Omar Teschke | Universidade Estadual de Campinas (original) (raw)
Papers by Omar Teschke
Nanotechnology, 2011
Nanochannels of the order of 20 nm in diameter and forming arrangements that were a few micrometr... more Nanochannels of the order of 20 nm in diameter and forming arrangements that were a few micrometres wide were fabricated on nanometre-thick ice-like deposits on planar mica surfaces at room temperature. Because an atomic force microscopy tip can write lines on ice-like layers covering mica substrates in air that are stable under invariant conditions of humidity and temperature, the water films were modulated with nanochannels. By analysing the shape and morphology of the material removed after channel fabrication for various time intervals, the channel profile was shown to vary with a scale of a tenth of a second. In this configuration (hydrophobic tip and hydrophilic substrate, 65% RH), at the channel top region there were only aggregates of loose flakes formed after the film inscription but no liquid. Apparently, the Kelvin effect is responsible for the nanochannel profile variation with time, but the calculated and measured values of the drainage time constant are at variance by six orders of magnitude. This reduction of the mass transfer is associated with the small dimensions of the ∼ 10 nm-wide channels.
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1989
World Journal of Microbiology and Biotechnology, 2005
Chemical Physics Letters, 2010
In this Letter, we report scanning force microscopy images with sufficient lateral resolution to ... more In this Letter, we report scanning force microscopy images with sufficient lateral resolution to microscopically identify the distinct ice-like structures on mica at finite humidity. The pattern calculated by Odelius et al. (1997) [1] for bilayers, e.g. a 2D ice-like structure that coincides with the unit cell of mica, was observed at molecular clusters edges and an ice-like with a hexagonal structure at its center. Other regions showing structures with a periodicity of 0.76±0.07nm, possibly associated with a rhombohedral structure, and 0.63±0.06nm a cubic structure, may be described as regions with compactly bonded intermixed structures.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2000
ABSTRACT Forces acting on atomic force microscope tips during scanning of films of ionic surfacta... more ABSTRACT Forces acting on atomic force microscope tips during scanning of films of ionic surfactant molecules adsorbed from aqueous solutions onto hydrophilic substrates are measured. Near critical micellar concentration images of mica substrates show aggregate regions at the interface. Force versus distance curves indicate that aggregates are the thickest adsorbed structures on the substrate. However, topographic images registered at low scanning speed (15 μm/s) show that these aggregates appear as holes, consequently observed as inverted in contrast images. In atomic force microscope imaging of soft structures such as surfactants or biological material, inverted images may be observed when the tip penetrates the scanned layers. This penetration can be adjusted by changing the force applied by the tip, which results in different images. In order to obtain the conventional atomic force microscope contrast in scanned images the applied force set point is determined by the analysis of the force versus distance curves.© 2000 American Vacuum Society.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determ... more The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determined by measurements of the film dielectric permittivity. Before the advent of atomic force microscopy the dielectric permittivity was a macroscopic parameter, appropriate only for describing uniform environments since its profile was difficult to measure for local intermolecular interactions and its spatial distribution was frequently settled without experimental justification. Here, we show that atomic force microscopy made it possible to measure the dielectric permittivity profile in a scale below 5 nm for adsorbed layers of self-assembled surfactant films in water. The measured values of the film's dielectric permittivity and the film's thickness determine the compactness of the adsorbed film and consequently the presence of water molecules in the film and the conformal structure of the adsorbed molecules.
28th Symposium on Microelectronics Technology and Devices (SBMicro 2013), 2013
ABSTRACT Nickel-Platinum Silicide (NiPtSi) layers were formed using a Rapid Thermal Process (RTP)... more ABSTRACT Nickel-Platinum Silicide (NiPtSi) layers were formed using a Rapid Thermal Process (RTP) furnace. The metal thin films were deposited by RF Magnetron Sputtering using a Ni(Pt) target (97% Ni and 3% Pt) onto a Si (100) substrate. The silicidation of the samples were performed at temperature ranged from 450°C to 900°C. Raman spectroscopy was used to study the vibrational modes and the phases of the obtained NiSi layers. An Atomic Force Microscopy (AFM) and Four Point probe were used to investigate the quality of the layer's surface and its sheet resistance. The exhibited results of large thermal stability window and low sheet resistance of 1~2.5 O/sqr indicate good quality of the obtained silicide layer.
Physical Review E, 2001
The arrangement of water molecules at charged aqueous interfaces is an important question in biol... more The arrangement of water molecules at charged aqueous interfaces is an important question in biology, electrochemistry, and geochemistry. Theoretical studies suggest that the molecules become arranged in several layers adjacent to a solid interface. Using atomic force microscopy we have measured the water dielectric-permittivity profile perpendicular to mica surfaces. The measured variable permittivity profile starting at epsilon approximately 4 at the interface and increasing to epsilon=80 about 10 nm from the surface suggests a reorientation of water molecule dipoles in the presence of the mica interfacial charge.
Nanotechnology, 2011
Nanochannels of the order of 20 nm in diameter and forming arrangements that were a few micrometr... more Nanochannels of the order of 20 nm in diameter and forming arrangements that were a few micrometres wide were fabricated on nanometre-thick ice-like deposits on planar mica surfaces at room temperature. Because an atomic force microscopy tip can write lines on ice-like layers covering mica substrates in air that are stable under invariant conditions of humidity and temperature, the water films were modulated with nanochannels. By analysing the shape and morphology of the material removed after channel fabrication for various time intervals, the channel profile was shown to vary with a scale of a tenth of a second. In this configuration (hydrophobic tip and hydrophilic substrate, 65% RH), at the channel top region there were only aggregates of loose flakes formed after the film inscription but no liquid. Apparently, the Kelvin effect is responsible for the nanochannel profile variation with time, but the calculated and measured values of the drainage time constant are at variance by six orders of magnitude. This reduction of the mass transfer is associated with the small dimensions of the ∼ 10 nm-wide channels.
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1989
World Journal of Microbiology and Biotechnology, 2005
Chemical Physics Letters, 2010
In this Letter, we report scanning force microscopy images with sufficient lateral resolution to ... more In this Letter, we report scanning force microscopy images with sufficient lateral resolution to microscopically identify the distinct ice-like structures on mica at finite humidity. The pattern calculated by Odelius et al. (1997) [1] for bilayers, e.g. a 2D ice-like structure that coincides with the unit cell of mica, was observed at molecular clusters edges and an ice-like with a hexagonal structure at its center. Other regions showing structures with a periodicity of 0.76±0.07nm, possibly associated with a rhombohedral structure, and 0.63±0.06nm a cubic structure, may be described as regions with compactly bonded intermixed structures.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2000
ABSTRACT Forces acting on atomic force microscope tips during scanning of films of ionic surfacta... more ABSTRACT Forces acting on atomic force microscope tips during scanning of films of ionic surfactant molecules adsorbed from aqueous solutions onto hydrophilic substrates are measured. Near critical micellar concentration images of mica substrates show aggregate regions at the interface. Force versus distance curves indicate that aggregates are the thickest adsorbed structures on the substrate. However, topographic images registered at low scanning speed (15 μm/s) show that these aggregates appear as holes, consequently observed as inverted in contrast images. In atomic force microscope imaging of soft structures such as surfactants or biological material, inverted images may be observed when the tip penetrates the scanned layers. This penetration can be adjusted by changing the force applied by the tip, which results in different images. In order to obtain the conventional atomic force microscope contrast in scanned images the applied force set point is determined by the analysis of the force versus distance curves.© 2000 American Vacuum Society.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determ... more The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determined by measurements of the film dielectric permittivity. Before the advent of atomic force microscopy the dielectric permittivity was a macroscopic parameter, appropriate only for describing uniform environments since its profile was difficult to measure for local intermolecular interactions and its spatial distribution was frequently settled without experimental justification. Here, we show that atomic force microscopy made it possible to measure the dielectric permittivity profile in a scale below 5 nm for adsorbed layers of self-assembled surfactant films in water. The measured values of the film's dielectric permittivity and the film's thickness determine the compactness of the adsorbed film and consequently the presence of water molecules in the film and the conformal structure of the adsorbed molecules.
28th Symposium on Microelectronics Technology and Devices (SBMicro 2013), 2013
ABSTRACT Nickel-Platinum Silicide (NiPtSi) layers were formed using a Rapid Thermal Process (RTP)... more ABSTRACT Nickel-Platinum Silicide (NiPtSi) layers were formed using a Rapid Thermal Process (RTP) furnace. The metal thin films were deposited by RF Magnetron Sputtering using a Ni(Pt) target (97% Ni and 3% Pt) onto a Si (100) substrate. The silicidation of the samples were performed at temperature ranged from 450°C to 900°C. Raman spectroscopy was used to study the vibrational modes and the phases of the obtained NiSi layers. An Atomic Force Microscopy (AFM) and Four Point probe were used to investigate the quality of the layer's surface and its sheet resistance. The exhibited results of large thermal stability window and low sheet resistance of 1~2.5 O/sqr indicate good quality of the obtained silicide layer.
Physical Review E, 2001
The arrangement of water molecules at charged aqueous interfaces is an important question in biol... more The arrangement of water molecules at charged aqueous interfaces is an important question in biology, electrochemistry, and geochemistry. Theoretical studies suggest that the molecules become arranged in several layers adjacent to a solid interface. Using atomic force microscopy we have measured the water dielectric-permittivity profile perpendicular to mica surfaces. The measured variable permittivity profile starting at epsilon approximately 4 at the interface and increasing to epsilon=80 about 10 nm from the surface suggests a reorientation of water molecule dipoles in the presence of the mica interfacial charge.
IEEE Sensors Journal, Jan 2014
Highly sensitive and selective functional nanobiosensors are being developed because they have s... more Highly sensitive and selective functional
nanobiosensors are being developed because they have significant
applications in the sustenance and conservation of natural
resources and can be used in projects to identify degraded and
contaminated areas (of both soil and water) and as
environmental quality indicators. In the present study, a
nanobiosensor was developed based on using theoretical models
(molecular docking and molecular dynamics simulations) based
on biomimicry of the action mechanism of herbicides in plants
coupled with atomic force microscopy (AFM) tools. The
herbicide molecules were detected at very low concentrations
using a unique sensor construction: the AFM probes and the
substrate were chemically functionalised to favour covalent
bonding and promote molecular flexibility, as well as to achieve
reproducible and accurate results. Computational methods were
used to determine the binding energies associated with the
enzyme-herbicide interactions, which were compared with
experimental results for adhesion forces. The theoretical results
showed that the diclofop herbicide could be assembled and
attached onto the mica substrate surface and the ACCase enzyme
on the AFM probe without damaging the diclofop molecule. The
experimental results showed that using a specific agrochemical
target molecule was more efficient than using other nonspecific
agrochemicals. On average, there was a 90% difference between
the values of specific recognition (diclofop) and nonspecific
recognition (imazaquin, metsulfuron and glyphosate). This result
validated the selectivity and specificity of the nanobiosensor. The
first evidence of diclofop detection by AFM probe sensors has
been presented in this work.