Sandeep Marka - Academia.edu (original) (raw)

Papers by Sandeep Marka

ACS Applied Materials & Interfaces

ACS Applied Materials & Interfaces, 2016

Exfoliated graphene oxide (EG)/MoO2 composites are synthesized by a simple solid-state graphenoth... more Exfoliated graphene oxide (EG)/MoO2 composites are synthesized by a simple solid-state graphenothermal reduction method. Graphene oxide (GO) is used as a reducing agent to reduce MoO3 and as a source for EG. The formation of different submicron sized morphologies such as spheres, rods, flowers, etc., of monoclinic MoO2 on EG surfaces is confirmed by complementary characterization techniques. As-synthesized EG/MoO2 composite with a higher weight percentage of EG performed excellently as an anode material in lithium-ion batteries. The galvanostatic cycling studies aided with postcycling cyclic voltammetry and galvanostatic intermittent titrations followed by ex situ structural studies clearly indicate that Li intercalation into MoO2 is transformed into conversion upon aging at low current densities while intercalation mechanism is preferably taking place at higher current rates. The intercalation mechanism is found to be promising for steady-state capacity throughout the cycling because of excess graphene and higher current density even in the operating voltage window of 0.005-3.0 V in which MoO2 undergoes conversion below 0.8 V.

Electrochimica Acta, 2015

Journal of Power Sources, 2015

RSC Adv., 2015

ABSTRACT 1 mm thick flexible few-layered graphene (FLG)/poly vinyl alcohol (PVA) composite sheets... more ABSTRACT 1 mm thick flexible few-layered graphene (FLG)/poly vinyl alcohol (PVA) composite sheets containing 0.1 and 0.5 Vol.% of FLG are prepared using an easy solution mixing process followed by a simple casting process. As-synthesized FLG is used as the filler. Morphology, structure and phase characteristics clearly showed the formation of composite. A maximum electromagnetic interference (EMI) shielding effectiveness (SE) of ~19.5 dB (in the X-band, 8.2–12.4 GHz) was obtained in case of the composite with 0.5 Vol.% of FLG. Absorption is found to be the dominant mechanism for EMI shielding. The high EMI SE is attributed to the network-like features formed by FLG in PVA matrix. EMI SE and absorption are understood by analysing dielectric behaviour, ac-conductivity and transparency to visible light of the composite sheets.

Superlattices and Microstructures, 2015

An easy and low temperature in-situ growth of MgO micro-rods on multi-layered graphene (MLG) in p... more An easy and low temperature in-situ growth of MgO micro-rods on multi-layered graphene (MLG) in poly vinyl alcohol (PVA) matrix is elucidated. MLG decked with nanosized fragments of MgO and PVA are used as the starting materials to form MgO micro-rods (width = 1lmandlength=1 lm and length = 1lmandlength=4 lm) and MLG filled PVA composite film. Simple solution mixing, spin coating and simple drying processes are used to obtain the PVA composite. The growth mechanism of MgO micro-rods and the role of PVA in the growth of MgO micro-rods are explained on the basis of the observed morphological, structural and phase characteristics and a further controlled synthesis experiment, respectively.

The Journal of Physical Chemistry C, 2015

We have used pulsed-laser deposition, following a specific sequence of heating and cooling phases... more We have used pulsed-laser deposition, following a specific sequence of heating and cooling phases, to grow ZnO nanorods on ZnO buffer/Si(100) substrates, in a 600 mT oxygen ambient, without catalyst. In these conditions, the nanorods preferentially self-organize in the form of vertically aligned, core/shell structures. X-ray diffraction analyses, obtained from 2θ−ω and pole figure scans, shows a crystalline (wurtzite) ZnO deposit with uniform c-axis orientation normal to the substrate. Field emission scanning electron microscopy, transmission electron microscopy (TEM), high resolution TEM, and selected area electron diffraction studies revealed that the nanorods have a crystalline core and an amorphous shell. The low-temperature (13 K) photoluminescence featured a strong I 6 (3.36 eV) line emission, structured green band emission, and a hitherto unreported broad emission at 3.331 eV. Further studies on the 3.331 eV band showed the involvement of deeply bound excitonic constituents in a single electron−hole recombination. The body of structural data suggests that the 3.331 eV emission can be linked to the range of defects associated with the unique crystalline ZnO/amorphous ZnO core/shell structure of the nanorods. The relevance of the work is discussed in the context of the current production methods of core/shell nanorods and their domains of application. Figure 3. (a, b, d) Field emission SEM and (c) SEM images of ZnO/ZnO core/shell nanorods grown by PLD at (a) 0°tilt (plane view), (b) 20°tilt, (c) 30°tilt, and (d) 85°tilt angles.

Proceedings of the 14th Asian Conference on Solid State Ionics (ACSSI 2014)(1AGSSEA), 2014

Surface and Coatings Technology, 2012

The growth patterns of chromium diboride thin films deposited by thermal evaporation on borosilic... more The growth patterns of chromium diboride thin films deposited by thermal evaporation on borosilicate glass, fused silica, single crystal Si and Cu substrates are reported. It is shown that the adhesion of films is best on Cu, whereas on the other substrate films of thickness of >200 nm are not stable. Scanning electron micrographs reveal that the films on Cu are marginally dense whereas on the other three substrates there is evidence for microporosity, clustering and three dimensional cracks. The as-deposited films on borosilicate glass substrates were amorphous independent of thickness. The films on fused silica, in contrast, crystallized at 60 nm thickness and showed the formation of boron deficient CrB 2 . At higher thickness there was evidence for both CrB 2 and the boron deficient Cr 2 B 3 or Cr 3 B 4 . In the case of films on Si substrate, the presence of both CrB 2 and the boron deficient Cr 2 B 3 or Cr 3 B 4 is evident. On Cu substrates, up to a thickness of 200 nm only reflections due to the CrB 2 phase are observable. At higher thickness the films consist of both CrB 2 and the boron deficient Cr 2 B 3 or Cr 3 B 4 phases. Nanoindentation studies reveal strong substrate dependent mechanical behavior. The hardness of the films is highest on fused silica with a value of 13.5 GPa. The highest hardness achieved on borosilicate glass and Cu substrates was 10 GPa. Interestingly, the Young's modulus value on all the substrates is less than 50% of the bulk value, ranging between 60 and 100 GPa. This has been correlated with the presence of microporosity and non-stoichiometry in the films. Spectral transmission studies on the films show that they become opaque on borosilicate glass and fused silica substrates at thicknesses > 150 nm. The reflectance of the Cu substrate is enhanced by 25% at 2500 nm due to the presence of the chromium diboride coatings.

Materials Letters, 2012

The present study highlights the growth and properties of chromium diboride films (100-300 nm thi... more The present study highlights the growth and properties of chromium diboride films (100-300 nm thickness) deposited on to various substrates (Cu, borosilicate glass and fused silica) by thermal evaporation process. Xray diffraction patterns showed that films were slightly boron deficient. This was confirmed using EDX measurements which indicated a nominal composition of CrB 1.5 . However, electron diffraction patterns showed the presence of CrB 2 leading to the inference that the films were composites of CrB 2 and CrB 1.5 . The films were nanocrystalline with crystallite sizes of the order of 15-20 nm. Scanning electron micrographs revealed that the film morphology is substrate dependent. The films on borosilicate glass and fused silica were optically transparent and insulating at thickness of~100 nm. The thicker films were opaque and conducting. There was enhancement in reflectance of Cu substrates from 25 to 50% in the near IR wavelength region due to the chromium boride coatings. The hardness of the films was 10 GPa on Cu while it was 8 GPa on glass substrates.