Portrait of Mr Robert Oven

Mr Robert Oven

Senior Lecturer in Electronic Engineering
Director of Education

About

Robert has been a Lecturer and Senior Lecturer at Kent since 1986.  He has published 44 reviewed papers on the modelling of ion implantation processes and more recently on ion diffusion in glass, electrically poled glass and optical assessment methods.  Since 2015 he has been Director of Education in EDA.  He is a member of the Faculty Education Committee and a member of the University Academic Standards and Quality Committee (ASQC).

Research interests

Physical electronics

Teaching

  •  DC Circuits in EL025 
  •  Electronic circuits and Systems in EL026
  • Electrostatics in EL024
  • Optical Communications in EL677
  • Electronic Instumentation and Measurement Systems EL565

Publications

Article

  • Oven, R. (2018). Comment on 'The most energy efficient way to charge the capacitor in a RC circuit' (D. Wang 2017 Phys. Educ. 52 065019). Physics Education [Online] 53. Available at: https://doi.org/10.1088/1361-6552/aab92f.
    In a recent paper (Wang. D. (2017) Phys. Educ. 52 065019) a comparison was made
    between the efficiency in charging a capacitor (C) in series with a resistor (R) using
    either a voltage source or a constant current source. The paper concluded that
    using a current source was more efficient. We show that this is not correct when the
    energy loss within the current source is considered. It is also shown that the energy
    loss is not dependent on the charging rate. A formal proof using calculus and
    simpler graphical arguments are presented.
  • Oven, R. (2017). AC impedance of poled glass during de-poling. Solid State Ionics [Online] 315:14-18. Available at: https://doi.org/10.1016/j.ssi.2017.11.018.
    It has been observed in the literature that when the DC poling voltage is removed at the end of the poling process in glass in a so called de-poling experiment, the small signal AC impedance as measured by impedance spectroscopy increases immediately. It is shown that this effect can be explained if the DC voltage causes nonlinear ionic conduction to occur in the poled layer. The DC field changes the barrier height over which ions have to jump from one site to another and this also effects the AC resistance; by removing the DC field the original barrier height is restored thus increasing the AC resistance. Analysis of experimental data using poled soda-lime glass supports this interpretation.
  • Oven, R. (2016). Measurement of the refractive index of electrically poled soda-lime glass layers using leaky modes. Applied Optics [Online] 55:9123-9130. Available at: http://doi.org/10.1364/AO.55.009123.
    Electrically poled layers have been formed in soda-lime glass using graphite electrodes in air. The refractive index and thickness of the poled glass layers have been measured by the analysis of leaky optical modes. These modes are supported by the poled layer and can be determined by analysis of the optical reflectivity measured with a prism coupler arrangement. A relatively constant refractive index ~ 1.486 in the poled glass region is measured, which is ~0.03 below the substrate index. The reflectivity data shows that the transition between poled and un-poled glass is very sharp and is consistent with ion transport models. The thickness of the poled glass region is consistent with the removal of Na+ and K+ ions from the poled region. The index and depth data is confirmed by interferometric measurements. The tensile stress in the poled glass layer is also estimated from optical birefringence measurements and is estimated to be ~0.3 GN/m2.
  • Oven, R. (2015). Measurement of planar refractive index profiles with rapid variations in glass using interferometry and total variation regularized differentiation. Journal of Modern Optics [Online] 62:S59-S66. Available at: http://doi.org/10.1080/09500340.2015.1083130.
    Planar refractive index profiles with rapid variations, formed in glass, are measured with interferometry. This involves forming a bevel in the glass and orientating the fringe pattern to be normal to the bevel edge. The index profile is determined by differentiation of the phase function of the fringe pattern. The differentiation has been performed using the total variation regularization method in order to preserve rapid changes in the derivative. This new approach avoids the necessity of filtering, in order to reduce noise, in the direction perpendicular to the bevel, which would otherwise smooth out the rapid index changes. The method is assessed using a model refractive index profile that contains an index gradient of 0.24 μm−1 and is then applied practically to measure the refractive index profile of electrically poled BK7 glass. The new approach allows the sharp transition in the index between poled and unpoled glass to be observed as well as the accumulation of potassium ions beyond the poled glass region.
  • Oven, R. (2014). Modified Charge Amplifier for Stray Immune Capacitance Measurements. IEEE Transactions on Instrumentation and Measurement [Online] 63:1748-1752. Available at: http://dx.doi.org/10.1109/TIM.2014.2298673.
    It is shown theoretically and by experimentation that the ac stray immune capacitance meter based on the charge amplifier circuit can be modified to reduce the effects of the parasitic capacitance across the feedback capacitor. This is achieved by simply introducing a unity gain buffer amplifier within the circuit loop.
  • Oven, R. (2011). Polarizability, Volume Expansion and Stress Contributions to the Refractive Index Change of Cu+-Na+ Ion Exchanged Waveguides in Glass. Applied Optics [Online] 50:5073-5079. Available at: http://dx.doi.org/10.1364/AO.50.005073.
    The refractive index of optical waveguides formed by electric field assisted Cu+-Na+ ion exchange in two types of glass is measured. Assuming, as in a previously published work, that the observed refractive index increase is solely due to polarizability changes, the difference in electronic polarizability between Cu+ and Na+ ions is determined by applying the Lorentz–Lorenz equation to the data. In our work, the concentration of exchanged ions, which is a necessary input to the Lorentz–Lorenz equation, is determined by combining optical data and electrical data obtained during the exchange. Values for the electronic polarizability difference are in agreement with that in the literature. However, when a correction is made, taking into consideration the measured volume expansion and stress in the glass, the calculated electronic polarizability difference is shown to increase by 19%.
  • Oven, R. (2010). Extraction of Phase Derivative Data from Interferometer Images using a Continuous Wavelet Transform to Determine Two-Dimensional Refractive Index Profiles. Applied Optics [Online] 49:4228-4236. Available at: http://dx.doi.org/10.1364/AO.49.004228.
    Two-dimensional refractive index profiles of ion exchanged channel waveguides in glass have been obtained from the analysis of interferometer data. To obtain depth data, a shallow bevel is produced in the glass by polishing. The refractive index profile information that is contained within the derivative of the phase data is extracted directly using a continuous wavelet transform algorithm. The algorithm used to characterise and smooth the wavelet ridge is discussed in detail.
  • Oven, R. (2009). Measurement of Two Dimensional Refractive Index Profiles of Channel Waveguides using an Interferometric Technique. Applied Optics [Online] 48:5704-5712. Available at: http://dx.doi.org/10.1364/AO.48.005704.
    Two dimensional refractive index profiles of ion exchanges channel waveguides in glass have been measured using an interferometric method. In order to obtain depth data, a shallow bevel is produced in the glass by polishing. A regularization algorithms for the extraction of the phase data from the interferometer image is presented. The method is applied to waveguides formed by the electric field assisted diffusion of Cu+ ions into a borosilicate glass. The index change obtained from the interferometer is in good agreement with that obtained from measurements on planar waveguides.
  • Oven, R. (2008). Mapping Method for the Comparison of Mode Data from Field Assisted Ion Diffused Guides. Optical Materials [Online] 31:291-295. Available at: http://dx.doi.org/10.1016/j.optmat.2008.04.010.
    It is shown that the mode data of field assisted ion exchange profiles in glass can be mapped onto one another when the refractive index profiles are shifted versions of each other, i.e. of the form n(x + s) where s is a shift distance. This allows the mode data of shallow guides to be compared with data of deeper guides. The mapping has utility in that the shallow guide may not support a sufficient number of modes in order for a refractive index profile reconstruction to be made.
  • Oven, R. (2007). Modeling the sequential electric field assisted diffusion into glass of two ion species. Journal of Applied Physics [Online] 101:113113. Available at: http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=JAPIAU000101000011@webtc.pdf&idtype=tocpdf.
    The sequential electric field assisted diffusion of two ion species into glass is modeled in this work. Using standard assumptions, two coupled nonlinear drift-diffusion equations are derived for the ion concentration distributions. These equations are solved numerically for the case where the two ion species each have a lower mobility than the indigenous sodium ions in the glass. It is shown that stationary state distributions form if the final species injected into the glass is the less mobile of the two. Analytical expressions are derived for the stationary state distributions. A possible application in integrated optics involving Ag+ and Cu+ ion diffusion is considered.
  • Oven, R. (2006). Surface Expansion of Channel Waveguides formed by Ion Exchange in Glass. Journal of Applied Physics [Online] 100. Available at: http://dx.doi.org/10.1063/1.2337785.
  • Oven, R. and Yin, M. (2006). Assessment of Ion Exchanged Channel Waveguides in Glass using Interference Microscopy. Optics Communications [Online] 260:506-510. Available at: http://dx.doi.org/10.1016/j.optcom.2005.10.061.
  • Oven, R. (2006). Tapered Waveguides produced by Ion Exchange in Glass with a Non-Uniform Electric Field. Journal of Lightwave Technology [Online] 24:4337-4344. Available at: http://www.opticsinfobase.org/abstract.cfm?URI=JLT-24-11-4337.
  • Oven, R. and Young, P. (2005). Microwave Loss of Coplanar Waveguides on Electrically Ion Depleted Borosilicate Glass. IEEE Microwave and Wireless Components Letters [Online] 15:125-127. Available at: http://dx.doi.org/10.1109/LMWC.2004.842858.
    The surface of a borosilicate glass has been modified by an electrical ion. depletion process with the aim of permanently removing sodium ions, thus, reducing its loss at microwave frequencies. The modified layer has sufficient depth such that coplanar waveguides formed on top of the glass exhibit lower loss in comparison with waveguides formed on undepleted glass.
  • Oven, R., Yin, M. and Davies, P. (2004). Characterization of planar optical waveguides formed by copper-sodium, electric field assisted, ion exchange in glass. Journal of Physics D: Applied Physics [Online] 37:2207-2215. Available at: http://dx.doi.org/10.1088/0022-3727/37/16/001.
    Planar waveguides have been formed by the electric field assisted diffusion of copper ions from a metallic copper film into a borosilicate glass (Corning 7740). The waveguides have been analysed using conventional prism coupling techniques and have been compared with the electric field assisted diffusion of silver into the same glass type. The measured refractive index profiles for copper Guides are shown to have nearly Fermi function shapes, which are consistent with the theory of field assisted ion diffusion in glass. It is shown, however, that the guide depth formed by copper or silver ions is laraer than that predicted by calculations based on the nominal C composition, possibly indicating that only a fraction of the sodium ions within the glass are mobile. Annealing experiments have been performed on the guides in order to determine the copper self-diffusion coefficient in the Glass. The coefficients are extracted from the data by fitting a non-linear diffusion equation model of ion motion in glass to the experimental profiles.
  • Yin, M., Oven, R. and Davies, P. (2004). Low-loss Cu+-Na+ ion exchanged optical channel waveguides in glass. Electronics Letters 40:1265-1266.
    Electric field assisted Cu+-Na+ ion exchanged optical channel waveguides have been produced in Coming 7740 borosilicate glass using a Cu film source. Average losses of 1.0, 0.45 and 0.3 dB/cm, at wavelengths of 633, 850 and 1300 nm, respectively, have been measured.
  • Oven, R., Ashworth, D. and Batchelor, S. (2001). Analytical Models for Concentration Profiles after Single and Double Reversals of the Electric Field during K+-Na+ Field Assisted Ion Exchanges in Glass. Journal of Physics D: Applied Physics [Online] 34:823-829. Available at: http://dx.doi.org/10.1088/0022-3727/34/5/321.
  • Ashworth, D., Bowyer, M. and Oven, R. (2000). Representation of ion implantation distributions in two and three dimensions. Journal of Physics D: Applied Physics [Online] 24:1120-1125. Available at: http://dx.doi.org/10.1088/0022-3727/24/7/015.
    The representation of two- and three-dimensional point response functions by Pearson frequency distribution curves is discussed for the case of energetic ions implanted into homogeneous, amorphous material. Comparisons are made between the Pearson curves and high-resolution Monte Carlo simulations. It is shown that no extra information is required to derive the three-dimensional representation once the two-dimensional representation is known.
  • Bowyer, M., Ashworth, D. and Oven, R. (2000). Central moments of ion implantation distributions derived by the backward Boltzmann transport equation compared with Monte Carlo simulations. Journal of Physics D: Applied Physics [Online] 25:1619-1629. Available at: http://dx.doi.org/10.1088/0022-3727/25/11/009.
    The authors study solutions to the backward Boltzmann transport equation (BBTE) specialized to equations governing moments of the distribution of ions implanted into amorphous targets. A central moment integral equation set has been derived starting from the classical plane source BBTE for non-central moments. A full generator equation is provided to allow construction of equation sets of an arbitrary size, thus allowing computation of moments of arbitrary order. A BBTE solver program has been written that uses the residual correction technique proposed by Winterbon (1970). A simple means is presented to allow direct incorporation of Biersack's two-parameter 'magic formula' into a BBTE solver program. Results for non-central and central moment integral equation sets are compared with Monte Carlo simulations, using three different formulae for the mean free flight path between collisions. Comparisons are performed for the ions B and As, implanted into the target a-Si, over the energy range 1 keV-1 MeV. The central moment integral equation set is found to have superior convergence properties to the non-central moment equation set. For As ions implanted into a-Si, at energies below approximately 30 keV, significant differences are observed, for third- and fourth-order moments, when using alternative versions for the mean free flight path. Third- and fourth-order moments derived using one- and two-parameter scattering mechanisms also show significant differences over the same energy range.
  • Oven, R., Ashworth, D. and Batchelor, S. (1999). Modelling the annealing of electric-field-assisted K+-Na+ ion exchanged planar waveguides manufactured in soda-lime glass. Journal of Physics D: Applied Physics [Online] 32:1124-1129. Available at: http://dx.doi.org/10.1088/0022-3727/32/10/308.
    An analytical model is developed and used to analyse the evolution in the refractive index profiles resulting from the annealing of electric-field-assisted K+-Na+ ion exchanged planar optical guides formed in soda-lime glass. The model takes into consideration diffusion effects and a relaxation effect that is observed to occur within the region of the glass into which the K+ ions are injected. Analyses of experimental results using the model show that the time constant for the relaxation mechanism depends on the annealing temperature and on the rate at which the K+ ions are injected into the glass, However, the degree of relaxation is relatively independent of these variables.
  • Oven, R., Batchelor, S. and Ashworth, D. (1999). Effects of annealing electric field assisted K+-Na+ ion exchanged soda-lime glass guides. Journal of Physics D: Applied Physics [Online] 32:650-655. Available at: http://dx.doi.org/10.1088/0022-3727/32/6/009.
    Soda-lime glass samples have been subjected to either a thermal or an electric field assisted K+-Na+ ion exchange. The effective refractive indices of the modes supported by the guides have been measured using a prism coupler before and after annealing and refractive index profiles have been reconstructed from the data. The effective refractive indices of the modes for guides produced by electric field assisted exchange exhibit an unusual evolution with annealing time. The area under the refractive index profiles produced from the measurements shows a significant reduction with annealing time. These features are not present in samples prepared by thermal ion exchange. The results are attributed to a relaxation mechanism operative only within regions of the glass that have been subjected to field assisted K+ ion injection.
  • Batchelor, S., Oven, R. and Ashworth, D. (1998). The effect of field reversals on refractive index profiles and stress in electric field assisted K+-Na+ ion-exchanged soda-lime glass. Journal of Physics D: Applied Physics [Online] 31:390-401. Available at: http://dx.doi.org/10.1088/0022-3727/31/4/008.
    Soda-lime glass samples have been subjected to both single and double field reversals during electric field assisted K+-Na+ ion exchanges in the temperature range 350-450 degrees C. Changes in refractive index profiles, chemical profiles and surface stress were observed during the exchanges and a comparison has been made with previous studies. It is shown that large reductions in surface stress seen after single field reversals, which have previously been attributed primarily to a stress relaxation mechanism, are mainly caused by the removal of a large number of K+ ions. For example, at 395 degrees C K+ ion removal accounts for 80-95% of the stress reduction. It is shown that the drift-diffusion model of ion transport, using concentration-independent self-diffusion coefficients, cannot consistently model this large ion removal rate. A new model is developed which is based on drift-diffusion transport with concentration-dependent self-diffusion coefficients. The effects of double field reversals are also investigated. It is suggested that the glass may undergo an irreversible change associated with K+ ion removal.
  • Oven, R., Batchelor, S. and Ashworth, D. (1997). Use of multiple-wavelength and/or TE/TM effective-refractive-index measurements to reconstruct refractive-index profiles. IEE Proceedings: Optoelectronics [Online] 144:213-219. Available at: http://dx.doi.org/10.1049/ip-opt:19971273.
    A method is presented whereby the refractive-index profile of a planar, surface-dielectric optical waveguide may be reconstructed from sets of effective refractive indices, measured at different wavelengths and/or with sets of effective refractive indices measured with TE and TM polarisation. The index change and the substrate index may be wavelength dispersive and birefringent. The method is compared, both theoretically and experimentally, with conventional single-wavelength method for a number of index profiles. This technique provides more information about the profile than can be obtained from one measured set and is used to analyse the index profiles of potassium ion exchange guides formed in soda-lime glass. The limitations of the technique are also discussed.
  • Batchelor, S., Oven, R. and Ashworth, D. (1996). Reconstruction of refractive index profiles from multiple wavelength mode indices. Optics Communications [Online] 131:31-36. Available at: http://dx.doi.org/10.1016/0030-4018(96)00252-0.
    A method is-presented whereby the refractive index profile of a planar, surface, dielectric optical waveguide may be reconstructed from sets of effective refractive indices, measured at different wavelengths. In order to allow for the dispersive nature of the glass, additional information from highly multi-mode guides, which are produced by the same manufacturing process as the guide under analysis, has been used in the method. The technique provides greater information about the profile than can be obtained from one measured set and is used here to analyse the profiles of potassium ion diffused guides formed in glass.
  • Bowyer, M., Ashworth, D. and Oven, R. (1996). Representation of two-dimensional ion implantation rest distributions by Pearson distribution curves for silicon technology. Solid-State Electronics [Online] 39:119-126. Available at: http://dx.doi.org/10.1016/0038-1101(95)00117-C.
    This is the second of two papers concerned with fitting Pearson curves to Monte Carlo simulations of implants into amorphous targets. In the first paper [Solid-St. Electron. 35, 1151 (1992)] it was shown that accurate Pearson curve fitting to projected range profiles is possible when implant profiles are available for which optimised moments can be generated. In the present paper we extend the fitting to simulations of two-dimensional rest distributions. Comparisons are made between Pearson curve fits and the original high-resolution implant profiles, in two-dimensions, for the ions B and As implanted into amorphous silicon. The profiles were derived from Monte Carlo simulations, each of one million ion trajectories. Fit coefficients are provided that allow the regeneration of the moment surfaces for the depth and implantation energy dependent lateral straggle and lateral kurtosis for the ions B, P, As and Sb implanted, with energies in the range 25-300 keV, into targets of amorphous silicon, silicon dioxide and silicon nitride. The depth-dependent lateral distribution is then constructed using symmetrical Pearson curves driven by analytical formulae for the moment surfaces. The two-dimensional rest distribution is then reconstructed from the product of this depth-dependent lateral distribution and the projected range distribution derived in the first paper.
  • Bowyer, M., Ashworth, D. and Oven, R. (1996). Generating ion implantation profiles in one and two dimensions .1. Density functions. Journal of Physics D: Applied Physics [Online] 29:1274-1285. Available at: http://dx.doi.org/10.1088/0022-3727/29/5/022.
    In this, the first of two papers, the problem of constructing ion implantation profiles in one and two dimensions from depth-independent spatial moments is discussed. Comparisons are made between Pearson and Johnson curves, constructed from moments produced by a transport equation solver, and profiles obtained directly from Monte Carte simulations. A set of such comparisons, using consistent input quantities, is performed over a range of ion-target mass ratios and energies. For projected range distributions of the ions B, P and As into a-Si, a single Johnson type (S-B) describes the implants over the energy range 1 keV to 1 MeV. The description using Pearson curves requires two types (I and VI). Also, taking the Monte Carlo data as a reference, the Johnson curves are equivalent, if not superior, to the Pearson curves in terms of fit accuracy. For lateral distributions of the same ion types over the same energy range it is shown that if the depth-dependent lateral kurtosis is less than 3.0, then the Pearson type II (bounded), Johnson type S-B (bounded) and the modified Gaussian (unbounded) curves prove acceptable representations. If the depth-dependent lateral kurtosis is greater than 3.0 then the Pearson type VII (unbounded) and Johnson type S-U (unbounded) curves are good representations.
  • Batchelor, S., Oven, R. and Ashworth, D. (1996). Characterisation of electric field assisted diffused potassium ion planar optical waveguides. Electronics Letters [Online] 32:2082-2083. Available at: http://dx.doi.org/10.1049/el:19961393.
    A simple drift transport model is used to predict the depth of planar optical waveguides produced by the electric field assisted ion exchange of potassium ions into soda-lime glass. The guide depth can be represented by a simple universal function of the voltage-process lime product. The model is fitted to experimental data over a wide range of applied potentials and times. Joule heating effects limit the accuracy of the model at large current densities.
  • Bowyer, M., Ashworth, D. and Oven, R. (1996). Generating ion implantation profiles in one and two dimensions .2. Depth-dependent moments and line-source responses. Journal of Physics D: Applied Physics [Online] 29:1286-1299. Available at: http://dx.doi.org/10.1088/0022-3727/29/5/023.
    In this, the second of two papers, various techniques and models are proposed for the extraction of depth-dependent lateral moments from the depth-independent mixed moments produced by transport equation solvers. These depth-dependent moments are then compared with those obtained directly from Monte Carlo simulations. A set of such comparisons, using consistent input quantities, is performed over a range of ion-target mass ratios and energies. The depth-dependent moments are then combined with Pearson and/or Johnson curves to form two-dimensional ion implantation profiles. Comparisons are made between these line-source responses (LSRs) and LSRs obtained directly from Monte Carlo simulations into a-Si for the various models over a range of energies and ion types. Selection of appropriate models leads to LSRs for the ions B, P and As implanted into a-Si which are in good agreement with Monte Carte simulations over three orders of magnitude of profile concentration. The techniques described will enable two-dimensional profile information to be stored and regenerated, quickly and efficiently, within process simulators so that rapid optimization of processing parameters may be achieved.
  • Oven, R. et al. (1995). Iterative Refinement Technique for Reconstructing Refractive-Index Profiles from Mode Indexes. Electronics Letters [Online] 31:229-231. Available at: http://dx.doi.org/10.1049/el:19950156.
    A method is presented whereby the refractive index profile of a planar, surface, dielectric optical waveguide may be reconstructed from a measured set of effective refractive indices in a way that is consistent with the Helmholtz equation. Profiles are compared with those obtained by conventional techniques which use the Wentzel-Kramers-Brillouin (WKB) approximation.
  • Ashworth, D., Oven, R. and Page, M. (1995). The Influence of the Pseudo-Mixed-Alkali Effect on the Field-Assisted Diffusion of Silver Ions into Glass for Optical Wave-Guides. Journal of Physics D: Applied Physics [Online] 28:657-664. Available at: http://dx.doi.org/10.1088/0022-3727/28/4/006.
    Results are presented from a study of the field-assisted diffusion of silver ions from silver films into soda-lime glass. These indicate that it is necessary to take into consideration the concentration dependence of the self-diffusion coefficient of both the silver and the sodium ions in a pseudo-mixed-alkali effect in order to predict the silver diffusion profiles accurately. A field assisted diffusion model that incorporates this effect is developed and model coefficients are deduced. The model is applied to post-bake diffusions and deep field-assisted diffusion profiles. The model is applicable to the design and manufacture of optical waveguides and lenses in glass by field-assisted diffusion.
  • Ashworth, D., Bowyer, M. and Oven, R. (1995). The Derivation and Moments Solution of Approximate Transport-Equations for the Implantation of Ions into Amorphous Targets. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms [Online] 100:471-482. Available at: http://dx.doi.org/10.1016/0168-583X(95)00347-9.
    Commencing with the LSS integro-differential equation, an approximate transport equation is derived from which the moments of the range distribution may be obtained. The resulting equation set is known as the Rent Range Algorithm (KRAL). The method for numerical solution of these equations, when written as a set of coupled second order ordinary differential equations (ODEs) of the initial value type, is then outlined. Solution is achieved by recasting the equation set in the form of first order ODEs designed for iterative solution. The technique used is an iterative refinement (or residual correction) procedure and the set of first order ODEs is called the Rent Optimised Range Algorithm (KORAL). Finally, the first three moments from KORAL, first and second order PRAL codes and the full transport equation code KUBBIC-91 are compared with Monte Carlo data obtained from a TRIM code modified to treat targets of infinite extent. Comparisons are performed using consistent nuclear and electronic energy loss models.
  • Bowyer, M., Ashworth, D. and Oven, R. (1994). A revised version of the Projected Range ALgorithm with numerical solutions. Radiation Effects and Defects in Solids: Incorporating Plasma Science and Plasma Technology [Online] null:535-557. Available at: http://dx.doi.org/10.1080/10420159408219811.
    In a previous paper a revised version of the Projected Range ALgorithm (PRAL) was presented. These new equations, called the Kent Range ALgorithm (KRAL), consider fully the motion of the ion in three dimensions. In the current paper we review a simple derivation of the KRAL equations starting from the standard LSS integral equations for moments of the range distribution. The resulting 2nd order ordinary differential equations are difficult to solve using classical numerical techniques. We present a modified set of equations called the Kent Optimised Range ALgorithm (KORAL) which is designed for iterative solution. Finally, we compare results from KORAL and 1st and 2nd order PRAL codes with Monte Carlo data from a TRIM code modified to treat targets of infinite extent. Comparisons are performed using consistent nuclear and electronic energy loss models.
  • Bowyer, M., Ashworth, D. and Oven, R. (1994). A Generalized Transport-Equation For Ion-Implantation Into Infinite Targets. Journal of Physics D: Applied Physics [Online] 27:2592-2600. Available at: http://dx.doi.org/10.1088/0022-3727/27/12/021.
    In this paper a transport equation (TE) is derived which incorporates arbitrary distribution functions and a cut-off energy. Integral equations for the gas-like and liquid free-flight path length distribution models are both incorporated into the transport theory computer code KUBBIC using the two-parameter differential nuclear scattering cross section. Simulations for the ion As implanted into a-Si are compared with those performed using a parallel processor Monte Carlo (MC) code based on TRIM. Excellent agreement is obtained when using four versions of the liquid model, including use of the Biersack free-flight path extension formula and the time integral hard sphere approximation. In addition, the effects of varying the maximum impact parameter are investigated as is the effect of the ordering of nuclear and electronic interactions. The TE formalism and solver presented in this paper serve as a powerful tool for testing new approximations which may be incorporated into MC codes in order to improve computational efficiency.
  • Oven, R., Bowyer, M. and Ashworth, D. (1993). A transport equation model that is consistent with Monte Carlo simulations of ion implantation into infinite targets. Journal of Physics: Condensed Matter 5:2157-2170.
    In this paper a transport equation (TE) is derived that matches closely (within the limitation of an infinite target) the transport model in the Monte Carlo code TRIM. Initially, the authors derive a TE that incorporates an arbitrary free-flight path length distribution function and a stopping energy. From this TE a coupled set of integral equations (for spatial moments up to order four) incorporating the liquid free-flight path model used in TRIM is derived. Also, for the gas-like model of the free-flight path length distribution, the equivalence is shown between the new TE and the LSS backward linearized Boltzmann equation extended by Brice to include an intermediate energy.
  • Oven, R., Ashworth, D. and Bowyer, M. (1992). Formulae for the Distribution of Ions under an Ideal Mask. Journal of Physics D: Applied Physics [Online] 25:1235-1237. Available at: http://dx.doi.org/10.1088/0022-3727/25/8/013.
    Analytical expressions are derived for the distribution of implanted ions under an ideal mask using Pearson II, Pearson VII, and modified Gaussian models for the lateral distribution of a single ion. These expressions are then used to calculate ion concentration contours under an ideal mask from fits to single-ion Monte Carlo generated projected range profiles and depth-dependent lateral standard deviations and kurtoses for 275 keV boron and phosphorus ions implanted into amorphous silicon. These contours are then compared with ion concentration contours under an ideal mask obtained from numerical convolution of the raw, two-dimensional Monte Carlo profile data with the aperture function. Good agreement is found over three orders of magnitude.
  • Bowyer, M., Ashworth, D. and Oven, R. (1992). Representation of ion implantation projected range profiles by Pearson distribution curves for silicon technology. Solid-State Electronics [Online] 35:1151-1166. Available at: http://dx.doi.org/10.1016/0038-1101(92)90016-6.
    In this paper a transport equation (TE) is derived that matches closely (within the limitation of an infinite target) the transport model in the Monte Carlo code TRIM. Initially, the authors derive a TE that incorporates an arbitrary free-flight path length distribution function and a stopping energy. From this TE a coupled set of integral equations (for spatial moments up to order four) incorporating the liquid free-flight path model used in TRIM is derived. Also, for the gas-like model of the free-flight path length distribution, the equivalence is shown between the new TE and the LSS backward linearized Boltzmann equation extended by Brice to include an intermediate energy.
  • Oven, R., Ashworth, D. and Page, M. (1992). On The Analysis of Field-Assisted Ion Diffusion into Glass. Journal of Physics: Condensed Matter [Online] 4:4089-4094. Available at: http://dx.doi.org/10.1088/0953-8984/4/16/009.
    The process of field-assisted diffusion of ions into glass is analysed theoretically without the introduction of a conventionally used quasi-neutral space-charge approximation. The analysis shows that the quasi-neutral approximation is valid over a wide range of injection rates and processing temperatures. This result, which is of relevance to the manufacture of glass-based optical waveguides by the field-assisted injection of silver or potassium ions, is achieved by analysing the stationary state solution of a model drift-diffusion equation.
  • Page, M., Oven, R. and Ashworth, D. (1991). Scaling rules for glass based planar optical waveguides made by field assisted ion diffusion. Electronics Letters [Online] 27:2073-2076. Available at: http://dx.doi.org/10.1049/el:19911285.
    Scaling rules implicit in the model for field assisted ion diffusion into glass have been experimentally observed in planar guides made by the diffusion of silver ions from silver films into soda-lime glass. These scaling rules are observed despite the relatively poor agreement between the refractive index profile and calculations.
  • Ashworth, D., Oven, R. and Bowyer, M. (1991). Lateral variance of implanted ions. Electronics Letters [Online] 27:1402-1403. Available at: http://dx.doi.org/10.1049/el:19910880.
    A quadratic model is presented whereby the depth-dependent lateral variance of ions implanted into amorphous targets may be estimated from a knowledge of the first seven moments of the distribution. The authors compare their results, and those derived using a perturbation approach of Lorenz et al., (1989) against high resolution Monte-Carlo data.
  • Ashworth, D., Bowyer, M. and Oven, R. (1991). A revised version of PRAL - the Projected Range Algorithm. Journal of Physics D: Applied Physics [Online] 24. Available at: http://dx.doi.org/10.1088/0022-3727/24/8/022.
    PRAL, a projected range algorithm is widely used to predict the first few moments of the spatial distribution of ions implanted into amorphous targets of infinite extent. It is shown here that PRAL contains mathematical defects. These are corrected in the new Kent range algorithm (KRAL) which is shown to be compatible with LSS theory. KRAL and PRAL predict the same range but the new algorithm is superior in its predictions of lateral and longitudinal standard deviations when compared with moments derived from the Monte Carlo code TRIM using the same differential nuclear scattering cross sections and electronic energy loss mechanisms.
  • Ashworth, D., Oven, R. and Mundin, B. (1990). Representation of ion implantation profiles by Pearson frequency distribution curves. Journal of Physics D: Applied Physics [Online] 23:870-876. Available at: http://dx.doi.org/10.1088/0022-3727/23/7/018.
    A method is described whereby ion implantation profiles in amorphous materials may be accurately represented by Pearson frequency distribution curves. The type of Pearson distribution to be used depends upon the implantation conditions but it is shown that the three main types, I, IV and VI, together with the transition types II, III, V, VII and the Gaussian are all suitable representations. Previous attempts to fit Pearson curves to implantation profiles have often failed due to semi-infinite moments being used instead of infinite moments. This approximation is only valid when the surface concentration of implanted ions is negligibly small.
  • Oven, R., Ashworth, D. and Al-Rawi, S. (1988). Impurity redistribution during sublimation in UHV. Solid-State Electronics [Online] 31:1650-1652. Available at: http://dx.doi.org/10.1016/0038-1101(88)90015-9.
  • Oven, R. and Ashworth, D. (1987). A comparison of two-dimensional ion-implantation profiles. Journal of Physics D: Applied Physics [Online] 20:1219-1219. Available at: http://dx.doi.org/10.1088/0022-3727/20/9/525.
  • Ashworth, D. and Oven, R. (1986). Theoretical predictions of the lateral spreading of implanted ions. Journal of Physics C: Solid State Physics [Online] 19:5769-5781. Available at: http://dx.doi.org/10.1088/0022-3719/19/29/004.
    The theoretical model and computer program (AAMPITS-3D) of Ashworth and coworkers (1985) for the calculation of three-dimensional distributions of implanted ions in multielement amorphous targets are extended to show that the lateral rest distribution is gaussian in a form with a lateral standard deviation (lateral-spread function) which is a function of depth beneath the target surface. A method is given whereby this function may be accurately determined from a knowledge of the projected range and chord range rest distribution functions. Examples of the lateral-spread function are given for boron, phosphorus and arsenic ions implanted into silicon and a detailed description is given of how the lateral-spread function may be used in conjunction with the projected range rest distribution function to provide a fully three-dimensional rest distribution of ions implanted into amorphous targets. Examples of normalised single ion isodensity contours computed from AMPITS-3D are compared with those obtained using the previous assumption of a lateral standard deviation which was independent of distance beneath the target surface.

Book section

  • Ashworth, D., Bowyer, M. and Oven, R. (1997). Numerical Solution of Transport Models. in: Smith, R. ed. Atomic and Ion Collisions in Solids and at Surfaces: Theory, Simulation and Applications. Cambridge University Press, pp. 123-128.
  • Ashworth, D., Bowyer, M. and Oven, R. (1997). The Rest Distribution of Primary Ions in Amorphous Targets. in: Smith, R. ed. Atomic and Ion Collisions in Solids and at Surfaces: Theory, Simulation and Applications. Cambridge University Press, pp. 161-202.

Conference or workshop item

  • Ashworth, D. et al. (1988). A method of measuring depth dependent lateral spreading of ions implanted into amorphous targets. in: UKIT '88 Conference. pp. 466-469.
  • Oven, R., Ashworth, D. and Hill, C. (1988). Simulation and Measurement of the Lateral Spreading of Ions Implanted into Amorphous Targets. in: 3rd International Conference on Simulation of Semiconductor Devices & Process. pp. 429-440.
  • Ashworth, D. and Oven, R. (1986). Computer simulation of the lateral spreading of implanted ions. in: 16th European Solid State Devices Research Conf. (ESSDERC). pp. 72-73.

Research report (external)

  • Oven, R. (2007). Definition of Demonstrators for Following Joint Research Activities.