P Sutter

Publications (26)105.81 Total impact

• Source

  Available from: whut.edu.cn

  Article: Formation and stabilization of single-crystalline metastable AuGe phases in Ge nanowires.

  E Sutter, P Sutter
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  ABSTRACT: We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable γ-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.
  Nanotechnology 07/2011; 22(29):295605. · 3.98 Impact Factor
• Article: Two-Color Ultrafast Photoexcited Scanning Tunneling Microscopy

  A. Dolocan, D. P. Acharya, P. Zahl, P. Sutter, N. Camillone
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  ABSTRACT: We report on two-color two-photon photoexcitation of a metal surface driven by ultrafast laser pulses and detected with a scanning tunneling microscope (STM) tip as a proximate anode. Results are presented for two cases: (i) where the tip is retracted from the surface far enough to prohibit tunneling, and (ii) where the tip is within tunneling range of the surface. A delay-modulation technique is implemented to isolate the two-color photoemission from concurrent one-color two-photon photoemission and provide subpicosecond time-resolved detection. When applied with the tip in tunneling range, this approach effectively isolates the two-photon photoexcited current signal from the conventional tunneling current and enables subpicosecond time-resolved detection of the photoexcited surface electrons. The advantage of the two-color approach is highlighted by comparison with the one-color case where optical interference causes thermal modulation of the STM tip length, resulting in tunneling current modulations that are orders of magnitude larger than the current due to photoexcitation of surface electrons. By completely eliminating this interference, and thereby avoiding thermal modulation of the STM tip length, the two-color approach represents an important step toward the ultimate goal of simultaneous subnanometer and subpicosecond measurements of surface electron dynamics by ultrafast-laser-excited STM.
  04/2011;
• Article: Enhanced light scattering of the forbidden longitudinal optical phonon mode studied by micro-Raman spectroscopy on single InN nanowires.

  E O Schäfer-Nolte, T Stoica, T Gotschke, F A Limbach, E Sutter, P Sutter, D Grützmacher, R Calarco
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  ABSTRACT: In the literature, there are controversies on the interpretation of the appearance in InN Raman spectra of a strong scattering peak in the energy region of the unscreened longitudinal optical (LO) phonons, although a shift caused by the phonon-plasmon interaction is expected for the high conductance observed in this material. Most measurements on light scattering are performed on ensembles of InN nanowires (NWs). However, it is important to investigate the behavior of individual nanowires and here we report on micro-Raman measurements on single nanowires. When changing the polarization direction of the incident light from parallel to perpendicular to the wire, the expected reduction of the Raman scattering was observed for transversal optical (TO) and E(2) phonon scattering modes, while a strong symmetry-forbidden LO mode was observed independently on the laser polarization direction. Single Mg- and Si-doped crystalline InN nanowires were also investigated. Magnesium doping results in a sharpening of the Raman peaks, while silicon doping leads to an asymmetric broadening of the LO peak. The results can be explained based on the influence of the high electron concentration with a strong contribution of the surface accumulation layer and the associated internal electric field.
  Nanotechnology 08/2010; 21(31):315702. · 3.98 Impact Factor
• Article: Highly polarized Raman scattering anisotropy in single GaN nanowires

  E. O. Schäfer-Nolte, T. Stoica, T. Gotschke, F. Limbach, E. Sutter, P. Sutter, R. Calarco
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  ABSTRACT: Single GaN nanowires and larger GaN ensembles are investigated by Raman spectroscopy. Spectra of nanowire ensembles prove the high crystal quality and are in agreement with selection rules for the wurtzite structure. Single nanowires are studied with a spatial resolution of the order of 400 nm for different polarization directions of the incident laser beam relative to the nanowire axis. In the single wire spectrum, only the A1(TO) was observed and the Raman intensity was suppressed for perpendicular polarization. These results confirm that Raman scattering in isolated GaN nanowires is governed by size effects.
  Applied Physics Letters 03/2010; 96(9):091907-091907-3. · 3.84 Impact Factor
• Article: Graphene growth on polycrystalline Ru thin films

  E. Sutter, P. Albrecht, P. Sutter
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  ABSTRACT: Monolayer graphene has been grown on polycrystalline Ru thin films on SiO ₂/ Si substrates. The Ru films have columnar structure with strongly aligned grains exposing flat (0001) surface facets. Adjacent grains show small relative tilts of their [0001] axes and variations in in-plane orientation. Graphene layers grown on this template cover the entire surface and have uniform monolayer thickness. Analysis of the graphene/Ru moiré structure shows that monocrystalline graphene domains are coherent across a large number of substrate grains. Hence, the size of monolayer graphene domains is not limited by grain boundaries in the metal template.
  Applied Physics Letters 10/2009; · 3.84 Impact Factor
• Article: Temperature dependent low energy electron microscopy study of Ge island growth on bare and Ga terminated Si(112).

  M Speckmann, Th Schmidt, J I Flege, J T Sadowski, P Sutter, J Falta
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  ABSTRACT: The pre-adsorption of Ga on Si(112) leads to a drastic change of the morphology of subsequently grown Ge islands. In contrast to the case for Ge growth on bare Si(112), even nanowire growth can be achieved on Ga terminated Si(112). Employing low energy electron microscopy and low energy electron diffraction, the initial phase of Ge nucleation and Ge island growth was systematically analysed for growth temperatures between 420 and 610 °C, both on clean and on Ga terminated Si(112). In both cases the island density exhibits an Arrhenius-like behaviour, from which diffusion barrier heights of about 1.3 and 1.0 eV can be estimated for growth with and without Ga pre-adsorption, respectively. The Ge island shape on the bare Si(112) surface is found to be nearly circular over the whole temperature range, whereas the shapes of the Ge islands on the Ga terminated Si(112) become highly anisotropic for higher temperatures. Ge nanowires with sizes of up to 2 µm along the [Formula: see text] direction are observed.
  Journal of Physics Condensed Matter 08/2009; 21(31):314020. · 2.55 Impact Factor
• Source

  Available from: Jan Ingo Flege

  Article: Nanoscale analysis of Ru(0001) oxidation using low-energy and photoemission electron microscopy.

  J I Flege, P Sutter
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  ABSTRACT: CO oxidation over oxygen-rich Ru(0001) surfaces is one of the most studied catalytic oxidation reactions in surface science and of widespread interest as a model system for the redox chemistry of transition metal model catalysts. Here, we present an extensive low-energy electron microscopy (LEEM) and photoemission electron microscopy study of the oxidation of Ru(0001), which constitutes a crucial step in understanding the overall surface reaction. After characterizing the different surface nanoscale morphologies observed depending on the oxidation temperature, three distinct oxygen-rich phases are identified by dark-field microscopy and local valence-band spectroscopy. Furthermore, in situ LEEM allows us to follow the growth of single rutile oxide nuclei in real time and determine the relevant activation barriers that induce quasi-one-dimensional growth of oxide nanorods, whose growth rate is limited by O incorporation.
  Journal of Physics Condensed Matter 08/2009; 21(31):314018. · 2.55 Impact Factor
• Source

  Available from: purdue.edu

  Article: Electronic structure of few-layer epitaxial graphene on Ru(0001).

  P Sutter, M S Hybertsen, J T Sadowski, E Sutter
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  ABSTRACT: The electronic structure of epitaxial monolayer, bilayer, and trilayer graphene on Ru(0001) was determined by selected-area angle-resolved photoelectron spectroscopy (micro-ARPES). Micro-ARPES band maps provide evidence for a strong electronic coupling between monolayer graphene and the adjacent metal, which causes the complete disruption of the graphene pi-bands near the Fermi energy. However, the perturbation by the metal decreases rapidly with the addition of further graphene sheets, and already an epitaxial graphene bilayer on Ru recovers the characteristic Dirac cones of isolated monolayer graphene. A graphene trilayer on Ru behaves like free-standing bilayer graphene. Density-functional theory based calculations show that this decoupling is due to the efficient passivation of metal d-states by the interfacial graphene layer.
  Nano Letters 07/2009; 9(7):2654-60. · 13.20 Impact Factor
• Article: From nanoislands to nanowires: Growth of germanium on gallium‐terminated silicon surfaces

  Th. Schmidt, J. I. Flege, M. Speckmann, T. Clausen, S. Gangopadhyay, A. Locatelli, T. O. Mentes, S. Heun, F. Z. Guo, P. Sutter, J. Falta
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  ABSTRACT: The influence of Ga pre-adsorption on Si(111), Si(113) and Si(112) surfaces on Ge growth has been investigated by low-energy electron diffraction and microscopy as well as X-ray photoemission spectroscopy. On Si(111), step edges and substrate domain boundaries are decorated with Ga at high deposition temperatures, enabling selective growth and alignment of three-dimensional Ge islands on a chemically modulated surface. On Si(113), a morphological modulation is achieved by Ga saturation, as the Si substrate decomposes into an ordered array of (112) and (115) facets. This results in the growth of Ge islands aligned at the facets. These islands exhibit an anisotropy, as they are elongated along []. Ga pre-adsorption on Si(112) smoothens the initially faceted bare surface, and subsequent Ge growth leads to the formation of nanoscale Ge wires. The results are discussed in terms of surface chemistry, as well as diffusion and strain relaxation anisotropy.
  Physica Status Solidi (A) Applications and Materials 06/2009; 206(8):1718 - 1722. · 1.46 Impact Factor
• Article: Scanning tunneling microscopy on epitaxial bilayer graphene on ruthenium (0001)

  E. Sutter, D. P. Acharya, J. T. Sadowski, P. Sutter
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  ABSTRACT: The atomic structure of epitaxial single and bilayer graphene on Ru(0001) was studied by scanning tunneling microscopy (STM). High-resolution imaging of the surface of single layer graphene shows a moiré with pronounced buckling and broken A/B carbon sublayer symmetry due to a strong interaction with the metal substrate. The top sheet of bilayer graphene is largely unperturbed by residual interactions with the substrate. Screened from the metal substrate, it shows the hallmarks of freestanding monolayer graphene: a honeycomb structure with equivalent carbon sublattices imaged in STM and a linear dispersion of π-bands near the Dirac point.
  Applied Physics Letters 03/2009; 94(13):133101-133101-3. · 3.84 Impact Factor
• Source

  Available from: Jan Ingo Flege

  Article: In situ structural imaging of CO oxidation catalysis on oxidized Rh(111)

  J I Flege, P Sutter
  Physical Review B 10/2008; 78:153402. · 3.69 Impact Factor
• Source

  Available from: Jan Ingo Flege

  Article: Structural imaging of surface oxidation and oxidation catalysis on Ru(0001)

  J I Flege, J Hrbek, P Sutter
  Physical Review B 10/2008; 78:165407. · 3.69 Impact Factor
• Source

  Available from: Jan Ingo Flege

  Article: Steering liquid Pt-Si nanodroplets on Si(100) by interactions with surface steps.

  P Sutter, P A Bennett, J I Flege, E Sutter
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  ABSTRACT: Liquid eutectic Pt-Si droplets, migrating across a Si(100) surface due to an applied temperature gradient, interact measurably with surface steps. An analysis of the interaction yields a critical size of hundreds of nanometers below which droplets are constrained to move parallel to monolayer steps. Bunches of closely spaced steps are capable of guiding larger, micron-sized droplets. This steering by steps or step bunches may be used for the controlled manipulation of liquid droplets on patterned surfaces, and affects fundamental surface processes such as coarsening.
  Physical Review Letters 10/2007; 99(12):125504. · 7.37 Impact Factor
• Source

  Available from: geochem.mines.edu

  Article: Short-range order of low-coverage Ti/Al(111): Implications for hydrogen storage in complex metal hydrides

  E Muller, E Sutter, P Zahl, C V Ciobanu, P Sutter
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  ABSTRACT: Using scanning tunneling microscopy and density functional theory, we characterize the population of low-coverage Ti atoms on Al(111) as a model surface system for transition metal doped alanate hydrogen storage compounds, such as NaAlH4. When deposited at room temperature, Ti is kinetically trapped in first-layer substitutional sites, avoids nearest-neighbor locations, and preferentially forms next-nearest-neighbor pairs, similar to a structure that has been predicted to dissociate H-2 with no energy barrier. The results on this well-defined system suggest the presence of a large population of Ti-pair complexes that may catalyze the dissociative chemisorption of hydrogen in Ti-doped alanate storage materials. (c) 2007 American Institute of Physics.
  Applied Physics Letters 01/2007; 90(15). · 3.84 Impact Factor
• Source

  Available from: bnl.gov

  Article: Au‐Induced Encapsulation of Ge Nanowires in Protective C Shells

  E. Sutter, P. Sutter
  Advanced Materials 09/2006; 18(19):2583 - 2588. · 13.88 Impact Factor
• Article: Assembly of Ge nanocrystals on SiO2 via a stress-induced dewetting process

  E Sutter, P Sutter
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  ABSTRACT: We use epitaxial Ge islands on silicon-on-insulator (001) to initiate and drive the dewetting of the ultrathin (<8 nm) Si template layer. The process exposes the underlying SiO2 layer and transforms the Ge islands into oxide-supported, electrically isolated, Ge-rich nanocrystals. We investigate the process of dewetting and demonstrate that it can be used for the controlled assembly of nanocrystals—from isolated single ones to dense arrays.
  Nanotechnology 06/2006; 17(15):3724. · 3.98 Impact Factor
• Article: Scanning tunneling microscopy on ultrathin silicon on insulator (100)

  P. Sutter, W. Ernst, E. Sutter
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  ABSTRACT: (100)-oriented ultrathin silicon-on-insulator (SOI) with Si template thickness at or below 10 nm, normally fully depleted due to carrier trapping in surface states, can be made conducting by terminating the surface with monolayer amounts of Ge. With this modification, which preserves the morphology of the surface, imaging with atomic resolution by scanning tunneling microscopy (STM) becomes possible. STM imaging is used to demonstrate surface smoothing by a thin (few monolayers) Si buffer at high temperature. Tunneling spectroscopy shows a high sheet resistance of the SOI sample, caused by a partial dewetting of the oxide supported Si template during thermal surface cleaning. High-resolution imaging and spectroscopy by STM will enable studies, at the atomic scale, of technologically relevant processes on ultrathin SOI.
  Applied Physics Letters 10/2004; 85(15):3148-3150. · 3.84 Impact Factor
• Article: Extended shape evolution of low mismatch Si1−xGex alloy islands on Si(100)

  E. Sutter, P. Sutter, J. E. Bernard
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  ABSTRACT: The sequence of shape transitions in low mismatch, dilute coherent Si1−xGex (x<0.2) alloy islands was documented by scanning tunneling microscopy and cross-sectional transmission electron microscopy. In dilute Si1−xGex islands we observe an extended shape evolution involving a new “barn” shape formed by introduction of steep {111} facets not observed at higher mismatch strain. This extended shape evolution implies a delayed onset of plastic deformation as a result of an altered competition between strain relaxation via coherent islands and the introduction of dislocations in this regime. © 2004 American Institute of Physics.
  Applied Physics Letters 03/2004; 84(13):2262-2264. · 3.84 Impact Factor
• Article: High-resolution mapping of nonuniform carrier transport at contacts to polycrystalline CdTe/CdS solar cells

  P. Sutter, E. Sutter, T. R. Ohno
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  ABSTRACT: We demonstrate a spectroscopic technique based on scanning tunneling microscopy that provides high-resolution maps of local carrier transport across contacts to polycrystalline thin-film solar cells. Using this technique, preferential transport channels across a p+-ZnTe/p-CdTe back contact of a p-CdTe/n-CdS solar cell are imaged with 20 nm spatial resolution. Transport across this contact is highly nonuniform. Large areas of high resistance coexist with nanoscale low-resistance regions that are strongly correlated with grain boundaries in the CdTe absorber. These results suggest an important role of grain boundaries as near-contact conducting channels. © 2004 American Institute of Physics.
  Applied Physics Letters 03/2004; 84(12):2100-2102. · 3.84 Impact Factor
• Article: Initial surface roughening in Ge/Si(001) heteroepitaxy driven by step-vacancy line interaction.

  P Sutter, I Schick, W Ernst, E Sutter
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  ABSTRACT: The initial surface roughening during Ge epitaxy on Si(001) is shown to arise from an effective repulsion between S(A) surface steps and dimer vacancy lines (VLs). This step-VL interaction gradually inactivates a substantial fraction of adatom attachment sites at the growth front, causing a rapid increase in the rate of two-dimensional island nucleation. The mutual repulsion hinders the crossing of S(A) surface steps over VLs in the second layer, thus organizing the developing surface roughness into a periodic array of anisotropic 2D terraces. Isolated (105) facets forming at specific sites on this ordered template mediate the assembly of first 3D Ge islands.
  Physical Review Letters 11/2003; 91(17):176102. · 7.37 Impact Factor