Owing to their simple chemistry and structure, controllable geometry, and a plethora of unusual y... more Owing to their simple chemistry and structure, controllable geometry, and a plethora of unusual yet exciting transport properties, carbon nanotubes (CNTs) have emerged as exceptional channels for fundamental nanofluidic studies, as well as building blocks for future fluidic devices that can outperform current technology in many applications. Leveraging the unique fluidic properties of CNTs in advanced systems requires a full understanding of their physical origin. Recent advancements in nanofabrication technology enable nanofluidic devices to be built with a single, nanometer-wide CNT as a fluidic pathway. These novel platforms with isolated CNT nanochannels offer distinct advantages for establishing quantitative structure-transport correlations in comparison with membranes containing many CNT pores. In addition, they are promising components for single-molecule sensors as well as for building nanotube-based circuits wherein fluidics and electronics can be coupled. With such advanced device architecture, molecular and ionic transport can be manipulated with vastly enhanced control for applications in sensing, separation, detection, and therapeutic delivery. Recent achievements in fabricating isolated-CNT nanofluidic platforms are highlighted, along with the most-significant findings each platform enables for water, ion, and molecular transport. The implications of these findings and remaining open questions on the exceptional fluidic properties of CNTs are also discussed.
ABSTRACT Plasmonic nanoantennas offer exciting perspectives for promoting and investigating light... more ABSTRACT Plasmonic nanoantennas offer exciting perspectives for promoting and investigating light-driven chemical reactions. In particular, core/shell semiconductor beads coupled to gold nanoantennas represent an ideal platform for a systematic evaluation of multiple processes stimulated by light at different frequencies. Here we report the detailed fabrication of gold bowties on SiO2/TiO2 core/shell micro- and nano-beads, which is based on the combination of colloidal synthesis, atomic layer deposition and a modified version of induced deposition mask lithography. The critical steps of fabrication, including choice of mask material, etching rate and experimental setup are analyzed and strategies to pursue a successful fabrication of different nanoantennas are discussed.
Microfabricated devices designed to provide phase contrast in the transmission electron microscop... more Microfabricated devices designed to provide phase contrast in the transmission electron microscope must be free of phase distortions caused by unexpected electrostatic effects. We find that such phase distortions occur even when a device is heated to 300 °C during use in order to avoid the formation of polymerized, carbonaceous contamination. Remaining factors that could cause unwanted phase distortions include patchy variations in the work function of a clean metal surface, radiation-induced formation of a localized oxide layer, and creation of a contact potential between an irradiated area and the surround due to radiation-induced structural changes. We show that coating a microfabricated device with evaporated carbon apparently eliminates the problem of patchy variation in the work function. Furthermore, we show that a carbon-coated titanium device is superior to a carbon-coated gold device, with respect to radiation-induced electrostatic effects. A carbon-coated, hybrid double-sideband/single-sideband aperture is used to record in-focus, cryo-EM images of monolayer crystals of streptavidin. Images showing no systematic phase error due to charging are achievable under conditions of low-dose data collection. The contrast in such in-focus images is sufficient that one can readily see individual streptavidin tetramer molecules. Nevertheless, these carbon-coated devices perform well for only a limited length of time, and the cause of failure is not yet understood.
A novel design is described for an aperture that blocks a half-plane of the electron diffraction ... more A novel design is described for an aperture that blocks a half-plane of the electron diffraction pattern out to a desired scattering angle, and then--except for a narrow support beam--transmits all of the scattered electrons beyond that angle. Our proposed tulip-shaped design is thus a hybrid between the single-sideband (ssb) aperture, which blocks a full half-plane of the diffraction pattern, and the conventional (i.e. fully open) double-sideband (dsb) aperture. The benefits of this hybrid design include the fact that such an aperture allows one to obtain high-contrast images of weak-phase objects with the objective lens set to Scherzer defocus. We further demonstrate that such apertures can be fabricated from thin-foil materials by milling with a focused ion beam (FIB), and that such apertures are fully compatible with the requirements of imaging out to a resolution of at least 0.34nm. As is known from earlier work with single-sideband apertures, however, the edge of such an apert...
ABSTRACT We report here a spectroscopic study on plasmonic ring resonators at grazing angle incid... more ABSTRACT We report here a spectroscopic study on plasmonic ring resonators at grazing angle incidence. With the magnetic component of the infrared light perpendicular to the ring plane (TM), we successfully observed a strong resonance signal at Mid- to Near-IR frequencies. Comparing to simulations, we identify that this signal is due to the resonance of the TM wave with the surface plasmon propagation of the metal rings. We provide a solution to measure direct magnetic resonance by using a grazing incidence objective on a FTIR microscope. We also demonstrate a method to realize magnetic resonance at optical frequencies by channeling the surface plasmon in a closed metallic ring.
ABSTRACT We report the results of a spectroscopic study of a single layer of nanoscale metallic s... more ABSTRACT We report the results of a spectroscopic study of a single layer of nanoscale metallic single closed ring resonators on a free- standing thin membrane at near-normal and grazing angles of incidence^[1]. When the magnetic component of the light is perpendicular to the ring plane, we observe a so-called ``double'' negative index of refraction at near-infrared frequencies attributed to a strong magnetic dipolar resonance and a broad electric resonance in this metamaterial. We experimentally identify the different resonance modes and the spectral region of negative refractive index on a series of samples with different feature and lattice sizes, using multi- oscillator fits and comparing to electromagnetic simulations. [1] Z. Hao, M. C. Martin, B. Harteneck, S. Cabrini, E. H. Anderson, Appl. Phys. Lett., in press (2008).
We report a technique for single ion doping of field effect transistors through monitoring of cha... more We report a technique for single ion doping of field effect transistors through monitoring of changes in the source-drain currents at room temperature [1]. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, micro-scale transistors by electron beam assisted etching. Device currents increase due to the generation of positively charged defects in gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization. We discuss integration of single ion doping for the development of silicon based quantum computer structures with donor electron and nuclear spin qubits. [1] A. Batra, et al., Appl. Phys. Lett. 91, 193502 (2007)
A model is proposed for gain saturation in free-electron lasers operating with a bunched electron... more A model is proposed for gain saturation in free-electron lasers operating with a bunched electron beam. A simple method to evaluate the steady-state intensity as a function of the optical cavity length is given, and the results is in close agreement with the intensity measured in the Los Alamos free-electron-laser experiment by Newnam et al. (1985).
We report on the fabrication of two-dimensional photonic crystals (2D-PC) structures by means of ... more We report on the fabrication of two-dimensional photonic crystals (2D-PC) structures by means of a focused ion beam (FIB), which is an alternative process well suited for the fast prototyping of high quality 2D-PC devices. Through FIB process the removal of materials is achieved without the use of a patterned resist mask. We have fabricated two different short in-plane cavities: the ridge geometry configuration, obtained through trenches etched down to the bottom cladding by means of a FIB process, and a second identical cavity terminated by a 2D-PC back mirror consisting of a triangular lattice of air holes in GaAs slab. Both the ridge cavity and the photonic crystal cavity have been optically characterized by detecting their edge-emitted photoluminescence. As expected, by virtue of its higher back mirror reflectivity leading to lower cavity losses, the 2D-PC cavity shows the occurrence of amplified spontaneous emission at an excitation power density three times lower than in the standard ridge cavity.
Proceedings of Spie the International Society For Optical Engineering, Sep 1, 2002
In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which i... more In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which is mainly due to the availability of nearly ideal optical sources for diffractive optics. Synchrotrons of the latest generation and free electron lasers (in the near future) are sources that can produce x-ray beams with low divergence, whose wavelength can be tuned over a range of several keV and whose spectrum can be monochromatised within a band pass Δλ/λ< 10-4. In this paper we present the design, fabrication and use of novel diffractive optical elements that, beyond simple focusing, can perform new optical functions in the range of soft X-rays: multi-focusing in single or multiple focal planes and beam shaping of a generic monochromatic beam into a desired continuous geometrical pattern. The design is based on scalar diffraction approaches using iterative or direct algorithms to calculate the optical function. Diffractive optical elements with 100x100 microns size and 100 nanometers resolution have been fabricated using e-beam lithography and their optical functions have been tested in differential interference contrast microscopy. We suggest their use also in mask-less lithography and chemical vapor deposition induced by extreme ultraviolet and x-ray radiation.
Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building block... more Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building blocks for atomically thin, flexible optoelectronic and catalytic devices. Although challenging for two-dimensional systems, sub-diffraction optical microscopy provides a nanoscale material understanding that is vital for optimizing their optoelectronic properties. Here we use the 'Campanile' nano-optical probe to spectroscopically image exciton recombination within monolayer MoS2 with sub-wavelength resolution (60 nm), at the length scale relevant to many critical optoelectronic processes. Synthetic monolayer MoS2 is found to be composed of two distinct optoelectronic regions: an interior, locally ordered but mesoscopically heterogeneous two-dimensional quantum well and an unexpected ∼300-nm wide, energetically disordered edge region. Further, grain boundaries are imaged with sufficient resolution to quantify local exciton-quenching phenomena, and complimentary nano-Auger microscopy ...
Owing to their simple chemistry and structure, controllable geometry, and a plethora of unusual y... more Owing to their simple chemistry and structure, controllable geometry, and a plethora of unusual yet exciting transport properties, carbon nanotubes (CNTs) have emerged as exceptional channels for fundamental nanofluidic studies, as well as building blocks for future fluidic devices that can outperform current technology in many applications. Leveraging the unique fluidic properties of CNTs in advanced systems requires a full understanding of their physical origin. Recent advancements in nanofabrication technology enable nanofluidic devices to be built with a single, nanometer-wide CNT as a fluidic pathway. These novel platforms with isolated CNT nanochannels offer distinct advantages for establishing quantitative structure-transport correlations in comparison with membranes containing many CNT pores. In addition, they are promising components for single-molecule sensors as well as for building nanotube-based circuits wherein fluidics and electronics can be coupled. With such advanced device architecture, molecular and ionic transport can be manipulated with vastly enhanced control for applications in sensing, separation, detection, and therapeutic delivery. Recent achievements in fabricating isolated-CNT nanofluidic platforms are highlighted, along with the most-significant findings each platform enables for water, ion, and molecular transport. The implications of these findings and remaining open questions on the exceptional fluidic properties of CNTs are also discussed.
ABSTRACT Plasmonic nanoantennas offer exciting perspectives for promoting and investigating light... more ABSTRACT Plasmonic nanoantennas offer exciting perspectives for promoting and investigating light-driven chemical reactions. In particular, core/shell semiconductor beads coupled to gold nanoantennas represent an ideal platform for a systematic evaluation of multiple processes stimulated by light at different frequencies. Here we report the detailed fabrication of gold bowties on SiO2/TiO2 core/shell micro- and nano-beads, which is based on the combination of colloidal synthesis, atomic layer deposition and a modified version of induced deposition mask lithography. The critical steps of fabrication, including choice of mask material, etching rate and experimental setup are analyzed and strategies to pursue a successful fabrication of different nanoantennas are discussed.
Microfabricated devices designed to provide phase contrast in the transmission electron microscop... more Microfabricated devices designed to provide phase contrast in the transmission electron microscope must be free of phase distortions caused by unexpected electrostatic effects. We find that such phase distortions occur even when a device is heated to 300 °C during use in order to avoid the formation of polymerized, carbonaceous contamination. Remaining factors that could cause unwanted phase distortions include patchy variations in the work function of a clean metal surface, radiation-induced formation of a localized oxide layer, and creation of a contact potential between an irradiated area and the surround due to radiation-induced structural changes. We show that coating a microfabricated device with evaporated carbon apparently eliminates the problem of patchy variation in the work function. Furthermore, we show that a carbon-coated titanium device is superior to a carbon-coated gold device, with respect to radiation-induced electrostatic effects. A carbon-coated, hybrid double-sideband/single-sideband aperture is used to record in-focus, cryo-EM images of monolayer crystals of streptavidin. Images showing no systematic phase error due to charging are achievable under conditions of low-dose data collection. The contrast in such in-focus images is sufficient that one can readily see individual streptavidin tetramer molecules. Nevertheless, these carbon-coated devices perform well for only a limited length of time, and the cause of failure is not yet understood.
A novel design is described for an aperture that blocks a half-plane of the electron diffraction ... more A novel design is described for an aperture that blocks a half-plane of the electron diffraction pattern out to a desired scattering angle, and then--except for a narrow support beam--transmits all of the scattered electrons beyond that angle. Our proposed tulip-shaped design is thus a hybrid between the single-sideband (ssb) aperture, which blocks a full half-plane of the diffraction pattern, and the conventional (i.e. fully open) double-sideband (dsb) aperture. The benefits of this hybrid design include the fact that such an aperture allows one to obtain high-contrast images of weak-phase objects with the objective lens set to Scherzer defocus. We further demonstrate that such apertures can be fabricated from thin-foil materials by milling with a focused ion beam (FIB), and that such apertures are fully compatible with the requirements of imaging out to a resolution of at least 0.34nm. As is known from earlier work with single-sideband apertures, however, the edge of such an apert...
ABSTRACT We report here a spectroscopic study on plasmonic ring resonators at grazing angle incid... more ABSTRACT We report here a spectroscopic study on plasmonic ring resonators at grazing angle incidence. With the magnetic component of the infrared light perpendicular to the ring plane (TM), we successfully observed a strong resonance signal at Mid- to Near-IR frequencies. Comparing to simulations, we identify that this signal is due to the resonance of the TM wave with the surface plasmon propagation of the metal rings. We provide a solution to measure direct magnetic resonance by using a grazing incidence objective on a FTIR microscope. We also demonstrate a method to realize magnetic resonance at optical frequencies by channeling the surface plasmon in a closed metallic ring.
ABSTRACT We report the results of a spectroscopic study of a single layer of nanoscale metallic s... more ABSTRACT We report the results of a spectroscopic study of a single layer of nanoscale metallic single closed ring resonators on a free- standing thin membrane at near-normal and grazing angles of incidence^[1]. When the magnetic component of the light is perpendicular to the ring plane, we observe a so-called ``double&#39;&#39; negative index of refraction at near-infrared frequencies attributed to a strong magnetic dipolar resonance and a broad electric resonance in this metamaterial. We experimentally identify the different resonance modes and the spectral region of negative refractive index on a series of samples with different feature and lattice sizes, using multi- oscillator fits and comparing to electromagnetic simulations. [1] Z. Hao, M. C. Martin, B. Harteneck, S. Cabrini, E. H. Anderson, Appl. Phys. Lett., in press (2008).
We report a technique for single ion doping of field effect transistors through monitoring of cha... more We report a technique for single ion doping of field effect transistors through monitoring of changes in the source-drain currents at room temperature [1]. Implant apertures are formed in the interlayer dielectrics and gate electrodes of planar, micro-scale transistors by electron beam assisted etching. Device currents increase due to the generation of positively charged defects in gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel regions. Implant damage is repaired by rapid thermal annealing, enabling iterative cycles of device doping and electrical characterization. We discuss integration of single ion doping for the development of silicon based quantum computer structures with donor electron and nuclear spin qubits. [1] A. Batra, et al., Appl. Phys. Lett. 91, 193502 (2007)
A model is proposed for gain saturation in free-electron lasers operating with a bunched electron... more A model is proposed for gain saturation in free-electron lasers operating with a bunched electron beam. A simple method to evaluate the steady-state intensity as a function of the optical cavity length is given, and the results is in close agreement with the intensity measured in the Los Alamos free-electron-laser experiment by Newnam et al. (1985).
We report on the fabrication of two-dimensional photonic crystals (2D-PC) structures by means of ... more We report on the fabrication of two-dimensional photonic crystals (2D-PC) structures by means of a focused ion beam (FIB), which is an alternative process well suited for the fast prototyping of high quality 2D-PC devices. Through FIB process the removal of materials is achieved without the use of a patterned resist mask. We have fabricated two different short in-plane cavities: the ridge geometry configuration, obtained through trenches etched down to the bottom cladding by means of a FIB process, and a second identical cavity terminated by a 2D-PC back mirror consisting of a triangular lattice of air holes in GaAs slab. Both the ridge cavity and the photonic crystal cavity have been optically characterized by detecting their edge-emitted photoluminescence. As expected, by virtue of its higher back mirror reflectivity leading to lower cavity losses, the 2D-PC cavity shows the occurrence of amplified spontaneous emission at an excitation power density three times lower than in the standard ridge cavity.
Proceedings of Spie the International Society For Optical Engineering, Sep 1, 2002
In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which i... more In our days, there is an increased interest for extreme ultraviolet and x-ray microscopy, which is mainly due to the availability of nearly ideal optical sources for diffractive optics. Synchrotrons of the latest generation and free electron lasers (in the near future) are sources that can produce x-ray beams with low divergence, whose wavelength can be tuned over a range of several keV and whose spectrum can be monochromatised within a band pass Δλ/λ< 10-4. In this paper we present the design, fabrication and use of novel diffractive optical elements that, beyond simple focusing, can perform new optical functions in the range of soft X-rays: multi-focusing in single or multiple focal planes and beam shaping of a generic monochromatic beam into a desired continuous geometrical pattern. The design is based on scalar diffraction approaches using iterative or direct algorithms to calculate the optical function. Diffractive optical elements with 100x100 microns size and 100 nanometers resolution have been fabricated using e-beam lithography and their optical functions have been tested in differential interference contrast microscopy. We suggest their use also in mask-less lithography and chemical vapor deposition induced by extreme ultraviolet and x-ray radiation.
Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building block... more Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building blocks for atomically thin, flexible optoelectronic and catalytic devices. Although challenging for two-dimensional systems, sub-diffraction optical microscopy provides a nanoscale material understanding that is vital for optimizing their optoelectronic properties. Here we use the 'Campanile' nano-optical probe to spectroscopically image exciton recombination within monolayer MoS2 with sub-wavelength resolution (60 nm), at the length scale relevant to many critical optoelectronic processes. Synthetic monolayer MoS2 is found to be composed of two distinct optoelectronic regions: an interior, locally ordered but mesoscopically heterogeneous two-dimensional quantum well and an unexpected ∼300-nm wide, energetically disordered edge region. Further, grain boundaries are imaged with sufficient resolution to quantify local exciton-quenching phenomena, and complimentary nano-Auger microscopy ...
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Papers by Stefano Cabrini