Anupam Roy

Anupam Roy
University of Texas at Austin | UT · Microelectronics Research Center

PhD

About

82
Publications
17,455
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,272
Citations
Citations since 2017
34 Research Items
1071 Citations
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200
2017201820192020202120222023050100150200
Additional affiliations
July 2014 - present
University of Texas at Austin
Position
  • Research Associate
February 2012 - June 2014
University of Texas at Austin
Position
  • PostDoc Position
August 2008 - February 2012
Indian Association for the Cultivation of Science
Position
  • Research Scholar and Research Associate
Education
August 2003 - July 2004
August 2001 - July 2003
Jadavpur University
Field of study
  • Physics

Publications

Publications (82)
Article
Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been investigated by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images show the presence of short range (7x7) order on the air-oxidized surface. Comparison with FTs of STM images from a clean Si(111)-(7x7)...
Article
Full-text available
We report on low temperature transport studies of Bi2Te3 topological insulator thin films grown on Si(111)-(7 × 7) surface by molecular beam epitaxy. A sharp increase in the magnetoresistance with magnetic field at low temperature indicates the existence of weak anti-localization. The measured weak anti-localization effect agrees well with the Hika...
Article
We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the...
Article
We present an ultra-high vacuum scanning tunneling microscopy (STM) study of structural defects in molybdenum disulfide thin films grown on silicon substrates by chemical vapor deposition. A distinctive type of grain boundary periodically arranged inside an isolated triangular domain, along with other inter-domain grain boundaries of various types,...
Preprint
Chromium selenide thin films were grown epitaxially on Al${_2}$O${_3}$(0001) and Si(111)-(7${\times}$7) substrates using molecular beam epitaxy (MBE). Sharp streaks in reflection high-energy electron diffraction and triangular structures in scanning tunneling microscopy indicate a flat smooth film growth along the c-axis, and is very similar to tha...
Article
Full-text available
We investigate here the strain-induced growth of Cu at 600 °C and its interactions with a thermally grown, 270 nm-thick SiO2 layer on the Si(111) substrate. Our results show clear evidence of triangular voids and formation of triangular islands on the surface via a void-filling mechanism upon Cu deposition, even on a 270 nm-thick dielectric. Differ...
Article
Full-text available
Spin–orbit coupling (SOC) in materials plays a crucial role in interconversion between spin and charge currents. In reduced dimensions, SOC effects are enhanced and have been the focus of intensive experimental and theoretical research, both for their novel spin-dependent phenomena and for their potential exploitation in new spintronics devices. Th...
Article
Full-text available
Although electrostatic gating with liquid electrolytes has been thoroughly investigated to enhance electrical transport in two-dimensional (2D) materials, solid electrolyte alternatives are now actively being researched to overcome the limitations of liquid dielectrics. Here, we report direct growth of few-layer (3−4L) molybdenum disulfide (MoS2),...
Article
Using in-situ scanning tunneling microscopy (STM) we have investigated the evolution of Si(111)-7×7 surfaces, prepared under ultrahigh vacuum condition, upon Ar⁺ ion sputtering and subsequent annealing. We have monitored how the surface atomic arrangement changes upon annealing of the sputtered Si(111)-7×7 surface. Sputtering renders the Si(111)-7×...
Article
Full-text available
To achieve large area growth of transition metal dichalcogenides of uniform monolayer thickness, we demonstrate metal–organic chemical vapor deposition (MOCVD) growth under low pressure followed by a high-temperature sulfurization process under atmospheric pressure (AP). Following sulfurization, the MOCVD-grown continuous MoS2 film transforms into...
Article
Full-text available
Two distinct stacking orders in ReS2 are identified without ambiguity and their influence on vibrational, optical properties and carrier dynamics are investigated. With atomic resolution scanning transmission electron microscopy (STEM), two stacking orders are determined as AA stacking with negligible displacement across layers, and AB stacking wit...
Article
We investigate the role of growth temperature and metal/chalcogen flux in atmospheric pressure chemical vapor deposition (APCVD) growth of MoSe2 and WSe2 on Si/SiO2 substrates. Using scanning electron microscopy and atomic force microscopy, we observe that the growth temperature and transition metal flux strongly influence the domain morphology and...
Article
Chromium selenide thin films were grown epitaxially on Al2O3(0001) and Si(111)-(7 × 7) substrates using molecular beam epitaxy. Sharp streaks in reflection high-energy electron diffraction and triangular structures in scanning tunneling microscopy indicate flat smooth film growth along the c axis, which is very similar to that from a hexagonal surf...
Preprint
Full-text available
Two distinct stacking orders in ReS2 are identified without ambiguity and their influence on vibrational, optical properties and carrier dynamics are investigated. With atomic resolution scanning transmission electron microscopy (STEM), two stacking orders are determined as AA stacking with negligible displacement across layers, and AB stacking wit...
Article
Full-text available
Resistive switching (RS) induced by electrical bias is observed in numerous materials, including 2D hexagonal boron nitride (hBN), which has been used in resistive random access memories (RRAMs) in recent years. For practical high‐density, cross‐point memory arrays, compared with bipolar memories, nonpolar (or unipolar) devices are preferable in te...
Article
Chemical vapor deposition of 2D materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy driven or diffusion driven....
Article
Single atomic layers of two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for integration of optical and electronic circuits due to their extraordinary optical oscillator strength and large exciton binding energy. Customizing the exciton energy of the TMDs is a direct way to control the light-matter interaction....
Article
The synthesis of lateral heterostructures assembled by atomically-thin materials with distinct intrinsic properties is important for future heterojunction-embedded two-dimensional (2D) devices. Here we report an etching-assisted chemical vapor deposition method to synthesize large-area continuous lateral graphene/hexagonal boron nitride (Gr/h-BN) h...
Article
Full-text available
Atomically thin molybdenum disulfide (MoS2), a member of the transition metal dichalcogenide (TMDC) family, has emerged as the prototypical two-dimensional (2D) semiconductor with a multitude of interesting properties and promising device applications spanning all realms of electronics and optoelectronics. While possessing inherent advantages over...
Article
Full-text available
Recently high density (HD) nonmagnetic (NM) cobalt has been discovered in a cobalt thin film, grown on Si(111). This cobalt film had a natural cobalt oxide at the top. The oxide layer forms when the film is taken out of the electron-beam deposition chamber and exposed to air. Thin HD NM cobalt layers were found near the cobalt/silicon and the cobal...
Article
Full-text available
Defect-carrier interaction in transition metal dichalcogenides (TMDs) plays important roles in carrier relaxation dynamics and carrier transport, which determines the performance of electronic devices. With femtosecond laser time-resolved spectroscopy, we investigated the effect of grain boundary/edge defects on the ultrafast dynamics of photoexcit...
Article
Full-text available
Understanding defect effect on carrier dynamics is essential for both fundamental physics and potential applications of transition metal dichalcogenides. Here, the phenomenon of oxygen impurities trapping photo-excited carriers has been studied with ultrafast pump-probe spectroscopy. Oxygen impurities are intentionally created in exfoliated multila...
Article
We report here the synthesis of MoS2 nanostructures by a simple liquid phase exfoliation of MoS2 powder in organic solvents followed by microwave treatment. The probe sonication and the microwave treatment play an important role in rolling and curling of the MoS2 nanosheets to give rise to MoS2 spheres and rod/tube like-structures with diameter app...
Article
Full-text available
Due to competing long range ferromagnetic order, the transition metals Fe, Co and Ni are not superconductors at ambient pressure. While superconductivity was observed in a non-magnetic phase of Fe, stabilized under pressure, it is yet to be discovered in Co and Ni under any experimental conditions. Here, we report emergence of superconductivity in...
Article
Full-text available
As the focus of applied research in topological insulators (TI) evolves, the need to synthesize large-area TI films for practical device applications takes center stage. However, constructing scalable and adaptable processes for high-quality TI compounds remains a challenge. To this end, a versatile van der Waals epitaxy (vdWE) process for custom-f...
Article
Full-text available
In two dimensional (2D) transition metal dichalcogenides, defect-related processes can significantly affect carrier dynamics and transport properties. Using femtosecond degenerate pump-probe spectroscopy, exciton capture, and release by mid-gap defects have been observed in chemical vapor deposition (CVD) grown monolayer MoSe2. The observed defect s...
Article
This study illustrates short-term relaxation in CeOx- based resistive random access memory (RRAM) devices. Our results suggest that the noise of the serial selector device can impact the short-term relaxation, reduce the operating window of the RRAM, and increase the read error. Our findings indicate that the application of longer initial forming p...
Article
We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magn...
Article
We electrically detect charge current induced spin polarization on the surface of a molecular beam epitaxy grown Bi2Te3thin film in a two-terminal device with a ferromagnetic MgO/Fe contact and a nonmagnetic Ti/Au contact. The two-point resistance, measured in an applied magnetic field, shows a hysteresis tracking the magnetization of Fe. A theoret...
Article
Full-text available
Magnetism of 3d transition metals at high density has always received wide interest due to existence of magnetism at the core of the Earth. For ferromagnetic cobalt, although there is a theoretical prediction that its magnetic moment would vanish when the density increases to about 1.4 times the normal value, so far there is no experimental evidenc...
Article
An annealing method capable of forming highly activated shallow junctions in Ge CMOS is still lacking. For the first time, nonmelt submillisecond laser spike annealing (LSA) is demonstrated to achieve high activation level, excellent diffusion control, and resulting low contact resistivity for both n-type and p-type Ge junctions when using P and B...
Article
Quantum interference effects and electron-electron interactions are found to play an important role in two-dimensional (2D) bulk transport of topological insulator (TI) thin films, which were previously considered as 2D electron gas (2DEG) and explained on basis of Hikami-Larkin-Nagaoka formula and Lee-Ramakrishnan theory. The distinct massive Dira...
Article
Transition metal-oxide resistive random-access memories seem to be a viable candidate as the next-generation storage technology because transition metals have multiple oxidation states and are good ionic conductors. A wide range of transition metal oxides have recently been studied; however, fundamental understanding of the switching mechanism is s...
Article
Achieving damage-free, uniform, abrupt, ultra-shallow junctions while simultaneously controlling the doping concentration on the nanoscale is an ongoing challenge to the scaling down of electronic device dimensions. Here, we demonstrate a simple method of effectively doping ΙΙΙ-V compound semiconductors, specifically InGaAs, by a solid phase doping...
Article
Nanoscale metal oxide memristors have potential in the development of brain-inspired computing systems that are scalable and efficient1-3. In such systems, memristors represent the native electronic analogues of the biological synapses. However, the characteristics of the existing memristors do not fully support the key requirements of synaptic con...
Article
Layered transition metal dichalcogenides which are part of the two dimensional materials family are experiencing rapidly growing interest owing to their diverse physical and optoelectronic properties. Large area controllable synthesis of these materials is required for transition from lab scale research to practical applications. In this work, we p...
Conference Paper
Full-text available
Resistive random access memory (RRAM) is attractive as a promising candidate for next generation nonvolatile memory due to its potential scalability beyond 10 nm feature size using a crossbar structure, fast switching speed, low operating power, and good reliability. Cerium oxide has high dielectric constant and various valance states, making ceriu...
Conference Paper
Full-text available
Dielectric engineering using high-κ oxides, such as atomic layer deposited (ALD) Al2Ox and HfOx, has been in widespread use to enhance the mobility of molybdenum disulfide (MoS2) based field effect transistors (FETs) [1,2]. This performance enhancement of MoS2 FETs in a high-κ environment is mainly attributed to the screening of Coulomb scattering...
Article
To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-k oxides, respectively. The goal of this work is t...
Article
Full-text available
In this work, low operating voltage and high resistance ratio of different resistance states of binary transition metal oxide based resistive random access memories (RRAMs) are demonstrated. Binary transition metal oxides with high dielectric constant have been explored for RRAM application for years. However, CeOx is considered as a relatively new...
Article
Reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry and other physical property measurements are used to investigate the structure, morphology, magnetic and magneto-transport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular...
Conference Paper
Field effect transistors based on ultra-thin transition metal dichalcogenides suffer from high contact resistances due to the Schottky barrier formed between the metal and the semiconducting channel. An effective way to overcome this issue is to dope the semiconducting channel in order to reduce the Schottky barrier width, thereby enabling efficien...
Conference Paper
We studied low temperature magnetoresistance in molecular beam epitaxy grown topological insulator Bi2Se3 and Bi2Te3 thin films. The surface and structural characterization of the grown films showed smooth epitaxial growth on Si(111). The magnetoresistance has been measured at low temperatures (2 - 20 K) with magnetic fields upto 9 T. The full rang...
Conference Paper
Cr2Te3 is one of the very intriguing compounds in chromium chalcogenides family because of its unusual magnetic and magneto-transport properties. Here we have presented studies of molecular beam epitaxy (MBE) grown (001)-oriented Cr2Te3 thin films on Al2O3(0001) and Si(111)-(7×7) surfaces. Reflection high energy electron diffraction (RHEED), scanni...
Article
Full-text available
Ultrathin C-doped Ge (Ge:C) buffers are used as effective buffer layers to grow thin and smooth Si1−x Gex relaxed virtual substrates on Si over a wide range of Ge content (x = 0.23, 0.38, 0.50, 0.65, 1) by ultrahigh vacuum chemical vapor deposition. High degree of relaxation (≥90%) in thin Si1−x Ge x films (∼50 nm thick) is demonstrated using this...
Article
Full-text available
We have studied angle dependent magnetoresistance of Bi2Te3 thin film with field up to 9 T over 2–20 K temperatures. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the...
Article
Sub-monolayer Co deposition on clean Si(111)–(7 × 7) surfaces has been found to form nanoscale CoSi2 islands with a surrounding trench of one Si bilayer depth and mainly hexagonal shape. The trench surface structure is largely like that of the disordered ‘1 × 1’ phase of the Si(111)-7 × 7 ↔ ‘1 × 1’ phase transition and comprises mostly disordered S...
Article
Full-text available
We report on the growth of a monolayer thick fractal nanostructures of Ag on flat-top Ag islands, grown on Si(111). Upon application of a voltage pulse at an edge of the flat-top Ag island from a scanning tunneling microscope tip, Ag atoms climb from the edge onto the top of the island. These atoms aggregate to form precisely one-atom thick nanostr...
Conference Paper
Following the theoretical prediction about Bi2X3 (X=Se, Te) being a topological insulator (TI) because of strong spin-orbit interactions, interest has grown in integrating these materials with Si technology for potential future devices. In this work, we will be presenting the epitaxial TI structures grown by molecular beam epitaxy (MBE) by codeposi...
Article
Full-text available
We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample...
Article
We study a minimal model to understand the formation of clusters on surfaces in the presence of surface defects. We consider reaction diffusion model in which atoms undergoes reactions at the defect centers to form clusters. Volume exclusion between particles is introduced through a drift term in the reaction diffusion equation that arises due the...
Article
Full-text available
We study a reaction diffusion model which describes the formation of patterns on surfaces having defects. Through this model, the primary goal is to study the growth process of Ge on Si surface. We consider a two species reaction diffusion process where the reacting species are assumed to diffuse on the two dimensional surface with first order inte...
Article
Growth of Ag films on Br- and H-passivated Si(111) surfaces and the annealing behaviour have been investigated by Rutherford backscattering spectrometry, scanning electron microscopy and photoemission electron microscopy techniques. Upon annealing the phenomenon of thermal grooving was observed in the Ag films. Depending on the annealing temperatur...
Article
Full-text available
We report a phenomenon of strain-driven shape transition in the growth of nanoscale self-organized endotaxial CoSi2 islands on Si (100) substrates. Small square shaped islands as small as 15\times15 nm2 have been observed. Islands grow in the square shape following the four fold symmetry of the Si (100) substrate, up to a critical size of 67 \times...
Article
Ge atoms have been deposited on domain-patterned clean Si(111)-(7 × 7) and oxidized Si(111)-(7 × 7) surfaces. Clustering of Ge from the deposited Ge adatoms on these two kinds of surfaces shows contrasting patterns. On the clean Si surface, clustering predominantly occurs on domain boundaries, which include step edges on two sides. This leaves smal...
Article
Growth of Ag islands under ultra-high vacuum condition on air-oxidized Si(110)-(5 × 1) surfaces has been investigated by in situ reflection high energy electron diffraction and ex situ scanning electron microscopy and cross-sectional transmission electron microscopy. A thin oxide is formed on Si via exposure of the clean Si(110)-(5 × 1) surface to...
Article
Full-text available
Growth of narrow-neck, epitaxial as well as non-epitaxial and nearly spherical Ge islands on air-exposed Si(111)-(7\times7) surfaces has been investigated by in-situ scanning tunnelling microscopy (STM) and ex-situ high resolution cross-sectional transmission electron microscopy (HRXTEM). A thin oxide is formed on Si(111)-(7\times7) surfaces via ai...
Conference Paper
Full-text available
We have investigated the modifications of flat-top Ag islands on Si (111)-7×7 reconstructed surfaces upon application of a tip-pulse voltage by scanning tunneling microscopy (STM). The triggering of tip-pulse voltage causes the climbing of adatoms on the top of the island through “Coulomb sink” charging effect. The monolayer height coverage of the...
Conference Paper
Quantum size effects in electronic and magnetic behaviour in self-organized nanostructures are presented. Magic heights of Ag islands on Si(111) surfaces due to electronic confinement are discussed. Investigations of electronic structure by scanning tunneling spectroscopy (STS) showing evolution of electronic density of states at Fermi level with f...
Article
Parallel stripes of nanostructures on an n-type Si substrate have been fabricated by implanting 30 keV Ga+ ions from a focused ion beam (FIB) source at three different fluences: 1 � 1015, 2 � 1015 and 5 � 1015 ions/cm2. Two sets of implantation were carried out. In one case, during implantation the sub- strate was held at room temperature and in th...
Conference Paper
Full-text available
Growth of Ag film on Br‐ and H‐passivated Si(111) surfaces was examined by Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM) and photoemission electron microscopy (PEEM) techniques. The phenomenon of thermal grooving was observed after annealing at higher temperatures. Hierarchical desorption of Ag from the grain b...