arXiv subjects

Vamsi Borra

Publications and source records attributed to Vamsi Borra.

15 recordsLinked to original sources

arXiv2025

Inhibition of whisker growth by crafting more decomposition-resistant Ti2SnC MAX phase through vanadium solid solution

The exceptional synergy of ceramic and metallic properties within MAX phases positions them as highly promising for a wide array of applications. However, their stability has been threatened by the phenomenon of A-site metal whisker growth. Herein, we have significantly mitigated tin whisker growth in Ti2SnC by incorporating vanadium solutes at its M-site. With an increase in vanadium concentration, there is a marked reduction in the degree of decomposition of the M-site solid solution when subjected to the same level of externally destructive treatments, thereby inhibiting whisker proliferation. Both experimental outcomes and theoretical calculations reveal that the vanadium solid solution augments the hardness, Pughs ratio, and Poissons ratio of Ti2SnC, enhancing its mechanical strength and toughness. The incorporation of V atoms introduces stronger V C and V Sn bonds, as evidenced by its electronic density of states and bulk modulus, thus significantly bolstering the resistance of MAX phases against decomposition and effectively curtailing whisker growth. Additionally, the phenomenon reported in this paper also conforms to the electrostatic theory of whisker growth. This work for the first time achieves the suppression of A-site whisker growth through an M-site solid solution, thereby extending their potential for applications where durability and reliability are paramount.

cond-mat.mtrl-sci↗

arXiv2024

A High-Temperature Thermocouple Development by Additive Manufacturing: Tungsten-Nickel (W-Ni) and Molybdenum (Mo) Integration with Ceramic Structures

Additive manufacturing holds more potential to enable the development of ceramic-based components. Ceramics offer high resistance to heat, high fracture toughness, and are extremely corrosion resistant. Thus, ceramics are widely used in sectors such as the aerospace industry, automotive, microelectronics, and biomedicine. Using various additive manufacturing platforms, ceramics with complex and uniquely designed geometry can be developed to suit specific applications. This project aims at innovating high-temperature thermocouples by embedding conductive metal pastes into a ceramic structure. The paste used includes tungsten, molybdenum, and antimony. The metal pastes are precisely extruded into a T-shaped trench inside the ceramic matrix. Following specific temperature ranges, the ceramic matrix is sintered to improve the properties of the material. The sensors produced can function at extremely high temperatures and are thereby suitable for high-temperature environments. Comparative testing of the 3D sintered sensors with conventional temperature sensors shows high correlation between the two classes of sensors. The resulting R-squared value of 0.9885 is satisfactory which implies the reliability and accuracy of 3D sintering sensors are satisfactory in temperature sensing applications.

physics.chem-ph↗

arXiv2023

Effect of laser irradiation on the tribological properties of RFsputtered nickel oxide (NiO) thin films

The present work aims at investigating the effect of laser irradiation on the tribological properties of RF-sputtered NiO thin films deposited on industrial grade aluminum substrate. A semiconductor laser based on Nd:YAG operating at its 4th harmonic wavelength, lambda = 266 nm with varying laser fluence and spot size of about 5 um is irradiated on the NiO film. The localized heating allows for smoothening of the NiO film along with contributions to the changes in the stoichiometry of NiO (reduction of excess oxygen). In particular, the effects of tuning laser fluence and the subsequent tribology tests pertaining to the coefficient of friction variations for tribological tests are discussed.

physics.app-ph↗

arXiv2023

Laser-Based Fabrication of Microstructures on Nickel Thin Films and Its Applications in On-Chip Thin Film Inductors

This work reports on the fabrication of microbump structures on Ni films by single-pulse, localized laser irradiation. Conditions for the reproducible formation of such microstructures have been identified in terms of laser-irradiation and film parameters after systematic studies involving a relevant parameter space. The cracks and voids morphology of the sputtered films was rendered undesirable and hence, smoother Ni thin film of same thickness (200nm) were deposited by vacuum evaporation. The continuous nature of the film resulted in radially symmetric thermal expansion and deformation, thus achieving a high yield of microstructures. An improvement in the inductance and the quality factor of on-chip spiral inductors incorporating such laser-microstructured ferromagnetic nickel thin films was observed, which demonstrates the potential of such a laser-based method for fabrication or fine tuning of various micro-/nanoelectric/electronic sensor and other components and systems.

eess.SY↗

arXiv2023

Harmonic content analysis of a soft starting variable frequency motor drive based on FPGA

As the demands for electric vehicles, electric aircrafts, unmanned aircraft systems, and other motor-driven systems increase, high-performance motor drives employing variable frequency control with higher efficiency and reliability are becoming increasingly important parts of the ever-changing technological landscape. This study proposes a Field Programmable Gate Array (FPGA)-based variable frequency soft-starting motor drive for a three-phase induction motor. The inverter output voltage and the load currents are analyzed for the harmonic contents using MATLAB. In the experimental realization, a four-pole squirrel cage delta-connected induction motor is utilized with a switching frequency of 4 kHz. The current and voltage characteristics of the induction motor are studied under different operating conditions to study harmonic contents and the effect of changing soft-start duration. The findings demonstrate a low-cost, flexible control of the induction motor with improved harmonic performance.

eess.SY↗

arXiv2023

Transient Thermal and Electrical Characteristics of a Cylindrical LiFeS2 Cell with Equivalent Circuit Model

This study examines the discharge behaviour of a cylindrical LiFeS2 cell to evaluate the parameters that can be used to predict and estimate the nonlinear dynamic response of a battery. A linear model is developed to simulate the discharge behaviour and examine the thermal behaviour. In particular, a commercial-grade battery is discharged with the industry-standard hybrid power pulsing characterization (HPPC) test and the current and voltage responses are recorded. The dynamic system is modelled with the equivalent circuit model (ECM) through MATLAB Simulink. A block diagram representation of the equivalent circuit model governing equations was developed. The parameter estimation tool was utilized to reduce the error and fit the simulation results to the experimental voltage responses, in order to obtain state of charge dependent dynamic parameters. Those parameters were then used in a Dual-Potential Multi-Scale Multi-Domain (MSMD) Battery Model solved in ANSYS Fluent to analyze the thermal behaviour by acquiring the temperature profiles and the temperature distribution within the cell. The nonlinear behaviour of the battery was characterized and the equivalent circuit model parameters were identified and are shown to agree with the experimental voltage responses. Furthermore, it is found that the battery temperature increased by 7.35 deg and was distributed uniformly within the cell.

eess.SY↗

arXiv2023

Modification of Tin (Sn) Metal Surfaces by Surface Plasmon Polariton Excitation

We report on the modification of tin (Sn) film surfaces under a laser beam irradiation that triggers surface plasmon polariton (SPP) excitations. The observed surface features in the form of small raised grains, with well-defined rooting, look similar to tin whisker nodules. We attribute the appearance of those features to the field-induced nucleation caused by the SPP related strong electric field. Possible implications of our findings include accelerated-life testing for tin whisker growth-related reliability as well as applications to nanoparticle nucleation.

cond-mat.mtrl-sci↗

arXiv2023

Fabrication of optically smooth Sn thin films

The fabrication of optically smooth thin Sn films by vacuum or electrodeposition techniques is usually challenging. Little has been published on how to address this challenge mainly because very few applications require such smooth Sn surfaces. The excitation of surface plasmon polaritons on Sn surfaces by prism-based methods represents a case that requires very smooth surfaces and has motivated this work. It is shown that the deposition rate and the substrate temperature of a vacuum evaporation method can be optimized to obtain very smooth Sn films and this is supported by direct imaging evidence from atomic force microscopy and scanning electron microscopy.

cond-mat.mtrl-sci↗

arXiv2023

Sn whisker growth mitigation by using NiO sublayers

The potential of NiO sublayers for whisker growth mitigation has been examined. A thin NiO film was applied on a Cu-coated substrate before the deposition of a thicker Sn layer. The growth of Sn whiskers was then followed by optical and scanning electron microscopy and was compared with the whisker growth on a control sample without the NiO sublayer. No whiskers were observed on the sample with the NiO layer even after 12 months, whereas the control sample developed whiskers of size and density that is generally expected, based on the vast amount of published work on the topic. The mechanisms of whisker growth and whisker growth suppression are briefly discussed as well.

cond-mat.mtrl-sci↗

arXiv2023

Threshold Switching in CdTe Photovoltaics

With the ubiquitous acceptance of PVs, the number of devices manufactured annually is following an exponential trend. Yet, the manufacturing process of important brands of thin film solar cells involves a tedious and expensive step of laser scribing. The time-consuming and technologically involved laser scribing method remains widely used to contact the device electrodes. This work examines an alternative method (threshold switching phenomenon) to create an enduring conductive path in cadmium telluride (CdTe) PV, which eliminates the pitfalls in conventional scribing technology. The samples undergoing threshold switching show a promising sign of the conductive path compared to the control samples. This method could potentially lead to the manufacturing technology saving time, money, and raw materials along with added reliability and efficiency.

cond-mat.mtrl-sci↗

arXiv2023

Cultivating Metal Whiskers by Surface Plasmon Polariton Excitation

This work presents a preliminary experimental study on the possibility to initiate growth of whiskers on the surfaces of some technologically important metals utilizing the enhanced electric field of surface plasmon polaritons (SPPs). The results provide evidence that a relatively high concentration of what appear to be whisker nuclei form in the region where SPPs were excited, whereas no such changes are observed on the untreated surface.

cond-mat.mtrl-sci↗

arXiv2023

Metal whisker growth induced by localized, high-intensity DC electric fields

In this work, a very high, locally applied electric field was used to induce whisker nucleation on an Sn film. The field was generated by using a conductive AFM tip and applying a voltage bias between the sample and the conductive cantilever>The tip-sample separation distance was thus controllable, and any dielectric breakdown could be avoided. At locations where the AFM tip was positioned for an extended period, minuscule whiskers were observed, whose growth direction matched vertical orientation of the field.

cond-mat.mtrl-sci↗

arXiv2018

The statistics of tin whisker diameters versus the underlying film grains

We compare the statistics of tin whisker diameters to that of the underlying film grains. Both are well approximated by the lognormal distributions. However, the parameters of those distributions can be rather different, not confirming the assumption that each whisker grows from a single grain. We conclude that several adjacent grains with similar crystal orientations can contribute to a whisker development. Our observations are consistent with the recent theory of multi-filament whisker structure. A modification of the particle size log-normal distribution is developed clarifying the nature of its dispersion.

cond-mat.mtrl-sci↗

arXiv2017

Microscopic structure of metal whiskers

We present TEM images of the interior of metal whiskers (MW) grown on electroplated Sn films. Along with earlier published information, our observations focus on a number of questions, such as why MWs' diameters are in the micron range (significantly exceeding the typical nano-sizes of nuclei in solids), why the diameters remain practically unchanged in the course of MW growth, what is the nature of MW diameter stochasticity, and what is the origin of the well-known striation structure of MW side surfaces. In an attempt to address such questions we performed an in-depth study of MW structure at the nanoscale by detaching a MW from its original film, reducing its size to a thin slice by cutting its sides by a focused ion beam, and performing TEM on that structure. Our observations revealed a rich nontrivial morphology suggesting that MW may consist of many side by side grown filaments. This structure appears to extend to the outside whisker surface and be the reason for the striation. In addition, we put forward a theory where nucleation of multiple thin metal needles results into micron-scale and larger MW diameters. This theory is developed in the average field approximation similar to the roughening transitions of metal surfaces. The theory also predicts MW nucleation barriers and other observed features.

cond-mat.mtrl-sci↗

arXiv2017

Whisker growth on Sn thin film accelerated under gamma-ray irradiation

We report on growth of tin (Sn) metal whiskers that is significantly accelerated under gamma-ray irradiation. The studied Sn thin film, evaporated on glass substrate, was subjected to a total of ~60 hours of irradiation over the course of 30 days. The irradiated sample demonstrated the enhanced development, in both whisker densities and lengths, resulting in an acceleration factor of ~50. This makes gamma-ray irradiation a candidate tool for accelerated testing of whisker propensity. We attribute the observed enhancement to electrostatic fields created by charged defects in the glass substrate under ionizing radiation of gamma-rays.

cond-mat.mtrl-sci↗