Zhida Xu

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (20)50.91 Total impact

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    ABSTRACT: Wafer-scale nano-mushroom sensor was demonstrated with the refractive index sensitivity of 373 nm/RIU, resulting in significant color shift detectable by eye. It also works for surface-enhanced Raman spectroscopy with the enhancement factor of 10^7.
    CLEO: Science and Innovations; 06/2014
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    ABSTRACT: Recently developed classes of monocrystalline silicon solar microcells (u-cell) can be assembled into modules with characteristics (i.e., mechanically flexible forms, compact concentrator designs, and high-voltage outputs) that would be impossible to achieve using conventional, wafer-based approaches. In this paper, we describe a highly dense, uniform and non-periodic nanocone forest structure of black silicon (bSi) created on optically-thin (30 um) u-cells for broadband and omnidirectional light-trapping with a lithography-free and high-throughput plasma texturizing process. With optimized plasma etching conditions and a silicon nitride passivation layer, black silicon u-cells, when embedded in a polymer waveguiding layer, display dramatic increases of as much as 65.7% in short circuit current, as compared to a bare silicon device. The conversion efficiency increases from 8% to 11.5% with a small drop in open circuit voltage and fill factor.
    Nanotechnology 06/2014; 25(30). · 3.84 Impact Factor
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    ABSTRACT: We present an optofluidic sensor based on an elastomeric two-dimensional (2D) grating integrated inside a hemispherical fluid chamber. A laser beam is diffracted before (reflection) and after (transmission) going through the grating and liquid in the dome chamber. The sensing mechanism is investigated and simulated with a finite-difference time-domain-based electromagnetic method. For the experiment, by analyzing the size, power, and shape of the 2D diffraction patterns, we can retrieve multiple parameters of the liquid, including the refractive index, pressure, and opacity with high sensitivity. We demonstrate that the glucose concentration can be monitored when mixed in a different concentrated phosphate-buffered saline solution. The free-solution binding of bovine serum albumin (BSA) and anti-BSA IgG is detected with this optical sensor. This low-cost, multifunctional, and reliable optofluidic sensor has the potential to be used as a monitor of biofluid, such as blood in hemodialysis.
    Journal of the Optical Society of America A 12/2013; 30(12):2466-72. · 1.67 Impact Factor
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    ABSTRACT: Portable low-cost sensors and sensing systems for the identification and quantitative measurement of bacteria in field water are critical in preventing drinking water from being contaminated by bacteria. In this article, we reported the design, fabrication and testing of a low-cost, miniaturized and sensitive bacteria sensor based on electrical impedance spectroscopy method using a smartphone as the platform. Our design of microfluidics enabled the pre-concentration of the bacteria which lowered the detection limit to 10 bacterial cells per milliliter. We envision that our demonstrated smartphone-based sensing system will realize highly-sensitive and rapid in-field quantification of multiple species of bacteria and pathogens.
    12/2013;
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    ABSTRACT: After made black by a reactive ion etching process and SiNx deposition, unprecedentedly, the efficiency of ultrathin solar microcell was improved from 8% to 11.5% and short circuit current increased by 65.7%.
    Optical Nanostructures and Advanced Materials for Photovoltaics; 11/2013
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    ABSTRACT: A high-density and -uniformity sub-100 nm surface-oxidized silicon nanocone forest structure is created and integrated onto the existing texturization microstructures on a photovoltaic device surface by a one-step high-throughput plasma-enhanced texturization method. We suppressed the broadband optical reflection on chemically textured grade-B silicon solar cells for up to 70.25% through this nanomanufacturing method. The performance of the solar cell is improved with the short-circuit current increased by 7.1%, fill factor increased by 7.0%, and conversion efficiency increased by 14.66%. Our method demonstrates the potential to improve the photovoltaic device performance with low-cost and high-throughput nanomanufacturing technology.
    Applied Optics 07/2012; 51(19):4430-5. · 1.69 Impact Factor
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    ABSTRACT: Black silicon with slanted nanopillar array on planar and microstructure was produced for surface-enhanced Raman spectroscopy (SERS). The angle dependence of etching angle and nanopillar slanted angle was investigated with scanning electron microscopy.
    Photonics Conference (IPC), 2012 IEEE; 01/2012
  • Zhida Xu, Xinhao Wang, G.L. Liu
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    ABSTRACT: Flexible 2D grating with nano-pyramids array used for in-situ and highly sensitive measurement of refractive index and pressure of fluid is demonstrated for potential application in blood monitoring in dialysis.
    Photonics Conference (IPC), 2012 IEEE; 01/2012
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    ABSTRACT: Asymmetric assembly of nanomaterials has attracted broad interests because of their unique anisotropic properties that are different from those based on the more widely reported symmetric assemblies. Despite the potential advantages, programmable fabrication of asymmetric structure in nanoscale remains a challenge. We report here a DNA-directed approach for the assembly of asymmetric nanoclusters using Janus nanoparticles as building blocks. DNA-functionalized spherical gold nanoparticles (AuNSs) can be selectively attached onto two different hemispheres of DNA-functionalized Janus nanoparticle (JNP) through DNA hybridization. Complementary and invasive DNA strands have been used to control the degree and reversibility of the assembly process through programmable base-pairing interactions, resulting in a series of modular and asymmetric nanostructures that allow systematic study of the size-dependent assembly process. We have also shown that the attachment of the AuNSs onto the gold surface of the Janus nanoparticle results in red shifting of the UV-vis and plasmon resonance spectra.
    ACS Nano 12/2011; 6(1):802-9. · 12.03 Impact Factor
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    ABSTRACT: One-dimensional nanostructures, such as nanowhisker, nanorod, nanowire, nanopillar, nanocone, nanotip, nanoneedle, have attracted significant attentions in the past decades owing to their numerous applications in electronics, photonics, energy conversion and storage, and interfacing with biomolecules and living cells. The manufacturing of nanostructured devices relies on either bottom-up approaches such as synthesis or growth process or top-down approaches such as lithography or etching process. Here we report a unique, synchronized, and simultaneous top-down and bottom-up nanofabrication approach called simultaneous plasma enhanced reactive ion synthesis and etching (SPERISE). For the first time the atomic addition and subtraction of nanomaterials are concurrently observed and precisely controlled in a single-step process permitting ultrahigh-throughput, lithography-less, wafer-scale, and room-temperature nanomanufacturing. Rapid low-cost manufacturing of high-density, high-uniformity, light-trapping nanocone arrays was demonstrated on single crystalline and polycrystalline silicon wafers, as well as amorphous silicon thin films. The proposed nanofabrication mechanisms also provide a general guideline to designing new SPERISE methods for other solid-state materials besides silicon.
    ACS Nano 09/2011; 5(10):8002-12. · 12.03 Impact Factor
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    ABSTRACT: We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon nanocones which we call black silver substrate. The black silver substrate with dense and homogeneous nanocone forest structure is fabricated on wafer level with a mass producible nanomanufacturing method. The black silver substrate is able to efficiently trap and convert incident photons into localized plasmons in a broad wavelength range, which permits the enhancement in optical absorption from UV to NIR range by 12 times, the visible fluorescence enhancement of ~30 times and the NIR Raman scattering enhancement factor up to ~108. We show a considerable potential of the black silver substrate in high sensitivity and broadband optical sensing and imaging of chemical and biological molecules.one)
    Proc SPIE 09/2011;
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    ABSTRACT: Molecular probe arrays printed on solid surfaces such as DNA, peptide, and protein microarrays are widely used in chemical and biomedical applications especially genomic and proteomic studies (Pollack et al 1999 Nat. Genet. 23 41-6, Houseman et al 2002 Nat. Biotechnol. 20 270-4, Sauer et al 2005 Nat. Rev. Genet. 6 465-76) as well as surface imaging and spectroscopy (Mori et al 2008 Anal. Biochem. 375 223-31, Liu et al 2006 Nat. Nanotechnol. 1 47-52, Liu 2010 IEEE J. Sel. Top. Quantum Electron. 16 662-71). Unfortunately the printed molecular spots on solid surfaces often suffer low distribution uniformity due to the lingering 'coffee stain' (Deegan et al 1997 Nature 389 827-9) problem of molecular accumulations and blotches, especially around the edge of deposition spots caused by solvent evaporation and convection processes. Here we present, without any surface chemistry modification, a unique solid surface of high-aspect-ratio silver-coated silicon nanocone arrays that allows highly uniform molecular deposition and thus subsequent uniform optical imaging and spectroscopic molecular detection. Both fluorescent Rhodamine dye molecules and unlabeled oligopeptides are printed on the metallic nanocone photonic substrate surface as circular spot arrays. In comparison with the printed results on ordinary glass slides and silver-coated glass slides, not only high printing density but uniform molecular distribution in every deposited spot is achieved. The high-uniformity and repeatability of molecular depositions on the 'coffee stain'-free nanocone surface is confirmed by laser scanning fluorescence imaging and surface enhanced Raman imaging experiments. The physical mechanism for the uniform molecular deposition is attributed to the superhydrophobicity and localized pinned liquid-solid-air interface on the silver-coated silicon nanocone surface. The unique surface properties of the presented nanocone surface enabled high-density, high-uniformity probe spotting beneficial for genomic and proteomic microarrays and surface molecular imaging.
    Nanotechnology 06/2011; 22(24):245710. · 3.84 Impact Factor
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    ABSTRACT: We demonstrate surface plasmon-induced enhancements in optical imaging and spectroscopy on silver coated silicon nanocones which we call black silver. The black silver with dense and homogeneous nanocone forest structure is fabricated with a mass-producible nanomanufacturing method. It can efficiently trap and convert incident photons into localized plasmons in broad wavelength range, permitting the enhancement in optical absorption from ultraviolet to near infrared range by 12 times, the visible fluorescence enhancement of ∼ 30 times and the Raman scattering enhancement factor up to ∼ 108. We show the potential of the black silver in high sensitivity and broadband optical sensing of molecules.
    Applied Physics Letters 06/2011; 98(24). · 3.79 Impact Factor
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    ABSTRACT: Anomalous surface-enhanced Raman scattering (SERS) peaks were identified for liquid sample stored in polypropylene (PP) centrifuge tubes for months. We observed unexpected Raman peaks during experiments with thiamine hydrochloride aqueous solutions stored in PP tubes for 2 months. In order to identify the contaminants, we have performed SERS experiments on deionized (DI) water stored in PP centrifuge tubes for 2 months and compared them with those from fresh DI water sample. We have also carried out ultraviolet (UV) absorption spectra for both fresh and contaminated water. We believe that the water is contaminated because of chemicals leaching from the PP tube. From the gas chromatography-mass spectrometry data, the main contaminants were found to be phthalic acid (PA) and its derivatives. Further SERS and UV absorption experiment for PA correlated well with the anomalous peaks identified earlier. We qualitatively confirmed the identification and quantitatively estimated the concentration of the suspect contaminants as between 1 and 10 µM with both SERS and UV absorption spectroscopy. With UV absorption spectroscopy, we precisely estimated the concentration as 2.1 µM. We have shown that the sample in PP tube can be contaminated by the leaching chemicals upon long-term storage, and suggest SERS and UV absorption spectroscopy as two quick and simple techniques to detect the contamination. Copyright © 2011 John Wiley & Sons, Ltd.
    Journal of Raman Spectroscopy 04/2011; 42(11):1939 - 1944. · 2.68 Impact Factor
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    ABSTRACT: We demonstrated gold-coated polymer surface enhanced Raman scattering (SERS) substrates with a pair of complementary structures--positive and inverted pyramid array structures fabricated by a multiple-step molding and replication process. The uniform SERS enhancement factors over the entire device surface were measured as 7.2×104 for positive pyramid substrates while 1.6×106 for inverted pyramid substrates with Rhodamine 6G as the target analyte. Based on the optical reflection measurement and finite difference time domain simulation result, the enhancement factor difference is attributable to plasmon resonance matching and to SERS ``hot spots'' distribution. With this simple, fast, and versatile complementary molding process, we can produce polymer SERS substrates with extremely low cost, high throughput, and high repeatability.
    Journal of Nanophotonics 01/2011; 5(1):3526-. · 1.64 Impact Factor
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    ABSTRACT: We demonstrate a surface-enhanced Raman scattering (SERS) substrate consisting of a closely spaced metal nanodome array fabricated on flexible plastic film. We used a low-cost, large-area replica molding process to produce a two-dimensional periodic array of cylinders that is subsequently overcoated with SiO(2) and silver thin films to form dome-shaped structures. Finite element modeling was used to investigate the electromagnetic field distribution of the nanodome array structure and the effect of the nanodome separation distance on the electromagnetic field enhancement. The SERS enhancement from the nanodome array substrates was experimentally verified using rhodamine 6G as the analyte. With a separation distance of 17 nm achieved between adjacent domes using a process that is precisely controlled during thin film deposition, a reproducible SERS enhancement factor of 1.37 × 10(8) was demonstrated. The nanoreplica molding process presented in this work allows for simple, low-cost, high-throughput fabrication of uniform nanoscale SERS substrates over large surface areas without the requirement for high resolution lithography or defect-free deposition of spherical microparticle monolayer templates.
    Nanotechnology 10/2010; 21(41):415301. · 3.84 Impact Factor
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    ABSTRACT: Surface enhanced Raman spectroscopy (SERS) has been increasingly utilized as an analytical technique with significant chemical and biological applications (Qian et al 2008 Nat. Biotechnol. 26 83; Fujita et al 2009 J. Biomed. Opt. 14 024038; Chou et al 2008 Nano Lett.8 1729; Culha et al 2003 Anal. Chem. 75 6196; Willets K A 2009 Anal. Bioanal. Chem. 394 85; Han et al 2009 Anal. Bioanal. Chem. 394 1719; Sha et al 2008 J. Am. Chem. Soc. 130 17214). However, production of a robust, homogeneous and large-area SERS substrate with the same ultrahigh sensitivity and reproducibility still remains an important issue. Here, we describe a large-area ultrahigh-uniformity tapered silver nanopillar array made by laser interference lithography on the entire surface of a 6 inch wafer. Also presented is the rigorous optical characterization method of the tapered nanopillar substrate to accurately quantify the Raman enhancement factor, uniformity and repeatability. An average homogeneous enhancement factor of close to 10(8) was obtained for benzenethiol adsorbed on a silver-coated nanopillar substrate.
    Nanotechnology 10/2010; 21(39):395701. · 3.84 Impact Factor
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    ABSTRACT: Nanocone structures were fabricated by a unique etching-passivation process as the substrates for Surface Enhanced Raman Spectroscopy (SERS). This novel nanostructured SERS substrate allowed reaching unprecedented detection limits (fM of Rhodamin6G; pM of crude peptides), and supported the detection of subtle changes in peptide probe sequences, such as single amino acid phosphosphorylation or mutation. Thus, surface-conjugated peptides could be used as highly potent biological nano-sensors for sensitive profiling of specific protein mediated chemical changes on nano-sensing probes. We hope such kinase-enzyme activity screening array device and technol ogy will advance all aspects of Life Sciences, and potentially be applied to environment monitoring.
    01/2010;
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    ABSTRACT: We demonstrate a surface-enhanced Raman scattering substrate consisting of a closely spaced metal nanodome array fabricated on flexible plastic film. We used a low cost, large area replica molding process to produce a 2-dimensional periodic array of cylinders that is subsequently overcoated with SiO2 and silver thin films to form dome-shaped structures. Finite element modeling was used to investigate the electromagnetic field distribution of the nanodome array structure and the effect of the nanodome separation distance on the electromagnetic field enhancement. The SERS enhancement from the nanodome array substrates was experimentally verified using rhodamine 6G as the analyte. With a separation distance of 17 nm achieved between adjacent domes using a process that is precisely controlled during thin film deposition, a reproducible SERS enhancement factor of 1.37 × 108 was demonstrated. The nanoreplica molding process presented in this work allows for simple, low cost, high-throughput fabrication of uniform nanoscale SERS substrates over large surface areas without the requirement for high resolution lithography or defect-free deposition of spherical microparticle monolayer templates.
    Sensors, 2010 IEEE; 01/2010
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    ABSTRACT: The performance of infrared (IR) sensing bimaterial cantilevers depends upon the thermal, mechanical and optical properties of the cantilever materials. This paper presents bimaterial cantilevers that have a layer of black silicon nanocone arrays, which has larger optical absorbance and mechanical compliance than single crystal silicon. The black silicon consists of nanometer-scale silicon cones of height 104–336 nm, fabricated using a three-step O2–CHF3–Ar + Cl2 plasma process. The average cantilever absorbance was 0.16 over the 3–10 μm wavelength region, measured using a Fourier transform infrared (FTIR) microspectrometer. The measured cantilever responsivity to incident IR light compares well to a model of cantilever behavior that relate the spectral absorbance, heat transfer, and thermal expansion. The model also provides further insights into the influence of the nanocone height on the absorbance and responsivity of the cantilever. Compared to a cantilever with smooth single crystal silicon, the cantilever with black silicon has about 2× increased responsivity. The nanocone array fabrication technique for silicon bimaterial cantilevers presented here could be applied to other IR sensors.
    Sensors and Actuators A: Physical. 199:143–148.

Publication Stats

55 Citations
50.91 Total Impact Points

Institutions

  • 2010–2014
    • University of Illinois, Urbana-Champaign
      • Department of Electrical and Computer Engineering
      Urbana, Illinois, United States
  • 2011
    • Lawrence Berkeley National Laboratory
      • Life Sciences Division
      Berkeley, California, United States