Surface phenomena in plasma environments

Plasma interactions and their effects on materials depend on a number of factors, including the pre-existing environment, the properties of surface materials and the characteristics of the system. An additional dimension is the question of mission: some payloads may be much more sensitive to plasma interactions than others. As an example, a payload whose objective is to measure the ambient environment will be more sensitive to any effects than will a power system. Material specific effects include charging and its associated effects, which can result in short- and long-term damage. Selection of materials for a particular application requires consideration of all factors and assessment of effects due to all causes. Proper selection and suitability determination requires analysis to identify the actual environment combined with testing under exposure to single and combined environment factors

The performance of high voltage; outdoor insulation in polluted environments

"An iron wire, 12000 feet in length, was suspended about five feet from the ground by silk cords; one end of it was connected to the globe of an electrical machine, and at the other a lead ball was hung in order to perceive when the matter reached it. After five or six turns of the wheel, the matter had passed along the whole wire and communicated its virtue to the ball, which instantly attracted and repelled light bodies. 2. As this ball was equally electrified with every part of the wire, it is probable that the electric matter would instantly pervade a wire of a still greater length, provided we had a proper apparatus for the purpose. 3. Several metals and other conductors were substituted in place of the ball, and all received the electricity in the same manner. The ball and touched with other non-conductors, :when' the finger, gave a luminous spark and as smart a shock as when the end of the wire next to 'the 'gTobe·vas touched. All these effects instantly ceased whenever .. any person not electrified touched any part of the wire and commenced again a few seconds after his hand was withdrawn. The same effects are produced, though with more difficultly, when hair or woollen ropes were substituted in place of the silk ones: But they were entirely stopped by hemp ropes or when the silk ones were wetted.

Field Emission Studies Toward Improving the Performance of DC High Voltage Photoelectron Guns

Field emission is the main mechanism that prevents DC high voltage photoemission electron guns from operating at the very high bias voltages required to produce low emittance beams. Gas conditioning is shown to eliminate field emission from cathode electrodes used inside DC high voltage photoelectron guns. Measurements and simulation results indicate that gas conditioning eliminates field emission from cathode electrodes via two mechanisms: sputtering and implantation, with the benefits of implantation reversed by heating the electrode. The field emission characteristics of 5 stainless steel electrodes varied significantly upon the initial application of voltage but improved to nearly the same level after helium and krypton gas conditioning, exhibiting less than 10 pA field emission at - 225kV bias voltage with a 50 mm cathode/anode gap, corresponding to a field strength ∼ 13 MV/m. Field emission could be reduced with either krypton or helium, but there were conditions related to gas choice, voltage and field strength that were more favorable than others. The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. Out of 8 electrodes (6 niobium and 2 stainless steel), the best niobium electrode performed better than the best stainless steel electrodes. Large grain niobium exhibited no measurable field emission (\u3c 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18.7 MV/m. Surface evaluation of all electrodes suggested no correlation between the surface roughness and the field emission current. Removing surface particulate contaminations and protrusions using an effective polishing and cleaning technique helps to prevent field emission. Mechanical polishing using silicon carbide paper and diamond paste is a common method of obtaining a mirror like surface finish on the cathode electrodes. However, it sometimes results rolled-over tips and embedded contamination. A different polishing technique was considered: electropolishing. Three stainless steel cathode electrodes with different initial surface roughness were electropolished by a commercial vendor, and evaluated inside a high voltage test stand. They exhibited less field emission than the diamond paste polished electrodes at the initial application of high voltage; but they were less receptive to ion implantation, which is a beneficial aspect of gas conditioning that serves to increase the work function of the cathode surface. Ultimately, the electropolished electrodes exhibited more field emission than diamond-paste polished electrodes

Electroluminescence in epitaxial thin film zns and znse

The application of the metalorganic chemical vapour deposition technique to the production of II-VI compound semiconductor electroluminescent devices is discussed. Both low field MIS minority carrier injection devices and high field impact excitation structures are considered, and comparisons are drawn with more commiercially orientated electroluminescent displays. The epitaxial growth of ZnS and ZnSe onto (100) orientated GaAs substrates, using the reactions between dimethyl zinc and the hydrides HgS and H2Se, is described. Details are given of a novel epitaxial MISi device processing technology, in which a ZnS I-layer also acts as an etch-stop, thus enabling chemical removal of the GaAs substrate. Metal electrodes deposited directly onto the ZnS and ZnSe allow the electrical and electroluminescent characteristics of these epitaxial II-VI compound layers to be investigated in the absence of any influence from the substrate material. X-ray diffraction and reflection high energy electron dififraction confirm that the structures are epitaxial and of excellent crystallinity. It is demonstrated in an electron beam induced current study that conduction in the epitaxial MIS devices is highly uniform, and this is manifested in a uniform spatial distribution of electroluminescence. A description is given of high field impact excitation electroluminescent devices, in which the ZnS layer is doped with manganese during MOCVD growth. The spatial distribution of EL in these devices is shown to be non-uniform, and thus indicative of filamentary conduction in the ZnS:Mn, in accordance with a recently proposed dielectric breakdown model of instability. It is demonstrated that the transient characteristics of the epitaxial structures correlate with those of commercial polycrystalline devices, and are also consistent with the predictions of a dynamic model of instability. As a result of filamentary conduction, both epitaxial and polycrystalline devices are prone to degradation through localised dielectric breakdown. These breakdown events generally result in a gradual erosion of the active electrode area, although, under certain operating conditions, mobile filaments can cause rapid destruction of epitaxial structures. The columnar microstructure of sputtered devices appears to prevent such filament mobility, and it is concluded that, although filamentary conduction is a result of the carrier injection mechanism and is independent of the crystallinity, the associated damage is strongly influenced by the microstructure of the device

Process techniques study of integrated circuits Final scientific report

Surface impurity and structural defect analysis on thermally grown silicon oxide integrated circui

Application of High-Voltage Discharges for Disinfecting Water

A three-factor experiment is conducted on the disinfection of water by treatment with high-voltage discharges formed to achieve an electro-hydraulic effect, in order to detect optimal conditions and rules for the course of the processes under study. In the study, a high-voltage installation with an electro-hydraulic spark gap, an EnSURE luminometer (Hygiena) for measuring the level of hygiene of water and its solutions, test tubes for determining the total number of ATP in AquaSnap Total brand water (AQ100X) are used as materials and equipment. The influence of design parameters and exposure modes of an electro-hydraulic installation on the properties of water as a result of the generation of high-voltage discharges is investigated; experimental data are revealed for measuring the level of microbiological contamination of the water sample, which, according to the analysis of the data obtained, is reduced, which can serve as the basis for the possibility of the potential use of the effects of high-voltage discharges as a method of preparing water under irrigation in greenhouses; optimal ratios of factors for disinfecting a pond water sample from a source of artificial origin are revealed: operating voltage 19.9 kV, capacitance 0.1445 μF and the number of discharges 2861 pieces

An investigation of electron tunnelling and conduction in Langmuir films

Thesis from Leicester PolytechnicLangmuir films offer the possibility of obtaining unifo:r:m, well­ordered, insulating structures of defined and controllable thickness. In this thesis, techniques for the fabrication of these films and the nature of the conduction process in single and multi-layer films of stearic acid/stearate sandwiched between metal electrodes (HIM devices) are discussed. A sophisticated film fabrication system has been designed and implemented and methods necessary for obtaining films of high integrity established. Structural characterisation studies using various techniques demonstrate that the resultant films are unifo:r:m, of predictable composition and substantially free of defects. In single layer MIM devices, detailed observations of the voltage and temperature dependence of the current suggest that the predominant conduction mechanism is direct electron tunnelling between the metal electrodes. This has been confirmed with the aid of additional experiments, including consideration of the role of the oxide film(s) invariably present in the canpleted device and investigation of the inelastic component of the tunnel current. It is argued that the latter provides unequivocal evidence that a significant proportion of all conduction is by electron tunnelling. In multilayer (3-5 layers) MIM devices, the importance of Schottky emission as a mechanism for conduction has been confirmed through a careful examination of the current-voltage relationship and on the basis of the temperature dependence of the current at fixed voltage. Finally, the techniques of Auger and X-ray photoelectron spectro­scopy have been employed to provide further insight into the nature of film adhesion and composition. These observations, where possible, have been correlated with the results of electrical measurements

Electrical and material properties of thin film perovskites

PhD ThesisThis thesis presents a study of negative capacitance in the robust perovskite BaTiO3. Negative capacitance is an unstable state in ferroelectrics, which explains why there is a lack of experimental evidence in the literature. A positive capacitance in a series capacitor configuration allows stabilisation of negative capacitance. The key finding is the stabilisation of negative capacitance at room temperature in BaTiO3. Temperature constraints in back-end-of-line processing should be at 500 °C or below in order to avoid diffusion of dopants and to inhibit high resistivity silicide phases. Three deposition techniques, pulsed laser deposition, atomic layer deposition and sputter deposition are used to investigate the material and electrical properties of perovskites for back-end integration within this temperature constraint. SrTiO3, Ba0.8Sr0.2TiO3 and BaTiO3 are all explored as possible solutions for tunable capacitance under low temperature processing. Evidence is shown for SrTiO3 displaying fully crystallised structures through pulsed laser deposition at 500 °C growth temperature. A refined model of effective oxide thickness is used to calculate interfacial layers that impact metal-oxide-semiconductor capacitors. The model is applied to SrTiO3 metal-insulator-metal capacitors in terms of a dead layer. Calculation of the dead layer thickness, which has been previously unattainable using solely the series capacitance model, is carried out using the effective oxide thickness model. However, transmission electron microscopy images suggest that a physical layer of ‘dead’ material is abesnt in the capacitors. The results support the hypothesis of an intrinsic explanation to the dead layer phenomenon. ii Finally, pulsed laser deposited BaTiO3 is explored in terms of ferroelectricity when integrated with Si using Pt/Ti/SiO2/Si substrates. Here, a mixed phase relationship is shown in the films of BaTiO3 in which the cubic phase, responsible for paraelectricity, dominates at room temperature. Increasing film thickness also correlates with higher remnant polarization in the films. The result confirms a size driven phase transition in thin film BaTiO3 which has preveously been studied on perovskite free-standing films or nanoparticles

Indium phosphide - langmuir film mis devices

Langramuir blodgett films are an interesting example of two dimensional order structure. Their fabrication involves the building-up of a multilayer firmly repeated deposition of single monomolecular layers upon the substrate material. The resultant structure is of defined thickness and excellent uniformity. Because of these qualities, Langmuir films enjoy potential applicatons in many areas of modern science. In particular , their excellent insulating properties have led to the proposition of their use within the semiconductor device industry. Indium phosphide, although a relatively new semiconductor, is already becoming an important device material, particularly in areas where its high mobility gives rapid device response and good high frequency operation. This thesis combines these two materials, and looks at the electrical behaviour of InP/Langmuir film metal-insulator-semiconductor (MIF devices and their associated structures. The Langrauir-Blodgett process is a low temperature deposition technique, and thus induces little or no surface damage to its recipient substrate. Because of this, it is likely that the chemical surface of the InP, prior to deposition, will be of critical importance in defining the device characteristics. This has in fact been found to b'. the case, and a detailed study of the correlation between ESCA surface chemical information and vice electrical data has been undertaken. In addition, the device results obtained have been found be rather different to those produced by the use of a conventional high temperature deposition process. In order to capitalise upon the use of these organic insulating films, and the sensitive nature of the InP surface, the effect of various gases upon these device structures have been investigated. The study has revealed the existence of many interesting bulk and interface effects, and is likely to form the basis of a more detailed programme aiming to develop a range of solid state sensors