N. Fuschillo

Amorphous Oxide Layers on Gold and Nickel Films Observed by Electron Microscopy

Thin films of vapor‐deposited nickel and gold, supported only by copper grids, were annealed inside the electron microscope. The microstructures were recorded as a function of temperature. The originally continuous thin films of nickel (150 A thick) and gold (400 A thick) form discontinuous islands at temperatures of 700° and 600°C, respectively. The islands of metal are supported by a thin amorphous membrane, in the nickel films identified as NiO, that accounts for the high tensile strengths observed on thin films.

Dielectric properties of amorphous Nb2O5 thin films

The dielectric constant, a.c. resistance and loss tangent tan δ of amorphous Nb2O5 films with Nb electrodes have been investigated in the frequency range 3 Hz to 5 × 106 Hz, as a function of temperature and applied field. The capacitance decreases with frequency ƒ according to a C(ƒ)∝ƒ−0.3 relation in the range 3 Hz 2 × 10su5 Hz. The activation energy of a dielectric oscillator is 0.032 eV; C−V, G−V and tan δ−V data are presented. The real and imaginary parts of the complex dielectric constant e∗ = e′ − je″ and polarizability α∗ = α′ − jα″ were calculated from the data. The Cole-Cole (e″versus e′), Scaife (α″versus α′) and tan δ versus log ƒ plots indicate the existence of two relaxation times below 8 × 103 Hz. The films are in a thickness range where the principal conduction mechanism is hopping conduction, as shown by the σ(ƒ)∝ƒn relation, with 0.75

Crystallization in Thin Films of Carbon and Silicon Monoxide

Thin films of carbon or of silicon monoxide were observed while heated to 1000°C inside the electron microscope. Spherical graphite nuclei, approximately 200 A in diameter, appear at 200°C in the carbon films. These nuclei maintain their spherical form to a temperature of 600°C while growing to 1800 A in diameter. At this size the spheres become unstable and convert to crystals of hexagonal symmetry. At 700°C the crystals revert to spheres 3600 A in diameter. The silicon monoxide films form 150‐A nuclei at 350°C; no further changes are noted until at 800°C the film recrystallizes. The recrystallized silicon monoxide film is identified as β crystobalite. For both materials, the nucleation temperatures and the sizes and shapes of the crystallites at a given temperature depended on the thicknesses of the films.

Semi-transparent solar collector window systems

Semi-transparent window solar collectors which can be integrated with opaque wall collectors for space heating and ventilation are described for buildings containing large quantities of glass. Simpler, inexpensive, retractable systems are also described. Such systems can have rapid impact on fuel savings. The achievement of 20 per cent grey-scale light transmission combined with 75 per cent thermal utilization of the total solar energy seems feasible. The collector system works by means of semi-transparent thin absorber and reflector coatings on double-glaze windows. Vents at the top and bottom of the double-coated window system permit convective flow of solar-heated air currents for space heating on cold sunny days, convective room ventilation on warm sunny days, and thermal insulation in the absence of sunshine. An account is given of experimental work on sunlight-absorbing and reflecting materials and coatings for implementation of the window systems. These metallic, (alloy or bilayer) and semi-conductor coatings also have applications to Schottky barrier and conventional solar cells and αϵ coatings for solar thermal collectors.

Hopping conduction in amorphous Nb2O5 thin films

Abstract The low field conduction mechanism in amorphous Nb 2 O 5 doped with Nb is investigated by measurements of the ac conductivity as a function of frequency (3 Hz−6 × 10 6 Hz), dc conductivity as a function of temperature (100–400 K), capacitance as a function of frequency (3 Hz−6 × 10 6 Hz) and conductance G as a function of voltage at 10 3 Hz. Loss tangent and quality factor data are also given because of their technical and scientific relevance. Evidence for hopping conduction at low applied fields is presented by the following results: (1) a monotonic increase in ac conductivity σ ( ω ) αω n where 0.5 n 6 Hz; (2) a linear dependence of current on voltage at low fields; and (3) low activation energy for dc conduction with a transition at 210 K to a still lower activation energy; and (4) a decrease in polarizability with frequency. At high fields, E > 10 5 V/cm, dc conductivity is dominated by the field emission mechanism of the Poole-Frenkel or Poole type.

Structure and electrical conductivity of cosputtered gold‐chromium alloy films

Cosputtering of Au and Cr produces polycrystalline thin films in the entire compositional range up to solubility limits of 49 at.% Cr in Au corresponding to the phase diagram of bulk material. Compositions of the Au–Cr system were checked by electron‐probe microanalysis. The change in lattice constant with addition of Cr in Au shows exactly the same deviation from Vegards law as bulk. The resistivity changes with increasing Cr content are presented and the temperature coefficient is found to be constant in the range ‐150–160°C.

Electrical conduction and dielectric breakdown in crystalline NiO and NiO(Li) films

Charge transport, including dielectic breakdown in NiO films (2−10 μ thick), is studied as a function of doping (0−0.4 at.% Li), temperature (−150−+150 °C), frequency (0−108 Hz), and voltage using sputtered nickel contact electrodes. The current I is found to vary as V1 at low and as V3 at higher fields until a breakdown field Es is reached which varies with Li concentration N as Es∝T exp(−N). The field E1 at which I−V nonlinearity begins is given by E1 ?0.2(2kT/eae′) and E1∝T exp(1/T). The ac conductivity σ (ω) ∝ω2τ2/(1+ω2τ2) and the dc conductivity σ=σ0 exp(−Eth/kT). These transport properties are shown to be consistent with the hopping−carrier model. Under current−controlled conditions, reversible dielectric breakdown (i.e., repetitive switching) was associated with the field−induced delocalization of charge carriers. The results are consistent with the view that the charge carriers prior to reversible dielectric breakdown are small polarons.

Dielectric properties of NiO and NiO(Li)

Abstract The dielectric constant of NiO produced by the oxidation of Ni has been studied as a function of frequency up to 108 Hz and of temperature from 300° to 550°K. The effect of Li doping on the dielectric constant has also been investigated. In addition, the behavior of the a.c. conductivity σ(ω) as a function of frequency ω has been determined up to 108Hz and the loss tangent tan δ has been calculated. The results are interpreted on the basis of a non-adiabatic hopping mechanism at lower frequencies and an adiabatic hopping mechanism at higher frequencies. The dielectric breakdown field as a function of Li concentration has also been determined and is found to decrease exponentially with increasing Li concentration. In the NiNiONi structure, the capacitance is independent of the applied field up to fields of 10 5 V cm , and the resistivity is high up to fields of 10 5 V cm .

Structure, Growth, and Properties of Twist and Tilt Grain Boundaries in Bicrystals of NaCl

Grain boundaries having from 2° to 45° mismatch across the interface were grown for pure tilt and pure twist misorientation in NaCl by the Czochralski technique. The method of crystal growth and the techniques required for good control of the misorientation and the planarity of the grain boundary are described. The substructure of twist and tilt NaCl bicrystals was examined using both optical and electron‐microscopic techniques. The tilt grain boundaries were found to be strong mechanically and not easily cleaved apart. The twist grain boundaries were very weak mechanically, especially at mismatch angles greater than 20°, and exhibited anomalously rapid diffusion or capillary flow effects along the grain boundary.Grain boundaries in the bicrystals were examined by: (1) pulling the crystals apart at the grain boundary and (2) by polishing away one side of the bicrystal to within 0.5 mm of the grain boundary. (The grain boundary surface could then be examined by focusing through the layer of NaCl.) Both of ...

Semiconductor behavior in amorphous AuSiO thin films

Abstract Films consisting of AuSiO formed by co-deposition have conductivity versus temperature behavior which can show either amorphous semiconductor or metallic characteristics depending on the volume percent of gold and heat treatment. Similar phenomena have been observed in CrSiO films. In this investigation preliminary results are presented on the electrical conductivity and substructure as revealed by electron microscopy of AuSiO films containing 15 vol % and 50 vol % Au. Several of the possible conduction mechanisms explaining the observed behavior are discussed.