Petra Reinke
University of Virginia, Materials Science and Engineering, Faculty Member
- Nanoelectronics, Surface Science, Silicon Photonics, PHOTOELECTRON SPECTROSCOPY, Scanning tunneling microscopy, Manganese, and 11 moreFullerenes, Materials Science and Engineering, QD magnetic doping, Physics, Engineering, Materials Science, Graphene, Spintronics, Geopolymer Concrete, Nanoscience, and Nanotechnologyedit
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The study of thin film magnetic materials and the doping of semiconductors with magnetically active dopant atoms has received increased attention due their potential applications in magnetic memory devices and spintronics. We observe the... more
The study of thin film magnetic materials and the doping of semiconductors with magnetically active dopant atoms has received increased attention due their potential applications in magnetic memory devices and spintronics. We observe the deposition of Mn on the Si(100) 2x1 reconstructed surface in the sub-monolayer regime with STM. Short Mn wires with a length of 5 to about 20 atoms are formed an oriented perpendicular to the Si-dimer rows. At higher coverage some Mn wires are anchored with one end of the wire at the edge and extend onto the lower lying surface. The region in between the wires is particularly interesting: if the Mn wire distance is reduced the dimers change their orientation and are tilted, or begin to form zig-zag lines. The wire length and dimer deformation is likely governed by local strain. We will discuss the wire statistics (lengths, orientation, and position), control of their growth and present first data on the electronic structure of the wires. The growth ...
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Ni-Cr and Ni-Cr-Mo alloys owe their outstanding corrosion resistance to the surface enrichment of passivating Cr(III) oxides and synergistic effect of Cr and Mo in case of Mo-containing alloys [1-3]. However, the specific roles of minor... more
Ni-Cr and Ni-Cr-Mo alloys owe their outstanding corrosion resistance to the surface enrichment of passivating Cr(III) oxides and synergistic effect of Cr and Mo in case of Mo-containing alloys [1-3]. However, the specific roles of minor elements are not well understood especially with respect to precise location of Mo relative to the oxide/metal interface, nor the atomistic processes responsible for protective-oxide layer growth and breakdown. The composition, structure and thickness of the passivating oxide films are challenging to characterize considering their nanoscale dimensions and the high electric field imposed during growth in solution. Key processes that take place within the oxide and regulate passivation are controlled by defect interactions that are atomic, ionic, and electronic in nature and currently poorly understood, often needed to be studied at the resolution and detection limits of experimental methods [4]. Common electrochemical methods such as AC and DC electro...
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The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of... more
The annealing of sub-critical Ge wetting layers (WL < 3.5 ML) initiates the formation of 3D nanostructures, whose shape and orientation is determined by the WL thickness and thus directly related to the strain energy. The emergence of these nanostructures, hillocks and pre-quantum dots, is studied by scanning tunneling microscopy. A wetting layer deposited at 350 °C is initially rough on the nanometer length-scale and undergoes a progressive transformation and smoothening during annealing at T < 460 °C when vacancy lines and the 2xn reconstruction are observed. The metastable Ge WL then collapses to form 3D nanostructures whose morphology is controlled by the WL thickness: first, the hillocks, with a wedding cake-type structure where the step edges run parallel to the ⟨110⟩ direction, are formed from thin wetting layers, while {105}-faceted structures, called pre-quantum dots (p-QDs), are formed from thicker layers. The wetting layer thickness and thus the misfit strain energy...
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The effects of substrate treatment, growth temperature, and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy and atomic force microscopy. We demonstrate that a... more
The effects of substrate treatment, growth temperature, and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy and atomic force microscopy. We demonstrate that a combination of acid-etched substrates and high temperature deposition (400 °C) will result in smooth films with well-defined terraces (up to 30 nm wide) that are suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on the phosphoric acid-treated substrates present reduced nucleation density during the initial stages of film growth which results in long and wide terraces. Due to the ≈16% lattice mismatch in the Ni(001)/MgO(001) system, film growth at 400 °C yields discontinuous films and a two-step growth process is necessary to obtain a continuous layer. Ni...
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Metal clusters with less than 50 atoms, are of great interest in the development of true nanoscale electronics. The electronic structure is strongly size dependent and future applications rely on a narrow size distribution. Our goal was... more
Metal clusters with less than 50 atoms, are of great interest in the development of true nanoscale electronics. The electronic structure is strongly size dependent and future applications rely on a narrow size distribution. Our goal was to investigate the possibility to use fullerene surfaces as templates in the formation of cluster arrays, to analyze the cluster-fullerene interface and the electronic structure of the components. This study was performed by using photoelectron spectroscopy, and scanning tunneling microscopy and spectroscopy (UHV-conditions). The Au-cluster size is controlled by the coverage and the fullerene lattice limits the cluster surface mobility, making them accessible to STM analysis. The fullerene matrix enhances the cluster stability and ripening occurs above 500 K. A comprehensive description of the Au-cluster-fullerene system has been achieved and includes the interface characteristics, local and global electronic structure, and the spatial distribution o...
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The combination of Silicon with an element with a large magnetic moment such as Manganese is highly desirable for the development of novel spintronics devices. We present a study on the surface-driven synthesis of Mn-nanostructures on the... more
The combination of Silicon with an element with a large magnetic moment such as Manganese is highly desirable for the development of novel spintronics devices. We present a study on the surface-driven synthesis of Mn-nanostructures on the Si(100) (2x1) surface using STM and photoelectron spectroscopy. The Si-surface functions as a template and monoatomic Mn-nanowires are formed, which always run perpendicular
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The combination of Si and Ge with Mn is a critical step in the development of novel spintronics devices. We investigate the magnetic doping of Si, Si-surfaces and Ge- quantum dots with Mn. A surface-driven route is used for the addition... more
The combination of Si and Ge with Mn is a critical step in the development of novel spintronics devices. We investigate the magnetic doping of Si, Si-surfaces and Ge- quantum dots with Mn. A surface-driven route is used for the addition of Mn and allows a stringent control of the Mn-Si and Mn-Ge interaction. The evolution of nanostructures is observed
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Research Interests: Materials Science, Self Assembly, Transmission Electron Microscopy, Atomic Force Microscopy, Molecular beam epitaxy, and 9 moreNational Science Foundation, Scanning tunneling microscopy, Thin Film, Superparamagnetism, Quantum Dot, Ferromagnetic Materials, Ferromagnetism, X Ray Photoelectron Spectroscopy, and Dilute magnetic semiconductor
Fullerene thin films are deposited on defect-rich Highly Oriented Pyrolitic Graphite (HOPG) and investigated by scanning tunneling microscopy (STM). These films exhibit a wealth of novel structural and electronic features which are not... more
Fullerene thin films are deposited on defect-rich Highly Oriented Pyrolitic Graphite (HOPG) and investigated by scanning tunneling microscopy (STM). These films exhibit a wealth of novel structural and electronic features which are not present in fullerene layers deposited on pristine graphite surfaces. Molecule nanostructures comprised of single molecules with a greatly enhanced apparent size, trimer structures, and hexamer structures are observed. The geometry of these molecular structures is linked to the stacking of the C60 layer, and ...
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Abstract: The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). Mn is deposited... more
Abstract: The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). Mn is deposited on the Ge QD and WL surface in sub-monolayer concentrations, and subsequently annealed up to temperature of 400 C. Bonding and surface topography were measured with STM during the annealing process. Mn forms flat islands on the Ge {105} facet, whose shape and position is guided by the ...
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Understanding of magnetic doping of Group-IV semiconductors is critical for the realization of spintronics devices. We present STM investigations of room temperature, sequential and co-deposition of Mn and Co on Si (100)-2x1. Monoatomic... more
Understanding of magnetic doping of Group-IV semiconductors is critical for the realization of spintronics devices. We present STM investigations of room temperature, sequential and co-deposition of Mn and Co on Si (100)-2x1. Monoatomic Mn-nanowires, which self-assemble on the Si surface, lose their continuity after deposition of 0.04-0.08 ML of Co. This loss in continuity is expressed in the wire length distributions, which are dominated by Mn dimers and ultrashort wires. Protrusions with a height of 0.5-0.8 {\ AA} above the surface of ...
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The magnetic doping of Ge-quantum dots (QD) and Ge thin film materials has garnered considerable interest due their anticipated use in nanoscale spintronics device structures. In this study we probe with scanning tunneling microscopy the... more
The magnetic doping of Ge-quantum dots (QD) and Ge thin film materials has garnered considerable interest due their anticipated use in nanoscale spintronics device structures. In this study we probe with scanning tunneling microscopy the interaction of Mn with the growth surfaces in strain-driven synthesis of Ge-QDs on Si(100)-(2x1). The growth surfaces are the Ge-QD\textbraceleft 105\textbraceright facet and the Ge(100) surface of the wetting layer (WL). Mn interactions with the QD\textbraceleft 105\textbraceright facet is particularly interesting, and shows the ...
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Ni-based superalloys offer a unique combination of mechanical properties, corrosion resistance and high temperature performance. Near ambient pressure X-ray photoelectron spectroscopy was used to study in operando the initial steps of... more
Ni-based superalloys offer a unique combination of mechanical properties, corrosion resistance and high temperature performance. Near ambient pressure X-ray photoelectron spectroscopy was used to study in operando the initial steps of oxidation for Ni-5Cr, Ni-15Cr, Ni-30Cr and Ni-15Cr-6W at 500 °C, p(O2)=10−6 mbar. The comparison of oxide evolution for these alloys quantifies the outsized impact of W in promoting chromia formation. For the binary alloys an increase in chromia due to Cr-surface enrichment is followed by NiO nucleation and growth thus seeding a dual-layer structure. The addition of W (Ni-15Cr-6W) shifts the reaction pathways towards chromia thus enhancing oxide quality. Density functional theory calculations confirm that W atoms adjacent to Cr create highly favorable oxygen adsorption sites. The addition of W supercharges the reactivity of Cr with oxygen essentially funneling oxygen atoms into Cr sites. The experimental results are discussed in the context of surface ...
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The molecular-level processes responsible for fractal-dendritic growth of second-layer C60 islands on large and compact first-layer C60 islands deposited on graphite substrate are investigated by a combination of scanning tunneling... more
The molecular-level processes responsible for fractal-dendritic growth of second-layer C60 islands on large and compact first-layer C60 islands deposited on graphite substrate are investigated by a combination of scanning tunneling microscopy (STM) and kinetic Monte Carlo (kMC) simulations. Molecular dynamics (MD) simulations are performed to determine the activation barriers and jump rates for diffusion of C60 molecules on a C60 layer.
The initial growth stage of thin film on graphite substrate has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The layer grows in a quasi-layer-by-layer mode and forms round, monolayer high... more
The initial growth stage of thin film on graphite substrate has been investigated by scanning tunneling microscopy in ultrahigh vacuum at room temperature. The layer grows in a quasi-layer-by-layer mode and forms round, monolayer high islands on the graphite surface. The islands are confined by terraces on the graphite surface and the mobility of fullerenes across steps is low in all layers.
We investigated the doping of thin films of tetrahedral amorphous carbon (ta-C) and cubic boron nitride (c-BN) with europium. The films were grown by mass selected ion beam deposition and doped with europium during growth. Analysis was... more
We investigated the doping of thin films of tetrahedral amorphous carbon (ta-C) and cubic boron nitride (c-BN) with europium. The films were grown by mass selected ion beam deposition and doped with europium during growth. Analysis was performed in vacuo using photoelectron spectroscopy and ex vacuo with conversion electron Mössbauer, Fourier transform infrared and cathodoluminescence spectroscopy. Successful incorporation of europium into the c-BN films is achieved.
Fullerenes are covalently bonded spherical carbon clusters which assemble to extended van der Waals bonded solids and are recognized as the third carbon allotrope, in addition to diamond and graphite. 1 The pristine material possesses... more
Fullerenes are covalently bonded spherical carbon clusters which assemble to extended van der Waals bonded solids and are recognized as the third carbon allotrope, in addition to diamond and graphite. 1 The pristine material possesses interesting properties but the addition of foreign elements as dopants can lead to a considerable expansion in the variability of properties.
Abstract Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO 2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface... more
Abstract Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO 2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO 2 thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition.
Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris (triphenylphosphine) iridium (I), on hydrogen passivated Si (111) surfaces to form a self-assembled monolayer (SAM). The iridium complex was... more
Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris (triphenylphosphine) iridium (I), on hydrogen passivated Si (111) surfaces to form a self-assembled monolayer (SAM). The iridium complex was synthesized prior to chemical addition, for which modified reaction conditions were chosen. Following addition, the silicon surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV).
A 'standard', single null lower diverted discharge has been developed to enable continuous monitoring of the first wall conditions and to characterise the effectiveness and influence of wall conditioning in the TCV tokamak.
C60 adsorbed on graphite represents an interesting case of physical adsorption, where the primary attractive interactions are van der Waals. Although physisorption is generally thought of as a very weak form of adsorption with adsorption... more
C60 adsorbed on graphite represents an interesting case of physical adsorption, where the primary attractive interactions are van der Waals. Although physisorption is generally thought of as a very weak form of adsorption with adsorption energies 0.5 eV, many studies have now been carried out on larger organic molecules which, although their bond to the surface is primarily due to dispersion interactions, have larger adsorption energies that can exceed 1 eV on graphite, 1, 2 an energy scale often associated with chemisorption.
The formation of the carbide interface between polycrystalline molybdenum and hydrogen-free carbon films is investigated at different substrate temperatures (ambient, 400 and 600° C) with photoelectron spectroscopy in the ultraviolet... more
The formation of the carbide interface between polycrystalline molybdenum and hydrogen-free carbon films is investigated at different substrate temperatures (ambient, 400 and 600° C) with photoelectron spectroscopy in the ultraviolet (UPS) and X-ray regime (XPS). A carbon beam is created by electron beam evaporation of graphite and the stepwise in-situ deposition of carbon allows to follow the evolution of the interface.
The interaction of water and oxygen with a polycrystalline diamond film was investigated using XANES (X-ray absorption near edge structure) spectroscopy. A novel reactor design allowed to access pressure ranges up to 4.0 mbar and... more
The interaction of water and oxygen with a polycrystalline diamond film was investigated using XANES (X-ray absorption near edge structure) spectroscopy. A novel reactor design allowed to access pressure ranges up to 4.0 mbar and simultaneous recording of the gas phase and sample spectra at the C K-and O K-edges, respectively. The diamond surface is inert with respect to the interaction with water in the investigated temperature below 500° C.
The combination of spin-and charge based electronics in future devices requires the magnetic doping of group IV semiconductors, and the formation of ferromagnetic contacts. The doping of Mn with Si is one of the material systems which is... more
The combination of spin-and charge based electronics in future devices requires the magnetic doping of group IV semiconductors, and the formation of ferromagnetic contacts. The doping of Mn with Si is one of the material systems which is discussed in this context. The present study focuses on the growth of Mn on a Si (100)(2x1) surface, and the evolution of the surface was observed as a function of Mn coverage with synchrotron-based photoelectron spectroscopy.
The co-deposition of silicon and C60 leads to the formation of a composite material, where the concentration of the components can be controlled via the respective particle fluxes. Information on the composition and electronic properties... more
The co-deposition of silicon and C60 leads to the formation of a composite material, where the concentration of the components can be controlled via the respective particle fluxes. Information on the composition and electronic properties of the thin layers is obtained by photoelectron spectroscopy in the ultraviolet (UPS) and X-ray regime (XPS), while transmission electron microscopy (TEM) was employed for selected samples.
The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental... more
The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition.
Abstract Heteroepitaxial Ge 0.98 Mn 0.02 quantum dots (QDs) on Si (001) were grown by molecular beam epitaxy. The standard Ge wetting layer-hut-dome-superdome sequence was observed, with no indicators of second phase formation in the... more
Abstract Heteroepitaxial Ge 0.98 Mn 0.02 quantum dots (QDs) on Si (001) were grown by molecular beam epitaxy. The standard Ge wetting layer-hut-dome-superdome sequence was observed, with no indicators of second phase formation in the surface morphology. We show that Mn forms a dilute solid solution in the Ge quantum dot layer, and a significant fraction of the Mn partitions into a sparse array of buried, Mn-enriched silicide precipitates directly underneath a fraction of the Ge superdomes.
Abstract: The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). Mn is deposited... more
Abstract: The interaction of Mn with Ge quantum dots (QD), which are bounded by {105} facets, and the strained Ge wetting layer (WL), terminated by a (001) surface, is investigated with scanning tunneling microscopy (STM). Mn is deposited on the Ge QD and WL surface in sub-monolayer concentrations, and subsequently annealed up to temperature of 400 C. Bonding and surface topography were measured with STM during the annealing process.