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.     

Boron ions B interaction with Si(100) and Ge(100) surfaces

The goal of this work is simulation of possible structures, formed by boron ions (B⁺) during adsorption on Si(100) and Ge(100) surfaces. Calculations were carried out using a semi-empirical method, known as the Modified Neglect of Differential Overlap method (MNDO). The surface was simulated using of Si₄₉(Ge₄₉) and Si₆₃(Ge₆₃) clusters. Results of quantum-chemical calculations the boron ion (B⁺) interaction with Si(100) − 2 × 1 and Ge(100) − 2 × 1 surfaces are presented and show adsorption barriers for boron ions and migration barriers of adsorbed boron ion (during migration along surface dimer row and along surface dimer).     

Ag films formed simultaneously on (111) and (100) NaCl

The ranges of epitaxial deposition have been explored for Ag evaporated simultaneously under high vacuum onto three NaCl substrate surfaces designated (111), (100)_E and (100)_c. The first substrate consisted of a thin (111)-oriented monocrystalline NaCl film deposited onto air-cleaved mica. The substrate designated (100)_E consisted of a thin (100)-oriented monocrystalline NaCl film evaporated onto air-cleaved NaCl, and that designated (100)_c consisted of air- cleaved NaCl. The occurrence of monocrystalline and polycrystalline films and their microstructure were determined by transmission electron microscopy and diffraction as a function of deposition rare R and substrate temperature T. The results are presented on 1n R versus$\text{1}\text{T}$ plots. Activation energies for the transition from a low temperature polycrystalline region to a higher temperature monocrystalline region were determined as approximately 0.8 and 1.0 eV respectively for (111) and (100)_E NaCl substrates. No such transition was found in the case of (100)_c substrates. In the case of (100)_E substrates a steep high temperature demarcation line (activation energy 3.9 eV) was found to separate the monocrystalline region from a high temperature polycrystalline region. The latter region was identified with the coalescence stage of film growth. These results agree with earlier reports suggesting that the coalescence stage rather than the nucleation stage is pre-eminent in determining the occurrence of epitaxy.     

Cu films formed simultaneously on (111) and (100) NaCl

Copper films were deposited simultaneously in high vacuum on three different monocrystalline NaCl substrates: evaporated (111) NaCl on mica, evaporated (100) NaCl and air-cleaved (100) NaCl. The occurence and microstructure of monocrystalline or polycrystalline copper films were determined by transmission electron microscopy and diffraction as a function of deposition rate R and substrate temperature T. When log R was plotted against 1/T, straight lines could be drawn separating the monocrystalline and the polycrystalline regions. Activation energies for the polycrystalline to monocrystalline transition of Cu films were calculated to be 1.48, 1.22 and 1.27 eV for the (111), evaporated (100) and air-cleaved (100) NaCl substrates respectively. It is shown that these results can be related to the atomistic theory of nucleation by Walton. Moreover, the results indicate that both the binding energy U between a single adatom and a growing oriented cluster and the atomic adsorption energy Q_ad on the substrate surface are proportional to the planar atom densities in the growing cluster and in the substrate surface respectively. It is further shown that while the activation energies for Cu films formed on the two (100) substrate surfaces are about the same, the actual epitaxial temperatures for the same R are significantly different.     

Ultra-thin zinc oxide film on Mo(100)

Zinc oxide films on a single crystal Mo(100) substrate were fabricated by annealing the pre-deposited metal Zn films in 10^− 5-10^− 4 Pa O₂ ambience at 300-525 K, and were characterized by in situ Auger electron spectroscopy, electron energy loss spectroscopy, low energy electron diffraction and high-resolution electron energy loss spectroscopy. The results show that the atomic ratio of oxygen to zinc in zinc oxide film is significantly dependent on sample annealing temperature and O₂ pressure. A stoichiometric zinc oxide film has been obtained under ∼10^− 4 Pa O₂ at about 400 K. A redshift of Fuchs-Kliewer phonon energy correlated with surface oxygen deficiency is observed.     

Study of fluorine contamination on MgO(100) surfaces

The fluorine contamination on MgO(100) surfaces is studied using Electron Stimulated Desorption (ESD) and Auger Electron Spectroscopy (AES). While Ar⁺ ion sputtering is very effective to clean the carbon contamination on the surface, the fluorine content does not significantly decrease. Thermal treatments of the sample considerably increase the F surface concentration due to its diffusion from the bulk to the surface. Heating the sample at 700 K simultaneously with H₂O exposure produces a decrease in the fluorine signal. The ion kinetic energy distribution of the F⁺ ion shows two peaks at 2.4 and 5 eV. The threshold energy of the F⁺ ion desorption is at 60 eV.     

Solid-state dewetting of Pt on (100) SrTiO3

Continuous thin films of Pt on (100) SrTiO₃ substrates were dewetted to form Pt particles at 1,150 °C, using an oxygen partial pressure of 10^?20 atm. After retraction of thick (50 or 100 nm) Pt films, SrTiO₃ anisotropic rods, slightly depleted in Ti, were found on the surface of the substrate. Rods did not form after dewetting of thinner (10 nm) Pt films. After dewetting, a ~10 nm thick interfacial phase was found between the Pt and the SrTiO₃. The interfacial phase, based on Sr and containing ~25 at% oxygen, is believed to be a transient state, formed due to Ti depletion from the substrate, resulting in a Pt(Ti) solution in the particles. The interfacial phase forms due to the low oxygen partial pressure used to equilibrate the system, and is expected to influence the electrical properties of devices based on Pt–SrTiO₃.     

High-temperature superconducting dual-mode resonator on (100) MgO substrate

We report, for the first time to our knowledge, a clear resonant peak split in the range of 7.7–9.7 GHz in a perturbed dual-mode disk-type resonator (DMDR) made of YBa₂Cu₃O_7–x (YBCO) superconducting thin film on MgO substrate. Epitaxial YBCO superconducting thin films were grown on (100) MgO substrates by pulsed laser deposition technique. The critical temperature of superconducting thin film on MgO substrate was 85 K. Superconducting dualmode disk resonators were designed by microwave design software, EEsof, and patterned by photolithography and a wet-etch process. The unloaded quality factor (Q_UL) of the superconducting DMDR was found to be 1,312 at 77 K. We believe this type of DMDR can be utilized for dual-mode resonator-based filters for satellite communications.     

Aligned tungsten oxide nanowires on tungsten (100) substrates

WO₃ nanowires in body center cubic structure were grown on W (100) substrates by heating in an argon atmosphere. Scanning electron microscope and transmission electron microscope characterizations show the WO₃ NWs grew along the [100] crystallographic orientation and were aligned in three directions. The diameter of WO₃ NWs is in the range of several to 20 nm and the length is up to 1 µm. Field emission measurements show that the field emission current density can reach 1.8 mA/cm² under electrical field 10 V/µm and the turn-on field can be as low as 2.6 V/µm.     

n-GaAs(100)表面及Na/n-GaAs(100)界面的光电子谱研究

采用X射线光电子谱(XPS)及紫外光电子谱(UPS),对经5keV Ar~+离子轰击后的n-GaAs(100)表面及其Na/GaAs(100)界面作了详细的研究。并且和Na/n-GaAs(100)-(4×1)界面进行比较,以揭示Ar~+离子轰击对金属/n-GaAs(100)界面的影响。结果表明,经5keV氩离子轰击后的n-GaAs(100)表面,其功函数较n-GaAs(100)-(4×1)表面大0.3eV。而且,Na在低覆盖度时(θ≤0.02ML)。轰击后的GaAs(100)表面,Na/n-GaAs(100)界面费米能级移动量为0.7eV,而Na/n-GaAs(100)-(4×1)界面,其费米能级移动量仅为0.3eV。     

First-principles study of near surface point defects stability in Si (100) and SiGe(100)

Calculations based on Density Functional Theory are carried out to study interstitial generation close to the Si(100) surface with further consideration of effects related to the presence of substitutional Ge atoms on the surface. Defect structures, vacancy and Si interstitial, and associated energies are calculated. We observe that germanium atoms tend to increase the stability of created defects, promote the generation of interstitials through drastic structural changes and blocks the climb of Si interstitials towards the surface.     

Nonlocal Effects on the Surface Resistance of High-Temperature Superconductors with (100) and (110) Surfaces

The low-temperature surface resistance R _s of d-wave superconductors is calculated as function of frequency assuming normal state quasiparticle mean free paths l in excess of the penetration depth. Results depend strongly on the geometric configuration. In the clean limit, two contributions to R _s with different temperature dependencies are identified: photon absorption by quasiparticles and pair breaking. The size of nonlocal corrections, which can be positive or negative depending on frequency decreases for given l as the scattering phase shift _N is increased. However, except in the unitarity limit _N =0.5, nonlocal effects should be observable.     

Peculiarities of the MBE growth of nanowhiskers on GaAs(100) substrates

We have studied the formation of nanowhiskers (NWs) by molecular beam epitaxy (MBE) on GaAs(100) substrates. The MBE growth of NWs exhibits two stages (initial and developed) and leads to the formation of NWs with surface morphology of two types (nucleation and intergrowth). The stage of developed growth is characterized by the predominant formation of intergrown NWs oriented in the 〈111〉B direction, having (110) habit (including the NW tip surface) and hexagonal cross sections with a transverse size within 50–300 nm. It was found that the transverse size of a hexagonal NW may significantly differ from that of an Au-GaAs melt droplet. The ratio of longitudinal and transverse dimensions of intergrown NWs can be on the order of 150 and above. When the transverse size of NWs exceeds a certain value (about 200 nm), the crystal length exhibits a slight decrease. The existence of two types of morphology is indicative of inhomogeneous character of the NW growth on a GaAs(100) surface, which depends on the catalyst droplet size, effective thickness of the deposited GaAs layer, and the growth temperature.     

Temperature dependence of the growth of gallium oxide on CoGa(100)

The oxidation of a CoGa(100) surface at high temperatures has been studied by scanning tunnelling microscopy (STM) and auger electron spectroscopy (AES). When CoGa(100) is oxidised at a sufficiently high temperature (>600 K), an ordered Ga₂O₃ film is formed. The stability of the film depends on the sample temperature and partial oxygen pressure of the ambient gas. At negligible oxygen pressure (<10⁻¹¹ mbar) the oxide is stable up to 850 K. At an oxygen pressure of 10⁻⁶ mbar the oxide is stable up to 930 K and some of the oxide remains present up to 970 K. The oxide film is found to be very uniform. The thickness of the film is constant and independent of the oxidation temperature (600 K<T<930 K), oxygen pressure (<10⁻⁶ mbar), and exposure (10⁻⁴–10⁻² mbar.s≈10²–10⁴ L). We find a clear improvement of the order of the oxide film surface with increasing oxidation temperature. In STM images, a domain structure of the oxide film is observed. The size of the domains increases by a factor of 5–10 when the oxidation temperature is increased from 700 to 900 K.     

Si基Si_(1-x-y)Ge_xC_y合金生长中C的影响

报道了Si基Si1 x yGexCy 合金生长中C对Ge组分和生长速率的抑制作用 ,提出一个Si、Ge、C原子的排列构型 ,从理论上给出了C对Ge组分的抑制度和Ge/C原子比的关系 ,并指出在富Ge情况下C对Ge的抑制作用会趋向于饱和。     

重构表面上Si薄膜生长的模拟研究

建立了Si(100)-(2×1)表面上Si薄膜生长的Kinetic Monte Carlo(KMC)模型,并对薄膜生长的初始阶段进行了研究.结果表明:在一定的入射率下存在一最佳成岛温度,该温度随入射率的增大而升高,并满足函数关系T=T0 bln(F c).     

Semipolar GaN Layers Grown on Nanostructured Si(100) Substrate

We propose a new method for growing semipolar GaN films on a Si(100) substrate with an array of sub-100-nm-sized V-grooves formed on the surface. It is shown that, using such a nanostructured substrate for metalorganic hydride vapor-phase epitaxy, it is possible to obtain GaN (101?1?) epilayers deviating by an angle of about 62° from the polar direction and having an X-ray rocking curve with a minimum FWHM value of ω_θ ~ 60 arcmin.