High-voltage Contact Research Articles

Expanded Electrochemical Capabilities of the Electrospray Ion Source Using Porous Flow-Through Electrodes as the Upstream Ground and Emitter High-Voltage Contact

Use of a porous flow-through electrode at the upstream ground contact or at both the upstream ground contact and the high-voltage emitter contact in an electrospray ion source was shown to provide for new types of electrochemical experiments utilizing only the electrochemistry inherent to electrospray. The normal stainless steel bore-through union serving as the upstream grounding point in a floated electrospray emitter system was replaced with a high surface area porous flow-through electrode assembly to achieve effective electrochemical reduction of analytes at this point in positive ion mode, and effective electrochemical oxidation of analytes in negative ion mode. This was demonstrated by the oxidation of 3,4-dihydroxybenzoic acid and reserpine in negative ion mode and by the reduction of thionine in positive ion mode. In the case of reversible oxidation (3,4-dihydroxybenzoic acid) and reduction (thionine) processes, partial rereduction and reoxidation of the products due to reaction with products generated by cathodic and anodic processes at the emitter were observed, respectively. By implementing two high surface area porous flow-through electrodes in the system, one as the upstream grounding point and the other as the emitter electrode, a multiple-step reaction scheme was achieved that included consecutive electrochemical reduction and oxidation reactions and a following chemical reaction as demonstrated by the hydroquinone tagging of an initially disulfide-linked peptide.

Improving the dynamic avalanche breakdown of high voltage planar devices using semi-resistive field plates

The problem of breakdown voltage degradation during transient state is well known for SIPOS terminated or passivated devices. The goal of this paper is to physically explain, model and improve the dynamic behaviour of SIPOS terminated diodes. An RC network model for the SIPOS layer will be used. This model is implemented in a circuit simulator and we put in evidence the cause of the problem: the difference in potential repartition between the static and the dynamic mode. In the static mode the potential at the surface of silicon is distributed linearly between the high voltage contact and the anode (grounded), but in dynamic mode, its repartition is almost parabolic. The SIPOS/oxide/silicon structure equivalent circuit is analysed using circuits theory. We prove that the breakdown voltage degradation during transient state is due to the ratio between the SIPOS layer capacitance and the oxide layer one. A solution to improve the dynamic behaviour up to 3000V/μs is proposed.

Electrodynamic transition in solid armature railguns

An important research problem for solid armature railguns is understanding the sudden transition from low-voltage sliding electrical contact between the rails and armature to high-voltage contact involving a plasma arc. Although an armature can fail in many ways and thereby "transition," two distinct transition mechanisms currently limit the performance of solid armature electromagnetic (EM) launchers. One mechanism, broadly termed "wear-induced transition," results from uneven or excessive loss of material from the contact interface. The other mechanism is associated with a rapid reduction in driving current (negative dI/dt). A series of experiments have shown the waveform-induced transition mechanism is independent of the state of wear of an armature. This paper explores this mechanism, which we call "electrodynamic transition," and seek to explain the cause of transition as an electromechanical instability that disrupts the liquid film interface between armature and rail. Using 3-D finite element analyses (FEA), we observed the development of localized forces at the edges of the armature as the driving current drops rapidly. This behavior, we believe, may cause molten material to be ejected from the armature-rail contact region.

Electrolytic deposition of metals on to the high-voltage contact in an electrospray emitter: implications for gas-phase ion formation

Electrolytic deposition of metals on to the high-voltage contact in an electrospray emitter: implications for gas-phase ion formation

Electrolytic deposition of metals on to the high-voltage contact in an electrospray emitter: implications for gas-phase ion formation.

The electrospray ion source is an electrolytic flow cell. Electrolytic reactions in the electrospray emitter maintain the production of charged droplets by this ion source that contain an excess of ions of one polarity. These redox reactions necessarily change the composition of the solution that initially enters the emitter. As a result, the ions ultimately observed in the gas phase by electrospray mass spectrometry (ESMS) may be substantially influenced by both the nature and extent of these electrochemical reactions. It is demonstrated in this paper that Ag(+), Cu(2+) and Hg(2+) ions in solution can be electrolytically reduced and deposited as the respective metals on to the surface of the high-voltage contact in the electrospray emitter in negative ion mode electrospray. The deposited metals are shown to be liberated from the surface by switching the electrospray high-voltage polarity to operate in the positive ion mode. The deposited metals are oxidized in positive ion mode, releasing the metal ions back into solution where they are detected in the electrospray mass spectrum. In a semi-quantitative analysis, it was found that up to 50% of the Ag(+) in a 2.5 microM solution was deposited on the high-voltage contact of the emitter as the solution flowed through the emitter. Deposition of Cu(2+) and Hg(2+) was less efficient. These data illustrate that in the analysis of metals by ESMS, one must be aware that both the concentration and form of the metals may be altered by electrochemical processes in the emitter. Hence reduction or oxidation of metals in the electrospray emitter, which may remove ions from solution, or change metal valence, would be expected to impact both quantitative metal determinations and metal speciation attempts using ESMS.

Electrolytic corrosion of a stainless-steel electrospray emitter monitored using an electrospray–photodiode array system

An electrospray–photodiode array (ES-PDA) system provides a useful alternative to ES-MS for the study of the electrolytic reactions that occur at the point of high voltage (or ground) contact in an ES ion source emitter. These electrolytic reactions charge-balance the loss of an excess of ions of one polarity in the charged ES droplets. This ES-PDA approach is particularly useful when the redox products are either neutral or difficult to detect in the gas phase unaltered. The latter is the case for the multiply charged metal ions derived from ES emitter corrosion. In this study, the anodic corrosion of iron in a stainless-steel ES emitter, detected optically as tris(1,10-phenanthroline)iron(II), [Fe(phen)3 ]2+ , was found using the ES-PDA system to account for the majority of the charge-balancing current under the conditions used. The metal ions derived from emitter corrosion may be produced at levels sufficient to cause chemical background problems in ES-MS. Probably because of the relatively high concentration detection limits of ES-MS for multiply charged inorganic species, this problem has not yet been a major issue. One expects further use of ES as a nebulization source for ICP-AES and ICP-MS, because of the much better concentration detection limits of these techniques, to bring this issue to the forefront.

Passivation and surface leakage in CdZnTe spectrometers

The subject of surface leakage and passivation in spectrometers fabricated in high pressure Bridgman CdZnTe crystals with evaporated gold contacts has been examined. The surface leakage has been found to be the dominant mechanism of dark current leakage in metal–semiconductor–metal detectors with noninjecting contacts. Several passivation techniques have been examined with various degrees of success in terms of reducing the mean value and the power spectral density of dark noise characteristics. An insulating polymer was applied on the bare surface reducing the total leakage current by the factor of 6–7, while favorably affecting the dark noise spectral density by decreasing the corner frequency of the low frequency noise. However, a considerable surface leakage has been observed even in these apparently passivated spectrometers. A three terminal device with iso-potential high voltage contacts has been fabricated and tested, exhibiting a reduction of the total dark current leakage by approximately two orders of magnitude. With this three terminal design, the bulk resistivity of typical high pressure Bridgman crystals is correctly determined and found to be ∼2⋅1011 Ω⋅cm.

Carrier transport mechanisms through the metal/p-type diamond semiconductor interface

Abstract Carrier transport mechanisms at p-diamond/metal interfaces were studied by analyzing the dependencies of the specific contact resistivities ( ρ c ) on the measurement temperature and the acceptor concentration ( N A ). A variety of metals, such as Ti, Mo, Cr (carbide forming metals), Pd and Co (carbon soluble metals), were deposited on boron-doped polycrystalline diamond films, and the ρ c values were measured by a transmission line method. A constant Schottky barrier height (SBH) of around 0.5 eV was measured for these annealed contacts, and the reason was believed to be due to phase transformation from metastable diamond to a stable conductive graphite layer in the vicinity of the diamond/metal interface. By controlling the crystal structure at the diamond/metal interface, non-annealed ohmic and high-voltage Schottky contacts were successfully developed.

945. Investigations of changes in the state of surface of electrodes of vacuum high-voltage contacts during life: V V Oreshkin and V G Slutskiy,Rep of Ryazan Radiotech Inst, No 35, 1973, 137–142 ( in Russian)

945. Investigations of changes in the state of surface of electrodes of vacuum high-voltage contacts during life: V V Oreshkin and V G Slutskiy,Rep of Ryazan Radiotech Inst, No 35, 1973, 137–142 ( in Russian)