Suman Iyer - Academia.edu (original) (raw)

Papers by Suman Iyer

International Journal of Ceramic Engineering & Science

Journal of the mechanical behavior of biomedical materials, 2018

The development of a suitable polymeric bioactive composite with hydroxyapatite as a filler is on... more The development of a suitable polymeric bioactive composite with hydroxyapatite as a filler is one of the very actively pursued areas in bioapplications. This report concerns development of such a novel polymeric biocomposite viz. poly (aryl ether) ketone-poly (dimethylsiloxane) with a small percentage of nano carbon fibres and varying percentages of nanohydroxyapatite particulates as fillers. The earlier characterization of this material involving mechanical, thermal and bio-compatibility studies showed optimum improved behaviour at about 7% nanohydroxyapatite loading as reported elsewhere. In this study, the wear and friction response of this biocomposite was tested in air under dry sliding conditions against hard steel using a pin-on-disc apparatus. Interestingly, the adhesive wear characteristics of this nanocomposite with varying nanohydroxyapatite percentages showed a trend similar to that in other characteristics with lowest wear occurring around the same nanohydroxyapatite p...

Transactions of the Indian Ceramic Society, 2011

Cellulose and chitosan are two of the most abundant naturally occurring substances which are bein... more Cellulose and chitosan are two of the most abundant naturally occurring substances which are being increasingly used for developing biodegradable polymer composites given the current environmental concerns. In this report, the wear performance of nanocomposites of cellulose acetate phthalate (CAP) and chitosan reinforced with surface functionalized nanoclay (NC) is studied using a pin-on-disc (PoD) tester. The earlier basic material characterization of these nanocomposites has shown improvement in mechanical and thermal properties with the addition of NC, with a kind of optimum behaviour at around 6% NC addition. In the present study, with nanocomposite pin sliding on the steel disc, for lower loads (5 N and 10 N), the wear coefficient K was observed to be in the range 2.9 x 0−5 − 2.7 x 10−4 mm3.m−1.N−1 and for higher load of 30 N, it was in the higher range (2.7 x 10−4 − 6.9 x 10−3 mm3.m−1.N−1). In this adhesive wear mode, as expected from the earlier study, the wear coefficient was minimum for the composite with 6% NC for all the three load conditions used. On the other hand, in the abrasive wear case, with the pin sliding on SiC abrasive paper covered disc, a different trend was seen with the reference 0% nanoclay sample showing less wear (5.25 x 10−3 mm3.m−1.N−1) than 6% NC containing sample. An attempt is made to understand this difference in the wear behaviour bringing in the heterogeneous nature of the test material and the dispersed nature of the reinforcing nanoclay.

physica status solidi (a), 1985

IETE Journal of Research, 1994

Hard, low stress diamond-like carbon films have been deposited by plasma assisted chemical vapour... more Hard, low stress diamond-like carbon films have been deposited by plasma assisted chemical vapour deposition technique, The various substrates include soft IR components like ZnS and ZnSe windows, Gaseous precursors such as propene, ethyl alcohol and acetone have been used to synthesize the films to study the nature of precursors in determining the film compatibility with the underlying component (substrate), The residual compressive stresses, the Young's modulus and the adhesion energy of the films have been estimated to be 10(10) dynes/cm(2), 10(10) N/m(2) and 1000 ergs/cm(2) respectively. To alleviate film failure, a study on the effects of additive gases such as hydrogen and the use of buffer layers such as ZrO2, has been undertaken, The diamond-like carbon films produced here are hard (5000 kg/mm(2)), specularly smooth in the wavelength region from 2.5 mu m to 20 mu m, with no microstructural features and have excellent adhesion on ZnS and ZnSe windows. The figure of merit of these films for aero-space applications has been evaluated by subjecting the film-buffer layer ZnS or ZnSe composite stack to wind, dust and rain erosion studies and by establishing the integrity of the specular IR transmittance of the stack upto 16 or 20 mu m as the case may be.

Physical Review B, 1997

In this paper, recent results on band A emission in chemical vapor-deposited diamond films have b... more In this paper, recent results on band A emission in chemical vapor-deposited diamond films have been analyzed within a vibronic model. The blue-band A ͑2.8 eV͒ spectra from undoped diamond films grown by two different techniques have been simulated using the same phonon density distribution g(⍀) and Huang-Rhys factor (S). The same g(⍀) at higher S gives a good fit with the green band A ͑2.32 eV͒ as well. This model provides a reasonable alternative approach to the long standing donor-acceptor pair recombination model. ͓S0163-1829͑97͒06908-7͔

MRS Proceedings, 2001

ABSTRACTWe have carried out measurements to try to correlate amorphous silicon film properties wi... more ABSTRACTWe have carried out measurements to try to correlate amorphous silicon film properties with companion solar cell device performance. The dc plasma deposited intrinsic films were prepared with various hydrogen dilution levels, and increasing power levels to increase growth rate. The electronic properties were determined using admittance spectroscopy and drive-level capacitance profiling (DLCP) techniques as well as transient photocapacitance and photocurrent spectroscopy. Cell and film performance were explored in both as-grown and light-soaked states. We observed that, although cell performance decreased systematiclly with increasing growth rate, it depended on factors other than the deep defect density in the matched films. On the other hand, we did observe that increases in defect density caused by the light-induced degradation led to fairly predictable decreases in the cell fill factors.

Wear, 2009

Erosion due to turbulence is a predominant factor in plant design for slurry handling. DUCOM Inst... more Erosion due to turbulence is a predominant factor in plant design for slurry handling. DUCOM Instruments (P) Ltd. has built a "counter rotating double disc erosion tester" to analyse surfaces for erosion due to turbulence. Volume loss of Stainless Steel and aluminum as a function of varying time, particle hardness, speed and slurry concentration is evaluated in this erosion tester. Individual study on the effect of corrosion on the total volume loss is conducted and found to be high in alumina slurry and low in silica slurry.

Thin Solid Films, 1997

We have investigated diamond deposition on porous silicon (PS) substrates without any pretreatmen... more We have investigated diamond deposition on porous silicon (PS) substrates without any pretreatment for nucleation enhancement, We find that the widely held expectation that, the highly rough nature of the PS surface would necessarily lead to a significant enhancement in the diamond nucleation density, does not hold. For the diamond deposition conditions used in this study, the nucleation density on PS (106 cm-2) is similar to that on untreated c-Si substrate. This indicates an absence of extra high-energy nucleation sites in spite of the micro-columnar surface of PS. As a result, the incubation time was often much longer on PS than on heavily scratched c-Si for the same diamond deposition conditions. Under such conditions, the XRD patterns of deposit on PS showed silicon carbide-related peaks in addition to weak diamond peaks. The results are compared with the earlier observations regarding diamond deposition on PS pretreated with diamond abrasive or negative DC bias. The comparative study, which needs further explanation, indicates a synergistic relation between the negative DC bias pretreatment and the effect of porosity of the substrate on diamond nucleation on PS substrate.

Physical Review Letters, 1987

Physica Status Solidi (a), 1983

A modified DLTS technique for characterization of surface states in MOS structures is proposed. I... more A modified DLTS technique for characterization of surface states in MOS structures is proposed. It involves scanning the bias while applying small filling pulses at constant temperature. The surface states behave as discrete levels when the pulses are small. Results on a Cu-Si0,-p-Si tunnel diode are presented as example. Eine modifizierte DLTS-Technik zur Charakterisierung der Oberfliichenzustiinde in MOS-Strukturen wird vorgeschlagen, die in einer hderung (scanning) der Vorspannung besteht, wghrend kleine Fullimpulse bei konstanter Temperatur angelegt werden. Die Oberfliichenzustiinde zeigen sich als diskrete Niveaus, wenn die Impulse klein sind. Als Beispiel werden die Ergebnisse an einer Cu-Si0,-p-Si-Tunneldiode mitgeteilt.

Journal of Applied Physics, 1984

ABSTRACT

Journal of Applied Physics, 1988

Experimental evidence that phosphorus in silicon is neutralized by hydrogenation is presented by ... more Experimental evidence that phosphorus in silicon is neutralized by hydrogenation is presented by measuring changes in sheet resistance and Hall mobility carrier in heavily phosphorus-doped polycrystalline films.

Journal of Applied Physics, 1985

... Iyer 232/C, Milk Colony, Bangalore-560 012, India Vikram Kumar Department of Physics and Mate... more ... Iyer 232/C, Milk Colony, Bangalore-560 012, India Vikram Kumar Department of Physics and Materials Research Laboratory, Indian Institute of Science, Bangalore-560 012 ... from ke PL {ND+p\{ ND+p\ (2) where e is the static dielectric constant and к is the Boltz-mann constant. ...

Japanese Journal of Applied Physics, 1989

It is rigorously proved that, if adiabatic switching off of the interaction is properly implement... more It is rigorously proved that, if adiabatic switching off of the interaction is properly implemented, as demanded by formal time-dependent S-matrix theory, even the Keldyshtype theories of multiphoton ionization require energy conservation without allowing for the ponderomotive energy, which only contributes an unobservable phase. The importance of ponderomotive effects in above-threshold ionization therefore needs to be reexamined .

International Journal of Quantum Chemistry, 1986

The matrix elements of the spin-free Hamiltonian between two atomic configuration state functions... more The matrix elements of the spin-free Hamiltonian between two atomic configuration state functions (CSF'S) in the L-S coupling scheme are expressed in terms of the atomic integrals Fk's and G"s. Using these general expressions, the matrix elements have been obtained for all the atomic configurations with three valence electrons that have not been solved so far by earlier methods. The scope for applying this new approach to obtain the Auger line energies and the promotion energies of metals that involve more than two partially filled shells is indicated. The energy expressions for some of the relevant configurations are tabulated.

Diamond and Related Materials, 1993

Abstract Deposition onto GaAs of dielectric film with good interfacial properties is difficult ow... more Abstract Deposition onto GaAs of dielectric film with good interfacial properties is difficult owing to the high surface state densities at the GaAs surface. Study of diamond-like carbon (DLC)/GaAs heterostructures is worthwhile because of the advantageous properties of ...