Vijay Toutam | National Physical Laboratory (original) (raw)

Papers by Vijay Toutam

Materials Research Bulletin, 2015

ABSTRACT Electrical characterization of grain boundaries (GB) of Cu-deficient CZTS (Copper Zinc T... more ABSTRACT Electrical characterization of grain boundaries (GB) of Cu-deficient CZTS (Copper Zinc Tin Sulfide) thin films was done using atomic force microscopy (AFM) techniques like conductive atomic force microscopy (CAFM), Kelvin Probe Force Microscopy (KPFM) and Scanning Capacitance Microscopy (SCM). Absorbance spectroscopy was done for optical band gap calculations and Raman, XRD and EDS for structural and compositional characterization. Hall measurements were done for estimation of carrier mobility. CAFM and KPFM measurements showed that the currents flow mainly through grain boundaries (GB) rather than grain interiors. SCM results showed that charge separation mainly occurs at the interface of grain and grain boundaries and not all along the grain boundaries.

Thin Solid Films

A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18 nm thick... more A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18 nm thickness for the combined (Ta + Si) layer, was evaluated to explore the individual layer thickness and the interface mixing behavior using different surface characterization techniques like Time-of-Flight Secondary Ion Mass Spectrometry (TOFSIMS), X-ray Reflectometry (XRR) and Kelvin Probe Force Microscopy (KPFM). These results were compared with measurements performed earlier using cross section Transmission Electron Microscopy (TEM). The TOFSIMS depth profile results indicate the individual thickness of Si and Ta layers to be 8.1 nm and 5.9 nm respectively which are less than the corresponding actual thickness measured by cross section TEM as 10.5 nm and 7.5 nm. The difference in thickness measurement has been explained in the light of ion bombardment induced atomic mixing in the interface during sputter depth profiling. A scanning electron micrograph shows the actual crater and its edges ...

Applied Surface Science, 2015

ABSTRACT Polydimethyl siloxane (PDMS) and Silica (SiO2) nanoparticle composite blocks of three di... more ABSTRACT Polydimethyl siloxane (PDMS) and Silica (SiO2) nanoparticle composite blocks of three different batches (CB1–CB3) made by varying the size of SiO2 nanoparticles (NP), are studied for the degree of hydrophilization and retainability after oxidation by contact angle measurements (CA) and force distance spectroscopy (FDS) using Atomic Force Microscope (AFM). While CA measurements have shown high hydrophilization and retainability for CB3, F-D spectroscopy has reiterated the observation and has shown long range interactive forces and high Debye length of the electrostatic double layer formed. These results are in agreement with the radius ratio rule of binary sphere system for high density packing in the composite and thereby for strong hydrophilization and retainability due to reinforcement and restricted diffusion of uncured polymer.

The Journal of Physical Chemistry C, 2008

... They are thankful to Department of Science and Technology for support and to the Veeco-India ... more ... They are thankful to Department of Science and Technology for support and to the Veeco-India Nano Laboratory for providing the AFM facility. They also thank Ms. Supreet for assistance. ... Catal., A 2000 43 194 195. 17. Costello, CK; Kung, MC; Oh, HS; Wang, Y.; Kung, HH Appl. ...

International Journal of Nanoscience, 2011

ABSTRACT Evaluating the electrical nature of carbon nanotubes (CNTs) from a collection requires e... more ABSTRACT Evaluating the electrical nature of carbon nanotubes (CNTs) from a collection requires establishing electrical contacts across individual CNTs lying on a dielectric layer. In this work, it is shown how a dielectric layer may be inserted underneath a chosen CNT. This has been accomplished by the electron beam induced carbonaceous deposition process in the presence of moisture and residual hydrocarbons present in the SEM chamber. When performed at a CNT location on a Si substrate, the CNT instead of getting buried underneath is found to be lifted on top of the carbonaceous platform, as if due to nonwetting nature of CNT surface. By ¯xing one end of the CNT on the Ag/Si substrate using a Pt deposit and lifting rest of the length to lie on a carbonaceous platform, the IÀV data from nanotubes of varying resistances have been collected using conducting AFM. The chosen nanotubes have also been examined by Raman measure-ments. The method is particularly useful while working with a random collection of nanotubes resulting from a chemical process.

AIP Advances, 2013

ABSTRACT Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage... more ABSTRACT Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage during local anodic oxidation (LAO) using atomic force microscope (AFM). Corona effect and segregation of cobalt in the vicinity of the rings is studied using magnetic force microscopy and energy dispersive spectroscopy. Double ring formation is attributed to the interaction of ablated material with the induced magnetic field during LAO. Steepness of forward bias transport characteristics from the unperturbed region of the CMS film suggest a non equilibrium spin contribution. Such mesoscopic textures in magnetic films by AFM tip can be potentially used for memory storage applications.

Applied Physics Letters, 2014

Thin Solid Films, 2012

ABSTRACT A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18... more ABSTRACT A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18 nm thickness for the combined (Ta + Si) layer, was evaluated to explore the individual layer thickness and the interface mixing behavior using different surface characterization techniques like Time-of-Flight Secondary Ion Mass Spectrometry (TOFSIMS), X-ray Reflectometry (XRR) and Kelvin Probe Force Microscopy (KPFM). These results were compared with measurements performed earlier using cross section Transmission Electron Microscopy (TEM). The TOFSIMS depth profile results indicate the individual thickness of Si and Ta layers to be 8.1 nm and 5.9 nm respectively which are less than the corresponding actual thickness measured by cross section TEM as 10.5 nm and 7.5 nm. The difference in thickness measurement has been explained in the light of ion bombardment induced atomic mixing in the interface during sputter depth profiling. A scanning electron micrograph shows the actual crater and its edges created due to the sputtering including the multilayer for real view of the structure. The XRR observations however reveal better agreement with the cross section TEM data, both being non-destructive in nature. Attempts were made to characterize the multilayer using KPFM technique which clearly elucidated the grating type cross section of the structure.

Solid State Sciences, 2005

We describe a method of resistless photolithography using laser for the fabrication of microscopi... more We describe a method of resistless photolithography using laser for the fabrication of microscopic markers and electrodes. A single shot of laser (355 nm, 100 mJ) is used to induce local surface melting and thus transfer a pattern from the mask (TEM grid) on to the ...

Solid State Communications, 2007

ABSTRACT Oxide nanopatterns have been drawn on Si (100), (110) and (111) substrates using the AFM... more ABSTRACT Oxide nanopatterns have been drawn on Si (100), (110) and (111) substrates using the AFM based method of local anodic oxidation (LAO) employing negative tip voltages of 5, 8 and 10 V. The same tip was used in all the cases and experimental parameters such as tip velocity and humidity were kept fixed. The total volume occupied by the oxide estimated based on the z-profiles of the raised patterns as well as of the trenches obtained after removing the oxide by treating with dilute HF, is similar to that of vitreous SiO2 at a moderate tip voltage of 8 V. A smaller voltage of 5 V produced a defect oxide (SiOx) as seen on the (111) surface while, a tip voltage of 10 V gave rise to a porous oxide that occupied, in relation to vitreous SiO2, ∼14% more volume in the case of (100) and (111) surfaces and ∼35% with the (110) surface. The nature of the oxide is related to the surface densities of the substrates, the (110) surface being dense requires more voltage to initiate oxidation but produces voluminous oxide. Nanoindentation on the LAO pattern yielded a hardness value of 4.3 GPa.

Nanotechnology, 2007

ABSTRACT Nanometric trench patterns have been drawn on polyvinylpyrrolidone films coated on Si su... more ABSTRACT Nanometric trench patterns have been drawn on polyvinylpyrrolidone films coated on Si substrates, employing an atomic force microscope using a conducting tip under a bias of −12 V with respect to the substrate ground and a moderate writing speed of 0.5 µm s−1. The obtained trenches have been used as nanomolds to create line patterns filled with Au nanocrystals (mean diameter, 3.5 nm). Importantly, scanning electron microscopy measurements showed that the region around the polymer trenches is subjected to an electric field stress from the tip. Thus the modified region was exploited in chemically adsorbing C60, as shown by electrical force microscopy and Raman spectroscopy measurements. The utility of the method is demonstrated by measuring the I–V characteristics of a nanopattern of C60.

Journal of Physics: Condensed Matter, 2010

We have studied the intrinsic doping level and gate hysteresis of graphene-based field effect tra... more We have studied the intrinsic doping level and gate hysteresis of graphene-based field effect transistors (FETs) fabricated over Si/SiO(2) substrates. It was found that the high p-doping level of graphene in some as-prepared devices can be reversed by vacuum degassing at room temperature or above depending on the degree of hydrophobicity and/or hydration of the underlying SiO(2) substrate. Charge neutrality point (CNP) hysteresis, consisting of the shift of the charge neutrality point (or Dirac peak) upon reversal of the gate voltage sweep direction, was also greatly reduced upon vacuum degassing. However, another type of hysteresis, consisting of the change in the transconductance upon reversal of the gate voltage sweep direction, persists even after long-term vacuum annealing at 200 °C, when SiO(2) surface-bound water is expected to be desorbed. We propose a mechanism for this transconductance hysteresis that involves water-related defects, formed during the hydration of the near-surface silanol groups in the bulk SiO(2), that can act as electron traps.

Journal of Nanoscience and Nanotechnology, 2009

Nanopatterning of Si(100) surfaces deposited with Au films from physical and chemical methods, ha... more Nanopatterning of Si(100) surfaces deposited with Au films from physical and chemical methods, has been carried out using a AFM set up mounted with a conducting tip. At a tip bias of -12 V, the LAO patterns drawn on various Au/SiOx surfaces have been compared with those on bare Si. The height of the oxide patterns is several times higher in the case of Au covered Si surfaces compared to patterns on bare Si surface. The enhancement in LAO is related to the catalytic activity of Au nanoparticulates at SiOx interface.

Journal of Applied Physics, 2008

Chemical Physics Letters, 2007

... Au. The optical spectrum exhibits an absorption band around 520 nm ascribable to the surface ... more ... Au. The optical spectrum exhibits an absorption band around 520 nm ascribable to the surface plasmon [13] (Fig. ... array. The optical absorption spectrum of the Ag sol showed a characteristic plasmon band at 450 nm (see Fig. 3b). ...

$Research paper thumbnail of Effect of SiO $ _ {2} $ surface treatment on graphene transistors fabricated on Si: SiO $ _ {2} $ substrates using a lithography free process$

Bulletin of the American …, 2010

Reversal of p-doping to n-doping and hysteresis effects in graphene transistors on Si:SiO$_{2 }$ ... more Reversal of p-doping to n-doping and hysteresis effects in graphene transistors on Si:SiO$_{2 }$ have been reported before. In this detailed experimental study, comparison is made between electronic transport characteristics of single graphene layer transistors where the ...

Applied Physics Letters, 2008

ABSTRACT The properties of self-assembled InAs/GaAs quantum rings are investigated by conductive ... more ABSTRACT The properties of self-assembled InAs/GaAs quantum rings are investigated by conductive atomic force microscopy. Our two-dimensional current maps and current-voltage curves show a lower conductivity of the central ring hole as compared to rim and surrounding planar region. This result is quite surprising if we take into account the compositional profile of quantum rings: being the region with the highest In concentration, one would expect the central hole to be the region with the highest conductivity. However, including the presence of a surface oxide into numerical simulations yields consistent results, which show the same qualitative behavior as the measured conductivities.

Applied Physics Letters, 2013