Publications by authors named "Abhinav Prakash"

17 Publications

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Dopant Segregation Inside and Outside Dislocation Cores in Perovskite BaSnO and Reconstruction of the Local Atomic and Electronic Structures.

Nano Lett 2021 May 11;21(10):4357-4364. Epub 2021 May 11.

Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States.

Distinct dopant behaviors inside and outside dislocation cores are identified by atomic-resolution electron microscopy in perovskite BaSnO with considerable consequences on local atomic and electronic structures. Driven by elastic strain, when A-site designated La dopants segregate near a dislocation core, the dopant atoms accumulate at the Ba sites in compressively strained regions. This triggers formation of Ba vacancies adjacent to the core atomic sites resulting in reconstruction of the core. Notwithstanding the presence of extremely large tensile strain fields, when La atoms segregate inside the dislocation core, they become B-site dopants, replacing Sn atoms and compensating the positive charge of the core oxygen vacancies. Electron energy-loss spectroscopy shows that the local electronic structure of these dislocations changes dramatically due to segregation of the dopants inside and around the core ranging from formation of strong La-O hybridized electronic states near the conduction band minimum to insulator-to-metal transition.
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http://dx.doi.org/10.1021/acs.nanolett.1c00966DOI Listing
May 2021

Metallic line defect in wide-bandgap transparent perovskite BaSnO.

Sci Adv 2021 Jan 15;7(3). Epub 2021 Jan 15.

Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.

A line defect with metallic characteristics has been found in optically transparent BaSnO perovskite thin films. The distinct atomic structure of the defect core, composed of Sn and O atoms, was visualized by atomic-resolution scanning transmission electron microscopy (STEM). When doped with La, dopants that replace Ba atoms preferentially segregate to specific crystallographic sites adjacent to the line defect. The electronic structure of the line defect probed in STEM with electron energy-loss spectroscopy was supported by ab initio theory, which indicates the presence of Fermi level-crossing electronic bands that originate from defect core atoms. These metallic line defects also act as electron sinks attracting additional negative charges in these wide-bandgap BaSnO films.
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http://dx.doi.org/10.1126/sciadv.abd4449DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7810381PMC
January 2021

Self-Assembled Periodic Nanostructures Using Martensitic Phase Transformations.

Nano Lett 2021 Feb 2;21(3):1246-1252. Epub 2020 Dec 2.

Department of Chemical Engineering and Materials Science, University of Minnesota, Twin Cities, Minneapolis, Minnesota 55455, United States.

We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic phase transformations. We demonstrate this approach in a thin film of perovskite SrSnO with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variable photonic crystal. Our results show the realistic possibility of designing large-area self-assembled periodic structures using martensitic phase transformations with the potential of implementing "built-to-order" nanostructures for tailored optoelectronic functionalities.
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http://dx.doi.org/10.1021/acs.nanolett.0c03708DOI Listing
February 2021

Response to Letters to the Editor on Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks: Revised and Expanded Results.

ACS Nano 2020 09;14(9):10764-10770

Center for Nanoscale Materials, Argonne National Laboratory Lemont, Illinois 60439, United States.

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http://dx.doi.org/10.1021/acsnano.0c04897DOI Listing
September 2020

Aerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth Masks.

ACS Nano 2020 May 24;14(5):6339-6347. Epub 2020 Apr 24.

Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States.

The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10 μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, respectively, the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton-silk, cotton-chiffon, cotton-flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (, thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.
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http://dx.doi.org/10.1021/acsnano.0c03252DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834PMC
May 2020

Separating Electrons and Donors in BaSnO via Band Engineering.

Nano Lett 2019 12 21;19(12):8920-8927. Epub 2019 Nov 21.

Department of Chemical Engineering and Materials Science , University of Minnesota , Minneapolis , Minnesota 55414 , United States.

Separating electrons from their source atoms in La-doped BaSnO, the first perovskite oxide semiconductor to be discovered with high room-temperature electron mobility, remains a subject of great interest for achieving high-mobility electron gas in two dimensions. So far, the vast majority of work in perovskite oxides has focused on heterostructures involving SrTiO as an active layer. Here we report the demonstration of modulation doping in BaSnO as the high room-temperature mobility host without the use of SrTiO. Significantly, we show the use of angle-resolved hard X-ray photoelectron spectroscopy (HAXPES) as a nondestructive approach to not only determine the location of electrons at the buried interface but also to quantify the width of electron distribution in BaSnO. The transport results are in good agreement with the results of self-consistent solution to one-dimensional Poisson and Schrödinger equations. Finally, we discuss viable routes to engineer two-dimensional electron gas density through band-offset engineering.
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http://dx.doi.org/10.1021/acs.nanolett.9b03825DOI Listing
December 2019

STEM beam channeling in BaSnO/LaAlO perovskite bilayers and visualization of 2D misfit dislocation network.

Ultramicroscopy 2020 Jan 24;208:112863. Epub 2019 Oct 24.

Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA. Electronic address:

A study of the STEM probe channeling in a heterostructured crystalline bilayer specimens is presented here with a goal to guide STEM-based characterization of multilayer structures. STEM analysis of perovskite BaSnO/LaAlO bilayers is performed and the dominating effects of beam channeling on HAADF- and LAADF-STEM are illustrated. To study the electron beam channeling through BaSnO/LaAlO bilayers, probe intensity depth profiles are calculated, and the effects of probe defocus and atomic column alignment are discussed. Characteristics of the beam channeling are correlated to resulting ADF-STEM images, which is then tested by comparing focal series of plan-view HAADF-STEM images to those recorded experimentally. Additionally, discussions on how to visualize the misfit dislocation network at the BaSnO/LaAlO interface using HAADF- and LAADF-STEM images are provided.
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http://dx.doi.org/10.1016/j.ultramic.2019.112863DOI Listing
January 2020

Electrostatic Control of Insulator-Metal Transition in La-doped SrSnO Films.

ACS Appl Mater Interfaces 2019 Feb 18;11(8):7666-7670. Epub 2019 Feb 18.

Department of Chemical Engineering and Materials Science , University of Minnesota, Twin Cities , Minneapolis , Minnesota 55455 , United States.

We investigate the ion gel gating of wide bandgap oxide, La-doped SrSnO films grown using radical-based molecular beam epitaxy. An applied positive bias resulted in a reversible electrostatic control of sheet resistance over 3 orders of magnitude at low temperature driving sample from Mott variable range hopping to a weakly localized transport. Analysis of low temperature transport behavior revealed electron-electron interaction and weak localization effects to be the dominant scattering mechanisms. A large voltage window (-4 V ≤ V ≤ +4 V) was obtained for reversible electrostatic doping of SrSnO films showing robustness of stannate with regards to redox chemistry with electrolyte gating irrespective of the bias type.
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http://dx.doi.org/10.1021/acsami.8b22034DOI Listing
February 2019

Engineering SrSnO Phases and Electron Mobility at Room Temperature Using Epitaxial Strain.

ACS Appl Mater Interfaces 2018 Dec 4;10(50):43802-43808. Epub 2018 Dec 4.

National Synchrotron Radiation Laboratory , University of Science and Technology of China , Hefei , Anhui 230026 , China.

High-speed electronics require epitaxial films with exceptionally high carrier mobility at room temperature (RT). Alkaline-earth stannates with high RT mobility show outstanding prospects for oxide electronics operating at ambient temperatures. However, despite significant progress over the last few years, mobility in stannate films has been limited by dislocations because of the inability to grow fully coherent films. Here, we demonstrate the growth of coherent, strain-engineered phases of epitaxial SrSnO (SSO) films using a radical-based molecular beam epitaxy approach. Compressive strain stabilized the high-symmetry tetragonal phase of SSO at RT, which, in bulk, exists only at temperatures between 1062 and 1295 K. We achieved a mobility enhancement of over 300% in doped films compared with the low-temperature orthorhombic polymorph. Using comprehensive temperature-dependent synchrotron-based X-ray measurements, electronic transport, and first principles calculations, crystal and electronic structures of SSO films were investigated as a function of strain. We argue that strain-engineered films of stannate will enable high mobility oxide electronics operating at RT with the added advantage of being optically transparent.
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http://dx.doi.org/10.1021/acsami.8b16592DOI Listing
December 2018

Multifocal Electroretinography in Diabetic Retinopathy With and Without Macular Edema.

Ophthalmic Surg Lasers Imaging Retina 2018 10;49(10):780-786

Background And Objectives: To characterize the electroretinographic response of the macula by multifocal electroretinography (mfERG) in nonproliferative diabetic retinopathy (NPDR) with and without diabetic macular edema (DME) and correlate it with best-corrected visual acuity (BCVA) and foveal thickness on spectral-domain optical coherence tomography (SD-OCT).

Patients And Methods: Prospective, observational case series. Forty eyes of 22 patients with treatment-naïve NPDR underwent recording of BCVA, fundus fluorescein angiography (FFA), and SD-OCT. Groups A and B were classified as 20 eyes each having NPDR with DME (central foveal thickness [CFT] ≥ 275 μm) and without DME (CFT < 275 μm), respectively. First-order kernel mfERG responses recorded according to ISCEV guidelines were grouped into five concentric rings centered on the fovea for analysis.

Results: Mean P1 and N1 amplitudes (nv/deg) were significantly decreased compared to normal values in each of the five rings in both groups (P < .01); however, the values between the two groups were comparable. BCVA was significantly and positively correlated with P1 (r = 0.454, P = .003) and N1 amplitude (r = 0.468, P = .002) and significantly and negatively correlated with P1 (r= -0.534, P < .01) and N1 implicit times (r= -0.570, P < .01) in all patients. P1 (r= -0.531, P < .01) and N1 amplitude (r= -0.367, P = .02) in the central ring of mfERG had a significant negative correlation with macular thickness in the corresponding foveal ring of SD-OCT in all patients.

Conclusions: mfERG reflects retinal dysfunction irrespective of the occurrence of DME in patients with NPDR. Correlation with BCVA reinforces that mfERG should be used to objectively assess the macular function in these patients. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:780-786.].
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http://dx.doi.org/10.3928/23258160-20181002-06DOI Listing
October 2018

Depletion Mode MOSFET Using La-Doped BaSnO as a Channel Material.

ACS Appl Mater Interfaces 2018 Jun 18;10(25):21061-21065. Epub 2018 Jun 18.

The high room-temperature mobility that can be achieved in BaSnO has created significant excitement for its use as channel material in all-perovskite-based transistor devices such as ferroelectric field effect transistor (FET). Here, we report on the first demonstration of n-type depletion-mode FET using hybrid molecular beam epitaxy grown La-doped BaSnO as a channel material. The devices utilize a heterostructure metal-oxide semiconductor FET (MOSFET) design that includes an epitaxial SrTiO barrier layer capped with a thin layer of HfO used as a gate dielectric. A field-effect mobility of ∼70 cm V s, a record high transconductance value of >2mS/mm at room temperature, and the on/off ratio exceeding 10 at 77 K were obtained. Using temperature- and frequency-dependent transport measurements, we quantify the impact of the conduction band offset at the BaSnO/SrTiO interface as well as bulk and interface traps on device characteristics.
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http://dx.doi.org/10.1021/acsami.8b05229DOI Listing
June 2018

THz characterization and demonstration of visible-transparent/terahertz-functional electromagnetic structures in ultra-conductive La-doped BaSnO Films.

Sci Rep 2018 Feb 23;8(1):3577. Epub 2018 Feb 23.

Department of Electrical and Computer Engineering, The University of Utah, Salt Lake City, UT, 84112, USA.

We report on terahertz characterization of La-doped BaSnO (BSO) thin-films. BSO is a transparent complex oxide material, which has attracted substantial interest due to its large electrical conductivity and wide bandgap. The complex refractive index of these films is extracted in the 0.3 to 1.5 THz frequency range, which shows a metal-like response across this broad frequency window. The large optical conductivity found in these films at terahertz wavelengths makes this material an interesting platform for developing electromagnetic structures having a strong response at terahertz wavelengths, i.e. terahertz-functional, while being transparent at visible and near-IR wavelengths. As an example of such application, we demonstrate a visible-transparent terahertz polarizer.
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http://dx.doi.org/10.1038/s41598-018-22038-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5824812PMC
February 2018

Wide bandgap BaSnO films with room temperature conductivity exceeding 10 S cm.

Nat Commun 2017 05 5;8:15167. Epub 2017 May 5.

Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, Minneapolis, Minnesota 55455, USA.

Wide bandgap perovskite oxides with high room temperature conductivities and structural compatibility with a diverse family of organic/inorganic perovskite materials are of significant interest as transparent conductors and as active components in power electronics. Such materials must also possess high room temperature mobility to minimize power consumption and to enable high-frequency applications. Here, we report n-type BaSnO films grown using hybrid molecular beam epitaxy with room temperature conductivity exceeding 10 S cm. Significantly, these films show room temperature mobilities up to 120 cm V s even at carrier concentrations above 3 × 10 cm together with a wide bandgap (3 eV). We examine the mobility-limiting scattering mechanisms by calculating temperature-dependent mobility, and Seebeck coefficient using the Boltzmann transport framework and ab-initio calculations. These results place perovskite oxide semiconductors for the first time on par with the highly successful III-N system, thereby bringing all-transparent, high-power oxide electronics operating at room temperature a step closer to reality.
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http://dx.doi.org/10.1038/ncomms15167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5424175PMC
May 2017

Repeat fluid- gas exchange for failed primary macular hole surgery.

Indian J Ophthalmol 2014 Nov;62(11):1104-1105

ICARE Eye Hospital and Postgraduate Institute, Noida, Uttar Pradesh, India.

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http://dx.doi.org/10.4103/0301-4738.146736DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4290209PMC
November 2014

Recombinant production of self-assembling β-structured peptides using SUMO as a fusion partner.

Microb Cell Fact 2012 Jul 3;11:92. Epub 2012 Jul 3.

Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.

Background: Self-assembling peptides that form nanostructured hydrogels are important biomaterials for tissue engineering scaffolds. The P₁₁-family of peptides includes, P₁₁-4 (QQRFEWEFEQQ) and the complementary peptides P₁₁-13 (EQEFEWEFEQE) and P₁₁-14 (QQOrnFOrnWOrnFOrnQQ). These form self-supporting hydrogels under physiological conditions (pH 7.4, 140 mM NaCl) either alone (P₁₁-4) or when mixed (P₁₁-13 and P₁₁-14). We report a SUMO-peptide expression strategy suitable for allowing release of native sequence peptide by SUMO protease cleavage.

Results: We have expressed SUMO-peptide fusion proteins from pET vectors by using autoinduction methods. Immobilised metal affinity chromatography was used to purify the fusion protein, followed by SUMO protease cleavage in water to release the peptides, which were recovered by reverse phase HPLC. The peptide samples were analysed by electrospray mass spectrometry and self-assembly was followed by circular dichroism and transmission electron microscopy.

Conclusions: The fusion proteins were produced in high yields and the β-structured peptides were efficiently released by SUMO protease resulting in peptides with no additional amino acid residues and with recoveries of 46% to 99%. The peptides behaved essentially the same as chemically synthesised and previously characterised recombinant peptides in self-assembly and biophysical assays.
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http://dx.doi.org/10.1186/1475-2859-11-92DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3512519PMC
July 2012