
Jerrold FloroUniversity of Virginia | UVa · Department of Materials Science and Engineering
Jerrold Floro
PdD Materials Science and Engineering
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169
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May 2016 - present
August 2006 - May 2016
August 2006 - present
Publications
Publications (169)
This report is the first analysis of the coexistence and microstructure of the equilibrium phases in the Fe-Pd L1 0 + L1 2 eutectoid region. Coexistence of L1 0 + L1 2 is observed at higher temperatures (650 $$^\circ {\text{C}}$$ ∘ C ), resulting in L1 0 polytwin plates with internal boundaries that are decorated by L1 2 . For higher Pd content, th...
Challenges in developing novel alloys, specifically for use in laser powder bed fusion, may be overcome by in situ alloying of elemental powders during laser melting. This process could expedite prototyping of various alloy compositions and alleviate the restrictions and cost barriers of creating custom made alloy powder. In this research, the effi...
Scanning laser melting was employed to investigate directional solidification in Al-Cu thin films, 200 and 500 nm thick. The Al-Cu alloy films, with both eutectic and hypoeutectic compositions, were co-deposited on fused silica substrates by magnetron sputtering. Melting of the films was carried out in air using a CW laser, as a function of the sca...
Defects in epitaxial Ru(0001) films on c-plane sapphire, with nominal thicknesses of 10–80 nm, deposited at 350 °C and step-annealed to 950 °C, were characterized using transmission electron microscopy. The variation of Ru and sapphire lattice parameters with temperature is such that the misfit strain for the observed 30° rotated-honeycomb epitaxia...
Gas-atomized powders are commonly used in additive manufacturing, specifically laser powder bed fusion, due to their high flowability during recoating. Morphological changes can occur in particles that are irradiated by the laser during additive manufacturing, but are not incorporated into the melt pool. These irradiated particles will affect the r...
A β‐FeSi2–SiGe nanocomposite is synthesized via a react/transform spark plasma sintering technique, in which eutectoid phase transformation, Ge alloying, selective doping, and sintering are completed in a single process, resulting in a greatly reduced process time and thermal budget. Hierarchical structuring of the SiGe secondary phase to achieve c...
Richard “Rick” Vinci: A remembrance - Volume 44 Issue 7 - Jerrold A. Floro
We report the first detailed investigation into how exchange-coupled magnetic properties evolve during the formation of the Co-Pt L10 + L12 nanochessboards, which self-assemble by a pseudo-spinodal mechanism below the eutectoid isotherm. The maximum observed coercivities exceed 3 kOe, but these values are more than 5 times lower than the largest va...
In this paper, we report Lorentz Transmission Electron Microscopy (LTEM) observations of magnetic domain structures in a near-eutectoid Co40Pt60 alloy. The crystallographic microstructure is characterized using conventional bright field/dark field TEM imaging. The magnetic induction orientation inside magnetic domains is extracted from Fresnel thro...
Hybrid organic-inorganic materials are among the latest class of materials proposed for thermoelectric applications. The organic-inorganic interface is critical in determining the effective transport properties of the hybrid material. We study the thermoelectric properties of the tetrafluoro-tetracyanoquinodimethane (F 4 TCNQ)-silicon interface. Tr...
Spectral linewidths are used to assess a variety of physical properties, even as spectral overlap makes quantitative extraction difficult owing to uncertainty. Uncertainty, in turn, can be minimized with the choice of appropriate experimental conditions used in spectral collection. In response, we assess the experimental factors dictating uncertain...
Ordered arrays of semiconductor quantum dots may provide new electronic, optical, or thermoelectric functionalities. In this work, we create ordered two-dimensional arrays of Si-Ge quantum dots by heteroepitaxial growth on Si (001) with pre-patterned pits. Instead of growing the dots directly at elevated temperatures, we first grow conformal alloy...
The magnetization configuration of a novel nano-chessboard structure consisting of L1 0 and L1 2 phases in a Co 40 Pt 60 alloy is investigated using Lorentz transmission electron microscopy (LTEM) and micro-magnetic simulations. We show high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lo...
We use aluminum nano-inclusions in silicon to demonstrate the dominance of elastic modulus mismatch induced scattering in phonon transport. We use time domain thermoreflectance to measure the thermal conductivity of thin films of silicon co-deposited with aluminum via molecular beam epitaxy resulting in a Si film with 10% clustered Al inclusions wi...
To complement recent experimental findings [Vetter et al., APL Mater. 4, 096103 (2016)] on strong exchange coupling effects in Co-Pt nanochessboards featuring a single peak in the first-order reversal curve density plot and associated magnetic hardening as the characteristic structural dimension is reduced below the critical correlation length, the...
We developed a novel React/Transform Spark Plasma Sintering approach for nanocomposite synthesis, providing accelerated phase transformation and selective alloying. We synthesized compositionally tunable SiGe alloy particles, embedded within a β-FeSi2 matrix, both with nanoscale grain size. This is achieved simply by adding a few atomic percent of...
The beta-FeSi2/Si semiconducting nanocomposite is a promising thermoelectric system with eco-friendly materials. We show that small quantities of Ge can enhance the thermoelectric properties and widen
the design space, if Ge content and spatial disposition can be controlled. We investigated the use of solidification combined with solid-state transf...
Aberration Corrected Lorentz Microscopy to Investigate Magnetic Domain Walls in Co-Pt Nano-Chessboards - Volume 23 Issue S1 - Isha Kashyap, Jerrold A. Floro, Yongmei M. Jin, Marc De Graef
Semiconducting β-FeSi2 is a candidate thermoelectric material whose constituents are abundant and eco-friendly, but significant improvements in the relevant properties are needed. This work investigates eutectoid decomposition, α-FeSi2 → β-FeSi2 + Si, as a means to modify microstructure and control thermal transport. Process conditions are adjusted...
We investigate the heteroepitaxial Si0.5 Ge 0.5 quantum dot site-selection on a patterned Si(001) substrate by continuously varying the underlying substrate pattern morphology from pit-in-terrace to quasi-sinusoidal. The pit-in-terrace morphology leads to well-ordered quantum dots centered in the pits over a wide range of pattern wavelengths. Howev...
The Co-Pt nanochessboard is a quasi-periodic, nanocomposite tiling of L10 and L12 magnetic phases that offers a novel structure for the investigation of exchange coupling, relevant to permanent magnet applications. Periodicity of the tiling is controlled by the rate of cooling through the eutectoid isotherm, resulting in control over the L10-L12 ex...
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...
Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si1-xGex thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surfa...
The existence of an L10–L12 hybrid ordered phase for face-centered cubic (fcc) crystal symmetry was first theorized by William Shockley in 1938, but has not been verifiably observed to date. Ordered magnetic thin films of Fe38.5Pd61.5, the expected L10–L12 eutectoid composition, grown epitaxially on MgO(0 0 1) substrates by pulsed laser deposition,...
Periodic, highly uniform arrays of dome-like Ge quantum dots (QDs) with 50 nm interdot pitch have been achieved on Si (001). The Si surface was patterned using ultra-low-dose focused ion beam and defect-selective etching, resulting in a continuously height-modulated, “egg-carton” morphology. The directed self-assembly process is robust, occurring a...
Epitaxial growth of SiGe alloy films under certain kinetically limiting conditions has previously been shown to lead to the self-assembly of nanostructures called Quantum Dot Molecules, QDMs. These QDMs consist of an assembly of pyramidal pits and elongated pyramidal islands, which exist at the edges of the pits. We investigate the nano-scale chemi...
This work examines Si overgrowth to encapsulate 3C-SiC quantum dot arrays epitaxially grown on Si substrates. Using transmission electron microscopy, we show how the crystalline quality of the Si cap depends on the growth conditions. Overgrowth at 300 °C leads to a planar, epitaxial Si cap, but with small crystallographic rotations in the cap above...
Heteroepitaxial Ge quantum dots were grown on Si (001) by molecular beam epitaxy, with a Mn co-deposition flux giving a nominal composition of Ge0.9Mn0.1. At this large Mn flux, and with growth temperatures of 450 °C required for Ge quantum dot self-assembly, extensive second phase formation occurred. Atomic force microscopy reveals that quantum do...
Heteroepitaxy of SiGe alloys on Si (001) under certain growth conditions has previously been shown to cause self-assembly of nanostructures called Quantum Dot Molecules, QDMs, where pyramidal pits and 3D islands cooperatively form. QDMs have potential applications to nanologic device architectures such as Quantum Cellular Automata that relies on lo...
Epitaxial films of Fe38.5Pd61.5 at the L10-L12 eutectoid composition have been grown on MgO (001) oriented substrates by pulsed laser deposition. The effect of deposition temperature on the magnetic, microstructural, and crystallographic natures of these films are discussed. The films in this study exhibit atomic ordering with increasing deposition...
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). These surfaces constitute the growth surfaces in the growth of Mn-doped QDs. Mn is deposited on the Ge QD and WL surface in sub-monolayer...
Heteroepitaxy of SiGe alloys on Si (001) under certain growth conditions has previously been shown to cause self-assembly of nanostructures called Quantum Dot Molecules, QDMs, where pyramidal pits and 3D islands cooperatively form. QDMs have potential applications to nanologic device architectures such as Quantum Cellular Automata that relies on lo...
Artificially ordered quantum dot (QD) arrays may create unique
functionalities such as cluster qubits and spintronic bandgap
systems.footnotetextC. E. Pryor, M. E. Flatte, and J. Levy,
Applied Physics Letters 95, 232103 (2009) We fabricate directed
self-assembled Ge/SiC/Si arrays with fine control over QD size and
spatial arrangement on the sub-35...
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 sur...
Heteroepitaxial Ge{sub 1-x}Mn{sub x} quantum dots (QDs) were grown on Si (001) by molecular beam epitaxial co-deposition, with x = 0 to 0.10, in order to explore the interaction between Mn content, surface morphological evolution, and magnetism. Morphological evolution typical of the Ge/Si (001) system was observed, where the effect of Mn on surfac...
Precise spatial ordering of quantum dots (QDs) may enable predictable quantum states due to direct exchange interactions of confined carriers. The realization of predictable quantum states may lead to unique functionalities such as spin cluster qubits and spintronic band gap systems. To define exemplary quantum architectures, one must develop contr...
Lateral growth of highly elongated SiGe islands in one dimension has been achieved by ex-situ substrate patterning using a focused ion beam (FIB) to create an array of surface grooves in the Si substrate. Growth of Si0.7Ge0.3 on this template results in preferential formation of strain-relieving islands next to the edges of the grooves under kineti...
Heteroepitaxial Ge0.98Mn0.02 quantum dots 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 pa...
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. Bondin...
Artificially ordered quantum dot (QD) arrays, where confined carriers can interact via direct exchange coupling, may create unique functionalities such as cluster qubits and spintronic bandgap systems. Development of such arrays for quantum computing requires fine control over QD size and spatial arrangement on the sub-35 nm length scale. We employ...
Amorphous Ge{sub 1-x}Mn{sub x} thin films have been prepared by co-depositing Ge and Mn on SiO{sub 2}/Si using an ultrahigh vacuum molecular beam epitaxy system. Across a range of growth temperatures and Mn concentrations (2.8 at. %, 10.9 at. %, and 21.3 at. %), we achieved enhanced magnetic and electrical properties with non-magnetic codopants dis...
The electronic states of strained self-assembled Ge quantum dots
embedded in silicon provide an attractive system for controlling
electron spin interactions via direct exchangeootnotetextC. E.
Pryor, M. E. Flatte, and J. Levy, Applied Physics Letter 95, 232103
(2009) . Directed self-assembly of sub-10 nm Ge islands are fabricated
to produce lateral...
Group IV dilute magnetic semiconductors (DMS) are candidates for the development of spin based devices due to their compatibility with the traditional semiconductor technology. Ge:Mn alloy thin films grown homoepitaxially on Ge (001) exhibit dilute ferromagnetic behavior, but growth temperatures must be kept below about 200°C to prevent second phas...
We examine the fundamental phonon mechanisms affecting the interfacial thermal conductance across a single layer of quantum dots (QDs) on a planar substrate. We synthesize a series of GexSi1−x QDs by heteroepitaxial self-assembly on Si surfaces and modify the growth conditions to provide QD layers with different root-mean-square (rms) roughness lev...
Artificially ordered Ge quantum dot (QD) arrays, where confined carriers can
interact via exchange coupling, may create unique functionalities such as
cluster qubits and spintronic bandgap systems. Development of such arrays for
quantum computing requires fine control over QD size and spatial arrangement on
the sub-35 nm length scale. We employ fin...
Low temperature epitaxial breakdown of inhomogeneously strained Si capping
layers is investigated. By growing Si films on coherently strained GeSi quantum
dot surfaces, we differentiate effects of surface roughness, strain, and growth
orientation on the mechanism of epitaxial breakdown. Using atomic force
microscopy and high resolution cross-sectio...
Mn ions have been reported to segregate into intermetallic precipitates or form coherent clusters in crystalline Ge(1-x)Mn(x) thin films. In this study, we investigated the microstructure of amorphous Ge(1-x)Mn(x) synthesized using low temperature molecular beam epitaxy, and observed the self-assembly of Mn rich nanostructures in Ge matrix with bot...
Directed self-assembly of sub-10 nm Ge islands is a candidate for
producing laterally coupled quantum dot molecules with
geometrically-defined spin exchange couplings. The islands are created
by the nucleation of Ge islands on nanoscale SiC templates defined by
direct-write electron-beam lithography.ootnotetextO. Guise, J.
Ahner, J. John T. Yates,...
We study the coupled effects of ion beam chemistry and morphology on the assembly of templated epitaxial nanostructures. Using a focused ion beam (FIB) system equipped with a mass-selecting filter, we pattern Si substrates with local ion doses of Si, Ge and Ga to control subsequent Ge(x)Si(1 - x) epitaxial nanostructure assembly. This capability to...
We examine variations in the basic structure of quantum dot molecules (fourfold quantum dot nanostructures forming around a central facetted pit) in the SixGe1-x/Si(100) system. Arrays of quantum dot molecules are seeded by Ga+ focused ion beam (FIB) prepatterning of the Si substrate prior to epitaxial Si buffer layer growth and GexSi1-x film depos...
Conventional heteroepitaxial thin film growth may result in a film whose epitaxial orientation is metastable. One method of probing the relative energies of various film orientations is epitaxial grain growth. Epitaxial grain growth selects the orientation having lowest total free energy, including the free energy of both the film-substrate interfa...
Contains reports on eight research projects.
Contains table of contents for Part I, table of contents for Section 1, description of Submicron Structures Laboratory research, reports on twelve research project and a list of publications.
Contains table of contents for Part I, table of contents for Section 1 and reports on fourteen research projects.
Contains reports on twelve research projects.
Contains reports on sixteen research projects.
Wurtzite ZnO nanorods were grown from solution onto coarse-grain bulk polycrystalline Ag substrates to explore the nature of preferred heteroepitaxial orientations. ZnO nanorods grow copiously on grains with <111> and <001> surface normals. Two epitaxial orientations were observed: {0001} ZnO ‖ {111} Ag with <20> ZnO ‖ <10> Ag and {0001} ZnO ‖ {001...
We explored the properties of Mn doped magnetic Group IV semiconductors with the ultimate goal of providing a new structure for logic switches that have extremely low bit switching energy. Precipitate-free amorphous Ge(1-x)Mn(x) thin films have been prepared by co-depositing Ge and Mn on SiO(2)/Si using a Molecular Beam Epitaxy (MBE) system. We var...
Directed self assembly of sub-10-nm Ge islands are candidates for
producing laterally coupled quantum dot molecules with geometrically
defined spin exchange couplings. We describe low-temperature
magnetotransport measurements on small arrays of Ge islands grown on
semi-insulating silicon substrates. The islands are created by a
technique for precis...
We employ focused ion beam patterning of single crystal Si(100) surfaces to template the assembly of Ge(Si) nanostructure arrays. The evolution and final structures of the templated arrays are determined by combinations of transmission electron, low energy electron microscope, focused ion beam and scanning probe microscopies. It is shown how the po...
We investigate the stress evolution in situ during the potentiostatic electrodeposition of metastable, nanostructured Au-Ni alloy films and develop a correlation between alloy composition, deposition rate, growth mode, and the observed stress state. We find that the internal stresses during Au-Ni deposition can be explained, at least for Ni-rich fi...
Film stress and microstructure evolution during the growth of a Ni bicrystal film are investigated by molecular dynamics simulations. The nominal surface orientation of the growing film was (111) and the grain boundaries are Σ79 symmetrical tilt grain boundaries. The growth mode is layer by layer; two-dimensional (2D) islands nucleate on the surfac...
To examine further the strain relaxation produced by inclined threading dislocations in AlGaN, a heterostructure with three AlGaN layers having successively increasing Ga contents and compressive strains was grown on an AlN template layer by metalorganic vapor-phase epitaxy. The strain state of the layers was determined by x-ray diffraction (XRD) a...
We describe methods for assembly of quantum dots (QDs) into arrays of any symmetry, and methods for nanoscale doping of individual QDs. We have previously shown how the Ga+ focused ion beam (FIB) can template Si(1 0 0) surfaces for controlled Ge QD nucleation. Local Ga-induced reduction of the wetting layer thickness also suppresses QD nucleation a...
of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
Atomic simulations of the growth of polycrystalline Ni demonstrate that deposited atoms incorporate into the film at boundaries, resulting in compressive stress generation. Incorporated atoms can also leave the boundaries and thus relieve compressive stress. This leads to a complex interplay between growth stress, adatom incorporation, and surface...
Atomistic simulations will be presented revealing fundamental stress generation mechanisms during later stages of thin film growth when substrate coverage is complete and the film is thickening. Typically, films exhibit texture with grain boundaries intersecting the surface. In situ growth stress experiments reveal compressive stress generation dur...
Ex situ focused ion-beam (FIB) patterning of arrays of holes on Si (001) substrates results in the subsequent formation of SiGe quantum dot molecules at each of the patterned sites during heteroepitaxial growth under kinetically limited growth conditions where island formation is constrained. These quantum dot molecules are fourfold self-assembled...
A variety of surface morphologies can be formed by controlling kinetic parameters during heteroepitaxial film growth. The system reported is a Si0.7Ge0.3 film grown by molecular beam epitaxy at 550 °C and a 1 Å∕s deposition rate, producing quantum dot molecule (QDM) structures. These nanostructures are very uniform in size and shape, allowing strai...
The stress evolution during electrodeposition of NiMn from a sulfamate-based bath was investigated as a function of Mn concentration and current density. The NiMn stress evolution with film thickness exhibited an initial high transitional stress region followed by a region of steady-state stress with a magnitude that depended on deposition rate, si...
Heteroepitaxial growth of SixGe1-x on Si (001) substrates under conditions of reduced adatom mobility results in limited formation of stress-relieving islands occurring only at energetically favorable sites. These favorable sites are at the edges of shallow pyramidal pits that form at random locations on the film surface under these conditions. How...
Experimental results are presented for stress evolution, in vacuum and electrolyte, for the first monolayer of Cu on Au(111). In electrolyte the monolayer is pseudomorphic and the stress-thickness change is -0.60 N/m, while conventional epitaxy theory predicts a value of +7.76 N/m. In vacuum, the monolayer is incoherent with the underlying gold. Us...
Heteroepitaxial growth of GeSi alloys on Si (001) under deposition conditions that partially limit surface mobility leads to an unusual form of strain-induced surface morphological evolution. We discuss a kinetic growth regime wherein pits form in a thick metastable wetting layer and, with additional deposition, evolve to a quantum dot molecule—a s...
Transmission electron microscopy and x-ray diffraction were used to assess the microstructure and strain of AlxGa1−xN(x=0.61–0.64) layers grown on AlN. The compressively-strained AlGaN is partially relaxed by inclined threading dislocations, similar to observations on Si-doped AlGaN by P. Cantu, F. Wu, P. Waltereit, S. Keller, A. E. Romanov, U. K....
Island coalescence during Volmer–Weber thin film growth is generally accepted to be a source of tensile stress. However, the stochastic nature of unpatterned film nucleation and growth prevents meaningful comparison of stress measurements taken during growth to that predicted by theoretical models. We have overcome this by systematically controllin...
Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1−xN∕GaN heterostructures with 0.14⩽x⩽1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocati...
Heteroepitaxial growth of AlxGa1−xN alloy films on GaN results in large tensile strain due to the lattice mismatch. During growth, this strain is partially relieved both by crack formation and by the coupled introduction of dense misfit dislocation arrays. Extensive transmission electron microscopy measurements show that the misfit dislocations ent...
The evolution of stress during electrodeposition of Ni films on Au substrates has been investigated as a function of bath chemistry and deposition conditions to examine the microstructural origins of the compressive stress observed during deposition from an additive-free sulfamate bath. Three likely mechanisms for the generation of compressive stre...
We describe a new route to hierarchical assembly of semiconductor nanostructures, employing guided organization of self-assembling epitaxial quantum dot molecules in the GexSi1-x/Si(100) system. The quantum dot molecule comprises a shallow strain relieving pit, defined by {105} facets, and bounded by 4-fold {105}-faceted islands. Through topographi...
Growth of Si0.7Ge0.3 on Si under kinetically limited conditions results in the formation of shallow strain-relieving pits that only partially penetrate the wetting layer. Upon annealing at the growth temperature of 550°C, these pits elongate in one of the 〈100〉 directions and obtain near-{105} facets. The length-to-width aspect ratio of the resulti...
Heteroepitaxial growth of Si(0.7)Ge(0.3)/Si(001) films under kinetically limited conditions leads to self-assembly of fourfold quantum dot molecules. These structures obtain a narrowly selected maximum size, independent of film thickness or annealing time. Size selection arises from efficient adatom trapping inside the central pit of the quantum do...
We provide an overview of a novel self-assembly process that occurrs during GeSi/Si(001) strain-layer heteroepitaxy under conditions of limited adatom mobility. Suppression of copious surface diffusion leads to limited three-dimensional roughening in the form of pits that partially consume a thick, metastable wetting layer. The material ejected fro...
The ability of future integrated metal-semiconductor micro-systems such as RF MEMS to perform highly complex functions will depend on developing freestanding metal structures that offer improved conductivity and reflectivity over polysilicon structures. For example, metal-based RF MEMS technology could replace the bulky RF system presently used in...
Epitaxial growth of Si0.7Ge0.3/Si(001) under kinetically limited conditions results in the initial formation of shallow pyramidal pits with {501} facets, similar to an inverted "hut" structure. As growth is continued, the pit edges become decorated by islands that elongate to form a continuous wall surrounding each pit. These "quantum fortress" str...