Imperial College London

ProfessorNeilAlford

Central FacultyOffice of the Provost

Associate Provost (Academic Planning)
 
 
 
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Contact

 

+44 (0)20 7594 6724n.alford

 
 
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Assistant

 

Miss Catherine Graham +44 (0)20 7594 3330

 
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Location

 

2..05 (in RSM) or 3.09 (in the Faculty Building)Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

406 results found

Le Goupil F, Bennett J, Axelsson A-K, Valant M, Berenov A, Bell AJ, Comyn TP, Alford NMet al., 2015, Electrocaloric enhancement near the morphotropic phase boundary in lead-free NBT-KBT ceramics, Applied Physics Letters, Vol: 107, ISSN: 1077-3118

The electrocaloric effects (ECEs) of the morphotropic phase boundary (MPB) composition 0.82(Na0.5Bi0.5)TiO3-0.18(K0.5Bi0.5)TiO3 (NBT-18KBT) are studied by direct measurements. The maximum ECE ΔTmax = 0.73 K is measured at 160 °C under 22 kV/cm. This corresponds to an ECE responsivity (ΔT/ΔE) of 0.33 × 10−6 K m/V, which is comparable with the best reported values for lead-free ceramics. A comparison between the direct and indirect ECE measurements shows significant discrepancies. The direct measurement of both positive and negative electrocaloric effect confirms the presence of numerous polar phases near the MPB of NBT-based materials and highlights their potential for solid-state cooling based on high field-induced entropy changes.

Journal article

Wu X, Zhang X, Price D, Ryan M, Riley J, Alford N, Centeno A, Xie Fet al., 2015, Broadband plasmon photocurrent generation from Au nanoparticles/ mesoporous TiO2 nanotube electrodes, Solar Energy Materials and Solar Cells, Vol: 138, Pages: 80-85, ISSN: 0927-0248

There has been an increasing interest in plasmon-induced enhancement of solar cells and more recently in the direct generation of photocurrent using noble metal nanoparticles with their Localised Surface Plasmon Resonance (LSPR) in the visual part of the spectrum. In this paper we report broadband plasmon photocurrent generation using novel Au nanoparticle incorporated mesoporous TiO2 nanotube electrodes. Plasmonic induced photocurrent due to hot electrons is observed over a broad wavelength range (~500 to 1000 nm). Incident photon-to-electron conversion efficiency (IPCE) measurements undertaken showed a maximum photocurrent enhancement of 200 fold around 700–730 nm wavelength.

Journal article

Braic L, Vasilantonakis N, Zou B, Maier SA, Alford NM, Zayats AV, Petrov PKet al., 2015, Optimizing strontium ruthenate thin films for near-infrared plasmonic applications, Scientific Reports, Vol: 5, ISSN: 2045-2322

Several new plasmonic materials have recently been introduced in order to achieve better temperature stability than conventional plasmonic metals and control field localization with a choice of plasma frequencies in a wide spectral range. Here, epitaxial SrRuO3 thin films with low surface roughness fabricated by pulsed laser deposition are studied. The influence of the oxygen deposition pressure (20–300 mTorr) on the charge carrier dynamics and optical constants of the thin films in the near-infrared spectral range is elucidated. It is demonstrated that SrRuO3 thin films exhibit plasmonic behavior of the thin films in the near-infrared spectral range with the plasma frequency in 3.16–3.86 eV range and epsilon-near-zero wavelength in 1.11–1.47 μm range that could be controlled by the deposition conditions. The possible applications of these films range from the heat-generating nanostructures in the near-infrared spectral range, to metamaterial-based ideal absorbers and epsilon-near-zero components, where the interplay between real and imaginary parts of the permittivity in a given spectral range is needed for optimizing the spectral performance.

Journal article

Roqan IS, Venkatesh S, Zhang Z, Hussain S, Bantounas I, Franklin JB, Flemban TH, Zou B, Lee J-S, Schwingenschlogl U, Petrov PK, Ryan MP, Alford NMet al., 2015, Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes, Journal of Applied Physics, Vol: 117, ISSN: 1089-7550

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline Gdx Zn 1−xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.

Journal article

Breeze J, Tan K-J, Richards B, Sathian J, Oxborrow M, Alford NMet al., 2015, Enhanced magnetic Purcell effect in room-temperature masers, NATURE COMMUNICATIONS, Vol: 6, ISSN: 2041-1723

Journal article

Venkatesh S, Franklin JB, Ryan MP, Lee J-S, Ohldag H, McLachlan MA, Alford NM, Roqan ISet al., 2015, Defect-band mediated ferromagnetism in Gd-doped ZnO thin films, JOURNAL OF APPLIED PHYSICS, Vol: 117, ISSN: 0021-8979

Journal article

Tileli V, Duchamp M, Axelsson A-K, Valant M, Dunin-Borkowski RE, Alford NMet al., 2014, On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films, Nanoscale, Vol: 7, Pages: 218-224, ISSN: 2040-3372

The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces.

Journal article

Kozyrev A, Mikhailov A, Ptashnik S, Petrov PK, Alford Net al., 2014, Selective normal mode excitation in multilayer thin film bulk acoustic wave resonators, Applied Physics Letters, Vol: 105, ISSN: 1077-3118

A method for selective normal mode excitation in thin film bulk acoustic wave resonators, based on multilayer structures with any number of ferroelectric films in the paraelectric phase, is presented. The possibility to control the excitation of thin film bulk acoustic resonators' normal modes by simultaneous manipulating both the polarities and the magnitudes of the dc bias voltages applied to the ferroelectric layers is demonstrated. The proposed method was verified using the Lakin's model, modified to describe the electro-mechanical behavior of a structure with four active ferroelectric layers.

Journal article

Appleby DJR, Ponon NK, Kwa KSK, Ganti S, Hannemann U, Petrov PK, Alford NM, O'Neill Aet al., 2014, Ferroelectric properties in thin film barium titanate grown using pulsed laser deposition, JOURNAL OF APPLIED PHYSICS, Vol: 116, ISSN: 0021-8979

Journal article

Appleby DJR, Ponon NK, Kwa KSK, Zou B, Petrov PK, Wang T, Alford NM, O'Neill Aet al., 2014, Experimental observation of negative capacitance in ferroelectrics at room temperature, Nano Letters, Vol: 14, Pages: 3864-3868, ISSN: 1530-6992

Effective negative capacitance has been postu-lated in ferroelectrics because there is a hysteresis in plots ofpolarization-electricfield. Compelling experimental evidenceof effective negative capacitance is presented here at roomtemperature in engineered devices, where it is stabilized by thepresence of a paraelectric material. In future integrated circuits,the incorporation of such negative capacitance into MOSFETgate stacks would reduce the subthreshold slope, enabling lowpower operation and reduced self-heating.

Journal article

Le Goupil F, Axelsson A-K, Valant M, Lukasiewicz T, Dec J, Berenov A, Alford NMet al., 2014, Effect of Ce doping on the electrocaloric effect of SrxBa1-xNb2O6 single crystals, APPLIED PHYSICS LETTERS, Vol: 104, ISSN: 0003-6951

Journal article

Le Goupil F, Axelsson A-K, Dunne LJ, Valant M, Manos G, Lukasiewicz T, Dec J, Berenov A, Alford NMet al., 2014, Anisotropy of the Electrocaloric Effect in Lead-Free Relaxor Ferroelectrics, ADVANCED ENERGY MATERIALS, Vol: 4, ISSN: 1614-6832

Journal article

Petrov PK, Zou B, Wang Y, Perkins JM, McComb DW, Alford NMet al., 2014, STO/BTO Modulated Superlattice Multilayer Structures with Atomically Sharp Interfaces, ADVANCED MATERIALS INTERFACES, Vol: 1, ISSN: 2196-7350

Journal article

Altynnikov AG, Gagarin AG, Gaidukov MM, Tumarkin AV, Petrov PK, Alford N, Kozyrev ABet al., 2014, Suppression of slow capacitance relaxation phenomenon in Pt/Ba0.3Sr0.7TiO3/Pt thin film ferroelectric structures by annealing in oxygen atmosphere, APPLIED PHYSICS LETTERS, Vol: 104, ISSN: 0003-6951

Journal article

Donchev E, Gammon PM, Pang JS, Petrov PK, Alford NMet al., 2014, Systematic study of metal-insulator-metaldiodes with a native oxide, Conference on Thin Films for Solar and Energy Technology VI, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

Conference paper

Wu X, Scott K, Xie F, Alford Net al., 2014, A reversible water electrolyser with porous PTFE based OH− conductive membrane as energy storage cells, Journal of Power Sources, Vol: 246, Pages: 225-231, ISSN: 0378-7753

Journal article

Axelsson A-K, Valant M, Le Goupil F, Berenov AV, Alford Net al., 2014, Lead-Free and “Exotic” Electrocaloric Materials, Electrocaloric Materials: New Generation of Coolers, Editors: Correia, Zhang, Publisher: Springer, Pages: 125-146, ISBN: 978-3-642-40263-0

Book chapter

Breeze JD, Alford NMCN, 2013, Device and method for generating stimulated emission of microwave or radio frequency radiation, WO2013175235 A1

Patent

Axelsson A-K, Aguesse F, Tileli V, Valant M, Alford NMet al., 2013, Growth mechanism and magnetism of CoFe2O4 thin films; Role of the substrate, JOURNAL OF ALLOYS AND COMPOUNDS, Vol: 578, Pages: 286-291, ISSN: 0925-8388

Journal article

Doig KI, Aguesse F, Axelsson AK, Alford NM, Nawaz S, Palkar VR, Jones SPP, Johnson RD, Synowicki RA, Lloyd-Hughes Jet al., 2013, Coherent magnon and acoustic phonon dynamics in tetragonal and rare-earth-doped BiFeO3 multiferroic thin films, PHYSICAL REVIEW B, Vol: 88, ISSN: 2469-9950

Journal article

Aguesse F, Axelsson A-K, Reinhard P, Tileli V, Rupp JLM, Alford NMet al., 2013, High-temperature conductivity evaluation of Nb doped SrTiO3 thin films: Influence of strain and growth mechanism, THIN SOLID FILMS, Vol: 539, Pages: 384-390, ISSN: 0040-6090

Journal article

Xie F, Pang J, Centeno A, Ryan M, Riley J, Alford Net al., 2013, Nanoscale control of Ag nanostructures for plasmonic fluorescence enhancement of near-infrared dyes, Nano Research, Vol: 6, Pages: 495-510, ISSN: 1998-0124

Potential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based detection techniques. Metal induced fluorescence enhancement offers the possibility of increasing the sensitivity of protein detection in clinical applications. We report the use of tunable plasmonic silver nanostructures for the fluorescence enhancement of a near-infrared (NIR) dye (Alexa Fluor 790). Extensive fluorescence enhancement of ∼2 orders of magnitude is obtained by the nanoscale control of the Ag nanostructure dimensions and interparticle distance. These Ag nanostructures also enhanced fluorescence from a dye with very high quantum yield (7.8 fold for Alexa Fluor 488, quantum efficiency (Qy) = 0.92). A combination of greatly enhanced excitation and an increased radiative decay rate, leading to an associated enhancement of the quantum efficiency leads to the large enhancement. These results show the potential of Ag nanostructures as metal induced fluorescence enhancement (MIFE) substrates for dyes in the NIR “biological window” as well as the visible region. Ag nanostructured arrays fabricated by colloidal lithography thus show great potential for NIR dye-based biosensing applications.

Journal article

Valant M, Kolodiazhnyi T, Arcon I, Aguesse F, Axelsson A-K, Alford NMet al., 2013, Response to "Comment on "The Origin of Magnetism in Mn-Doped SrTiO3'", ADVANCED FUNCTIONAL MATERIALS, Vol: 23, Pages: 2231-2232, ISSN: 1616-301X

Journal article

Xie F, Centeno A, Zou B, Ryan MP, Riley DJ, Alford NMet al., 2013, Tunable synthesis of ordered Zinc Oxide nanoflower-like arrays, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 395, Pages: 85-90, ISSN: 0021-9797

Journal article

Turcaud JA, Morrison K, Berenov A, Alford NM, Sandeman KG, Cohen LFet al., 2013, Microstructural control and tuning of thermal conductivity in La0.67Ca0.33MnO3 +/-delta, SCRIPTA MATERIALIA, Vol: 68, Pages: 510-513, ISSN: 1359-6462

Journal article

Axelsson A-K, Le Goupil F, Dunne LJ, Manos G, Valant M, Alford NMet al., 2013, Microscopic interpretation of sign reversal in the electrocaloric effect in a ferroelectric PbMg1/3Nb2/3O3-30PbTiO(3) single crystal, APPLIED PHYSICS LETTERS, Vol: 102, ISSN: 0003-6951

Journal article

Zou B, Petrov PK, Alford NM, 2013, SrRuO3 thin films grown on MgO substrates at different oxygen partial pressures, JOURNAL OF MATERIALS RESEARCH, Vol: 28, Pages: 702-707, ISSN: 0884-2914

Journal article

Xie F, Centeno A, Ryan MR, Riley DJ, Alford NMet al., 2013, Au nanostructures by colloidal lithography: from quenching to extensive fluorescence enhancement, J. Mater. Chem. B, Vol: 1, Pages: 536-543

Enhanced local electric fields are created by nanoparticles when pumped at wavelengths corresponding to Localised Surface Plasmon Resonance (LSPR) modes, leading to Metal Induced Fluorescence Enhancement (MIFE). This paper describes the fluorescent enhancement due to reproducible and tuneable Au nanostructures on glass substrates fabricated over large areas by colloidal lithography. Interparticle separation, particle resonance, and the fluorescent dye properties (quantum yield and emission/excitation wavelengths) are all important factors influencing the fluorescent enhancement. A maximum fluorescence enhancement of 69 times from near infra-red (NIR) dye Alexa Fluor[registered sign] 790 was observed.

Journal article

Centeno A, Xie F, Alford N, 2013, Predicting the fluorescent enhancement rate by Au and Ag nanospheres using FDTD analysis, Iet Nanobiotechnology

Journal article

Mojarad SA, Goss JP, Kwa KSK, Petrov PK, Zou B, Alford N, O'Neill Aet al., 2012, Anomalous resistive switching phenomenon, JOURNAL OF APPLIED PHYSICS, Vol: 112, ISSN: 0021-8979

Journal article

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