arXiv subjects

Mythili Surendran

Publications and source records attributed to Mythili Surendran.

16 recordsLinked to original sources

arXiv2025

Evaluation of carbon incorporation in sulfide thin films grown by hybrid pulsed laser deposition

Vapor-pressure-mismatched materials, such as transition metal chalcogenides, have emerged as key electronic, photonic, and quantum materials. Hybrid pulsed laser deposition (hPLD) has become a preferred method for epitaxial or textured growth of these materials; however, unintentional carbon (C) incorporation remains a persistent concern, particularly when using organic chalcogen precursors as safer alternatives to toxic hydrides. The mechanisms governing C incorporation and its impact on film growth and properties in hPLD remain poorly understood. Here, we investigate the influence of C-containing side products generated from organosulfur precursor pyrolysis on ZnS, BaTiS$_3$, and TiS$_2$ thin films grown by hPLD using tert-butyl disulfide (TBDS). Structural characterization via X-ray diffraction and atomic force microscopy, combined with secondary ion mass spectrometry, is used to systematically examine the effects of growth temperature and TBDS partial pressure on film morphology, crystallinity, and C incorporation. Optimal growth temperatures of 400{\deg}C, 500{\deg}C, and 700{\deg}C are identified for ZnS, TiS$_2$, and BaTiS$_3$, respectively. Growth above or below these temperatures leads to increased C incorporation at both the interface and within the film, correlating with degraded texture. In contrast, highly textured films exhibit minimal C content, comparable to films grown without TBDS. For TiS$_2$, C incorporation depends strongly on TBDS pressure, with 10$^{-1}$ Pa identified as the optimal pressure for minimizing contamination. At higher pressures, loss of preferential texture is observed, likely due to C graphitization poisoning the interface and bulk. These results provide new insight into process-induced C impurities in hPLD-grown chalcogenide thin films and have important implications for sulfide-based thin film technologies.

cond-mat.mtrl-sci↗

arXiv2025

Crystal Growth of Chalcogenides and Oxy-Chalcogenides Using Chloride Exchange Reaction

Chalcogenides and oxy-chalcogenides, including complex chalcogenides and transition metal dichalcogenides, are emerging semiconductors with direct or indirect band gaps within the visible spectrum. These materials are being explored for various photonic and electronic applications, such as photodetectors, photovoltaics, and phase-change electronics. Understanding the fundamental properties of these materials is crucial for optimizing their functionalities. Therefore, the availability of large, high-quality single crystals of chalcogenides and oxy-chalcogenides is essential for a better comprehension of their structure and properties. In this study, we present a novel crystal growth method that utilizes the exchange reaction between BaS and ZrCl$_4$/ HfCl$_4$. By carefully controlling the stoichiometric ratio of the binary sulfide to the chloride, we can grow single crystals of several materials, such as ZrS$_2$, HfS$_2$, BaZrS$_3$, and ZrOS. This method results in large single crystals with a short reaction time of 24 to 48 hours. High-resolution thin film diffraction and single-crystal X-ray diffraction confirm the quality of the crystals produced through this exchange reaction. We also report the optical properties of these materials investigated using photoluminescence and Raman measurements. The chloride exchange reaction method paves the way for the synthesis of single crystals of chalcogenides and oxy-chalcogenide systems with a short reaction time but with low mosaicity and can be an alternative growth technique for single crystals of materials that are difficult to synthesize using conventional growth techniques.

cond-mat.mtrl-sci↗

arXiv2025

Textured growth and electrical characterization of Zinc Sulfide on back-end-of-the-line (BEOL) compatible substrates

Scaling of transistors has enabled continuous improvements in logic device performance, especially through materials engineering. However, surpassing horizontal limitations in chip manufacturing requires a vertical, third dimension. Three-dimensional integration of high-performance logic demands solving the challenge of low-temperature (less than 450{\deg}C) synthesis of high-mobility n-type and p-type semiconductor thin films for back-end-of-line (BEOL) compatible transistors. Metal oxides, particularly indium oxides alloyed with gallium and tungsten, are promising n-type channel materials, but suitable p-type materials for BEOL remain scarce. Zinc sulfide (ZnS), a wide band-gap semiconductor, shows room-temperature p-type conductivity when doped with copper and crystallizes below 400{\deg}C. Here, we report growth of crystalline ZnS thin films by pulsed laser deposition on amorphous and polycrystalline surfaces including silicon nitride, thermal silicon dioxide, yttrium oxide, hafnium dioxide, sapphire, platinum, and titanium nitride. X-ray diffraction reveals out-of-plane texturing across all surfaces, while grazing incidence wide-angle X-ray scattering probes in-plane crystalline quality. Surface and interface properties are assessed using X-ray reflectivity and atomic force microscopy. Electrical characterization via J-V measurements (ZnS on Pt) and metal-oxide-semiconductor capacitor (ZnS on silicon dioxide) measurements show low leakage current ($10^{-5} A/cm^2$ at 0.40 MV/cm) and bilayer capacitor behavior, suggesting ZnS is highly intrinsic with minimal electrically active defects. Further work on doping ZnS with copper or other p-type elements is needed to realize ZnS as a dopable wide band-gap semiconductor for BEOL integration. This work demonstrates a novel thin-film growth method for sulfide semiconductors under BEOL-compatible conditions.

cond-mat.mtrl-sci↗

arXiv2024

Electrical contacts for high performance optoelectronic devices of BaZrS3 single crystals

Chalcogenide perovskites such as BaZrS3 are promising candidates for next generation optoelectronics such as photodetectors and solar cells. Compared to widely studied polycrystalline thin films, single crystals of BaZrS3 with minimal extended and point defects, are ideal platform to study the material's intrinsic transport properties and to make first-generation optoelectronic devices. However, the surface dielectrics formed on BaZrS3 single crystals due to sulfating or oxidation have led to significant challenges to achieving high quality electrical contacts, and hence, realizing the high-performance optoelectronic devices. Here, we report the development of electrical contact fabrication processes on BaZrS3 single crystals, where various processes were employed to address the surface dielectric issue. Moreover, with optimized electrical contacts fabricated through dry etching, high-performance BaZrS3 photoconductive devices with a low dark current of 0.1 nA at 10 V bias and a fast transient photoresponse with rise and decay time of <0.2 s were demonstrated.

cond-mat.mtrl-sci↗

arXiv2024

A strategy for fabricating micro-scale freestanding single-crystalline complex oxide device arrays

We present a general fabrication strategy for freestanding single-crystalline complex oxide device arrays via wet chemical etching-based microfabrication processes and epitaxial lift-off. Here, we used 0.5Ba(Zr$_{0.2}$Ti$_{0.8}$)O$_3$-0.5Ba(Zr$_{0.7}$Ti$_{0.3}$)O$_3$ (BCZT) as a model relaxor ferroelectric oxide system and La$_{0.7}$Sr$_{0.3}$MnO$_3$ as the sacrificial layer for demonstration. Arrays of SrRuO$_3$ (SRO) / BCZT / SRO ferroelectric capacitor mesas were first defined and isolated on the growth wafer, and then they were released using epitaxial lift-off with lithography-defined surrounding etching holes, after which the freestanding device arrays were integrated onto a glass substrate. Our proposed strategy sheds light on preparing various freestanding single-crystalline oxide devices and paves the way for their heterogeneous integration onto arbitrary substates.

cond-mat.mtrl-sci↗

arXiv2024

Kinetic control of ferroelectricity in ultrathin epitaxial Barium Titanate capacitors

Ferroelectricity is characterized by the presence of spontaneous and switchable macroscopic polarization. Scaling limits of ferroelectricity have been of both fundamental and technological importance, but the probes of ferroelectricity have often been indirect due to confounding factors such as leakage in the direct electrical measurements. Recent interest in low-voltage switching electronic devices squarely puts the focus on ultrathin limits of ferroelectricity in an electronic device form, specifically on the robustness of ferroelectric characteristics such as retention and endurance for practical applications. Here, we illustrate how manipulating the kinetic energy of the plasma plume during pulsed laser deposition can yield ultrathin ferroelectric capacitor heterostructures with high bulk and interface quality, significantly low leakage currents and a broad "growth window". These heterostructures venture into previously unexplored aspects of ferroelectric properties, showcasing ultralow switching voltages ($<$0.3 V), long retention times ($>$10$^{4}$s), and high endurance ($>$10$^{11}$cycles) in 20 nm films of the prototypical perovskite ferroelectric, BaTiO$_{3}$. Our work demonstrates that materials engineering can push the envelope of performance for ferroelectric materials and devices at the ultrathin limit and opens a direct, reliable and scalable pathway to practical applications of ferroelectrics in ultralow voltage switches for logic and memory technologies.

physics.app-ph↗

arXiv2024

Growth of VO2-ZnS Thin Film Cavity for Adaptive Thermal Emission

Low-weight, passive, thermal-adaptive radiation technologies are needed to maintain an operable temperature for spacecraft while they experience various energy fluxes. In this study, we used a thin-film coating with the Fabry-Perot (FP) effect to enhance emissivity contrast ({\Delta}{\epsilon}) between VO2 phase-change states. This coating utilizes a novel hybrid material architecture that combines VO2 with a mid- and long-wave infrared transparent chalcogenide, zinc sulfide (ZnS), as a cavity spacer layer. We simulated the design parameter space to obtain a theoretical maximum {\Delta}{\epsilon} of 0.63 and grew prototype devices. Using X-ray diffraction, Raman spectroscopy, and Fourier Transform Infrared (FTIR) Spectroscopy, we determined that an intermediate buffer layer of TiO2 is necessary to execute the crystalline growth of monoclinic VO2 on ZnS. Through temperature-dependent FTIR spectroscopy measurements, our fabricated devices demonstrated FP-cavity enhanced adaptive thermal emittance.

physics.optics↗

arXiv2024

Hydrogen is not necessary for superconductivity in topotactically reduced nickelates

A key open question in the study of layered superconducting nickelate films is the role that hydrogen incorporation into the lattice plays in the appearance of the superconducting state. Due to the challenges of stabilizing highly crystalline square planar nickelate films, films are prepared by the deposition of a more stable parent compound which is then transformed into the target phase via a topotactic reaction with a strongly reducing agent such as CaH$_2$. Recent studies, both experimental and theoretical, have introduced the possibility that the incorporation of hydrogen from the reducing agent into the nickelate lattice may be critical for the superconductivity. In this work, we use secondary ion mass spectrometry to examine superconducting La$_{1-x}$X$_x$NiO$_2$ / SrTiO$_3$ (X = Ca and Sr) and Nd$_6$Ni$_5$O$_{12}$ / NdGaO$_3$ films, along with non-superconducting NdNiO$_2$ / SrTiO$_3$ and (Nd,Sr)NiO$_2$ / SrTiO$_3$. We find no evidence for extensive hydrogen incorporation across a broad range of samples, including both superconducting and non-superconducting films. Theoretical calculations indicate that hydrogen incorporation is broadly energetically unfavorable in these systems, supporting our conclusion that hydrogen incorporation is not generally required to achieve a superconducting state in layered square-planar nickelates.

cond-mat.supr-con↗

arXiv2024

Epitaxial rare-earth doped complex oxide thin films for infrared applications

Rare earth dopants are one of the most extensively studied optical emission centers for a broad range of applications such as laser optoelectronics, sensing, lighting, and quantum information technologies due to their narrow optical linewidth and exceptional coherence properties. Epitaxial doped oxide thin films can serve as a promising and controlled host to investigate rare-earth dopants suitable for scalable quantum memories, on-chip lasers and amplifiers. Here, we report high-quality epitaxial thin films of Tm-doped CaZrO$_3$ grown by pulsed laser deposition for infrared optoelectronic and quantum memory applications. We perform extensive structural and chemical characterization to probe the crystallinity of the films and the doping behavior. Low temperature photoluminescence measurements show sharp radiative transitions in the short-wave infrared range of 1.75 - 2 μm.

physics.optics↗

arXiv2023

Ruddlesden-Popper chalcogenides push the limit of mechanical stiffness and glass-like thermal conductivity in single crystals

Insulating materials featuring ultralow thermal conductivity for diverse applications also require robust mechanical properties. Conventional thinking, however, which correlates strong bonding with high atomic-vibration-mediated heat conduction, led to diverse weakly bonded materials that feature ultralow thermal conductivity and low elastic moduli. One must, therefore, search for strongly-bonded single crystals in which heat transport is impeded by other means. Here, we report intrinsic, glass-like, ultralow thermal conductivity and ultrahigh elastic-modulus/thermal-conductivity ratio in single-crystalline Ruddlesden-Popper Ban+1ZrnS3n+1, n = 2,3, which are derivatives of BaZrS3. Their key features are strong anharmonicity and intra-unit-cell rock-salt blocks. The latter produce strongly bonded intrinsic superlattices, impeding heat conduction by broadband reduction of phonon velocities and mean free paths and concomitant strong phonon localization. The present study initiates a paradigm of mechanically stiff phonon glasses.

cond-mat.mtrl-sci↗

arXiv2023

A hybrid pulsed laser deposition approach to grow thin films of chalcogenides

Vapor-pressure mismatched materials such as transition metal chalcogenides have emerged as electronic, photonic, and quantum materials with scientific and technological importance. However, epitaxial growth of vapor-pressure mismatched materials are challenging due to differences in the reactivity, sticking coefficient, and surface adatom mobility of the mismatched species constituting the material, especially sulfur containing compounds. Here, we report a novel approach to grow chalcogenides - hybrid pulsed laser deposition - wherein an organosulfur precursor is used as a sulfur source in conjunction with pulsed laser deposition to regulate the stoichiometry of the deposited films. Epitaxial or textured thin films of sulfides with variety of structure and chemistry such as alkaline metal chalcogenides, main group chalcogenides, transition metal chalcogenides and chalcogenide perovskites are demonstrated, and structural characterization reveal improvement in thin film crystallinity, and surface and interface roughness compared to the state-of-the-art. The growth method can be broadened to other vapor-pressure mismatched chalcogenides such as selenides and tellurides. Our work opens up opportunities for broader epitaxial growth of chalcogenides, especially sulfide-based thin film technological applications.

cond-mat.mtrl-sci↗

arXiv2022

Unconventional Charge-density-wave Order in a Dilute d-band Semiconductor

Electron-lattice coupling effects in low dimensional materials give rise to charge density wave (CDW) order and phase transitions. These phenomena are critical ingredients for superconductivity and predominantly occur in metallic model systems such as doped cuprates, transition metal dichalcogenides, and more recently, in Kagome lattice materials. However, CDW in semiconducting systems, specifically at the limit of low carrier concentration region, is uncommon. Here, we combine electrical transport, synchrotron X-ray diffraction and optical spectroscopy to discover CDW order in a quasi-one-dimensional (1D), dilute d-band semiconductor, BaTiS3, which suggests the existence of strong electron-phonon coupling. The CDW state further undergoes an unusual transition featuring a sharp increase in carrier mobility. Our work establishes BaTiS3 as a unique platform to study the CDW physics in the dilute filling limit to explore novel electronic phases.

cond-mat.mtrl-sci↗

arXiv2021

Epitaxial Thin Films of a Chalcogenide Perovskite

Chalcogenide perovskites have emerged as a new class of electronic materials, but fundamental properties and applications of chalcogenide perovskites remain limited by the lack of high quality epitaxial thin films. We report epitaxial thin film growth of BaZrS3, a prototypical chalcogenide, by pulsed laser deposition. X-ray diffraction studies show that the films are strongly textured out of plane and have a clear in-plane epitaxial relationship with the substrate. Electron microscopy studies confirm the presence of epitaxy for the first few layers of the film at the interface, even though away from the interface the films are polycrystalline with a large number of extended defects suggesting the potential for further improvement in growth. X-Ray reflectivity and atomic force microscopy show smooth film surfaces and interfaces between the substrate and the film. The films show strong light absorption near the band edge and photoluminescence in the visible region. The photodetector devices show fast and efficient photo response with the highest ON/OFF ratio reported for BaZrS3 films thus far. Our study opens up opportunities to realize epitaxial thin films, heterostructures, and superlattices of chalcogenide perovskites to probe fundamental physical phenomena and the resultant electronic and photonic device technologies.

cond-mat.mtrl-sci↗

arXiv2021

In situ Monitoring of Composition and Sensitivity to Growth Parameters of Pulsed Laser Deposition

Complex oxide perovskites have been widely studied for their diverse functional properties. When dimensionally reduced to epitaxial thin films and heterostructures these properties are frequently tunable, and the symmetry-breaking inherent to thin film structures can result in the emergence of new, novel, phenomena and properties. However, the ability to control and harness these structures relies on an atomic-level understanding and control of the growth process, made challenging by the lack of suitable in situ compositional characterization tools. In this work, the compositional-dependence of SrTiO3 on pulsed laser deposition growth parameters is investigated with in situ Auger electron spectroscopy and ex situ thin film x-ray diffraction, and verified with a simple escape depth model. We show that this is a suitable technique for monitoring subtle compositional shifts occurring during the deposition process, with broad implications for the continued development of thin film synthesis techniques.

cond-mat.mtrl-sci↗

arXiv2021

Direct Observation and Control of Surface Termination in Perovskite Oxide Heterostructures

The interfacial behavior of quantum materials leads to emergent phenomena such as two dimensional electron gases, quantum phase transitions, and metastable functional phases. Probes for in situ and real time surface sensitive characterization are critical for active monitoring and control of epitaxial synthesis, and hence the atomic-scale engineering of heterostructures and superlattices. Termination switching, especially as an interfacial process in ternary complex oxides, has been studied using a variety of probes, often ex situ; however, direct observation of this phenomena is lacking. To address this need, we establish in situ and real time reflection high energy electron diffraction and Auger electron spectroscopy for pulsed laser deposition, which provide structural and compositional information of the surface during film deposition. Using this unique capability, we show, for the first time, the direct observation and control of surface termination in complex oxide heterostructures of SrTiO3 and SrRuO3. Density-functional-theory calculations capture the energetics and stability of the observed structures and elucidate their electronic behavior. This demonstration opens up a novel approach to monitor and control the composition of materials at the atomic scale to enable next-generation heterostructures for control over emergent phenomena, as well as electronics, photonics, and energy applications.

cond-mat.mtrl-sci↗

arXiv2019

In situ Auger electron spectroscopy of complex oxide surfaces grown by pulsed laser deposition

The authors report in situ Auger electron spectroscopy (AES) of the surfaces of complex oxides thin films grown by pulsed laser deposition (PLD). The authors demonstrate the utility of the technique in studying chemical composition by collecting characteristic Auger spectra of elements from samples such as complex oxide thin films and single crystals as well as metal foils. In the case of thin films, AES studies can be performed with single unit cell precision by monitoring thickness during deposition with reflection high energy electron diffraction (RHEED). The authors address some of the challenges in achieving in situ and real time AES studies on complex oxide thin films grown by PLD. Sustained layer-by-layer PLD growth of a CaTiO3/LaMnO3 superlattice allows depth-resolved chemical composition analysis during the growth process. The evolution of the Auger spectra of the elements from individual layers were used to perform chemical analysis with monolayer-depth resolution.

cond-mat.mtrl-sci↗