Using a surface forces apparatus (SFA) we have investigated the effects of normal load (compressi... more Using a surface forces apparatus (SFA) we have investigated the effects of normal load (compression) and shear on the tribological properties of mica surfaces bearing Porphyridium sp. (a common naturally-occurring polysaccharide of the red microalgae, which molecular weight has been estimated to be 2-7 x 106 daltons) adsorbed from aqueous solution. The friction forces were monitored as a function of
ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent ... more ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si 0 signals corresponding to Si nanoclusters increases while Si 4+ signals related to a-SiO 2 disappears from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive ...
We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due ... more We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due to the nanoscale size and minute amounts of these particles in the synthesis yield, the structure was exclusively solved using electron diffraction methods. The atomic model of the new phase (a = 11.7 Å, P213) was deduced and found to be associated with the rocksalt-type structure. Kramers-Kronig analysis predicted different optical and electronic properties for the new phase, as compared to α-SnS.
We studied the effect of light availability on the skeletal aragonite microstructure of the reef-... more We studied the effect of light availability on the skeletal aragonite microstructure of the reef-building coral Fungia simplex. Scanning electron microscopy (SEM) of samples transplanted from light to shade conditions showed that the latter promoted a well-defined crystal alignment and dense packing. An X-ray diffraction (XRD) study of newly formed coral skeleton tissue showed a twofold increase in coherence length
ABSTRACT CdS semiconductor nanoparticles, with dimensions above and below the Bohr radius (2.5 nm... more ABSTRACT CdS semiconductor nanoparticles, with dimensions above and below the Bohr radius (2.5 nm) of bulk material, were prepared in a single-step benchtop procedure. The degree of quantum confinement in these nanoparticles was determined from their optical absorption and photoluminescence spectra. The size-dependent properties of the nanocrystals were studied by resonance Raman spectroscopy as a function of excitation wavelength and temperature. The spectra were composed of the fundamental longitudinal optical (LO) mode around 300 cm-1, along with the first and second overtones. The shapes and positions of the Raman peaks exhibited only a weak dependence on particle size even for the two extreme cases of bulk and nanostructures. We show that the ratio of the overtone to the fundamental LO frequency was sensitive to the particle diameter and decreased upon reduction of the particle diameter to values below the Bohr radius. Temperature-dependent Raman measurements of ultranarrow nanorods showed a small red shift with decreasing temperature. Very high anti-Stokes intensities were observed for the CdS nanoparticles.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2009
Luminescent and structural characteristics of SiO 2 layers exposed to double implantation by Si +... more Luminescent and structural characteristics of SiO 2 layers exposed to double implantation by Si + and C + ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO 2 layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700-750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350-700 nm. Subsequent annealing at 1000 or 1100 ° C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ~400, ~500, and ~625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp 3 bond hybridization. The nanosized amorphous inclusions in the Si + + C + implanted and annealed SiO 2 layer have been revealed by high-resolution transmission electron microscopy.
Protection of Metals and Physical Chemistry of Surfaces, 2010
... Deposition conditions of PbS nanocrystals in chemical bath from XPb(NO3)2 + 0.205 CS(NH2)2 ..... more ... Deposition conditions of PbS nanocrystals in chemical bath from XPb(NO3)2 + 0.205 CS(NH2)2 ... gap becomes smoother together with increasing of its effective width in nanocrystallinePbS (Fig. ... in opposite directions from the Fermi level with a decrease in the nanoparticle size. ...
Size-controlled ZnSe nanoparticles with high extents of atomic positional order are shown to exhi... more Size-controlled ZnSe nanoparticles with high extents of atomic positional order are shown to exhibit large size-dependent variations in their local electronic environments. Solid-state 77 Se and 67 Zn NMR spectra reveal increasingly broad distributions of 77 Se and 67 Zn environments with decreasing nanoparticle sizes, in contrast with high degrees of atomic positional order established by transmission electron microscopy and x-ray diffraction. First-principles calculations of NMR parameters distinguish between atomic positional and electronic disorder that propagate from the nanoparticle surfaces and yield insights on the order and disorder present.
The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultan... more The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultaneous in situ small-angle x-ray scattering and surface force measurements. We have used the XSFA-II to monitor shear-induced orientational transitions in a lyotropic model lubricant system. Upon applying small shear amplitudes (ϳ20 mm) to a relatively thick (ϳ800 mm) film, we observed evidence for the formation of an orientational boundary layer at the shearing surface. Time-resolved x-ray diffraction revealed the gradual transition to shear-favored orientation by growth of the boundary layer.
ABSTRACT Photoelectron spectroscopic measurements have been performed, with synchrotron radiation... more ABSTRACT Photoelectron spectroscopic measurements have been performed, with synchrotron radiation on PbSe/CdSe heteronanocrystals that initially consist of core-shell structures. The study of the chemical states of the main elements in the nanocrystals shows a reproducible and progressive change in the valence-band and core-level spectra under photon irradiation, whatever the core and shell sizes are. Such chemical modifications are explained in light of transmission electron microscopy observations and reveal a phase transformation of the nanocrystals: The core-shell nanocrystals undergo a morphological change toward a Janus structure with the formation of semidetached PbSe and CdSe clusters. Photoelectron spectroscopy gives new insight into the reorganization of the ligands anchored at the surface of the nanocrystals and the modification of the electronic structure of these heteronanocrystals.
Langmuir-Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavi... more Langmuir-Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavior, which is dependent on the type of the supporting substrate. While on polished silicon surfaces the photoluminescence (PL) of PDA is quenched, it is preserved on top of 2D patterned macro-porous silicon (2D-MPS). 2D-MPS, prepared by electrochemical etching of photo-lithographically pre-patterned silicon, is a 2D array of ca. 10 lm deep pores with lateral 2-4 lm repeating unit cells in orthogonal or hexagonal arrangements. LB films of PDA on such surfaces form membranes with continuous domains of the size sufficient to cover laterally many cell units. Apparently, the PL from this film results exclusively from the portion of the PDA membrane which is suspended over pore openings, while portions of the film which are attached to the silicon on top of the pores walls does not exhibit PL at all. We have used these membranes in different configurations and exposed them to different chemical and biological agents and followed the PL intensity change. This report demonstrates the effectiveness of the combined system: LB films of PDA on top of 2D-MPS as sensing probe for a variety of chemicals including, Cd ions and TNT explosives. In addition, the use of films of PDA, in which glycol-lipid were embedded, for binding and recognition of lectin protein, mimicking the cell membrane interaction with its environment, is also demonstrated.
One of the important factors limiting solar-cell efficiency is that incident photons generate one... more One of the important factors limiting solar-cell efficiency is that incident photons generate one electron-hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells 1 . Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions 1-3 . Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carriermultiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.
Using a surface forces apparatus (SFA) we have investigated the effects of normal load (compressi... more Using a surface forces apparatus (SFA) we have investigated the effects of normal load (compression) and shear on the tribological properties of mica surfaces bearing Porphyridium sp. (a common naturally-occurring polysaccharide of the red microalgae, which molecular weight has been estimated to be 2-7 x 106 daltons) adsorbed from aqueous solution. The friction forces were monitored as a function of
ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent ... more ABSTRACT Si and Ge nanocrystals were formed in alumina matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si 0 signals corresponding to Si nanoclusters increases while Si 4+ signals related to a-SiO 2 disappears from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive ...
We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due ... more We report a new phase in the binary SnS system, obtained as highly symmetric nanotetrahedra. Due to the nanoscale size and minute amounts of these particles in the synthesis yield, the structure was exclusively solved using electron diffraction methods. The atomic model of the new phase (a = 11.7 Å, P213) was deduced and found to be associated with the rocksalt-type structure. Kramers-Kronig analysis predicted different optical and electronic properties for the new phase, as compared to α-SnS.
We studied the effect of light availability on the skeletal aragonite microstructure of the reef-... more We studied the effect of light availability on the skeletal aragonite microstructure of the reef-building coral Fungia simplex. Scanning electron microscopy (SEM) of samples transplanted from light to shade conditions showed that the latter promoted a well-defined crystal alignment and dense packing. An X-ray diffraction (XRD) study of newly formed coral skeleton tissue showed a twofold increase in coherence length
ABSTRACT CdS semiconductor nanoparticles, with dimensions above and below the Bohr radius (2.5 nm... more ABSTRACT CdS semiconductor nanoparticles, with dimensions above and below the Bohr radius (2.5 nm) of bulk material, were prepared in a single-step benchtop procedure. The degree of quantum confinement in these nanoparticles was determined from their optical absorption and photoluminescence spectra. The size-dependent properties of the nanocrystals were studied by resonance Raman spectroscopy as a function of excitation wavelength and temperature. The spectra were composed of the fundamental longitudinal optical (LO) mode around 300 cm-1, along with the first and second overtones. The shapes and positions of the Raman peaks exhibited only a weak dependence on particle size even for the two extreme cases of bulk and nanostructures. We show that the ratio of the overtone to the fundamental LO frequency was sensitive to the particle diameter and decreased upon reduction of the particle diameter to values below the Bohr radius. Temperature-dependent Raman measurements of ultranarrow nanorods showed a small red shift with decreasing temperature. Very high anti-Stokes intensities were observed for the CdS nanoparticles.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2009
Luminescent and structural characteristics of SiO 2 layers exposed to double implantation by Si +... more Luminescent and structural characteristics of SiO 2 layers exposed to double implantation by Si + and C + ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO 2 layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700-750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350-700 nm. Subsequent annealing at 1000 or 1100 ° C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ~400, ~500, and ~625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp 3 bond hybridization. The nanosized amorphous inclusions in the Si + + C + implanted and annealed SiO 2 layer have been revealed by high-resolution transmission electron microscopy.
Protection of Metals and Physical Chemistry of Surfaces, 2010
... Deposition conditions of PbS nanocrystals in chemical bath from XPb(NO3)2 + 0.205 CS(NH2)2 ..... more ... Deposition conditions of PbS nanocrystals in chemical bath from XPb(NO3)2 + 0.205 CS(NH2)2 ... gap becomes smoother together with increasing of its effective width in nanocrystallinePbS (Fig. ... in opposite directions from the Fermi level with a decrease in the nanoparticle size. ...
Size-controlled ZnSe nanoparticles with high extents of atomic positional order are shown to exhi... more Size-controlled ZnSe nanoparticles with high extents of atomic positional order are shown to exhibit large size-dependent variations in their local electronic environments. Solid-state 77 Se and 67 Zn NMR spectra reveal increasingly broad distributions of 77 Se and 67 Zn environments with decreasing nanoparticle sizes, in contrast with high degrees of atomic positional order established by transmission electron microscopy and x-ray diffraction. First-principles calculations of NMR parameters distinguish between atomic positional and electronic disorder that propagate from the nanoparticle surfaces and yield insights on the order and disorder present.
The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultan... more The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultaneous in situ small-angle x-ray scattering and surface force measurements. We have used the XSFA-II to monitor shear-induced orientational transitions in a lyotropic model lubricant system. Upon applying small shear amplitudes (ϳ20 mm) to a relatively thick (ϳ800 mm) film, we observed evidence for the formation of an orientational boundary layer at the shearing surface. Time-resolved x-ray diffraction revealed the gradual transition to shear-favored orientation by growth of the boundary layer.
ABSTRACT Photoelectron spectroscopic measurements have been performed, with synchrotron radiation... more ABSTRACT Photoelectron spectroscopic measurements have been performed, with synchrotron radiation on PbSe/CdSe heteronanocrystals that initially consist of core-shell structures. The study of the chemical states of the main elements in the nanocrystals shows a reproducible and progressive change in the valence-band and core-level spectra under photon irradiation, whatever the core and shell sizes are. Such chemical modifications are explained in light of transmission electron microscopy observations and reveal a phase transformation of the nanocrystals: The core-shell nanocrystals undergo a morphological change toward a Janus structure with the formation of semidetached PbSe and CdSe clusters. Photoelectron spectroscopy gives new insight into the reorganization of the ligands anchored at the surface of the nanocrystals and the modification of the electronic structure of these heteronanocrystals.
Langmuir-Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavi... more Langmuir-Blodgett (LB) films of the conjugated polydiacetylene (PDA) exhibit spectroscopic behavior, which is dependent on the type of the supporting substrate. While on polished silicon surfaces the photoluminescence (PL) of PDA is quenched, it is preserved on top of 2D patterned macro-porous silicon (2D-MPS). 2D-MPS, prepared by electrochemical etching of photo-lithographically pre-patterned silicon, is a 2D array of ca. 10 lm deep pores with lateral 2-4 lm repeating unit cells in orthogonal or hexagonal arrangements. LB films of PDA on such surfaces form membranes with continuous domains of the size sufficient to cover laterally many cell units. Apparently, the PL from this film results exclusively from the portion of the PDA membrane which is suspended over pore openings, while portions of the film which are attached to the silicon on top of the pores walls does not exhibit PL at all. We have used these membranes in different configurations and exposed them to different chemical and biological agents and followed the PL intensity change. This report demonstrates the effectiveness of the combined system: LB films of PDA on top of 2D-MPS as sensing probe for a variety of chemicals including, Cd ions and TNT explosives. In addition, the use of films of PDA, in which glycol-lipid were embedded, for binding and recognition of lectin protein, mimicking the cell membrane interaction with its environment, is also demonstrated.
One of the important factors limiting solar-cell efficiency is that incident photons generate one... more One of the important factors limiting solar-cell efficiency is that incident photons generate one electron-hole pair, irrespective of the photon energy. Any excess photon energy is lost as heat. The possible generation of multiple charge carriers per photon (carrier multiplication) is therefore of great interest for future solar cells 1 . Carrier multiplication is known to occur in bulk semiconductors, but has been thought to be enhanced significantly in nanocrystalline materials such as quantum dots, owing to their discrete energy levels and enhanced Coulomb interactions 1-3 . Contrary to this expectation, we demonstrate here that, for a given photon energy, carrier multiplication occurs more efficiently in bulk PbS and PbSe than in quantum dots of the same materials. Measured carriermultiplication efficiencies in bulk materials are reproduced quantitatively using tight-binding calculations, which indicate that the reduced carrier-multiplication efficiency in quantum dots can be ascribed to the reduced density of states in these structures.
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Papers by Y. Golan