Papers by K.V.L.V. Narayanachari
The Dynamics of Oxygen Ion Exchange in Epitaxial Strontium Cobaltite Bilayers
Advanced Materials Interfaces
Tungsten Oxide Mediated Quasi-van der Waals Epitaxy of WS2 on Sapphire
ACS Nano
Cornell University - arXiv, Nov 8, 2022
Despite the huge advancement in knowledge discovery and data mining techniques, the X-ray diffrac... more Despite the huge advancement in knowledge discovery and data mining techniques, the X-ray diffraction (XRD) analysis process has mostly remained untouched and still involves manual investigation, comparison, and verification. Due to the large volume of XRD samples from high-throughput XRD experiments, it has become impossible for domain scientists to process them manually. Recently, they have started leveraging standard clustering techniques, to reduce the XRD pattern representations requiring manual efforts for labeling and verification. Nevertheless, these standard clustering techniques do not handle problem-specific aspects such as peak shifting, adjacent peaks, background noise, and mixed phases; hence, resulting in incorrect compositionphase diagrams that complicate further steps. Here, we leverage data mining techniques along with domain expertise to handle these issues. In this paper, we introduce an incremental phase mapping approach based on binary peak representations using a new threshold based fuzzy dissimilarity measure. The proposed approach first applies an incremental phase computation algorithm on discrete binary peak representation of XRD samples, followed by hierarchical clustering or manual merging of similar pure phases to obtain the final composition-phase diagram. We evaluate our method on the composition space of two ternary alloy systems
MOCVD of a Nanocomposite Film of Fe, Fe3O4 and Carbon Nanotubes from Ferric Acetylacetonate: Novel Thermodynamic Modeling to Reconcile with Experiment
MRS Proceedings, 2015
ABSTRACTThermodynamic modeling of the MOCVD process, using the standard free energy minimization ... more ABSTRACTThermodynamic modeling of the MOCVD process, using the standard free energy minimization algorithm, cannot always explain the deposition of hybrid films that occurs. The present investigation explores a modification of the procedure to account for the observed simultaneous deposition of metallic iron, Fe3O4, and carbon nanotubes from a single precursor. Such composite films have potential application in various device architectures and sensors, and are being studied as electrode material in energy storage devices such as lithium ion batteries and supercapacitors.With ferric acetylacetonate [Fe(acac)3] as the precursor, MOCVD in argon ambient results in a nanocomposite of CNT, Fe, and Fe3O4 (characterized by XRD and Raman spectroscopy) when growth temperature T and total reactor pressure P are in the range from 600°C-800°C and 5-30 torr, respectively. No previous report could be found on the single-step formation of a CNT-metal-metal oxide composite. Equilibrium thermodynamic...
RSC Advances, 2017
Annealing leads to grain growth and associated tensile strain in YSZ film, so initial compressive... more Annealing leads to grain growth and associated tensile strain in YSZ film, so initial compressive stress helps to grow larger grains.
Journal of Applied Physics, 2016
It is demonstrated here that growth stress has a substantial effect on the dielectric constant of... more It is demonstrated here that growth stress has a substantial effect on the dielectric constant of ZrO 2 thin films. The correct combination of parameters -phase, texture and stress -is shown to yield films with high dielectric constant and best reported equivalent oxide thickness of 0.8 nm. The stress effect on dielectric constant is twofold, firstly, by the effect on phase transitions and secondly by the effect on interatomic distances. We discuss and explain the physical mechanisms involved in the interplay between the stress, phase changes and the dielectric constant in detail. KEYWORDS: High-k dielectrics, in situ stress study in thin films, effect of stress on high-k dielectric, oxides thin films on germanium, reactive sputter deposition of oxides
Stress and Microstructural Evolution During the Growth of Transition Metal Oxide Thin Films by PVD
スパッタしたYSZ/Si膜の結晶粒成長と集合組織発達に及ぼす原位置応力の影響【Powered by NICT】
X-ray diffraction (XRD) is a widely used experiment in materials science to understand the compos... more X-ray diffraction (XRD) is a widely used experiment in materials science to understand the compositionstructure-property relationships of materials for designing and discovering new materials. A key aspect of XRD analysis is that the composition-phase diagram is composed of not only pure phases but also their mixed phases. Hard clustering approach treats the mixed phases as separate independent clusters from their constituent pure phases, hence, resulting in incorrect phase diagrams which complicate the next steps. Here, we present a novel clustering approach of XRD patterns by leveraging a fuzzy clustering technique that can significantly enhance the potential phase mapping and reduce the manual efforts involved in XRD analysis. The proposed approach first generates an initial composition-phase diagram and initial pure phase representations by applying the fuzzy c-means clustering algorithm, followed by hierarchical clustering to accomplish effortless manual merging of similar init...
Combinatorial Approach for Single-Crystalline TaON Growth: Epitaxial β-TaON (100)/α-Al2O3 (012)
ACS Applied Electronic Materials
Unexpected trends in the enhanced Ce3+ surface concentration in ceria–zirconia catalyst materials
Journal of Materials Chemistry A
Zirconium doping has a dramatically different influence on Ce reduction in the bulk than on the s... more Zirconium doping has a dramatically different influence on Ce reduction in the bulk than on the surface of ceria–zirconia.
Journal of Applied Physics
We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing c... more We present a study of co-sputtered VO2-SiO2 nanocomposite dielectric thin-film media possessing continuous temperature tunability of the dielectric constant. The smooth thermal tunability is a result of the insulator-metal transition in the VO2 inclusions dispersed within an insulating matrix. We present a detailed comparison of the dielectric characteristics of this nanocomposite with those of a VO2 control layer and of VO2/SiO2 laminate multilayers of comparable overall thickness. We demonstrated a nanocomposite capacitor that shows thermal capacitance tunability of ~60% between 25 o C to 100 o C at 1 MHz, with low leakage current. Such thermally tunable capacitors could find potential use in applications including sensing, thermal cloaks, and phase-change-based energy storage devices.
Journal of Applied Physics, 2012
Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria... more Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria stabilized zirconia (YSZ) is both an important functional oxide and a buffer layer material needed for integrating other functional oxides. Stress evolution during the growth of (100) and (111) oriented YSZ on Si (100) by radio frequency and reactive direct current sputtering has been investigated with an in-situ monitor and correlated with texture evolution. Films nucleated at rates <5 nm/min are found to be (111) oriented and grow predominantly under a compressive steady state stress. Films nucleated at rates >20 nm/min are found to be (100) oriented and grow under tension. A change in growth rate following the nucleation stage does not change the orientation. The value of the final steady state stress varies from À4.7 GPa to 0.3 GPa. The in-situ studies show that the steady state stress generation is a dynamic phenomenon occurring at the growth surface and not decided at film nucleation. The combination of stress evolution and texture evolution data shows that the adatom injection into the grain boundaries is the predominant source of compressive stress and grain boundary formation at the growth surface is the source of tensile stress.
We demonstrate a solid-state spiking artificial neuron based upon an insulator-to-metal (IMT) tra... more We demonstrate a solid-state spiking artificial neuron based upon an insulator-to-metal (IMT) transition material element that operates at an unprecedented low voltage (0.8 V). We have developed a general coupled electrical-thermal device model for IMT based devices to accurately predict experimental outcomes. From the experiment and simulation, we show that voltage scalability to sub 0.3 V is possible by scaling of the IMT based neuron.
Yttria stabilized zirconia (YSZ) films are being used both as functional oxide and buffer layers ... more Yttria stabilized zirconia (YSZ) films are being used both as functional oxide and buffer layers for integration of various other functional oxide films on Si substrates. As functional properties of these oxides are highly anisotropic in nature, highly oriented films are essential to realizing their fascinating properties. (111) and (100) textured YSZ films have been deposited on Si substrates by reactive-direct current (R-DC) sputtering. Annealing of these films leads to grain growth and improvement in texture. However, it strongly depends on the growth stresses developed during deposition of these films. Depending on stress harnessing in films/stacks, the texture was improved from rocking curve FWHM of 16 to 7 and 25 to 15 for (111) and (100) YSZ films respectively. A detailed analysis of the relation between stress and grain growth is carried out using an energy balance model. We have found that grain growth is limited by kinetics, though it should be possible from a thermodynamic viewpoint. It is observed that higher initial compressive stress aids significant grain growth ($150%) and texture-improvement ($57%) on annealing.
Stress is inevitable during thin film growth. It is demonstrated here that the growth stress has ... more Stress is inevitable during thin film growth. It is demonstrated here that the growth stress has a significant effect on the dielectric constant of high-k thin films. ZrO2 thin films were deposited on Ge by reactive direct current sputtering. Stress in these films was measured using in-situ curvature measurement tool. The growth stress was tuned from -2.8 to 0.1 GPa by controlling deposition rate. Dielectric permittivity of ZrO2 depends on temperature, phase, and stress. The correct combination of parameters—phase, texture, and stress—is shown to yield films with an equivalent oxide
thickness of 8 Å. Growth stresses are shown to affect the dielectric constant both directly by affecting lattice parameter and indirectly through the effect on phase stability of ZrO2.
ZrO 2 /Ge is potential high-k dielectric candidate to replace silicon based devices. Controlling ... more ZrO 2 /Ge is potential high-k dielectric candidate to replace silicon based devices. Controlling stress in zirconia film and stabilizing high dielectric constant phase is crucial for
high-k application. A precise control of stress and phase selectivity in high-k thin films is demonstrated. Thin films of ZrO 2 were grown by reactive sputter deposition. Wide range of growth stress in thin films from -0.3 to -2.8 GPa can be tuned by growth rate control. Adatom incorporation into grain oundary was the dominant source of observed stress. Phase selectivity in zirconia was achieved by tuning growth parameters.
Thermodynamic modeling of the MOCVD process, using the standard free energy
minimization algorith... more Thermodynamic modeling of the MOCVD process, using the standard free energy
minimization algorithm, cannot always explain the deposition of hybrid films that occurs. The
present investigation explores a modification of the procedure to account for the observed
simultaneous deposition of metallic iron, Fe 3 O 4 , and carbon nanotubes from a single precursor.
Such composite films have potential application in various device architectures and sensors, and
are being studied as electrode material in energy storage devices such as lithium ion batteries and
supercapacitors.
Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria... more Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria-stabilized zirconia is both, an important functional oxide and a buffer layer material needed for integrating other functional oxides. Stress evolution during the growth of (100) and (111) oriented YSZ on Si (100) by RF and DC sputtering has been investigated with an in-situ monitor. The results show that growth stress spans both compressive and tensile regimes depends on growth rate. Films are textured polycrystalline films that grow by the Volmer-Weber mode. The value of the stress varies from 40 MPa to -2.5 GPa depending on growth conditions. Growth rate is determined as a parameter to control orientation and stress levels of thin films grown. Mechanisms for generation of compressive stress are discussed: Laplace stress, atomic peening and chemical potential dependent adatom incorporation into grain boundaries. Adatom injection into the grain boundaries is the predominant mechanism in these observations.
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Papers by K.V.L.V. Narayanachari
thickness of 8 Å. Growth stresses are shown to affect the dielectric constant both directly by affecting lattice parameter and indirectly through the effect on phase stability of ZrO2.
high-k application. A precise control of stress and phase selectivity in high-k thin films is demonstrated. Thin films of ZrO 2 were grown by reactive sputter deposition. Wide range of growth stress in thin films from -0.3 to -2.8 GPa can be tuned by growth rate control. Adatom incorporation into grain oundary was the dominant source of observed stress. Phase selectivity in zirconia was achieved by tuning growth parameters.
minimization algorithm, cannot always explain the deposition of hybrid films that occurs. The
present investigation explores a modification of the procedure to account for the observed
simultaneous deposition of metallic iron, Fe 3 O 4 , and carbon nanotubes from a single precursor.
Such composite films have potential application in various device architectures and sensors, and
are being studied as electrode material in energy storage devices such as lithium ion batteries and
supercapacitors.