Anisotropic crystallite size analysis of textured nanocrystalline silicon thin films probed by X-ray diffraction

A newly developed X-ray technique is used, which is able to quantitatively combine texture, structure, anisotropic crystallite shape and film thickness analyses of nanocrystalline silicon films. The films are grown by reactive magnetron sputtering in a plasma mixture of H₂ and Ar onto amorphous SiO₂ and single-crystal (100)-Si substrates. Whatever the used substrate, preferred orientations are observed with texture strengths around 2-3 times a random distribution, with a tendency to achieve lower strengths for films grown on SiO₂ substrates. As a global trend, anisotropic shapes and textures are correlated with longest crystallite sizes along the 〈111〉 direction but absence of 〈111〉 oriented crystallites. Cell parameters are systematically observed larger than the value for bulk silicon, by approximately 0.005-0.015 Å.     

Biaxially textured Ag films by grazing ion beam assisted deposition

The effect of grazing incidence 4 keV Ar⁺ ion irradiation on the early stage of Ag thin film growth on amorphous Si was investigated. The double effect of axial and surface channeling resulted in grains oriented along the 〈110〉 axis in-plane, while the (111) out-of-plane texture was maintained. A slight average tilt of the (111) out-of-plane texture axis towards the ion beam direction is proposed to result from the difference between terrace and step edge sputtering yield. The observed tilt is consistent with a minimum erosion orientation of the surface profile.     

Fabrication of biaxially textured magnesium oxide thin films by ion-beam-assisted deposition

Biaxially textured MgO thin films were grown by ion-beam-assisted deposition. The film growth parameters of film thickness, ion-to-atom arrival ratio (r-value), ion beam angle, and ion beam voltage were studied. Film characterization was performed by X-ray diffraction, pole figure analysis, and atomic force microscopy (AFM). Full-width half-maximum (FWHM) of MgO (220) ?-scans and MgO (002) ω-scans, respectively, were used to evaluate in-plane and out-of-plane film texture. MgO (220) ?-scan FWHM of 3.2° and MgO (002) ω-scan FWHM of 1.2° was achieved on amorphous Si₃N₄-coated Si substrates using a 1500-V ion source oriented at 45° to the substrate normal and an r-value of 0.90. Depositions on metallic substrates yielded MgO (220) ?-scan FWHM values of 5.2° and MgO (002) ω-scan FWHM of 2.5°. Root-mean-square surface roughness of these films as measured by AFM was ≈2.3 nm.     

Magnetic properties of textured CoPd nanocrystalline thin films

CoPd is an important nanomaterial for magnetic and magneto-optic storage of information. In this work, CoPd alloyed thin films are grown via radio frequency magnetron sputtering on silicon, glass and polyimide substrates in a vacuum chamber with base pressure of 5 x 10(-8) mbar. The films are nanocrystalline with grain size between 4 and 80 nm. The magnetic properties of thoroughly textured CoPd alloyed thin films are compared to random polycrystalline ones. Magnetization hysteresis loops recorded under fields up to 12 kOe via a home-made magneto-optic Kerr-effect magnetometer reveal strong tendency for perpendicular magnetic anisotropy for the textured film. This anisotropy leads to the formation of well-defined stripe or labyrinthine ferromagnetic domains with the local spins oriented perpendicular to the film plane. The domain patterns and the hysteresis loops are simulated with micromagnetic calculations. Finally, an induced magnetic moment of 0.44 microB/atom is measured for Pd via X-ray magnetic circular dichroism and it is separated into spin and orbital magnetic moment contributions.     

Structural characterization of thin ZnS films by X-ray diffraction

Structural properties of electroluminescent ZnS: Mn thin films grown by atomic layer epitaxy, which emit yellow light with an external efficiency as high as 2%, are investigated. The films grown at 500°C have a strong preferred orientation: one-half of the 00·1 plane normals are aligned within 7° from the normal of the glass substrate. The length of coherently diffracting domains (crystallite size) in the direction of the normal obtained from the Fourier analysis of a line profile ranges from 30 to 160 nm. The average relative strain in the same direction is calculated to be 10^?3. The estimated dislocation density is about 10¹⁰ cm^?2.     

Isochronal hydrogenation of textured Mg/Pd thin films

Magnesium thin films of 350 nm, capped with Pd, were deposited on glass substrates and hydrogenated in two different conditions; namely isochronal and isothermal. As-deposited films were highly textured with Mg (001) parallel to the glass substrate. Experiments have shown that under isothermal conditions starting from 333 K, Mg films can absorb hydrogen producing MgH₂ with a random texture. When the films were heated slowly starting from the room temperature, hydrogenation gives rise to a textured MgH₂, where (110) parallel to the substrate. (101) is also present in this texture as a minor component. Formation of the textured hydride in isochronal loading was discussed within the context of the lattice mismatch in a Mg to MgH₂ transformation.     

Combining grazing incidence X-ray diffraction and X-ray reflectivity for the evaluation of the structural evolution of HfO2 thin films with annealing

Metal oxides of high dielectric constant are candidates to substitute SiO₂ as gate dielectric in complementary metal-oxide-semiconductor technology. In this contribution we present the application of X-ray techniques to the study of thermal stability of 5-, 10- and 20-nm-thick HfO₂ deposited by atomic layer deposition. Grazing incidence X-ray diffraction spectra are refined by Rietveld analysis. X-Ray reflectivity (XRR) data are fitted in order to evaluate the thickness, the surface roughness and the interface stability upon thermal processing between 300 and 1050 °C. The electronic density values obtained from the scattering coefficients of the crystallographic phase are compared to the values related to the critical angle of the XRR spectra. The thickness and the electronic density of the as grown layer are slightly affected by the thermal treatment. The surface and interfacial roughness are also very stable. The crystallographic ordering evolves starting from the amorphous structure of the as-deposited film towards the polycrystalline monoclinic HfO₂ films obtained by annealing at high temperatures. The results are discussed and compared to plan view and cross-sectional transmission electron microscopy images.     

Quantitative X-ray diffraction from thin films

We have developed a general procedure for quantitative structural refinement of superlattices and thin films. To analyze a wide variety of thin films, we developed the mathematical formalism necessary to include all types of randomness and changes in structural parameters. This formalism was used to implement a non-linear-fitting algorithm which is able to fit quantitatively the entire X-ray diffraction profile. The results from the structural refinement were compared to results obtained independently from other methods such as: Extended X-ray Absorption Fine Structure (EXAFS), X-ray Photoelectron Diffraction (XPD), chemical analysis, artificially roughened superlattices, etc. We also describe the application of this method to the refinement of thin film structures of high temperature superconductors where no independent information is available.     

Investigation of buried quantum dots using grazing incidence X-ray diffraction

Self-organized, buried InAs quantum dots covered by an AlAs diffusion barrier were investigated under UHV conditions using grazing incidence X-ray diffraction. The experimental data is compared to the simulated results obtained by Finite Element Method and Distorted Wave Born Approximation. We have found that the simulated data could be compared to the experimental one only after convolution by the resolution element which can be estimated from the experiment. By adjusting the simulation parameters we were able to find good agreement between the simulated and the measured data.     

Elastic-strain tensor and inhomogeneous strain in thin films by X-ray diffraction

Elastic residual and inhomogeneous defect-related strains are very important parameters when considering thin-film and microelectronics device properties and operation. In regard to the residual strain/stress modeling, we describe a novel approach to model diffraction line shifts caused by elastic residual or applied stresses in textured polycrystals. The model yields the complete texture-weighted strain and stress tensors as a function of crystallite orientations, the so-called weighted strain orientation distribution function. In the second part, we present an extension to the phenomenological thermodynamic theory for ferroelectrics. It includes the contribution of both residual-elastic lattice-misfit strain and inhomogeneous strain caused by lattice defects. The model yields correction terms for dielectric and ferroelectric quantities in terms of both elastic misfit strain and defect-related strain that was successfully applied to the pristine, W and Mn 1% doped Ba_0.6Sr_0.4TiO₃ epitaxial thin films grown on the LaAlO₃ substrate.     

Diffusion of copper in thin TiN films

The diffusivity of copper in thin TiN layers was determined in specimens prepared by r.f. sputtering a copper (80 nm) layer onto a TiN (200 nm) layer on sapphire and silicon substrates. Specimens were isothermally heat treated at 608, 635 and 700 °C at pressures lower than 2 × 10^?6 Pa; they were compositionally analyzed by Rutherford backscattering spectroscopy and Auger sputter profiling; and they were microstructurally characterized by transmission electron microscopy and electron diffraction. The diffusivity D = 9 × 10⁷cm²s^?1exp(?427 kJmol^?1/RT) from 608 to 700 °C. The mechanisms of copper diffusion were not bulk processes, but they were probably processes involving primarily grain boundaries in the TiN. This very low diffusivity at these temperatures makes TiN/Cu an excellent candidate for a high temperature metallization for silicon solar concentrator cells.     

Fabrication of highly c-axis textured ZnO thin films piezoelectric transducers by RF sputtering

The influence of fabrication parameters on ZnO film properties has been analyzed through conducting several experiment processes to develop an appropriate deposition condition for obtaining highly c-axis textured films. A transducer with the structure of Al/ZnO/Al/Si was fabricated at low deposition rate and under a temperature of 380 °C in a mixture of gases Ar:O₂ = 1:3, and RF power of 178 W. Pt/Ti was employed as the bottom electrode of the transducer fabricated in a suitable substrate temperature, which starts increasing at 380 °C with an increment of 20 °C for each 2 h stage of the deposition. Highly c-axis textured ZnO films have been successfully deposited on Pt/Ti/SiO₂/Si substrate under feasible conditions, including RF power of 178 W, substrate temperature of 380 °C, deposition pressure of 1.3 Pa and Ar:O₂ gas flow ratio of 50%. These conditions have been proposed and confirmed through investigating the influences of the sputtering parameters, such as substrate temperature, RF power and Ar:O₂ gas flow ratio, on the properties of ZnO films.     

Some observations on thin β-tin films by electron diffraction

Forbidden “110-type” reflections are present on some patterns of tin single-crystal films. Their intensities may vary in a large range and these reflections do not appear with polycrystalline samples. The other forbidden “002-type” reflections which were observed by other authors and ourselves are probably due to secondary elastic scattering, but the kind of “forbidden” spots studied here can be explained by dynamic interactions.     

Stress tuning in AIN thin films

Aluminium nitride films were deposited on fused silica by reactive dc magnetron sputtering from an Al-target in an Ar/N₂ atmosphere. In-situ measurements during deposition provided data concerning mechanical stresses inherent to the growing thin films. By variation of both the gas composition (Ar, N₂) and the total gas flow in the vacuum chamber, the occuring intrinsic stresses could be shifted in magnitude and direction. Stress values of the AIN films ranged from ?0.9 GPa (compressive) to +1.2 GPa (tensile) when the Ar/N₂ ratio was varied between 3:1 and 1:3 for the different total gas flows of 50 sccm, 100 sccm, and 200 sccm (corresponding to total gas pressures of approximately 2 × 10^?1 Pa, 4 × 10^?1 Pa, and 8 × 10^?1 Pa respectively). Investigations of optical and structural film properties were carried out and the results were related to the observed film stress.     

In-situ energy-dispersive X-ray diffraction of metal sulfide assisted crystallization of strongly (001) textured photoactive tungsten disulfide thin films

Highly (001) textured tungsten disulphide (WS₂) thin films were grown by rapid metal (Ni, Pd) sulfide assisted crystallization of amorphous reactively sputtered sulfur-rich tungsten sulfide (WS_3 + x) and by metal sulfide assisted sulfurization of tungsten metal films. The rapid crystallization was monitored by real-time in-situ energy dispersive X-ray diffraction (EDXRD). Provided that a thin nickel or palladium film was deposited prior to the deposition of WS_3 + x or W, the films crystallized very fast (about 20 nm/s) at temperatures above the metal sulfide eutectic temperature. After crystallization, isolated MeS_x crystallites are located on the surface of the WS₂ layer, which was proved by scanning electron microscopy. The metal sulfide assisted crystallized WS₂ layers exhibit a pronounced (001) orientation with large crystallites up to 2 µm. The in-situ EDXRD analysis revealed distinct differences of the two crystallization routes from tungsten and from amorphous, sulfur-rich WS_3 + x precursors, respectively. The crystallized WS₂ films showed photoactivity. Combined with the high absorption coefficient of 10⁵ cm^− 1 and a indirect band gap of 1.8 eV these properties make such films suitable for absorber layers in thin film solar cells.     

Nanocrystalline copper selenide thin films by chemical spray pyrolysis

Thin films of copper selenide were deposited onto amorphous glass substrates at various substrate temperatures by computerized spray pyrolysis technique. The as deposited copper selenide thin films were used to study a wide range of characteristics including structural, surface morphological, optical and electrical, Hall Effect and thermo-electrical properties. X-ray diffraction study reveals that the films are polycrystalline in nature with hexagonal (mineral klockmannite) crystal structure irrespective of the substrate temperature. The crystalline size is found to be in the range of 23–28 nm. The SEM study reveals that the grains are uniform with uneven spherically shaped and spread over the entire surface of the substrates. EDAX analysis confirmed the nearly stoichiometric deposition of the film at 350 °C. The direct band gap values are found to be in the range 2.29–2.36 eV depending on the substrate temperature. The Hall Effect study reveals that the films exhibit p-type conductivity. The values of carrier concentration and mobility for the film are found to be 5.02 × 10¹⁷ cm^?3 and 5.19 × 10^?3 cm² V^?1 s^?1; respectively for film deposited at 350 °C.     

Characterisation of ferroelectric thin films by X-ray diffraction and electron microscopy

In this work an example of the application of glancing angle X-ray diffraction (GAD), scanning (SEM) and transmission (TEM) electron microscopy techniques, on the study of the phase distribution and microstructure of PbZr_0.52Ti_0.48O₃ films deposited by two different methods, sol–gel and laser ablation, on different substrates, is reported. The investigations performed on the samples allowed us to obtain information on the phase distribution inside the films, on the diffusion processes occurred during the crystallisation treatments, on the presence of ferroelectric domains and on the structure of the columnar grains. The results showed that the electrical behaviour could be correlated to the microstructure of the films suggesting the best deposition conditions.