John Kut - Publications

Journal Publications

Thickness independence of true phase transition temperatures in barium trontium titanate films

Thickness independence of true phase transition temperatures in barium strontium titanate films, A. Lookman, R. M. Bowman, J. M. Gregg, J. Kut, S. Rios, M. Dawber, A. Ruediger, and J. F. Scott, J. Appl. Phys., Vol. 96, No. 1, 1 July 2004 (Received 25 November 2003; accepted 10 April 2004)

Journal of Applied Physics -- July 1, 2004 -- Volume 96, Issue 1, pp. 555-562

Abstract: The functional properties of two types of barium strontium titanate (BST) thin film capacitor structures were studied: one set of structures was made using pulsed-laser deposition (PLD) and the other using chemical solution deposition. While initial observations on PLD films looking at the behavior of Tm (the temperature at which the maximum dielectric constant was observed) and Tc* (from Curie-Weiss analysis) suggested that the paraelectric-ferroelectric phase transition was progressively depressed in temperature as BST film thickness was reduced, further work suggested that this was not the case. Rather, it appears that the temperatures at which phase transitions occur in the thin films are independent of film thickness. Further, the fact that in many cases three transitions are observable, suggests that the sequence of symmetry transitions that occur in the thin films are the same as in bulk single crystals. This new observation could have implications for the validity of the theoretically produced thin film phase diagrams derived by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)] and extended by Ban and Alpay [J. Appl. Phys. 91, 9288 (2002)]. In addition, the fact that Tm measured for virgin films does not correlate well with the inherent phase transition behavior, suggests that the use of Tm alone to infer information about the thermodynamics of thin film capacitor behavior, may not be sufficient.

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Effects of poling, and implications for metastable phase behavior in barium strontium titanate thin film capacitors

Effects of poling, and implications for metastable phase behavior in barium strontium titanate thin film capacitors, A. Lookman, J. McAneney, R. M. Bowman, J. M. Gregg, J. Kut, S. Rios, A. Ruediger, M. Dawber, and J. F. Scott, App. Phy. Lett., Vol. 85, No. 21, 22 November 2004 (Received 12 May 2004; accepted 30 September 2004)

Applied Physics Letters -- November 22, 2004 -- Volume 85, Issue 21, pp. 5010-5012

Abstract: Barium strontium titanate (Ba_0.5Sr_0.5TiO₃–BST) thin film capacitor structures were made using pulsed laser deposition, and their functional properties were monitored with varying temperature. It was found that poling at low temperature could induce distinct differences in the behavior of the dielectric constant and loss tangent, on heating. In relatively thick BST films (>~650nm), poling the sample at 80K produced a change from a single broad anomaly to one in which three distinct anomalies could be observed. The temperatures of these anomalies (~140, ~200, and ~260K) were close to those known to be associated with phase transitions in bulk. Monitoring changes in polarization loops with temperature confirmed the likelihood that the dielectric anomalies observed were indeed the result of phase transitions in the films. Unusually, though, when the films were poled at 150K, and then cooled to 80K prior to collection of dielectric data on heating, the dielectric anomaly around 140K was completely suppressed. The lack of a phase transition was confirmed by monitoring depolarization currents in the sample. It is suggested that poling has therefore allowed the phase state that existed at 150K to persist metastably down to 80K. For relatively thin BST films (<~400nm), poling at 80K only induced two distinct anomalies in the dielectric response (at ~200 and ~290K). Nevertheless, poling-related metastability could again be observed: when the samples were poled at 250K and then cooled to 80K prior to data collection on heating, the anomaly at ~200K was completely suppressed. These experiments suggest that metastable phase behavior could be commonplace in thin film ferroelectrics.

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Papers

Author: J. Kut Supervisor: Prof. J. F. Scott Nature: Experimental Length: 15 Pages Size: 2.02 MB Format: Adobe Acrobat Document	Temperature dependent permittivity and phase transitions in Ba_0.7Sr_0.3TiO₃ ferroelectric thin film oxides, J. Kut (May 2003) Abstract: Phase transitions in barium strontium titanate (BST 70/30) thin films were inferred using dielectric [e(T) ~ 110-180] and X-ray diffraction (XRD) thermal expansion measurements. A sandwiched Au/BST/Pt/BST/Au capacitor pair was electrically characterised from 30 to 300K under vacuum (<30 mTorr) over 270 hours: recording zero-bias capacitance [C(T) ~ 2-5nF] and loss tangent [D(T) ~ 2-5%] at 100mV (f = 10^5 Hz) by impedance analyzer, and remanent polarisation (P-E) [P_r(T)] (f=1 kHz, E <10^3 kV/cm) by computer-controlled hysteresis analyzer. The wafer was produced by a propionate-based chemical solution deposition (CSD) with ex situ gold sputtered (= 0.95mm^2) top electrodes on a polycrystalline single-phase Ba_0.7Sr_0.3TiO₃ 175nm perovskite layer, with a platinum [111] bottom electrode on a SiO₂/Si [111] substrate. The film demonstrated low leakage (I <10^-8A at 300kV/cm, =290K), low dielectric loss (tan d < 0.05), symmetric capacitance-voltage (C/V) and current-voltage (I/V) profiles, ferroelectric switching at cryogenic temperatures and a breakdown field (E_B) >10^3 at =290K. We report for the first time that all three phase transitions expected in bulk BST 70/30 were observed in thin film on heating, with comparable or lower transition temperatures. In particular, the presence (or otherwise) of certain transitions depended upon thermal history. This was not exhaustively investigated and is worthy of further study. Phase transitions in Barium Strontium Titanate thin film oxides, J. Kut (April 2003) Presentation Laboratory Photographs [ Return to top ]
Author: J. Kut Supervisor: Dr. H. Sirringhaus Nature: Experimental Length: 14 Pages Size: 1.04 MB Format: Adobe Acrobat Document	Mobility of carriers in semiconductors – injected holes in n-type germanium, J. Kut (February 2002) Abstract: The propagation of injected holes along a single-crystal of homogeneous n-type germanium (20.20 × 3.00 × 0.86 mm) was studied by analysing the spatial distribution of steady transient cluster profiles measured at a later time t_drift (< 180µs) after injection. Schottky surface contact needles (< 0.1mm tip) with variable separation (x < 8mm) electrically injected and collected holes, which were ‘swept’ through the bar by a pulsed longitudinal electric field (E < 10V cm-1 via ohmic contacts). Properties of interest were deduced: ambipolar drift mobility ( µ ≈ 900 – 2500 cm2 V-1 s-1 for T ≈ 270 – 350K) [≈ apparent minority hole drift mobility µp], ambipolar diffusion coefficient (D < 80cm^2 s^-1 for T ≈ 315K) [≈ hole diffusion coefficient D_p] and hole recombination lifetime ( τp < 70µs for T > 315K). With increasing temperature, mobility decreased as µ ∝ T^-3.5 and T^-3.9 in separate tests. Of particular interest was the ability to curve fit individual gaussian-like transients to the solution of the carrier density continuity equation—allowing lifetime, mobility and diffusion coefficient values to be readily extracted. Although the temperature dependence of lifetime and diffusion was not systematically investigated, it is well supported by this study and worthy of further research. [ Return to top ]
Author: J. Kut Nature: Computational Simulation Length: 21 Pages Size: 3.04 MB Format: Adobe Acrobat Document	Percolation on a 2D lattice – a Monte Carlo computational analysis, J.Kut (January 2002) Abstract: First-nearest neighbour (Von Neumann) site percolation through a finite square two-dimensional cartesian lattice was explored using Monte Carlo FORTRAN 95 simulations. In particular, the uncontrolled propagation, burn rate (lifetime τ) and percolation threshold pc (≡ maximum lifetime τmax) of a basic model forest fire was studied—where a proportion p of sites contain a tree. Various forest sizes (17 ad hoc lattices: 4-600 units²) across a range of p values (0-1 to 8.d.p) were tested, working predominantly with one of two (alternative) lifetime definitions. 50 days (1.2×10³ hours) of processing time was used [PIII 1.0GHz CPU ≈2000 bogoMIPS] in determining the percentage of burnt trees and mean lifetime values to minimal uncertainty. The simulations functioned as intended, allowing p_c for each model forest to be found via a polynomial function fit using a non-linear least-squares (NLLS) Marquardt-Levenberg algorithm. An inverse exponentional relationship of the form: ln (p_c) ∝ -xⁿ between lattice size x and p_c was observed, where for large forests ( ~100²) p_c ≈ 0.60 and as x → ∞, p_c→ ≈ 0.593916 ± 0.001158. Although alternative lattice configurations and other factors were not considered, they are well supported by this preliminary study and are worthy of further research. NAG FORTRAN 95 Forest Fire (Monte Carlo Percolation) on a 2D Lattice Simulation Source Code: [ fire.f90 ] Sample Output from the FORTRAN 95 program Animated Output example from the FORTRAN 95 program Linux Gnuplot Screenshots (JPEG): [ Image 1, Image 2, Image 3, Image 4 ] [ Return to top ]
Author: J. Kut Supervisor: Dr. J. R. A. Cleaver Nature: Experimental Length: 20 Pages Size: 2.35 MB Format: Adobe Acrobat Document	Phase-Locked Loops – characteristics and applications, J. Kut (October 2001) Abstract: The function of a complete phase-locked loop (PLL) feedback system was explored through the characterisation of the Philips HEF4046B complementary metal oxide semiconductor (CMOS) integrated circuit (IC). Applications of interest were investigated: fixed frequency multiplication (50 Hz → 204.8 kHz) with infinite inputlocked noise rejection, demodulation of frequency modulated waveforms (≈200 kHz carrier with <12.5 kHz) and clean-signal clock regeneration—as with digital data transmission pulse synchronisation. Phase comparators (PC) type one and two of the 4046 were tested, recording waveform and transfer characteristics at ≈100 kHz, using a dual-phase shift test circuit. In conjunction with the 4046’s voltage-controlled oscillator (VCO) (studied for an output of ƒ=0 to >1Mhz), basic closed-loop PLL operation was achieved for 42-112 kHz logic signals. All configurations performed to theory, allowing experimental confirmation of PC1/2 loop stability, ad hoc resistor-capacitor (RC) filter requirements, capture (2ƒC) and lock (2ƒL) frequency range, input/output phase difference and harmonic centre-frequency (ƒo) locking. Frequency multiplication [PC2], demodulation [PC1/2] and clock regeneration [PC1] were performed using a suitable phase comparator, whilst observing their transient responses and operation range. Although advanced PLL stability and filter characteristics were not directly tested, they are well supported by theory and are worthy of further study. [ Return to top ]
Author: J. Kut Nature: Experimental Length: 18 Pages Size: 2.09 MB Format: Adobe Acrobat Document	Microwaves and Waveguides - characteristics of propagation, J. Kut (March 2001) Abstract: This report investigates a range of issues affecting the propagation of electromagnetic microwave radiation, both within a waveguide and unconstrained in laboratory space1. A 10mW solid-state Gunn diode was used to provide a stable microwave source of λ ≈ 3.63cm (f ≈ 8.3GHz), which was feed into a rectangular conducting waveguide (2.25x1.00 cm). Measured intensity within the guide was based on the voltage induced across an adjustable standing wave detector (< 240mV DC), or outside by an identical mobile detector and horn. In conjunction with terminating reflectors (metal \|r\| ≈ 1 / graphite absorber \|r\| ≈ 0), waveguide reflection coefficients were found—and used to demonstrate that a gradual change in waveguide orientation ( 2π over d >> λ) avoided reflections caused by impedance mismatch. The apparatus performed as predicted by theory, illustrating that the microwave’s electric component propagates transversely in the guide (Transverse Electric Mode – TE10), and their polarised nature in open space. Although focusing microwaves through Fresnel half-period zones and evanescent waves were not extensively investigated, they are well supported by theory and are worthy of further research. [ Return to top ]
Author: J. Kut Nature: Experimental Length: 16 Pages Size: 3.71 MB Format: Adobe Acrobat Document	The Field Effect Transistor – Mixing and frequency doubling, J.Kut (November 2000) Abstract: This report investigates the use of non-linearity in FETs (Field Effect Transistors), for the mixing and frequency doubling of sinusoidal waveforms. The Motorola BF244B n-channel junction-FET was tested, recording its drain characteristics up to a drain voltage of 30V, and its mutual characteristics over a gate voltage of 0 to -4V. In conjunction with an LC (inductor-capacitor) circuit to provide resonant filtering (ω_res ≈ 8.9kHz), frequency doubling was studied using the FET as an inverting single-stage (1mA constant drain, 50k&ohm; drain resistance) 56x biased non-linear amplifier. The circuit performed as predicted by theory, with a FET mutual conductance β of 0.46 mA/V²; the input frequency ½ω_res was successfully doubled with the output proportional to the square of the input amplitude. Although mixing was not directly tested, it is well supported by simulations and experimental results, and is worthy of further research. [ Return to top ]
Author: J. Kut Nature: Experimental Length: 14 Pages Size: 2.72 MB Format: Adobe Acrobat Document	The Operational Amplifier – application in a radio receiver, J.Kut (April 2000) Abstract: This report investigates the behaviour and characteristics of a 741 IC (Integrated Circuit) operational amplifier, for audio amplification in a basic medium wave (amplitude modulated) radio receiver. The experiments conducted have looked at their use as a feedback amplifier with 100 times non-inverting gain, recording output gain at input frequencies ranging from 10Hz to 1MHz. In conjunction with a half-wave diode rectifier, RC (Resistor-Capacitor) filter and an LC (Inductor-Capacitor) circuit tuned to resonance of 1.03MHz—local radio was successfully received. The apparatus behaved as predicted by theory— however the discrepancy between the calculated and recorded resistance of the inductor coil raise issues worthy of further research. [ Return to top ]
Author: J. Kut Nature: Literature Review Length: 14 Pages Size: 1.04 MB Format: Adobe Acrobat Document	Quarks: An introduction to the most fundamental particles and the attempts to learn more, J. Kut (March 1999) Preface: In this document, I intend to provide an introduction to quarks—and the foundation behind its initial concept and characteristics. Rather than providing a historical text, I am forgoing names and dates, and instead attempting to illustrate the genius that originally struck the brilliant minds of those involved. Since quarks is the foundation of particle physics, I aim to explain concepts for the inquisitive mind, in order to avoid becoming overwhelmed with the complexity of both the theory and mathematics involved. [ Return to top ]
Author: J. Kut Nature: Experimental Length: 30 Pages Size: 1.31 MB Format: Adobe Acrobat Document	An investigation into factors affecting the behaviour of carbonated drinks, J.Kut (February 1999) Summary: Preliminary research and testing into a variety of potential factors affecting the rate of nucleation and subsequent bubbling of carbonated drinks was conducted. Extensive work focused on different types of nucleation centres—experimenting with drawing pins, ball bearings and a wide range of sandpaper. These choices have proven to be ideal and have yielded useful results. Work into the effect of ambient pressure on bubbling was also possible thanks to creative apparatus design. This has lead to a variety of new conclusions and relationships. Despite extensive practical work, there nevertheless remain many variables and other avenues left to pursue, which makes this an area well worth further study. Sadly, I have been unable to cover all the ground I originally set out to, due to a lack of time. [ Return to top ]
Author: J. Kut Nature: Literature Review Length: 14 Pages Size: 345 KB Format: Adobe Acrobat Document	Neutrinos: An insight into the discovery of the neutrino and the ongoing attempts to learn more, J.Kut (April 1998) Preface: In this document I intend to provide an introduction to neutrinos—and essentially its properties, flavours and the experiments surrounding its existence, as well as some of the questions which still remain. I am forgoing the usual historical account and instead of providing names and dates, I am attempting to provoke the thought that originally struck the brilliant minds of the many involved. As neutrino research is deeply integrated into the field of particle physics, I shall endeavour to explain terminology and concepts for the inquisitive mind, where necessary—without getting overly concerned about other areas of particle physics or the strenuous mathematics that would otherwise be involved. [ Return to top ]

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Last modified: Sunday, 01 May 2005
John Kut