ORCID Profile
0000-0001-9429-9768
Current Organisation
University of Manchester
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Compound Semiconductors | Nanotechnology | Nanoelectronics | Nanofabrication, Growth and Self Assembly
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering | Expanding Knowledge in Technology |
Publisher: IEEE
Date: 12-2010
Publisher: IEEE
Date: 12-2012
Publisher: IEEE
Date: 12-2012
Publisher: The Optical Society
Date: 25-09-2012
DOI: 10.1364/OE.20.023281
Publisher: IEEE
Date: 12-2012
Publisher: IEEE
Date: 12-2012
Publisher: IOP Publishing
Date: 20-02-2017
Abstract: Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2011
Publisher: American Chemical Society (ACS)
Date: 07-12-2010
DOI: 10.1021/JZ101026G
Publisher: IEEE
Date: 12-2012
Publisher: American Chemical Society (ACS)
Date: 08-03-2013
DOI: 10.1021/NL304170Q
Abstract: Devices based upon semiconductor nanowires provide many well-known advantages for next-generation photovoltaics, however, limited experimental techniques exist to determine essential electrical parameters within these devices. We present a novel application of a technique based upon two-photon induced photocurrent that provides a submicrometer resolution, three-dimensional reconstruction of photovoltaic parameters. This tool is used to characterize two GaAs nanowire-based devices, revealing the detail of current generation and collection, providing a path toward achieving the promise of nanowire-based photovoltaic devices.
Publisher: IEEE
Date: 10-2007
Publisher: American Chemical Society (ACS)
Date: 27-06-2007
DOI: 10.1021/NL071162X
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NA00479C
Abstract: For nanowire lasers, end-facets matter a rigorous statistical study demonstrates that short ultrasound or PDMA transfer provides optimized lasing performance.
Publisher: American Physical Society (APS)
Date: 24-09-2008
Publisher: IOP Publishing
Date: 03-08-2012
DOI: 10.1088/0957-4484/23/33/335704
Abstract: A practical bottleneck prohibiting the rapid, confident and damage-free electrical contacting of vapour-liquid-solid grown nanowires arises from the random spatial distribution and variation in quality of the nanowires, and the contact dimensions required. Established techniques such as electron-beam lithography or focused ion-beam deposition have challenges in scaling, damage or complexity that can make a large statistical s le difficult. We present a direct laser-writing technique to allow rapid electrical contacting of nanowires on a large variety of substrates.
Publisher: American Chemical Society (ACS)
Date: 25-04-2019
Publisher: American Chemical Society (ACS)
Date: 26-09-2014
DOI: 10.1021/NL503043P
Abstract: Achieving bulk-like charge carrier mobilities in semiconductor nanowires is a major challenge facing the development of nanowire-based electronic devices. Here we demonstrate that engineering the GaAs nanowire surface by overcoating with optimized AlGaAs shells is an effective means of obtaining exceptionally high carrier mobilities and lifetimes. We performed measurements of GaAs/AlGaAs core-shell nanowires using optical pump-terahertz probe spectroscopy: a noncontact and accurate probe of carrier transport on ultrafast time scales. The carrier lifetimes and mobilities both improved significantly with increasing AlGaAs shell thickness. Remarkably, optimized GaAs/AlGaAs core-shell nanowires exhibited electron mobilities up to 3000 cm(2) V(-1) s(-1), reaching over 65% of the electron mobility typical of high quality undoped bulk GaAs at equivalent photoexcited carrier densities. This points to the high interface quality and the very low levels of ionized impurities and lattice defects in these nanowires. The improvements in mobility were concomitant with drastic improvements in photoconductivity lifetime, reaching 1.6 ns. Comparison of photoconductivity and photoluminescence dynamics indicates that midgap GaAs surface states, and consequently surface band-bending and depletion, are effectively eliminated in these high quality heterostructures.
Publisher: American Chemical Society (ACS)
Date: 03-06-2014
DOI: 10.1021/JA504730J
Publisher: Springer Science and Business Media LLC
Date: 12-12-2013
DOI: 10.1038/NCOMMS3949
Abstract: Metamaterials, artificial electromagnetic media realized by subwavelength nano-structuring, have become a paradigm for engineering electromagnetic space, allowing for independent control of both electric and magnetic responses of the material. Whereas most metamaterials studied so far are limited to passive structures, the need for active metamaterials is rapidly growing. However, the fundamental question on how the energy of emitters is distributed between both (electric and magnetic) interaction channels of the metamaterial still remains open. Here we study simultaneous spontaneous emission of quantum dots into both of these channels and define the control parameters for tailoring the quantum-dot coupling to metamaterials. By superimposing two orthogonal modes of equal strength at the wavelength of quantum-dot photoluminescence, we demonstrate a sharp difference in their interaction with the magnetic and electric metamaterial modes. Our observations reveal the importance of mode engineering for spontaneous emission control in metamaterials, paving a way towards loss-compensated metamaterials and metamaterial nanolasers.
Publisher: OSA
Date: 2015
Publisher: IEEE
Date: 09-2013
Publisher: IEEE
Date: 12-2012
Publisher: Elsevier BV
Date: 03-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7NR09591K
Abstract: We present a systematic study of the performance of graphene–silicon Schottky diode photodetectors under varying operating conditions, demonstrating the influence of the substrate and interfacial oxide layer.
Publisher: IEEE
Date: 12-2012
Publisher: American Chemical Society (ACS)
Date: 28-06-2021
Publisher: IEEE
Date: 12-2012
Publisher: IEEE
Date: 12-2010
Publisher: IEEE
Date: 12-2012
Publisher: AIP Publishing
Date: 05-12-2011
DOI: 10.1063/1.3664633
Abstract: Phase-shifting interferometric imaging is shown to be a powerful analytical tool for studying graphene films, providing quantitative analysis of large area s les with an optical thickness resolution of ≤0.05 nm. The technique is readily able to identify single sheets of graphene and to quantitatively distinguish between layers composed of multiple graphene sheets. The thickness resolution of the technique is shown to result from the phase shift produced by a graphene film as incident and reflected light pass through it, rather than from path-length differences produced by surface height variations. This is enhanced by the high refractive index of graphene, estimated in this work to be nG = 2.99 ± 0.18.
Publisher: American Chemical Society (ACS)
Date: 09-11-2012
DOI: 10.1021/NL303787A
Abstract: We demonstrate luminescence from both the core and the shell of III-V semiconductor photonic nanowires by coupling them to plasmonic silver nanoparticles. This demonstration paves the way for increasing the quantum efficiency of large surface area nanowire light emitters. The relative emission intensity from the core and the shell is tuned by varying the polarization of the excitation source since their polarization response can be independently controlled. Independent control on emission wavelength and polarization dependence of emission from core-shell nanowire heterostructures opens up opportunities that have not yet been imagined for nanoscale polarization sensitive, wavelength-selective, or multicolor photonic devices based on single nanowires or nanowire arrays.
Publisher: American Chemical Society (ACS)
Date: 08-05-2019
Publisher: IEEE
Date: 12-2013
Publisher: Springer Science and Business Media LLC
Date: 17-11-2013
Publisher: American Chemical Society (ACS)
Date: 25-07-2017
DOI: 10.1021/ACS.NANOLETT.7B01725
Abstract: Single nanowire lasers based on bottom-up III-V materials have been shown to exhibit room-temperature near-infrared lasing, making them highly promising for use as nanoscale, silicon-integrable, and coherent light sources. While lasing behavior is reproducible, small variations in growth conditions across a substrate arising from the use of bottom-up growth techniques can introduce interwire disorder, either through geometric or material inhomogeneity. Nanolasers critically depend on both high material quality and tight dimensional tolerances, and as such, lasing threshold is both sensitive to and a sensitive probe of such inhomogeneity. We present an all-optical characterization technique coupled to statistical analysis to correlate geometrical and material parameters with lasing threshold. For these multiple-quantum-well nanolasers, it is found that low threshold is closely linked to longer lasing wavelength caused by losses in the core, providing a route to optimized future low-threshold devices. A best-in-group room temperature lasing threshold of ∼43 μJ cm
Publisher: American Chemical Society (ACS)
Date: 23-06-2021
Publisher: American Chemical Society (ACS)
Date: 17-05-2016
Publisher: IOP Publishing
Date: 13-07-2012
DOI: 10.1088/0022-3727/45/30/305102
Abstract: In this paper, a staircase plasmonic nano-antenna device is analysed both theoretically and experimentally. The tapered nano-antenna cavity with a grating leads to electric field enhancement factor (EF) as high as 31 close to 830 nm. The integration of a metallic grating aids the coupling of light coming from the vertical direction to the nano-antenna, increasing the electric field in the nano-antenna by a factor of 3. The smallest air gap width between the metallic regions of the fabricated nano-antenna is about 35 nm, fabricated using focused ion beam system. The small air gaps in the nano-antennas can generate very high intensity electric fields which can be used in applications in biological sensing and imaging, nanoparticle manipulations and enhancement of nonlinear effects. In this paper, to experimentally demonstrate that with the integration of a well designed grating and reflectors, the resonance inside the nano-antenna cavity is increased significantly, we exploit one application of this device: the enhancement of surface enhanced Raman scattering (SERS). The present structure can lead to SERS EFs above 1 million.
Publisher: IEEE
Date: 09-2012
Publisher: IOP Publishing
Date: 24-10-2013
DOI: 10.1088/0957-4484/24/46/465602
Abstract: We demonstrate the growth of InP nanowires on Si(111) using a thin InP buffer layer. The buffer layer is grown using a two-step procedure. The initial layer formation is ensured by using a very low growth temperature. An extremely high V/III ratio is necessary to prevent In droplet formation at this low temperature. The second layer is grown on the initial layer at a higher temperature and we find that post-growth annealing of the buffer layer does not improve its crystal quality significantly. It is found that the layers inherently have the (111)B polarity. Nanowires grown on this buffer layer have the same morphology and optical properties as nanowires grown on InP (111)B substrates. The vertical yield of the nanowires grown on the buffer layer is over 97% and we also find that crystal defects in the buffer layer do not affect the morphology, vertical yield or optical properties of the nanowires significantly.
Publisher: IEEE
Date: 09-2010
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4SC02424A
Abstract: When light is absorbed by a nanoring consisting of 6–24 porphyrin units, the excitation delocalizes over the whole molecule within 200 fs. Highly symmetric nanorings exhibit thermally enhanced super-radiance.
Publisher: American Chemical Society (ACS)
Date: 28-07-2009
DOI: 10.1021/NL9016336
Abstract: We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5NR06996C
Abstract: Single core–multishell nanowires with a radial quantum well are probed by micro-photoluminescence spectroscopy revealing low disorder in both the core and quantum well.
Publisher: IOP Publishing
Date: 16-08-2019
Publisher: American Chemical Society (ACS)
Date: 07-10-2019
Publisher: American Chemical Society (ACS)
Date: 19-03-2015
DOI: 10.1021/ACS.JPCLETT.5B00183
Abstract: Materials showing rapid intramolecular energy transfer and polarization switching are of interest for both their fundamental photophysics and potential for use in real-world applications. Here, we report two donor-acceptor-donor triad dyes based on perylene-bisimide subunits, with the long axis of the donors arranged either parallel or perpendicular to that of the central acceptor. We observe rapid energy transfer (<2 ps) and effective polarization control in both dye molecules in solution. A distributed-dipole Förster model predicts the excitation energy transfer rate for the linearly arranged triad but severely underestimates it for the orthogonal case. We show that the rapid energy transfer arises from a combination of through-bond coupling and through-space transfer between donor and acceptor units. As they allow energy cascading to an excited state with controllable polarization, these triad dyes show high potential for use in luminescent solar concentrator devices.
Publisher: American Physical Society (APS)
Date: 30-04-2007
Publisher: IEEE
Date: 08-2015
Publisher: Elsevier BV
Date: 09-2014
Publisher: American Chemical Society (ACS)
Date: 18-05-2022
Publisher: IOP Publishing
Date: 24-02-2021
Abstract: Fabricated from ZnO, III-N, chalcogenide-based, III-V, hybrid perovskite or other materials, semiconductor nanowires offer single-element and array functionality as photovoltaic, non-linear, electroluminescent and lasing components. In many applications their advantageous properties emerge from their geometry a high surface-to-volume ratio for facile access to carriers, wavelength-scale dimensions for waveguiding or a small nanowire-substrate footprint enabling heterogeneous growth. However, inhomogeneity during bottom-up growth is ubiquitous and can impact morphology, geometry, crystal structure, defect density, heterostructure dimensions and ultimately functional performance. In this topical review, we discuss the origin and impact of heterogeneity within and between optoelectronic nanowires, and introduce methods to assess, optimise and ultimately exploit wire-to-wire disorder.
Publisher: American Chemical Society (ACS)
Date: 14-07-2023
Publisher: American Chemical Society (ACS)
Date: 31-08-2012
DOI: 10.1021/NL301898M
Abstract: The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material, the NWs exhibit a long conductivity lifetime (>2 ns) and a high mobility (820 ± 120 cm(2)/(V s)). This is due to the weak influence of surface traps with respect to other III-V semiconducting NWs and to the favorable crystalline structure of the NWs achieved via strain-relieved growth.
Publisher: AIP Publishing
Date: 09-07-2012
DOI: 10.1063/1.4735002
Abstract: GaAs/AlxGa1−xAs core-shell nanowires were grown by metal organic chemical vapor deposition with optimized AlxGa1−xAs shell and twin-free Au-catalyzed GaAs cores. Time-resolved photoluminescence measurements were carried out on single nanowires at room temperature, revealing minority carrier lifetimes of 1.02 ± 0.43 ns, comparable to self-assisted nanowires grown by molecular beam epitaxy. The long minority carrier lifetimes are mainly attributed to improvement of the GaAs/AlxGa1−xAs interface quality. The upper limit of surface recombination velocity of the structure is calculated to be 1300 cm/s with the AlxGa1−xAs shell grown at 750 °C, which is comparable with planar double heterostructures.
Publisher: American Chemical Society (ACS)
Date: 28-01-2015
DOI: 10.1021/NL504566T
Abstract: Reliable doping is required to realize many devices based on semiconductor nanowires. Group III-V nanowires show great promise as elements of high-speed optoelectronic devices, but for such applications it is important that the electron mobility is not compromised by the inclusion of dopants. Here we show that GaAs nanowires can be n-type doped with negligible loss of electron mobility. Molecular beam epitaxy was used to fabricate modulation-doped GaAs nanowires with Al0.33Ga0.67As shells that contained a layer of Si dopants. We identify the presence of the doped layer from a high-angle annular dark field scanning electron microscopy cross-section image. The doping density, carrier mobility, and charge carrier lifetimes of these n-type nanowires and nominally undoped reference s les were determined using the noncontact method of optical pump terahertz probe spectroscopy. An n-type extrinsic carrier concentration of 1.10 ± 0.06 × 10(16) cm(-3) was extracted, demonstrating the effectiveness of modulation doping in GaAs nanowires. The room-temperature electron mobility was also found to be high at 2200 ± 300 cm(2) V(-1) s(-1) and importantly minimal degradation was observed compared with undoped reference nanowires at similar electron densities. In addition, modulation doping significantly enhanced the room-temperature photoconductivity and photoluminescence lifetimes to 3.9 ± 0.3 and 2.4 ± 0.1 ns respectively, revealing that modulation doping can passivate interfacial trap states.
Publisher: IEEE
Date: 11-2008
Publisher: American Chemical Society (ACS)
Date: 29-06-2012
DOI: 10.1021/NN300962Z
Abstract: The doping-dependent photoconductive properties of in idual GaAs nanowires have been studied by conductive atomic force microscopy. Linear responsivity against the bias voltage is observed for moderate n-doped GaAs wires with a Schottky contact under illumination, while that of the undoped ones exhibits a saturated response. The carrier lifetime of a single nanowire can be obtained by simulating the characteristic photoelectric behavior. Consistent with the photoluminescence results, the significant drop of minority hole lifetime, from several hundred to subpicoseconds induced by n-type doping, leads to the distinct photoconductive features. Moreover, by comparing with the photoelectric behavior of AlGaAs shelled nanowires, the equivalent recombination rate of carriers at the surface is assessed to be >1 × 10(12) s(-1) for 2 × 10(17)cm(-3) n-doped bare nanowires, nearly 30 times higher than that of the doping-related bulk effects. This work suggests that intentional doping in nanowires could change the charge status of the surface states and impose significant impact on the electrical and photoelectrical performances of semiconductor nanostructures.
Publisher: American Chemical Society (ACS)
Date: 04-11-2014
DOI: 10.1021/NN5034746
Abstract: We have measured ultrafast charge carrier dynamics in monolayers and trilayers of the transition metal dichalcogenides MoS2 and WSe2 using a combination of time-resolved photoluminescence and terahertz spectroscopy. We recorded a photoconductivity and photoluminescence response time of just 350 fs from CVD-grown monolayer MoS2, and 1 ps from trilayer MoS2 and monolayer WSe2. Our results indicate the potential of these materials as high-speed optoelectronic materials.
Publisher: American Chemical Society (ACS)
Date: 18-07-2016
DOI: 10.1021/ACS.NANOLETT.6B01528
Abstract: Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm(2) V(-1) s(-1)) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.
Publisher: IOP Publishing
Date: 09-2023
Publisher: American Chemical Society (ACS)
Date: 15-01-2019
Publisher: IOP Publishing
Date: 27-09-2012
DOI: 10.1088/0957-4484/23/41/415702
Abstract: Vertically oriented GaAs nanowires (NWs) are grown on Si(111) substrates using metal-organic chemical vapor deposition. Controlled epitaxial growth along the direction is demonstrated following the deposition of thin GaAs buffer layers and the elimination of structural defects, such as twin defects and stacking faults, is found for high growth rates. By systematically manipulating the AsH(3) (group-V) and TMGa (group-III) precursor flow rates, it is found that the TMGa flow rate has the most significant effect on the nanowire quality. After capping the minimal tapering and twin-free GaAs NWs with an AlGaAs shell, long exciton lifetimes (over 700 ps) are obtained for high TMGa flow rate s les. It is observed that the Ga adatom concentration significantly affects the growth of GaAs NWs, with a high concentration and rapid growth leading to desirable characteristics for optoelectronic nanowire device applications including improved morphology, crystal structure and optical performance.
Publisher: American Chemical Society (ACS)
Date: 13-02-2023
Publisher: IOP Publishing
Date: 11-08-2008
DOI: 10.1088/0957-4484/19/39/395704
Abstract: We have investigated the terahertz conductivity of extrinsic and photoexcited electrons in nanoporous indium phosphide (InP) at different pore densities and orientations. The form of electronic transport in the film was found to differ significantly from that for bulk InP. While photo-generated electrons showed Drude-like transport, the behaviour for extrinsic electrons deviated significantly from the Drude model. Time-resolved photoconductivity measurements found that carrier recombination was slow, with lifetimes exceeding 1 ns for all porosities and orientations. When considered together, these findings suggest that the surfaces created by the nanopores strongly alter the dynamics of both extrinsic and photoexcited electrons.
Publisher: Elsevier BV
Date: 07-2016
Publisher: IOP Publishing
Date: 09-05-2017
Publisher: American Chemical Society (ACS)
Date: 11-2011
DOI: 10.1021/JP207075Z
Publisher: American Chemical Society (ACS)
Date: 04-02-2020
Publisher: Wiley
Date: 24-04-2023
Abstract: Bottom–up production of semiconductor nanomaterials is often accompanied by inhomogeneity resulting in a spread in electronic properties which may be influenced by the nanoparticle geometry, crystal quality, stoichiometry, or doping. Using photoluminescence spectroscopy of a population of more than 11 000 in idual zinc‐doped gallium arsenide nanowires, inhomogeneity is revealed in, and correlation between doping and nanowire diameter by use of a Bayesian statistical approach. Recombination of hot‐carriers is shown to be responsible for the photoluminescence lineshape by exploiting lifetime variation across the population, hot‐carrier dynamics is revealed at the sub‐picosecond timescale showing interband electronic dynamics. High‐throughput spectroscopy together with a Bayesian approach are shown to provide unique insight in an inhomogeneous nanomaterial population, and can reveal electronic dynamics otherwise requiring complex pump‐probe experiments in highly non‐equilibrium conditions.
Publisher: Springer Science and Business Media LLC
Date: 17-03-2020
DOI: 10.1038/S41377-020-0279-Y
Abstract: Continuous room temperature nanowire lasing from silicon-integrated optoelectronic elements requires careful optimisation of both the lasing cavity Q -factor and population inversion conditions. We apply time-gated optical interferometry to the lasing emission from high-quality GaAsP/GaAs quantum well nanowire laser structures, revealing high Q -factors of 1250 ± 90 corresponding to end-facet reflectivities of R = 0.73 ± 0.02. By using optimised direct–indirect band alignment in the active region, we demonstrate a well-refilling mechanism providing a quasi-four-level system leading to multi-nanosecond lasing and record low room temperature lasing thresholds (~6 μJ cm −2 pulse −1 ) for III–V nanowire lasers. Our findings demonstrate a highly promising new route towards continuously operating silicon-integrated nanolaser elements.
Publisher: IEEE
Date: 12-2012
Publisher: American Chemical Society (ACS)
Date: 06-03-2015
Publisher: American Chemical Society (ACS)
Date: 08-12-2014
DOI: 10.1021/JZ5022153
Abstract: The topology of a conjugated molecule plays a significant role in controlling both the electronic properties and the conformational manifold that the molecule may explore. Fully π-conjugated molecular nanorings are of particular interest, as their lowest electronic transition may be strongly suppressed as a result of symmetry constraints. In contrast, the simple Kasha model predicts an enhancement in the radiative rate for corresponding linear oligomers. Here we investigate such effects in linear and cyclic conjugated molecules containing between 6 and 42 butadiyne-linked porphyrin units (corresponding to 600 C-C bonds) as pure monodisperse oligomers. We demonstrate that as the diameter of the nanorings increases beyond ∼10 nm, its electronic properties tend toward those of a similarly sized linear molecule as a result of excitation localization on a subsegment of the ring. However, significant differences persist in the nature of the emitting dipole polarization even beyond this limit, arising from variations in molecular curvature and conformation.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0TC01441A
Abstract: By combining in situ optical spectroscopy with a high spatial resolution mass spectrometry, we directly link the evolution in carrier recombination processes in perovskite films to light-induced ion migration.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8NR05285A
Abstract: Graphene–silicon-on-insulator (GSOI) photodetectors for high-speed free space light detection.
Publisher: American Chemical Society (ACS)
Date: 18-10-2013
DOI: 10.1021/NL4023385
Abstract: The effects of AlGaAs shell thickness and growth time on the minority carrier lifetime in the GaAs core of GaAs/AlGaAs core-shell nanowires grown by metal-organic chemical vapor deposition are investigated. The carrier lifetime increases with increasing AlGaAs shell thickness up to a certain value as a result of reducing tunneling probability of carriers through the AlGaAs shell, beyond which the carrier lifetime reduces due to the diffusion of Ga-Al and/or impurities across the GaAs/AlGaAs heterointerface. Interdiffusion at the heterointerface is observed directly using high-angle annular dark field scanning transmission electron microscopy. We achieve room temperature minority carrier lifetimes of 1.9 ns by optimizing the shell growth with the intention of reducing the effect of interdiffusion.
Publisher: AIP Publishing
Date: 28-08-2013
DOI: 10.1063/1.4819216
Abstract: We studied the structural properties, defect formation, and thermal stability of H in hydrothermally grown ZnO single crystals implanted with H- dose ranging from 2.5×1016 to 1×1017 cm−2. H implantation is found to create deformed layers with a uniaxial strain of 0.5–2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2–0.4% of the original implanted H concentration can still be detected in the s les by secondary ion mass spectrometry after annealing at a temperature up to 800 °C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the s les are cooled slowly from high temperature annealing. H implantation to a dose of 1×1017 cm−2 and followed by annealing at 800 °C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7TC01111C
Abstract: A laser fabrication process in commercial polymer films aimed at creating 3D conductive circuits shows promise for electrically contacting nano-structures.
Publisher: IEEE
Date: 08-2015
Publisher: IEEE
Date: 12-2012
Publisher: American Chemical Society (ACS)
Date: 19-07-2023
Publisher: American Chemical Society (ACS)
Date: 18-12-2015
DOI: 10.1021/NL5033843
Abstract: Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as erse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors.
Publisher: Proceedings of the National Academy of Sciences
Date: 09-06-2015
Abstract: We use transient spectroscopy to investigate the mechanism of singlet exciton fission, a quantum mechanical phenomenon in some organic molecules in which a spin-singlet excited state can split into two spin-triplet states. This process may be harnessed to boost solar cell efficiencies, but the underlying mechanism remains poorly understood. Central to most models is a triplet pair state, consisting of two triplets entangled into an overall spin-singlet configuration, but it has never before been optically detected. In a solution-based system, we detect a state with simultaneous singlet and triplet exciton character that dissociates to form triplet excitons in 120% yield. We consider that this intermediate constitutes a triplet pair state, and its observation allows important insight into the nature of triplet exciton coupling.
Publisher: American Physical Society (APS)
Date: 24-08-2010
Publisher: Springer Science and Business Media LLC
Date: 2011
DOI: 10.1557/OPL.2011.230
Abstract: We report the observation of an ultrafast (~ 430 fs) charge transfer process at the interface between a single-walled carbon nanotube (SWNT) wrapped by a semi-conducting polymer, poly(3-hexylthiophene) (P3HT), creating free polarons on both materials. The addition of excess P3HT as a surrounding network allows these free polarons to be long-lived at room temperature. Our results suggest that SWNT-P3HT blends incorporating only 1% fractions of SWNTs can achieve a charge separation efficiency comparable to a conventional 60:40 P3HT-fullerene blend, provided small-diameter tubes are embedded in an excess P3HT matrix.
Publisher: IEEE
Date: 12-2014
Publisher: American Chemical Society (ACS)
Date: 24-11-2010
DOI: 10.1021/NL1036484
Abstract: We have investigated the charge photogeneration dynamics at the interface formed between single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) using a combination of femtosecond spectroscopic techniques. We demonstrate that photoexcitation of P3HT forming a single molecular layer around a SWNT leads to an ultrafast (∼430 fs) charge transfer between the materials. The addition of excess P3HT leads to long-term charge separation in which free polarons remain separated at room temperature. Our results suggest that SWNT-P3HT blends incorporating only small fractions (1%) of SWNTs allow photon-to-charge conversion with efficiencies comparable to those for conventional (60:40) P3HT-fullerene blends, provided that small-diameter tubes are in idually embedded in the P3HT matrix.
Publisher: American Chemical Society (ACS)
Date: 07-12-2018
DOI: 10.1021/ACS.NANOLETT.8B04048
Abstract: Semiconductor nanowires suffer from significant non-radiative surface recombination however, heavy p-type doping has proven to be a viable option to increase the radiative recombination rate and, hence, quantum efficiency of emission, allowing the demonstration of room-temperature lasing. Using a large-scale optical technique, we have studied Zn-doped GaAs nanowires to understand and quantify the effect of doping on growth and lasing properties. We measure the non-radiative recombination rate ( k
Publisher: American Chemical Society (ACS)
Date: 21-12-2009
DOI: 10.1021/JP908760R
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2021
End Date: 2024
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2015
End Date: 2016
Funder: Royal Society
View Funded ActivityStart Date: 2020
End Date: 2022
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2020
End Date: 2024
Funder: UK Research and Innovation
View Funded ActivityStart Date: 2013
End Date: 12-2016
Amount: $400,000.00
Funder: Australian Research Council
View Funded Activity