Sergey Gorelik - Academia.edu (original) (raw)
Papers by Sergey Gorelik
Advances in Intelligent and Soft Computing, 2012
In this chapter we will summarize the main photothermal, photoacoustic and photomechanical effect... more In this chapter we will summarize the main photothermal, photoacoustic and photomechanical effects of coupling a laser beam into a material from the absorption of the laser light to the deactivation of vibrationally and electronically excited states. Some ...
Chemical communications (Cambridge, England), Jan 23, 2015
A new class of soluble Eu(iii) coordination polymers based on a tridentate ditopic pybox ligand h... more A new class of soluble Eu(iii) coordination polymers based on a tridentate ditopic pybox ligand has been developed displaying high metal emission quantum yields of up to 73% as well as a unique dynamic behaviour in solution.
The Journal of Physical Chemistry A, 1997
ABSTRACT The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2... more ABSTRACT The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2O) with free electron laser radiation in the 3 μm region (C−H stretch vibrational absorption band) and in the 6 μm region (CO stretch vibrational absorption band) has been achieved using the same laser. Results indicate that initial excitation of this dimer is more efficient for MPD then initial monomer excitation. Carbon isotope-selective MPD has been performed with an isotopic mixture, H12COOH + H13COOH (50% + 50%), at an irradiating wavelength of 5.56 μm. For this mixture, isotopic selectivity s = k12/k13 = 23 has been attained as a ratio of the rate constants of the H12COOH MPD and the H13COOH MPD, respectively. The isotopic selectivity for 13C in the naturally occurring mixture (1.1% of 13C-containing molecules) s = k13/k12 = 22 has been attained at an irradiating wavelength of 5.90 μm.
Soft Matter, 2011
A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using th... more A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using the layer-by-layer assembly of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on sacrificial templates with imprinted patterns of wells. ...
The Analyst, Jan 7, 2014
We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to ... more We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to 100 nm. This table allows for easy and quick estimation of the concentration and size of modified and mono-dispersed silver nanoparticles from their optical spectra. We obtained data by determining the silver content of citrate-stabilised silver nanoparticles using sodium cyanide to dissolve the nanoparticles, and measuring solution conductivity with a pH meter and a cyanide-ion selective electrode. The quantification of the silver ion concentration enabled the calculation of extinction coefficients. Experimentally calculated extinction coefficients, in the current work, are in good agreement with collated literature values measured by different authors with non-standardized methodology and each for a limited range of particle size. They are also in good agreement with our theoretical calculations using Mie theory. Thus, we provide a highly standardized and comprehensive tabulated refere...
International Journal of Nanoscience, 2009
A method is presented that enables the determination of transient absorption in Langmuir films ma... more A method is presented that enables the determination of transient absorption in Langmuir films made from a monolayer of spiropyran on water. This is achievable even though the optical pathlength of such a monolayer is < 10 −9 m. The approach is to monitor reflectivity changes close to the Brewster angle, where the background of reflected light is minimized. This is the key to the sensitivity of the method. Relatively speaking the small changes in reflectivity due to changes in both real and imaginary parts of the refractive index are easier to observe with the intrinsically low backgrounds at the Brewster angle. Notably using Fresnel equations we can show that the real and imaginary parts of the refractive index can be independently assessed for ultrathin films and monolayers using the approach presented.
Doklady Physical Chemistry
The fabrication of high-purity monoisotope silicon has recently stimulated considerable interest ... more The fabrication of high-purity monoisotope silicon has recently stimulated considerable interest , which is caused by the possibility of preparing perfect single crystals of silicon, a basic material for use in microelectronics. The higher heat conduction of 28 Si single crystals compared to that of single crystals with a natural abundance of isotopes was found in [2, 3] and explained in . Recently, the idea of creating a quantum computer based on monoisotope 28 Si doped with 31 P at definite points has been suggested [5]. It is not ruled out that 29 Si possessing a magnetic nucleus can also be used for this purpose. Because of the rich possibilities offered by monoisotope 28 Si for both fundamental studies and advance technology, searching for organosilicon compounds suitable for separation of silicon isotopes is a currently central problem.
Journal of Molecular and Engineering Materials, 2013
A series of quartz surfaces were modi¯ed with a series of crosslinkers and functional groups in o... more A series of quartz surfaces were modi¯ed with a series of crosslinkers and functional groups in order to obtain an azide-terminated monolayer, which was then used to immobilize pyrene onto the surface via alkyne-azide \click" chemistry. During the course of the immobilization, di®erent ratios of tert-butyl diphenyl chlorosilane were used to control the distribution and hence the photophysical properties of the pyrene on the surface. The preparative surface reactions and photophysical properties were investigated with contact angle, X-ray photoelectron spectroscopy, UV-visible absorption and emission spectroscopy. High surface coverage was achieved of just under 1molecule per nm 2 . At this coverage all emission from the pyrene was in the form of excimer emission. Excimer emission dominated at all surface coverages greater than 0.45 molecules per nm 2 . Below this coverage the monomer emission could also be observed. The conclusions that can be drawn are important for understanding the interactions of neighboring molecules in molecular monolayers. Our results suggest that at high surface coverage a substantial number of the pyrene molecules are already close enough to their neighbors that pairs of them can be directly excited to form excimer with no requirement for di®usion. This can be stated because the long wavelength end of the pyrene absorption and excitation spectra show a broad tail that is assigned to a charge transfer band resulting from an electron being directly transferred from a ground state pyrene to a neighboring pyrene molecule. Furthermore, absorption spectra shifts also indicate that the pyrene molecules undergo some interactions on the surface when they are closely packed.
RSC Advances, 2013
ABSTRACT We investigate the blend morphology and performance of bulk heterojunction organic photo... more ABSTRACT We investigate the blend morphology and performance of bulk heterojunction organic photovoltaic devices comprising the donor polymer, pDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}) and the fullerene acceptor, [70]PCBM ([6,6]-phenyl C71-butyric acid methyl ester). The blend morphology is heavily dependent upon the solvent system used in the fabrication of thin films. Thin films spin-coated from chloroform possess a cobblestone-like morphology, consisting of thick, round-shaped [70]PCBM-rich mounds separated by thin polymer-rich valleys. The size of the [70]PCBM domains is found to depend on the overall film thickness. Thin films spin-coated from a chloroform:dichlorobenzene mixed solvent system are smooth and consist of a network of pDPP-TNT nanofibers embedded in a [70]PCBM-rich matrix. Rinsing the films in hexane selectively removes [70]PCBM and allows for analysis of domain size and purity. It also provides a means for investigating exciton dissociation efficiency through relative photoluminescence yield measurements. Devices fabricated from chloroform solutions show much poorer performance than the devices fabricated from the mixed solvent system; this disparity in performance is seen to be more pronounced with increasing film thickness. The primary cause for the improved performance of devices fabricated from mixed solvents is attributed to the greater donor-acceptor interfacial area and resulting greater capacity for charge carrier generation.
2008 IEEE PhotonicsGlobal at Singapore, IPGC 2008, 2008
2010 Photonics Global Conference, PGC 2010, 2010
ABSTRACT Raman mapping was used to determine the distribution of fats inside of adipocytes and hu... more ABSTRACT Raman mapping was used to determine the distribution of fats inside of adipocytes and human mesenchymal stem cells during adipogenesis. This proved to be a successful way of mapping the lipid distribution within the cells because of the strong C-H stretching bands of the fats inside the lipid droplets. Furthermore using deuterated glucose in the cell culture medium it was possible to distinguish any fats in droplets or in the cytoplasm that were formed before and after adipogenesis was initiated, because those formed after displayed both C-H and C-D stretching bands. The distributions of the initial metabolites of glucose and the resulting fats in the lipid drops could also be mapped in this way.
Vibrational Spectroscopy, 2003
Fundamental frequencies of SiH 2 F 2 and their isotopic shifts were calculated using ab initio MP... more Fundamental frequencies of SiH 2 F 2 and their isotopic shifts were calculated using ab initio MP2 and QCISD(T) and DFT (B3LYP) methods. The accuracy of calculations was tested by comparison with experimental SiH 2 F 2 and SiD 2 F 2 frequencies. While most of the fundamental frequencies are predicted very well, the accuracy of calculations of the deuterium isotopic shift was found to be 20-40 cm À1 . The most noticeable shift on silicone isotope substitution was found to be $7 cm À1 for the Si-F stretch mode of B 2 symmetry. Some doubts upon the accuracy of the quantum chemical calculations of the silicone isotopic shifts induced us to find a more accurate method to calculate isotopic shifts. Therefore, the method of analytical calculation of isotopic shifts for the B 1 and B 2 vibration modes of dihaloid silanes was proposed and tested. The results of analytical calculations of the isotopic shifts of the Si-F and Si-Cl stretching vibrations of SiH 2 F 2 and SiH 2 Cl 2 molecules under isotopic substitution of silicone and chlorine atoms are reported. #
The Journal of Physical Chemistry A, 2003
The multiphoton absorption of infrared radiation induced dissociation of phenyltrifluorosilane (P... more The multiphoton absorption of infrared radiation induced dissociation of phenyltrifluorosilane (PhSiF 3 ) in a batch reactor. End product analysis from IR MPD of neat PhSiF 3 and the mixture of PhSiF 3 and Br 2 shows that the main dissociation channels are (1) the elimination of SiF 3 and (2) the elimination of H. Silicon isotopes have been enriched under the FEL irradiation of neat PhSiF 3 at 961 cm -1 (abundance of 30 Si in PhSiF 3 was increased from 3.10 ( 0.03% to 12.3 ( 0.1%) and 925 cm -1 (abundance of 28 Si in PhSiF 3 was increased from 92.2 ( 0.9% to 96.5 ( 0.9%).
Solar Energy Materials and Solar Cells, 2014
ABSTRACT We investigate the role of oxygen vacancies in photochromism of molybdenum oxide amorpho... more ABSTRACT We investigate the role of oxygen vacancies in photochromism of molybdenum oxide amorphous films. MoO3−x films with a wide range of initial stoichiometries are deposited using R.F. unbalanced magnetron sputtering. The evolution of visible light absorption in conjunction with Raman spectra for these films is studied in detail during the course of UV-irradiation to correlate the color change to the Mo6+ to Mo5+ conversion. For films which have an initially more complete stoichiometry, and hence lower oxygen vacancy concentration, the color change fully correlates with conversion of Mo6+ to Mo5+. This behavior is consistent with the group of models of photochromism of transition metal oxides which disregard the presence of oxygen vacancies in the films. However, coloration of the films with initially greater deviation from complete stoichiometry, and hence higher oxygen vacancy concentration, is not accompanied by any significant conversion of Mo6+ to Mo5+. This behavior is consistent with the group of models of photochromism of transition metal oxides which rely on the presence of oxygen vacancies. Overall, the reported results demonstrate the importance of the initial stoichiometry in the photochromism of MoO3−x amorphous films, particularly in the initial stages of UV-irradiation.
Small, 2012
Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template... more Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the water-air interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g(-1) can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers.
Science and Technology of Advanced Materials, 2011
We report the photochromic properties of amorphous MoO 3 films deposited by dc sputtering with di... more We report the photochromic properties of amorphous MoO 3 films deposited by dc sputtering with different O 2 flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O 2 partial pressure during the film deposition, which was controlled by the O 2 flow rate. The origins of this observation are discussed.
Russian Chemical Bulletin, 1998
Successful experiments on the isotope-selective infrared multiphoton dissociation (IR MPD) of nit... more Successful experiments on the isotope-selective infrared multiphoton dissociation (IR MPD) of nitromethane molecules in the region of stretching vibrations of the NO2 group have been performed for the first time under IR free electron laser (FEL) irradiation in a mixture with the natural content of the15N isotope of 0.4%. The content of the15N isotope in the products of NO dissociation
Russian Chemical Bulletin, 1998
Physical Chemistry Chemical Physics, 2008
A nanosecond pulsed IR (1.9 mm) laser rapidly heated water, in an open vessel, to temperatures we... more A nanosecond pulsed IR (1.9 mm) laser rapidly heated water, in an open vessel, to temperatures well below the boiling point. The subsequent dynamics of volume expansion were monitored using time-resolved interferometry in order to measure the increase in the water level in the heated area. The water expanded at less than the speed of sound, taking just less than 100 ns to increase its height by B500 nm at surface temperature jumps of 20 K. The initial expansion was followed by an apparent contraction and then a re-expansion. The first expansion phase occurred more slowly than the timescale for bulk H-bond re-structuring of the water, as determined from vibrational bands in the Raman spectra, and represents the limit to the rate at which the overpressure caused by sudden heating can be released. The second phase of the expansion was caused by hydrodynamic effects and is accompanied by morphological changes resulting in light scattering as well as droplet spallation.
Advances in Intelligent and Soft Computing, 2012
In this chapter we will summarize the main photothermal, photoacoustic and photomechanical effect... more In this chapter we will summarize the main photothermal, photoacoustic and photomechanical effects of coupling a laser beam into a material from the absorption of the laser light to the deactivation of vibrationally and electronically excited states. Some ...
Chemical communications (Cambridge, England), Jan 23, 2015
A new class of soluble Eu(iii) coordination polymers based on a tridentate ditopic pybox ligand h... more A new class of soluble Eu(iii) coordination polymers based on a tridentate ditopic pybox ligand has been developed displaying high metal emission quantum yields of up to 73% as well as a unique dynamic behaviour in solution.
The Journal of Physical Chemistry A, 1997
ABSTRACT The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2... more ABSTRACT The infrared multiphoton dissociation (IR MPD) of formic acid molecules (HCOOH → CO + H2O) with free electron laser radiation in the 3 μm region (C−H stretch vibrational absorption band) and in the 6 μm region (CO stretch vibrational absorption band) has been achieved using the same laser. Results indicate that initial excitation of this dimer is more efficient for MPD then initial monomer excitation. Carbon isotope-selective MPD has been performed with an isotopic mixture, H12COOH + H13COOH (50% + 50%), at an irradiating wavelength of 5.56 μm. For this mixture, isotopic selectivity s = k12/k13 = 23 has been attained as a ratio of the rate constants of the H12COOH MPD and the H13COOH MPD, respectively. The isotopic selectivity for 13C in the naturally occurring mixture (1.1% of 13C-containing molecules) s = k13/k12 = 22 has been attained at an irradiating wavelength of 5.90 μm.
Soft Matter, 2011
A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using th... more A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using the layer-by-layer assembly of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on sacrificial templates with imprinted patterns of wells. ...
The Analyst, Jan 7, 2014
We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to ... more We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to 100 nm. This table allows for easy and quick estimation of the concentration and size of modified and mono-dispersed silver nanoparticles from their optical spectra. We obtained data by determining the silver content of citrate-stabilised silver nanoparticles using sodium cyanide to dissolve the nanoparticles, and measuring solution conductivity with a pH meter and a cyanide-ion selective electrode. The quantification of the silver ion concentration enabled the calculation of extinction coefficients. Experimentally calculated extinction coefficients, in the current work, are in good agreement with collated literature values measured by different authors with non-standardized methodology and each for a limited range of particle size. They are also in good agreement with our theoretical calculations using Mie theory. Thus, we provide a highly standardized and comprehensive tabulated refere...
International Journal of Nanoscience, 2009
A method is presented that enables the determination of transient absorption in Langmuir films ma... more A method is presented that enables the determination of transient absorption in Langmuir films made from a monolayer of spiropyran on water. This is achievable even though the optical pathlength of such a monolayer is < 10 −9 m. The approach is to monitor reflectivity changes close to the Brewster angle, where the background of reflected light is minimized. This is the key to the sensitivity of the method. Relatively speaking the small changes in reflectivity due to changes in both real and imaginary parts of the refractive index are easier to observe with the intrinsically low backgrounds at the Brewster angle. Notably using Fresnel equations we can show that the real and imaginary parts of the refractive index can be independently assessed for ultrathin films and monolayers using the approach presented.
Doklady Physical Chemistry
The fabrication of high-purity monoisotope silicon has recently stimulated considerable interest ... more The fabrication of high-purity monoisotope silicon has recently stimulated considerable interest , which is caused by the possibility of preparing perfect single crystals of silicon, a basic material for use in microelectronics. The higher heat conduction of 28 Si single crystals compared to that of single crystals with a natural abundance of isotopes was found in [2, 3] and explained in . Recently, the idea of creating a quantum computer based on monoisotope 28 Si doped with 31 P at definite points has been suggested [5]. It is not ruled out that 29 Si possessing a magnetic nucleus can also be used for this purpose. Because of the rich possibilities offered by monoisotope 28 Si for both fundamental studies and advance technology, searching for organosilicon compounds suitable for separation of silicon isotopes is a currently central problem.
Journal of Molecular and Engineering Materials, 2013
A series of quartz surfaces were modi¯ed with a series of crosslinkers and functional groups in o... more A series of quartz surfaces were modi¯ed with a series of crosslinkers and functional groups in order to obtain an azide-terminated monolayer, which was then used to immobilize pyrene onto the surface via alkyne-azide \click" chemistry. During the course of the immobilization, di®erent ratios of tert-butyl diphenyl chlorosilane were used to control the distribution and hence the photophysical properties of the pyrene on the surface. The preparative surface reactions and photophysical properties were investigated with contact angle, X-ray photoelectron spectroscopy, UV-visible absorption and emission spectroscopy. High surface coverage was achieved of just under 1molecule per nm 2 . At this coverage all emission from the pyrene was in the form of excimer emission. Excimer emission dominated at all surface coverages greater than 0.45 molecules per nm 2 . Below this coverage the monomer emission could also be observed. The conclusions that can be drawn are important for understanding the interactions of neighboring molecules in molecular monolayers. Our results suggest that at high surface coverage a substantial number of the pyrene molecules are already close enough to their neighbors that pairs of them can be directly excited to form excimer with no requirement for di®usion. This can be stated because the long wavelength end of the pyrene absorption and excitation spectra show a broad tail that is assigned to a charge transfer band resulting from an electron being directly transferred from a ground state pyrene to a neighboring pyrene molecule. Furthermore, absorption spectra shifts also indicate that the pyrene molecules undergo some interactions on the surface when they are closely packed.
RSC Advances, 2013
ABSTRACT We investigate the blend morphology and performance of bulk heterojunction organic photo... more ABSTRACT We investigate the blend morphology and performance of bulk heterojunction organic photovoltaic devices comprising the donor polymer, pDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}) and the fullerene acceptor, [70]PCBM ([6,6]-phenyl C71-butyric acid methyl ester). The blend morphology is heavily dependent upon the solvent system used in the fabrication of thin films. Thin films spin-coated from chloroform possess a cobblestone-like morphology, consisting of thick, round-shaped [70]PCBM-rich mounds separated by thin polymer-rich valleys. The size of the [70]PCBM domains is found to depend on the overall film thickness. Thin films spin-coated from a chloroform:dichlorobenzene mixed solvent system are smooth and consist of a network of pDPP-TNT nanofibers embedded in a [70]PCBM-rich matrix. Rinsing the films in hexane selectively removes [70]PCBM and allows for analysis of domain size and purity. It also provides a means for investigating exciton dissociation efficiency through relative photoluminescence yield measurements. Devices fabricated from chloroform solutions show much poorer performance than the devices fabricated from the mixed solvent system; this disparity in performance is seen to be more pronounced with increasing film thickness. The primary cause for the improved performance of devices fabricated from mixed solvents is attributed to the greater donor-acceptor interfacial area and resulting greater capacity for charge carrier generation.
2008 IEEE PhotonicsGlobal at Singapore, IPGC 2008, 2008
2010 Photonics Global Conference, PGC 2010, 2010
ABSTRACT Raman mapping was used to determine the distribution of fats inside of adipocytes and hu... more ABSTRACT Raman mapping was used to determine the distribution of fats inside of adipocytes and human mesenchymal stem cells during adipogenesis. This proved to be a successful way of mapping the lipid distribution within the cells because of the strong C-H stretching bands of the fats inside the lipid droplets. Furthermore using deuterated glucose in the cell culture medium it was possible to distinguish any fats in droplets or in the cytoplasm that were formed before and after adipogenesis was initiated, because those formed after displayed both C-H and C-D stretching bands. The distributions of the initial metabolites of glucose and the resulting fats in the lipid drops could also be mapped in this way.
Vibrational Spectroscopy, 2003
Fundamental frequencies of SiH 2 F 2 and their isotopic shifts were calculated using ab initio MP... more Fundamental frequencies of SiH 2 F 2 and their isotopic shifts were calculated using ab initio MP2 and QCISD(T) and DFT (B3LYP) methods. The accuracy of calculations was tested by comparison with experimental SiH 2 F 2 and SiD 2 F 2 frequencies. While most of the fundamental frequencies are predicted very well, the accuracy of calculations of the deuterium isotopic shift was found to be 20-40 cm À1 . The most noticeable shift on silicone isotope substitution was found to be $7 cm À1 for the Si-F stretch mode of B 2 symmetry. Some doubts upon the accuracy of the quantum chemical calculations of the silicone isotopic shifts induced us to find a more accurate method to calculate isotopic shifts. Therefore, the method of analytical calculation of isotopic shifts for the B 1 and B 2 vibration modes of dihaloid silanes was proposed and tested. The results of analytical calculations of the isotopic shifts of the Si-F and Si-Cl stretching vibrations of SiH 2 F 2 and SiH 2 Cl 2 molecules under isotopic substitution of silicone and chlorine atoms are reported. #
The Journal of Physical Chemistry A, 2003
The multiphoton absorption of infrared radiation induced dissociation of phenyltrifluorosilane (P... more The multiphoton absorption of infrared radiation induced dissociation of phenyltrifluorosilane (PhSiF 3 ) in a batch reactor. End product analysis from IR MPD of neat PhSiF 3 and the mixture of PhSiF 3 and Br 2 shows that the main dissociation channels are (1) the elimination of SiF 3 and (2) the elimination of H. Silicon isotopes have been enriched under the FEL irradiation of neat PhSiF 3 at 961 cm -1 (abundance of 30 Si in PhSiF 3 was increased from 3.10 ( 0.03% to 12.3 ( 0.1%) and 925 cm -1 (abundance of 28 Si in PhSiF 3 was increased from 92.2 ( 0.9% to 96.5 ( 0.9%).
Solar Energy Materials and Solar Cells, 2014
ABSTRACT We investigate the role of oxygen vacancies in photochromism of molybdenum oxide amorpho... more ABSTRACT We investigate the role of oxygen vacancies in photochromism of molybdenum oxide amorphous films. MoO3−x films with a wide range of initial stoichiometries are deposited using R.F. unbalanced magnetron sputtering. The evolution of visible light absorption in conjunction with Raman spectra for these films is studied in detail during the course of UV-irradiation to correlate the color change to the Mo6+ to Mo5+ conversion. For films which have an initially more complete stoichiometry, and hence lower oxygen vacancy concentration, the color change fully correlates with conversion of Mo6+ to Mo5+. This behavior is consistent with the group of models of photochromism of transition metal oxides which disregard the presence of oxygen vacancies in the films. However, coloration of the films with initially greater deviation from complete stoichiometry, and hence higher oxygen vacancy concentration, is not accompanied by any significant conversion of Mo6+ to Mo5+. This behavior is consistent with the group of models of photochromism of transition metal oxides which rely on the presence of oxygen vacancies. Overall, the reported results demonstrate the importance of the initial stoichiometry in the photochromism of MoO3−x amorphous films, particularly in the initial stages of UV-irradiation.
Small, 2012
Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template... more Inspired by the amphiphilicity of graphene oxide (GO), the surface of water is used as a template for the assembly of a GO film. Methacrylate-functionalized GO sheets can be cross-linked instantaneously at the water-air interface to form a highly wrinkled membrane spreading over an extended area. The multiple covalent linkages amongst the GO sheets enhances the in-plane stiffness of the film compared to noncovalently bonded GO films. The highly convoluted GO membrane can be used in two applications: the promoting of spontaneous stem-cell differentiation towards bone cell lineage without any chemical inducers, and for supercapacitor electrodes. Due to reduced van der Waals restacking, capacitance values up to 211 F g(-1) can be obtained. The scalable and inexpensive nature of this assembly route enables the engineering of membranes for applications in regenerative medicine and energy-storage devices where secondary structures like nanotopography and porosity are important performance enhancers.
Science and Technology of Advanced Materials, 2011
We report the photochromic properties of amorphous MoO 3 films deposited by dc sputtering with di... more We report the photochromic properties of amorphous MoO 3 films deposited by dc sputtering with different O 2 flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O 2 partial pressure during the film deposition, which was controlled by the O 2 flow rate. The origins of this observation are discussed.
Russian Chemical Bulletin, 1998
Successful experiments on the isotope-selective infrared multiphoton dissociation (IR MPD) of nit... more Successful experiments on the isotope-selective infrared multiphoton dissociation (IR MPD) of nitromethane molecules in the region of stretching vibrations of the NO2 group have been performed for the first time under IR free electron laser (FEL) irradiation in a mixture with the natural content of the15N isotope of 0.4%. The content of the15N isotope in the products of NO dissociation
Russian Chemical Bulletin, 1998
Physical Chemistry Chemical Physics, 2008
A nanosecond pulsed IR (1.9 mm) laser rapidly heated water, in an open vessel, to temperatures we... more A nanosecond pulsed IR (1.9 mm) laser rapidly heated water, in an open vessel, to temperatures well below the boiling point. The subsequent dynamics of volume expansion were monitored using time-resolved interferometry in order to measure the increase in the water level in the heated area. The water expanded at less than the speed of sound, taking just less than 100 ns to increase its height by B500 nm at surface temperature jumps of 20 K. The initial expansion was followed by an apparent contraction and then a re-expansion. The first expansion phase occurred more slowly than the timescale for bulk H-bond re-structuring of the water, as determined from vibrational bands in the Raman spectra, and represents the limit to the rate at which the overpressure caused by sudden heating can be released. The second phase of the expansion was caused by hydrodynamic effects and is accompanied by morphological changes resulting in light scattering as well as droplet spallation.