Electron energy-loss spectroscopy study of thin film hafnium aluminates for novel gate dielectrics

We have used conventional high‐resolution transmission electron microscopy and electron energy‐loss spectroscopy (EELS) in scanning transmission electron microscopy to investigate the microstructure and electronic structure of hafnia‐based thin films doped with small amounts (6.8 at.%) of Al grown on (001) Si. The as‐deposited film is amorphous with a very thin (～0.5 nm) interfacial SiO_x layer. The film partially crystallizes after annealing at 700 °C and the interfacial SiO₂‐like layer increases in thickness by oxygen diffusion through the Hf‐aluminate layer and oxidation of the silicon substrate. Oxygen K‐edge EELS fine‐structures are analysed for both films and interpreted in the context of the films’ microstructure. We also discuss valence electron energy‐loss spectra of these ultrathin films.     

Structural analyses of Nd-doped CeO2 thin films deposited by pulsed laser deposition

CeO₂ thin films doped with neodymium oxides for application to gas sensors have been elaborated by the pulsed laser deposition technique. The films were deposited on orientated Si (100) substrates with variable deposition times (t = 90, 180 and 360 s) and molar fractions of Nd₂O₃ (0, 6.5, 15, 21.5 and 27 at.%). The resulting Nd–CeO₂ thin films were characterized by means of X‐ray diffraction analysis, scanning electron microscopy and transmission electron microscopy equipped with EDS (Energy Dispersive Spectrometer) microanalysis. From X‐ray diffraction analyses, it is clearly established that the texture is modified by Nd additions. The preferred (111) orientations of the CeO₂ crystals change into the (200) orientation. The morphology of the CeO₂ grains changes from triangles, for pure CeO₂ thin films, to spherical grains for Nd‐doped films. In addition, cell parameter analyses from X‐ray diffraction data show that a partial chemical substitution of Ce by Nd should occur in the face‐centred cubic lattice of ceria: this should give rise to Ce_1‐xNd_xO_2?z phases with oxygen non‐stoichiometry.     

Influence of Mg doping on the morphology and optical properties of ZnO films for enhanced H2 sensing

Highly oriented ZnO and Mg doped ZnO thin films were fabricated on Al₂O₃ substrate by sputtering at room temperature. The effect of Mg doping on the structural, optical, and morphological properties of ZnO film was investigated. The intensity of (002) peak in X‐ray diffraction measurements revealed the influence of Mg doping on the crystallinity and orientation of ZnO film. Photoluminescence (PL) results show that the Ultraviolet (UV) emission peak was shifted to lower wavelength side for Mg:ZnO film indicating the possibility for quantum confinement. UV–vis–NIR optical absorption revealed an improvement in optical transmittance from 70 to 85%, and corresponding optical band gap from 3.25 to 3.54 eV. Atomic force microscope (AFM) images revealed the nano‐size particulate microstructure of the films. The surface topography of Mg doped ZnO film confirmed decreased grain size with large surface roughness and increased surface area, favorable for sensing. Pure ZnO and Mg doped ZnO film were used as active layer and tested for its sensing performance to hydrogen. Compared to undoped ZnO, 22 at.% Mg doped ZnO film showed much higher sensor response to H₂ at a concentration as low as 200 ppm and at a lower operating temperature of 180°C. A linear sensor response was observed for H₂ concentration in the range of 100–500 ppm. Microsc. Res. Tech. 76:1118–1124, 2013. © 2013 Wiley Periodicals, Inc.     

Thermal Treatment Effects on Microstructure and Mechanical Properties of TiAlN Thin Films

Effects of thermal treatment on the modification of microstructure and mechanical properties of Ti_1–x Al _x N thin films (x=0.4–0.7) were investigated. It was found that the Al content plays a major role on the thermal stability and change of hardness following to heating under vacuum. The samples with the Al content x < 0.6 showed a reduction of hardness after annealing for 30 min at 1000 °C. The hardness difference between the as deposited and thermally treated samples decreased when the Al content of the films was increased. In contrast, the Al-rich samples (x > 0.6) showed a nanocomposite structure and their hardness increased after thermal treatment. Microstructural analysis by X-ray diffraction and transmission electron microscopy (TEM) revealed that the reduction of hardness in single-phase coatings is due to partial relaxation of compressive stress while the increase of hardness in the nanocomposite coatings arises from coherency stresses developed during thermal treatment.     

Growth and properties analysis of metal-organic chemical vapor deposited MgxZn1-xO films on C-Al2O3 substrates

Mg_xZn_1−xO (0 〈 x ⩽ 0.12) thin films with the wurtzite structure have been successfully grown on c-Al₂O₃ substrates by metal-organic chemical vapor deposition (MOCVD). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), photoluminescence (PL) spectrometry, and transmission measurements are performed to study the characteristics of Mg _x Zn_1−x O thin films. Results show that with increasing Mg content, the diffraction peak of Mg _x Zn_1−x O thin films shifts towards a higher diffraction angle (the biggest shift is 0.22°), and the full width at half maximum (FWHM) of the diffraction peak is broadened. Meanwhile, a blue-shift occurs at the near-band-edge (NBE) emission peak and the largest blue-shift of the band gap of the Mg _x Zn_1−x O films is 113 meV with Mg content x50.12. Therefore, the energy band gap of the Mg _x Zn_1−x O films is determined by Mg content in the thin films and the energy band gap increases with an increase of Mg content.     

Modelling and experimental investigations of thin filmsof Mg phosphorus‐doped tungsten bronzes obtainedby ultrasonic spray pyrolysis

In this study, the synthesis of thin films of Mg phosphorus doped tungsten bronzes (MgPTB; MgHPW₁₂O₄₀·29H₂O) by the self‐assembly of nano‐structured particles of MgPTB obtained using the ultrasonic spray pyrolysis method was investigated. As the precursor, MgPTB, prepared by the ionic exchange method, was used. Nano‐structured particles of MgPTB were obtained using the ultrasonic spray pyrolysis method. The nano‐structure of the particles used as the building blocks in the MgPTB thin film were investigated experimentally and theoretically, applying the model given in this article. The obtained data for the mean particle size and their size distribution show a high degree of agreement. These previously tailored particles used for the preparation of thin films during the next synthesis step, by their self‐assembly over slow deposition on a silica glass substrate, show how it is possible to create thin MgPTB films under advance projected conditions of the applied physical fields with a fully determined nanostructure of their building block particles, with a relatively small roughness and unique physical properties.     

Morphological variations of Mn‐doped ZnO dilute magnetic semiconductors thin films grown by succesive ionic layer by adsorption reaction method

Transparent conducting Mn‐doped ZnO thin films have been prepared by successive ionic layer by adsorption reaction (SILAR) method. The deposition conditions have been optimized based on their structure and on the formation of smoothness, adherence, and stoichiometry. The results of the studies by X‐ray diffraction, scanning electron microscope (SEM), reveal the varieties of structural and morphological modifications feasible with SILAR method. The X‐ray diffraction patterns confirm that the ZnO:Mn has wurtzite structure. The interesting morphological variations with dopant concentration are observed and discussed. The films' quality is comparable with those grown with physical methods and is suitable for spintronic applications. Microsc. Res. Tech. 76:751–755, 2013. © 2013 Wiley Periodicals, Inc.     

Structure and morphology of Mg–Al–Fe‐mixed oxides derivedfrom layered double hydroxides

The influences of the nature and the extent of M(III) ion substitution on the structure, morphology and surface properties of layered double hydroxides, LDHs [Mg_1?x M(III)_x(OH)₂](CO₃)_x/n·mH₂O, M(III) being Al or/and Fe and x= M(III)/[(Mg+M(III)], and derived mixed oxides were investigated. Three series: Mg?Al, Mg?Al?Fe and Mg?Fe were synthesized using low supersaturation co‐precipitation method at constant pH, with different Mg : Al : Fe ratio and x in the wide range from 0.15 to 0.7 in order to obtain complex, multi‐phase systems with disordered structure, developed surface area, acid–base and redox properties favourable for catalytic application. The morphology of LDHs and their derived mixed oxides did not change considerably although pronounced changes in structural and surface properties occur by thermal decomposition. The increase in Al amount, as well as the deviation of M(III) content from the optimal range for the single LDH phase synthesis, causes the formation of smaller particles and decrease of mixed oxide crystallite size. The nature and amount of M(III) influence the development of surface area, after thermal treatment, depending mainly on the presence of smaller mesopores, not visible by scanning electron microscope. Although the particle size has no considerable influence on the value of the surface area, it was observed that the samples with smaller particles (Mg–Al and Mg–Al–Fe series) have also higher surface area compared with the samples with larger particles (Mg–Fe series).     

Electron energy-loss near edge structure (ELNES) of InGaN quantum wells

Lasers and light‐emitting diodes (LEDs) that emit in the blue to green region are often based on In_xGa_1–xN quantum well structures. Ionization edges in the electron energy‐loss spectrum contain fine structures (called the energy‐loss near edge structure (ELNES)) and provide information about the electronic structure. In this paper we compare the experimental and calculated ELNES for the N‐K ionization edge of In_xGa_1–xN quantum wells. When the effects of the core‐hole are included in the calculations, agreement between experimental and calculated spectra is very good. Strain has been shown to accentuate the effects of In on the ELNES and moves the ionization edge onset down in energy, relative to the other features. These results suggest that ELNES may provide an alternative method to lattice imaging to determine the presence of strain in this system.     

Transmission electron microscopy characterization of the erbium silicide formation process using a Pt/Er stack on a silicon-on-insulator substrate

Very thin erbium silicide layers have been used as source and drain contacts to n‐type Si in low Schottky barrier MOSFETs on silicon‐on‐insulator substrates. Erbium silicide is formed by a solid‐state reaction between the metal and silicon during annealing. The influence of annealing temperature (450 °C, 525 °C and 600 °C) on the formation of an erbium silicide layer in the Pt/Er/Si/SiO₂/Si structure was analysed by means of cross‐sectional transmission electron microscopy. The Si grains/interlayer formed at the interface and the presence of Si grains within the Er‐related layer constitute proof that Si reacts with Er in the presence of a Pt top layer in the temperature range 450–600 °C. The process of silicide formation in the Pt/Er/Si structure differs from that in the Er/Si structure. At 600 °C, the Pt top layer vanishes and a (Pt–Er)Si_x system is formed.     

Characterization of nitride thin films by electron backscatter diffraction

Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light‐emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality. In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1° towards [101 0]_GaN), where the tilt is due to the inclination of the sapphire substrate (cut off‐axis by 10° from (0001)_sapphire towards (101 0)_sapphire). We compare EBSD patterns obtained from As‐doped GaN films grown by plasma‐assisted molecular beam epitaxy (PA‐MBE) with low and high As₄ flux, respectively. Higher As₄ flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.     

A tribological study of kinetically influenced ultrathin Au and Cu metal overlayers grown on dendrimer mediated Si

Evidence is presented here for deposition kinetic energy influences on the wear properties of Au and Cu films deposited by evaporation and sputtering on clean and poly(amidoamine) (PAMAM) dendrimer modified SiO _x substrates. Ramped load nanoscratch tests show increased resistance to wear in the presence of the dendrimer monolayer. Nanoscratch profiles indicate that the critical load to failure (scratch bearing capacity) is increased in the presence of a dendrimer interlayer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis of the wear tracks show that following film failure plowing is the predominant mechanism of wear for sputtered or evaporatively deposited Au. No obvious changes in the wear properties (a pure cutting mechanism) of Cu thin films are observed upon changing the kinetic energy of the incoming metal.     

Investigation on Structural,Morphological, Optical and Ammonia Sensing Properties Indium Doped Nano Crystalline ZnO Thin Films Synthesized by Spray Pyrolysis Technique

In the present work, nanostructured In doped ZnO thin films were synthesized using spray pyrolysis technique with different molarity concentrations (0.001–0.004). X-ray diffraction patterns confirms the polycrystalline nature of the films with hexagonal structure. The crystallite size is going to be increases with increase in dopant concentration. The field-emission scanning electron micrograph of undoped ZnO exhibits spherical shaped particles with intergrain pores and the intergrain pores decreases with increases in indium concentration. The transmittance and band gap is going to be decreases with increase in indium concentration. The ammonia (NH₃) sensing properties of the undoped ZnO and In doped ZnO thin films were carried out at room temperature and the sensing responses of the samples towards NH₃ concentrations were reported.     

A Two-Chamber Facility for Depositing Thin Films in a Transverse High-Frequency Discharge

A facility for depositing thin films in a transverse high-frequency discharge is described. The facility consists of two (basic and auxiliary) chambers. The basic chamber is intended for sputtering targets and depositing a thin film on the prepared substrate. The auxiliary chamber contains a system of replaceable electrodes and serves for the preliminary processing of a substrate and the subsequent action on the thin film obtained. The device was tested in an oxygen discharge at pressures of 1.0 to 15 hPa and a deposited specific high-frequency power of up to 6.5 W/cm³ at a frequency of 10 MHz with targets of Pb(Zr _x Ti _{x– 1})O₃ ferroelectric ceramics and showed satisfactory results.     

Optical transition process in AgOx super-resolution near-field structure

A sandwiched 15 nm AgO_x thin film of the super‐resolution, near‐field optical disk was studied using a confocal Z‐scan system. Nonlinear optical properties of quartz glass/ZnS–SiO₂ (170 nm)/AgO_x (15 nm)/ZnS–SiO₂ (40 nm) were measured using a Q‐switch Nd : YAG pulse laser of wavelength 532 nm, pulse width 0.7 ns, and 15.79 kHz repetition rate. Transmittance and reflectance of the sandwiched AgO_x thin film show important optical responses at the focused position of Z‐scan. The dissociation processes of AgO_x, recombination of the silver and oxygen, and the resonance of the localized surface plasmon of the nano‐composites of the AgO_x thin film are correlated to transmittance and reflectance at the focused position of the Z‐scan for different input laser powers. An irreversible upper threshold intensity of 4.40 × 10⁶ mW cm^?2 at the focused position was found. A reversible working window of the focusing intensity between 1.86 × 10⁶ and 4.40 × 10⁶ mW cm^?2 was measured with sandwiched AgO_x thin film alone. The near‐field interactions of the AgO_x thin film and the recording layers of super‐resolution near‐field optical disk are also discussed.     

Atomic force microscopy imaging of polycrystalline CuInSe2 thin films

In this study, atomic force microscopy (AFM) imaging has been used to study the structural properties of polycrystalline CuInSe₂ films, which are widely used as absorber materials in thin film solar cell devices. This technique demonstrated an excellent capability for the reproducible imaging of these rough polycrystalline materials. AFM imaging in combination with statistical analysis revealed distinct differences in the structural properties (i.e. grain width and height distributions, root‐mean‐square (RMS) and peak to valley (R_(p–v)) roughness values) as a function of the specific growth technique used and the bulk composition of the films. In the case of Cu‐rich films, prepared by the H₂Se/Ar treatment of Cu/In/Cu alloys, rough surface structures were in general observed. Statistical analysis revealed two distinct distribution of grains in these samples (1.0–2.5 μm and 3–5.5 μm) with large RMS and R_(p–v) roughness values of 380 nm and 2.6 μm, respectively. In‐rich films were characterized by the presence of much smaller, roughly circular clusters with a significant reduction in both the width and height distributions as well as RMS and R_(p–v) roughness values. The most successful growth techniques, in terms of producing homogeneous and dense films, were in the cases of H₂Se/Ar treated metallic InSe/Cu/InSe alloys and the coevaporation of all materials to form CuInSe₂. Both these techniques produced absorber films with very narrow grain width and height distributions as well as small roughness values. It was possible to establish that high efficiency devices are associated with the use of absorber films with narrow width distributions between 0.5 and 2 μm and small RMS (> 300 nm) roughness values. These values are used as a figure of merit in our laboratories to evaluate the structural properties of our CuInSe₂ thin films.     

Microstructure, chemical and tribological investigations of Mo x W1−x S y co-sputtered composite films

Mo _x W_1−x S _y composite films were co-sputtered by the combination of MoS₂ and WS₂ targets, which were shown to have much superior tribological performance with lower and more stable friction coefficient, longer durability and higher bearing resistance than pure MoS₂ films in room temperature air with a relative humidity of 45–50%. Especially for the Mo_0.6W_0.4S_1.6 (40 at.% WS₂) composite film, an increase in durability of more than a one order of magnitude was reached. X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to investigate the relationship between the microstructure and the tribological performance of the films. The composite films are shown to have a densified structure and accordingly improved oxidation resistance and lubrication properties. Moreover, the composite films have a lattice expansion in the c direction, along with a reduced the friction within the films.     

Thermal stability of Ti and Pt nanowires manufactured by Ga+ focused ion beam

Ti and Pt nanowires have been produced by ultra high‐vacuum molecular beam epitaxy deposition of Ti thin films and focused ion beam (FIB) deposition of Pt thin films, followed by cross‐sectional FIB sputtering to form electron‐transparent nanowires. The thermal stability of the nanowires has been investigated by in situ thermal cycling in a transmission electron microscope. Epitaxial single crystal Ti nanowires on (0001)Al₂O₃ substrates are microstructurally stable up to 550–600 °C, above which limited dislocation motion is activated shortly before the Ti‐wires oxidize. The amorphous FIB‐deposited Pt wires are stable up to 580–650 °C where partial crystallization is observed in vacuum. Faceted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimizing contact area with the underlying wire. The particles are face‐centred cubic (fcc) Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.     

Tribological and mechanical properties of carbon nitride thin coating prepared by ion-beam-assisted deposition

Carbon nitride thin films may become good competitors for diamond-like carbon, due to their high hardness, high wear resistance, and low friction coefficient. At present, there are only a few studies of the effect of CN _x coating hardness and internal stress on its tribological properties, such as coating life and frictional behaviour. This work deals with tribological and mechanical properties of a carbon nitride coating prepared by ion-beam-assisted deposition (IBAD). Friction coefficients in the range of 0.10–0.12 were observed for the best CN _x coatings sliding against silicon nitride under ambient conditions. A nonlinear correlation between coating life and its internal stress and hardness was found.     

Water Adsorption on Lubricated a-CH x in Humid Environments

Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work a quartz crystal microbalance was used to measure the uptake of water on amorphous hydrogenated carbon (a-CH _x ) films at room temperature and pressures of water corresponding to relative humidities of 25%. These experiments have used a-CH _x films of varying thickness with and without lubricant. The lubricants used included Fomblin Z-03, Z-disoc, and Z-tetraol deposited on the surfaces of a-CH _x films of various thickness. The amount of water adsorbed on the unlubricated a-CH _x films is roughly independent of a-CH _x film thickness. The presence of the lubricant reduces the amount of adsorbed water; however, the amount of water adsorbed in the presence of a lubricant does not depend significantly on the type of lubricant. These observations imply that water is adsorbed on the surfaces of the lubricant or the a-CH _x film rather than being absorbed in their bulk.