S. B. Newcomb

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

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Publications (106)250.49 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. · 2.86 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; · 6.73 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). · 3.52 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: Bright-field (BF) and annular dark-field (ADF) electron tomography in the transmission electron microscope (TEM) are used to characterize elongated porous regions or cracks (simply referred to as cracks thereafter) in micro-crystalline silicon (μc-Si:H) solar cell. The limitations of inferring the 3D geometry of a crack from a tilt series of images acquired from 100-nm-thick focused ion beam (FTB) milled TEM specimen are discussed. In an attempt to maximize the specimen tilt range and to reduce the effects of diffraction and phase contrast on the reconstruction, both BF and ADF electron tomography are used to acquire 360° tilt series of images from a FIB-prepared needle-shaped μc-Si:H specimen.
    Journal of Physics Conference Series 11/2011; 326(1):2057-.
  • S. B. Newcomb, W. M. Stobbs
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    ABSTRACT: The oxidation behaviour of 10Cr and 20Cr iron alloys, with nickel contents from 0 to 34 wt% both in air and in CO/CO2, is summarized with particular emphasis on the form and chemistry of the different scales as they were observed using transmission electron microscopy. The various modes of inward oxidation are for example characterized with ‘internal’ and ‘inner’ oxidation taking place under different circumstances. The role of carbon during oxidation in a CO/CO2 atmosphere is also discussed as is the way in which a given alloy can show either chemical or mechanical passivation failure in different environments.
    Journal of Microscopy 08/2011; 130(2):233 - 248. · 1.63 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: Electron energy-loss spectroscopy (EELS) is used to study the B distribution in a p-i-n layered solar cell structure. The boron concentration in the p-doped Si layer is expected to be ∼1021 cm−3 and should not exceed 1017 cm−3 in the neighbouring intrinsic layer. We show that B concentrations as low as 3×l020 cm−3 (0.6 at. %) can be measured using EELS. Our measurements are in close agreement with real space ab-initio multiple scattering calculations and secondary ion mass spectrometry measurements.
    Journal of Physics Conference Series 01/2011; 326(1).
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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. · 3.52 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; · 3.52 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 09/2010; 518:6921-6926. · 1.87 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). · 6.63 Impact Factor
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    ABSTRACT: Off-axis electron holography has been used to characterize a linear array of transistors, which was prepared for examination in cross-sectional geometry in the transmission electron microscope using focused ion beam milling. In reconstructed phase images, regions of silicon oxide that are located between metal contacts show unexpected elliptical phase contours centered several hundreds of nm from the specimen edge. The experimental images are compared with simulations performed using three-dimensional calculations of the electrostatic potential inside and outside the specimen, which take into account the mean inner potential of the specimen and the perturbed vacuum reference wave. The simulations suggest that the oxide layers contain a uniform volume density of positive charge and that the elliptical contours result from the combined effect of the electrostatic potential in the specimen and the external electrostatic fringing field.
    Journal of Physics Conference Series 02/2010; 209(1):012064.
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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: 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. · 6.63 Impact Factor

Publication Stats

381 Citations
250.49 Total Impact Points

Institutions

  • 2012
    • Catalan Institute of Nanoscience and Nanotechnology
      Barcino, Catalonia, Spain
  • 2011
    • Newport Laboratories
      Worthington, Minnesota, United States
    • Technical University of Denmark
      København, Capital Region, Denmark
  • 2008–2011
    • Tyndall National Institute
      Corcaigh, Munster, Ireland
    • Analog Devices, Inc.
      Norwood, Massachusetts, United States
  • 1983–2011
    • University of Cambridge
      • Department of Materials Science and Metallurgy
      Cambridge, England, United Kingdom
  • 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