Textured Polycrystalline Thin Films Research Articles

Control of morphology and orientation for textured nanocrystalline indium oxide thin film: A growth zone diagram

The function and performance of textured polycrystalline thin films are closely related to their microstructures. However, the corresponding growth mechanisms remain unclear, which brings obstacles to the effective engineering of the films' properties. In this work, textured nanocrystalline Indium Oxide (nc-In2O3) thin films are prepared and the growth mechanism is explored. Texture morphology within or beyond the prediction of Wulff's theorem and van der Drift's growth mechanism are both observed. The orientation of the textured film changes from (100)-preferred in quasi-equilibrium growth conditions to (111)-preferred in non-equilibrium growth conditions. From a microscopic perspective of adatoms' diffusion, different growth modes for the growth of the textured In2O3 thin films is classified and a quantitative growth zone model is developed. According to the zone model, the morphology and orientation of the films could be successfully designed and controlled by changing growth conditions.

Room temperature multiferroism in polycrystalline thin films of gallium ferrite

We have synthesized (010) textured polycrystalline thin films of gallium ferrite (GaFeO3 or GFO) on n-Si(100) and Pt/Si(111) substrates using sol-gel assisted spin coating technique. Structural characterization using x-ray diffraction and Raman spectroscopy confirms formation of single phase with crystallite size ∼37–47 nm. Magnetic characterization demonstrates saturated magnetic hysteresis loop at room temperature and indicates that due to reduced crystallite size, ferri to paramagnetic transition temperature, TC ∼300 K is higher compared to bulk GFO, reported earlier. Room temperature piezo-response force microscopic analysis reveals local ∼180° phase switching of ferroelectric domains at very high coercive field, ∼700 kV/cm, consistent with recent experimental and first-principles studies. Our study opens up the possibility of integrating polycrystalline GFO in novel room temperature multiferroic devices.

Double in-plane alignment in biaxially textured thin films

The scientific interest and technological relevance of biaxially textured polycrystalline thin films stem from their microstructure that resembles that of single crystals. To explain the origin and predict the type of biaxial texture in off-normally deposited films, Mahieu et al. have developed an analytical model [S. Mahieu et al., Thin Solid Films 515, 1229 (2006)]. For certain materials, this model predicts the occurrence of a double in-plane alignment, however, experimentally only a single in-plane alignment has been observed and the reason for this discrepancy is still unknown. The model calculates the resulting in-plane alignment by considering the growth of faceted grains with an out-of-plane orientation that corresponds to the predominant film out-of-plane texture. This approach overlooks the fact that in vapor condensation experiments where growth kinetics is limited and only surface diffusion is active, out-of-plane orientation selection is random during grain nucleation and happens only upon grain impingement. Here, we compile and implement an experiment that is consistent with the key assumptions set forth by the in-plane orientation selection model by Mahieu et al.; a Cr film is grown off-normally on a fiber textured Ti epilayer to pre-determine the out-of-plane orientation and only allow for competitive growth with respect to the in-plane alignment. Our results show unambiguously a biaxially textured Cr (110) film that possesses a double in-plane alignment, in agreement with predictions of the in-plane selection model. Thus, a long standing discrepancy in the literature is resolved, paving the way towards more accurate theoretical descriptions and hence knowledge-based control of microstructure evolution in biaxially textured thin films.

Growth, disorder, and physical properties of ZnSnN2

We examine ZnSnN2, a member of the class of materials contemporarily termed “earth-abundant element semiconductors,” with an emphasis on evaluating its suitability for photovoltaic applications. It is predicted to crystallize in an orthorhombic lattice with an energy gap of 2 eV. Instead, using molecular beam epitaxy to deposit high-purity, single crystal as well as highly textured polycrystalline thin films, only a monoclinic structure is observed experimentally. Far from being detrimental, we demonstrate that the cation sublattice disorder which inhibits the orthorhombic lattice has a profound effect on the energy gap, obviating the need for alloying to match the solar spectrum.

A multiscale mechanics approach for modeling textured polycrystalline thin films with nanothickness

A multiscale method is proposed for calculating elastic constants of textured polycrystalline thin films of nanothicknesses. In this method the molecular simulation and finite element method are hierarchically employed. The elastic constants for each single crystal are first calculated through the simulations of on- and off-axis tension tests of the single crystal using molecular statics. Subsequently, the constitutive relations for the single crystal are used in conjunction with a finite element code to study the macro-mechanical deformation and stresses in textured polycrystalline nanofilms. The result indicates that both film thickness and grain size influence the macro-Young's modulus and Poisson's ratio of the nanofilm. Specifically, for nickel, the value of the macro-Young's modulus decreases as film thickness decreases and increases as grain size decreases. The value of the macro-in-plane Poisson's ratio increases as the thickness decreases or grain size increases.

Growth and characterization of L1/sub 0/ FePt and CoPt [001] textured polycrystalline thin films

Thin [001] textured FePt and CoPt polycrystalline films (5 nm) were deposited with an MgO polycrystalline underlayer on an oxidized Si substrate followed by a Rapid Thermal Annealing (RTA) process. Structural analysis indicated the samples to be fully ordered after 10 minutes (min) of RTA at 700/spl deg/C. The magnetic hysteresis exhibited strong perpendicular anisotropy and a coercivity (H/sub c/) between 6 and 8 kOe. The measured and simulated angular dependence of H/sub c/ and remanent coercivity (H/sub re/) showed the possibility of domain wall motion or incoherent rotation. /spl delta/M curves demonstrated strong intergranular exchange coupling. MFM observations showed domain sizes to be 100-200 nm. Activation volumes (V/sub act/) were found to be /spl sim/0.4-0.5/spl times/10/sup -18/ cm/sup 3/. The temperature dependence of the coercivity (H/sub c/) indicated a weak pinning mechanism.

In situ thin-film texture determination

A kinematic theory of reflection high energy electron diffraction (RHEED) is presented for textured polycrystalline thin films. RHEED patterns are calculated for arbitrary texture situations and for any general crystallographic orientation that may be encountered in thin-film growth. It is shown that the RHEED pattern can be used as a fast and convenient tool for in situ texture characterization. The approach also permits quantitative extraction of angular dispersion parameters which are useful for optimizing thin-film growth conditions.

Domain structure and stability of MOCVD-derived ferroelectric thin films

Ferroelectric thin film have recieved much attention in recent years because of their useful ferroelectric and dielectric properties to the device industry. In this article, we will address the relationship between the microstructure and the corresponding dielectric properties of PT and PZT ferroelectric thin film grown by Metal-Organic Chemical Vapor Deposition (MOCVD). The formation of domains in the textured polycrystalline thin films and single crystalline thin films were studied using TEM micrographs. X-ray diffraction and AFM. Substrate materials included single crystalline MgO, LaAlO3 and highly textured LaNiO3 coated Si substrate. The domain stability is also addressed as a result of initial cooling after deposition, and of subsequent thermal cycling after initial cooling. The stability of electrical properties after repeated cycles of operation (i. e. fatigue behavior) are also discussed.

Electron Diffraction Patterns of Fibrous and Lamellar Textured Polycrystalline Thin Films. I. Theory

The reciprocal lattices of fibrous and lamellar textured polycrystalline thin films are analyzed on the basis of the number of distinct angles made between planes of {hkl} families with the texture axis. Tables of the maximum possible number of such distinct angles between any given direction/plane and all faces of a given family of planes for all the crystal systems are included in this paper. Based on these reciprocal lattices, parallel and tilted electron-diffraction-pattern characteristics of the textured films are elucidated. A method of indexing the arced electron diffraction patterns of the textured films is proposed. This method can be applied to both the fibrous and lamellar texture films of all crystal structures. Formulas that relate the angles subtended by diffraction arcs to the distribution angle of the texture axis are presented.