Pyramidal Crystallites Research Articles

Effect of intermittent time on structural, optoelectronic, luminescence properties of sprayed antimony doped tin oxide thin films

By implementing spray pyrolysis technique the influence of intermittent time on to the structural, optical and electrical properties of the antimony doped tin oxide (ATO) thin films were analyzed. It is seen that all the films exhibit tetragonal crystal structure with a preferential growth along the (211) and (301) planes. The crystallite size of the film estimated from the XRD pattern decreases with increase in intermittent time. The pyramidal crystallites formed due to coalescence are observed from SEM images. The average optical transmittance in the visible range is 75%. The calculated IR reflectivity was found to be in the range of 92–97%. For the typical film deposited with 15s intermittent time, the values of sheet resistance and resistivity of about 3.12Ω/▯ and 4.2×10−4Ωcm, respectively. The films deposited with 15s intermittent time has higher φ (23.95×10−3Ω−1) than the values of φ reported in literature for ATO films prepared by spray pyrolysis technique. All the above mentioned properties of the ATO films deposited by spray pyrolysis technique are useful for the production of low-cost, large area coatings of ATO films.

Shape Control of Electrodeposited Copper Films and Nanostructures through Additive Effects

The use of electrolyte additives to affect nanocrystallite shape and film morphology in electrodeposited copper films is presented. Linear sweep and cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods are employed to investigate the effects of alcohol additives and the organic additive malachite green (MG), on copper electrodeposited onto polycrystalline gold electrodes. The use of additives affects the deposition process by increasing cathodic peak potentials and decreasing corresponding peak currents. Copper films deposited from electrolyte solutions with additives show additive-specific nanostructure and crystallite morphology. Film analysis reveals a greater than five times reduction in both film roughness and grain size in the presence of even small concentrations of the additive MG. Use of MG results in the preferential electrodeposition of oriented, square pyramidal crystallites, while alcohol additives result in tetrahedral crystallite textures. These shape-controlled additive effects are supported by additive adsorption energy calculations, which indicate preferential interactions, and differential growth kinetics on different facets of the film's growing nanostructures during electrodeposition. This approach offers a new and cost-effective route to achieve shape-controlled surface nanostructure.

MORPHOLOGICAL AND CRYSTALLOGRAPHIC PROPERTIES OF RARE EARTH OXIDES COATINGS DEPOSITED BY DOUBLE DUAL BEAM-PLD

Various rare earth oxide nanostructures were synthesized for the first time by dual-double pulsed gas feeding/pulsed laser deposition. The optically transparent and insulating nanostructures do not exhibit the standard columnar configuration of rare earth oxide thin films but rather dense structures and a significant chemical stoichiometry. More precisely, they exhibit single crystallographic low temperature phases with preferential textures, generally similar to that of the bulk used powder targets. For the cubic fluorine type CeO 2 and Ho 2 O 3 films, an epitaxial growth is observed with a special feature noticed in the case of the Eu 2 O 3 nanostructure. For this latter, localized and very large oriented crystallites embedded in disordered packed pyramidal crystallites are observed.

Etching of CVD diamond films using oxygen ions in ECR plasma

Etching with oxygen ions produced by ECR plasma with an asymmetric magnetic mirror field was investigated as a potential technique for polishing CVD diamond. The morphology, structure and roughness of the diamond film surface before and after etching were analyzed respectively using scanning electron microscope (SEM), Raman spectroscopy and surface roughness measuring instrument. It was found that the ridges on diamond surface had been preferentially etched away and thereby the surface roughness decreased from 3.061 to 1.083μm after 4h etching. Meanwhile, non-diamond phase appeared on surface and dramatically increased with the extending of etching time. In order to fundamentally understand the etching mechanism, an etching model of diamond film was reasonably proposed on the ground of the experimental results and the theory of plasma physics. The as-generated ions taking screw movement are firstly accelerated along the magnetic field lines in the plasma and collisional presheath, and then deflected from their route towards the diamond film in the MP. When coming into Debye sheath, the motion of ions will be deflected further and strongly accelerated by electric field in the direction normal to the (111) crystal facets. This process gave rise to energetic ion bombardment towards every (111) crystal face, and thereby caused preferential etching of pyramidal crystallites.

Structural and optoelectronic properties of sprayed Sb:SnO2 thin films: Effects of substrate temperature and nozzle-to-substrate distance

The influence of substrate temperature and nozzle-to-substrate distance (NSD) on the structural, morphological, optical and electrical properties of Sb:SnO2 thin films prepared by chemical spray pyrolysis has been analyzed. The structural, morphological, optical and electrical properties were characterized by using XRD, SEM, UV-visible spectrophotometry and Hall effect measurement techniques. It was seen that the films are polycrystalline, having a tetragonal crystal structure with strong orientation along the (200) reflection. The pyramidal crystallites formed due to coalescence were observed from SEM images. The values of highest conductivity, optical transmittance and figure of merit of about 1449(Ω·cm)−1, 70 %and 5.2 × 10−3 □/Ω, respectively, were observed for a typical film deposited using optimal conditions (substrate temperature = 500 °C and NSD = 30 cm).

Conformational morphology of polyaniline grown on self-assembled monolayer modified silicon

Polyaniline (PANI) films with pyramidal shaped crystallites were prepared by self-organization on self-assembled monolayer (SAM) modified Si substrates. High-resolution atomic force microscopy (HR-AFM) shows that SAM has tridymite structural order and the PANI film has biphasic conformational morphology corresponding to face-on orientation and edge-on orientation. Order parameters obtained from power spectral density analysis of HR-AFM images of SAM and PANI films show that the pyramidal crystallites are in emeraldine salt (ES-I) form and the region between the crystallites is in emeraldine base (EB-II) form. The ordered lattice of PANI crystallites as observed by cross-sectional HR-TEM confirms its single crystalline nature as well as epitaxial growth. The heteroepitaxial growth of PANI is attributed to the structural order of interfacial SAM on Si.

Texture control of fluorine-doped tin oxide thin film

The texture control of transparent oxide thin film, the crystalline orientation, is very important, because it is related to the electrical resistivity and the optical transparency. It is known that the crystal orientation could be controlled by varying precursor source, gas flow rate, and deposition temperature. We deposited fluorine-doped tin oxide (FTO) thin film on aluminoborosilicate glass by spraying water-based solution and ethyl alcohol-added solution. We showed in this research that (200) and (301) preferential orientation of FTO thin film can be controlled by the addition of ethyl alcohol to FTO coating solution. (200) oriented FTO thin film deposited from ethyl alcohol-added solution comprises of pyramidal crystallites with {111} polar faces, which contain {101} contact twin planes. {101} contact twin planes forms salient reentrant angle which provides nucleating sites and makes crystallites grow abnormally. (301) orientation is thought through Periodic Bond Chains of tin hydroxide which forms prismatic long crystallites. Prismatic crystallites are comprised of {110} crystal faces which contain {101} repeated contact twin. It is very helpful to control (200) or (301) oriented crystal formation in transparent conducting oxide film, because the texture affects the electrical and optical properties of transparent conducting oxide film. We suggest that ethyl alcohol addition plays a role to form crystallites with {111} polar faces corresponding to (200) preferential orientation. The crystal morphologies are changed by doping elements, precursor sources, deposition conditions like flow rate and temperatures, and solvents.

Growth of highly oriented crystalline polyaniline films by self-organization

Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH 2) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate–polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.

Microstructure and physical properties of nanofaceted antimony doped tin oxide thin films deposited by chemical vapor deposition on different substrates

Antimony doped tin oxide SnO 2: Sb thin films have been fabricated by atmospheric pressure chemical vapour deposition at substrate temperature varying between 350 °C and 420 °C in a horizontal reactor, from a mixture of hydrated SnCl 2, SbCl 3 and O 2 gas. The films were grown on glass substrates and onto polished and porous n-type silicon. Doped films fabricated with various Sb (Sb/Sn %) contents ranging from undoped 0% to 4% were characterised employing different optical characterisation techniques, like X-ray diffraction, transmittance and reflectance in the wavelength range of 300 to 2500 nm and ellipsometry. The films exhibit the usual cassiterite diffraction pattern with high crystalline structure. Examination of the surface by scanning electron microscopy (SEM) showed that the films are textured made up of many pyramidal crystallites with nanofaceted surfaces, indicating highly stabilised material. The presence of inverted pyramids indicates that the crystallites grown by coalescence. The surface morphology was found to be independent on the kind of the substrate. From X-Ray spectra and SEM observations we get the texture the lattice constant and the grain size. The optical results provide information on film thickness, optical parameters and transmittance upon antimony concentration. The microstructure of the films, the grain growth topics (nucleation, coalescence…) depend strongly on deposition conditions and doping concentration. The observed variations of both the resistivity ρ and transmittance T are correlated to antimony atoms concentration which induced variation in the microstructure and in the size of SnO 2 nanograins (typically 20–40 nm). In this work, we have determined the feasibility of incorporating the correct amount of Sb atoms in tin oxide film by means of resistivity and transmission. SEM observations showed that the substrate do not affect the morphology.

Nanocrystalline structure and nanopore formation in modified thermal TiO 2 films

The anodic TiO 2 films on Ti 0 substrates were synthesized using different electrochemical techniques including potential step, potentiodynamic, and galvanostatic technique, from a 1 M Na 2 SO 4 + 10 mM NaF solution. The AFM imaging of film surfaces revealed that thin films ( h < 20 nm ) are composed of small spherical-shaped nanocrystals, up to 20 nm in size. In thicker TiO 2 films ( h > 20 nm ) , cylindrical nanopores with diameter of ca. 30 nm, are formed. In contrast to the nanocrystalline nature of anodic TiO 2 films, thermally grown TiO 2 films at 850 °C are composed of oriented large pyramidal crystallites (200–500 nm in size), which are transformed into even larger moulds (2– 3 μ m in size) at 1050 °C. Thermal films of this type have been known to show inferior surface properties leading to large reflectance losses and the presence of surface states, which promote the electron–hole recombination. In this paper, we propose a new way to remedy these disadvantages of thermal films by special low temperature electrochemical anodic treatment. We have found that by the anodic treatment of thermally grown TiO 2 films, it is possible to control the surface properties, such as the nanocrystalline structure and nanopore formation. These features are desirable for solar energy conversion devices and solar hydrogen production, where the enhancement of electrocatalytic activity by increasing real surface area, reduction of reflectance losses, and removal of surface states created by thermal growth, are of primary importance. The tested electrochemical treatment included program waveforms inducing nanocrystallinity and nanopore formation. The pulse-voltammetric procedures are proposed to control surface non-stoichiometry of TiO 2 films and surface-states density of the photoelectrodes.

Why Does Insect Antifreeze Protein from Tenebrio molitor Produce Pyramidal Ice Crystallites?

The antifreeze protein (AFP) reduces the growth rates of the ice crystal facets. In that process the ice morphology undergoes a modification. An AFP-induced surface pinning mechanism, through matching of periodic bond chains in two dimensions, enables two-dimensional regular ice-binding surfaces (IBSs) of the insect AFPs to engage a certain class of ice surfaces, called primary surfaces. They are kinetically stable surfaces with unambiguous and predetermined orientations. In this work, the orientations and molecular compositions of the primary ice surfaces that undergo growth rate reduction by the insect AFPs are obtained from first principles. Besides the basal face and primary prism, the ice surfaces engaged by insect AFPs include the specific ice pyramids produced by the insect AFP Tenebrio molitor (TmAFP). TmAFP-induced pyramids differ fundamentally from the ice pyramids produced by fish AFPs and antifreeze protein glycoproteins (AFPGs) as regards the ice surface configurations and the mode of interaction with the protein IBS. The molecular compositions of the TmAFP-induced pyramids are strongly bonded in two dimensions and have the constant face indices (101). In contrast, the molecular composition of the ice pyramids produced by fish AFPs and AFPGs are strongly bonded in only one direction and have variable face indices ( h 0 l), none of which equal (101). The thus far puzzling behavior of the TmAFP in producing pyramidal crystallites is fully explained in agreement with experiment.

Crystal growth in the low-temperature deposition of polycrystalline silicon thin film

In this study, the microstructure and property of poly-Si film, deposited using hot wire chemical vapor deposition (HWCVD) were investigated. A consequence of the low a-Si content in the poly-Si film was crystallites with well developed facets. The crystallite morphology was rhombic pyramidal while EBSD analysis revealed the existence of (111) contact twin planes. The facets of the rhombic pyramidal crystallites were based on {320} and {320}* planes, which have Σ3 twin relationship with respect to (111) contact twin plane.

Epitaxial growth of lithium fluoride on the (1 1 1) surface of CaF 2

Growth of lithium fluoride by molecular beam epitaxy on the (1 1 1) surface of calcium fluoride crystals was studied by TEM and LEED for crystal temperatures from 400 to 773 K and impinging lithium fluoride fluxes from 3×10 11 to 3×10 14 cm −2 s −1. Growth starts, usually, at the 〈1 1 0〉 steps on the (1 1 1) surface of CaF 2. For larger step distances and at later growth stages also growth on the terraces between the steps is found. Preferably, longish, roof-like crystallites are formed, which can be interpreted by growth of LiF(2 0 1 ̄ )[0 1 0] parallel to CaF 2(1 1 1)[ 1 ̄ 0 1]. To a lesser extent square crystallites, i.e. growth with LiF(0 0 1), and, rarely, three-folded pyramidal crystallites, i.e. growth with LiF(1 1 1) parallel to CaF 2(1 1 1), are observed. While the pyramidal crystallites show strict epitaxial orientation with LiF[ 1 ̄ 0 1]‖CaF 2[ 1 ̄ 0 1] and LiF[ 1 ̄ 0 1]‖CaF 2[1 2 ̄ 1], only about 80% of the square crystallites exhibit an epitaxial alignment, where LiF[1 0 0]‖CaF 2[ 1 ̄ 0 1] is preferred to LiF[1 1 0]‖CaF 2[ 1 ̄ 0 1]. The epitaxial relationships are discussed on the basis of theoretically calculated adsorption positions of the lithium fluoride monomer and dimer on the terrace and at the steps of the CaF 2(1 1 1) surface.

Structural stability of hydrogenated (100) surface of cubic boron nitride in comparison with diamond

In view of (1×1):2H dihydride/(2×1):H monohydride reconstruction, structural stability of (100) surfaces of both cBN and diamond was comparatively investigated by semiempirical molecular orbital methods using isoelectronic clusters of B52N42H80−2n(10−), N52B42H80−2n(10+), and C94H80−2n, to model (100)B and (100)N of cBN, and diamond surface, respectively, where n=0, 1, 2, or 3. The n denotes the number of monohydride dimers formed. These clusters were nanometer-sized pyramidal crystallites bound by four of {111} faces and one (100). The (100)N of cBN was found unique because of the great stability as (1×1):2H dihydride phase, which retains the bulk structure truncated at the surface without reconstruction and is expected to be chemically inert. This passivation seems to be related to the difficulty in chemical vapor deposition of high quality cBN. The (100)B of cBN was predicted to stabilize as (2×1):H monohydride phase as much as hydrogenated (100) of diamond does.

Nanoscopic trigonal pyramidal crystallites in WS 2− x sputtered thin films: a scanning tunnelling microscopy study of initial growth

We present original scanning tunnelling microscope (STM) images of the first growth stages of crystalline, textured WS 2− x thin films ( x=0.2−0.4) prepared by reactive RF magnetron sputtering. In the first 10–20 nm of thickness, the films grow in the shape of trigonal pyramids with typical lateral size in the 20 nm range. Step heights of 0.6 nm show that the films grow by molecular layers rather than by complete 2H or 3R polytypic unit cells of c parameters 1.2 or 1.8 nm. The triangular shapes reflect the symmetry of the trigonal prismatic unit and the pyramidal arrangement indicates a rhombohedral stacking. The growth process is three-dimensional, including some spiral growth.

Atomic force microscopy of mercury iodide crystal growth from porous media at room temperature

A real time observation of the growth of agglomerates of pyramidal crystallites of mercuric iodide on a porous glass surface using tapping mode atomic force microscopy is reported. Crystallites are observed to grow from the pores (5.0 nm diameter) onto the surface of the porous glass impregnated with mercuric iodide. Immediately after fracturing the impregnated porous glasses, topographical images reveal a surface with a root mean square roughness of 75–130 nm over a 5 μm×5 μm area, which is typical for surfaces of fractured porous glass. After 3 h, 60–90 nm pyramidal structures with a high aspect ratio (pyramid base to height) begin to appear on the surface. Some of the pyramidal structures agglometrate and form structures much larger and higher than the surrounding ones. The bottom of some of these agglomerated pyramids form equilateral triangles with dimensions of 300–500 nm, exhibiting a preferred orientation on the surface. 6 h after fracturing, micrometer‐size crystallites are observed. Most of the pyramidal structures are no longer observed and mostly needlelike features are covering the surface. Step heights consistent with multiples of the c axis of α‐mercuric ioide are observed on the micrometer‐sized crystallites. Some pyramidal structures are observed between the large crystallites, with sizes comparable to the early stage pyramidal structures. Raman and electronic spectra are also reported for mercuric iodide confined in porous glasses. The Raman spectra have peaks located at 39 and 141 cm−1, indicating that the confined mercuric iodide is stabilized in the yellow, orthorhombic (β phase) at room temperature. Confinement of mercuric iodide in pores with radii smaller than 3.75 nm results in the appearance of a new band at 145 cm−1 in the Raman spectra, suggesting the presence of a new or modified β phase of mercuric iodide. Further evidence supporting the presence of a new phase of mercuric iodide is found in the electronic spectra where an energy gap of 2.7 eV is observed, and lies between the energy gaps of the red, tetragonal, α phase (2.2 eV) and the yellow, orthorhombic β phase (3.1 eV) of mercuric iodide. The atomic force microscopy measurements provide a unique method for real time monitoring of the crystal growth and morphology changes of nanocrystalline mercuric iodide, while the spectroscopy provides insight to the phonon structure and energy gaps of the confined material.

Full-color photosensitive glass

New polychromatic (full-color photosensitive) glasses are described in which the full color spectrum is developed by photochemical precipitation of subcolloidal silver too small to scatter light. The brilliant colors are shown to be due to selective light absorption by randomly oriented silver-containing particles having controlled anisotropic shapes. The color photographic process and its chemistry are outlined. Controlled anisotropy is due to photo-silver-nucleated growth of elongated NaF⋅ (Na,Ag) X pyramidal crystallites, concentration of AgX at the apex, and subsequent photoprecipitation of this silver. Resultant colors are primarily a function of exposure flux (intensity × time) employing ultraviolet light (300 nm). The colors can be semiquantitatively described from electromagnetic theory assuming ellipsoidal metal particles suspended in a transparent dielectric medium. An absorption band moves across the visible spectrum as a function of particle eccentricity. Polychromatic glasses can be made having transparency, opacity, or a mixed pattern through photonucleation control of halide crystallite growth, which governs light scattering. Colors may be developed in either clear or opal areas; they can be restricted to the surface of the glass or generated to great depth. The colors appear permanent at ambient temperature and exhibit good thermal stability.