ORCID Profile
0000-0002-6491-3971
Current Organisations
St Michael's Hospital Keenan Research Centre for Biomedical Science
,
Toronto Metropolitan University
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Publications
Characterization of MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces
Publisher: Springer Science and Business Media LLC
Date: 12-01-2011
Abstract: In this study, MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces under ambient condition were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The radiation fluence used was 0.5 J/cm 2 at a pulse repetition rate of 25 MHz with 1 ms interaction time. SEM analysis of the irradiated surfaces showed self-assembled intermingled weblike nanofibrous structure in and around the laser-irradiated spots. Further TEM investigation on this nanostructure revealed that the nanofibrous structure is formed due to aggregation of Au-Si/Si nanoparticles. The XRD peaks at 32.2°, 39.7°, and 62.5° were identified as (200), (211), and (321) reflections, respectively, corresponding to gold silicide. In addition, the observed chemical shift of Au 4 f and Si 2 p lines in XPS spectrum of the irradiated surface illustrated the presence of gold silicide at the irradiated surface. The generation of Si/Au-Si alloy fibrous nanoparticles aggregate is explained by the nucleation and subsequent condensation of vapor in the plasma plume during irradiation and expulsion of molten material due to high plasma pressure.
Synthesis of Nanoscale Tips Using Femtosecond Laser Radiation under Ambient Condition
Publisher: Springer Science and Business Media LLC
Date: 29-11-2009
Enhancement in optical absorption of silicon fibrous nanostructure produced using femtosecond laser ablation
Publisher: AIP Publishing
Date: 20-07-2009
DOI: 10.1063/1.3168499
Abstract: Fibrous nanostructures are proposed for the application of solar cell. Irradiation of silicon surface with a few hundred femtosecond laser pulses of fluence 13 kJ/m2 at 13 MHz pulse frequency in air atmosphere results in the formation of fibrous nanostructure layer on the treated surface that leads to a significant decrease in the reflection of visible radiation. For the visible wavelength, the decreased reflection is a result of the nature of the nanostructure. The Raman peak shift in the irradiated surface confirms that the surface is changed to amorphous silicon due to fibrous nanostructure formation.
Composition of silicon fibrous nanostructures synthesized using ultrafast laser pulses under ambient conditions
Publisher: EDP Sciences
Date: 2015
Study of silicon nanofibrous structure formed by femtosecond laser irradiation in air
Publisher: Optica Publishing Group
Date: 27-07-2009
DOI: 10.1364/OE.17.013869
Abstract: In this study, we report first time the effect of laser pulse repetition frequency and pulse width of femtosecond laser radiation on silicon nanofibrous structure formation under ambient condition. Surface nanotexture analysis revealed the changes in fibrous structure density and size in respect of laser pulse width and repetition frequency. A phonon confinement model is used to explain the Raman spectra of processed specimens in order to understand the structure details of nanofibrous structure and hence to support the surface nanotexture analysis. The present investigation leads to a conclusion that nanofibrous structure is formed due to the aggregation of silicon nanoparticles and their size is estimated using the confinement model which is in the order of few nanometers.
Study of metallic fibrous nanoparticle aggregate produced using femtosecond laser radiation under ambient conditions
Publisher: IOP Publishing
Date: 07-05-2010
DOI: 10.1088/0957-4484/21/22/225601
Abstract: In this study, we report formation of weblike fibrous nanoparticle aggregate due to irradiation of bulk iron, aluminium and titanium s les using femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Electron microscopy analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanoparticle diameter varies between 5 and 40 nm and they are covered with an oxide layer of a few nanometres thick. X-ray diffraction and micro-Raman analysis revealed metallic and oxide phases in the nanostructure. The formation of a nanoparticle aggregate is explained by nucleation and condensation of vapour in the plasma plume and by phase explosion. Moreover the laser interaction time plays a significant role in the generation of nanostructure from bulk metals. This study provides evidence that femtosecond laser irradiation can be an ambient condition physical method for metallic fibrous nanoparticle aggregate generation.
Synthesis of TiO2 nanoscale rods with MHz femtosecond laser irradiation of single crystal surface and characterisation
Publisher: AIP Publishing
Date: 06-2011
DOI: 10.1063/1.3600705
Abstract: Growth of nanoscale rods on single crystal rutile TiO2 surface irradiated by MHz pulse repetition rate femtosecond laser in nitrogen environment without a catalyst or template is reported. The rods are of 100 nm in width to 1 micron length. Microraman analysis of the laser irradiated surface shows only a decrease in the intensity of active modes as compared to untreated surface. The growth of TiO2 nanorods can be explained by a method combining nanoparticles formation due to expulsion of molten material from laser irradiated spot and their subsequent growth by vapor-liquid-solid process.
Characterization of high temperature conductive graphite surfaces irradiated with femtosecond laser pulses
Publisher: Elsevier BV
Date: 09-2011
Enhancement of silicon nanostructures generation using dual wavelength double pulse femtosecond laser under ambient condition
Publisher: AIP Publishing
Date: 15-02-2010
DOI: 10.1063/1.3309422
Abstract: In this study we propose a unique method to increase the weblike silicon nanofibrous structures formation using dual wavelength double pulse femtosecond laser radiation under ambient condition. The augmentation of nanostructures is evidenced from the difference in nanofibrous structure layer thickness. Enhancement in generation is explained through the increase in excited state electrons with double pulse as compared to single pulse. Moreover the absorption characteristic of irradiated surface undergoes significant changes after the first pulse (515 nm) which enhances absorption for the second pulse (1030 nm) and consequently results in an increase in nanostructures.
Synthesis of Glass Nanofibers Using Femtosecond Laser Radiation Under Ambient Condition
Publisher: Springer Science and Business Media LLC
Date: 19-07-2009
DOI: 10.1007/S11671-009-9390-Y
Abstract: We report the unique growth of nanofibers in silica and borosilicate glass using femtosecond laser radiation at 8 MHz repetition rate and a pulse width of 214 fs in air at atmospheric pressure. The nanofibers are grown perpendicular to the substrate surface from the molten material in laser-drilled microvias where they intertwine and bundle up above the surface. The fibers are few tens of nanometers in thickness and up to several millimeters in length. Further, it is found that at some places nanoparticles are attached to the fiber surface along its length. Nanofiber growth is explained by the process of nanojets formed in the molten liquid due to pressure gradient induced from the laser pulses and subsequently drawn into fibers by the intense plasma pressure. The attachment of nanoparticles is due to the condensation of vapor in the plasma.
Related Organisations
St Michael's Hospital Keenan Research Centre For Biomedical Science
Location: Canada
Related Funding Activities
No related grants have been discovered for Krishnan Venkatakrishnan.