Steve Clowes

Dr Steven Clowes


Senior Lecturer, Director of Learning & Teaching MSc, DPhil
+44 (0)1483 689827
12 ATI 02

Biography

Research Interests

  • Magneto-transport and magneto-optics of compound semiconductors.
  • Spin dependent transport using optical orientation of electron spin.
  • Ultrafast spin dynamics in high spin-orbit coupled two dimensional systems.
  • III-V bismides for spintronic applications.
  • Quantum control of dopants in silicon for quantum information processing.
  • Silicon Solotronics- atomic scale electronic devices with THz control.

PhD opportunities are available in field of magento-transport and magneto-optics of narrowgap semiconductors, and soltronics. Please contact by email if interested.

Teaching

PHY2062 From Atoms to Lasers PHY3053 LabView for Researchers PHY3057 Semiconductor Physics and Technology PHY3056 Applied Magnetism and Superconductivity

Departmental Duties

Director of Learning and Teaching for Department of Physics Programme Director for Physics with Quantum Technologies undergraduate course. Coordinator and founder of the National Instruments Academy in the Faculty of Engineering and Physical Sciences, providing LabView training for post-graduate researchers and research staff.

Affiliations

Member of the Institute of Physics

Past and Current Grants

  • £675,777 EPSRC (PI) 'Non-magnetic semiconductor spintronics'€™, Oct 2007- Sept 2012
  • ££196,953 EPSRC (CI) 'Silicon based spintronics'€™, Oct 2009-Sept 2012
  • £106,044 Leverhulme Trust (CI) '€˜Direct magnetic measurement of excitonic induced magnetization in colloidal nanocrystal' Nov 2011-Nov 2013
  • £54,639 TSB (PI) Short KTP with Plastipack Ltd., July 2012-July 2013.
  • £20,024 EPSRC (PI) Impact Acceleration Account, July 2013-Jun 2014
  • £230,000 TSB (PI) Classic KTP with Plastipack Ltd July 2014-July 2017
  • £373,196 EPSRC (CI) 'Functional Nitride Nanocrystals for Quantum-Enhanced Technologies' Feb 2015-Feb 2018
  • £6,382,161 EPSRC (CI) 'Atomically Deterministic Doping and Readout For Semiconductor Solotronics (ADDRFSS)' Feb 2015 - Feb 2020

My publications

Publications

Magnus F, Clowes SK, Gilbertson AM, Branford WR, Barkhoudarov ED, Cohen LF, Singh LJ, Barber ZH, Blamire MG, Buckle PD, Buckle L, Ashley T, Eustace DA, McComb DW (2007) Electrical characterization of MgO tunnel barriers grown on InAs (001) epilayers, APPLIED PHYSICS LETTERS 91 (12) ARTN 122106 AMER INST PHYSICS
Magnus F, Yates KA, Clowes SK, Miyoshi Y, Bugoslavsky Y, Cohen LF, Aziz A, Burnell G, Blamire MG, Josephs-Franks PW (2008) Interface properties of Pb/InAs planar structures for Andreev spectroscopy, APPLIED PHYSICS LETTERS 92 (1) ARTN 012501 AMER INST PHYSICS
Rahman ATA, Bräuer-Krisch E, Brochard T, Adamovics J, Clowes S, Bradley D, Doran S (2010) Creation of sophisticated test objects for quality assurance of optical computed tomography scanners, Journal of Physics: Conference Series 250 pp. 215-219
Optical computed tomography (CT) shows great potential for radiation therapy dose verification in 3D. However, an effective quality assurance regime for the various scanners currently available still remains to be developed. We show how the favourable properties of the PRESAGE" radiochromic polymer may be exploited to create highly sophisticated QA phantoms. Five 60 mm-diameter cylindrical PRESAGE" samples were irradiated using the x-ray microbeam radiation therapy facility on the ID17 biomedical beamline at the European Synchrotron Radiation Facility. Samples were then imaged on the University of Surrey parallel-beam optical CT scanner and were designed to allow a variety of tests to be performed, including linearity, MTF (three independent measurements) and an assessment of geometric distortion. A small sample of these results is presented. It is clear that, although the method produces extremely high quality test objects, it is not practical on a routine basis, because of its reliance of a highly specialised radiation source. Hence, we investigated a second possibility. Two PRESAGE" samples were illuminated with ultraviolet light of wavelength 365 nm, using cheap masks created by laser-printing patterns onto overhead projector acetate sheets. There was good correlation between optical density (OD) measured by the CT scanner and the expected UV "dose" delivered. The results are highly encouraging and a proposal is made for a scanner test regime based on calibrated and well characterised PRESAGE" samples. © 2010 IOP Publishing Ltd.
Murdin BN, Merrick M, Litvinenko K, Murzyn P, Phillips PJ, Pidgeon CR, Zhang T, Clowes SK, Cohen LF, Buckle P, Ashley T (2004) Spin lifetimes in narrow gap semiconductors measured with free-electron and solid-state lasers, STATE-OF-THE-ART PROGRAM ON COMPOUND SEMICONDUCTORS XL (SOTAPOCS XL) AND NARROW BANDGAP OPTOELECTRONIC MATERIALS AND DEVICES II 2004 (2) pp. 253-258 ELECTROCHEMICAL SOCIETY INC
Singh LJ, Oliver RA, Barber ZH, Eustace DA, McComb DW, Clowes SK, Gilbertson AM, Magnus F, Branford WR, Cohen LF, Buckle L, Buckle PD, Ashley T (2007) Preparation of InAs(001) surface for spin injection via a chemical route, JOURNAL OF PHYSICS D-APPLIED PHYSICS 40 (10) pp. 3190-3193 IOP PUBLISHING LTD
Fobelets K, Alaudeen A, Ahmad MM, Clowes S, Zhang J (2004) Analysis of steam oxidation of crystalline SI1-XGEX using AFM and CABOOM, Proceedings - Electrochemical Society 7 pp. 175-179
Characterization of the Ge concentration in a Si1-xGe x heterojunction for x varying from 5% to 40% in steps of 5% is done by beveling and wet thermal oxidation of the exposed layers. The resulting difference in oxide thickness as a function of Ge concentration is visualized due to light interference. Different Ge concentrations are seen as different colors through an optical microscope. CABOOM - Characterization of the Alloy concentration by Beveling, Oxidation and Optical Microscopy - in combination with AFM - Atomic Force Microscopy, is used as a tool to study the oxidation kinetics of unstrained, crystalline Si1-xGex by wet thermal oxidation.
Clowes Steven, Silva S, Yahya I, Bonaccorso F, Ferrari AC (2015) Temperature dependent separation of metallic and semiconducting carbon nanotubes using gel agarose chromatography, Carbon 93 pp. 574-594 Elsevier
Post-synthesis separation of metallic (m-SWNTs) and semiconducting (s-SWNTs) single-wall carbon nanotubes (SWNTs) remains a challenging process. Gel agarose chromatography is emerging as an efficient and large scale separation technique. However, the full (100%) separation has not been achieved yet, mainly due to the lack of understanding of the underlying mechanism. Here, we study the temperature effect on the SWNTs separation via gel agarose chromatography, for four different SWNT sources. Exploiting a gel agarose micro-beads filtration technique we achieve up to 70% m-SWNTs and over 90% s-SWNTs, independent of the source material. The process is temperature dependent, with yields up to 95% for s-SWNT (HiPco) at 6 °C. Temperature affects the sodium dodecyl sulfate surfactant-micelle distribution along the SWNT sidewalls, thus determining the effectiveness of the SWNTs sorting by electronic type. The sorted SWNTs are then used to fabricate transistors with very low OFF-currents (106) and charge carriers mobility
Branford WR, Clowes SK, Bugoslavsky YV, Miyoshi Y, Cohen LF, Berenov AV, MacManus-Driscoll JL, Rager J, Roy SB (2003) Effect of chemical substitution on the electronic properties of highly aligned thin films of Sr(2-x)A(x)FeMoO(6) (A=Ca, Ba, La; x=0, 0.1), JOURNAL OF APPLIED PHYSICS 94 (7) pp. 4714-4716 AMER INST PHYSICS
Harris JJ, Zhang T, Branford WR, Clowes SK, Debnath M, Bennett A, Roberts C, Cohen LF (2004) The role of impurity band conduction in the low temperature characteristics of thin InSb films grown by molecular beam epitaxy, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 19 (12) PII S0268-1242(04)81234-3 pp. 1406-1410 IOP PUBLISHING LTD
Gardelis S, Androulakis J, Migiakis P, Giapintzakis J, Clowes SK, Bugoslavsky Y, Branford WR, Miyoshi Y, Cohen LF (2004) Synthesis and physical properties of arc melted NiMnSb, JOURNAL OF APPLIED PHYSICS 95 (12) pp. 8063-8068 AMER INST PHYSICS
Zhang T, Harris JJ, Branford WR, Bugoslavsky YV, Clowes SK, Cohen LF, Husmann A, Solin SA (2006) Tuning the inherent magnetoresistance of InSb thin films, APPLIED PHYSICS LETTERS 88 (1) ARTN 012110 AMER INST PHYSICS
Stachel S, Budkin GV, Hagner U, Bel'kov VV, Glazov MM, Tarasenko SA, Clowes SK, Ashley T, Gilbertson AM, Ganichev SD (2014) Cyclotron-resonance-assisted photon drag effect in InSb/InAlSb quantum wells excited by terahertz radiation, PHYSICAL REVIEW B 89 (11) ARTN 115435 AMER PHYSICAL SOC
Leontiadou MA, Litvinenko KL, Gilbertson AM, Pidgeon CR, Branford WR, Cohen LF, Fearn M, Ashley T, Emeny MT, Murdin BN, Clowes SK (2011) Experimental determination of the Rashba coefficient in InSb/InAlSb quantum wells at zero magnetic field and elevated temperatures, JOURNAL OF PHYSICS-CONDENSED MATTER 23 (3) ARTN 035801 IOP PUBLISHING LTD
Goncharova LV, Clowes SK, Fogg RR, Ermakov AV, Hinch BJ (2002) Phosphine adsorption and the production of phosphide phases on Cu(001), SURFACE SCIENCE 515 (2-3) PII S0039-6028(02)01978-7 pp. 553-566 ELSEVIER SCIENCE BV
Zhang T, Debnath M, Clowes SK, Branford WR, Bennett A, Roberts C, Cohen LF, Stradling RA (2004) InSb epilayers on GaAs(100) for spintronic and magneto-resistive sensor applications, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 20 (3-4) pp. 216-219 ELSEVIER SCIENCE BV
Yahya I, Stolojan V, Clowes S, Mustaza SM, Silva SRP (2010) Carbon nanotube field effect transistor measurements in vacuum, IEEE International Conference on Semiconductor Electronics, Proceedings, ICSE pp. 224-228
Three terminal measurements on a carbon nanotube field effect transistor (CNTFET) were carried out in high vacuum and the ambient, and its performance compared. The on-off current ratio, ION/IOFF, were 10 2 and 105 for devices operated in high vacuum and in ambient air, respectively. Here, we show that the conversion of p-type to ambipolar behavior may largely be attributed to the O2 in ambient doping the single walled carbon nanotubes (SWCNTs) in the active channel which consists of bundles of SWCNTs. Switching behaviour of these devices, with respect to constituent types of SWCNTs in the bundles will be discussed. © 2010 IEEE.
Bugoslavsky Y, Miyoshi Y, Clowes SK, Branford WR, Lake M, Brown I, Caplin AD, Cohen LF (2005) Possibilities and limitations of point-contact spectroscopy for measurements of spin polarization, PHYSICAL REVIEW B 71 (10) ARTN 104523 AMERICAN PHYSICAL SOC
Abdul Rahman AT, Bräuer-Krisch E, Brochard T, Adamovics J, Clowes SK, Bradley D, Doran SJ (2011) Sophisticated test objects for the quality assurance of optical computed tomography scanners., Phys Med Biol 56 (14) pp. 4177-4199
Optical computed tomography (CT), in conjunction with radiochromic gels and plastics, shows great potential for radiation therapy dose verification in 3D. However, an effective quality assurance (QA) regime for the various scanners currently available still remains to be developed. We show how the favourable properties of the PRESAGE® radiochromic polymer may be exploited to create highly sophisticated QA phantoms. Five 60 mm diameter cylindrical PRESAGE® samples were irradiated using the x-ray microbeam radiation therapy facility on the ID-17 biomedical beamline at the European Synchrotron Radiation Facility. Samples were then imaged on the University of Surrey parallel-beam optical CT scanner. The sample irradiations were designed to allow a variety of tests to be performed, including assessments of linearity, modulation transfer function (three independent measurements), geometric distortion and the effect of treatment fractionation. It is clear that, although the synchrotron method produces extremely high-quality test objects, it is not practical on a routine basis, because of its reliance on a highly specialized radiation source. Hence, we investigated a second possibility: three PRESAGE® samples were illuminated with ultraviolet light of wavelength 365 nm, using cheap masks created by laser-printing patterns onto overhead projector acetate sheets. There was good correlation between optical densities measured by the CT scanner and the expected UV 'dose' delivered. The results are encouraging and a proposal is made for a scanner test regime based on calibrated and well-characterized PRESAGE® samples.
Clowes SK, Branford WR, Gilbertson AM, Zhang T, Buckle L, Husmann A, Solin SA, Cohen LF (2007) Improved geometric control of the high-field linear magnetoresistance by metallic bridges in InSb arrays, Physics of Semiconductors, Pts A and B 893 pp. 1383-1384 AMER INST PHYSICS
Eustace DA, McComb DW, Buckle L, Buckle P, Ashley T, Singh LJ, Barber ZH, Gilbertson AM, Branford WR, Clowes SK, Cohen LF (2008) (S)TEM Characterisation of InAs/MgO/Co Multilayers, MICROSCOPY OF SEMICONDUCTING MATERIALS 2007 120 pp. 153-156 SPRINGER-VERLAG BERLIN
Wache R, Florescu M, Sweeney SJ, Clowes SK (2015) Selectively reflective transparent sheets, ACTIVE PHOTONIC MATERIALS VII 9546 SPIE-INT SOC OPTICAL ENGINEERING
Pidgeon CR, Murzyn P, Phillips PJ, Murdin BN, Litvinenko K, Merrick M, Cohen LF, Zhang T, Clowes SK, Buckle P, Ashley T (2004) Spin relaxation in InSb and InAs by 1-and 2-colour spectroscopy with free electron and solid state lasers, CONFERENCE DIGEST OF THE 2004 JOINT 29TH INTERNATIONAL CONFERENCE ON INFRARED AND MILLIMETER WAVES AND 12TH INTERNATIONAL CONFERENCE ON TERAHERTZ ELECTRONICS pp. 207-208 IEEE
Murdin BN, Litvinenko K, Clarke DG, Pidgeon CR, Murzyn P, Phillips PJ, Carder D, Berden G, Redlich B, van der Meer AF, Clowes S, Harris JJ, Cohen LF, Ashley T, Buckle L (2006) Spin relaxation by transient monopolar and bipolar optical orientation., Phys Rev Lett 96 (9)
We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the case of the material chosen, n-InSb, the increase was from 14 to 38 ps.
Litvinenko KL, Leontiadou MA, Li J, Clowes SK, Emeny MT, Ashley T, Pidgeon CR, Cohen LF, Murdin BN (2010) Strong dependence of spin dynamics on the orientation of an external magnetic field for InSb and InAs, APPLIED PHYSICS LETTERS 96 (11) ARTN 111107 AMER INST PHYSICS
Murdin BN, Litvinenko K, Allam J, Pidgeon CR, Bird M, Morrison K, Zhang T, Clowes SK, Branford WR, Harris J, Cohen LF (2005) Temperature and doping dependence of spin relaxation in n-InAs, PHYSICAL REVIEW B 72 (8) ARTN 085346 AMERICAN PHYSICAL SOC
Clowes SK, Miyoshi Y, Johannson O, Hickey BJ, Marrows CH, Blamire M, Branford WR, Bugoslavsky YV, Cohen LF (2004) Using PCAR to study Cu/Co bilayers, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 pp. E1471-E1473 ELSEVIER SCIENCE BV
Simmons RA, Jin SR, Sweeney SJ, Clowes SK (2015) Enhancement of Rashba interaction in GaAs/AlGaAs quantum wells due to the incorporation of bismuth, APPLIED PHYSICS LETTERS 107 (14) ARTN 142401 AMER INST PHYSICS
Camplin JP, Clowes SK, Cook JC, McCash EM (1997) A study of adsorbate vibrations at cryogenic temperatures, SURFACE REVIEW AND LETTERS 4 (6) pp. 1365-1370 WORLD SCIENTIFIC PUBL CO PTE LTD
Branford WR, Clowes SK, Bugoslavsky YV, Gardelis S, Androulakis J, Giapintzakis J, Grigorescu CEA, Manea SA, Freitas RS, Roy SB, Cohen LF (2004) Thickness dependence of Hall transport in Ni1.15Mn0.85Sb thin films on silicon, PHYSICAL REVIEW B 69 (20) ARTN 201305 AMERICAN PHYSICAL SOC
Litvinenko KL, Murdin BN, Allam J, Pidgeon CR, Bird M, Morris K, Branford W, Clowes SK, Cohen LF, Ashley T, Buckle L (2006) Spin relaxation in n-InSb/AlInSb quantum wells, NEW JOURNAL OF PHYSICS 8 PII S1367-2630(06)15617-7 IOP PUBLISHING LTD
Nordin MN, Li J, Clowes SK, Curry RJ (2012) Temperature dependent optical properties of PbS nanocrystals., Nanotechnology 23 (27)
A comprehensive study of the optical properties of PbS nanocrystals (NCs) is reported that includes the temperature dependent absorption, photoluminescence (PL) and PL lifetime in the range of 3-300 K. The absorption and PL are found to display different temperature dependent behaviour though both redshift as temperature is reduced. This results in a temperature dependent Stokes shift which increases from
Zhang T, Harris JJ, Branford WR, Clowes SK, Cohen LF, Solin SA (2006) Exploration of the inherent magnetoresistance in InSb thin films, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 21 (12) pp. 1543-1546 IOP PUBLISHING LTD
Litvinenko K, Leontiadou M, Li J, Bowyer E, Clowes S, Pidgeon CR, Murdin B (2011) Manipulation of spin dynamics in semiconductor structures by orientation of small external magnetic field, AIP Conference Proceedings 1399 pp. 657-658 American Institute of Physics
Electron spin relaxation times have been measured in InSb and InAs quantum wells and epi-layers in a moderate (
Zhang T, Harris JJ, Branford WR, Clowes SK, Cohen LF, Solin SA (2007) Inherent magnetoresistance and surface morphology of InSb thin films, Physics of Semiconductors, Pts A and B 893 pp. 561-562 AMER INST PHYSICS
Yahya I, Bonaccorso F, Clowes SK, Ferrari AC, Silva SRP Temperature dependent separation of metallic and semiconducting carbon nanotubes using gel agarose chromatography, PERGAMON-ELSEVIER SCIENCE LTD
Branford WR, Gilbertson AM, Buckle PD, Buckle L, Ashley T, Magnus F, Clowes SK, Harris JJ, Cohen LF (2008) Gate dependence of spin-splitting in an InSb/InAlSb quantum well, NARROW GAP SEMICONDUCTORS 2007 119 pp. 3-5 SPRINGER
Itskos G, Harbord E, Clowes SK, Clarke E, Van Dorpe P, Van Roy W, Cohen LF, Murray R (2007) Oblique Hanle measurements of InAs/GaAs quantum dot spin-light emitting diodes, Physics of Semiconductors, Pts A and B 893 pp. 1289-1290 AMER INST PHYSICS
Seddon EA, Malins AER, Petty M, Crapper MD, Wardell IRM, Hide AK, Hardiman M, Xu YB, Hucknall P, Greig D, Clowes S, McCash EM (1999) Amorphous alloys as secondary standards for electron spin polarimetry, MEASUREMENT SCIENCE AND TECHNOLOGY 10 (4) pp. 269-274 IOP PUBLISHING LTD
Leontiadou MA, Litvinenko KL, Clowes SK, Springholz G, Schwarzl T, Eibelhuber M, Heiss W, Pidgeon CR, Murdin BN (2011) Substantial temperature dependence of transverse electron g*-factor in lead chalcogenide multi-quantum wells, AIP Conference Proceedings 1416 pp. 178-180 American Institute of Physics
We report significant temperature dependence of the transverse electron g??factor in symmetric lead chalcogenide multi?quantum wells (MQWs). The g??factor values were extracted from the electron Larmor precessions recorded by means of a circularly polarized pump probe technique under the influence of transverse external magnetic field (Voigt geometry) in the temperature range between 10 and 150K. The reported g??factor values are in good agreement with theoretical predictions and available low temperature experimental data. Although temperature tuning of lead salt laser emission wavelengths has been the method of choice in these systems for many years, we demonstrate that temperature can also be used to modulate g?, and hence the spin lifetime in lead salt QW spintronic devices.
Branford WR, Singh LJ, Barber ZH, Kohn A, Petford-Long AK, Van Roy W, Magnus F, Morrison K, Clowes SK, Bugoslavsky YV, Cohen LF (2007) Temperature insensitivity of the spin-polarization in Co2MnSi films on GaAs (001), NEW JOURNAL OF PHYSICS 9 PII S1367-2630(07)34448-0 IOP PUBLISHING LTD
Branford WR, Clowes SK, Syed MH, Bugoslavsky YV, Gardelis S, Androulakis J, Giapintzakis J, Grigorescu CEA, Berenov AV, Roy SB, Cohen LF (2004) Large positive magnetoresistance in nonstoichiometric NiMnSb thin films on silicon, APPLIED PHYSICS LETTERS 84 (13) pp. 2358-2360 AMER INST PHYSICS
Li J, Litvinenko KL, Clowes SK, Gilbertson AM, Cohen LF (2012) Observation of spin dependent photocoductivity in InSb quantum well nanowires, Applied Physics Letters 101 (15) AIP
We report on the electrical detection of spin dependent photoconductivity in 500 nm wide InSb quantum well nanowires using the optical orientation of electron spins. By applying weak magnetic fields (H 200 mT), we observe a spin filtering effect of classical origin caused by spin dependent back scattering of electrons from the sidewalls. Spin dependent features in the longitudinal photovoltage decay with temperature and disappears at characteristic energy (H 50 K) consistent with the theoretical spin splitting and the thermal level broadening. We show that the observed signal is due to the inversion asymmetry of the quantum well, with an additional Zeeman contribution. © 2012 American Institute of Physics.
Clowes SK, Miyoshi Y, Bugoslavsky Y, Branford WR, Grigorescu C, Manea SA, Monnereau O, Cohen LF (2004) Spin polarization of the transport current at the free surface of bulk NiMnSb, PHYSICAL REVIEW B 69 (21) ARTN 214425 AMER PHYSICAL SOC
Nordin MN, Li J, Clowes SK, Curry RJ (2013) Reply to comment on 'Temperature dependent optical properties of PbS nanocrystals', NANOTECHNOLOGY 24 (28) ARTN 288002 IOP PUBLISHING LTD
Magnus F, Burnell G, Miyoshi Y, Yates KA, Bugoslavsky Y, Clowes SK, Josephs-Franks PW, Blamire MG, Cohen LF (2007) Planar Andreev spectroscopy in InAs, PHYSICS OF SEMICONDUCTORS, PTS A AND B 893 pp. 1281-1282 AMER INST PHYSICS
Murdin BN, Li J, Pang ML, Bowyer ET, Litvinenko KL, Clowes SK, Engelkamp H, Pidgeon CR, Galbraith I, Abrosimov NV, Riemann H, Pavlov SG, Hübers HW, Murdin PG (2013) Si:P as a laboratory analogue for hydrogen on high magnetic field white dwarf stars., Nat Commun 4 Nature Publishing Group
Laboratory spectroscopy of atomic hydrogen in a magnetic flux density of 10(5) T (1 gigagauss), the maximum observed on high-field magnetic white dwarfs, is impossible because practically available fields are about a thousand times less. In this regime, the cyclotron and binding energies become equal. Here we demonstrate Lyman series spectra for phosphorus impurities in silicon up to the equivalent field, which is scaled to 32.8 T by the effective mass and dielectric constant. The spectra reproduce the high-field theory for free hydrogen, with quadratic Zeeman splitting and strong mixing of spherical harmonics. They show the way for experiments on He and H(2) analogues, and for investigation of He(2), a bound molecule predicted under extreme field conditions.
Clowes SK, Seddon EA, McCash EM (2000) The adsorption and decomposition of chromium hexacarbonyl on Pd(100), SURFACE SCIENCE 464 (1) pp. L667-L672 ELSEVIER SCIENCE BV
Zhang T, Harris JJ, Clowes SK, Debnath M, Bennett A, Cohen LF, Lyford T, Fewster PF (2005) Evidence for dislocation-related amphoteric behaviour of Si dopant in high-mobility InSb thin films, SEMICONDUCTOR SCIENCE AND TECHNOLOGY 20 (12) pp. 1153-1156 IOP PUBLISHING LTD
Litvinenko KL, Murdin BN, Clowes SK, Nikzad L, Allam J, Pidgeon CR, Branford W, Cohen LF, Ashley T, Buckle L (2008) Density and well-width dependence of the spin relaxation in n-InSb/AlInSb quantum wells, NARROW GAP SEMICONDUCTORS 2007 119 pp. 19-21 SPRINGER
Gilbertson AM, Orr JMS, Buckle PD, Clowes S, Fearn M, Storey CJ, Buckle L, Cohen LF, Ashley T (2007) Low-temperature Schottky barrier tunneling in InSb/InxAl1-xSb quantum well heterostructures, PHYSICAL REVIEW B 76 (8) ARTN 085306 AMER PHYSICAL SOC
Branford WR, Roy SB, Clowes SK, Miyoshi Y, Bugoslavsky YV, Gardelis S, Giapintzakis J, Cohen LF (2004) Spin polarisation and anomalous Hall effect in NiMnSb films, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 pp. E1399-E1401 ELSEVIER SCIENCE BV
Murdin BN, Clowes SK (2008) Narrow gap semiconductors 2007, Springer
This book contains the invited and contributed papers which were presented at this meeting and serves to provide a broad overview of the current worldwide ...
Itskos G, Harbord E, Clowes SK, Clarke E, Cohen LF, Murray R, Van Dorpe P, Van Roy W (2006) Oblique Hanle measurements of InAs/GaAs quantum dot spin-light emitting diodes, APPLIED PHYSICS LETTERS 88 (2) ARTN 022113 AMER INST PHYSICS
Zhang T, Clowes SK, Debnath M, Bennett A, Roberts C, Harris JJ, Stradling RA, Cohen LF, Lyford T, Fewster PF (2004) High-mobility thin InSb films grown by molecular beam epitaxy, APPLIED PHYSICS LETTERS 84 (22) pp. 4463-4465 AMER INST PHYSICS
Branford WR, Husmann A, Solin SA, Clowes SK, Zhang T, Bugoslavsky YV, Cohen LF (2005) Geometric manipulation of the high-field linear magnetoresistance in InSb epilayers on GaAs(001), APPLIED PHYSICS LETTERS 86 (20) ARTN 202116 AMER INST PHYSICS
Cook JC, Clowes SK, McCash EM (1997) Reflection absorption IR studies of vibrational energy transfer processes and adsorption energetics, JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 93 (13) pp. 2315-2322 ROYAL SOC CHEMISTRY
Stachel S, Olbrich P, Zoth C, Hagner U, Stangl T, Karl C, Lutz P, Bel'kov V, Clowes SK, Ashley T, Gilbertson A, Ganichev S (2012) Interplay of spin and orbital magnetogyrotropic photogalvanic effects in InSb/AlInSb quantum well structures, Physical Review B (Condensed Matter and Materials Physics) 85 045305 American Physical Society
We report on the observation of linear and circular magnetogyrotropic photogalvanic effects in InSb/AlInSb quantum well structures. We show that intraband (Drude-like) absorption of terahertz radiation in the heterostructures causes a dc electric current in the presence of an in-plane magnetic field. The photocurrent behavior upon variation of the magnetic field strength, temperature and wavelength is studied. We show that at moderate magnetic fields the photocurrent exhibits a typical linear field dependence. At high magnetic fields, however, it becomes nonlinear and inverses its sign. The experimental results are analyzed in terms of the microscopic models based on asymmetric relaxation of carriers in the momentum space. We demonstrate that the observed nonlinearity of the photocurrent is caused by the large Zeeman spin splitting in InSb/AlInSb structures and an interplay of the spin-related and spin-independent roots of the magnetogyrotropic photogalvanic effect.
Li Juerong, Gilbertson AM, Litvinenko Konstantin, Cohen LF, Clowes Steven (2012) Transverse focusing of spin-polarized photocurrents, Physical Review B (Condensed Matter and Materials Physics) 85 (4) 045431 American Physical Society
We measure transverse magnetically focused photocurrent signals in an InSb/InAlSb quantum well device. Using optical spin orientation by modulated circularly polarized light an electron spin-dependent signal is observed due to the spin-orbit interaction. Simulations of the focusing signal are performed using a classical billiard ball model, which includes both spin precession and a spin-dependent electron energy. The simulated data suggest that a signal dependent on the helicity of the incident light is expected for a Rashba parameter ± > 0.1 eVÅ and that a splitting of the focusing signal is not expected to be observed in linear polarized photocurrent and purely electrical measurements.
Murdin B. N., Litvinenko K., Clarke D. G., Pidgeon C. R., Murzyn P., Phillips P. J., Carder D., Berden G., Redlich B., van der Meer A. F. G., Clowes S., Harris J. J., Cohen L. F., Ashley T., Buckle L. (2006) Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, Physical Review Letters 96 (096603)

We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin
polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either
by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy
below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by
resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the
case of the material chosen, n-InSb, the increase was from 14 to 38 ps.

Litvinenko K. L., Murdin B. N., Allam J., Pidgeon C. R., Bird M., Morris K., Branford W., Clowes S. K., Cohen L. F., Ashley T., Buckle L. (2006) Spin relaxation in n-InSb/AlInSb quantum wells, New Journal of Physics 8 (4)

We have used time resolved spectroscopy to measure the relaxation of spin polarization in InSb/AlInSb quantum wells (QWs) as a function of temperature and mobility. The results are consistent with the D'yakonov?Perel (DP) mechanism for high mobility samples over the temperature range from 50 to 300 K. For low mobility samples at high temperature the Elliott?Yafet and DP mechanisms become comparable. We show that the mobility can in certain circumstances determine which mechanism is dominant, and that above 1 m2 V-1 s-1 in 20 nm wide InSb QWs it is the DP mechanism. We also give a criterion for the maximum spin lifetime in terms of mobility and temperature, and show that for our 20 nm wide QWs this corresponds to 0.5 ps at 300 K and mobility 1 m2 V-1 s-1.

Litvinenko K L, Murdin B N, Allam J, Pidgeon C R, Bird M, Morris K, Branford W, Clowes S K, Cohen L F, Ashley T, Buckle L (2006) Spin Relaxation in N-InSb/AlInSb Quantum Wells, New Journal of Physics 8 (4)

We have used time resolved spectroscopy to measure the relaxation of spin polarization in InSb/AlInSb quantum wells (QWs) as a function of temperature and mobility. The results are consistent with the D'yakonov - Perel (DP) mechanism for high mobility samples over the temperature range from 50 to 300 K. For low mobility samples at high temperature the Elliott - Yafet and DP mechanisms become comparable. We show that the mobility can in certain circumstances determine which mechanism is dominant, and that above 1 m(2) V-1 s(-1) in 20 nm wide InSb QWs it is the DP mechanism. We also give a criterion for the maximum spin lifetime in terms of mobility and temperature, and show that for our 20 nm wide QWs this corresponds to 0.5 ps at 300 K and mobility 1 m(2) V-1 s(-1).

Murdin B N, Litvinenko K, Clarke D G, Pidgeon C R, Murzyn P, Phillips P J, Carder D, Berden G, Redlich B, van der Meer A F, Clowes S, Harris J J, Cohen L F, Ashley T, Buckle L (2006) Spin Relaxation by Transient Monopolar and Bipolar Optical Orientation, Physical Review Letters 96 (9)

We have used two-color time-resolved spectroscopy to measure the relaxation of electron spin polarizations in a bulk semiconductor. The circularly polarized pump beam induces a polarization either by direct excitation from the valence band, or by free-carrier (Drude) absorption when tuned to an energy below the band gap. We find that the spin relaxation time, measured with picosecond time resolution by resonant induced Faraday rotation in both cases, increases in the presence of photogenerated holes. In the case of the material chosen, n-InSb, the increase was from 14 to 38 ps.

Murdin B. N., Litvinenko K., Allam J., Pidgeon C. R., Bird M., Morrison K., Zhang T., Clowes S. K., Branford W. R., Harris J., Cohen L. F. (2005) Temperature and doping dependence of spin relaxation in n-InAs, Physical Review B 72 (085346)

We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in the narrow gap semiconductor material n-InAs as a function of temperature, doping, and pump wavelength. The results are consistent with the D'Yakonov-Perel mechanism for temperatures between 77 and 300 K. However, the data suggest that electron-electron scattering should be taken into account in determining the dependence of the spin lifetime on the carrier concentration in the range 5.2×1016?8.8×1017 cm?3. For a sample with doping of 1.22×1017 cm?3 the spin lifetime was 24 ps at room temperature. By applying a magnetic field in the sample plane we also observed coherent precession of the spins in the time domain, with a g>/i> factor g*=?13, also at room temperature.

Murdin B N, Litvinenko K, Allam J, Pidgeon C R, Bird M, Morrison K, Zhang T, Clowes S K, Branford W R, Harris J, Cohen L F (2005) Temperature and Doping Dependence of Spin Relaxation in n-InAs, Physical Review B 72 (8)

We have used time-resolved spectroscopy to measure the relaxation of spin polarizations in the narrow gap semiconductor material n-InAs as a function of temperature, doping, and pump wavelength. The results are consistent with the D'Yakonov-Perel mechanism for temperatures between 77 and 300 K. However, the data suggest that electron-electron scattering should be taken into account in determining the dependence of the spin lifetime on the carrier concentration in the range 5.2x10(16)-8.8x10(17) cm(-3). For a sample with doping of 1.22x10(17) cm(-3) the spin lifetime was 24 ps at room temperature. By applying a magnetic field in the sample plane we also observed coherent precession of the spins in the time domain, with a g factor g(*)=-13, also at room temperature.

Li Juerong, Gilbertson AM, Litvinenko Konstantin, Cohen LF, Clowes Steven (2012) Transverse focusing of spin-polarized photocurrents, Physical Review B - Condensed Matter and Materials Physics 85 (4) 045431 American Physical Society
We measure transverse magnetically focused photocurrent signals in an InSb/InAlSb quantum well device. Using optical spin orientation by modulated circularly polarized light an electron spin-dependent signal is observed due to the spin-orbit interaction. Simulations of the focusing signal are performed using a classical billiard ball model, which includes both spin precession and a spin-dependent electron energy. The simulated data suggest that a signal dependent on the helicity of the incident light is expected for a Rashba parameter ±0.1eVand that a splitting of the focusing signal is not expected to be observed in linear polarized photocurrent and purely electrical measurements. © 2012 American Physical Society.
Peach Tomas, Homewood Kevin, Lourenco Manon, Hughes M, Saeedi Kaymar, Stavrias Nikolaos, Li Juerong, Chick Steven, Murdin Benedict, Clowes Steven (2018) The Effect of Lattice Damage and Annealing Conditions on the Hyperfine Structure of Ion Implanted Bismuth Donors in Silicon, Advanced Quantum Technologies 1 (2) 1800038 Wiley
This study reports on high energy bismuth ion implantation into silicon with a particular emphasis on the effect that annealing conditions have on the observed hyperfine structure of the Si:Bi donor state. A suppression of donor bound exciton, D0X, photoluminescence is observed in implanted samples which have been annealed at 700 °C relating to the presence of a dense layer of lattice defects that is formed during the implantation process. Hall measurments at 10 K show that this implant damage manifests itself at low temperatures as an abundance of p?type charge carriers, the density of which is observed to have a strong dependence on annealing temperature. Using resonant D0X photoconductivity, we are able to identify the presence of a hyperfine structure in samples annealed at a minimum temperature of 800 °C; however, higher temperatures are required to eliminate effects of implantation strain.
Group V donors in silicon are extremely promising candidates for applications within quantum technologies due to their long spin coherence lifetimes and existing compatibility within the microelectronics industry. However, there are various technical challenges which need to be overcome in order to achieve this potential. This body of work aims to address two such fabrication challenges and attempt to provide solutions which will aid the realisation of silicon and donor based quantum architectures.
Bismuth donors display a vast potential for the implementation as spin qubits however there are limited techniques to controllably fabricate a high quality Si:Bi doped system. Ion implantation is the leading candidate to achieve this although there are concerns that the violent mechanism of Bi+ bombardment into the silicon lattice will significantly degrade the condition of the crystal environment. Therefore, the formation of bismuth donor states in silicon using ion implantation is studied with a specific emphasis on the quality of dopant incorporation. Using a combination of electrical measurements and donor bound exciton spectroscopy it is determined that, under the appropriate annealing conditions, it is possible to produce ion implanted bismuth donors in an environment free from the effects of lattice strain. This therefore motivates the use of ion implanted samples as an alternative to bulk doped Si:Bi for applications within quantum technologies. Implanted samples are then fabricated into simple two terminal devices and used in electrically detected THz spectroscopy measurements. Using a free electron laser, the resonant excitation of implanted bismuth donors is observed, however the characteristic properties of photoconductivity spectra strongly suggest that devices are being heated significantly.
Finally, an alternative to bulk silicon is studied as a vehicle for quantum technologies. Specifically, the fabrication requirements to controllably align single crystal silicon nanowires is studied using a process known as dielectrophoresis, DEP. Here it is demonstrated that, under the appropriate experimental conditions, it is possible to utilise DEP to manipulate single silicon nanowires to fabricate a wide range of devices. This could prove highly beneficial for the integration of this material within quantum technologies.