Patents
V. Santhanam, S. K. Sivaraman,"Methods for preparing metal and metal oxide nanoparticles", US 8361188,
G. Schmid, U. Simon, D. Jaeger, V. Santhanam, T. Reuter, "Microelectronic component with electrically accessible metallic clusters", US 7602069 ; EP 1748501
Book Chapters
V. Santhanam, "Scalable synthesis of noble metal nanoparticles", in Nanoscale and Microscale Phenomena , Eds. Y. Joshi, S. Khandekar, Springer, India (2015)
V. Santhanam, R.P. Andres, "Metal Nanoparticles: Self-assembly into Electronic Nanostructures", in The Dekker Encyclopedia of Nanoscience and Nanotechnology , 3rd edition, Eds. S.E. Lyshevski, Marcel Dekker Inc., New York (2014)
Journal Publications
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K. Agrawal and V. Santhanam, "Electrochemical cycling durability of platinum overlayers formed by self-terminating electrodeposition", Int. J. Hydrog. Energy 51 (C), 722-731 (2024)
More than four Self-Terminating Electrodeposition cycles are needed to meet the US Department of Energy durability target.
(a) Chronoamperogram for 8 STED cycles of platinum deposition, (b) Comparison of anodic portion of chronoamperogram measured in solutions with and without K2PtCl4 salt, (c) XPS signal (normalized to gold signal) from Pt4f region for samples formed using various numbers of STED cycles. The raw data is represented as grey symbols (d) Comparison of platinum loading estimates by various methods with ICP-OES measurements.
(a) CVs measured after the durability test for samples fabricated using 1,4,8,12 and 20 STED cycles. (b) Magnified view of the PtO reduction peak after the durability test. (c) Platinum coverage (θPt) as a function of number of STED cycles after the durability test. (d–h) Representative FESEM images of platinum overlayers comprising 1 (d), 4 (e), 8 (f), 12 (g) and 20 (h) STED cycles. after the durability test. CVs were performed in 0.1 M HClO4, at 100 mV s−1 scan rate. The scale bar represents 2
More than four Self-Terminating Electrodeposition cycles are needed to meet the US Department of Energy durability target.
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K. Agrawal, A.A. Naik, S. Chaudhary, D. Parvatalu and V. Santhanam, "Prudent Practices in Ex-Situ Durability Analysis Using Cyclic Voltammetry for Platinum-based Electrocatalysts", Chem-Asian J 16(21), 3311-3325 (2021)
CV Tutorial Review
Prudent practices for ex-situ durability analysis: Nonelectrochemists working on PEMFC electrocatalyst development are baffled by inconsistent data artefacts during prolonged cyclic voltammetry tests. A closer look at experimental details reveals the need for prudent practices to avoid such artefacts. Herein, we emphasize prudent practices for beginners to avoid missteps and achieve repeatable results during lengthy ex-situ durability analysis.
Ex-situ durability analysis with (a) poor practices (b) prudent practices. Insets show corresponding trends for computed Hupd charges. Note, average values from three samples are used to evaluate the trend in the inset of panel b.
CV Tutorial Review
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A. Kumar and V. Santhanam, "Paper Swab based SERS Detection of Non-Permitted Colourants from Dals and Vegetables Using a Portable Spectrometer", Anal. Chim. Acta 1090, 106–113 (2019)
Colour me NOT! U will be Caught
(a) Pictorial illustration of the steps in the print-expose-develop process, (b) Representative FESEM image of developed silver nanowires with a nominal silver loading of 1 mg cm-2 on Kimwipe tissue paper.
(a) Photograph of the ozoniser and the setup used for ozonisation, (b) SERS spectra from swabs of green chillies before and after the ozonisation. Even after ozonisation MG peaks, albeit at a lower intensity,are still present, which shows the presence of dye even after ozonisation.
Colour me NOT! U will be Caught
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P. Joshi and V. Santhanam, "Inkjet-based fabrication process with control over the morphology of SERS active silver nanostructures", Ind.Eng.Chem.Res. 57 (15), 5250–5258 (2018)
(a) A schematic illustration of the steps involved in the fabrication process. (b) A chemical reaction scheme for the formation of silver from silver halide by photographic processing
(a) SERS signal comparison of substrates with nanoparticle and nanowire morphology using 1173 cm-1 vibration under 532 and 785 nm laser illumination with the constant silver loading of 0.067 mg/cm2. (b) Evaluation of average SERS substrate enhancement factor by comparison of SERS signal from the substrate with nanoparticle morphology and nanowire morphology with the silver loading of 0.5 mg/cm2 against bulk Raman signal under 532 nm laser illumination.
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P. Joshi and V. Santhanam, "Strain-sensitive inkjet-printed nanoparticle films on flexible substrates", IEEE Sensors Letters, 2 (1), pp.1-4 March(2018)
Dilver chloride printing and development into nanoparticles on PEL coated plastic OHP sheets
Gold toned silver nanoparticles on stretchable latex substrate
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D. O. Schmidt, N. Raab, M. Noyong, V. Santhanam, R. Dittman and U. Simon, "Resistive Switching of sub-10 nm TiO2 Nanoparticle Self-Assembled Monolayers", Nanomaterials. 7(11), 370 (2017)
Representative TEM images of the synthesized TiO2 nanoparticles (NPs)
Schematic drawing for the self-assembly of a TiO2 NP monolayer
wo I–V curves recorded on different TiO2 NP monolayers exhibiting bipolar resistive switching (BRS) behavior
Representative TEM images of the synthesized TiO2 nanoparticles (NPs)
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S. Kumar and V. Santhanam, "Inkjet Printed Electroadhesive Pads on Paper", Int. J.Nanotechnol.. 14 (9-11), 859- 866 (2017)
Digital photograph and schematic cross-section showing the setup used for shear load testing of interdigitated electrodes. Click on the image for youtube link.
Design layout of interdigitated electrodes along with dimensions.
Digital photographs (below) of fixed sample, developed sample, developed sample after HVI, and developed sample after HVII and corresponding magnified sections with intensity profile overlapped along the marked lines.
Digital photograph and schematic cross-section showing the setup used for shear load testing of interdigitated electrodes. Click on the image for youtube link.
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P. Joshi and V. Santhanam, "Paper-based SERS Active Substrates on Demand ", RSC Adv.. 6 (72), 68545-68552 (2016)
Silver nanostructures on paper fabricated using our Print-expose-develop cycle act as efficient SERS substrates and swabs for analytical applications
The choice of paper substrate was a standard lanbwipe as it showed the lowest background signal for excitation at 532 nm. For 785 nm excitation, even copier paper is suitable.
This figuredemonstrates the successful use of these paper-based substrates as a ‘swab’, wherein the substrate is brought in close contact with a surface to pick up the analyte of interest. A common fungicide, Thiram, has also been detected well below its MRL value, by swabbing directly on a contaminated apple peel.
Silver nanostructures on paper fabricated using our Print-expose-develop cycle act as efficient SERS substrates and swabs for analytical applications
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I. Banerjee, V. Kumaran, and V. Santhanam, "Fabrication of Electrodes with Ultralow Platinum Loading by RF Plasma Processing of Self-Assembled Arrays of Au@Pt Nanoparticles", Nanotechnol. 27, 305401 (2016)
RF plasma treatment of Au@Pt nanoparticle arrays doubles their mass based electrocatalytic activity
Evolution of morphology and electrocatalytic activity as a function of RF argon plasma treatment duration for self-assembled gold reference sample, nanoparticle bilayer films with varying Pt/Au ratios, and platinum reference sample.
Representative CV curves obtained after various RF argon plasma treatment durations for self-assembled nanoparticle bilayer films with Pt/Au ratio of 0.88. (a) 1st cycle of CO stripping test, (b) methanol oxidation test and (c) ORR test.
RF plasma treatment of Au@Pt nanoparticle arrays doubles their mass based electrocatalytic activity
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I. Banerjee, V. Kumaran, and V. Santhanam, "Synthesis and Characterization of Au@Pt Nanoparticles with Ultrathin Platinum Overlayers", J. Phys. Chem. C , 119 (11), 5982–5987 (2015)
Gold nanoparticles coated with two monolayers of Platinum atoms exhibit equivalent HOR activity as solid Platinum nanoparticle
Microscopic and Spectroscopic Characterization of the sysnthesized Au@Pt nanoparticles
Bilayers of Au@Pt films exhibit HOR and MOR activity after RF plasma treatment to remove ligands.
Gold nanoparticles coated with two monolayers of Platinum atoms exhibit equivalent HOR activity as solid Platinum nanoparticle
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S. K. Parmar, and V. Santhanam, " In situ formation of silver nanowire networks on paper", Curr. Sci. 107(2), 262-269 (2014). A corrected version of Fig.3
Supplementary Movies
Inkjet printing meets Silver halide photography (aka. "Salt printing") to form patternbeed and conductive films on paper/plastic substrates
Light exposure induced "latent sites" leads to nanowire network formation, while without light exposure only "pebbles" of silver are formed upon reduction
The paper based electrodes adhere quite well onto the porous paper substrate and remain active even after a thousand bending cycles. Good news for flexible devices.
Inkjet printing meets Silver halide photography (aka. "Salt printing") to form patternbeed and conductive films on paper/plastic substrates
Highlighted in the news/TV media
(The Telegraph, Knowhow section, 04/08/2014)
(Science Monitor, DD Rajya Sabha TV, 08/08/2015)
Useful insight on nanowire growth mechanism (Handouts for school children in Germany!)
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S Kumar, V Bhat, K J Vinoy, and V. Santhanam, "Using an Office Inkjet Printer to Define the Formation of Copper Films on Paper", IEEE Trans. Nanotechnol, 13 (1), 160-164 (2014)
Front and back profiles of UWB antennas fabricated using inkjet printing on paper and using lithography on Kapton substrates. The copper film on paper appears darker.
Cross-section of el;ectrodepositedcopper film as well as optical profilometry confirm that a 2 micron film has been deposited (Note: the thickness of the copper film on Kapton is 17 microns)
S11 performance of the planar UWB antennas on paper is similar to those fabricated using photolithography.
Front and back profiles of UWB antennas fabricated using inkjet printing on paper and using lithography on Kapton substrates. The copper film on paper appears darker.
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A. Sureka, and V. Santhanam, "Optical properties of metal nanoparticles usingdiscrete dipole approximation", Journal of young investigators. April (2013)
DDASCAT code available freely at www.ddscat.org by Bruce Draine and Piotr Flatau was used to discretize individual nanostructures and calculate their optical properties
The code and discretization grid were cross-checked by computing optical scattering spectra of spherical gold and silver nanoparticles. The size dependence was captured well, as expected from Mie scattering
The electric field vectors (Polarization plots) are displayed at resonant wavelengths for triangular gold nanostructures of different sizes and aspect ratios.
DDASCAT code available freely at www.ddscat.org by Bruce Draine and Piotr Flatau was used to discretize individual nanostructures and calculate their optical properties
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S. K. Sivaraman, and V. Santhanam, " Realization of thermally durable close-packed 2D goldnanoparticle arrays using self-assembly and plasma etching", Nanotechnol. 23, 255603 (2012). Image analysis program
Cartoon depicts the loss of functionality after thermal annealing of ligand coated nanoparticles and contrasts it with the superior performance of "bare" nanoparticle arrays, obtained after RF plasma treatment
Monolayer Protected Nanoparticles (MPNs) have been self-assembled on a water surface and transfer-printed onto desired substrates. The figure shows arrays with different interparticle spacings.
The modular approach is compatible with various substrates and paper based SERS swabs have been fabricated using self-assembled silver-coated gold nanoparticle arrays
Cartoon depicts the loss of functionality after thermal annealing of ligand coated nanoparticles and contrasts it with the superior performance of "bare" nanoparticle arrays, obtained after RF plasma treatment
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G. Muralidharan, Navakanta Bhat, and V. Santhanam, " Scalable processes for fabricating non-volatile memory devices using self-assembled 2D arrays of gold nanoparticles as charge storage nodes", Nanoscale, 3 (11), 4575–4579 (2011)
Wafer-scale nanoparticle arrays were formed and transfer printed onto silicon substrates to form the floating gate layer of a MOS capacitor
The fabricated devices show excellent retention as well as endurance performance, comparable to industry standards
Macroscopic uniformity of memory window characteristics is shown by the histogram.
Wafer-scale nanoparticle arrays were formed and transfer printed onto silicon substrates to form the floating gate layer of a MOS capacitor
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S. K. Sivaraman, Sanjeev Kumar, and V. Santhanam, " Monodisperse sub-10 nm gold nanoparticles by reversing the order of addition in Turkevich method – The role of chloroauric acid", J. Colloid Interf. Sci. 361 (2), 543-547 (2011)
Simply reversing the order of reagent addition in the popular "citrate protocol" leads to monodisperse sub-10 nm nanoparticles within a few minutes!
Reversing the order of addition leads to mondosisperse particles, as a function of the Molar Ratio of Citrate to Gold chloride
Even if the kinetics is very slow, the system exhibits a "memory" of the order of addition
Simply reversing the order of reagent addition in the popular "citrate protocol" leads to monodisperse sub-10 nm nanoparticles within a few minutes!
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G. Muralidharan, L. Subramanian, S. K. Nallamuthu, V. Santhanam, and Sanjeev Kumar " Effect of Reagent Addition Rate and Temperature on Synthesis of Gold Nanoparticles in Microemulsion Route", Ind.Eng.Chem.Res. 50 (14), 8786–8791 (2011)
Controlled addition of reducing agent to microemeulsion
The rate of addition had a slight effect on the particle size distribution of the nanoparticles produced
Controlled addition of reducing agent to microemeulsion
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G. Muralidharan, S. K. Sivaraman, and V. Santhanam, " Effect of substrate on particle arrangement in arrays formed by self-assembly of polymer grafted nanoparticles", Nanoscale, 3 (5), 2138–2141 (2011).
Capillary immersion forces play the dominant role in determining interparticle spacing of evaporatively self-assembled ligand coated arrays.
Substrate predominantly affects the interparticle spacing in the plane, while the solvent affects the coiled nature of the ligand and thus height of the film.
"Funky" evaporation schemes can lead to the formation of rectangular lattices, indicating that shearing polymer coated nanoparticle arrays can lead to non-hexagonal packing arrangements
Capillary immersion forces play the dominant role in determining interparticle spacing of evaporatively self-assembled ligand coated arrays.
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S. K. Sivaraman, Sanjeev Kumar, and V. Santhanam, "Room temperature synthesis of gold nanoparticles -- Size-control by slow addition", Gold Bull 43(4), 275-286 (2010)
Schematic expounds the importance of the pH of the precursor solutions (rather the important role of the speciation of precursor salts) in synthesizing gold nanoparticles at room temperature using tannic acid as the reducing agent
By adjusting the pH of precursor solution, nanoparticles were formed at room temperature without the need for heating. This reduces complexity of reactor design during scale-up to continuous flows
Slow drop-wise addition leads to monodisperse particles with smaller mean diameters!
Schematic expounds the importance of the pH of the precursor solutions (rather the important role of the speciation of precursor salts) in synthesizing gold nanoparticles at room temperature using tannic acid as the reducing agent
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K.G. Patil, V. Santhanam, S.K. Biswas, and K.G. Ayappa, "Combined atomic force microscopy and modeling study of the evolution of octadecylamine films on a mica surface", J. Phys. Chem. C , 114 (8), 3549–3559 (2010)
Octadecylamine physisorption onto surfaces, a classical model for oil lubricants in engines, is captured using AFM experiments that confirmed the formation of multilayers within seconds
Physisorbed multilayer film thickness were measured in a statistically significant manner using appropriately designed experiments
Octadecylamine physisorption onto surfaces, a classical model for oil lubricants in engines, is captured using AFM experiments that confirmed the formation of multilayers within seconds
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S. K. Sivaraman, I. Elango, Sanjeev Kumar, and V. Santhanam, "A green protocol for room temperature synthesis of silver nanoparticles in seconds", Curr. Sci. 97(7), 1055-1059 (2009)
A plausible molecular structure of the average component in tannic acid
Silver nanoparticles from 3 nm onwards could be synthesized at room temperature using different molar ratios of tannic acid
A snapshot of silver nanoparticles being formed continuously in a coaxial flow microreactor
A plausible molecular structure of the average component in tannic acid
Highlighted in the news media
Conference Proceedings
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K. Agrawal, S. Chaudhary, D. Parvatalu, and V. Santhanam "Durability of Platinum Overlayers formed By Self-Terminating Electrodeposition". ECS Transactions, 104(8), 379 (2021). https://doi.org/10.1149/10408.0379ecst
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G. Muralidharan, Navakanta Bhat, and V. Santhanam, "Ultra-high density floating gate devices using self-assembled 2D arrays of gold nanoparticles", In IEEE International Conference on Emerging Electronics (ICEE), December 2012, (pp. 1-4), Mumbai.
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S. Perala, V. Santhanam and Sanjeev Kumar, “Synthesis of transition-metal nanoparticles: applicability of two-step mechanism", Proc. 4th Population Balance Modelling Conference (PBM 2010), pp 75--85, September 15--17, 2010, Berlin
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S. K. Sivaraman, D. Mohana Rao, Sanjeev Kumar and V. Santhanam, “Role of Coagulation in the Synthesis of Gold Nanoparticles by Citrate Reduction”, The Fourth Asian Particle Technology Symposium (APT 2009), September 14-16, 2009, Delhi
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D. Mohana Rao, M. Anusha, J. Chakraborty, S.K. Sivaraman , Sanjeev Kumar, and V. Santhanam, "Kinetics and modeling of gold nanoparticle formation", CHEMFERENCE'09, Chennai
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S. K. Sivaraman, Alok. Kr. Srivastava, and V. Santhanam, "Fabrication of Nanoparticle Arrays",CHEMCON - 2007, Kolkutta