arXiv subjects

Shailendra K. Saxena

Publications and source records attributed to Shailendra K. Saxena.

13 recordsLinked to original sources

arXiv2025

Protein-Based Electrical Junctions with Robust Biocompatible Carbon Electrodes Exhibit Activation-less Charge Transport down to 10 K

The integration of functional proteins into solid-state electronic devices remains a central challenge in molecular bioelectronics due to the fragile nature of protein structures and their complex charge-transport behaviour. Here, we present a robust crosswire evaporated top-contact device based on bacteriorhodopsin (bR) single bilayers (SBL), configured as Au/Cys/bR(SBL)/eC/Au (simplified as Au/bR/eC). The evaporated carbon (eC) top electrode forms a conformal, non-invasive contact that suppresses filament formation and ensures electrical integrity across the cross-wire intersecting area (about 200 micron^2). Structural and spectroscopic analyses confirm that the solid-state bR films maintain the native absorption spectrum and have functional photocycle activity after electrode deposition, implying that their native conformation is not significantly affected. Remarkably, electron transport (ETp) through the 9 nm bR-SBL junctions is temperature-independent within 300 K - 10 K, excluding thermally activated hopping, while the length is incompatible with coherent tunneling. Under green illumination, the junctions exhibit a reversible, photo-induced current enhancement (Jgreen/Jdark = 2), ascribed to light-driven conformational changes rather than direct photoexcitation. The Au/bR/eC architecture thus establishes a thermally non-activated, conformationally mediated transport mechanism via a stable, cryo-compatible solid-state protein junction. This work provides a scalable platform for integrating light-responsive biomolecules into future bio-optoelectronic and neuromorphic devices.

physics.bio-ph↗

arXiv2017

Generalization of Phonon Confinement Model for Interpretation of Raman Line-Shape from Nano-Silicon

A comparative analysis of two Raman line-shape functions has been carried out to validate the true representation of experimentally observed Raman scattering data for semiconducting nanomaterials. A modified form of already existing phonon confinement model incorporates two basic considerations, phonon momentum conservation and shift in zone centre phonon frequency. After incorporation of the above mentioned two factors, a rather symmetric Raman line-shape is generated which is in contrary to the usual asymmetric Raman line-shapes obtained from nanostructured semiconductor. By fitting an experimentally observed Raman scattering data from silicon nanostructures, prepared by metal induced etching, it can be established that the Raman line-shape obtained within the framework of phonon confinement model is a true representative Raman line-shape of sufficiently low dimensions semiconductors.

cond-mat.mes-hall↗

arXiv2017

Tent--Shaped Surface Morphologies of Silicon: Texturization by Metal Induced Etching

Nano--metal/semiconductor junction dependent porosification of silicon (Si) has been studied here. The silicon (Si) nanostructures (NS) have been textured on n-- and p-- type silicon wafers using Ag and Au metal nano particles induced chemical etching. The combinations of n--Si/Ag and p--Si/Au form ohmic contact and result in the same texturization on the Si surface on porosification where tent--shaped morphology has been observed consistently with n-- and p--type Si. Whereas, porosification result in different surface texturization for other two combinations (p--Si/Ag and n--Si/Au) where Schottkey contacts are formed. Quantitative analysis have been done using ImageJ to process the SEM images of SiNS, which confirms that the tent like SiNS are formed when etching of silicon wafer is done by AgNPs and AuNPs on n and p type Si wafer respectively. These easily prepared sharp tent--shaped Si NSs can be used for enhanced field emission applications.

cond-mat.mes-hall↗

arXiv2017

Three-fold Constructive Perturbation for Significant Enhancement in Field Emission from Nickel Oxide Nano-Thorn

A power efficient and stable field emission (FE) has been reported here from Nickel Oxide nanostructures. Modification in device geometry and surface micro- (nano-) structure has been found helpful in addressing the bottlenecks in achieving an efficient FE . In terms of threshold and turn on fields, three orders of magnitude better electron FE has been observed in the nickel oxide nanopetals (NiO-NPs) fabricated using simple hydrothermal technique. Uniform and vertically aligned NiO-NPs structures, grown on very flat conducting surface (FTO coated glass), show sharp needles like structures on the top edges of the flakes. These ultrafine structures play the main role in field emission to start at such a low turn on fields. The FE data (J-E plot) has been fitted with Fowler-Nordheim (FN) equation to estimate threshold field value and field enhancement factor which are found to be 3 V/mm and $\sim$ 5 $\times$ 10$^6$ respectively.

physics.app-ph↗

arXiv2017

Observation, Evidence and Origin of Room Temperature Magnetodielectric Effect in Mn doped LaGaO3

We report an observation of room temperature magnetodielectric (RTMD) effect in Mn doped LaGaO3. Results of frequency dependent magnetoresistance (FDMR) measurements discards the possibility of any magnetoresistive contribution in the observed MD effect. The intrinsic nature of MD coupling has been validated/evidenced by means of magnetic field dependent Raman spectroscopy and explained in terms of modified volume strain governed by magnetic field induced rerotation of spin coupled Mn-orbitals. Ultimately, present RTMD effect is attributed to magneto-compression/magnetostriction associated with spin-phonon coupling as evidenced in the form of magnetic field induced hardening of symmetric stretching (SS) MnO6 octahedral Raman modes. Presently studied Mn doped LaGaO3 can be a candidate for magnetodielectric applications.

cond-mat.mtrl-sci↗

arXiv2016

Metastable behavior of Urbach tail states in BaTiO3 across phase transition

The temperature dependent diffuse reflectance spectroscopy measurements were carried out on the polycrystalline samples of BaTiO3 across the tetragonal to cubic structural phase transition temperature. The values of various optical parameters such as band gap (Eg), Urbach energy (EU) and Urbach focus (E0) are estimated in the range of 300 K to 470K. It is observed that near structural phase transition temperatures there exists two value of E0, suggesting presence of electronic heterogeneity over wide temperature range. Further near transition temperature EU shows metastability i.e. value of EU at temperature T is not constant but is a function of time (t). Interestingly it is observed that the ratio of EU(t=0)/ EU(t = tm), is almost remains constant at 295 K (pure tetragonal phase) and at 450 K (pure cubic phase), whereas this ratio shows decreasing behavior close to structural phase transition temperature, which confirms the presence of electronic metastibility in the pure BaTiO3. The observed metastibility can be fitted with the stretch exponents relaxation behavior, suggesting the presence of dynamic heterogeneous electronic disorder present in the sample across the transition. Further it appears that these metastable Urbach tail states (electronic disorder) may couple with the soft phonon modes and responsible for the observed terahertz dielectric relaxation (Phys. Rev. Lett. 101, 167402 (2008)). Further; present studies suggest that the optical studies appear to be more sensitive to probe the disorder/heterogeneity present in the sample.

cond-mat.str-el↗

arXiv2016

In-situ spectroscopic studies of viologen based electrochromic device

Fabrication and operation of simple solid state electrochromic devices using ethyl viologen diperchlorate in a polymer matrix is presented here. In-situ Raman and transmission/absorption studies have been done to establish the origin of bias induced color change, between a transparent and navy blue color, in the electrochromic device. The origin of bias induced color change has been attributed to the bias induced redox switching between its viologen dication and free redicle forms. Fundamental reason behind colour changes of viologen molecule has been established. In-situ UV-Vis spectra reveals that the navy blue color of the device under biased condition is not due to increase in the transparency corresponding to blue wavelength but due to suppression of the transparency corresponding to the complementary colors. Absorption modulation has been reported from the device with good ON/OFF contrast of the device.

cond-mat.mes-hall↗

arXiv2016

Role of Metal Nanoparticles on porosification of silicon by metal induced etching (MIE)

Porosification of silicon (Si) by metal induced etching (MIE) process have been studies here to understand the etching mechanism. The etching mechanism has been discussed on the basis of electron transfer from Si to metal ion (Ag$^+$) and metal to H$_2$O$_2$. Role of silver nanoparticles (AgNPs) in the etching process has been investigated by studying the effect of AgNPs coverage on surface porosity. A quantitative analysis of SEM images, done using Image J, shows a direct correlation between AgNPs coverage and surface porosity after the porosification. Density of Si nanowires (NWs) also varies as a function of AgNPs fractional coverage which reasserts the fact that AgNPs governs the porosification process during MIE.

cond-mat.mes-hall↗

arXiv2016

Half-metallicity in Armchair Boron Nitride Nanoribbons: A First-Principles Study

Using density functional theory, we predict half-metallicity in edge hydrogenated armchair boron nitride nanoribbons (ABNNRs). The predicted spin polarization is analyzed in detail by calculating electronic and magnetic properties of these hydrogenated ABNNRs by means of first-principles calculations within the local spin-density approximation (LSDA). ABNNRs with only edge B atoms passivated by H atoms are found to be half-metallic (regardless of their width) with a half-metal gap of 0.26 eV. Upto 100% spin polarized charge transport is predicted across the Fermi level owing to the giant spin splitting. Transmission spectrum analysis also confirms the separation of spin up and spindown electronic channels. It is revealed that H-passivation of only edge N atoms transforms non-magnetic bare ribbons into energetically stable magnetic semiconductors whereas hydrogenation of both the edges does not affect the electronic and magnetic state of bare ribbons significantly. The results are promising towards the realization of inorganic spintronic devices.

cond-mat.mes-hall↗

arXiv2015

Interplay between Phonon Confinement and Fano Effect on Raman line shape for semiconductor nanostructures: Analytical study

Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of line-shape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other.

cond-mat.mes-hall↗

arXiv2014

Micro-Raman and field emission studies of silicon nanowires prepared by metal assisted chemical etching

Micro-Raman scattering and electron field emission characteristics of silicon nanowires (SiNWs) synthesized by metal assisted chemical etching (MACE) are investigated. Scanning electron microscopy images reveal the growth of well aligned vertical SiNWs. Raman shift and size relation from bond-polarizability model has been used to calculate exact confinement sizes in SiNWs. The Si optical phonon peak for SiNWs showed a downshift and an asymmetric broadening with decreasing diameter of the SiNWs due to quantum confinement of optical phonons. The field emission characteristics of these SiNWs are studied based by carrying out current-voltage measurements followed by a theoretical analysis using Fowler-Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. Field emission from these SiNWs exhibits significant enhancement in turn-on field and total emission current with decreasing nanowire size. The reported results in the current study indicate that MACE is a simple technique to prepare well-aligned SiNWs with potentials for applications in field emission devices.

cond-mat.mes-hall↗

arXiv2014

Comparison of porous silicon prepared using metal-induced etching (MIE) and laser-induced etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.

cond-mat.mes-hall↗

arXiv2013

Evolution of Asymmetric Raman line-shape from nano-structures

A step-by-step evolution of an asymmetric Raman line-shape function from a Lorentzian line-shape is presented here for low dimensional semiconductors. The evolution reported here is based on the phonon confinement model which is successfully used in literature to explain the asymmetric Raman line-shape from semiconductor nano-structures. Physical significance of different terms in the theoretical asymmetric Raman line-shape has been explained here. Better understanding of theoretical reasoning behind each term allows one to use the theoretical Raman line-shape without going into details of theory from first principle. This will enable one to empirically derive a theoretical Raman line-shape function for any material if information about its phonon dispersion, size dependence etc is known.

cond-mat.mes-hall↗