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Enhancing the graphene photocurrent using surface plasmons and a p-n junction

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Light(Science & Applications) 2020年第1期9卷 793-802页

作者： Di Wang Andres E.Llacsahuanga Allcca Ting-Fung Chung Alexander V.Kildishev Yong P.Chen Alexandra Boltasseva Vladimir M.Shalaev School of Electrical and Computer Engineering Purdue UniversityWest LafayetteIN 47907USA Birck Nanotechnology Center Purdue UniversityWest LafayetteIN 47907USA Department of Physics and Astronomy Purdue UniversityWest LafayetteIN 47907USA Purdue Quantum Science and Engineering Institute(PQSEI) Purdue UniversityWest LafayetteIN 47907USA

The recently proposed concept of graphene photodetectors offers remarkable properties such as unprecedented compactness,ultrabroadband detection,and an ultrafast response ***,owing to the low optical absorption of pristine monolayer graphene,the intrinsically low responsivity of graphene photodetectors significantly hinders the development of practical *** address this issue,numerous efforts have thus far been made to enhance the light–graphene interaction using plasmonic *** approaches,however,can be significantly advanced by leveraging the other critical aspect of graphene photoresponsivity enhancement-electrical junction *** has been reported that the dominant photocarrier generation mechanism in graphene is the photothermoelectric(PTE)***,the two energy conversion mechanisms involved in the graphene photodetection process are light-to-heat and heat-to-electricity *** this work,we propose a meticulously designed device architecture to simultaneously enhance the two conversion ***,a gap plasmon structure is used to absorb a major portion of the incident light to induce localized heating,and a pair of split gates is used to produce a p-n junction in graphene to augment the PTE current *** gap plasmon structure and the split gates are designed to share common key components so that the proposed device architecture concurrently realizes both optical and electrical *** experimentally demonstrate the dominance of the PTE effect in graphene photocurrent generation and observe a 25-fold increase in the generated photocurrent compared to the un-enhanced *** further photocurrent enhancement can be achieved by applying a DC bias,the proposed device concept shows vast potential for practical applications.

关键词： electrical plasmon hinder

Fast and accurate machine learning prediction of phonon scattering rates and lattice thermal conductivity

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npj Computational Materials 2023年第1期9卷 1367-1376页

作者： Ziqi Guo Prabudhya Roy Chowdhury Zherui Han Yixuan Sun Dudong Feng Guang Lin Xiulin Ruan Department of Mechanical Engineering Purdue UniversityWest Lafayette 47907-2088 INUSA The Birck Nanotechnology Center Purdue UniversityWest Lafayette 47907-2088 INUSA Department of Mathematics Purdue UniversityWest Lafayette 47907-2088 INUSA

Lattice thermal conductivity is important for many applications,but experimental measurements or first principles calculations including three-phonon and four-phonon scattering are expensive or even *** learning approaches that can achieve similar accuracy have been a long-standing open *** recent progress,machine learning models using structural information as descriptors fall short of experimental or first principles *** study presents a machine learning approach that predicts phonon scattering rates and thermal conductivity with experimental and first principles *** success of our approach is enabled by mitigating computational challenges associated with the high skewness of phonon scattering rates and their complex contributions to the total thermal *** learning between different orders of phonon scattering can further improve the model *** surrogates offer up to two orders of magnitude acceleration compared to first principles calculations and would enable large-scale thermal transport informatics.

关键词： spite learning principles

Perfluoroalkyl acid transformation and mitigation by nNiFe-activated carbon nanocomposites in steady-state flow column studies

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Journal of Environmental Sciences 2023年第5期127卷 678-687页

作者： Mahsa Modiri-Gharehveran Younjeong Choi Jenny E.Zenobio Linda S.Lee Department of Agronomy Purdue UniversityWest LafayetteIN 47907USA Interdisciplinary Ecological Sciences&Engineering Purdue UniversityWest LafayetteIN 47907USA

The ongoing contamination of groundwater with per-and polyfluoroalkyl substances(PFAS)has resulted in a global and rapidly growing interest in PFAS groundwater *** technologies that lead to PFAS destruction are often limited by not addressing all PFAS,being energy-intensive or not being suited for in-situ *** developed nNiFeactivated carbon(AC)nanocomposites and demonstrated varying degrees of PFAS reduction and fluoride generation with these nanocomposites in batch reactors for several *** we explore nNiFe-AC’s effectiveness to transform perfluoroalkyl acid acids(PFAAs)under steady-state flow(0.0044 to 0.15 mL/min)in nNiFe-AC:sand packed *** experiments included,two perfluorooctane sulfonate(PFOS)in deionized water and two PFAA mixtures in deionized water or bicarbonate buffer containing five perfluoroalkyl carboxylates(PFCAs,C5-C9)and three perfluoroalkyl sulfonates(PFSAs,C4,C6 and C8)at temperatures of 50 or 60℃ were *** transformation was similar in PFOS-only and PFAA mixture column ***,%PFAA transformation under flow conditions exceeded what we observed previously in batch reactors with up to 53%transformation of a PFAA mixture with∼8%*** chain PFAS dominated the PFAAs transformed and a bicarbonate matrix appeared to reduce overall *** breakthrough was slower than predicted from only sorption due to transformation;some longer chain PFAS like PFOS did not ***,nNiFe-AC technology with both in-situ and ex-situ potential application was shown to be a plausible part of a treatment train needed to address the ongoing challenge for cleaning up PFAS-contaminated waters.

关键词： PFAAs PFAS Zero valent iron Nanoparticles Remediation Groundwater

Converting Molecular Vibration to Mechanical Wave for Bond-Selective Imaging of Deep Tissue

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Chinese Journal of Chemical Physics 2015年第4期28卷 -页

作者： Jie Hui Ji-xin Cheng Department of Physics and Astronomy Purdue University West Lafayette Indiana 47907 USA Weldon School of Biomedical Engineering Purdue University West Lafayette Indiana 47907 USADepartment of Chemistry Purdue University West Lafayette Indiana 47907 USA

As an emerging label-free imaging modality with chemical selectivity and millimeter-depth resolvability, vibrational photoacoustic imaging provides a new avenue to map chemical content in biological tissue. It heralds the potential for detection of white matter loss and regeneration, assessment of breast tumor margin, and clinical diagnosis of vulnerable plaques in atherosclerosis. In this work, we provide an overview of the development of bond-selective photoacoustic imaging and various biomedical applications enabled by this new technology.

关键词： Label-free Vibrational spectroscopy Chemical imaging

Achieving large transport bandgaps in bilayer graphene

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Nano Research 2015年第10期8卷 3228-3236页

作者： Tao Chu Zhihong Chen SchoolofElectricalandComputerEngineeringandBirckNanotechnologyCenter PurdueUniversityWestLafayetteIN47907USA

Since opening sizable bandgaps in bilayer graphene （BLG） was proven possible, BLG has attracted considerable attention as a promising high-mobility candidate material for many electronic and optoelectronic applications. However, the bandgaps observed in the transport experiments reported in the literature are far smaller than both the theoretical predictions and the bandgaps extracted from optical measurements. In this study, we investigate the factors preventing the formation of large bandgaps and demonstrate that a -200-meV transport bandgap can be opened in BLG by scaling the gate dielectric and employing a ribbon channel to suppress the percolative transport. This is the largest transport bandgap that has been achieved in BLG to date.

关键词： bilayer graphene transport bandgap percolation on/off ratios

Parallel Nanoimprint Forming of One-Dimensional Chiral Semiconductor for Strain-Engineered Optical Properties

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Nano-Micro Letters 2020年第11期12卷 242-254页

作者： Yixiu Wang Shengyu Jin Qingxiao Wang Min Wu Shukai Yao Peilin Liao Moon JKim Gary JCheng Wenzhuo Wu School of Industrial Engineering Purdue UniversityWest LafayetteIN 47907USA Flex Laboratory Purdue UniversityWest LafayetteIN 47907USA Department of Materials Science and Engineering University of Texas at DallasRichardsonTX 75080USA School of Materials Engineering Purdue UniversityWest LafayetteIN 47907USA Birck Nanotechnology Center Purdue UniversityWest LafayetteIN 47907USA Regenstrief Center for Healthcare Engineering Purdue UniversityWest LafayetteIN 47907USA

The low-dimensional,highly anisotropic geometries,and superior mechanical properties of one-dimensional(1D) nanomaterials allow the exquisite strain engineering with a broad tunability inaccessible to bulk or thin-film *** capability enables unprecedented possibilities for probing intriguing physics and materials science in the 1-D *** the techniques for introducing controlled strains in 1D materials,nanoimprinting with embossed substrates attracts increased attention due to its capability to parallelly form nanomaterials into wrinkled structures with controlled periodicities,amplitudes,orientations at large scale with nanoscale ***,we systematically investigated the strain-engineered anisotropic optical properties in Te nanowires through introducing a controlled strain field using a resist-free thermally assisted nanoimprinting *** magnitude of induced strains can be tuned by adjusting the imprinting pressure,the nanowire diameter,and the patterns on the *** observed Raman spectra from the chiral-chain lattice of 1D Te reveal the strong lattice vibration response under the *** results suggest the potential of 1D Te as a promising candidate for flexible electronics,deformable optoelectronics,and wearable *** experimental platform can also enable the exquisite mechanical control in other nanomaterials using substrate-induced,on-demand,and controlled strains.

关键词： Chiral semiconductor Nanowires Nanoimprinting Strain engineering Optical property

Microsecond scale vibrational spectroscopic imaging by multiplex stimulated Raman scattering microscopy

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Light(Science & Applications) 2015年第1期4卷 454-462页

作者： Chien-Sheng Liao Mikhail N Slipchenko Ping Wang Junjie Li Seung-Young Lee Robert A Oglesbee Ji-Xin Cheng Weldon School of Biomedical Engineering Purdue UniversityWest LafayetteIN 47907USA Department of Biological Sciences Purdue UniversityWest LafayetteIN 47907USA Department of Chemistry Purdue UniversityWest LafayetteIN 47907USA

Real-time vibrational spectroscopic imaging is desired for monitoring cellular states and cellular processes in a label-free *** spectroscopic imaging of highly dynamic systems is inhibited by relatively slow spectral acquisition on millisecond to second ***,we report microsecond scale vibrational spectroscopic imaging by lock-in free parallel detection of spectrally dispersed stimulated Raman scattering *** a homebuilt tuned amplifier array,our method enables Raman spectral acquisition,within the window defined by the broadband pulse,at the speed of 32 μs and with close to shot-noise limited detection *** with multivariate curve resolution analysis,our platform allows compositional mapping of lipid droplets in single live cells,observation of intracellular retinoid metabolism,discrimination of fat droplets from protein-rich organelles in Caenorhabditis elegans,spectral detection of fast flowing tumor cells and monitoring drug diffusion through skin tissue in *** reported technique opens new opportunities for compositional analysis of cellular compartment in a microscope setting and high-throughput spectral profiling of single cells in a flow cytometer setting.

关键词： optical microscopy Raman scattering vibrational spectroscopy

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Chilling stress drives organ-specific transcriptional cascades and dampens diurnal oscillation in tomato

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Horticulture Research 2023年第8期10卷 241-253页

作者： Tina Agarwal Xiaojin Wang Frederick Mildenhall Iskander MIbrahim Sujith Puthiyaveetil Kranthi Varala Department of Horticulture and Landscape Architecture Purdue UniversityWest LafayetteIN 47907USA Purdue Center for Plant Biology Purdue UniversityWest LafayetteIN 47907USA Department of Biochemistry Purdue UniversityWest LafayetteIN 47907USA

Improving chilling tolerance in cold-sensitive crops,***,requires knowledge of the early molecular response to low temperature in these under-studied *** elucidate early responding processes and regulators,we captured the transcriptional response at 30 minutes and 3 hours in the shoots and at 3 hours in the roots of tomato post-chilling from 24℃ to 4℃.We used a pre-treatment control and a concurrent ambient temperature control to reveal that majority of the differential expression between cold and ambient conditions is due to severely compressed oscillation of a large set of diurnally regulated genes in both the shoots and *** compression happens within 30 minutes of chilling,lasts for the duration of cold treatment,and is relieved within 3 hours of return to ambient *** study also shows that the canonical ICE1/CAMTA-to-CBF cold response pathway is active in the shoots,but not in the *** stress induces synthesis of known cryoprotectants(trehalose and polyamines),in a CBF-independent manner,and induction of multiple genes encoding proteins of photosystems I and *** study provides nuanced insights into the organ-specific response in a chilling sensitive plant,as well as the genes influenced by an interaction of chilling response and the circadian clock.

关键词： oscillation roots ambient

A mass-customizable dermal patch with discrete colorimetric indicators for personalized sweat rate quantification

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Microsystems & Nanoengineering 2019年第1期5卷 406-417页

作者： Vaibhav Jain Manuel Ochoa Hongjie Jiang Rahim Rahimi Babak Ziaie School of Mechanical Engineering Purdue UniversityWest LafayetteIN 47907USA School of Electrical and Computer Engineering Purdue UniversityWest LafayetteIN 47907USA Birck Nanotechnology Center Purdue UniversityWest LafayetteIN 47907USA

In this paper,we present a disposable,colorimetric,user-friendly and mass-customizable dermal patch for chronological collection and discrete real-time in situ measurement of sweat secretion over a small area of *** patch consists of a laminated filter paper patterned into radially arranged channels/fingers with water-activated dyes at their *** channels are filled during perspiration,their tips change color once fully saturated,providing easily identifiable levels of water loss which in turn can be mapped to personal dehydration *** patch can be manufactured at low cost in a variety of sizes to allow hydration monitoring for individuals participating in activities under different conditions(intensity,temperature,humidity,etc.).Furthermore,we describe an analytical model that enables mass customization of such a flexible wearable system accommodating a broad range of sweat rates and volumes to generate patch designs that are personalized to an individual’s sweat rate,desired time of usage,and the temporal resolution of the required *** a proof-of-concept demonstration,we characterized laser-fabricated patches that cover(7 cm×5 cm)area of skin having various wicking materials,thicknesses(180–540μm),and pore sizes(3–11μm).Tests were conducted at various flow rates simulating different sweating intensities in the range of 1.5–15 mg/cm^(2)/*** results for the case of a half-marathon runner targeting 90 min of usage and sweating at a rate of 1.5 mg/cm2/min indicated measurement accuracy of 98.3%when the patch is completely filled.

关键词： patch sizes filled