V. J. Logeeswaran

University of California, Davis, Davis, California, United States

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Publications (57)49.87 Total impact

  • Emre Yengel · Hakan Karaagac · Logeeswaran VJ · M. Saif Islam
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    ABSTRACT: Recent studies in monocrystalline semiconductor solar cells are focused on mechanically stacking multiple cells from different materials to increase the power conversion efficiency. Although, the results show promising increase in the device performance, the cost remains as the main drawback. In this study, we calculated the theoretical limits of multistacked 1D and 2D microstructered inorganic monocrstalline solar cells. This system is studied for Si and Ge material pair. The results show promising improvements in the surface reflection due to enhanced light trapping caused by photon-microstructures interactions. The theoretical results are also supported with surface reflection and angular dependent power conversion efficiency measurements of 2D axial microwall solar cells. We address the challenge of cost reduction by proposing to use our recently reported mass-manufacturable fracture-transfer- printing method which enables the use of a monocrystalline substrate wafer for repeated fabrication of devices by consuming only few microns of materials in each layer of devices. We calculated thickness dependent power conversion efficiencies of multistacked Si/Ge microstructured solar cells and found the power conversion efficiency to saturate at 26% with a combined device thickness of 30 μm. Besides having benefits of fabricating low-cost, light weight, flexible, semi-transparent, and highly efficient devices, the proposed fabrication method is applicable for other III-V materials and compounds to further increase the power conversion efficiency above 35% range. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    SPIE, San Diego; 09/2015
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    ABSTRACT: We synthesized catalyst-free �-Ga2O3 nanorods with terminated ultra-sharp tips by heat treating single crystalline GaAs in a chemical vapor deposition (CVD) chamber without introducing a precursor. The unique, straight-forward, synthetic route and a possible growth mechanism are discussed to explain the different morphology of the grown nanorods and the ultra-sharp nanostructures. The morphology and structure of the nanorods were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Raman-spectroscopy. The ultra-sharp tips were found to have radii of ∼3–5 nm and were utilized to achieve enhanced field emission. The field emission characteristics demonstrated a turn-on field of 2.1 V�m−1, a threshold electric field of 5.6 V�m−1, and a geometrical field enhancement factor of 3786, making them comparable to nanostructured diamond and highly oriented single wall carbon nanotubes.
    Science of Advanced Materials 02/2015; 7(2):211-218. DOI:10.1166/sam.2015.2160 · 2.60 Impact Factor
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    ABSTRACT: We have designed, fabricated, and tested a microcorona driven (MCD) vibrating element. The vibrating element consists of a mass plate at the end of a cantilever. The proof mass is selectively driven by either one or two microcorona ionizers. During the dc negative corona discharge, the build-up of negative space charge electrostatically repelled the cathodes on the mass plate against the mechanical elastic force of the spring, damping force, and electrostatic force. This resulted in the wideband mechanical self-excitation of the MCD vibrating element. Using laser Doppler vibrometry (LDV), two resonance frequencies of out-of-plane modes were measured experimentally at peak values of 896 and 1312 Hz, and it was consistent with the ANSYS finite element modal analysis results at ~823 and 1323 Hz, respectively. The transition from Trichel pulse mode to diffuse glow mode resulted in a discontinuity in the experimental plot of proof mass velocity versus applied voltage. The MCD vibrating element consumed a maximum power of ~100 mW and had a maximum resultant driving force of ~0.45 μN in the first observed driving mode. The maximum out-of-plane oscillation amplitude measured was to be ~2 μm
    Journal of Microelectromechanical Systems 01/2015; 24(1):224-231. DOI:10.1109/JMEMS.2014.2328615 · 1.75 Impact Factor
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    ABSTRACT: A process of heterogeneously integrating organically modified siliceous aerogel (Ormosil) films onto microstructured substrates is presented. These substrates are architecturally designed to mimic photon detectors for remote sensing applications. Here, ultrasonically homogenized Ormosil sols are drop-cast onto silicon micropyramidal arrays then dried in the ambient to produce highly porous low-density siliceous films with excellent uniformity. The highly facile process yields films endowed with high optical transmittance, high static contact angle of 168°, excellent thermal stability up to 400 °C and, to some extent, excellent adhesion to the microstructured substrates on which they sit. Additional planarization benefits are easily afforded by controlling the substrate arraignment during the ambient drying process which the sol undergoes. In contrast, only conformal films were obtained when sols were spin coated over similar microstructured substrates. In correlating the resultant macroporous films’ structural integrity with the underlying substrate topography, this study established that the weak physical bond between the facets of the microstructures and gel acts as crack nucleation points that induce and exacerbate crack propagation within the film. This phenomenon does not manifest itself when thinner films are prepared even on the same microstructured substrates as well as films of similar thickness on planar substrates. Initial studies establish that the non-homogenized sols can yield macroscopic aerogel monoliths with properties akin to those exhibited by supercritically dried monoliths. It is our belief that this study can enlighten the intricacies and pitfalls encountered when fabricating macroscopically monolithic Ormosil films over topographically structured surfaces
    Acta Materialia 06/2014; 72:159. DOI:10.1016/j.actamat.2014.03.021 · 4.47 Impact Factor
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    Hakan Karaagac · V. J. Logeeswaran · M. Saif Islam
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    ABSTRACT: In this study, regularly patterned and hierarchically structured silicon (Si) micro-scale pillars and walls with high aspect ratio were fabricated using the deep reactive ion etching (DRIE) process. Dense arrays of ZnO nanowires were hydrothermally grown on the surface of the Si structures subsequent to the deposition of Aluminum–ZnO (AZO) thin films onto the vertically oriented p- and n-type Si micro-scale pillars and walls – resulting in three-dimensional (3D) heterostructures. Electrical and optical measurements of the fabricated p–n nano-heterojunctions demonstrate strong capabilities for detecting ultraviolet (UV)–visible (VIS) photons with drastically reduced reflection loss. We also demonstrate low-voltage sensing of gases using these structures through the field ionization process.
    Physica Status Solidi (A) Applications and Materials 07/2013; 210(7). DOI:10.1002/pssa.201329135 · 1.62 Impact Factor
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    Matthew Monari Ombaba · V. J. Logeeswaran · M. Saif Islam
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    ABSTRACT: In this paper we report a novel application of electrically conductive film (ECF) of Ag sub-micron particles that includes both isotropic and anisotropic film technologies in providing simultaneous electrical contact and mechanical anchor between fracture transfer-printed (1-D) single crystal semiconductor micro- and nano-pillars and a carrier substrate. We assembled silver sub-micron particles (AgSP) monolayers with varying particle diameters and investigated their optical and electrical characteristics prior to their incorporation into thermoplastic polymers. It was found that transfer-printing of the Si micropillar arrays, into electrically conductive thermoplastic receiver substrates, made of films of AgSP/PMMA blends atop metallic substrates could be effectively achieved to yield electrically interfaced 1-D Si micropillar arrays with retention of their orientation and integrity according to the SEM images. The carrier substrate can potentially be reused to generate additional Si micropillar arrays that can be similarly harvested.
    Applied Physics A 04/2013; 111(1):251-259. DOI:10.1007/s00339-012-7516-z · 1.70 Impact Factor
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    Hakan Karaagac · V. J. Logeeswaran · M. Saif Islam
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    ABSTRACT: In this paper, high aspect ratio vertically oriented p-silicon (100) micropillars and microwalls were fabricated using the deep reactive ion etching (DRIE) process with the BOSCH recipe of cyclical passivation and etching. Two different patterns were etched; uniform pillar arrays of dimensions ~15µm (height) x 2µm (diameter) and wall arrays of dimensions ~1.5µm (width) x 25µm (height). Three-dimensional (3D) heterostructures of n-ZnO/p-Si heterostructures were fabricated from growing hydrothermally dense arrays of ZnO nanowires (290-400 nm in length and 48-80 nm in diameter) and depositing Aluminum-ZnO (AZO) thin film onto the high aspect ratio vertically oriented p-silicon micropillars and microwalls. The performances of the fabricated heterostructure optoelectronic devices were characterized for different applications including solar cells, photodetectors and field ionization gas sensors.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2012; DOI:10.1117/12.945974 · 0.20 Impact Factor
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    ABSTRACT: We describe an experiment to interface and characterize silver nanoparticle (AgNPs) aggregates that are self-assembled and plastically deformable on a thin gold (Au) film deposited on glass substrate. The electrical characterization is done using an electrical nanoprobe attached to a nano-manipulator inside a scanning electron microscope (SEM). Electrical current-voltage (I-V) measurements are made between the electrical nanoprobe in contact with the nanoparticle and the Au film. The Ag nanoparticles have diameters ranging between ~200-800nm and are self-assembled on a thiolated 100nm Au film. Application of a contact force via the nanoprobe even after substantial particle deformation reveals initially a small non-linear current. Upon current annealing through Joule heating, significant improvement in the electrical contact at the AgNP/substrate interface was observed. This is most likely based on bonding of the AgNPs to the Au film after passage of a high current. The need for such an annealing/sintering step will be critical in forming good ohmic contacts at ambient conditions during transfer printing of semiconductor micro/nanopillars.
    MRS Online Proceeding Library 01/2012; 1429. DOI:10.1557/opl.2012.1531
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    ABSTRACT: We report an experimental investigation on employing Ag nanoparticles to provide electrical and mechanical contacts between transfer-printed semiconductor devices in the shape of micro/nano- wires and pillars. The Ag nanoparticles have diameters ranging between 200-800nm and are assembled on a 200nm Au film deposited on glass substrates. With a customized tool, an ensemble of silicon pillars were brought into contact with the silver (Ag) nanoparticles (AgNPs) by precisely controlling the displacement and applied force (pressure). Current-voltage measurements were done at force resolution of ~0.2N. The test method aims to illuminate the pillar-particle contact mechanism using the nanoparticles as conductive fillers for the next generation of high performance heteroepitaxial device transfer-printing applications.
    MRS Online Proceeding Library 01/2012; 1429. DOI:10.1557/opl.2012.1532
  • Encyclopedia of Nanotechnology, 01/2012: pages 583-587; , ISBN: 978-90-481-9750-7
  • Encyclopedia of Nanotechnology, 01/2012: pages 587-587; , ISBN: 978-90-481-9750-7
  • Encyclopedia of Nanotechnology, 01/2012: pages 604-604; , ISBN: 978-90-481-9750-7
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    Logeeswaran VJ · M. Saif Islam · Mei Lin Chan · David A Horsley · Wei Wu
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    ABSTRACT: In this paper, we present a method to realize a three dimensional (3D) homogeneous and isotropic negative index materials (3D-NIMs) fabricated using a low cost and massively parallel manufacturable microfabrication and microassembly technique. The construction of self- assembled 3D-NIM array was realized through two dimensional (2-D) planar microfabrication techniques exploiting the as-deposited residual stress imbalance between a bi-layer consisting of e-beam evaporated metal (650nm of chromium) and a structural layer of 500nm of low stress silicon nitride deposited by LPCVD on a silicon substrate. A periodic continuation of a single rectangular unit cell consisting of split-ring resonators (SRR) and wires were fabricated to generate a 3D assembly by orienting them along all three Cartesian axes. The thin chromium and silicon nitride bi-layer is formed as hinges. The strain mismatch between the two layers curls the structural layer (flap) containing the SRR upwards. The self-assembled out-of-plane angular position depends on the thickness and material composing the bi-layer. This built-in stress-actuated assembly method is suitable for applications requiring a thin dielectric layer for the SRR. The split-ring resonators and other structures are created on the membrane which is then assembled into the 3-D configuration.
    MRS Online Proceeding Library 01/2011; 919. DOI:10.1557/PROC-0919-J02-01
  • Matthew Ombaba · V. J Logeeswaran · M. Saif Islam
    MRS Online Proceeding Library 01/2011; 1303. DOI:10.1557/opl.2011.588
  • Logeeswaran VJ · Matthew Ombaba · M.Saif Islam
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    ABSTRACT: In this paper, we demonstrate a heterogeneous integration technique that preserves the integrity, order, shape, and fidelity of vertically aligned single-crystal semiconductor micro- and nano- pillars by harvesting and transferring them from a single crystal substrate to a low-cost carrier substrate. The mechanism of the transfer technique exploits a combination of vertical embossing and lateral fracturing of the crystalline pillars with the assistance of a spin-coated polymer layer on a carrier substrate as well as facilitating multilayer process device integration. Specifically, the novel use of a water soluble adhesive polymer from MasterBond that acts simultaneously as a mechanical transfer polymer and as a sacrificial harvest layer further expands the versatility of this approach. Arrays of vertical micropillars of average height ~15)μm and diameter ~1.5μm on a die silicon substrate of 5mm x 5mm were fabricated via transformative top-down approaches (DRIE) on a single crystal silicon substrate and then transferred to a different target carrier substrate using the adhesive polymer assisted bendingfracturing process. The adhesive polymer is odorless, non-conducting, easy to process, spincoatable, optically transparent, resistant to heat, high mechanical strength and easily cures at room temperature. The original pillar wafers may be used repeatedly after polishing for generating more devices and are minimally consumed. Low contact resistances are formed for electrical addressing using metals and conducting thermoplastics of Ag nanoparticles. This heterogeneous integration technique potentially offers enhanced photon semiconductor interactions, while enabling multimaterial integration such as silicon with compound semiconductors (InP, GaAs etc.) for applications, including high speed electronics, low-cost and flexible electronics, displays, tactile sensors, and energy conversion systems.
    MRS Online Proceeding Library 01/2011; 1303. DOI:10.1557/opl.2011.411
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    Logeeswaran VJ · Aaron M. Katzenmeyer · M. Saif Islam
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    ABSTRACT: Development of devices that can be fabricated on amorphous substrates using multiple single-crystal semiconductors with different physical, electrical, and optical characteristics is important for highly efficient portable and flexible electronics, optoelectronics, and energy conversion devices. Reducing the use of single-crystal substrates can contribute to low-cost and environmentally benign devices covering a large area. We demonstrate a technique to harvest and transfer vertically aligned single-crystal semiconductor micro- and nanopillars from a single-crystal substrate to a low-cost carrier substrate while simultaneously preserving the integrity, order, shape, and fidelity of the transferred pillar arrays. The transfer technique facilitates multilayer process integration by exploiting a vertical embossing and lateral fracturing method using a spin-coated polymer layer on a carrier substrate. Electrical contacts are formed using a bilayer of metal and conducting polymer such as gold (Au) and polyaniline (PAni). In this method, the original single-crystal substrate can be repeatedly used for generating more devices and is minimally consumed, whereas in conventional fabrication methods, the substrate is employed solely as a mechanical support. This heterogeneous integration technique potentially offers devices with low physical fill factor contributing to lower leakage current and noise, reduced parasitic capacitance, and enhanced photon-semiconductor interactions, and enables heterogeneous multimaterial integration such as silicon with compound semiconductors for rapidly expanding large-scale applications, including low-cost and flexible electronics, displays, tactile sensors, and energy conversion systems.
    IEEE Transactions on Electron Devices 09/2010; 57(8-57):1856 - 1864. DOI:10.1109/TED.2010.2051195 · 2.47 Impact Factor
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    M. Saif Islam · V.J. Logeeswaran
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    ABSTRACT: New discoveries in materials on the nanometer- length scale are expected to play an important role in addressing ongoing and future challenges in the field of communication. Devices and systems for ultra-high-speed short- and long-range communication links, portable and power-efficient computing devices, high-density memory and logics, ultra-fast interconnects, and autonomous and robust energy scavenging devices for accessing ambient intelligence and needed information will critically depend on the success of next-generation emerging nanomaterials and devices. This article presents some exciting recent developments in nanomaterials that have the potential to play a critical role in the development and transformation of future intelligent communication networks.
    IEEE Communications Magazine 07/2010; 48(6-48):112 - 120. DOI:10.1109/MCOM.2010.5473872 · 4.01 Impact Factor
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    ABSTRACT: We demonstrate a smooth and low loss silver (Ag) optical superlens capable of resolving features at 1/12th of the illumination wavelength with high fidelity. This is made possible by utilizing state-of-the-art nanoimprint technology and intermediate wetting layer of germanium (Ge) for the growth of flat silver films with surface roughness at subnanometer scales. Our measurement of the resolved lines of 30 nm half-pitch shows a full-width at half-maximum better than 37 nm, in excellent agreement with theoretical predictions. The development of this unique optical superlens leads promise to parallel imaging and nanofabrication in a single snapshot.
    Applied Physics Letters 01/2010; 96(4):043102-043102-3. DOI:10.1063/1.3293448 · 3.30 Impact Factor
  • M K Kwon · J Y Kim · VJ Logeeswaran · Y J Teng · H L Hsu · P A Baeza · I Arslan · M S Islam
    Proceedings of SPIE; 01/2010
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    ABSTRACT: We report a novel method to fabricating single crystal and highly oriented 1-D Silicon micropillars and nanowires and then transferring them to coat a target surface of any topology using an innovative harvest/lift-off process. This method enables highly crystalline micro- and nano- pillars of different materials with diverse bandgaps and physical properties to be fabricated on appropriate mother substrates and transferred to form multilayered 3D stacks for multifunctional devices. This approach not only ensures the incorporation of any kind of material (with the best device characteristics) on a single substrate facilitating substrate-free device fabrications on any topology, but also allows the repeated use of a mother substrate for continual production of new devices. This capability of fabricating substrate-less devices will offer a universal platform for material integration and allow solar active devices to be coated on various surface topologies that would be suitable for solar hydrogen generation.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2009; DOI:10.1117/12.828744 · 0.20 Impact Factor

Publication Stats

262 Citations
49.87 Total Impact Points


  • 2006–2015
    • University of California, Davis
      • Department of Electrical and Computer Engineering
      Davis, California, United States
  • 2007
    • University of California, Santa Cruz
      Santa Cruz, California, United States
  • 2000–2004
    • National University of Singapore
      • Department of Mechanical Engineering
      Singapore, Singapore