S. B. Newcomb

Catalan Institute of Nanoscience and Nanotechnology, Barcino, Catalonia, Spain

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Publications (63)156.4 Total impact

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    ABSTRACT: Pore propagation during anodization of (100) n-InP electrodes in aqueous KOH was studied in detail by scanning and transmission electron microscopy (SEM and TEM). Pores emanating from surface pits propagate along the 111A crystallographic directions to form, in the early stages of anodization, porous domains with the shape of a tetrahedron truncated symmetrically through its center by a plane parallel to the surface of the electrode. This was confirmed by comparing the predictions of a detailed model of pore propagation with SEM and TEM observations. The model showed in detail how 111A pore propagation leads to domains with the shape of a tetrahedron truncated by a (100) plane. Observed cross sections corresponded in detail and with good precision to those predicted by the model. SEM and TEM showed that cross sections were trapezoidal and triangular, respectively, in the two cleavage planes of the wafer, and TEM showed that they were rectangular parallel to the surface plane, as predicted. Aspect ratios and angles calculated from observed cross sections were in good agreement with predicted values. The pore patterns observed were also in good agreement with those predicted and SEM observations of the surface further confirmed details of the model. © 2013 The Electrochemical Society. [DOI: 10.1149/2.107306jes] All rights reserved.
    Journal of The Electrochemical Society 05/2013; 160:260-270. · 2.59 Impact Factor
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    ABSTRACT: We report on a method to enhance the light-emission efficiency of printable thin films of a polymer doped with luminescent (CdSe)ZnS nanocrystals via metallic nanoparticles and nanoimprinted photonic crystals. We experimentally show a strong fluorescence enhancement of nanocrystals by coupling exciton-plasmon with the localized surface plasmon of metallic nanoparticles. The emitted light is efficiently diffracted by photonic crystals structures directly imprinted in the nanocomposite polymer. By combining the field susceptibility technique with optical Bloch equations, we examine the interaction of the quantum and plasmonic entities at small distances.
    Nanoscale 11/2012; · 6.23 Impact Factor
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    ABSTRACT: Hafnium erbium oxide (HfErOx) thin films were formed using atomic layer deposition. The effect of using different Hf:Er pulse ratios on the electrical and structural properties of the HfErOx thin films (∼9 nm) in metal–insulator–metal (MIM) capacitor structures have been investigated and comparisons made between as-deposited and annealed samples. We report the stabilisation of the higher dielectric constant (k) tetragonal/cubic phase by optimising the Hf:Er pulse ratio. The dielectric properties post thermal anneal at 500 °C were studied. A leakage current in the order of ∼1 × 10−8 (A/cm2) at a voltage of 1 V and a capacitance equivalent thickness of ∼1.4 nm have been achieved post thermal annealing at 500 °C.
    Microelectronic Engineering 06/2012; 94:7–10. · 1.22 Impact Factor
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    ABSTRACT: Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces.
    Applied Physics Letters 04/2012; 100(14). · 3.79 Impact Factor
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    ABSTRACT: We present a systematic study of Si dopant implantation and activation in p-type In0.53Ga0.47As in an attempt to optimize the source and drain regions of an n-channel III-V metal–oxide–semiconductor field-effect transistor. Test structures based on the transfer length method were fabricated on Si-implanted p-In0.53Ga0.47As/p-InP buffer/semi-insulting InP. A Doehlert design of experiment (DOE) was used to investigate the effect of annealing temperature and time on the electrical properties of the samples. The DOE covered an experimental domain of 625–725 °C and 15–45 s. The current–voltage characteristics of all tested structures exhibited excellent ohmic behavior. The DOE revealed a minimum sheet resistance of (195.6 ± 3.4) Ω/□ for an optimum anneal condition of 715 °C for 32 s. Nonalloyed Au/Ge/Au/Ni/Au contacts, on the sample annealed at 675 °C for 30 s (center point of the experimental domain), exhibited a low specific contact resistance of (7.4 ± 4.5) × 10−7 Ω cm2. The sample annealed at 675 °C for 30 s was further investigated using secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (XTEM) analyses. SIMS revealed that Si ions did not diffuse with annealing, while XTEM showed the formation of characteristic loop defects potentially responsible for the sheet resistance and specific contact resistance degradation.
    Semiconductor Science and Technology 01/2012; 27(8). · 1.92 Impact Factor
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    ABSTRACT: O'Connor, E. Cherkaoui, K. Monaghan, S. O'Connell, D. Povey, I. Casey, P. Newcomb, S. B. Gomeniuk, Y. Y. Provenzano, G. Crupi, F. Hughes, G. Hurley, P. K.
    Journal of Applied Physics 01/2012; 111. · 2.21 Impact Factor
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    ABSTRACT: In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide ( NH <sub>4</sub>)<sub>2</sub> S concentrations in the passivation of n -type and p -type In <sub>0.53</sub> Ga <sub>0.47</sub> As . Samples were degreased and immersed in aqueous ( NH <sub>4</sub>)<sub>2</sub> S solutions of concentrations 22%, 10%, 5%, or 1% for 20 min at 295 K, immediately prior to atomic layer deposition of Al <sub>2</sub> O <sub>3</sub> . Multi-frequency capacitance-voltage (C-V) results on capacitor structures indicate that the lowest frequency dispersion over the bias range examined occurs for n -type and p -type devices treated with the 10 % ( NH <sub>4</sub>)<sub>2</sub> S solution. The deleterious effect on device behavior of increased ambient exposure time after removal from 10 % ( NH <sub>4</sub>)<sub>2</sub> S solution is also presented. Estimations of the interface state defect density ( D <sub> it </sub>) for the optimum 10 % ( NH <sub>4</sub>)<sub>2</sub> S passivated In <sub>0.53</sub> Ga <sub>0.47</sub> As devices extracted using an approximation to the conductance method, and also extracted using the temperature-modified high-low frequency C-V method, indicate that the same defect is present over n -type and p -type devices having an integrated D <sub> it </sub> of ∼2.5×10<sup>12</- - sup> cm <sup>-2</sup> (±1×10<sup>12</sup> cm <sup>-2</sup>) with the peak density positioned in the middle of the In <sub>0.53</sub> Ga <sub>0.47</sub> As band gap at approximately 0.37 eV (±0.03 eV) from the valence band edge. Both methods used for extracting D <sub> it </sub> show very good agreement, providing evidence to support that the conductance method can be applied to devices incorporating high- k oxides on In <sub>0.53</sub> Ga <sub>0.47</sub> As .
    Journal of Applied Physics 02/2011; · 2.21 Impact Factor
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    ABSTRACT: The atomic layer deposition of high dielectric constant oxides like HfO <sub>2</sub> on III-V substrates such as In <sub>0.53</sub> Ga <sub>0.47</sub> As leads to a poor interface, with the growth of In <sub>0.53</sub> Ga <sub>0.47</sub> As native oxides regardless of the surface pretreatment and passivation method. The presence of the native oxides leads to poor gate leakage current characteristics due to the low band gap of the native oxides and the presence of potential wells at the interface. In addition, the poor quality of this interface leads to very large interface state defect densities, which are detrimental to metal-oxide-semiconductor-based device performance. A wide band gap interlayer replacing the native oxide layer would remove the potential wells and provide a larger barrier to conduction. It may also assist in the improvement of the interface quality, but the problem remains as to how this native oxide interlayer cannot only be removed but prevented from regrowing. In this regard, the authors present electrical results showing that the atomic layer deposition (ALD) growth of a thin (∼1 nm ) Al <sub>2</sub> O <sub>3</sub> layer before the ALD growth of HfO <sub>2</sub> causes a removal/reduction of the native oxides on the surface by a self-cleaning process without subsequent regrowth of the native oxides. As a result, there are significant improvements in gate leakage current densities, and significant improvements in the frequency dispersion of capacitance versus gate voltage, even when a defective In <sub>0.53</sub> Ga <sub>0.47</sub> As epitaxial layer on an InP substrate is employed. Measurements at different - - temperatures confirm that the frequency dispersion is mainly due to interface state defect responses and another weakly temperature dependent mechanism such as border traps, after accounting for the effects of nonideal In <sub>0.53</sub> Ga <sub>0.47</sub> As epitaxial layer growth defects where applicable.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 02/2011; · 1.36 Impact Factor
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    ABSTRACT: Salauen, Amelie Trommer, Jens Newcomb, Simon B. Povey, Ian M. Salauen, Mathieu Keeney, Lynette O'Mahony, Aileen Pemble, Martyn E.
    Chemical Vapor Deposition 01/2011; 17:114-122. · 1.32 Impact Factor
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    ABSTRACT: Energy barriers at interfaces of (100)InP with atomic-layer deposited Al2O3 are determined using internal photoemission of electrons. The barrier height between the top of the InP valence band and bottom of the alumina conduction band is found to be 4.05±0.10 eV corresponding to a conduction band offset of 2.7 eV. An interlayer associated with the oxidation of InP may result in a lower barrier for electron injection potentially leading to charge instability of the insulating stack. A wide-gap P-rich interlayer has a potential to reduce this degrading effect as compared to In-rich oxides.
    Applied Physics Letters 09/2010; 97(13):132112-132112-3. · 3.79 Impact Factor
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    ABSTRACT: High mobility III-V substrates with high- k oxides are required for device scaling without loss of channel mobility. Interest has focused on the self-cleaning effect on selected III-V substrates during atomic layer deposition of Al <sub>2</sub> O <sub>3</sub> . A thin (∼1 nm ) Al <sub>2</sub> O <sub>3</sub> interface control layer is deposited on In <sub>0.53</sub> Ga <sub>0.47</sub> As prior to HfO <sub>2</sub> growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by ∼50 % while maintaining scaling trends. Significant reductions in leakage current density and increased breakdown voltage are found, indicative of a band structure improvement due to the reduction/removal of the In <sub>0.53</sub> Ga <sub>0.47</sub> As native oxides.
    Applied Physics Letters 09/2010; · 3.79 Impact Factor
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    ABSTRACT: Photonic crystals made from noble metals such as silver are an interesting class of material for many applications such as chemical sensing, solar cells or photonics. Their fabrication suffers from a lack of reproducibility, and complicated and aggressive processes. In this paper we show a simple and reproducible method based on the black and white photography process, to get a self standing 3D silver photonic crystal. Their characterization by SEM and TEM allowed us to interpret the process, and optical analysis made in reflection and transmission were used to find out eventual coupling between surface plasmon polaritons and the photonics properties of the structure itself.
    Journal of Materials Chemistry 08/2010; 20(36). · 5.97 Impact Factor
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    ABSTRACT: MgO has been suggested as a possible high- k dielectric for future complementary metal-oxide semiconductor processes. In this work, the time dependent dielectric breakdown (TDDB) characteristics of 20 nm MgO films are discussed. Stress induced leakage current measurements indicate that the low measured Weibull slopes of the TDDB distributions for both n -type and p -type devices cannot be attributed to a lower trap generation rate than for SiO <sub>2</sub> . This suggests that much fewer defects are required to trigger breakdown in MgO under voltage stress than is the case for SiO <sub>2</sub> or other metal-oxide dielectrics. This in turn explains the progressive nature of the breakdown in these films which is observed both in this work and elsewhere. The reason fewer defects are required is attributed to the morphology of the films.
    Journal of Applied Physics 02/2010; · 2.21 Impact Factor
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    ABSTRACT: The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 degrees C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 degrees C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented. (C) 2010 Elsevier B.V. All rights reserved.
    Thin Solid Films 01/2010; 518:6921-6926. · 1.87 Impact Factor
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    ABSTRACT: In this paper we present our development of a SF6/Cl2-based plasma etch recipe for a LAM Research 4720 etch chamber. Our tungsten plasma etch recipe is used to pattern nanoscale resistor features integrated within a novel IR sensor process. We characterised the nanoscale etch in terms of five primary process parameters using a 16-run V fractional factorial experiment, to provide accurate estimates of all main effects and two-factor interactions. The experimental results determined the target levels for the etch process parameters. Our optimised nanoscale tungsten etch module was then integrated within a CMOS/MEMs-compatible nanobolometer infrared (IR) sensor fabrication flow. Our use of tungsten improves the reliability of the sensor pixels at elevated stress current levels, when compared with equivalent Ti-based pixel structures, and demonstrates the potential of tungsten as a CMOS-compatible nanobolometer material.
    Microelectronic Engineering 01/2010; 87:1634-1639. · 1.22 Impact Factor
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    ABSTRACT: Photonic crystals made from noble metals such as silver are an interesting class of material for many applications such as chemical sensing, solar cells or photonics. Their fabrication suffers from a lack of reproducibility, and complicated and aggressive processes. In this paper we show a simple and reproducible method based on the black and white photography process, to get a self standing 3D silver photonic crystal. Their characterization by SEM and TEM allowed us to interpret the process, and optical analysis made in reflection and transmission were used to find out eventual coupling between surface plasmon polaritons and the photonics properties of the structure itself.
    Journal of Materials Chemistry 01/2010; 20:7870. · 5.97 Impact Factor
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    ABSTRACT: In this work results are presented on the structural analysis, chemical composition, and interface state densities of HfO <sub>2</sub> thin films deposited by atomic layer deposition (ALD) from Hf [ N ( CH <sub>3</sub>)<sub>2</sub>]<sub>4</sub> and H <sub>2</sub> O on In <sub>0.53</sub> Ga <sub>0.47</sub> As / InP substrates. The structural and chemical properties are investigated using high resolution cross-sectional transmission electron microscopy and electron energy loss spectroscopy. HfO <sub>2</sub> films (3–15 nm) deposited on In <sub>0.53</sub> Ga <sub>0.47</sub> As are studied following a range of surface treatments including in situ treatment of the In <sub>0.53</sub> Ga <sub>0.47</sub> As surface by H <sub>2</sub> S exposure at 50–350 ° C immediately following the metal organic vapor phase epitaxy growth of the In <sub>0.53</sub> Ga <sub>0.47</sub> As layer, ex situ treatment with ( NH <sub>4</sub>)<sub>2</sub> S , and deposition on the native oxides of In <sub>0.53</sub> Ga <sub>0.47</sub> As with no surface treatment. The structural analysis indicates that the In <sub>0.53</sub> Ga <sub>0.47</sub> As surface preparation prior to HfO <sub>2</sub> film deposition influences the thickness of the HfO <sub>2</sub></f- ormula> film and the interlayer oxide. The complete interfacial self-cleaning of the In <sub>0.53</sub> Gas <sub>0.47</sub> As native oxides is not observed using an ALD process based on the Hf [ N ( CH <sub>3</sub>)<sub>2</sub>]<sub>4</sub> precursor and H <sub>2</sub> O . Elemental profiling of the HfO <sub>2</sub>/ In <sub>0.53</sub> Ga <sub>0.47</sub> As interface region by electron energy loss spectroscopy reveals an interface oxide layer of 1–2 nm in thickness, which consists primarily of Ga oxides. Using a conductance method approximation, peak interface state densities in the range from 6×10<sup>12</sup> to 2×10<sup>13</sup> cm <sup>-2</sup>  eV <sup>-1</sup> are estimated depending on the surface preparation.
    Journal of Applied Physics 11/2009; · 2.21 Impact Factor
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    ABSTRACT: Thin layers of indium tin oxide are widely used as transparent coatings and electrodes in solar energy cells, flat-panel displays, antireflection coatings, radiation protection and lithium-ion battery materials, because they have the characteristics of low resistivity, strong absorption at ultraviolet wavelengths, high transmission in the visible, high reflectivity in the far-infrared and strong attenuation in the microwave region. However, there is often a trade-off between electrical conductivity and transparency at visible wavelengths for indium tin oxide and other transparent conducting oxides. Here, we report the growth of layers of indium tin oxide nanowires that show optimum electronic and photonic properties and demonstrate their use as fully transparent top contacts in the visible to near-infrared region for light-emitting devices.
    Nature Nanotechnology 05/2009; 4(4):239-44. · 31.17 Impact Factor
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    ABSTRACT: The relationship between the nanoscale structure of vanadium pentoxide nanotubes and their ability to accommodate Li+ during intercalation/deintercalation is explored. The nanotubes are synthesized using two different precursors through a surfactant-assisted templating method, resulting in standalone VOx (vanadium oxide) nanotubes and also “nano-urchin”. Under highly reducing conditions, where the interlaminar uptake of primary alkylamines is maximized, standalone nanotubes exhibit near-perfect scrolled layers and long-range structural order even at the molecular level. Under less reducing conditions, the degree of amine uptake is reduced due to a lower density of V4+ sites and less V2O5 is functionalized with adsorbed alkylammonium cations. This is typical of the nano-urchin structure. High-resolution TEM studies revealed the unique observation of nanometer-scale nanocrystals of pristine unreacted V2O5 throughout the length of the nanotubes in the nano-urchin. Electrochemical intercalation studies revealed that the very well ordered xerogel-based nanotubes exhibit similar specific capacities (235 mA h g−1) to Na+-exchange nanorolls of VOx (200 mA h g−1). By comparison, the theoretical maximum value is reported to be 240 mA h g−1. The VOTPP-based nanotubes of the nano-urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437 mA h g−1, which is a considerable advance for VOx based nanomaterials and one of the highest known capacities for Li+ intercalated laminar vanadates.
    Advanced Functional Materials 04/2009; 19(11):1736 - 1745. · 9.77 Impact Factor
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    ABSTRACT: Electrical properties of metal-oxide-semiconductor capacitors using atomic layer deposited HfO2 on n-type GaAs or InxGa1−xAs (x = 0.53, 0.30, 0.15) epitaxial layers were investigated. Capacitance-voltage (CV) measurements indicated large temperature and frequency dispersion at positive gate bias in devices using n-type GaAs and low In content (x = 0.30, 0.15) InxGa1−xAs layers, which is significantly reduced for devices using In0.53Ga0.47As. For In0.53Ga0.47As devices, the CV response at negative gate bias is most likely characteristic of an interface state response and may not be indicative of true inversion. The conductance technique on Pd/HfO2/In0.53Ga0.47As/InP shows reductions in interface state densities by In0.53Ga0.47As surface passivation and forming gas annealing (325 °C).
    Applied Physics Letters 03/2009; 94(10):102902-102902-3. · 3.79 Impact Factor

Publication Stats

240 Citations
156.40 Total Impact Points

Institutions

  • 2012
    • Catalan Institute of Nanoscience and Nanotechnology
      Barcino, Catalonia, Spain
  • 2008–2011
    • Tyndall National Institute
      Corcaigh, Munster, Ireland
    • Analog Devices, Inc.
      Norwood, Massachusetts, United States
  • 2010
    • Dublin City University
      • School of Physical Sciences
      Dublin, L, Ireland
  • 2002–2009
    • University of Limerick
      • • Materials and Surface Science Institute (MSSI)
      • • Department of Electronic and Computer Engineering
      Luimneach, Munster, Ireland