullerene-sulfur compounds were found to be unstable at high vacuum conditions. Both materials C₆₀S₁₆ and C₇₀S₄₈ are non-conductive at room temperature with conductivities less then 10⁻⁵ (Ω/cm).     

Atomic layer deposition of calcium oxide and calcium hafnium oxide films using calcium cyclopentadienyl precursor

Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al₂O₃ capping layer occurred hygroscopic and converted to Ca(OH)₂ after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al₂O₃ capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO₂ growth cycles at 230 and 300 °C. HfCl₄ was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca₂Hf₇O₁₆ or Ca₆Hf₁₉O₄₄. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca₂Hf₇O₁₆. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2.     

Crystal texture selection in epitaxies of orthorhombic antiferromagnetic YMnO3 films

The orthorhombic phase of YMnO₃ has been epitaxially stabilized on SrTiO₃ single crystal substrates. Changing the substrate orientation, the out-of-plane orientation of the epitaxial films can be tuned to (001), (101), or (100). Depending on the orientation, the films present varied crystal domain structures and lattice strains. Single domain YMnO₃(100) films have been grown on SrTiO₃(110) substrates, whereas they present two and three crystal variants on SrTiO₃(001) and SrTiO₃(111), respectively. Epitaxial stress in each domain is anisotropic, tensile in one direction and compressive in the other. It has consequences in the texture selection when domains with different out-of-plane orientation can grow epitaxially. Antiferromagnetism of YMnO₃ films has been confirmed by measuring the exchange bias field induced in an underlying ferromagnetic SrRuO₃ layer.     

Epitaxial growth of AlN on single crystal Mo substrates

We have grown AlN films on single-crystalline Mo(110), (100), and (111) substrates using a low temperature pulsed laser deposition (PLD) growth technique and investigated their structural properties. Although c-axis oriented AlN films grow on Mo(100), the films contain 30° rotated domains due to the difference in the rotational symmetry between AlN(0001) and Mo(100). AlN films with only poor crystalline quality grow on Mo(111) substrates, probably due to the poor surface morphology and high reactivity of the substrates. On the other hand, single crystal AlN films grow epitaxially on Mo(110) substrates with an in-plane relationship of AlN[11-20] // Mo[001]. Reflection high-energy electron diffraction or electron backscattered diffraction analysis has revealed that neither in-plane 30° rotated domains nor cubic phase domains exist in the AlN films. X-ray reflectivity measurements have revealed that the heterointerface between AlN and Mo prepared by PLD at 450 °C is quite abrupt. These results indicate that PLD epitaxial growth of AlN on single crystal Mo substrates is quite promising for the fabrication of future high frequency filter devices.     

Single-crystal heteroepitaxial growth of PbxSn1−xTe films on germanium substrates by r.f. sputtering

Single-crystal heteroepitaxial growth of Pb_xSn_1?xTe films was achieved by r.f. sputtering deposition onto single crystals of germanium (both 〈100〉 and 〈111〉 orientations), although there is a large mismatch (～12%) in the lattice parameters between the grown film and the substrate.The structures of the r.f. sputtered films were investigated by high energy electron diffraction microscopy, electron surface replicas and scanning electron microscopy.Differences in the substrate temperature needed for the epitaxial growth on 〈100〉 or 〈111〉 orientations are attributed to the tendency of Pb_xSn_1?xTe films to grow parallel to the (100) plane, which is the cleavage plane of the NaCl structure. This causes a mixed (100)-oriented phase in addition to the (111) orientation expected from the symmetry of the substrate surface in the case of (111) germanium substrates.Examples of the effects on the heterogeneous nucleation of the substrate temperature and deposition rate are shown for both orientations.The first stages of growth (initial reactions with the substrates) and the thickness and concentration profiles were investigated by ion beam backscattering analysis.Channelling techniques confirmed the high degree of order in the single- crystal structure of films deposited on large areas (～1 cm²).     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Adsorption-Controlled Growth of BiFeO3 by MBE and Integration with Wide Band Gap Semiconductors

BiFeO3 thin films have been deposited on (001) SrTiO3, (101) DyScO3, (011) DyScO3, (0001) AlGaN/GaN, and (0001) 6H-SiC single crystal substrates by reactive molecular beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth over-pressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO₃ to control stoichiometry in accordance with thermodynamic calculations. Four-circle x-ray diffraction and transmission electron microscopy reveal phase-pure, epitaxial films with rocking curve full width at half maximum values as narrow as 7.2 arc seconds (0.002°). Epitaxial growth of (0001)-oriented BiFeO3 thin films on (0001) GaN, including AlGaN HEMT structures, and (0001) SiC has been realized using intervening epitaxial (111) SrTiO₃ / (100) TiO₂ buffer layers. The epitaxial BiFeO3 thin films have 2 in-plane orientations: [1120] BiFeO>sub>3 || [1120] GaN (SiC) plus a twin variant related by a 180° in-plane rotation. This epitaxial integration of the ferroelectric with the highest known polarization, BiFeO3, with high bandgap semiconductors is an important step toward novel field-effect devices.     

残余应力对SrRuO3薄膜磁学及电输运性能的影响

采用射频磁控溅射法在单晶SrTiO₃ (STO)衬底和硅(Si)衬底上制备出不同取向的SrRuO₃ (SRO)薄膜, 对薄膜的残余应力进行了分析, 并研究了应力对不同取向SRO薄膜磁学性能与电输运特性的影响。根据X射线衍射(XRD)结果分析可知, Si基SRO薄膜为多晶单轴取向薄膜, 且应力来源主要为热失配拉应力; STO基SRO薄膜为外延薄膜, 其应力主要为热失配压应力和外延压应力; 磁学性能测试表明, (001)取向SRO薄膜比(110)取向薄膜拥有更高的居里温度T_C; 压应力提高了(001)取向SRO薄膜的T_C, 却降低了(110)取向薄膜的T_C。电阻性能测试表明, 对于在同种类型衬底上沉积的SRO薄膜, (001)取向的薄膜的剩余表面电阻比(RRR)高于(110)取向的薄膜。另外, 拉应力引起了薄膜微结构的无序度增加, 弱化了表面电阻率的温度依赖性, 提高了金属绝缘体转变温度(T_MI)。     

Change of light holes valence band in lead-tin telluride films by isovalent substitution of chalcogen atoms

Rotational weak-field magnetoresistance measurements at 78 K were used to determine the parameters of the valence band of light holes for Pb_0.8Sn_0.2Te and Pb_0.8Sn_0.2Te_0.98S_0.02 epitaxial films grown on (111)-oriented BaF₂. It was shown that an isovalent substitution of 2% of tellurium atoms by sulphur atoms in solid solution films of lead telluride-tin telluride leads to the decrease of the energy splitting value of valence band valleys Δσ_v from 18 meV to 2 meV. The physical reasons for this phenomenon were analysed. Obtained experimental data were compared with the results of other experiments on photoluminescence and concentration dependencies of thermoEMP coefficient.     

Structural and dielectric properties of (001) and (111)-oriented BaZr0.2Ti0.8O3 epitaxial thin films

We have grown and characterized BaZr_0.2Ti_0.8O₃ (BZT) epitaxial thin films deposited on (001) and (111)-oriented SrRuO₃-buffered SrTiO₃ substrates by pulsed laser deposition. Structural and morphological characterizations were performed using X-ray diffractometry and atomic force microscopy, respectively. A cube-on-cube epitaxial relationship was ascertained from the θ-2θ and φ diffractograms in both (001) and (111)-oriented films. The (001)-oriented films showed a smooth granular morphology, whereas the faceted pyramid-like crystallites of the (111)-oriented films led to a rough surface. The dielectric response of BZT at room temperature was measured along the growth direction. The films were found to be ferroelectric, although a well-saturated hysteresis loop was obtained only for the (001)-oriented films. High leakage currents were observed for the (111) orientation, likely associated to charge transport along the boundaries of its crystallites. The remanent polarization, coercive field, dielectric constant, and relative change of dielectric permittivity (tunability) of (111)-oriented BZT were higher than those of (001)-oriented BZT.     

Hot-wire growth of multi-phase carbon nitride films

This paper describes the growth of multi-phase carbon nitride films using hot-wire chemical vapor deposition (HWCVD) on (100)-oriented crystalline Si substrates. A mixture of either CH₄/NH₃ or CH₄/N₂ was activated over a hot tungsten filament under varying deposition conditions. The samples were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). AFM micrographs show the presence of facetted crystallites. The XRD peaks observed were compared with theoretical predictions for -C₃N₄ and β-C₃N₄—the two ultra-hard phases of carbon nitride. The results suggest the presence of -C₃N₄ and β-C₃N₄, as well as other unidentified phases in our films. We also calculated the equilibrium concentration of the various gas species as a function of temperature and pressure. Our results indicate that CN and C₂N₂ radicals are possible precursors to carbon nitride growth.     

Preparation of (001)-oriented Pb(Zr,Ti)O/sub 3/ thin films and their piezoelectric applications

Preparation of (001)-oriented Pb(Zr,Ti)O₃ (PZT) thin films and their applications to a sensor and actuators were investigated. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001)-oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d₃₁, of -100 pm/V, and an extremely low relative dielectric constant, epsiv_r, of 240. The PZT thin films on Si substrate had a very high d₃₁ of -150 pm/V and an epsiv_r = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.