H.L. Gaigher

Microstructures of electrodeposited CdS layers

Cadmium sulfide (CdS) thin films were electrodeposited on two conducting oxide substrates from aqueous solutions at temperatures between 30 and 90 °C. The as-deposited films were characterized using scanning electron microscopy, transmission electron diffraction, atomic force microscopy and Raman spectroscopy and were found to be crystalline at all temperatures. The microstructural development of the films is also discussed based on field emission scanning electron microscopy and atomic force microscopy studies. The composition of the films was found to be independent of the deposition temperature, with a slight difference in the Cd/S ratio on the different substrates.

The fcc-hcp phase transition in electrodeposited epitaxial cobalt films☆

Abstract Thin (50–500 A) films of cobalt were electrodeposited from sulphate solutions having pH values in the range 1·9–5 onto thin (001) single-crystal copper substrates. Bicrystals and stripped deposits were examined by transmission electron microscopy and electron diffraction. Deposits from solutions with 45 g/l boric acid were essentially fcc for all pH values. Stacking faults, associated with imperfect misfit dislocations, converted only a very small fraction of the fcc cobalt into the hcp structure. Deposits from lightly-buffered (6 g/l boric acid) solutions contained small crystallites of hcp cobalt provided the solution pH ≳ 3. Growth of the hcp phase is probably associated with the presence of colloidal hydroxide at the cathode surface.

The structure of gold silicide in thin Au/Si films☆

Abstract Vacuum-deposited Au/Si double layers were heat treated to the eutectic temperature and were examined by transmission electron diffraction. Electron diffraction patterns ascribed to crystalline silicides were observed. Some of the patterns and associated d spacings were in satisfactory agreement with a primitive cubic unit cell with a = 6.75 A as proposed previously. Other diffraction patterns were consistent with the assumption of an orthorhombic unit cell with a = 6.8, b = 7.5 and c = 9.56 A .

A transmission electron microscope study of electrodeposited nickel films on (001) copper substrates

Abstract Nickel was electrodeposited on to (001) single-crystal copper films. Deposit thickness were in the range 10 A to 500 A. Bicrystals and stripped deposits were examined by transmission electron microscopy and high-resolution electron diffraction. Misfit, as a function of thickness, was determined from moire fringe spacings, splitting of diffraction spots and the spacing of misfit dislocations. The misfit was found to be less than that of vapour-deposited films at corresponding thicknesses. The misfit as calculated from the spacing of misfit dislocations was not in agreement with the misfit as determined from moire fringes or electron diffraction. These discrepancies might be due to foreign material incorporated in the deposit.

Effect of residual gas pressure on the epitaxial growth of vacuum-deposited chromium on Cu{111} substrates

Abstract Transmission electron microscopy, electron diffraction and Auger electron spectroscopy were used to study the effect of vacuum conditions on the epitaxial growth of vacuum-deposited chromium films of thicknesses less than 40 nm on Cu{111} substrates. The chromium films were condensed (i) in ultrahigh vacuum at 10 −9 Torr, (ii) at total pressures of 10 −5 , 10 −6 and 5 × 10 −8 Torr and (iii) at oxygen partial pressures of 5 × 10 −9 , 10 −7 and 10 −6 Torr. The presence of contaminants during the chromium evaporation suppressed the formation of Kurdjumov-Sachs orientations. A low oxygen partial pressure was most effective in altering the orientation and morphology of the deposits.

Epitaxial growth of chromium on Cu{111} substrates

Abstract Deposits of chromium (1–40 nm thick) condensed in ultrahigh vacuum (about 10 −9 Torr) onto Cu{111} films at room temperature (about 300 K) were examined by transmission electron microscopy, electron diffraction and Auger electron spectroscopy (AES). Diffraction patterns consistent with Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS) orientations were observed. Arcing of the chromium reflections indicated a continuous distribution of alignments within a ±6° spread about the exact NW orientation. Dark field and defocusing phase contrast techniques revealed small (about 28 nm) irregularly shaped chromium grains within which smaller parallel-oriented subcrystallites, elongated approximately in the Cr〈001〉 direction, exist. AES confirmed the existence of discontinuos chromium deposits for thicknesses of about 6 nm or less and indicated the presence of a thin layer of Cr 2 O 3 .

The effect of substrate surface contamination on the electrolytic growth of epitaxial nickel films

Abstract Thin (001) single-crystal copper substrates were contaminated by exposure to the atmosphere. Electrodeposition of nickel took place upon the contaminated surface. Duplex films as well as stripped deposits were examined by transmission electron microscopy and electron diffraction. In contrast to deposition onto clean substrates, small three-dimensional (3-D) nuclei formed at the start of deposition. Deposits became continuous at an average thickness of ≈50A. Apart from the small initial nuclei, larger block-like growths were observed. Contrast phenomena as well as the results of misfit measurements suggested that the lattices were initially strained to give a coherent nickel-copper interface.

The orientation and morphology of chromium deposits on hot Cu{111} substrates

Abstract Chromium (1.5–20 nm thick) was vapour deposited in ultrahigh vacuum (2×10 -9 Torr) onto single-crystal Cu{111} films. The copper substrate temperatures T s were in the range 75–256 °C. Transmission electron microscopy and electron diffraction were used to study the orientation and morphology of the deposits. For T s ≲ °C the electron diffraction patterns showed arced chromium reflections consistent with a distribution of orientations between Nishiyama- Wassermann (NW) and Kurdjumov-Sachs (KS) at ±5° 16′ from NW. A greater tendency towards KS was observed as T s increased to about 130 °C. For T s = 190 and 256 °C relatively well-defined KS orientations occured. These results are interpreted in terms of various geometric models of f.c.c.-b.c.c. interfaces. At T s ≲ 85 °C the morphology was qualitatively similar to that observed for room temperature substrates: flat irregularly shaped crystals within which a substructure of parallel-oriented crystallites with elongated shape existed. For T s ≲ 130 °C the morphology changed from the flat irregularly shaped crystals to isolated three- dimensional crystals with an elongated shape. The long direction of the crystals was approximately parallel to the direction of least misfit, i.e. Cr〈111〉  Cu〈110〉.

The epitaxial growth of vanadium on Cu{111} substrates

Abstract Vanadium was electron beam deposited to thickness in the range 2–10 nm onto single-crystal Cu{111} films. Deposition was carried out in a vacuum of 2×10−9 Torr, and the substrate temperatures Ts were 25, 100, 200, 240 and 300°C. The orientation relationships and growth morphology of the deposits were examined by transmission electron microscopy and electron diffraction. For Ts=25°C, Nishiyama-Wassermann orientations occurred. An orientation relationship close to Kurdjumov-Sachs was observed at Ts=240 and 300°C. Atomic row matching considerations suggest that this orientation in fact represents a second-order epitaxy corresponding to V{110}〈113〉|Cu{111}〈112〉. The appearance of this orientation is apparently linked to a change from layer-like to island growth.

The effect of solution pH on the misfit of thin electrodeposits of nickel on single-crystal copper substrates

Abstract Nickel was electrodeposited onto thin (001) single-crystal copper substrates. Deposit thicknesses were in the range 10–500 A. The misfit, determined by electron diffraction, was measured as a function of thickness for deposits prepared from electrolytes with pH values of 2·4, 3·3 and 5·7. At any given thickness the measured misfit increased with decreasing pH. Transmission electron microscopy confirmed that the epitaxial deposits were initially in a state of relatively high tensile strain. Misfit dislocations were generated to relieve the strain. The relatively high residual strain in deposits plated from high pH solutions, as compared to those plated from low pH solution, is explained in terms of the extent to which codeposited foreign substances prevented dislocation glide.