Nelson Garcés

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Daniel Cassany

Pompeu Fabra University

Henry Tantaleán

Universidad Nacional Mayor de San Marcos

Ramiro Barberena

National Scientific and Technical Research Council

Gary Feinman

Field Museum

Francisco Pazzarelli

Universidad Nacional de Córdoba

Horacio Chiavazza

Universidad Nacional de Cuyo

Harvey Weiss

Yale University

Magaly Quinones Negrete

ULADECH

Manuel J Lis

Universitat Politecnica de Catalunya

Anders Burman

University of Gothenburg

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Papers by Nelson Garcés

INDUCCION PROFESIONAL DOCENTE

Relationship between the EPR SI5 Signal and the 0.65 eV Electron Trap in 4H- and 6H-SiC Polytypes

Materials Science Forum, 2006

Annealing of multivacancy defects in 4H-SiC

Physical Review B, 2006

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High-k Dielectrics

Applied Physics Express, 2011

We report the effects of GaN surface pretreatments on the material and electrical properties of A... more We report the effects of GaN surface pretreatments on the material and electrical properties of Al2O3 dielectric deposited by atomic layer deposition (ALD). A layer of Al2O3 was deposited at different temperatures on metal organic chemical vapor deposition grown n-GaN that was treated with either H2O2:H2SO4 (1:5, piranha), HCl:H2O (1:1, HCl), or HF:H2O (1:1, HF) prior to Al2O3 deposition. The Al2O3 layers on piranha- and HF-treated GaN were observed to be uniformly smooth. The piranha pretreatment resulted in the lowest hysteresis. Pretreatment of the GaN surface with piranha removes carbon and hydroxylates the surface, resulting in better quality ALD Al2O3.

Graphene functionalization and seeding for dielectric deposition and device integration

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2012

Atomic Layer Deposition of Dielectrics on Graphene

Graphene Nanoelectronics, 2012

Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit ... more Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer.

Mode-locked 2- μ m wavelength fiber laser using a graphene-saturable absorber

Optical Engineering, 2013

Impact of surface treatments on high-κ dielectric integration with Ga-polar and N-polar GaN

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2014

ABSTRACT Gallium- and nitrogen-polar GaN surfaces are subjected to a variety of pretreatments, in... more ABSTRACT Gallium- and nitrogen-polar GaN surfaces are subjected to a variety of pretreatments, including oxidation, before the application of high-κ dielectrics by atomic layer deposition (ALD) in order to assess the “best” preparation of smooth, clean, and electrically high-performing dielectric semiconductor interfaces. In terms of topographical and chemical cleanliness, a pretreatment with a wet chemical piranha etch (H2SO4:H2O2) was found to be optimum for both surfaces, and additionally, (NH4)2S is effective for N-polar surfaces. Both thermal and plasma oxidations were employed for controlled growth of native oxides. For Ga-polar surfaces, all native oxides were as smooth as pretreated surfaces, while for N-polar surfaces, all native oxides are much rougher except for very short, high temperature oxidations. ALD Al2O3 films on Ga-polar surfaces are smoother for pretreated surfaces than for as-received surfaces, whereas for N-polar surfaces the opposite is true. In general, ALD HfO2 films on Ga-polar surfaces are rougher (0.8 nm rms) than Al2O3 films (0.1 nm rms), whereas for piranha treated N-polar surfaces, HfO2 films are smoother than Al2O3 films. For Ga-polar surfaces, capacitance–voltage measurements of simple Al2O3 (measured κ = 9) capacitors show the smallest hysteresis for unintentionally oxidized surfaces (0.37 V), whereas simple HfO2 (measured κ = 14) capacitors show the smallest hysteresis for a thermal GaOx at the interface (0.1 V). In both cases, the thicker the GaOx at the interface the larger the negative threshold voltage shift—suggesting an electron trap. Calculated total trapped charges associated with the dielectrics range from 3.2 × 10

Plasma-assisted atomic layer deposition of nanolaminates for gate dielectric applications

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2014

Fluorine functionalization of epitaxial graphene for uniform deposition of thin high-κ dielectrics

Carbon, 2012

... Virginia Wheeler Corresponding author contact information , E-mail the corresponding author ,... more

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High- k Dielectrics

Applied Physics Express, 2011

Selective switching of GaN polarity on Ga-polar GaN using atomic layer deposited Al 2 O 3

Applied Physics Express, 2014

ABSTRACT Patterned layers of Al2O3 prepared by atomic layer deposition (ALD) are used to produce ... more ABSTRACT Patterned layers of Al2O3 prepared by atomic layer deposition (ALD) are used to produce structures of alternating polarity (c-plane orientation) of GaN on Ga-polar GaN epilayers. Annealing prior to epitaxial growth allows the amorphous ALD layers to attain sufficient crystallinity, which enables N-polar GaN growth over the annealed ALD Al2O3 and Ga-polar growth over the bare substrate. Transmission electron microscopy and electron channeling contrast imaging were carried out to characterize the structural nature of the material and confirm crystallinity. ALD Al2O3 may be suitable for fabricating novel variable-polarity devices, particularly where growth on native, Ga-polar GaN substrates is beneficial. (C) 2014 The Japan Society of Applied Physics

Identification of trapping sites for OH − molecular ions in CdWO 4

Journal of Physics and Chemistry of Solids, 2000

Infrared absorption bands due to OH− molecular ions have been investigated in single crystals of ... more Infrared absorption bands due to OH− molecular ions have been investigated in single crystals of CdWO4. The peak positions of these OH− absorptions depend strongly on the nature of the adjacent entity (either an impurity or vacancy) responsible for trapping the proton. Six OH− spectra were observed in the undoped, and intentionally doped CdWO4 crystals included in our study. The respective trapping entities are the monovalent impurity ions Li+, Na+ and Cu+ substituting for the Cd2+ ions, the pentavalent impurities Nb5+ and Ta5+ substituting for the W6+ ions, and the Cd vacancies. Peak positions and widths of the individual absorption bands were monitored as a function of temperature. Electron paramagnetic resonance (EPR) helped assign specific absorption bands to the Cu+–OH− and VCd–OH− centers. A 900°C thermal anneal in air converted the Cu+–OH− centers to Cu2+ ions (observable with EPR). Illuminating a crystal with 325 nm light at temperatures near 90 K caused a hole to be trapped adjacent to a VCd–OH− center, thus forming an h+–VCd–OH− center, which was observable with EPR also.

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Identification of the intrinsic self-trapped hole center in KD2PO4

The intrinsic ``self-trapped'' hole center in KD2PO4 crystals has been identified using... more The intrinsic ``self-trapped'' hole center in KD2PO4 crystals has been identified using electron paramagnetic resonance and electron-nuclear double resonance. These defects, labeled [D2PO4]o centers, can be formed at 77 K by irradiating with either 60 kV x rays or the fourth harmonic (266 nm) of a pulsed Nd:YAG laser. The hole is equally shared by two adjacent oxygen ions, and hyperfine interactions with one phosphorus and two equivalent deuterons are observed. The sample used in this investigation was approximately 80% deuterated, thus both [D2PO4]o and [HDPO4]o centers were detected, with the former being dominant. These intrinsic self-trapped hole centers are of interest because of their potential role in the transient optical absorption produced in KD2PO4 crystals at room temperature by intense 266 nm laser pulses.

Photoinduced behavior of the VCCSi- pair defect in 4H-SiC grown by physical vapor transport and halide chemical vapor deposition

Journal of Applied Physics, 2009

Two different photothresholds of the carbon vacancy-carbon antisite pair defect (VCCSi-) in 4H-Si... more Two different photothresholds of the carbon vacancy-carbon antisite pair defect (VCCSi-) in 4H-SiC are observed using photoinduced electron paramagnetic resonance. The defect appeared after illumination with photon energy greater than 0.75 eV in two samples grown by halide chemical vapor deposition (HCVD) and one by physical vapor transport (PVT), all with activation energies (Ea) below 0.80 eV. In HCVD and PVT samples with higher activation energies, the defect was not detected with photon excitation less than 2.1 eV. The increase in VCCSi- parallels changes in the negatively charged carbon vacancy VC- in the samples with low Ea. For SiC samples with high Ea, the concentration of the anitisite-vacancy pair also increases with VC- and, in addition, is accompanied by a simultaneous decrease in VC+. The results are interpreted in terms of two defect levels, one for the double negative-to-negative transition of VCCSi at 0.75 eV below the conduction band edge and another for the negative-to-neutral transition of the defect at 2.1 eV above the valence band edge. The model yielding these levels also suggests that the neutral-to-negative and negative-to-double negative transitions of the isolated carbon vacancy are within a few tenths of an eV of each other and are located close to the conduction band edge.

Thermoluminescence study of stoichiometric LiNbO3 crystals

Journal of Applied Physics, 2002

Thermoluminescence (TL), optical absorption, and electron paramagnetic resonance (EPR) have been ... more Thermoluminescence (TL), optical absorption, and electron paramagnetic resonance (EPR) have been used to characterize point defects in Mg-doped stoichiometric LiNbO3. A broad TL emission, peaking at 440 nm, is observed near 94 K when these crystals are irradiated at 77 K and then rapidly warmed. X rays and below-band-gap lasers (325 and 355 nm) are equally effective in producing the TL peak. During excitation, holes are trapped on oxygen ions adjacent to lithium vacancies and electrons are trapped on niobium ions at regular lattice sites. These defects both have characteristic EPR spectra, and the trapped electron center has an optical absorption band peaking at 1200 nm. Upon warming, the electrons become thermally unstable near 94 K and migrate to the trapped-hole sites where radiative recombination occurs. We suggest that the near-edge charge-transfer absorption band from Fe3+ impurities, nominally present, provides the mechanism by which below-band-gap light initially produces the separately trapped holes and electrons.

Electron-nuclear double-resonance study of Mn2+ ions in ZnGeP2 crystals

Physical Review B, 2005

Electron nuclear double resonance (ENDOR) and the related pulse technique of pulse field sweep EP... more Electron nuclear double resonance (ENDOR) and the related pulse technique of pulse field sweep EPR (PFSEPR) were used to probe the site I environment of Mn2+ in the oxalate-ATP complex of pyruvate kinase. Assignment of features and an estimate of hyperfine couplings have shown proximity of protons to the metal ions through their dipolar interaction and proximity of 31P and 17O because of a contact interaction from direct Mn(2+)-ligand covalent spin transfer. Since Mn2+ is a spin5/2 ion whose Ms = +/- 1/2, +/- 3/2, and +/- 5/2 electron spin states can all contribute to EPR and ENDOR, we have developed experimental and theoretical strategies for elucidating hyperfine couplings to the Mn2+ electron spin states. Solvent-exchangeable proton ENDOR features were evident with couplings very similar to the hyperfine couplings of H2O in [Mn(H2O)6]2+. ENDOR of exchangeable, more distant protons originated from a dipolar coupling such as could be expected from protons residing 5.5 A from Mn2+ and hydrogen-bonded to a nonliganding oxygen or nitrogen. Nonexchangeable proton ENDOR features indicated dipolar coupling to proton(s) from the protein residing at approximately 4.5 A from the Mn2+. The approximately 4-MHz 31P phosphate hyperfine couplings in Mn(II)-nucleotide models and in pyruvate kinase were similar, but a detailed ENDOR and PFSEPR comparison revealed that the hyperfine coupling to the ATP gamma-phosphate in pyruvate kinase was approximately 10% less than coupling to phosphates of Mn(II)-nucleotides. [In pyruvate kinase only the gamma-phosphate has been shown to bind to Mn2+ at site I (Lodato &amp; Reed, 1987).](ABSTRACT TRUNCATED AT 250 WORDS)

Electron paramagnetic resonance and electron-nuclear double resonance study of Mn2+ ions in CdGeAs2 crystals

Physica Status Solidi B-basic Solid State Physics, 2006

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been use... more Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to characterize Mn2+ (3d5) ions in CdGeAs2 crystals grown by the horizontal Bridgman method. These samples were p-type with room-temperature hole concentrations ranging from 2 × 1015 cm–3 to 5 × 1016 cm–3. The Mn2+ ions substitute for the Cd2+ ions in this tetragonal chalcopyrite lattice, and form “deep” isoelectronic centers. Their g values and crystal-field parameters are g‖ = 2.0025, g⊥ = 2.0011, D = 118.8 MHz, a + 2/3F = 18.4 MHz, and a = –0.3 MHz. The hyperfine and nuclear electric quadrupole parameters for the 55Mn nucleus are A‖ = –154.94 MHz, A⊥ = –155.69 MHz, and P = 0.622 MHz. Hyperfine parameters for one set of nearby Cd nuclei and two sets of nearby As nuclei were also determined using ENDOR. No evidence was found in these doped bulk crystals to suggest that Mn4+ ions substitute for Ge4+ ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Role of copper in the green luminescence from ZnO crystals

Applied Physics Letters, 2002

... sample was an undoped high quality crystal grown by the chemical vapor transport method ... A... more

Optical absorption and electron-nuclear double resonance study of Ni+ ions in AgGaSe2 crystals

Journal of Physics-condensed Matter, 2004

Optical absorption, electron paramagnetic resonance (EPR) and electron-nuclear double resonance (... more Optical absorption, electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) have been used to characterize Ni+ ions substituting for Ag+ ions in AgGaSe2 crystals. These Ni+ ions are responsible for a strongly polarized optical absorption band peaking near 2.2m (the maximum absorption occurs with ). Phonon structure is resolved at low temperature. This infrared band, which is present even

INDUCCION PROFESIONAL DOCENTE

Relationship between the EPR SI5 Signal and the 0.65 eV Electron Trap in 4H- and 6H-SiC Polytypes

Materials Science Forum, 2006

Annealing of multivacancy defects in 4H-SiC

Physical Review B, 2006

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High-k Dielectrics

Applied Physics Express, 2011

Graphene functionalization and seeding for dielectric deposition and device integration

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2012

Atomic Layer Deposition of Dielectrics on Graphene

Graphene Nanoelectronics, 2012

Mode-locked 2- μ m wavelength fiber laser using a graphene-saturable absorber

Optical Engineering, 2013

Impact of surface treatments on high-κ dielectric integration with Ga-polar and N-polar GaN

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2014

Plasma-assisted atomic layer deposition of nanolaminates for gate dielectric applications

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2014

Fluorine functionalization of epitaxial graphene for uniform deposition of thin high-κ dielectrics

Carbon, 2012

... Virginia Wheeler Corresponding author contact information , E-mail the corresponding author ,... more

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High- k Dielectrics

Applied Physics Express, 2011

Selective switching of GaN polarity on Ga-polar GaN using atomic layer deposited Al 2 O 3

Applied Physics Express, 2014

Identification of trapping sites for OH − molecular ions in CdWO 4

Journal of Physics and Chemistry of Solids, 2000

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Identification of the intrinsic self-trapped hole center in KD2PO4

Photoinduced behavior of the VCCSi- pair defect in 4H-SiC grown by physical vapor transport and halide chemical vapor deposition

Journal of Applied Physics, 2009

Thermoluminescence study of stoichiometric LiNbO3 crystals

Journal of Applied Physics, 2002

Electron-nuclear double-resonance study of Mn2+ ions in ZnGeP2 crystals

Physical Review B, 2005

Electron paramagnetic resonance and electron-nuclear double resonance study of Mn2+ ions in CdGeAs2 crystals

Physica Status Solidi B-basic Solid State Physics, 2006

Role of copper in the green luminescence from ZnO crystals

Applied Physics Letters, 2002

... sample was an undoped high quality crystal grown by the chemical vapor transport method ... A... more

Optical absorption and electron-nuclear double resonance study of Ni+ ions in AgGaSe2 crystals

Journal of Physics-condensed Matter, 2004

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