<p>Organic semiconductors have been studied thoroughly and are well understood, though the effects in which oxygen and humidity have on them are less well known. In this thesis we immerse copper phthalocyanine thin films deposited at two different substrate temperatures and with two different thicknesses to an environment with oxygen pressures from 10 mbar to 210 mbar and water vapor pressures from 5 mbar to 13 mbar. The conductivity of our thin films at atmospheric oxygen and water pressure ranged from as high as 6:7 &times; 10^&minus;4 S/m and as low as 9:6 &times; 10^&minus;5 S/m, about 7 orders of magnitude less than silicon and germanium. At the smallest oxygen doping, the conductivity ranged from as high as 4:9 &times; 10^&minus;5 S/m to as low as 1:1 &times; 10^&minus;5 S/m. We can conclude that the small grain samples are more easily doped by oxygen, the small grain samples have a larger sensitivity gain than the large grain samples, and the intrinsic conductivity increases as both grain size decreases and as film thickness decreases. </p>

Conditions have been established for the epitaxial growth, by vacuum evaporation at 10^-6 torr, of single crystal films of the dihydrides of gadolinium,terbium, dysprosium, holmium and erbium, on the cube, dodecahedral and octahedral faces of rock salt. The film structures have been investigated by electron microscopy and diffraction. Lattice parameter measurements on single crystal and polycrystalline specimens indicate that thin films (less then 200A) are face-centred-cubic dihydrides whereas thick films (>900A) are dominated by hexagonal close-packed metallic structure. Films of intermediate thickness exhibit a mixed (f.c.c. dihydride and h.c.p. metal) phase. The effects,on the structure of Gd and Tb dihydride films, of such parameters as substrate nature and temperature, vacuum environment, annealing and hydrogen treatment have been studied. Some nucleation and decoration studies have been conducted for gadolinium and terbium dihydrides. The electrical resistivity and temperature coefficient of resistance of polycrystalline films of the dihydrides of gadolinium, terbium, dysprosium, holmium and erbium, grown on glass slides, have been measured in vacuo. Resistivity measurements on the dihydride films, made in the temperature range 77K to 573K indicate generally metallic conduction characteristics. Studies of the changes of resistivity on annealing the dihydride films in the presence of a stream of hydrogen gas support the conclusion that the films become converted to semiconducting trihydrides having negative temperature coefficient of resistance.

A sensitivity study is conducted on the polarimetric measurable [delta] = ([delta]p-[delta]s), the differential change of phase on reflection air/metallic p s-film. A computer aided study shows the quantity A to he sensitive to the extinction coefficient k and to film thickness. It is only sensi-tive to the refractive index n in certain ranges of n , k and for certain d values. For films of d 2001, A becomes insensitive to n but maintains high sensitivity to k , while ford &pound;200 A it shows some sensitivity to n as well as k in certain ranges of lower values of k 2.5. An interferometric technique due to Tolansky (1944), is used to determine A as a function of 6 , the angle of incidence for films of Ag , Au and At at different wavelengths in the visible region of the spectrum. It is shown that this interferometric technique, when critically applied, is capable of an accuracy of +/-0.003. The extinction coefficients of films investigated are found from curves of A vs n for constant values of k . They are shown to be accurate to +/-0.03 when A is accurate to +/-0.003 tt thus rendering a simple and inexpensive technique an accurate and effective method for the determination of the extinction coefficient of highly reflecting metallic films. A new optical system to produce multiple beam interference fringes of variable chromaticity in the first order is described. The system enables the surveying of features within the order. It also removes the ambiguity met in conventional monochromatic interferometry concerning the order of interference to which a fringe may belong. White light multiple fringes are obtained first and the orders are recognized. Some outlines are projected for investigating the sensitivity of the optical phase properties of metallic films, namely the phase changes on reflection air/metallic film [beta], dielectric substrate/metallic film [beta] and in transmission [gamma], at normal incidence, to n, k and d . It is proposed to try to explain and link the behaviour of these phase quantities with thickness for d 200. in terms of n and k. Also a compact new monochromator to produce fringes of variable chromaticity for surface microtopography studies is projected.

Measurements of the lattice thermal conductivity of in lium antimonide (n=10¹⁴ to 10¹⁷ and p=10¹⁵ to 10¹⁷ cm^-3) single crystal samples have been performed in the temperature range of 1.2 to 10&deg;K, and for the lower temperatures in magnetic fields up to 40 KG. A new 8-bit microprocessor controlled system was constructed to make fully automatic measurements under optimised conditions. This enabled thermal conductivity measurements to be made to an accuracy of 2% absolute and 0.1% relative. The zero field results are in good agreement with theory and with previous measurements. The thermal conductivity of the p-InSb decreased with increase of magnetic field. The acceptor ground state is four fold degenerate and the thermal phonons could only be scattered by transition within the quartet of energy levels. It was found that Ge doped sample (P = 2.8 x 10¹⁵ cm^-3 at 1.23&deg;K) exhibited a broad minimum when the field reached about 40 KG which was due to the first order Zeeman splitting of the acceptor ground state. Quantum oscillations of thermal conductivity of highly doped n-type samples were observed in a magnetic field. The period of oscillation was the same as the Shubnikov-de liaas oscillation of electrical conductivity and it is shown that the oscillation occurs because the electron-phonon interaction osciliates with magnetic field as the Fermi level crosses successive Landau levels.

Rare earth metal films have been prepared in Ultra-high Vacuum (U.H.V.) and work function measurements made, in situ, by a vibrating capacitor technique. The effects of aging in U.H.V. and of atmospheric contamination have been studied. Measurements have been made on Gd above and below the Curie temperature, before and after annealing at 390K by means of a novel nichrome-film heater (developed for U.H.V. use). The resistivities of the rare earth films were determined by an in situ potential probe method in conjunction with interferometric thickness measurements. Work function measurements have also been made on other metal films and on silicon surfaces to provide data relevant to theoretical work on point-contact detectors for far infra-red radiation.

The static indentation hardness test has been applied to the study of the environment effects on hardness, plastic deformation, and fracture properties of silicon carbide crystals. Measurements of microhardness on the (0001) planes show that the hardness of silicon carbide is significantly lowered by water absorbed from the air. Upon annealing the crystals, at very high temperatures, the hardness is found to increase. A three-dimensional distribution of stress, beneath an indenter, has been evaluated using 'elastic equations'. The mechanics of crack initiation around the contact circle of a spherical indenter with the specimen has been analysed. The crack extension force, for a crack propagating downward from the surface of the specimen, has been evaluated. Evidence of plastic deformation by slip is provided by a number of indentations, specially those with the spherical and double-cone indenters. (1010) is the preferred slip plane.

A new technique has been developed for producing mono-crystalline foils of some alkali halides for transmission electron microscopy. The formation mechanism of the crystals has been investigated. The foils, which have two free faces have been used as electron transparent substrates to grow epitaxial films of gold, on one or both surfaces of the substrates. It has been shown that by covering the above foils with a thin layer of another alkali halide, bending contours suitable for measuring the thickness of the foils, are produced. A chamber has been designed and constructed for transporting the specimen from the preparation vacuum system into the electron microscope without exposing it to the atmosphere. The variation of pressure inside the chamber has been measured and some possible modifications have been suggested. The device has been used to study the nucleation and growth from the vapour phase of LiF, NaF, NaCl, KOI, KBj, KI and Rbl, on electron transparent substrates of mica and potassium chloride. The crystallographic and atomic orientations of the above materials with respect to atomic arrangement of the substrates have been studied. It has been shown that the alkali halides form continuous films at average thicknesses below 2.5 nm on substrates of mica and KCl. The effect of the heat treatment during and after growth of the films has been studied. The effects of atmospheric moisture on the overgrowths have been studied in detail, and it has been shown that there are some similarities between the effects of atmospheric moisture and the heat treatment on the hygroscopic alkali halides. It has been shown that when thin deposits of NaCl on the substrate of KCl are heated, diffusion or re-evaporation of the deposit does not occur randomly. The consequent possibility of the existence of periodic defect sites has been discussed. From a general consideration of the results it is concluded that (a) Chemical interactions are a dominant factor in the epitaxial growth of alkali halides on mica and KCl. (b) The alkali halides deposited from vapour consist of flat crystallites at the earliest stages of growth at room temperature.

No description available.

No description available.

<p> In this dissertation, the nature of magnetism in transition-metal-doped phthalocyanines (TMPc, TM = Co, Ni, Cu, V, and Mn, chemical formula: C₃₂H₁₆N₈TM) is investigated by measuring their magnetization (M) and ac susceptibilities in magnetic fields up to 90 kOe and covering the wide temperature range of 0.5 K to 300 K. These low temperatures and high magnetic field measurements combined with detailed analysis of the data have provided new information about the nature of magnetism of TMPc. The powder samples used here were structurally characterized using x-ray diffraction and scanning electron microscopy.</p><p> TMPc are a class of organic semiconductors with potential applications in spintronics and they are planar molecules with the TM atom at the center bound to four N atoms and forming a linear chain along the monoclinic b-axis. Because of this symmetry, the ground states of TMPc often violate the Hunds&rsquo; rules; e.g. the S = 3/2 state for d⁵ Mn(II) in &beta;-MnPc, S = 1/2 state for the d⁷ Co(II) in &beta;-CoPc, and S = 0 state for the d⁸ Ni(II) in NiPc. The magnetic properties of TMPc are also affected by the stack angle &delta; between the orientation of the molecular plane and the b-axis, &delta; being 65&deg; (45&deg;) for &alpha; (&beta;) phase. </p><p> For both &alpha;-CuPc and &beta;-CuPc, M vs. T data fit well with the Bonner-Fisher model for S = 1/2 antiferromagnetic (AFM) Heisenberg linear chain yielding the Cu²⁺-Cu²⁺ exchange constant J_ex/k_B = - 1.7 K (- 0.2 K) for &alpha;-CuPc(&beta;-CuPc). This order of magnitude difference in J_ex/k_B is likely due to the smaller Cu²⁺-Cu²⁺ distance in &alpha;-phase than in &beta;-phase. The M vs. H at 2 K and 5 K data are interpreted including the effect of the exchange coupling. </p><p> For &beta;-CoPc, the predicted peak in &chi; vs. T data by Bonner-Fisher model was observed at T_max = 1.9 K for the first time yielding the Heisenberg exchange constant J_ex/k_B = - 1.5 K between the Co²⁺-Co²⁺ ions. The isothermal data of M vs. H at 1 K shows good agreement with the Bonner-Fisher model; M vs. H at 5 K data is interpreted by including the effect of the exchange interaction. </p><p> For VOPc (phase II), the analysis of the M vs. T data shows VO²⁺ electronic state with spin S = 1/2 and &thetas; = - 0.1 indicates a very weak AFM exchange coupling between neighboring VO²⁺ ions which implies the near-perfect paramagnetism of VOPc. This conclusion is also supported by the analysis of the M vs. H data at several temperatures. The diamagnetic nature of &beta;-NiPc corresponding to the S = 0 state for the 3d⁸ Ni(II) is confirmed by measurements and analysis of the magnetization with temperature-independent susceptibility &chi;_D = - 3.38 &times; 10^-7 emu/gOe. The observed ferromagnetic component in the &beta;-NiPc powder sample is identified with Fe impurity. </p><p> For &beta;-MnPc with S = 3/2, detailed analysis of the dc and ac susceptibilities leads to the conclusion of the absence of 3-dimensional long range magnetic ordering in this system contrary to previous reports. This conclusion is supported by the Arrott plots and lack of a peak in the ac susceptibilities and specific heat near the quoted T_C &ap; 8.6 K. Instead, &beta;-MnPc is best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J_ex/k_B = 2.6 K and the single ion anisotropy energy constant |D|/kB = 8.3 K. The absence of 3D long-range ordering is consistent with the measured |D| being >J_ex.</p>