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49 results on '"Deitz, Julia I."'

1. Manipulating Acoustic and Plasmonic Modes in Gold Nanostars

Author

Chatterjee, Sharmistha, Ricciardi, Loredana, Deitz, Julia I., Williams, Robert E. A., McComb, David W., and Strangi, Giuseppe

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

In this contribution experimental evidence of plasmonic edge modes and breathing acoustic modes in gold nanostars (AuNS) is reported. AuNS are synthesized in a surfactant-free, one-step wet-chemistry method. Optical extinction measurements of AuNS confirm the presence of localized surface plasmon resonances (LSPRs), while electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) shows the spatial distribution of LSPRs and reveals the presence of acoustic breathing modes. Plasmonic hot-spots generated at the pinnacle of the sharp spikes, due to the optically active edge dipolar mode, allow significant intensity enhancement of local fields, hot-electron injection, and thus useful for size detection of small protein molecules. The breathing modes observed away from the apices of the nanostars are identified as stimulated dark modes - they have an acoustic nature - and likely originate from the confinement of the surface plasmon by the geometrical boundaries of a nanostructure. The presence of both types of modes is verified by numerical simulations. Both these modes offer the possibility to design nanoplasmonic antenna based on AuNS, which can provide information both on mass and polarizability of biomolecules using a two-step molecular detection process., Comment: 19 pages, 9 figures

Published
2019
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2. Ferromagnetic Epitaxial {\mu}-Fe$_{2}$O$_{3}$ on {\beta}-Ga$_{2}$O$_{3}$: A New Monoclinic form of Fe$_{2}$O$_{3}$

Author

Jamison, John S., May, Brelon J., Deitz, Julia I., Chien, Szu-Chia, McComb, David W., Grassman, Tyler J., Windl, Wolfgang, and Myers, Roberto C.

Subjects
Condensed Matter - Materials Science
Abstract

Here we demonstrate a new monoclinic iron oxide phase ({\mu}-Fe$_{2}$O$_{3}$), epitaxially stabilized by growth on (010) {\beta}-Ga$_{2}$O$_{3}$. Density functional theory (DFT) calculations find that the lattice parameters of freestanding {\mu}-Fe$_{2}$O$_{3}$ are within ~1% of those of {\beta}-Ga$_{2}$O$_{3}$ and that its energy of formation is comparable to that of naturally abundant Fe$_{2}$O$_{3}$ polytypes. A superlattice of {\mu}-Fe$_{2}$O$_{3}$/{\beta}-Ga$_{2}$O$_{3}$ is grown by plasma assisted molecular beam epitaxy, with resulting high-resolution x-ray diffraction (XRD) measurements indicating that the {\mu}-Fe$_{2}$O$_{3}$ layers are lattice-matched to the substrate. The measured out-of-plane (b) lattice parameter of 3.12 $\pm$ 0.4 {\AA} is in agreement with the predicted lattice constants and atomic-resolution scanning transmission electron microscopy (STEM) images confirm complete registry of the {\mu}-Fe$_{2}$O$_{3}$ layers with {\beta}-Ga$_{2}$O$_{3}$. Finally, DFT modeling predicts that bulk {\mu}-Fe$_{2}$O$_{3}$ is antiferromagnetic, while the interface region between {\mu}-Fe$_{2}$O$_{3}$ and {\beta}-Ga$_{2}$O$_{3}$ leads to ferromagnetic coupling between interface Fe$^{3+}$ cations selectively occupying tetrahedral positions. Magnetic hysteresis persisting to room temperature is observed via SQUID measurements, consistent with the computationally predicted interface magnetism., Comment: 19 pages and 7 figures

Published
2019
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5. Focused Ion Beam Nano-thermometry

Author

Deitz, Julia I, primary, Ruggles, Timothy J, additional, Rosenberg, Samantha G, additional, Lam, Mila N, additional, Jauregui, Luis, additional, Williard, John, additional, Perry, Daniel L, additional, Boro, Joseph, additional, and Hodges, Wyatt, additional

Published
2023
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13. Ferromagnetic Epitaxial ��-Fe$_{2}$O$_{3}$ on ��-Ga$_{2}$O$_{3}$: A New Monoclinic form of Fe$_{2}$O$_{3}$

Author

Jamison, John S., May, Brelon J., Deitz, Julia I., Chien, Szu-Chia, McComb, David W., Grassman, Tyler J., Windl, Wolfgang, and Myers, Roberto C.

Subjects
Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

Here we demonstrate a new monoclinic iron oxide phase (��-Fe$_{2}$O$_{3}$), epitaxially stabilized by growth on (010) ��-Ga$_{2}$O$_{3}$. Density functional theory (DFT) calculations find that the lattice parameters of freestanding ��-Fe$_{2}$O$_{3}$ are within ~1% of those of ��-Ga$_{2}$O$_{3}$ and that its energy of formation is comparable to that of naturally abundant Fe$_{2}$O$_{3}$ polytypes. A superlattice of ��-Fe$_{2}$O$_{3}$/��-Ga$_{2}$O$_{3}$ is grown by plasma assisted molecular beam epitaxy, with resulting high-resolution x-ray diffraction (XRD) measurements indicating that the ��-Fe$_{2}$O$_{3}$ layers are lattice-matched to the substrate. The measured out-of-plane (b) lattice parameter of 3.12 $\pm$ 0.4 �� is in agreement with the predicted lattice constants and atomic-resolution scanning transmission electron microscopy (STEM) images confirm complete registry of the ��-Fe$_{2}$O$_{3}$ layers with ��-Ga$_{2}$O$_{3}$. Finally, DFT modeling predicts that bulk ��-Fe$_{2}$O$_{3}$ is antiferromagnetic, while the interface region between ��-Fe$_{2}$O$_{3}$ and ��-Ga$_{2}$O$_{3}$ leads to ferromagnetic coupling between interface Fe$^{3+}$ cations selectively occupying tetrahedral positions. Magnetic hysteresis persisting to room temperature is observed via SQUID measurements, consistent with the computationally predicted interface magnetism., 19 pages and 7 figures

Published
2019
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17. Degradation Mechanism in Cu(In,Ga)Se2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Author

Karki, Shankar, primary, Paul, Pran, additional, Deitz, Julia I., additional, Poudel, Deewakar, additional, Rajan, Grace, additional, Belfore, Benjamin, additional, Danilov, Evgeny O., additional, Castellano, Felix N., additional, Grassman, Tyler J., additional, Arehart, Aaron, additional, Rockett, Angus, additional, and Marsillac, Sylvain, additional

Published
2019
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29. Impact of Water Ingress on Molybdenum Thin Films and Its Effect on Cu(In,Ga)Se2 Solar Cells

Author

Karki, Shankar, Deitz, Julia I., Rajan, Grace, Soltanmohammad, Sina, Poudel, Deewakar, Belfore, Benjamin, Bhandari, Gandhari, Grassman, Tyler J., Rockett, Angus, and Marsillac, Sylvain

Abstract

Solar cell degradation can occur through many pathways and at the different stages of the fabrication process, notably because of the water condensation. In the case of Cu(In,Ga)Se2 (CIGS) solar cells, the impact of water ingress on Mo back contact can be substantial for not only the film itself but also the device performance and reliability. Microstructural modification, change in film morphology, loss in reflectance, and increased resistivity because of the moisture ingress were observed via X-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry, and four-point probe measurements, respectively. Secondary ion mass spectrometry measurements revealed drastic changes in the alkali (Na, K) profiles in both the CIGS and Mo layers, likely because of the modification of their diffusion coefficient through Mo. This, in turn, negatively impacts the solar cell efficiency by decreasing both fill factor and open-circuit voltage. Additional experiments, modifying the substrate and utilizing a NaF postdeposition treatment, highlight the mechanisms of degradation as being due to both a modification of the Mo/CIGS interface and the lack of alkali diffusion after water ingress.

Published
2020
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35. Ferromagnetic Epitaxial μ-Fe2O3on β-Ga2O3: A New Monoclinic Form of Fe2O3

Author

Jamison, John S., May, Brelon J., Deitz, Julia I., Chien, Szu-Chia, McComb, David W., Grassman, Tyler J., Windl, Wolfgang, and Myers, Roberto C.

Abstract

Here we demonstrate a new monoclinic iron oxide phase (μ-Fe2O3), epitaxially stabilized by growth on (010) β-Ga2O3. Density functional theory (DFT) calculations find that the lattice parameters of freestanding μ-Fe2O3are within ∼1% of those of β-Ga2O3, and that its energy of formation is comparable to that of naturally abundant Fe2O3polytypes. A superlattice of μ-Fe2O3/β-Ga2O3is grown by plasma assisted molecular beam epitaxy, with resulting high-resolution X-ray diffraction (XRD) measurements indicating that the μ-Fe2O3layers are lattice-matched to the substrate. The measured out-of-plane (b) lattice parameter of 3.12 ± 0.4 Å is in agreement with the predicted lattice constants and atomic-resolution scanning transmission electron microscopy (STEM) images confirm complete registry of the μ-Fe2O3layers with β-Ga2O3. Finally, DFT modeling predicts that bulk μ-Fe2O3is antiferromagnetic, while the interface region between μ-Fe2O3and β-Ga2O3leads to ferromagnetic coupling between interface Fe3+cations selectively occupying tetrahedral positions. Magnetic hysteresis persisting to room temperature is observed via SQUID measurements, consistent with the computationally predicted interface magnetism.

Published
2019
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36. Degradation Mechanism in Cu(In,Ga)Se2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Author

Karki, Shankar, Paul, Pran, Deitz, Julia I., Poudel, Deewakar, Rajan, Grace, Belfore, Benjamin, Danilov, Evgeny O., Castellano, Felix N., Grassman, Tyler J., Arehart, Aaron, Rockett, Angus, and Marsillac, Sylvain

Abstract

The impact of moisture and heat treatment on the microstructural, chemical, and electrical properties of Cu(In,Ga)Se2 films and their collective effect on the solar cell device performance was studied. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements show that water exposure causes surface modification and alters the alkali metal distribution, while no composition or structural effect was observed. Deep level transient and optical spectroscopies revealed that the trap densities (NT) for both the EV + 0.65 eV and EV + 0.98 eV traps increase after water exposure, while the majority carrier concentration (NA) decreases. Time-resolved photoluminescence (PL) and steady-state PL measurements indicated the presence of static, not dynamic, quenching. Reduction of open-circuit voltage (VOC) and fill factor (FF) was observed for the devices but was not associated with a change of recombination mechanism, which remains in the absorber space charge region. A small increase in series resistance and shunt conductance accounts for most of the FF change, while the modification in both NA and NT yield most of the change in VOC. A gradient of majority carrier concentration, related to the alkali profile, also yields a small voltage-dependent current collection after moisture and heat treatment.

Published
2019
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47. Direct Nanoscale Characterization of Deep Levels in AgCuInGaSe2 Using Electron Energy‐Loss Spectroscopy in the Scanning Transmission Electron Microscope.

Author

Deitz, Julia I., Paul, Pran K., Farshchi, Rouin, Poplavskyy, Dmitry, Bailey, Jeff, Arehart, Aaron R., McComb, David W., and Grassman, Tyler J.

Subjects
*ENERGY dispersive X-ray spectroscopy, *ELECTRON energy loss spectroscopy, *TRANSMISSION electron microscopes, *ELECTRON spectroscopy, *SCANNING electron microscopes, *DEEP level transient spectroscopy, *ELECTRON microscopes
Abstract

A new experimental framework for the characterization of defects in semiconductors is demonstrated. Through the direct, energy‐resolved correlation of three analytical techniques spanning six orders of magnitude in spatial resolution, a critical mid‐bandgap electronic trap level (EV + 0.56 eV) within Ag0.2Cu0.8In1−xGaxSe2 is traced to its nanoscale physical location and chemical source. This is achieved through a stepwise, site‐specific correlated characterization workflow consisting of device‐scale (≈1 mm2) deep level transient spectroscopy (DLTS) to survey the traps present, scanning probe–based DLTS (scanning‐DLTS) for mesoscale‐resolved (hundreds of nanometers) mapping of the target trap state's spatial distribution, and scanning transmission electron microscope based electron energy‐loss spectroscopy (STEM‐EELS) and X‐ray energy‐dispersive spectroscopy for nanoscale energy‐, structure, and chemical‐resolved investigation of the defect source. This first demonstration of the direct observation of sub‐bandgap defect levels via STEM‐EELS, combined with the DLTS methods, provides strong evidence that the long‐suspected CuIn/Ga substitutional defects are indeed the most likely source of the EV + 0.56 eV trap state and serves as a key example of this approach for the fundamental identification of defects within semiconductors, in general. [ABSTRACT FROM AUTHOR]

Published
2019
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48. Heterodimeric Plasmonic Nanogaps for Biosensing.

Author

Chatterjee, Sharmistha, Ricciardi, Loredana, Deitz, Julia I., Williams, Robert E. A., McComb, David W., and Strangi, Giuseppe

Subjects
PLASMONICS, GOLD nanoparticles, SINGLE molecule detection
Abstract

We report the study of heterodimeric plasmonic nanogaps created between gold nanostar (AuNS) tips and gold nanospheres. The selective binding is realized by properly functionalizing the two nanostructures; in particular, the hot electrons injected at the nanostar tips trigger a regio-specific chemical link with the functionalized nanospheres. AuNSs were synthesized in a simple, one-step, surfactant-free, high-yield wet-chemistry method. The high aspect ratio of the sharp nanostar tip collects and concentrates intense electromagnetic fields in ultrasmall surfaces with small curvature radius. The extremities of these surface tips become plasmonic hot spots, allowing significant intensity enhancement of local fields and hot-electron injection. Electron energy-loss spectroscopy (EELS) was performed to spatially map local plasmonic modes of the nanostar. The presence of different kinds of modes at different position of these nanostars makes them one of the most efficient, unique, and smart plasmonic antennas. These modes are harnessed to mediate the formation of heterodimers (nanostar-nanosphere) through hot-electron-induced chemical modification of the tip. For an AuNS-nanosphere heterodimeric gap, the intensity enhancement factor in the hot-spot region was determined to be 106, which is an order of magnitude greater than the single nanostar tip. The intense local electric field within the nanogap results in ultra-high sensitivity for the presence of bioanalytes captured in that region. In case of a single BSA molecule (66.5 KDa), the sensitivity was evaluated to be about 1940 nm/RIU for a single AuNS, but was 5800 nm/RIU for the AuNS-nanosphere heterodimer. This indicates that this heterodimeric nanostructure can be used as an ultrasensitive plasmonic biosensor to detect single protein molecules or nucleic acid fragments of lower molecular weight with high specificity. [ABSTRACT FROM AUTHOR]

Published
2018
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49. Investigation of digital alloyed AlInSb metamorphic buffers.

Author

Grassman, Tyler J., Krishna, Sanjay, Dahiya, Vinita, Deitz, Julia I., Hollingshead, David A., and Carlin, John A.

Subjects
GALLIUM antimonide, MOLECULAR beam epitaxy, SUPERLATTICES, X-ray diffraction, TRANSMISSION electron microscopy, PHOTOLUMINESCENCE, SURFACE morphology
Abstract

Al1-xInxSb metamorphic step-graded buffers with Al0.6In0.4Sb terminal layers, designed to serve as a virtual substrate to support integrated InAs0.5Sb0.5 long-wave infrared absorber layers, were grown on GaSb wafers via molecular beam epitaxy. Two different structural profiles were used to define the effective composition of each buffer step: one based on digital alloys (1 nm period, ∼1.6 unit cells) and the other based on short period superlattices (10 nm period, ∼16 unit cells). Characterization via optical Nomarski microscopy, x-ray diffraction reciprocal space mapping, and transmission electron microscopy indicates that the digital alloy based structure behaves similar to that expected for a conventional bulk ternary alloy based structure, while the short period superlattice structure exhibits significantly hindered relaxation within the buffer layers. [ABSTRACT FROM AUTHOR]

Published
2018
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