Laurene Tetard

University of Central Florida, Orlando, Florida, United States

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Publications (48)243.61 Total impact

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    ABSTRACT: This paper describes a simple method to develop a high Voc low band gap PSCs. In addition, we introduce two new AFM-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer. With the help of ternary solvent processing of the active layer and C60 buffer layer, we develop a bulk heterojunction PSC with Voc more than 0.9V and conversion efficiency 7.5%. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFM (MSAFM) are introduced to study the morphology and physical properties of the structures constitutive of the active layers of the PSCs. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor-acceptor phases in the active layer of the PSCs. Finally, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a superior increase in photocurrent measured in the PTB7/ICBA sample obtained with the ternary solvent processing.
    No preview · Article · Jan 2016 · ACS Applied Materials & Interfaces
  • L Tetard · A Passian · R H Farahi · T Thundat · B H Davison
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    ABSTRACT: The non-destructive, simultaneous chemical and physical characterization of materials at the nanoscale is an essential and highly sought-after capability. However, a combination of limitations imposed by Abbe diffraction, diffuse scattering, unknown subsurface, electromagnetic fluctuations and Brownian noise, for example, have made achieving this goal challenging. Here, we report a hybrid approach for nanoscale material characterization based on generalized nanomechanical force microscopy in conjunction with infrared photoacoustic spectroscopy. As an application, we tackle the outstanding problem of spatially and spectrally resolving plant cell walls. Nanoscale characterization of plant cell walls and the effect of complex phenotype treatments on biomass are challenging but necessary in the search for sustainable and renewable bioenergy. We present results that reveal both the morphological and compositional substructures of the cell walls. The measured biomolecular traits are in agreement with the lower-resolution chemical maps obtained with infrared and confocal Raman micro-spectroscopies of the same samples. These results should prove relevant in other fields such as cancer research, nanotoxicity, and energy storage and production, where morphological, chemical and subsurface studies of nanocomposites, nanoparticle uptake by cells and nanoscale quality control are in demand.
    No preview · Article · Aug 2015 · Nature Nanotechnology
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    ABSTRACT: Cerium oxide (ceria) nanoparticles (CNPs) were synthesized in poly(ethylene glycol)s (PEGs) of different molecular weights (MWs; 300, 600, 1500, 3000, 4000, and 6000 Da) with water as a cosolvent, and changes in physicochemical properties, especially morphology and size, were monitored as a function of time. High-resolution transmission electron microscopy (HRTEM) was performed for all solutions and revealed octahedral, star morphologies for CNPs coated with 1500 MW PEG. Raman and FTIR spectroscopy, HRTEM images, conductivity, and electrophoretic mobility imply the self-assembly of small spherical particles to octahedral, star-shaped particles by means of a fractal assembly method. Dynamic light scattering measures were used to create an empirical growth model of the observed octahedral self-assembly. It was also determined that PEG polymer chain lengths and age-dependent redox activities of CNPs limit or allow this assembly owing to molecular-weight-dependent physicochemical properties. This study highlights the significance of ageing on solution-based nanoparticles and its implications in the use of nanoparticles over long periods of time. As PEG-ylated nanoparticles have found extensive use in biomedical applications, we have tested the aged particles in vitro for toxicity.
    No preview · Article · Jul 2015 · ChemPlusChem
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    Zenan Yu · Laurene Tetard · Lei Zhai · Jayan Thomas
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    ABSTRACT: Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.
    Full-text · Article · Mar 2015 · Energy & Environmental Science
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    ABSTRACT: Anthropogenic nanomaterials (ANMs), once produced, will inevitably be present in the environment. Depending on their environmental stability and level of toxicity, ANMs raise some concern regarding their potential impact on the surrounding animal, aquatic and plant life. In this study, we demonstrate for the first time the effect of ultra-small size (< 5 nm) semiconductor ANMs on the germination and growth of seeds of Snow Peas model plant system (Pisum sativum) using a N-Acetyl Cysteine (NAC) coated core-shell CdS:Mn/ZnS Qdots as a heavy metal ion containing model ANM. We present combined results of fluorescence confocal, Atomic Force Microscopy (AFM) and Raman imaging of Quantum dot (Qdot) to track the uptake and localization (translocation) in plant tissue. It was found that Qdots were localized on the surface seed coat, epidermis and intercellular regions. Germination, growth and chlorophyll content of the seedlings were found to be strongly dependent on Qdot dosage and time of seed incubation with Qdots. Interestingly, no acute Cd metal toxicity was observed while at Qdot concentration below 40 μg/mL, and seed germination and growth processes were promoted.
    Preview · Article · Feb 2015
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    ABSTRACT: Outstanding challenges in nanoscale characterization call for non-invasive, yet sensitive subsurface characterization of low-density materials such as polymers. In this work, we present new evidence that Mode Synthesizing Atomic Force Microscopy can be tuned to detect minute changes in low-density materials such as the ones engendered in an electro-sensitive polymer during electron beamlithography,surpassingallcommonnanoscalemechanicaltechniques. Moreover we propose a 3D reconstruction of the exposed polymer regions using successive high-resolution frames acquired at incremental depth inside the sample. In addition, the results clearly show the influence of increasing dwell time on the depth profile of the nano-sized exposed regions. Hence the simple approach described here can be considered an unprecedented capability for sensitive nanoscale tomography of soft materials with promising applications in material sciences, and biology.
    Full-text · Article · Jan 2015 · Nano Research
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    ABSTRACT: Semiconductor fluorescent quantum dots (Qdots) are popularly used as bioimaging taggants in live cell imaging and spectroscopy. In recent years, Qdots taggants are emerging in agricultural applications. Studies are primarily focused on nanotoxicity of ultra-small size water-soluble Qdots in plant systems. Nanotoxicity is correlated with Qdot core composition and surface coating. However, Qdots with certain chemical composition and surface coating may boost plant growth. In this study, we report that N-acetyl cysteine (NAC) capped ∼3.5 nm size ZnS:Mn/ZnS Qdots (NAC-Qdot) are efficiently uptaken by the snow pea ( Pisum sativum L., a model plant ) vascular system, enhancing the root growth at a dose level of 80 μg/mL. Fluorescence microscopy studies confirmed localization of NAC-Qdots in the intercellular regions. Germination and growth of the snow pea seeds were found to be strongly dependent on Qdot dosage and incubation time with Qdots. Seed germination reached 100% within 48 hours of NAC-Qdot exposure. Based on our preliminary findings, it is suggested that NAC-Qdot can be used as systemic plant nutrient material for boosting the seed germination and plant growth.
    No preview · Article · Jan 2015 · MRS Online Proceeding Library
  • Panit Chantharasupawong · Laurene Tetard · Jayan Thomas
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    ABSTRACT: Advances in active manipulation of light at the nanoscale are rapidly emerging with the concept of plexcitonic coupling at the interface between plasmonics nanostructures and excitonic molecules. In this work, we devise a simple fabrication scheme to produce and optimize large area tunable plasmonic substrates for strong plasmon-exciton interactions. By tuning the diameter of the nanoholes using a simple plasma etching process, we demonstrate the potential of our approach to deliver tunable plasmonic substrates. Thus, large enhancements of fluorescence and Raman scattering could be measured. Moreover, hybridized states appearing in the presence of excitonic molecules (RG6) give rise to anticrossing behaviors in extinction spectroscopy, a phenomenon also known as Rabi-splitting. The results demonstrate the great potential of our large nanofabricated arrays as plexcitonic substrates for numerous applications, including sensors, light harvesters, and all-optical switches.
    No preview · Article · Oct 2014 · The Journal of Physical Chemistry C
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    ABSTRACT: We report, for the first time, a one-step hydrothermal (HT) process to design and synthesize water-dispersible chitosan nanoparticles loaded with mixed valence copper. Interestingly, this HT copper-chitosan biocompatible composite exhibits exception-ally high antimicrobial properties. A comprehensive characterization of the composite indicates that the hydrothermal process results in the formation of monodispersed nanoparticles with average size of 40 ± 10 nm. FT-IR and Raman spectroscopic studies unveiled that the hydrolysis of the glycoside bonds as the origin of the depolymerization of chitosan. Furthermore, X-Ray Photoelectron Spectroscopy measurements confirmed the presence of mixed valence copper states in the composite, while UV– Vis and FT-IR studies revealed the chemical interac-tion of copper with the chitosan matrix. Hence, the extensive spectroscopic data provide strong evidence that the chitosan structure was rearranged to capture copper oxide nanoparticles. Finally, HT copper-chitosan composite showed a complete killing effect when tested against both Gram negative (E. coli) and Gram positive (S. aureus) bacteria at metallic copper concentration of 100 lg/ml (1.57 mM). At the same concentration, neither pure chitosan nor copper elic-ited such antimicrobial efficacy. Thus, we show that HT process significantly enhances the synergistic antimicrobial effect of chitosan and copper in addition to increasing the water dispersibility. Srijita Basumallick and Parthiban Rajasekaran have equally contributed to this work.
    Full-text · Article · Oct 2014 · Journal of Nanoparticle Research
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    Full-text · Dataset · Sep 2014
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    Full-text · Dataset · Sep 2014
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    ABSTRACT: This paper reports on advances toward quantitative non-destructive nanoscale subsurface investigation of a nanofabricated sample based on mode synthesizing atomic force microscopy with heterodyne detection, addressing the need to correlate the role of actuation frequencies of the probe fp and the sample fs with depth resolution for 3D tomography reconstruction. Here, by developing a simple model and validating the approach experimentally through the study of the nanofabricated calibration depth samples consisting of buried metallic patterns, we demonstrate avenues for quantitative nanoscale subsurface imaging. Our findings enable the reconstruction of the sample depth profile and allow high fidelity resolution of the buried nanostructures. Non-destructive quantitative nanoscale subsurface imaging offers great promise in the study of the structures and properties of complex systems at the nanoscale.
    No preview · Article · Aug 2014 · Applied Physics Letters
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    ABSTRACT: Photorefractive polymer composites have gained considerable attention due to their fascinating applications like 3D displays and 3D Telepresence. In this report, the performance of a novel PR polymer composite doped with graphene is studied. The addition of graphene laminates to a photorefractive composite results in up to threefold enhancement of space charge (SC) field build-up time. From our optical and electrical measurements, the faster build-up time is attributed to larger charge generation resulting from electronic interaction between graphene and the 7-DCST chromophores.
    Preview · Article · Jul 2014
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    ABSTRACT: We present a new approach to develop highly ordered magnetite (Fe3O4) nanoparticle-patterned nanohole arrays with desirable magnetic properties for a variety of technological applications. In this work, the sub-100 nm nanohole arrays have been successfully fabricated from a pre-ceramic polymer mold using spin-on nanoprinting (SNAP). These nanoholes were then filled with monodispersed, spherical Fe3O4 nanoparticles of about 10 nm diameter using a novel magnetic drag and drop procedure. The nanohole arrays filled with magnetic nanoparticles were imaged using magnetic force microscopy (MFM). Magnetometry and MFM measurements revealed room temperature ferromagnetism in the Fe3O4-filled nanohole arrays, while the as-synthesized Fe3O4 nanoparticles exhibited superparamagnetic behavior. As revealed by MFM measurements, the enhanced magnetism in the Fe3O4-filled nanohole arrays originated mainly from the enhanced magnetic dipole interactions of Fe3O4 nanoparticles within the nanoholes and between adjacent nanoholes. Nanoparticle filled nanohole arrays can be highly beneficial in magnetic data storage and other applications such as microwave devices and biosensor arrays that require tunable and anisotropic magnetic properties.
    Full-text · Article · Jul 2014 · Small
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    ABSTRACT: A simple, but efficient drag and drop method to fill highly ordered sub‐100 nm nanoholes with monodispersed 10 nm Fe3O4 nanoparticles is demonstrated by M.‐H. Phan, J. Thomas, and colleagues on page 2840. Magnetization and magnetic force microscopy results confirm the magnetism enhancement in these Fe3O4‐filled nanohole arrays compared to the as‐synthesized nanoparticles. Nanoparticle‐filled nanohole arrays can be highly beneficial for a variety of applications including magnetic data storage and biosensing.
    Full-text · Article · Jul 2014 · Small
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    ABSTRACT: Among the enduring challenges in nanoscience, subsurface characterization of living cells holds major stakes. Developments in nanometrology for soft matter thriving on the sensitivity and high resolution benefits of atomic force microscopy have enabled detection of subsurface structures at the nanoscale. However, measurements in liquid environments remain complex, in particular in the subsurface domain. Here we introduce liquid-mode synthesizing atomic force microscopy (l-MSAFM) to study both the inner structures and the chemically induced intracellular impairments of living cells. Specifically, we visualize the intracellular stress effects of glyphosate on living keratinocytes skin cells. This new approach, l-MSAFM, for nanoscale imaging of living cell in their physiological environment or in presence of a chemical stress agent could resolve the loss of inner structures induced by glyphosate, the main component of a well-known pesticide (RoundUp™). This firsthand ability to monitor the cell's inner response to external stimuli non-destructively and in liquid, has the potential to unveil critical nanoscale mechanisms of life science.
    Full-text · Article · Jul 2014 · Nanotechnology
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    ABSTRACT: We demonstrate that the photoluminescence (PL) of single-layer molybdenum disulfide (MoS2) can be significantly tuned by controlled exposure to oxygen plasma. With the variation of the plasma exposure time, the PL changes from a very high intensity to complete quenching accompanied by clear changes in Raman spectra where gradual reduction of MoS2 peaks were observed along with the appearance of new MoO3 peaks. Using band structure calculations, we show that the creation of MoO3 disordered domains upon exposure to oxygen plasma leads to a direct to indirect bandgap transition in single-layer MoS2 resulting in PL quenching.
    Preview · Article · May 2014
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    ABSTRACT: We demonstrate that the photoluminescence (PL) of single-layer molybdenum disulfide (MoS2) can be significantly tuned by controlled exposure to oxygen plasma. With the variation of the plasma exposure time, the PL changes from a very high intensity to complete quenching accompanied by clear changes in Raman spectra where gradual reduction of MoS2 peaks were observed along with the appearance of new MoO3 peaks. Using band structure calculations, we show that the creation of MoO3 disordered domains upon exposure to oxygen plasma leads to a direct to indirect bandgap transition in single-layer MoS2 resulting in PL quenching.
    Preview · Article · Apr 2014 · The Journal of Physical Chemistry C
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    ABSTRACT: Achieving tunability of two dimensional (2D) transition metal dichalcogenides (TMDs) functions calls for the introduction of hybrid 2D materials by means of localized interactions with zero dimensional (0D) materials. A metal-semiconductor interface, as in gold (Au) - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science as it constitutes an outstanding platform to investigate plasmonic-exciton interactions and charge transfer. The applied aspects of such systems introduce new options for electronics, photovoltaics, detectors, gas sensing, catalysis, and biosensing. Here we consider pristine MoS2 and study its interaction with Au nanoislands, resulting in local variations of photoluminescence (PL) associated with various Au-MoS2 hybrid configurations. By controllably depositing monolayers of Au on MoS2 to form Au nanostructures of given size and thickness, we investigate the electronic structure of the resulting hybrid systems. We present strong evidence of PL quenching of MoS2 as a result of charge transfer from MoS2 to Au: p-doping of MoS2. The results suggest new avenues for 2D nanoelectronics, active control of transport or catalytic properties.
    Full-text · Article · Apr 2014 · Scientific Reports
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    ABSTRACT: We demonstrate that the electrical property of a single layer molybdenum disulfide (MoS2) can be significantly tuned from semiconducting to insulating regime via controlled exposure to oxygen plasma. The mobility, on-current and resistance of single layer MoS2 devices were varied up to four orders of magnitude by controlling the plasma exposure time. Raman spectroscopy, X-ray photoelectron spectroscopy and density functional theory studies suggest that the significant variation of electronic properties is caused by the creation of insulating MoO3-rich disordered domains in the MoS2 sheet upon oxygen plasma exposure, leading to an exponential variation of resistance and mobility as a function of plasma exposure time. The resistance variation calculated using an effective medium model is in excellent agreement with the measurements. The simple approach described here can be used for the fabrication of tunable two dimensional nanodevices on MoS2 and other transition metal dichalcogenides.
    Full-text · Article · Apr 2014 · Nanoscale

Publication Stats

405 Citations
243.61 Total Impact Points

Institutions

  • 2014-2015
    • University of Central Florida
      • Department of Chemistry
      Orlando, Florida, United States
    • Université de Reims Champagne-Ardenne
      Rheims, Champagne-Ardenne, France
  • 2011-2015
    • Oak Ridge National Laboratory
      • Biosciences Division
      Oak Ridge, Florida, United States
  • 2008-2012
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States