Epitaxial recrystallization of HDPE-quenched ultrathin films on oriented iPP substrates

The recrystallization behavior of high-density polyethylene (HDPE) on the highly oriented isotactic polypropylene (iPP) substrates at temperatures below the melting temperature of HDPE has been investigated by means of transmission electron microscopy. The results obtained by the bright-field observation and the electron diffraction show that upon annealing the HDPE-quenched films on the oriented iPP substrates at temperatures below 125°C, only a small amount of HDPE recrystallizes on the iPP substrate with [001]_HDPE//[001]_iPP, while annealing the HDPE-quenched films at temperatures above 125°C, all of the HDPE crystallites recrystallize epitaxially on the iPP substrate with [001]_HDPE//[101]_iPP. © 1997 John Wiley & Sons, Inc. J Polym Sci B: 35 : 1415–1421, 1997     

Low Pressure Chemical Vapor Deposition of III/V-Nitrides Using Organometallics and Hydrazoic Acid Precursors

In and Ga nitride films have been deposited on various substrates using organometallics and hydrazoic acid (HN₃) as nitrogen precursor. The film deposition was carried out under low pressure (10^?510 ^?6 Torr) and low V/III ratios (1-10). XPS analysis indicated that the ln(Ga):N atomic ratio of unity can be easily achieved by adjusting the experimental conditions. For the growth of InN on Si(100) substrate, 308-nm photon beam is needed to speed up the film deposition rate. He(II) UPS spectra of InN films are in good agreement with the result of a pseudo-potential calculation for InN valence band, while the spectra of GaN compare favorably with a recent semi-ab-initio calculation and with the UPS results of GaN single crystal films. The bandgap of our GaN films is ～ 3.3 cV as determined by photoluminescence and UV-VIS absorption spectra. Raman spectra taken from GaN Films showed peaks at 66 and 88 meV for TO and LO phonons, respectively, indicating a wurtzite structure of the GaN. In a corresponding X-ray diffraction spectrum, the (002) peak is about 400 times more intense than that of the (101) peak, suggesting that the GaN layers are highly oriented with the c-axis normal or nearly so to the Al₂O₃ substrate.     

Crystallization of textured PbTiO3 films deposited from gels

Sol-gel processed PbTiO₃ thin films have been deposited by spin coating onto different subtrates; Si[111], Si/Al, Si/SiO₂/Cr/Pt, MgO[100], SrTiO₃[100] and sapphire. Interactions between the substrate and PbTiO₃ films after heat treatment have been studied by X-ray diffraction and Rutherford Back Scattering. When deposited onto sapphire and Si[111], PbTiO₃ films exhibit a preferred orientation with (101) perpendicular to the substrate. These films become oriented along (100) onto MgO and (001) onto SrTiO₃[100] substrates. A strong channelling effect is observed by the RBS technique when the film is oriented along the c axis on SrTiO₃[100] suggesting that these films are epitaxially grown. The diffusion of metal atoms during the thermal treatment gives rise to the formation of lead silicate on Si[111] substrates. As a result a pyrochlore phase is formed. Lead titanate films on Si/SiO₂/Cr/Pt and Si/Al substrates are polycrystalline and do not exhibit any texture.     

High-resolution transmission electron microscopy investigation of nanostructures in SnO2 thin films prepared by pulsed laser deposition

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO₂ thin films onto glass substrates. The nanocrystallites and microstructures in SnO₂ thin films grown by PLD techniques have been investigated in detail by using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The PLD process was carried out at room temperature under a working pressure of about 2×10⁻⁶ mbar. Experimental results indicate that thin films are composed of a polycrystalline SnO₂ and an amorphous SnO phase. In particular, the presence of such an amorphous SnO phase in the thin films greatly limits their practical use as gas-sensing devices. HRTEM observations revealed that SnO₂ nanocrystallites with tetragonal rutile structure embed in an amorphous SnO matrix, which are approximatively equiaxed. These approximatively equiaxed SnO₂ nanocrystallites contain a high density of defects, such as twin boundaries and edge dislocations. The grain growth of SnO₂ thin films may be discussed in terms of the coalescent particle growth mechanism.     

Structural Organization of Layers in Octakis-(trimethylsiloxy)octasilsesquioxane

Oktakis-(trimethylsiloxy)octasilsesquioxane [(CH₃)₃SiO]₈(SiO_1.5)₈ has been studied by X-ray diffraction (DRON-RM4, R=192 mm, CuK radiation) and structural organization of layers in this compound has been analyzed. Irrespective of the type of the support used, the layers obtained by chemical vapor deposition are ideally orientated polycrystalline films in the [001] direction. The type of the planar lattice followed by the molecules was determined from crystal structure analysis in the direction indicated.     

Crystalline orientation of the InN films prepared by atmospheric pressure halide chemical vapor deposition

The structural analysis of the hexagonal InN film prepared on a Si(100) substrate by the AP-HCVD technique using InCl₃ and NH₃ as starting materials were carried out by the X-ray pole figure analysis. The deposited films consist of the hexagonal InN pillar crystals. It was found that the pillar crystals, which have random rotation around the 100 axis, were grown at an angle of 70–90° to the substrate.     

Phase relationships in the pseudo-binary 2(ZnTe)-CuInTe2 system

Subsolidus phase relationships in the 2(ZnTe)_x(CuInTe₂)_1−x system were investigated by TEM experiments combined with EDX analysis. The samples were prepared by the solid-state reaction of the elements during long annealing times, followed by either quenching in ice-cold water, or by controlled cooling at different rates. Using the chemical compositions of single and coexisting phases at various temperatures, the boundaries of the two-phase region have been determined. At room temperature, the two-phase region extends from x=0.10 to 0.31. For x<0.10 only mixed crystals with tetragonal structure exist. Between x=0.31 and 1 alloys with the cubic structure are stable.The morphology of the tetragonal domains and their orientation relationship to the cubic matrix were determined by SAD, TEM and HRTEM experiments. The tetragonal phase embedded within the cubic matrix has a flat ellipsoidal shape, whose short axis coincides with the tetragonal c-axis. The three topotaxial orientation relationships between the tetragonal domains and the surrounding cubic matrix were found to be: [001]_tetr.∥[100]_cub., [001]_tetr.∥[010]_cub. and [001]_tetr.∥[001]_cub.. There is an indication that the nucleation starts from small regions displaying cation ordering according to the CuPt-type structure. Reaching the two-phase equilibrium, the tetragonal domains as well as the surrounding cubic phase are free of this cation ordering.     

Dielectric properties and I-V characteristics of (Pb<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>)TiO<Subscript>3</Subscript> thin films improved by TiO<Subscript>2</Subscript> buffer layers

A TiO₂ thin buffer layer was introduced between the (Pb_0.4Sr_0.6)TiO₃ (PST) film and the Pt/Ti/SiO₂/Si substrate in an attempt to improve their electrical properties. Both TiO₂ and PST layers were prepared by a chemical solution deposition method. It was found that the TiO₂ buffer layer increased the (100)/(001) preferred orientation of PST and decreased the surface roughness of the films, leading to an enhancement in electrical properties including an increase in dielectric constant and in its tunability by DC voltage, as well as a decrease in dielectric loss and leakage current density. At an optimized thickness of the TiO₂ buffer layer deposited using 0.02 mol/l TiO₂ sol, the 330-nm-thick PST films had a dielectric constant, loss and tunability of 1126, 0.044 and 60.7% at 10 kHz, respectively, while the leakage current density was 1.95 × 10⁻⁶ A/cm² at 100 kV/cm.     

On the relaxation/transformation of NiO-dissolved TiO2 condensates with fluorite-type derived structures

Nd-YAG-laser pulse irradiation of clamped Ni/Ti plates in oxygen was employed to synthesize fluorite-type (f) derived TiO₂ condensates dissolved up to 5 at% Ni²⁺ of the cations. The nanocondensates less than 20 nm in size are nearly cubo-octahedral in shape and tended to transform martensitically to monoclinic (m) baddeleyite-type following the crystallographic relationship (100)_f//(110)_m; [001]_f//[001]_m. The condensates twice larger in size, with considerable matrix constraint, are nearly spherical in shape and consist of mosaic m-twin variants following complicated crystallographic relationships with each other and with the relic f-phase: (010)_f//()_m; [001]_f//[001]_m. The charge and volume compensating oxygen vacancies due to NiO dissolution in the dense TiO₂ condensates could facilitate the relaxation and amorphization process.     

Structural study of lanthanum nickelate thin films deposited on different single crystal substrates

Fabrications of La₂NiO_4+δ thin film layers by liquid-injection metalorganic chemical vapor deposition were tried on different single crystals substrates: (001)Si, (001)MgO, (001)LaAlO₃ and (001)SrTiO₃. As results of structural characterizations, polycrystalline dendritic layers of La₂NiO_4+δ tetragonal (or orthorhombic) phase were observed on (001)Si substrates while layers of a perovskite-like cubic structure were observed on the other single crystal substrates. From a high-resolution TEM study of a layer deposited on (001)MgO, such a perovskite-like cubic structure exhibits many planar structural faults likely similar to planes of oxygen vacancies of the La₂NiO_4+δ orthorhombic structure. A thin intermediate epitaxial layer of NiO phase was also identified. Using a X-ray texture diffractometer, the layer structure on (001)MgO, (001)LaAlO₃ and (001)SrTiO₃ was confirmed to be of cubic structure with 〈100〉 axes parallel to those of the substrate. The T dependence of the resistivity of a layer deposited on (001)MgO substrate was found to be of a semi-conducting behavior.     

Thickness dependent physical properties of close space evaporated In2S3 films

In recent years, In₂S₃ is considered as a promising buffer layer in the fabrication of heterojunction solar cells. Film thickness is one of the important parameters that alters the physical characteristics of the grown layers significantly. The effect of film thickness on the structural, morphological, optical and electrical properties of close space evaporated In₂S₃ layers has been studied. In₂S₃ thin films with different thicknesses in the range, 100–700 nm were deposited on Corning glass substrates at a constant substrate temperature of 300 °C. The films were polycrystalline exhibiting strong crystallographic orientation along the (103) plane. The deposited films showed mixed phases of both cubic and tetragonal structures up to a thickness of 300 nm. On further increasing the film thickness, the layers showed only tetragonal phase. With increase of film thickness, both the crystallite size and surface roughness in the films were found to be increased. The optical constants such as refractive index and extinction coefficient of the as-grown layers have been calculated from the optical transmittance data in the wavelength range, 300–2500 nm. The optical transmittance of the films was decreased from 82% to 64% and the band gap varied in the range, 2.65–2.31 eV with increase of film thickness. The electrical resistivity as well as the activation energy was evaluated and found to decrease with film thickness. The detailed study of these results was presented and discussed.     

Variation of lattice dimensions in epitaxial SnS films on MgO(001)

Epitaxial and polycrystalline SnS films were prepared on MgO(001) and glass substrates using molecular beam epitaxy. The films were characterized by X-ray diffraction method. The orientations of epitaxial films were (010)[100]SnS||(001)[100]MgO or (010)[001]SnS||(001)[100]MgO. Lattice parameters of the polycrystalline film closely resembled those of bulk SnS at room temperature. However, the lattice parameters of epitaxial films varied widely and were very different from those of bulk SnS at room temperature. Considering the lattice dimensions and a/c ratio, the films roughly correspond to bulk SnS at elevated temperatures from 371 to 666 K. SEM images of the films showed needle- or circular-like SnS crystallites segregated from the epitaxial films. Respective energies of indirect band gaps of the films and refractive index of the polycrystalline film were estimated using results of optical transmission experiments.     

The oxygen sensitive properties of (LaBa)Co2O5+δ thin films fabricated by polymer-assisted deposition technique

(LaBa)Co₂O_5+δ (LBCO) thin films were successfully fabricated on Si (001) substrates by polymer-assisted deposition method. Microstructures were examined by X-ray diffraction technique, which confirmed the films were a single phase, pseudo cubic structure. The electrical transport properties of the films were investigated by the temperature dependence of films resistance, which suggested that LBCO films have typical semiconductor properties. After circle tests, the oxygen–hydrogen response rate did not show obvious variation in the specific temperature environment of 580 °C. This demonstrates that the LBCO thin films have a superior stability in both oxygen and hydrogen (6 % H₂, 94 % N₂) environment. Simultaneously, the drastic changes of films resistance (from ~10⁶ to ~10² Ω) with the switch of redox (O₂–H₂) environment within such a short time (~2.2 s) indicated that LBCO films have an excellent oxygen sensitive property and extraordinary fast surface exchange rate.     

Fabrication and electron transport properties of epitaxial films of electron-doped 12CaO·7Al2O3 and 12SrO·7Al2O3

Epitaxial growth and electron doping of 12CaO·7Al₂O₃ (C12A7) and 12SrO·7Al₂O₃ (S12A7) are reported. The C12A7 films were prepared on Y₃Al₅O₁₂ (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.     

Comparative study of the structural,optical, and electrical properties of CuAlO<Subscript>2</Subscript> thin films on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and YSZ substrates via chemical solution deposition

Single-phase delafossite CuAlO₂ thin films are deposited successfully on Al₂O₃ (001) and YSZ (100) substrates using the chemical solution method. X-ray diffraction data present that the CuAlO₂ film on the Al₂O₃ (001) substrate is epitaxial, whereas that on YSZ (100) is c-axis oriented; the same is also demonstrated by the HRTEM images and SAED patterns. Optical transmittance spectra exhibit that both films have high transparency in the visible region. However, in this region, the optical transmittance of the CuAlO₂ thin film deposited on (001) Al₂O₃ is inferior to that deposited on (100) YSZ. This optical anomaly can be attributed to surface scattering. Electrical transport measurements show that the resistivity of the film on (001) Al₂O₃ is one order lower than that on (100) YSZ, suggesting that in-plane orientation is significant in improving hole mobility.     

The structure of CeAlO3 by Rietveld refinement of X-ray powder diffraction data

The room temperature structure of perovskite CeAlO₃ has been reinvestigated by X-ray powder diffraction. The Rietveld refinement has confirmed the tetragonal symmetry; but revealed a super cell, a=5.32489(6) Å and c=7.58976(10) Å, with the space group I4/mcm. In CeAlO₃, the distortion from the ideal cubic perovskite is caused by the cooperative tilting of the AlO₆ octahedra around the primitive cubic [001]_p-axis.     

Impact of substrate on some physical properties of PrFe0.5Ni0.5O3 thin films

We carried out the structural, morphological and transport study of PrFe_0.5Ni_0.5O₃ thin films prepared by pulsed laser deposition (PLD) over various substrates. Different substrates like LaAlO₃ (001),GaAs(001) and Si(001) were used for deposition to understand effect of lattice mismatch on various physical properties. The film deposited on LaAlO₃ was of best quality with well (001)-oriented and having good crystalline properties. Whereas, film deposited on GaAs(001) is well textured. Both films shows semiconducting behavior and resistance of the film deposited on GaAs(001) shows larger than that of film deposited on LAO. However, film deposited on Si, also shows polycrystalline growth with unusual metallic behavior. We tried to correlate this behavior with strain-induced growth of these films. Other possibilities for this unusual trend is also explored.     

Stabilized epitaxial films of hexagonal Ni1−xS on MgO(001)

This study used molecular beam epitaxy to prepare epitaxial Ni_1−xS films with NiAs-type structures on MgO(001) substrates. The films were characterized using X-ray diffraction method. Nickel vacancies showed an ordered arrangement of alternating metal-rich and metal-deficient layers along the c-axis. The orientations of epitaxial films were (001) [1,−1,0]Ni_1−xS||(001)[110]MgO and its equivalents because of the coexistence of the trigonal axis of the Ni_1−xS film and the four-fold rotation axis of the MgO substrate. Film compositions were obtained using intensity ratios between 0 0 1 and 0 0 2 reflections and EPMA results. They were dependent on substrate temperature. The relation between lattice parameters and the composition, as determined by the intensity ratio, nearly agrees with that of previously reported bulk Ni_1−xS. The films were stable at room temperature after 1 year, which contrasts with deterioration of bulk Ni_1−xS. This paper presents SEM and RHEED assessments of the film's morphology and structure.     

Zur Umwandlung von Greigit (Fe3S4) in Pyrrhotin (FeS) durch Elektronenstrahlen

On the Phase Transition of Greigite (Fe₃S₄) to Pyrrhotite (FeS) by Electron Beam The phase transition of mackinawite to pyrrhotite via greigite, which occurs on heating by means of electron beam in an electron microscope, is examined. An orientation relationship {111}_G//(001)_p and <110>_G//[110]_p can be applied at the transition of greigite to pyrrhotite.     

TEM Investigations of Spinel-forming Solid State Reactions: Mechanism,film orientation,and interface structure during MgAl2O4 formation on MgO (001) and Al2O3 (1 1.2) single crystal substrates

The formation of well-oriented MgAl₂O₄ spinel films by solid state reactions between (i) a MgO (001) substrate and an Al₂O₃ vapour and (ii) a sapphire (1 1 .2) substrate and a deposited solid MgO film, respectively, is experimentally investigated. Composition, structure and morphology of the films are characterized by XRD, SEM, TEM/SAED, and EDX. The reaction fronts involved are investigated by cross-sectional atomic resolution transmission electron microscopy (ARM). The direction of the overall diffusion flux and the kind of diffusing species are determined in experiments using inert markers of sub-micron size. There are common features and, however, distinct differences between cases (i) and (ii). On MgO (001) substrates, the MgAl₂O₄ films grow in a simple cube-to-cube orientation: MgAl₂O₄(001) ∥ MgO(001); MgAl₂O₄[100] ∥ MgO [100]. The films consist of small grains about 25 to 50 nm in diameter, the orientation of which is symmetrically distributed around the exact orientation, with maximum deviations of about ±2°. On sapphire (1 1 .2) substrates the MgAl₂O₄ films grow almost in the orientation MgAl₂O₄(001) ∥ Al₂O₃(1 1 .2); MgAl₂O₄[010] ∥ Al₂O₃[11.0]. These films consist of larger grains about 100 nm in diameter, the orientation of which systematically deviates from the above orientation by unidirectional rotations up to 5 to 6° around the substrate [11.0] axis. The structures of the reaction fronts show corresponding differences, which are discussed in terms of different mechanisms occurring at the initial stage of the spinelforming reaction because of the different crystallographic conditions at the beginning of the reactions.