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Ahn A.C.,Massachusetts General Hospital | Gow B.J.,Massachusetts General Hospital | Martinsen R.G.,University of Oslo | Zhao M.,University of California at Davis | And 3 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

The Kelvin probe measures surface electrical potential without making physical contact with the specimen. It relies on capacitive coupling between an oscillating metal tip that is normal to a specimen's surface. Kelvin probes have been increasingly used to study surface and electrical properties of metals and semiconductors and are capable of detecting material surface potentials with submillivolt resolution at a micrometer spatial scale. Its capability for measuring electrical potential without being confounded by electrode-specimen contact makes extending its use towards biological materials particularly appealing. However, the theoretical basis for applying the Kelvin probe to dielectric or partially conductive materials such as biological tissue has not been evaluated and remains unclear. This study develops the theoretical basis underlying Kelvin probe measurements in five theoretical materials: highly conductive, conductive dielectric with rapid charge relaxation, conductive dielectric with slow charge relaxation, perfect dielectric, and tissue with a bulk serial resistance. These theoretically derived equations are then computationally analyzed using parameters from both theoretical specimens and actual biomaterials-including wet skin, dry skin, cerebrospinal fluid, and tendon. Based on these analyses, a Kelvin probe performs in two distinct ways depending on the charge relaxation rates of the sample: The specimen is treated either as a perfect dielectric or as highly conductive material. Because of their rapid relaxation rate and increased permittivity biomaterials behave similarly to highly conductive materials, such as metal, when evaluated by the Kelvin probe. These results indicate that the Kelvin probe can be readily applied to studying the surface potential of biological tissue. © 2012 American Physical Society.


Baikie I.D.,KP Technology Ltd. | Grain A.,KP Technology Ltd. | Sutherland J.,KP Technology Ltd. | Law J.,KP Technology Ltd.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2015

We describe a novel photoemission technique utilizing a traditional Kelvin probe as a detector of electrons/atmospheric ions ejected from metal and semiconductor surfaces (Al, Ag, Au, Si) illuminated by a Deep Ultra-Violet (DUV) source at ambient pressure. In Constant Final State Yield Spectroscopy (CFSYS) the incident photon energy is rastered rather than applying a variable retarding electric field as in conventional UPS. For both ambient- and near ambient pressure-photoemission spectroscopy (NAP-PES) the CFSYS configuration overcomes the limitation of inelastic electron scattering in air. This arrangement can be applied in several operational modes: using the DUV source to determine the absolute work function (ϕ{symbol}) of the metal with 50-100 meV resolution and also the Kelvin probe, under dark conditions, to measure Contact Potential Difference (CPD) with an accuracy of 1-3 meV. We show that the metal photoresponse agrees with Fowler theory. We have used CPD and linear extrapolated photoemission measurements to produce an energy level diagram for the native-oxide covered Si. We propose a model of photoemission in air involving atmospheric ions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Van Aken B.B.,Energy Research Center of the Netherlands | Bakker K.J.,Energy Research Center of the Netherlands | Heijna M.C.R.,Energy Research Center of the Netherlands | Reid D.,KP Technology Ltd. | And 2 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2010

The Kelvin probe is a non-contact, non-destructive vibrating capacitor device that measures the work function difference between a conducting sample and a vibrating tip. This contribution focuses on inline monitoring of the surface (photo)voltage of deposited silicon layers. We apply a custom-built in situ Kelvin probe, operated in a roll-to-roll PECVD system, located immediately after the plasma zones to enable direct feedback to the controlling system of the plasma deposition. The surface photovoltage of nip thin film Si solar cells increases with increasing Voc. The results imply that inline, contactless measurements of the open-circuit voltage are possible and that thus monitoring the doped layer quality during roll-to-roll production is feasible. © 2010 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim.


Baikie I.D.,KP Technology Ltd | Grain A.C.,KP Technology Ltd | Sutherland J.,KP Technology Ltd | Law J.,KP Technology Ltd
Energy Procedia | Year: 2014

We describe a novel dual-mode Kelvin probe featuring ambient pressure Photoemission Spectroscopy (PES), which yields information on the absolute work function (φ) of a metal and the Ionisation Potential (IP) of a semiconductor, coupled with a high resolution Contact Potential Difference capability which can be extended to Surface Photovoltage measurements. The relative energy resolution are 50 meV for PES and 1-3 meV for CPD. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used UPS. We propose a mechanism of atmospheric ion generation and show that for the metal photoresponse obeys Fowler Theory. The relationship between CPD and photoelectric threshold is a useful tool in characterizing the electrical behavior of materials. We illustrate this with native oxide covered Cu and n-type Si. Further we show that the photoresponse can be used to generate the near Fermi-level Density of States (DOS) in Iron and Nickel-Phthalocyanine. © 2014 The Authors.


Harwell J.R.,University of St. Andrews | Baikie T.K.,University of St. Andrews | Baikie T.K.,KP Technology Ltd. | Baikie I.D.,KP Technology Ltd. | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2016

The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials. © 2016 the Owner Societies.


Aytun T.,Sabanci University | Turak A.,Sabanci University | Turak A.,Max Planck Institute for Intelligent Systems (Stuttgart) | Baikie I.,KP Technology Ltd. | And 2 more authors.
Nano Letters | Year: 2012

Although ambient processing is the key to low-cost organic solar cell production, high-vacuum thermal evaporation of LiF is often a limiting step, motivating the exploration of solution processing of LiF as an alternative electrode interlayer. Submonolayer films are realized with the assistance of polymeric micelle reactors that enable LiF particle deposition with controlled nanoscale surface coverage. Scanning Kelvin probe reveals a work function tunable with nanoparticle coverage with higher values than that of bare indium tin oxide (ITO). © 2011 American Chemical Society.


Halek G.,Wroclaw University of Technology | Baikie I.D.,KP Technology Ltd. | Teterycz H.,Wroclaw University of Technology | Halek P.,Wroclaw University of Technology | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2013

In this paper platinum (Pt) doped tungsten trioxide (WO3) layers have been investigated. The structures were prepared in the standard thick film technology. A scanning electron microscope (SEM) was used for the microstructure analysis of the gas sensitive layers. The work function was examined by using a scanning Kelvin probe (SKP). The Kelvin probe is a non-contact and non-destructive method to provide work function measurements and surface analysis. This tool is very sensitive to any surface potential changes of the investigated material. The measurements preformed by using the SKP shows that the screen printed WO3 layers were very homogenous and no significant defects are present. The Pt dopants added to the gas sensitive layer created small clusters on the surface of the WO3 grains. The presence of those additives changes the potential barrier between the metal oxide crystals and caused a decrease of the sensing layer conductance at low dopants concentration, until the exceed of the percolation threshold. Moreover, due to the introduction of additives a change in the activation energy was observed which has influence on the sensor parameters and resulted in increase of the sensitivity to isopropyl alcohol. © 2012 Elsevier B.V. All rights reserved.


Baikie I.D.,KP Technology Ltd | Grain A.C.,KP Technology Ltd | Sutherland J.,KP Technology Ltd | Law J.,KP Technology Ltd
Applied Surface Science | Year: 2014

We describe a novel photoemission technique utilizing a traditional Kelvin probe as a detector of electrons/atmospheric ions ejected from metallic surfaces (Au, Ag, Cu, Fe, Ni, Ti, Zn, Al) illuminated by a deep ultra-violet (DUV) source under ambient pressure. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used with UPS. This arrangement can be applied in several operational modes: using the DUV source to determine the photoemission threshold (Φ) with 30-50 meV resolution and also the Kelvin probe, under dark conditions, to measure contact potential difference (CPD) between the Kelvin probe tip and the metallic sample with an accuracy of 1-3 meV. We have studied the relationship between the photoelectric threshold and CPD of metal surfaces cleaned in ambient conditions. Inclusion of a second spectroscopic visible source was used to confirm a semiconducting oxide, possibly Cu2O, via surface photovoltage measurements with the KP. This dual detection system can be easily extended to controlled gas conditions, relative humidity control and sample heating/cooling. © 2014 The Authors.


Ibrahim N.,Northumbria University | Ibrahim N.,University Malaysia Perlis | Poulidi D.,Northumbria University | Rivas M.E.,Northumbria University | And 2 more authors.
Electrochimica Acta | Year: 2012

The role of sodium surface species in the modification of a platinum (Pt) catalyst film supported on 8 mol% yttria-stabilised-zirconia (YSZ) was investigated under a flow of 20 kPa oxygen at 400°C. Cyclic and linear sweep voltammetry were used to investigate the kinetics of the oxygen charge transfer reaction. The Pt/YSZ systems of both 'clean' and variable-coverage sodium-modified catalyst surfaces were also characterised using SEM, XPS and work function measurements using the Kelvin probe technique. Samples with sodium coverage from 0.5 to 100% were used. It was found that sodium addition modifies the binding energy of oxygen onto the catalyst surface. Cyclic voltammetry experiments showed that higher overpotentials were required for oxygen reduction with increasing sodium coverage. In addition, sodium was found to modify oxygen storage and/or adsorption and diffusion increasing current densities at higher cathodic overpotential. Ex situ XPS measurements showed the presence of sodium hydroxide, carbonate and/or oxide species on the catalyst surface, while the Kelvin probe technique showed a decrease of approximately 250 meV in the work function of samples with more than 50% sodium coverage (compared to a nominally 'clean' sample). © 2012 Elsevier Ltd. All rights reserved.


Patent
KP Technology Ltd. | Date: 2013-02-21

A measurement apparatus for surface analysis carried out in a gaseous environment such as air comprises a measurement device capable of measuring a contact potential difference between a probe and a surface, and a light source that triggers photoelectric emission from a sample. The apparatus may operate in dual photoemission and contact potential difference (CPD) measurement modes.

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