Nanoindentation experiments on some amorphous hydrogenated carbon (a-C:H) thin films on silicon

Ultra-low-load indentation (nanoindentation) experiments have been used to investigate the load-displacement characteristics of two types of hydrogenated carbon films (a hard and a soft version 230 and 210 nm thick, respectively) deposited from methane on to (1 0 0) single-crystal silicon wafers by a radio frequency plasma-assisted chemical vapour deposition process. Further, the technique was used to explore the changes in the properties of the films with heat treatment in vacuum at temperatures of up to 650°C. In all cases, the elastic and plastic properties of the films were compared at indentation loads in the range 0–60 mN, the higher loads causing indentor displacements greater than the thickness of the films. For the harder, stiffer coating, penetration resistance was found to decrease with increasing indenter displacement, reflecting the greater load-carrying role taken by the softer silicon with increasing applied load. However, for the softer coating, penetration resistance generally increased with displacement, perhaps reflecting progressive compaction of the coating in addition to the increasing role of the silicon. In both cases, heat treatment severely degraded the mechanical properties of the films due to thermally induced chemical changes and, in the case of the hard coating, relaxation of residual stresses. Scanning electron microscopy of both nanoindentations and low-load microhardness indentations clearly reveals the deformation mechanisms associated with contact stresses to include flow and fracture of the film and interfacial decohesion.     

Investigation into the growth and electromechanical properties of Pb(Mg1/3Nb2/3)O3 thin films

Pulsed laser deposition (PLD) has been used to fabricate relaxor thin films and thin film capacitors based on the Pb(Mg_1/3Nb_2/3)O₃ system. Best capacitor structures show dielectric constants (_r) of 1000 and losses (tan ) 0.02 at 1 kHz at 300 K. Electromechanical investigations show that tensile longitudinal strains of up to 0.2% can be achieved in these films.     

Adsorption of polyvinylpyrrolidone (PVP) and its effect on the consolidation of suspensions of nanocrystalline CeO2 particles

CeO₂ particles with an average size of 9 nm were synthesized under hydrothermal conditions. The adsorption of polyvinylpyrrolidone (PVP) on to the particle surfaces was measured in aqueous suspensions in the pH range of 3.7 to 11.5. The amount of adsorbed PVP decreased significantly with increasing pH value. For suspensions prepared at a pH value of 3.7, complete adsorption occurred for 2.5 wt% of PVP added to the suspension. Further additions of PVP produced a gradual increase in the adsorption until a limiting value was reached when the total amount of PVP added to the suspension was 10 wt%. At this PVP concentration, 6 wt% of the PVP was adsorbed and 4 wt% remained free in solution. The effect of the adsorbed PVP on the microstructural homogeneity of films deposited by spin coating of suspensions was investigated. With no addition of PVP, crack-like voids were prevalent in the dried and sintered films. Crack-free films were obtained from suspensions containing 10 wt% of PVP. Higher PVP additions (25 wt%) produced an increase in the viscosity of the suspension but no observable change in the microstructural homogeneity of the films. The use of adsorbed polymers for steric stabilization coupled with data from the adsorption isotherms is shown to provide a rational approach to the deposition of homogeneous films from suspensions of nanocrystalline particles.     

Deformations in KCI single crystals by spherical and pyramidal indentor

An indentation test, using a steel ball and a diamond quadrangular pyramid indentor, were carried out on the {100} cleaved crystal face of KCI single crystals. The dislocation structures and strain hardening around an indent were examined. In addition, macroscopic deformations such as pile-up and the shape of the indent were investigated. It became clear that — because of the anisotropy of these crystals, plastic deformations, the crystals' area and the strain hardening around the indents — are larger in the 110 direction than in the 100 direction, and a regular correspondence relation was confirmed, experimentally, between hardness and dislocation density.     

Synthesis and characterization of a high-temperature oxide lubricant

PbMoO₄ is a potential solid lubricant for use at elevated temperatures in oxidizing environments. Pulsed laser deposition (PLD) was utilized to grow thin films of this material because it allows good control over film chemistry and crystallinity. Films were grown at different substrate temperatures in vacuum and in partial pressures of oxygen. The chemistry and crystallinity of the films were evaluated using X-ray photoelectron spectroscopy, Raman spectroscopy, and glancing angle X-ray diffraction. Friction coefficients and wear lives were measured using a ball-on-flat tribometer at room temperature and 700C. Films deposited in vacuum, at room temperature and at 300C, were oxygen deficient. To adjust chemistry and crystallinity, films were grown in a partial pressure of oxygen (i.e. 6.7×10^–1 Pa). Stoichiometric, crystalline films of PbMoO₄ were produced when films were grown at 300C in this environment. PbMoO₄ films were lubricious ( = 0.35) and long lived at 700C, but at room temperature had high friction and failed quickly. The properties of the films grown at the different conditions are discussed.     

Nucleation control of diamond synthesized by microwave plasma CVD on cemented carbide substrate

Diamond was coated on to cemented carbide substrate by microwave plasma CVD, in which nucleation control of diamond crystals was investigated under constant deposition conditions; total pressure 30 torr, CH₄ flow rate 1 ml min^–1, H₂ flow rate 199 ml min^–1 and microwave power 550 W. Nucleation tends to occur selectively on the edge part of WC grains of the cemented carbide substrate with coarse WC grain size of about 1 m, where the nucleation density was 9×10⁶ cm^–2. The density increased to about 5×10⁷ cm^–2 when using a finegrained substrate (WC grain size 0.5 m). A considerably enhanced nucleation was observed by introducing a number of fine microflaws on to the substrate surface. Microflawing treatment with diamond fine powder (grain size 0–1/4 m) suspended in an ultrasonic cleaner bath was effective for increasing the diamond nucleation density up to 5×10⁸ cm^–2. The grain size of grown diamond crystals decreased with increasing microflawing time.     

Electrostatic Spray Deposition of Perovskite-Type Oxides Thin Films with Porous Microstructure

The deposition of perovskite-type oxides thin films [La_0.8Sr_0.2MnO₃ and La_1–xSr_xCo_1–yFe_yO₃ (0 x 0.4 and 0 y 1)] was investigated using the electrostatic spray deposition (ESD) technique. Lanthanum nitrate, strontium chloride and manganese nitrate, or cobalt nitrate and iron nitrate were dissolved into a mixture of 33 vol% ethanol and 67 vol% butyl carbitol, which was used as precursor solution. The effect of process parameters, such as deposition temperature, deposition time and concentration of precursor solution, on the surface morphology and microstructure of thin films were examined with scanning electron microscope (SEM). The deposited La_0.8Sr_0.2MnO₃ and La_1–xSr_xCo_1–yFe_yO₃ thin films were amorphous at the used deposition temperature (573K). Subsequently, the samples were heated at 1173 K for 2 h and were studied using X-ray diffraction (XRD). As the result, the crystal structure of the samples transformed to the desired perovskite phase. The chemical analysis of the thin films was investigated using energy dispersion X-ray (EDX) analysis. The observed chemical compositions of the samples were in a fair agreement with the ones of the starting solutions.     

Illumination-induced surface charges on thin diamond films at different wavelengths

Contact angle studies of pure water droplets were carried out on thin diamond films. The films were deposited on a fresh Si 111 wafer by plasma assisted chemical vapour deposition (PACVD) and confirmed to be diamond by Raman spectroscopy and scanning electron microscopy. Advancing and receding contact angles were measured as a function of droplet volume by using different incident wavelengths: red, green and violet. Large differences in the contact angles were observed, depending on the wavelength of the incident light. These differences are usually related to the existence of illumination-induced surface charges or electromagnetically active inhomogeneities in the diamond films. The results show that this technique is sufficiently sensitive to correlate changes in the contact angle with changes in the wavelength used.     

Deformation in spinel

Stoichiometric MgAl₂O₄ spinel was deformed in compression at temperatures from 1790 to 1895 C and the dislocation structures analysed by transmission electron microscopy. {1 1 1}1 1 0 slip was observed on both the primary and cross-slip systems, and there was much secondary slip as well; all six 1 1 0 Burgers vectors were present in electron micrographs. This secondary slip leads to very high work-hardening rates, approximately/70 at 1790 C, where is the shear modulus. Since it is known that deformation in nonstoichiometric (alumina-rich) spinel crystals occurs by {1 1 0}1 1 0 slip, the electrostatic and geometric aspects of 1/4 110 dislocations moving on {1 1 1} and {1 1 0} planes are considered in some detail. It is porposed that the octahedral cation vacancies present in non-stoichiometric spinel diffuse to dislocations during deformation and thus favour {1 1 0} slip.     

Dislocations and stacking fault energy in silicon ditelluride

The stacking fault energy in silicon ditelluride single crystals has been determined for different dislocation configurations observed by electron microscopy. The configurations studied are dislocation ribbons and dislocation nodes, and the ratio of the stacking fault energy to the shear modulus is estimated as / = 1.6×10^–11 cm. Some common features observed in electron microscopy are also discussed in terms of dislocation networks of extended and contracted nodes and symmetrical or asymmetrical three-fold ribbons, as well as various dislocation interactions.     

Sputtered Films of PdMn for Thermometry and Bolometry

Measurements of the magnetic sensitivity of thin sputtered films of PdMn alloy demonstrate the viability of this material for high resolution thermometry. The thinnest films (thickness 1.0 m) show significant domain scale noise below the Curie Temperature, T_c, while thicker films (thickness 10 m) show reliable non-hysteretic behavior throughout the temperature range of interest. The thin films show the effects of demagnetization with the field perpendicular to the surface, but a fine screen in this orientation shows good response with no evidence of saturation and a manageable degree of demagnetization.     

On deformation twins and twin-related lamellae in TiAl

The crystal orientation relationships and atomic arrangements across deformation twin planes and twin-related lamellar interfaces in 1 1 0 projection directions in TiAl are examined crystallographically. Atomic arrangements across the true-twin plane and the true-twin-related lamellar interface are shown to be identical, while the atomic arrangements across the pseudo-twin plane and the pseudo-twin-related lamellar interface are quite different. Atom locations at the true-twin plane and the true-twin-related lamellar interface do not violate the atomic order in both crystals while those at the pseudo-twin plane or the pseudo-twin-related lamellar interface are shown to violate the atomic order. 1 1 0 zone diffraction pattern simulations show that the true-twins and the true-twin-related lamellae cannot be distinguished using the 1 1 0 zone diffraction patterns. Not every 1 1 0 zone diffraction pattern can be utilized to distinguish between any two different twin relationships. The true-twin and the pseudo-twin can only be distinguished using 1 0 1] zone diffraction patterns, while true-twin-related and pseudo-twin-related lamellae are distinguishable by only using 1 1 0] zone diffraction patterns.     

Evidence of hexagonal diamond in plasma-deposited carbon films

Hexagonal diamond grains of 30 nm diameter together with graphite and SiC are seen in predominantly amorphous carbon films deposited at low temperature on Si substrates from a CH₄ plasma vapour source. The different crystalline phases are identified by grazing-angle X-ray diffraction which allows for substrate rotation and tilting to enable the 2 peaks to be correlated with the angular displacements of specific planes. Electron energy-loss spectroscopy shows the chemical composition of the films to be predominantly carbon with traces of oxygen. Raman spectroscopy shows the peaks to be associated with amorphous carbon and graphite, together with a peak at 1170 cm^–1 which is attributed to microcrystalline hexagonal diamond.     

Time-dependent structural modifications in tin oxide thin films under environmental conditions

Time-dependent crystalline structure and surface morphology of transparent conducting thin films of undoped tin oxide have been studied under environmental conditions by X-ray diffractometry and scanning electron microscopy. Tin oxide thin films were produced, via chemical vapour deposition, in three batches; two batches with single deposition at substrate temperatures of 400 C and 560 C, respectively, and the third batch produced by double deposition firstly at 560 C and then at 400 C substrate temperature. It is found that the crystallinity of the as-grown tin oxide thin films produced by single deposition degrades with shelf-life period and an amorphous phase is developed under environmental conditions. In the tin oxide films produced by double deposition there was no degradation in the crystallinity of the films, but a change in the preferential crystallite orientation was observed. The implications are discussed.     

On the mechanism of feathery crystallisation of aluminium

The growth of twinned crystals of aluminium on solidification is discussed with reference to the structure of the growing tip. It is shown that one must differentiate between two types of 112 growth directions in the twin boundary. Normally, all the tips grow in the same type of 112 growth direction and this particular type may give the tip a favourable shape, possibly by producing a sharp edge. If a tip is growing in a less favourable 112 direction, the favourable type can be established by the twins changing sides. This is observed to occur regularly in the continuous casting method according to Hunter. The re-entrant edge mechanism is not supported by the present results.     

Transmission electron microscopy of dislocations in nickel oxide single crystals

The dislocation structure of NiO single crystals used in diffusion studies has been examined by transmission electron microscopy. The crystals contain dislocations (the dislocation density being 4 × 10¹² m^–2) that are probably a result of the growth process. The dislocations have a Burgers vector ofa/2 110. On annealing at temperatures above 1400° C the density is reduced to 7 × 10¹¹ m^–2, most of the dislocations forming low angle boundary arrays. The dislocation density was found to be much greater in the vicinity (within 1m) of a mechanically polished surface.     

Preparation and characterization of Ce-doped BaTiO3 thin films by pulsed laser deposition

Thin films of BaTiO₃ doped with 5.5 mol%CeO₂ have been deposited on Pt/Si substrate by pulsed laser deposition. These films crystallize on the tetragonal BaTiO₃ structure without any preferential orientation. Ce-doped BaTiO₃ films deposited by PLD at 675°C in 30 Pa ambient oxygen exhibits a smooth surface: mean surface roughness (Rms) of 48 nm, mean size of grain of 40 Å, average size of aggregates of 315 nm. Thin films as prepared presented good dielectric characteristics: dielectric constant and dielectrics loss (tan ) at a frequency of 1 KHz were 220 and 0.2, respectively. The temperature dependence of dielectric constant exhibited a diffuse ferroelectric to paraelectric phase transition at about 0–10°C. The ferroelectric nature of Ce-doped BaTiO₃ film was confirmed by the hysteresis of the C-V curves.     

Formation of large diamond crystals in oxyacetylene flame chemical vapour deposition

Diamond coatings were deposited on diamond-polished molybdenum substrates from a premixed oxyacetylene flame for a long time (up to 4 h) at substrate temperatures between 700 and 950°C, acetylene-to-oxygen ratios 1.02–1.07 and total flow rates between 230 and 310 standard Lh^–1. The coatings contain, in addition to the densely populated octahedral crystals making a continuous layer of determined thickness, a number of individual large cuboctahedral crystals sticking out far above the layer. A large cuboctahedral crystal is formed from an octahedral one when the latter reaches a certain height at which its temperature becomes sufficiently high for the octahedron-to-cuboctahedron conversion to take place. This conversion was found to occur by a flattening of the octahedron pyramid tip whereby a {100} face perpendicular to the growth direction is formed. Both the height of the crystal and size of the {100} face increase upon further deposition, reaching up to 230 m above the octahedral crystals layer and up to about 200 m, respectively. The large crystals have smooth {100} faces, but otherwise often have an irregular shape which may be due to a high temperature favouring deposition of non-diamond carbon.     

Texture study of two molybdenum shaped charge liners by neutron diffraction

The textures of two different conical shaped liners, fabricated by the same forging processes from arc-cast and powder-sintered ingots, were investigated by using neutron-diffraction measurements and three-dimensional orientation-distribution-function (ODF) analysis. The major textures of both liners could be described by the (1 1 1) uv w and (1 0 0) u v w type. The two liners had essentially identical texture at the 8 cm position (measured from the base of the cone) with strong sheet-type texture components, i.e. (1 1 1) ¯1 0 1, (1 1 1) ¯1 1 0 and (1 0 0) 0 1 1. However, the dominant textures at the 3 cm positions were 1 1 1 and 1 0 0 fibre textures with the fibre axes oriented parallel to the normal direction in both liners. A strong cube texture was observed at the 3 cm position of the arc-cast liner but it was not observed for the powder-sintered liner. The arc-cast liner had a generally higher degree of texture than the powder-sintered liner.     

Optical investigation of thin films of liquid–crystalline lutetium bisphthalocyanine

Thin films of bis[4,5,4,5,4,5,4,5]-octakis(hexylthiophthalocyanine) of lutetium(III) were prepared by spin coating at different speeds in the range of 2000–6000 rpm. The films undergo phase transition on heat treatment at temperatures above 120 °C and the formation of a mesophase. The Q-bands in the visible absorption spectra of the films are broader and become red shifted compared to ones obtained for molecules in chloroform solution. Heat treatment produces molecular ordering, which is believed to be due to the edge-to-edge interaction between neighboring Pc moieties. Reduced film thickness and changes in optical constants are also attributed to thermally induced molecular reorganization corresponding to the liquid crystalline phase. AFM and polarized microscopy images are consistent with the phase transformations.