Co-reporter:David Magginetti, Kun Tian, Ashutosh Tiwari
Solid State Communications 2017 Volume 249() pp:34-37
Publication Date(Web):January 2017
DOI:10.1016/j.ssc.2016.10.011
•β-Tantalum shows greatly improved spin Hall effect (SHE) as compared to platinum.•Spin Seebeck effect using β-Ta/YIG structure is reported down to 4 K.•Negative sign of SHE in β-Ta makes it promising for use in energy harvesting.Development of thermoelectric energy harvesting devices has hit a stumbling block due to the intrinsically linked electrical and thermal conductivities of materials. However, this field can still be improved by employing devices that take advantage of spin-based effects. A temperature gradient can be converted to a spin-polarized current in a ferrimagnetic insulator by the spin Seebeck effect (SSE), and that spin current can be converted to an electrical voltage in a heavy metal by the Inverse spin Hall effect (ISHE). Thus, the thermal energy capture and charge production steps can be separated into two distinct regions of the thermoelectric device, allowing separate tuning of electrical and thermal conductivities. The second step of this process, spin current to electrical voltage conversion, is controlled by the strength and sign of ISHE in the metal, and platinum has become the standard for this purpose. However, here we report a better candidate, β-Tantalum, which shows a spin Seebeck voltage approximately 4 times higher than that of Pt at room temperature. The temperature dependence of spin Seebeck in YIG/β-Ta also closely follows that of YIG/Pt, consistent with magnon spin current theory. The sign of the spin Seebeck voltage in Ta found to be opposite to that of Pt, making the two materials highly complementary for fabricating spintronics-based thermoelectric modules for practical applications.
Co-reporter:Haritha Sree Yaddanapudi, Nathan Hickerson, Shrikant Saini, Ashutosh Tiwari
Vacuum 2017 Volume 146(Volume 146) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.vacuum.2017.01.016
•Transparent wood for smart building applications.•Simple and economical approach to fabricate transparent wood.•Biodegradable approach.•70% of transmission and about 49% haze for practical applications.•Enhanced mechanical properties for practical applications.A major fraction of the electricity that is generated in the world is used in the building sector, particularly as a source of light. One way to reduce the consumption of electricity in buildings is by utilizing natural light with the help of environmentally friendly resources such as transparent wood. Removing the lignin from wood followed by impregnating environmentally friendly polymers whose refractive index matches the refractive index of the cell wall helps in obtaining transparent wood. Hence, herewith we report a simple and low-cost method of fabricating transparent wood from beech wood (Fagus grandifolia) while retaining its 3-dimensional structure. The surface morphology of the synthesized transparent wood was studied by using scanning electron microscopy. Brunauer Emmet Teller measurements were carried out to determine the specific surface area. FTIR measurements were performed to study the wood chemistry. Optical measurements showed a maximum optical transmittance of 70% and a maximum haze of 49% for 0.1 mm and 0.7 mm thick wood samples, respectively. Mechanical testing showed that the transparent wood has a higher tensile strength and hardness when compared to the delignified wood. The fabricated transparent wood with high transmittance and enhanced mechanical properties is a potential candidate material for light transmitting building materials and transparent solar cell windows.
Co-reporter:Kun Tian, Gene Siegel, Ashutosh Tiwari
Materials Science and Engineering: C 2017 Volume 71() pp:195-199
Publication Date(Web):1 February 2017
DOI:10.1016/j.msec.2016.10.006
•A simple colorimetric method for detection of Hg2 + in water was proposed.•Au nanoparticles and 2,6-pyridinedicarboxylic acid were used for sensing Hg2 +.•Sensing mechanisms were demonstrated by TEM and UV–Visible measurements.•It showed the solution color changes from red to blue upon addition of Hg2 +.•The method selectively detected Hg2 + among seventeen different metal ions.The development of simple and cost-effective methods for the detection and treatment of Hg2 + in the environment is an important area of research due to the serious health risk that Hg2 + poses to humans. Colorimetric sensing based on the induced aggregation of nanoparticles is of great interest since it offers a low cost, simple, and relatively rapid procedure, making it perfect for on-site analysis. Herein we report the development of a simple colorimetric sensor for the selective detection and estimation of mercury ions in water, based on chitosan stabilized gold nanoparticles (AuNPs) and 2,6-pyridinedicarboxylic acid (PDA). In the presence of Hg2 +, PDA induces the aggregation of AuNPs, causing the solution to change colors varying from red to blue, depending on the concentration of Hg2 +. The formation of aggregated AuNPs in the presence of Hg2 + was confirmed using transmission electron microscopy (TEM) and UV–Vis spectroscopy. The method exhibits linearity in the range of 300 nM to 5 μM and shows excellent selectivity towards Hg2 + among seventeen different metal ions and was successfully applied for the detection of Hg2 + in spiked river water samples. The developed technique is simple and superior to the existing techniques in that it allows detection of Hg2 + using the naked eye and simple and rapid colorimetric analysis, which eliminates the need for sophisticated instruments and sample preparation methods.
Co-reporter:Kun Tian, Bharati Tudu, Ashutosh Tiwari
Vacuum 2017 Volume 146(Volume 146) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.vacuum.2017.01.018
•ZnO thin films were deposited on polymer substrates by pulsed laser deposition.•Film qualities were characterized by XRD, AFM, EDAX, and UV-Visible measurements.•Resistivity measurements were performed over temperature range from 10 K to 300 K.•ZnO films on polymer substrates showed fast photo-response to UV-light.The emerging technological demand of light weight, transparent and flexible electronic devices has raised the exploration of new semiconductor materials beyond silicon. ZnO has the potential to be integrated into flexible electronics matrix due to its excellent electrical and optical properties. Here, we have fabricated ZnO thin films on flexible polymer substrates, polyimide (Kapton) and polyethylene naphthalate (PEN), at room temperature and at 100 °C using PLD. These films grew along (002) axis of the hexagonal wurtzite lattice and show n-type semiconducting nature. Crystallinity of films on Kapton is better than that on PEN. Films grown at 100 °C show improved optical transmittance and lower thermal activation energy. Film deposited on Kapton at 100 °C shows highest Hall mobility and lowest resistivity values. UV photoconductivity measurements show good opto-electronic properties for these films. Films on Kapton show higher photocurrent value and faster response and decay time (∼1 s). Seebeck coefficient measurement shows higher thermopower values of 82 μV/K for films on PEN. These characteristics make the low temperature pulse laser deposited ZnO films on Kapton and PEN attracting for electronic devices with various opto- and thermo-electrical applications.
Co-reporter:Yinong Yin, Bharati Tudu, Ashutosh Tiwari
Vacuum 2017 Volume 146(Volume 146) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.vacuum.2017.04.015
•Oxide materials are potential candidates for high-temperature thermoelectric applications.•Notable progress on oxide thermoelectrics has been made.•p-type (Ca3Co4O9) and n-type (SrTiO3, ZnO, and CaMnO3) thermoelectric materials are discussed.•Novel fabrication approaches can effectively improve their thermoelectric properties.•High power oxide thermoelectric modules can be fabricated.Due to the growing concern on depletion of non-renewable resources, waste heat harvesting has become one of the effective approaches for solving the energy shortage issue. Oxide thermoelectric materials have the advantages of low cost, environment-friendly manufacturing and chemical stability at high temperatures. However, compared to traditional thermoelectric materials, they exhibit only modest thermoelectric properties due to their low electrical- and high thermal conductivity. Numerous studies have been done to improve their thermoelectric response by doping. These oxide materials mainly include the p-type Ca3Co4O9 and n-type ZnO, SrTiO3, and CaMnO3. By connecting these both types of thermoelectric oxides in series, a module which is capable of generating considerable power can be obtained. In this review, we present the progress made on p-type and n-type thermoelectric oxides in recent years. We discuss the electronic structure of these oxides as it plays an important role in determining the thermoelectric properties. We also discuss the advanced modules which have been fabricated using these thermoelectric oxide couples.
Co-reporter:Bharati Tudu, Ashutosh Tiwari
Vacuum 2017 Volume 146(Volume 146) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.vacuum.2017.01.031
•Materials with perpendicular magnetic anisotropy are superior for data storage applications.•Perpendicular spin transfer torque driven MRAM is the future of RAM.•Higher TMR, thermal stability, lower writing current, etc. are key parameters for perpendicular MRAM.•Different families of perpendicular magnetization materials have been developed.•New fabrication approaches and detailed studies are needed.The incessant demand for higher density, faster access time and lower power consuming memory devices such as random access memories have driven tremendous research and development of materials with out-of-plane magnetization. Magnetic materials with strong out-of-plane magnetization, i.e. perpendicular magnetic anisotropy (PMA), offer superior qualities compared to the in-plane anisotropy materials for hard disk drive and magnetoresistive random access memory (MRAM) devices and have been successfully commercialized in the last decade. With the recent demonstration of spin-transfer torque (STT) magnetic switching, an urge for new materials has emerged for promising STT-MRAM applications. Here, we present a brief overview of PMA materials for two important data storage applications: perpendicular recording and MRAM. We review the various PMA materials developed in recent years for STT-MRAM applications. We discuss the major requirements, challenges and future prospects of these materials for future STT-MRAM devices.
Co-reporter:Y. P. Venkata Subbaiah;K. J. Saji ;A. Tiwari
Advanced Functional Materials 2016 Volume 26( Issue 13) pp:2046-2069
Publication Date(Web):
DOI:10.1002/adfm.201504202
Two-dimensional inorganic materials are emerging as a premiere class of materials for fabricating modern electronic devices. The interest in 2D layered transition metal dichalcogenides is especially high. Particularly, 2D MoS2 is being heavily researched due to its novel functionalities and its suitability for a wide range of electronic and optoelectronic applications. In this article, the progress in mono/few layer(s) MoS2 research is reviewed by focusing primarily on the layer dependent evolution of crystal, phonon, and electronic structure. The review includes extensive detail into the methodologies adapted for single or few layer(s) MoS2 growth. Further, the review covers the versatility of 2D MoS2 for a broad range of device applications. Recent advancements in the field of van der Waals heterostructures are also highlighted at the end of the review.
Co-reporter:Kachirayil J. Saji;Kun Tian;Michael Snure
Advanced Electronic Materials 2016 Volume 2( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/aelm.201500453
2D materials are considered promising candidates for developing next-generation high-performance energy efficient electronic, optoelectronic, and valley-tronic devices. Though metal oxides are widely used in the fabrication of many advanced devices, very little work has been reported on their properties in 2D limit. This article reports the discovery of a new 2D materials system, 2D tin monoxide (SnO). Layer by layer growth of SnO on sapphire and SiO2 substrates is demonstrated using a pulsed laser deposition method. The number of SnO layers is controlled by controlling the number of laser shots during the deposition process. Raman spectroscopic and X-ray photoelectron spectroscopic analysis confirms the formation of phase pure SnO layers. Field effect transistors (FETs) using few layer SnO channels grown on SiO2 substrates are successfully fabricated. These FETs show typical p-channel conduction with field effect mobility ranging from 0.05 to 1.9 cm2 V−1 s−1. Field effect mobility varies with the number of SnO layers and decreases on either sides of the optimum layer numbers (12), which is explained based on charge screening and interlayer coupling in layered materials.
Co-reporter:Kachirayil J. Saji, Y.P. Venkata Subbaiah, Kun Tian, Ashutosh Tiwari
Thin Solid Films 2016 Volume 605() pp:193-201
Publication Date(Web):30 April 2016
DOI:10.1016/j.tsf.2015.09.026
•We reviewed recent developments on p-type SnO thin film research.•Discussed the optical and electrical properties of SnO thin films•Bipolar conduction in SnO is discussed.•Optoelectronic properties of SnO–ZnO composite system are discussed.•Proposed SnO–ZnO heterojunction band structureTin monoxide (SnO) is considered as one of the most important p-type oxides available to date. Thin films of SnO have been reported to possess both an indirect bandgap (~ 0.7 eV) and a direct bandgap (~ 2.8 eV) with quite high hole mobility (~ 7 cm2/Vs) values. Moreover, the hole density in these films can be tuned from 1015–1019 cm− 3 just by controlling the thin film deposition parameters. Because of the above attributes, SnO thin films offer great potential for fabricating modern electronic and optoelectronic devices. In this article, we are reviewing the most recent developments in this field and also presenting some of our own results on SnO thin films grown by pulsed laser deposition technique. We have also proposed a p–n heterostructure comprising of p-type SnO and n-type ZnO which can pave way for realizing next-generation, all-oxide transparent electronic devices.
Co-reporter:Shiang Teng, Gene Siegel, Megan C. Prestgard, Wei Wang, Ashutosh Tiwari
Electrochimica Acta 2015 Volume 161() pp:343-350
Publication Date(Web):10 April 2015
DOI:10.1016/j.electacta.2015.02.117
•Copper nanoparticles were embedded in the highly porous carbonized wood electrodes.•Copper nanoparticle serves as the pseudocapacitive specie to increase the energy density.•The porous copper-wood electrodes exhibit excellent electrochemical performances with high capacitance, excellent rate capability and stability.Copper nanoparticle-loaded carbonized wood electrodes were synthesized and characterized for the use as supercapacitor electrodes. The electrodes were fabricated by soaking beech wood samples in Cu(NO3)2 solution followed by carbonization at 800 °C under a N2 atmosphere. The copper nanoparticle content in the electrodes was controlled by varying the concentration of the Cu(NO3)2 solution from 0.5 to 2 M. Subsequent X-ray diffraction and scanning electron microscopy measurements confirm that cubic copper was formed and the copper nanoparticles were anchored uniformly both on the surface as well as deep within the pores of the wood electrode. Cyclic voltammetry measurements showed that all of the electrodes had a typical pseudo-capacitive behavior, as indicated by the presence of redox reaction peaks. Charge–discharge testing also confirmed the pseudo-capacitive nature of the electrodes. The reversible oxidation of Cu into Cu2O and CuO was verified by performing X-ray photoelectron spectroscopy at different stages of the charge–discharge cycle. The Cu-loaded wood electrodes exhibited excellent cyclability and retaining 95% of their specific capacitance even after 2000 cycles. A maximum specific capacitance of 888 F/g was observed while discharging the 7 wt% Cu electrode at 200 mA/g in a 2 M KOH electrolyte solution. These results demonstrated the potential of the copper nanoparticle-loaded wood electrodes as cheap and high performance supercapacitor electrodes.
Co-reporter:Kun Tian, Saji Alex, Gene Siegel, Ashutosh Tiwari
Materials Science and Engineering: C 2015 Volume 46() pp:548-552
Publication Date(Web):1 January 2015
DOI:10.1016/j.msec.2014.10.064
A novel electrochemical glucose sensor was developed by employing a composite film of plant-like Zinc oxide (ZnO) and chitosan stabilized spherical gold nanoparticles (AuNPs) on which Glucose oxidaze (GOx) was immobilized. The ZnO was deposited on an indium tin oxide (ITO) coated glass and the AuNPs of average diameter of 23 nm were loaded on ZnO as the second layer. The prepared ITO/ZnO/AuNPs/GOx bioelectrode exhibited a low value of Michaelis–Menten constant of 1.70 mM indicating a good bio-matrix for GOx. The studies of electrochemical properties of the electrode using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that, the presence of AuNPs provides significant enhancement of the electron transfer rate during redox reactions. The linear sweep voltammetry (LSV) shows that the ITO/ZnO/AuNPs/GOx based sensor has a high sensitivity of 3.12 μA·mM− 1·cm− 2 in the range of 50 mg/dL to 400 mg/dL glucose concentration. The results show promising application of the gold nanoparticle modified plant-like ZnO composite bioelectrode for electrochemical sensing of glucose.
Co-reporter:Kun Tian, Megan Prestgard, Ashutosh Tiwari
Materials Science and Engineering: C 2014 Volume 41() pp:100-118
Publication Date(Web):1 August 2014
DOI:10.1016/j.msec.2014.04.013
•Most recent advances in nonenzymatic glucose sensors have been reviewed.•The principles of electrochemical detection and glucose oxidation are discussed.•This review is organized based on different biosensor materials.•We focus on noble metals, metal oxides, polymers, carbon nanotubes and graphene.•Potential use of spintronics in glucose sensor technology has been proposed.Currently, there is an overwhelming demand for the development and improvement of glucose sensors. Not only has the number of people requiring these sensors significantly increased over the last decade, so has the demand to make sensors which are both biocompatible and have increased sensing capabilities as compared to current technologies. In order to meet these needs, a move towards nonenzymatic glucose sensors has begun. These new sensors have garnered significant interest due to their capacity to achieve continuous glucose monitoring, their high stability compared to traditional glucose sensors, and the ease of their fabrication. Research has been extensively geared towards the preparation of these nonenzymatic glucose sensors from novel materials, often with unique micro- or nano-structures, which possess ideal properties for electrochemical biosensor applications. In recent years, a variety of materials including noble metals, metal oxides, carbon nanotubes, graphene, polymers, and composites have been explored for their electrocatalytic response to the oxidation of glucose. In this review, the most recent advances in nonenzymatic glucose sensors are visited, with the focus being on the last five years of research.
Co-reporter:Prashant K. Sarswat, Michael Snure, Michael L. Free, Ashutosh Tiwari
Thin Solid Films 2012 Volume 520(Issue 6) pp:1694-1697
Publication Date(Web):1 January 2012
DOI:10.1016/j.tsf.2011.07.052
We have fabricated single phase Cu2ZnSnS4 (CZTS) films using a specially designed 3-stage electrochemical system. Sequential electrodepositon of constituent metallic layers was carried out on SnO2/F coated glass substrates using a platinum counter electrode and a saturated calomel reference electrode. Unique bath compositions were formulated for each of these constituents. Sequentially deposited tri-layer stacks were annealed in sulfur environment to get CZTS phase. Detailed structural, morphological and optical characterization experiments were performed using several techniques including x-ray diffraction, Raman and UV–visible spectroscopy, scanning electron microscopy and atomic force microscopy. All characterization experiments indicated that the films are single phase with a measured direct band gap of 1.5 eV.
Co-reporter:Paul Slusser;Dhananjay Kumar
JOM 2011 Volume 63( Issue 10) pp:
Publication Date(Web):2011 October
DOI:10.1007/s11837-011-0169-0
This paper presents the magnetic behavior of CeO2-δ films doped with two non-magnetic transition metal elements: copper and zinc. High quality films were grown on LaAlO3 (001) substrate using a pulsed laser deposition technique. Detailed structural characterization and magnetic property measurements were performed. Our results showed that Cu-doped CeO2-δ films exhibit room temperature ferromagnetism while Zn-doped CeO2-δ films are non-magnetic.
Co-reporter:Michael Snure;Dhananjay Kumar
JOM 2009 Volume 61( Issue 6) pp:72-75
Publication Date(Web):2009 June
DOI:10.1007/s11837-009-0092-9
ZnO-based diluted magnetic semiconductors (DMS) have attracted a great deal of research attention and controversy over the past decade. The initial attention was sparked by the prediction of above-room-temperature ferromagnetism in Mn-doped ZnO by T. Dietl. This was followed by a surge of reports of ferromagnetism in thin film transition metal (TM)-doped ZnO. However, reported values of magnetic moments and Curie temperatures were inconsistent, which led to controversy over the origin of the observed ferromagnetism. In this paper we review a number of TM-doped ZnO-based DMS in order to clarify which materials are likely ferromagnetic.
Co-reporter:Michael Sygnatowicz, Ashutosh Tiwari
Materials Science and Engineering: C 2009 29(3) pp: 1071-1076
Publication Date(Web):
DOI:10.1016/j.msec.2008.08.036
Co-reporter:Saji Alex, Kun Tian, Shiang Teng, Gene Siegel, Ashutosh Tiwari
Journal of Crystal Growth (15 November 2014) Volume 406() pp:12-17
Publication Date(Web):15 November 2014
DOI:10.1016/j.jcrysgro.2014.08.008
•Single crystalline gold nanoplates were synthesized in aqueous solution.•A natural polymer, chitosan, is used as the reducing and capping agent.•Molar ratio of the reagents plays a major role in the formation of the nanoplates.•Nanoplates were mainly hexagonal with width around 10 μm.A simple, rapid and green chemical method for the synthesis of single crystalline gold nanoplates of several micrometeres in size has been demonstrated. The synthesis involved the reduction of HAuCl4 in aqueous solution using low molecular weight chitosan at boiling temperature for 25 min. The [Au3+]:[chitosan] molar ratio plays an important role in the formation of gold nanoplates and found that an optimized molar ratio in the range of 80 to 125 was suitable for the formation of nanoplates. The size and morphology of the nanoplates can be tuned by adjusting the molar ratio. In this process, the chitosan functions both as a reducing as well as a stabilizing agent and no other special agents were added to induce the nanoplate formation. The obtained nanoplates were single crystals with (1 1 1) planes as the basal planes with shapes of hexagonal, triangular, or truncated triangular plates.
