Solid State Physics

Drawing graphene nanoribbons on SiC by ion implantation

by Sefaattin Tongay

Cover Image Feb13th Applied Physics Letters

The most downloaded article in Feb 2012 and 3rd downloaded article in March 2012

We describe a straightforward technique for selective graphene growth and nanoribbon production onto 4H- and 6H-SiC.... more We describe a straightforward technique for selective graphene growth and nanoribbon production onto 4H- and 6H-SiC. The technique presented is as easy as ion implanting regions where graphene layers are desired followed by annealing to 100 degrees C below the graphitization temperature (T-G) of SiC. We find that ion implantation of SiC lowers the T-G, allowing selective graphene growth at temperatures below the T-G of pristine SiC and above T-G of implanted SiC. This results in an approach for patterning device structures ranging from a couple tens of nanometers to microns in size without using conventional lithography and chemical processing. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682479]

Spintronics and quantum optics in InAs/GaAs quantum dots

by Claudio Polisseni

Third year project report for my BSc degree. Credit to Prof. Murray and Dr. Spencer for the help and the support they gave me.

Spin polarization of two-dimensional electrons in GaAs quantum wells around Landau level filling ν = 1 from NMR measurements of gallium nuclei

by Sorin Melinte

Rectification at Graphene-Semiconductor Interfaces: Zero-Gap Semiconductor-Based Diodes

by Sefaattin Tongay

Extinction of ferromagnetism in highly ordered pyrolytic graphite by annealing

by Sefaattin Tongay

Epitaxy and chemical reactions during thin-film formation from low-energy ions: new kinetic pathways, new phases, and new properties

by Nicole Herbots

Nicole Herbots, O.C. Hellman
ARIZONA STATE UNIVERSITY, Departmentof PhysicsandAstronomy, Tempe AZ 85287
0. Vancauwenberghe* MASSACHUSETTS INSTITUTE OFTECHNOLOGY, DepartmentofMaterialsScience & Engineering,Cambridge, MA 02139

Ref: Mat. Res. Soc. Symp. Proc. Vol. 235. pp. 749-762 (1992)

ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of... more ABSTRACT
Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption. The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(lOO) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.

Random imperfection fields to model the size effect in laboratory wood specimens

by Sara Casciati

Casciati S. and Domaneschi M. (2007). “Random imperfection fields to model the size effect in laboratory wood specimens”. Structural Safety, 29(4), 308-321. ISSN: 0167-4730.

DATA E LUOGO DI PUBBLICAZIONE: October 2007; Elsevier Science Bv, 1000 AE Amsterdam, Netherlands.

ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on... more ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.
In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.
The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.

KEYWORDS: Biaxial tests; Finite element model; Imperfections; Laboratory tests; Random field; Wood specimens

IBMM of OH adsorbates and interphases on Si-based materials

by Nicole Herbots

N. Herbots , Qian Xing, M. Hart, J.D. Bradley, D.A. Sell, R.J. Culbertson, Barry J. Wilkens
Department of Physics, Arizona State University, Tempe, AZ 85287-1504, USA
FINAL REFERENCE:
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 272, 1 February 2012, Pages 330-333

Proceedings of the 17th International Conference on Ion Beam Modification of Materials (IBMM 2010)

Please cite this article as

N. Herbots. Q. Xing et al., IBMM of OH adsorbates and interphases on Si-based materials, Nucl. Instr. and Meth. , Vol 272, pp 330-333 (2012),
doi:10.1016/j.nimb.2011.01.094

Using ion beam modification, films composed of synthesized
‘‘interphases’’ of ordered silica on OH-passivated (1... more Using ion beam modification, films composed of synthesized
‘‘interphases’’ of ordered silica on OH-passivated (1 X 1) Si(100) underwent surface electro-chemical changes quantified by surface free energy via Sessile drop method and contact angle analysis using Young’s equation and Van Oss theory. IBMM caused the surface free energies initially ranging from 26.0 mJ/m2 to 57.3 mJ/m2 to converge to 43.1–45.4 mJ/m2 for various passivated and as-received wafer samples alike. Although TMAFM also identified topographic changes, these changes did not correlate to the change of surface free energies. Ion beam modification of the ordered silica film on Si(100) surface is analyzed using 3.045 MeV 16O(a, a)16O nuclear resonance scattering (NRS) in conjunction with channeling in (1 1 1) direction, which demonstrated the convergence of the partially ordered oxygen to amorphous at about 55 microCoulombs/mm2 He++ flux. Additionally, Si surface peak channeling in (1 0 0) and (1 1 1) directions also experienced an uptrend in areal density as incident ion flux increased, while the rotating random Si signal height remains stable, showing a disruption in the surface order during IBMM.

A quantitative model of point defect diffusivity and recombination in ion beam deposition and combined ion and molecular deposition

by Nicole Herbots

O. Vancauwenberghe, N. Herbots, and O. C. Hellman MassachusettsInstituteo/Technology, 77MassachusettsAvenue. Cambridge. jWassachusetts02139
(Received 18 October 1990; accepted 12 February 1991)
J. Vac. Sci. Techno!. B 9 (4), JullAug 1991, p.2027-2033 0134-211X/911042027-07$01.00 @ 1991 American Vacuum Society 2027

We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam... more We are investigating the use of low energy ions (< 1 keV) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description of IBD. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the IBD growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.

Atomic displacement free interfaces and atomic registry in SiO2/(1x1) Si(100). Journal of Applied Physics. Vol 100. No 10 (2006) 104109-10410.

by Nicole Herbots

Shaw, J. M. ; Herbots, N. ; Hurst, Q. B. ; Bradley, D. ; Culbertson, R. J. ; Atluri, V. ; Queeney, K. T.

JOURNAL OF APPLIED PHYSICS Volume: 100 Issue: 10 Article Number: 104109 DOI: 10.1063/1.2358835 Published: NOV 15 2006

We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100)... more We use ion beam analysis to probe the structure and interface of ultrathin thermal oxide films grown on (1x1) Si(100) surfaces prepared using the Herbots-Atluri [U.S. patent No. 6,613,677 (Sept. 2, 2003)] wet chemical clean. We discover that these oxide layers are structurally registered with the substrate lattice with no interfacial structural disorder. Registry of Si atoms is most pronounced along < 111 > directions relative to the Si substrate, consistent with a beta-cristobalite epitaxial phase. This structurally registered phase transitions to an amorphous structure approximately 2 nm from the interface.(c) 2006

Nuclear Quantum Effects In Solids Using a Colored-Noise Thermostat

by Michele Ceriotti

Quantum-mechanical calculations of zircon to scheelite transition pathways in ZrSiO_ {4}

by JULIA CONTRERAS-GARCIA

Origin of incommensurate modulations in the high-pressure phosphorus IV phase

by JULIA CONTRERAS-GARCIA

Potassium under pressure: A pseudobinary ionic compound

by JULIA CONTRERAS-GARCIA

Chemical bonding in crystalline solids. Implementation and development of the topological analysis of elf in the solid state

by JULIA CONTRERAS-GARCIA

Bases for Understanding Polymerization under Pressure: The Practical Case of CO2

by JULIA CONTRERAS-GARCIA

Bonding changes across the-cristobalitestishovite transition path in silica

by JULIA CONTRERAS-GARCIA

A new polymorph with a layered structure-CaTe2O5

by JULIA CONTRERAS-GARCIA

Optical and electronic properties of dense sodium

by JULIA CONTRERAS-GARCIA

The bulk modulus of cubic spinel selenides: an experimental and theoretical study

by JULIA CONTRERAS-GARCIA