Papers by Karen L Kavanagh
Applied Physics Letters, 1999
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MRS Advances, 2018
ABSTRACTThe effects of crystal orientation and doping on the surface energy, γT, of native oxides... more ABSTRACTThe effects of crystal orientation and doping on the surface energy, γT, of native oxides of Si(100) and Si(111) are measured via Three Liquid Contact Angle Analysis (3LCAA) to extract γT, while Ion Beam Analysis (IBA) is used to detect Oxygen. During 3LCAA, contact angles for three liquids are measured with photographs via the “Drop and Reflection Operative Program (DROP™). DROP™ removes subjectivity in image analysis, and yields reproducible contact angles within < ±1°. Unlike to the Sessile Drop Method, DROP can yield relative errors < 3% on sets of 20-30 drops. Native oxides on 5 x 1013 B/cm3 p- doped Si(100) wafers, as received in sealed, 25 wafer teflon boats continuously stored in Class 100/ISO 5 conditions at 24.5°C in 25% controlled humidity, are found to be hydrophilic. Their γT, 52.5 ± 1.5 mJ/m2, is reproducible between four boats from three sources, and 9%…
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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1996
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Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2017
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Nanoscale, Jan 20, 2017
Aligned, individual iron square cuboid nanoparticles have been achieved by taking advantage of ep... more Aligned, individual iron square cuboid nanoparticles have been achieved by taking advantage of epitaxial, three-dimensional-island growth on GaAs(001) during electrodeposition at low deposition rates. The nanoparticles exhibit lateral dimensions between 10 and 80 nm and heights below 40 nm. Surface {100} facets predominate with a thin crystalline oxide shell that protects the nanoparticles during prolonged storage in air. The single crystallinity of the iron in combination with structural alignment leads to an in-plane magnetic anisotropy. These immobilized, oriented, and stable nanoparticles are promising for applications in nanoelectronic, sensor, and data storage technologies, as well as for the detailed analysis of the effect of shape and size on magnetism at the nanoscale.
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Semiconductor Science and Technology, 2016
Epitaxial Fe contacts have been fabricated onto the top half of free-standing, Te-doped GaAs nano... more Epitaxial Fe contacts have been fabricated onto the top half of free-standing, Te-doped GaAs nanowires (NWs) via electrodeposition. Electrical isolation from the substrate via a polymeric layer enabled the measurement of electrical transport through individual wires. Using a fixed probe within a scanning electron microscope, an average metal-semiconductor diode barrier height of 0.69 ± 0.03 eV (ideality factor 1.48 ± 0.02) was found.
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MRS Proceedings, 1990
ABSTRACTThis paper summarizes methods used to create cross-sectional samples for transmission ele... more ABSTRACTThis paper summarizes methods used to create cross-sectional samples for transmission electron microscopy and introduces another variant of the technique all of which rely upon some combination of lithographic patterning and reactive ion etching. The basic idea pursued in using these techniques was to form, from a preselected location, samples that had a large transparent area without use of mechanical polishing or ion milling. Samples were successfully prepared in this manner, but room for improvement remains due to the limited range of diffraction conditions available for imaging or diffraction pattern formation.
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The Journal of Physical Chemistry C, 2012
ABSTRACT By preparing phenyl-terminated monolayers on hydrogen-terminated silicon (111), we show ... more ABSTRACT By preparing phenyl-terminated monolayers on hydrogen-terminated silicon (111), we show that their higher surface densities in comparison with n-alkyl monolayers improves their electrical properties (lower reverse-bias currents, higher effective barrier heights, and closer-to-unity ideality factors) when contacted using either mercury drop or thermally deposited gold electrodes. Consistent with these macroscopic results, the ballistic electron emission microscopy characterization shows a significant decrease in ballistic current and higher local barrier height for the phenyl-terminated monolayers, when compared with gold | n-alkyl monolayer | silicon junctions. We propose that increased intermolecular interaction through π–π stacking of the phenyl head-groups stabilizes the monolayer structure at the buried interface and inhibits the penetration of thermally deposited gold atoms.
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The Journal of Physical Chemistry B, 2006
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Semiconductor Science and Technology, 2014
ABSTRACT Engineered or &#39;virtual&#39; substrates are of interest to extend the range o... more ABSTRACT Engineered or &#39;virtual&#39; substrates are of interest to extend the range of epitaxially-grown semiconductor heterostructures available for device applications. To this end, elastically strain-relaxed square features up to 30 µm in size and having an in-plane lattice constant as much as 0.49% larger than the lattice constant of GaAs were fabricated from MOCVD-grown GaAs/In0.08Ga0.92As/GaAs heterostructures by the in-place bonding method, using either AlAs or Al0.7Ga0.3As as the sacrificial layer. TEM images show that the solution-bonded interface is flat with a network of sessile edge dislocations that accommodates the different in-plane lattice constants of the feature and the GaAs substrate and a small rotation of the bonded features. Micro-Raman spectroscopy, which has a spatial resolution of ~1 µm, was shown to be useful for characterizing lattice mismatch strain ≥ 0.0023, i.e. with an order of magnitude lower sensitivity than high-resolution XRD.
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Semiconductor Science and Technology, 2007
ZnSe nanowires were grown on Si substrates by Au-catalyzed vapour phase growth at 725 °C. A detai... more ZnSe nanowires were grown on Si substrates by Au-catalyzed vapour phase growth at 725 °C. A detailed structural and microstructural investigation has been carried out using electron diffraction and high-resolution transmission electron microscopy (HRTEM). Modulated twins have been observed along the nanowire axial direction along the entire length of the nanowires. Faceting has been observed on the side surfaces of the wires with a larger twinning periodicity. The formation mechanism of these twinning-modulated nanowires is discussed. The optical properties are correlated with the microstructure of the nanowires. These twinning-modulated ZnSe nanowires might have great potential as building blocks for optoelectronic nanodevices.
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Journal of Crystal Growth, 2009
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Journal of Applied Physics, 1987
... c) ]. Another mechanism by which misfit segments can be generated is the multiplication proce... more ... c) ]. Another mechanism by which misfit segments can be generated is the multiplication process described by Hagen and Strunk ... strain is relaxed, the relative rate of nucleation of second partíais in the faulted glide planes will increase, thereby ... (1) and (2) van der Merwe&#x27;s expres ...
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Journal of Applied Physics, 2012
ABSTRACT Tellurium (Te)-doping of Au-catalyzed GaAs nanowires (NWs) grown by metalorganic vapor p... more ABSTRACT Tellurium (Te)-doping of Au-catalyzed GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy (MOVPE) via the vapor-liquid-solid (VLS) mechanism is presented. Electrical measurements were performed inside a scanning electron microscope by contacting a tungsten nanoprobe to the Au end of individual NWs grown on a heavily n-type GaAs substrate. Rectifying current-voltage (I-V) characteristics are observed due to the formation of a junction at the Au nanoparticle (NP)/NW interface. The electron concentration ne and contact barrier heights, φ0b, were determined from the analyses of these characteristics. As expected, φ0b increased (from 0.63 ± 0.03 eV to 0.71 ± 0.02 eV) with decreasing Te-precursor flow rate, corresponding to a decrease in ne from (9 ± 1) × 1017 cm−3 to (1.5 ± 0.5) × 1017 cm−3. Meanwhile, undoped NWs had space-charge-limited characteristics. There was a large influence of the residual gallium (Ga) in the NP, on barrier properties, controlled by the group V precursor flow (on or off) during the cooling of the NW sample at the end of the growth process. With the group V flow off during cooling, a decrease in φ0b from 0.79 ± 0.04 eV to 0.63 ± 0.03 eV is observed consistent with a higher Ga alloy concentration in the NP, confirmed by energy dispersive spectroscopy measurements. We also demonstrate the fabrication of core/shell, undoped/Te-doped, GaAs NWs with very high Te doping (∼1019 cm−3).
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Journal of Applied Physics, 2012
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Journal of Applied Physics, 1996
ABSTRACT We have investigated the effects of buffer strain relaxation on the transport properties... more ABSTRACT We have investigated the effects of buffer strain relaxation on the transport properties of two‐dimensional electron gases (2DEGs). The 2DEGs consist of modulation‐doped In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As heterostructures grown lattice‐mismatched to GaAs via compositionally step‐graded In x Ga 1-x As buffers, with different composition gradients, or lattice‐matched to InP. We find a variation in 2DEG electronic properties which occurs simultaneously with large differences in epilayer tilt and mosaic spread in the step‐graded buffers. This indicates a correlation between the mechanism of buffer strain relaxation and the 2DEG transport properties. © 1996 American Institute of Physics.
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IEEE Electron Device Letters, 2005
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IEEE Electron Device Letters, 1999
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Papers by Karen L Kavanagh