Gobind Basnet - Academia.edu (original) (raw)

Papers by Gobind Basnet

Bulletin of the American Physical Society, Mar 15, 2017

paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses... more paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses, ∼300 nm widths, and greater than 100 µm lengths (giving length-to-thickness aspect ratios of well over 10 3). These structures are useful for opto-electronic studies and as nanoscale electrodes. Growing these ultra-long, branchless, crystalline structures requires controlling the Mullins-Sekerka instability, which is necessary for maintaining the template-free growth of the ribbon but has the unwanted effect of inducing side-branching. The 0.75-1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to the reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. An electrochemical, linear stability analysis illustrates how voltage amplitude and excess noise cause side-branching. Limitations of this linear theory will be discussed. An outcome of this study is the controlled application of electrical noise in order to produce targeted structures, such as Y-shaped nanoribbons.

Bulletin of the American Physical Society, May 24, 2016

Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field... more Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field emission. Their geometry confines the propagation of conduction electrons, giving rise to effects not seen in the bulk, such as ballistic currents and surface plasmon polaritons (SPPs) [2]. Dynamics within the wire are probed with laser-induced field emission from the nanowire tip. A balanced Mach-Zehnder interferometer is used to split and delay pulses up to 170 ps from a Ti:Saph oscillator (800 nm, 50 fs) in a pump-probe scheme. The output beamsplitter of the interferometer is mounted on a translation stage to control the separation of the pump and probe beams with sub-micron precision. The beams are focused to 3 µm spots on the tip and shaft of a nanowire, mounted under vacuum at 2×10 −7 mTorr, by an off-axis parabolic mirror. Field-emitted electrons are counted by a channel electron multiplier. We discuss experimental results of our pump-probe experiments taken at different pump positions. Optical control of electron dynamics within these nanowires may lead to a truly on-demand source of single and multiple electron pulses. [1] B. Ozturk, I.

Applied Physics Letters, Jun 25, 2018

Bulletin of the American Physical Society, 2017

paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses... more paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses, ∼300 nm widths, and greater than 100 µm lengths (giving length-to-thickness aspect ratios of well over 10 3). These structures are useful for opto-electronic studies and as nanoscale electrodes. Growing these ultra-long, branchless, crystalline structures requires controlling the Mullins-Sekerka instability, which is necessary for maintaining the template-free growth of the ribbon but has the unwanted effect of inducing side-branching. The 0.75-1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to the reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. An electrochemical, linear stability analysis illustrates how voltage amplitude and excess noise cause side-branching. Limitations of this linear theory will be discussed. An outcome of this study is the controlled application of electrical noise in order to produce targeted structures, such as Y-shaped nanoribbons.

Bulletin of the American Physical Society, 2016

Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field... more Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field emission. Their geometry confines the propagation of conduction electrons, giving rise to effects not seen in the bulk, such as ballistic currents and surface plasmon polaritons (SPPs) [2]. Dynamics within the wire are probed with laser-induced field emission from the nanowire tip. A balanced Mach-Zehnder interferometer is used to split and delay pulses up to 170 ps from a Ti:Saph oscillator (800 nm, 50 fs) in a pump-probe scheme. The output beamsplitter of the interferometer is mounted on a translation stage to control the separation of the pump and probe beams with sub-micron precision. The beams are focused to 3 µm spots on the tip and shaft of a nanowire, mounted under vacuum at 2×10 −7 mTorr, by an off-axis parabolic mirror. Field-emitted electrons are counted by a channel electron multiplier. We discuss experimental results of our pump-probe experiments taken at different pump positions. Optical control of electron dynamics within these nanowires may lead to a truly on-demand source of single and multiple electron pulses. [1] B. Ozturk, I.

Applied Physics Letters, 2018

Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, p... more Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, provides spatially coherent and temporally short electron pulses. The properties of the photoelectron yield give insight into both the material properties of the nanostructure and the exciting laser focus. Ultralong nanoribbons, grown as a single crystal attached to a metallic taper, are sources of electron field emission that have not yet been characterized. In this report, photoemission from gold nanoribbon samples is studied and compared to emission from tungsten and gold tips. We observe that the emission from sharp tips generally depends on one transverse component of the exciting laser field, while the emission of a blunted nanoribbon is found to be sensitive to both components. We propose that this property makes photoemission from nanoribbons a candidate for position-sensitive detection of the longitudinal field component in a tightly focused beam.

Applied Physics Letters, 2017

This paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm × ∼300... more This paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm × ∼300 nm cross sections and >100 μm lengths (giving length-to-thickness aspect ratios of >103). These structures are useful for opto-electronic studies and as nanoscale electrodes. The 0.75–1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. The inter-relatedness of voltage-amplitude, noise, and side-branching in electrochemical nanoribbon growth is demonstrated.

Applied physics letters, Jan 26, 2018

AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires f... more AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires from simple salt solutions using the Directed Electrochemical Nanowire Assembly method. Nanowire diameters were tuned from the submicron scale to 40 nm by adjusting the AC voltage frequency and the growth solution concentration. The structural properties of the nanowires, including shape and crystallinity, were identified using electron microscopy. Hysteresis loops obtained along different directions of an individual nanowire using vibrating sample magnetometry showed that the magnetocrystalline anisotropy energy has the same order of magnitude as the shape anisotropy energy. Additionally, the saturation magnetization of an individual cobalt nanowire was estimated to be close to the bulk single crystal value. A small cobalt nanowire segment was grown from a conductive atomic force microscope cantilever tip that was utilized in magnetic force microscopy (MFM) imaging. The fabricated MFM ti...

Bulletin of the American Physical Society, Mar 15, 2017

paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses... more paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses, ∼300 nm widths, and greater than 100 µm lengths (giving length-to-thickness aspect ratios of well over 10 3). These structures are useful for opto-electronic studies and as nanoscale electrodes. Growing these ultra-long, branchless, crystalline structures requires controlling the Mullins-Sekerka instability, which is necessary for maintaining the template-free growth of the ribbon but has the unwanted effect of inducing side-branching. The 0.75-1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to the reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. An electrochemical, linear stability analysis illustrates how voltage amplitude and excess noise cause side-branching. Limitations of this linear theory will be discussed. An outcome of this study is the controlled application of electrical noise in order to produce targeted structures, such as Y-shaped nanoribbons.

Bulletin of the American Physical Society, May 24, 2016

Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field... more Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field emission. Their geometry confines the propagation of conduction electrons, giving rise to effects not seen in the bulk, such as ballistic currents and surface plasmon polaritons (SPPs) [2]. Dynamics within the wire are probed with laser-induced field emission from the nanowire tip. A balanced Mach-Zehnder interferometer is used to split and delay pulses up to 170 ps from a Ti:Saph oscillator (800 nm, 50 fs) in a pump-probe scheme. The output beamsplitter of the interferometer is mounted on a translation stage to control the separation of the pump and probe beams with sub-micron precision. The beams are focused to 3 µm spots on the tip and shaft of a nanowire, mounted under vacuum at 2×10 −7 mTorr, by an off-axis parabolic mirror. Field-emitted electrons are counted by a channel electron multiplier. We discuss experimental results of our pump-probe experiments taken at different pump positions. Optical control of electron dynamics within these nanowires may lead to a truly on-demand source of single and multiple electron pulses. [1] B. Ozturk, I.

Applied Physics Letters, Jun 25, 2018

Bulletin of the American Physical Society, 2017

paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses... more paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm thicknesses, ∼300 nm widths, and greater than 100 µm lengths (giving length-to-thickness aspect ratios of well over 10 3). These structures are useful for opto-electronic studies and as nanoscale electrodes. Growing these ultra-long, branchless, crystalline structures requires controlling the Mullins-Sekerka instability, which is necessary for maintaining the template-free growth of the ribbon but has the unwanted effect of inducing side-branching. The 0.75-1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to the reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. An electrochemical, linear stability analysis illustrates how voltage amplitude and excess noise cause side-branching. Limitations of this linear theory will be discussed. An outcome of this study is the controlled application of electrical noise in order to produce targeted structures, such as Y-shaped nanoribbons.

Bulletin of the American Physical Society, 2016

Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field... more Lincoln-Gold nanowires [1], with diameters less than 100 nm, are novel sources for electron field emission. Their geometry confines the propagation of conduction electrons, giving rise to effects not seen in the bulk, such as ballistic currents and surface plasmon polaritons (SPPs) [2]. Dynamics within the wire are probed with laser-induced field emission from the nanowire tip. A balanced Mach-Zehnder interferometer is used to split and delay pulses up to 170 ps from a Ti:Saph oscillator (800 nm, 50 fs) in a pump-probe scheme. The output beamsplitter of the interferometer is mounted on a translation stage to control the separation of the pump and probe beams with sub-micron precision. The beams are focused to 3 µm spots on the tip and shaft of a nanowire, mounted under vacuum at 2×10 −7 mTorr, by an off-axis parabolic mirror. Field-emitted electrons are counted by a channel electron multiplier. We discuss experimental results of our pump-probe experiments taken at different pump positions. Optical control of electron dynamics within these nanowires may lead to a truly on-demand source of single and multiple electron pulses. [1] B. Ozturk, I.

Applied Physics Letters, 2018

Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, p... more Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, provides spatially coherent and temporally short electron pulses. The properties of the photoelectron yield give insight into both the material properties of the nanostructure and the exciting laser focus. Ultralong nanoribbons, grown as a single crystal attached to a metallic taper, are sources of electron field emission that have not yet been characterized. In this report, photoemission from gold nanoribbon samples is studied and compared to emission from tungsten and gold tips. We observe that the emission from sharp tips generally depends on one transverse component of the exciting laser field, while the emission of a blunted nanoribbon is found to be sensitive to both components. We propose that this property makes photoemission from nanoribbons a candidate for position-sensitive detection of the longitudinal field component in a tightly focused beam.

Applied Physics Letters, 2017

This paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm × ∼300... more This paper describes the electrochemical growth of branchless gold nanoribbons with ∼40 nm × ∼300 nm cross sections and >100 μm lengths (giving length-to-thickness aspect ratios of >103). These structures are useful for opto-electronic studies and as nanoscale electrodes. The 0.75–1.0 V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. The inter-relatedness of voltage-amplitude, noise, and side-branching in electrochemical nanoribbon growth is demonstrated.

Applied physics letters, Jan 26, 2018

AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires f... more AC electric fields were utilized in the growth of individual high-aspect ratio cobalt nanowires from simple salt solutions using the Directed Electrochemical Nanowire Assembly method. Nanowire diameters were tuned from the submicron scale to 40 nm by adjusting the AC voltage frequency and the growth solution concentration. The structural properties of the nanowires, including shape and crystallinity, were identified using electron microscopy. Hysteresis loops obtained along different directions of an individual nanowire using vibrating sample magnetometry showed that the magnetocrystalline anisotropy energy has the same order of magnitude as the shape anisotropy energy. Additionally, the saturation magnetization of an individual cobalt nanowire was estimated to be close to the bulk single crystal value. A small cobalt nanowire segment was grown from a conductive atomic force microscope cantilever tip that was utilized in magnetic force microscopy (MFM) imaging. The fabricated MFM ti...