Sandeep Gorantla

Lukasiewicz Research Network – PORT Polish Center for Technology Development · Special Materials Area

Unprotected copper conductors are prone to oxidation and corrosion, especially when in contact with salt water or at high temperature. In this study, we compared commercially available coating with graphene oxide and plasma-enhanced chemical vapor deposition (PECVD) graphene coated wires in terms of antioxidation and anticorrosion protection. Sampl...

The com bined application of SEM/FIB cross-section lamella preparation and S/TEM characterization of individual aeolian quartz silt grains revealed two types of polymineralic coating (com posed of Fe oxides/hydroxides, Al-silicates, together with relatively coarse incorporated crystals such as anhedral potassium feldspar and idiomorphic hematite) o...

Cu-based materials are used in various industries, such as electronics, power generation, and catalysis. In particular, monolayered cuprous oxide (Cu2O) has potential applications in solar cells owing to its favorable electronic and magnetic properties. Atomically thin Cu2O samples derived from bulk cuprite were characterized by high-resolution tra...

Composite silica-titania waveguide films of refractive index ca. 1.8 are fabricated on glass substrates using a sol-gel method and dip-coating technique. Tetraethyl orthosilicate and tetraethyl orthotitanate with molar ratio 1:1 are precursors. Fabricated waveguides are annealed at 500 °C for 60 min. Their optical properties are studied using ellip...

Due to the antisurfactant properties of arsenic atoms, the self-induced dodecagonal GaN microrods can be grown by molecular beam epitaxy (MBE) in Ga-rich conditions. Since temperature is a key parameter in MBE growth, the role of temperature in the growth of GaN microrods is investigated. The optimal growth temperature window for the formation of G...

Conventionally thermal oxidation of GaN is performed in either dry or wet oxygen ambient. In this work thermal oxidation in water vapor ambient, together with the two above mentioned modes, is characterized. All three GaN oxidation modes were comprehensively studied structurally and optically using a wide range of experimental methods. Thermal oxid...

A better understanding of the molecular beam epitaxy (MBE) grown AlGaN layers is crucial for the development of UV emitters based on III-nitrides. In this work, the growth kinetics of AlGaN structures deposited by plasma-assisted MBE under Ga-rich conditions on AlGaN/AlN/sapphire templates is studied in detail. The surface quality of the layers and...

Hexagonal boron nitride (h-BN), together with other members of the van der Waals crystal family, has been studied for over a decade, both in terms of fundamental and applied research. Up to now, the spectrum of h-BN-based devices has broadened significantly, and systems containing the h-BN/III-V junctions have gained substantial interest as buildin...

The growth and properties of the GaN cap layers crystallized by metalorganic vapor phase epitaxy were studied concerning the composition of the underlying AlGaN layer, type of induced strains and the desorption of the GaN during the initial cooling step after the epitaxy process. The composition of the underlying AlGaN layers was controlled by the...

We present the studies of structural and magnetic properties of graphene composites prepared with several quantities of a-Fe2O3 dopant of 5, 25 and 50% made with either ethanol or acetone. Our studies showed the presence of a weak magnetic order up to room temperature and saturation magnetization of about 0.2 emu/g in pure commercial graphene. With...

Nano‐ and micro‐rods of GaN offer many functionalities that are not present in regular flat nanostructures. Therefore, development of new growth methods of such structures is a hot topic. In this work the arsenic‐induced growth of GaN microrods under Ga‐rich conditions in the molecular beam epitaxy is presented. It is a self‐catalyst vapor–liquid–s...

2D intrinsic ferromagnetic materials are highly anticipated in spintronic devices due to their coveted 2D limited magnetism. However, 2D non‐layered intrinsic ferromagnets have received sporadic attention, which is largely attributed to the fact that their synthesis is still a great challenge. Significantly, manganese phosphide (MnP) is a promising...

An all-oxide thermoelectric generator for high-temperature operation depends on a low electrical resistance of the direct p-n junction. Ca 3 Co 4-x O 9+δ and CaMnO 3-δ exhibit p-type and n-type electronic conductivity, respectively, and the interface between these compounds is the material system investigated here. The effect of heat treatment (at...

Modulation spectroscopy was applied to study the N-polar GaN surface barrier height dependency on ambient gas type in GaN/GaN:Si and GaN/AlGaN/GaN heterostructures. The built-in electric field in the undoped layer of the GaN/GaN:Si structure was determined by an analysis of a Franz-Keldysh oscillation present in spectra and used to calculate the su...

The dry transfer of AB stacked bilayer high quality SiC epitaxial graphene is presented. Monolayers were also transferred for comparison. Large continuous layers exceeding hundreds of microns were successfully transferred. Structural characterization, using Raman and TEM methods, are used to assess the uniformity and the quality of the transferred...

Ce1-xEuxO2 nanocubes, with maximum Eu content x = 0.4, were synthesized by a simple hydrothermal method. Application of various experimental techniques (SEM-EDS, STEM-EDS, XPS, ICP-AES) revealed a uniform distribution of Eu and Ce in the nanocubes, but some oxygen depletion near the surface was detected. A model explaining the effect of the Eu dopi...

Cuprous oxide (Cu₂O) is a promising material for large scale photovoltaic applications. The efficiencies of thin film structures are, however, currently lower than those for structures based on Cu₂O sheets, possibly due to their poorer transport properties. This study shows that post-deposition rapid thermal annealing (RTA) of...

The interface between ZnO and Cu₂O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu₂O in magnetron sputtered samples....

Silicon-based tandem heterojunction solar cells utilizing cuprous oxide (Cu₂O) as the top absorber layer show promise for high-efficiency conversion and low production cost. In the present study, single phase Cu₂O films have been realized on n-type Si substrates by reactive magnetron sputtering at 400^oC. The obtaine...

Cuprous oxide (Cu2O) is a low-cost, nontoxic semiconductor interesting for photovoltaic applications. Together with ZnO it forms a p-n junction diode. With a theoretically estimated conversion efficiency of 18 % [1] it is envisaged as a potential material system for the next generation thin-film based solar cells. However, experimentally reported e...

Aside from unusual properties of mono-layer graphene, bi-layer has been shown to have even more interesting physics, in particular allowing bandgap opening with dual gating for proper interlayer symmetry. Such properties, promising for device applications, ignited significant interest in understanding and controlling the growth of bi-layer graphene...

Cu2O/ZnO has been envisaged as a potential material system for the next generation thin film solar cells. So far, the experimental efforts to obtain conversion efficiencies close to the theoretically predicted value have failed. Combining aberration-corrected (scanning) transmission electron microscopy and density functional theory modelling, we ha...

Epitaxial Cu2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu2O films exhibit a columnar growth manner apart from a ∼5 nm thick CuO interfacial layer. In comparison to the reactive...

Investigation of charge transport mechanisms across inhomogeneous nanoparticle (NP) layers in heterojunctions is one of the key technological challenges nowadays for developing novel hybrid nanostructured functional elements. Here, we successfully demonstrate for the first time the fabrication and characterization of a novel hybrid organic/inorgani...

The great application potential for two-dimensional (2D) membranes (MoS2, WSe2, graphene and so on) aroused much effort to understand their fundamental mechanical properties. The out-of-plane bending rigidity is the key factor that controls the membrane morphology under external fields. Herein we provide an easy method to reconstruct the 3D structu...

Supplementary Figures 1-14, Supplementary Discussion and Supplementary References

In this work we report on the growth of single crystalline Bi2Se3 nanostructures (nanoribbons, nanoflakes, and nanowires) by catalyst-free decomposition sublimation in sealed silica ampules. The nanostructures directly grow on Si/SiO2 substrates by a vapor-solid growth mechanism and show high degree of crystallinity with dimensions of >10 μm in len...

We present a comparative, combined ab initio and experimental study of sodium and lithium storage in amorphous (glassy) carbon (a-C) vs. graphite. Amorphous structures are obtained by fitting stochastically generated structures to a reference radial distribution function. Li insertion is thermodynamically favored in both graphite and a-C. While sod...

The initial isolation of graphene in 2004 spawned massive interest in this two-dimensional pure sp2 carbon structure due to its incredible electrical, optical, mechanical, and thermal effects. This in turn led to the rapid development of various characterization tools for graphene. Examples include Raman spectroscopy and scanning tunneling microsco...

In this in situ study, details of the coalescence of Pt nanoparticles encapsulated within carbon nanotubes are investigated whilst under electron irradiation in aberration corrected transmission electron microscopy. Coalescence occurs via the direct attachment of atoms on the surface, particle reorientation and relaxation.

Graphene was grown on a Ni (1 1 1) thin layer, used as a substrate. The Ni layer itself was grown on single crystal sapphire (0 0 0 1). Carbon was deposited by chemical vapor deposition using a mixture of methane, argon and hydrogen at atmospheric pressure implementing a constant gas flow (4.8-5 l/min) varying both the gas composition and the depos...

By modifying the cooling rate, a Cu50Zr45Ti5 alloy with various structures was developed. A fully glassy rod and specimens with different sizes and volume fractions of nanocrystals were produced. The relationship between the structure and mechanical properties of the Cu50Zr45Ti5 alloy was investigated. The different structures result in a transitio...

The decrease of thermal conductivity is crucial for the development of efficient thermal energy converters. Systems composed of a periodic set of very thin layers show among the smallest thermal conductivities reported to-date. Here, we fabricate in an unconventional but straight forward way hybrid superlattices consisting of a large number of nano...

Iron in Graphene Carbon or other covalently bonded materials, like boron nitride, can form two-dimensional sheets because of the strong bonding between the atoms. In contrast, metals share electrons in a three-dimensional delocalized way, and this could preclude the formation of thin stable sheets. Nevertheless, Zhao et al. (p. 1228 ) observed pure...

A platform for producing stabilized Pt atoms and clusters through the combination of an N-doped graphene support and atomic layer deposition (ALD) for the Pt catalysts was investigated using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). It was determined, using imaging and spectroscopy techniques, that...

Linker-free TiO2/CdSe hybrid nanorods (NRs) were prepared by growing CdSe QDs in the presence of TiO2 NR seeds using seeded–growth type colloidal injection approach. TEM studies revealed the abundant formation of anatase TiO2 NRs with different lengths. We found that the as-prepared TiO2 seeds determined the morphology of TiO2/CdSe NRs. The photoph...

Despite significant advances in the synthesis of nanostructures, our understanding of the growth mechanisms of nanowires and nanotubes grown from catalyst particles remains limited. In this study we demonstrate a straight forward route to grow co-axial amorphous B/BOx nanowires and BOx nanotubes using gold catalyst particles inside a transmission e...

The role of sample chamber configuration for the chemical vapor deposition of graphene over copper was investigated in detail. A configuration in which the gas flow is unrestricted was shown to lead to graphene with an inhomogeneous number of layers (between 1 and 3). An alternative configuration in which one end of the inner tube (in which the sam...

Often synthetic graphene requires transfer onto an arbitrary substrate prior to use because the substrate it was originally synthesized on is inappropriate for either electrical measurement or characterization. While a variety of routes have been developed they are substrate dependant and often involve the use of harsh treatments. Here we present a...

The employment of Ni–Mo films has recently been shown to yield strictly homogeneous single-layer graphene. In this study, we systematically investigate the different stages of nucleation and growth of graphene over Ni–Mo layers. The studies reveal that the Ni film breaks up and diffuses into the underlying Mo foil, forming a Ni–Mo intermetallic. Nu...

Single-walled carbon nanotubes are shown to have self-repairing capabilities exceeding that predicted by theory. Time-series aberration-corrected low-voltage transmission electron microscopy is used to study the defect dynamics of single-walled carbon nanotubes in situ. We confirm experimentally previous theoretical predictions for the agglomeratio...

In this work the effect of mechanical milling on the structure, thermal stability and hardness of single phase Al62.5Cu25Fe12.5 icosahedral quasi-crystals has been investigated for different milling intensities. The results indicate that, irrespective of the milling intensity used, the quasi-crystals transform to a body-centered cubic (bcc) phase d...

Van der Waals epitaxial growth of graphene on c-plane (0001) sapphire by CVD without a metal catalyst is presented. The effect of CH(4) partial pressure, growth temperature, and H(2)/CH(4) ratio were investigated and growth conditions optimized. The formation of mono-layer graphene was shown by Raman spectroscopy, optical transmission, grazing inci...

We fabricate inorganic thin film transistors with bending radii of less than 5μm maintaining their high electronic performance with on-off ratios of more than 100000 and subthreshold swings of 160mV/dec. The fabrication technology relies on the roll-up of highly strained semiconducting nanomembranes, which compacts planar transistors into three-dim...

For the characterization of light materials using transmission electron microscopy, a low electron acceleration voltage of 80 kV or even 60 kV is attractive due to reduced beam damage to the specimen. The concomitant reduction in resolving power of the microscope can be restored when using spherical aberration (C(s) ) correctors, which for the most...

Electron beams in transmission electron microscopes are very attractive to engineer and pattern graphene toward all-carbon device fabrication. The use of condensed beams typically used for sequential raster imaging is particularly exciting since they potentially provide high degrees of precision. However, technical difficulties, such as the formati...

A triple yielding phenomenon resulting in high fracture strength (up to 2360 ± 10 MPa) and large ductility (up to 13.5 ± 0.5%) during compressive deformation is first discovered and systematically investigated in metastable Cu47.5Zr47.5Al5 composites. Based on electron microscopy and X-ray diffraction studies, the major deformation mechanisms at th...

Aluminum borate is attractive in that the material has excellent mechanical properties, chemical inertness, high temperature stability, and a low coefficient of thermal expansion. Moreover, aluminum borate has advantages over a more traditional material, SiC, in that it does not readily oxidize at high temperature and can be produced at lower cost....

We report the encapsulation of the antiferromagnetic and magnetoelectric oxide Cr2O3 inside both multi - and single-walled carbon nanotubes. This is achieved by a two step post-synthesis filling process which involves the filling of nanotubes with CrO3 either from aqueous solution or from the molten phase, followed by appropriate annealing sequence...

Microstructure and magnetic properties of phase separating Gd55−xHfxCo25Al20 metallic glasses are investigated for x = 0, 10, 20, 27.5, 35, 45 and 55 at. %. The Gd–Hf–Co–Al alloy system undergoes typical liquid–liquid phase separation during quenching and decomposes into Gd-rich and Hf-rich amorphous phases. The microstructural features such as len...

A novel approach for alternating current (AC)-driven organic light-emitting devices is reported, which uses the concept of molecular doping in organic semiconductors. Doped organic charge-transport layers are used to generate charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes. Bright...

The pulsed-laser evaporation synthesis of silica nanofibers and crystalline binary nanoparticles is investigated in detail. By careful adjustment of the synthesis parameters one can tailor the product to form high yield nanofibers or binary nanoparticles. Some control on their diameters is also possible through the synthesis parameters. Oxidation o...

Epitaxial films of Fe3O4(111) are electrodeposited on single-crystal Ni(111). The lattice mismatch reduces from +138% in the ⟨011⟩ directions to −0.7% by forming a coincidence lattice in which 5 unit meshes of O overlap with 12 unit meshes of Ni.

The molecular structure and dynamics of carbon nanostructures is much discussed throughout the literature, mostly from the theoretical side because of a lack of suitable experimental techniques to adequately engage the problem. A technique that has recently become available is low-voltage aberration-corrected transmission electron microscopy. It is...

The interaction of single-walled carbon nanotubes (SWCNTs) and α-sexithiophene (6T) was studied by Raman spectroscopy and by in situ Raman spectroelectrochemistry. The encapsulation of 6T in SWCNT and its interaction causes a bleaching of its photoluminescence, and also small shifts of its Raman bands. The Raman features of the SWCNT with embedded...

We present in situ experimental observations of fullerenes seamlessly fusing to single-walled carbon nanotubes. The morphing-entry of a fullerene to the interior of a nanotube is also captured. The confined (1D) motion of the newly-encapsulated fullerene within its host attests to the actual change from the exterior to interior.

(Cu0.5Zr0.5)100−xAlx (x = 5, 6, 8) bulk metallic glasses (BMGs) were deformed in tension. Besides ductility up to 0.5%, the material shows work-hardening behaviour. Both effects are attributed to the deformation-induced precipitation of B2 CuZr nanocrystals and the formation of twins in the nanocrystals larger than 20 nm. The precipitation of the n...

Antiferromagnetic and magnetoelectric Cr2O3 surfaces strongly affect the electronic properties in half-metallic CrO2. We show the presence of a Cr2O3 surface layer on CrO2 grains by high-resolution transmission electron microscopy. The effect of these surface layers is demonstrated by measurements of the temperature variation of the magnetoelectric...

Bulk metallic glasses (BMGs) generally fail in a brittle manner under uniaxial, quasistatic loading at room temperature. The lack of plastic strain is a consequence of shear softening, a phenomenon that originates from shear-induced dilation that causes plastic strain to be highly localized in shear bands. So far, significant tensile ductility has...

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Stable junctions between a single carbon chain and two single-wall carbon nanotubes were produced via coalescence of functionalized fullerenes filled into a single-wall carbon nanotube and directly imaged by in situ transmission electron microscopy. First principles quantum chemical calculations support the observed stability of such molecular junc...

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C60 molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular...