Showing papers on "Absorption spectroscopy published in 2002"

Band gap fluorescence from individual single-walled carbon nanotubes.

Abstract: Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.

Structure-Assigned Optical Spectra of Single-Walled Carbon Nanotubes

Abstract: Spectrofluorimetric measurements on single-walled carbon nanotubes (SWNTs) isolated in aqueous surfactant suspensions have revealed distinct electronic absorption and emission transitions for more than 30 different semiconducting nanotube species. By combining these fluorimetric results with resonance Raman data, each optical transition has been mapped to a specific (n,m) nanotube structure. Optical spectroscopy can thereby be used to rapidly determine the detailed composition of bulk SWNT samples, providing distributions in both tube diameter and chiral angle. The measured transition frequencies differ substantially from simple theoretical predictions. These deviations may reflect combinations of trigonal warping and excitonic effects.

Effects of F- Doping on the Photocatalytic Activity and Microstructures of Nanocrystalline TiO2 Powders

Abstract: A novel and simple method for preparing highly photoactive nanocrystalline F--doped TiO2 photocatalyst with anatase and brookite phase was developed by hydrolysis of titanium tetraisopropoxide in a mixed NH4F−H2O solution. The prepared F--doped TiO2 powders were characterized by differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV−vis absorption spectroscopy, photoluminescence spectra (PL), transmission electron microscopy (TEM), and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results showed that the crystallinity of anatase was improved upon F- doping. Moreover, fluoride ions not only suppressed the formation of brookite phase but also prevented phase transition of anatase to rutile. The F--doped TiO2 samples exhibited stronger absorption in the UV−visible range with a red shift in the band gap transition. The photocatalytic activity of F--doped TiO2 powders prep...

Theoretical Studies of the Ground and Excited Electronic States in Cyclometalated Phenylpyridine Ir(III) Complexes Using Density Functional Theory

Abstract: The ground state and low-lying excited electronic states in the Ir(III) complex Ir(ppy)3, and in the related complexes Ir(ppy)2(acac) and Ir(ppy)2(bza), are studied using density functional theory techniques [where ppy = 2-phenylpyridine, acac = acetoylacetonate, and bza = benzyolacetonate]. Ir complexes of ppy have been the subject of numerous photophysical absorption and luminescence experiments and have been examined as potential donors in organic light emitting diodes (OLEDs). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Optimized geometries are compared to experimentally observed structures. Excited triplet and singlet states are examined using time-dependent density functional theory (TDDFT). The calculated energies of the lowest triplet state (2.4−2.6 eV) and lowest singlet state (2.6−2.7 eV) in the three complexes are in good agreement with experimental absorption spectra and luminescence studies. All of ...

Fabrication, Patterning, and Optical Properties of Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) Phosphor Films via Sol−Gel Soft Lithography

Abstract: Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol−gel process combined with soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscopy (AFM) and optical microscopy, UV/vis transmission and absorption spectra, photoluminescence (PL) spectra, and lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 400 °C and the crystallinity increased with the increase of annealing temperatures. Transparent nonpatterned phosphor films were uniform and crack-free, which mainly consisted of grains with an average size of 90 nm. Patterned gel and crystalline phosphor film bands with different widths (5−60 μm) were obtained. Significant shrinkage and a few defects were observed in the patterned films during the heat treatment process. The doped rare earth ions (A) show...

Nanostructures of polyaniline doped with inorganic acids

Abstract: With an average diameter of 150−340 nm and a conductivity of 10-1−100 S/cm, nanostructures (e.g., nanotubes or nanorods) of polyaniline (PANI) were synthesized by a self-assembly method in the presence of inorganic acids (e.g., HCl, H2SO4, HBF4, and H3PO4) as dopants. It was found that the morphology, size, and electrical properties of the resulting nanostructures depended on the dopant structures and the reaction conditions. In particular, all these PANI nanostuctures showed hydrophilic features, and the contact angles with water were measured to be about 27−40° depending on the dopant. The FTIR spectrum, UV−vis absorption spectrum, XPS, and X-ray diffraction were used to characterize the molecular structures of the nanostructures. It was found that their main chain structure and electric structure were identical to those of the emeraldine salt form of PANI. The micelles formed by anilinium cations act as the template like in the formation of PANI nanostructures.

Transition metal-doped zinc chalcogenides: Spectroscopy and laser demonstration of a new class of gain media

Abstract: The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr/sup 2+/, Co/sup 2+/, Ni/sup 2+/, or Fe/sup 2+/ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise. The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 /spl mu/m which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 /spl mu/m for Cr and from 2.8-4.0 /spl mu/m for Co, Cr luminesces strongly at room temperature; Co exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures, Cr/sup 2+/ is estimated to have the highest quantum yield at room temperature among the media investigated with values of /spl sim/75-100%. Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgF/sub 2/ pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 /spl mu/m, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the Cr/sup 2+/ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalcogenides; Co/sup 2+/ may also serve usefully, but laser demonstrations yet remain to be performed.

Role of copper in the green luminescence from ZnO crystals

Abstract: Electron paramagnetic resonance (EPR), photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu+ (3d10) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu2+ (3d9) EPR spectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is don...

Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy

Abstract: A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1×10-11 cm-1 Hz-1/2. The instrument has been used for sensitive measurements of CO, CH4, C2H2 and NH3.

On the absorption spectra of complex ions. II

Abstract: The secular determinants obtained in the previous paper are solved for the energy levels which are important in the absorption spectra of the normal complex ions, leaving the crystalline field strength as a parameter. The values of B and C (Racah's parameters) there needed are determined from the observed spectra of free ions or in some cases by extrapolation. The f -values of the transitions which connect the energy levels calculated are estimated and compared with the observed intensities. The difference of the spectral width among absorption bands and lines is also considered using the energy diagram obtained. Following the assignments determined by the above considerations, the calculated positions of lines and bands are rather in good agreement with the experimental data in divalent ions [MX 6 ] 2+ (M=Cr, Mn, Fe, Co, Ni), when we adjust the crystalline field parameter D q suitably. In trivalent ions [MX 6 ] 3+ (M=Ti, V, Cr, Mn, Fe), it is necessary besides the adjustment of D q to use smaller values ...

The ionized gas and nuclear environment in NGC 3783. I. Time-averaged 900 kilosecond Chandra grating spectroscopy

Abstract: We present results from a 900 ks exposure of NGC 3783 with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The resulting X-ray spectrum, which covers the 0.5-10 keV energy range, has the best combination of signal-to-noise ratio and resolution ever obtained for an AGN. This spectrum reveals absorption lines from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also possible absorption lines from H-like and He-like Ar and Ca as well as H-like C. We also identify inner-shell absorption from lower ionization ions such as Si VII-Si XII and S XII-S XIV. The iron absorption spectrum is very rich; L-shell lines of Fe XVII-Fe XXIV are detected, as well as probable resonance lines from Fe XXV. A strong complex of M-shell lines from iron ions is also detected in the spectrum. The absorption lines are blueshifted relative to the systemic velocity by a mean velocity of -590 ± 150 km s-1. We resolve many of the absorption lines, and their mean FWHM is 820 ± 280 km s-1. We do not find correlations between the velocity shifts or the FWHMs with the ionization potentials of the ions. Most absorption lines show asymmetry, having more extended blue wings than red wings. In O VII we have resolved this asymmetry to be from an additional absorption system at approximately -1300 km s-1. The two X-ray absorption systems are consistent in velocity shift and FWHM with the ones identified in the UV lines of C IV, N V, and H I. Equivalent width measurements for all absorption and emission lines are given and column densities are calculated for several ions. We resolve the narrow Fe Kα line at 6398.2 ± 3.3 eV to have an FWHM of 1720 ± 360 km s-1, which suggests that this narrow line may be emitted from the outer part of the broad-line region or the inner part of the torus. We also detect a "Compton shoulder" redward of the narrow Fe Kα line, which indicates that it arises in cold, Compton-thick gas.

Optical studies of solid hydrogen to 320 GPa and evidence for black hydrogen

Abstract: The quest for metallic hydrogen at high pressures represents a longstanding problem in condensed matter physics1,2. Recent calculations3,4,5,6 have predicted that solid hydrogen should become a molecular metal at pressures above 300 GPa, before transforming into an alkali metal; but the strong quantum nature of the problem makes the predictions difficult. Over a decade ago, an optical study7 of hydrogen was made using a diamond anvil cell to reach 250 GPa. However, despite many subsequent efforts, quantitative studies8,9,10,11 at higher pressures have proved difficult and their conclusions controversial. Here we report optical measurements of solid hydrogen up to a pressure of 320 GPa at 100 K. The vibron signature of the H2 molecule persists to at least 316 GPa; no structural changes are detected above 160 GPa, and solid hydrogen is observed to turn completely opaque at 320 GPa. We measure the absorption edge of hydrogen above 300 GPa, observing features characteristic of a direct electronic bandgap. This is at odds with the most recent theoretical calculations that predict much larger direct transition energies and the closure of an indirect gap3,4,5,6. We predict that metal hydrogen should be observed at about 450 GPa when the direct gap closes.

Wavelength Dependence of the Absorption of Black Carbon Particles: Predictions and Results from the TARFOX Experiment and Implications for the Aerosol Single Scattering Albedo

Abstract: Measurements are presented of the wavelength dependence of the aerosol absorption coefficient taken during the Tropical Aerosol Radiative Forcing Observational Experiment (TARFOX) over the northern Atlantic. The data show an approximate lamda(exp -1) variation between 0.40 and 1.0 micrometers. The theoretical basis of the wavelength variation of the absorption of solar radiation by elemental carbon [or black carbon (BC)] is explored. For a wavelength independent refractive index the small particle absorption limit simplifies to a lambda(exp -1) variation in relatively good agreement with the data. This result implies that the refractive indices of BC were relatively constant in this wavelength region, in agreement with much of the data on refractive indices of BC. However, the result does not indicate the magnitude of the refractive indices. The implications of the wavelength dependence of BC absorption for the spectral behavior of the aerosol single scattering albedo are discussed. It is shown that the single scattering albedo for a mixture of BC and nonabsorbing material decreases with wavelength in the solar spectrum (i.e., the percentage amount of absorption increases). This decease in the single scattering albedo with wavelength for black carbon mixtures is different from the increase in single scattering allied for most mineral aerosols (dusts). This indicates that, if generally true, the spectral variation of the single- scattering albedo can be used to distinguish aerosol types. It also highlights the importance of measurements of the spectral variation of the aerosol absorption coefficient and single scattering albedo.

Synthesis and Characterization of Carbon Nanotube−Nanocrystal Heterostructures

Abstract: Oxidized single-walled carbon nanotubes (SWNTs) have been reacted with cadmium selenide (CdSe) nanocrystals, capped with mercaptothiol derivatives, as well as with titanium dioxide (TiO2) nanocrystals, functionalized with 11-aminoundecanoic acid to form nanoscale heterostructures, characterized by transmission electron microscopy and infrared spectroscopy. The reaction with acid-terminated CdSe nanocrystals and acid-terminated tubes was facilitated with the aid of intermediary linking agents, such as ethylenediamine and semicarbazide, in an amide-forming reaction in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, EDC. Based on electronic absorption spectroscopy, charge transfer is thought to proceed from the nanocrystal to the nanotube in the CdSe−nanotube system, whereas in the TiO2−nanotube system, charge transfer is expected to occur from the nanotube to the nanocrystal.

The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-Averaged 900 ks Chandra Grating Spectroscopy

Abstract: We present results from a 900 ks exposure of NGC 3783 with the High-Energy Transmission Grating Spectrometer on board the Chandra X-ray Observatory. The resulting X-ray spectrum has the best combination of signal-to-noise and resolution ever obtained for an AGN. This spectrum reveals absorption lines from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also possible absorption lines from H-like and He-like Ar and Ca. We also identify inner-shell absorption from lower-ionization ions such as Si_VII-Si_XII and S_XII-S_XIV. The iron absorption spectrum is very rich; L-shell lines of Fe_XVII-Fe_XXIV are detected, strong complex of M-shell lines, and probable resonance lines from Fe_XXV. The absorption lines are blueshifted relative to the systemic velocity by a mean velocity of -590+-150 km/s. We resolve many of the absorption lines, and their mean FWHM is 820+-280 km/s. We do not find correlations between the velocity shifts or the FWHMs with the ionization potentials of the ions. Most absorption lines show asymmetry, having more extended blue wings than red wings. In O_VII we have resolved this asymmetry to be from an additional absorption system at ~ -1300 km/s. The two X-ray absorption systems are consistent in velocity shift and FWHM with the ones identified in the UV lines of C IV, N V, and H I. Equivalent width measurements for all lines are given and column densities are calculated for several ions. We resolve the narrow Fe_K\alpha line at 6398.2+-3.3 eV to have a FWHM of 1720+-360 km/s, which suggests that this narrow line may be emitted from the outer part of the broad line region or the inner part of the torus. We also detect a `Compton shoulder' redward of the narrow Fe_K\alpha line which indicates that it arises in cold, Compton-thick gas.

Collective vibrational modes in biological molecules investigated by terahertz time-domain spectroscopy

Abstract: We present well-resolved absorption spectra of biological molecules in the far-IR (FIR) spectral region recorded by terahertz time-domain spectroscopy (THz- TDS). As an illustrative example we discuss the absorption spectra of benzoic acid, its monosubstitutes salicylic acid (2-hydroxy-benzoic acid), 3- and 4-hydroxybenzoic acid, and aspirin (acetylsalicylic acid) in the spectral region between 18 and 150 cm 1 . The spectra exhibit distinct features originating from low-frequency vibrational modes caused by intra- or intermolecular collective motion and lattice modes. Due to the collective origin of the observed modes the absorption spectra are highly sensitive to the overall structure and configuration of the molecules, as well as their environment. The THz-TDS procedure can provide a direct fingerprint of the molecular structure or conformational state of a compound. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospec- troscopy) 67: 310 -313, 2002

Excitons in a photosynthetic light-harvesting system: a combined molecular dynamics, quantum chemistry, and polaron model study.

Abstract: The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with an approach that combines molecular dynamics simulations with quantum chemistry calculations and a polaron model analysis. The molecular dynamics simulation of light-harvesting (LH) complexes was performed on an 87 055 atom system comprised of a LH-II complex of Rhodospirillum molischianum embedded in a lipid bilayer and surrounded with appropriate water layers. For each of the 16 B850 bacteriochlorophylls (BChls), we performed 400 ab initio quantum chemistry calculations on geometries that emerged from the molecular dynamical simulations, determining the fluctuations of pigment excitation energies as a function of time. From the results of these calculations we construct a time-dependent Hamiltonian of the B850 exciton system from which we determine within linear response theory the absorption spectrum. Finally, a polaron model is introduced to describe both the excitonic and coupled phonon degrees of freedom by quantum mechanics. The exciton-phonon coupling that enters into the polaron model, and the corresponding phonon spectral function, are derived from the molecular dynamics and quantum chemistry simulations. The model predicts that excitons in the B850 BChl ring are delocalized over five pigments at room temperature. Also, the polaron model permits the calculation of the absorption and circular dichroism spectra of the B850 excitons from the sole knowledge of the autocorrelation function of the excitation energies of individual BChls, which is readily available from the combined molecular dynamics and quantum chemistry simulations. The obtained results are found to be in good agreement with the experimentally measured absorption and circular dichroism spectra.

Broadband absorption spectroscopy in turbid media by combined frequency-domain and steady state methodologies

Abstract: A technique for measuring broadband near-infrared absorption spectra of turbid media (12) uses a combination of frequency-domain and steady-state reflectance methods Most of the wavelengths coverage is provided by steady-state measurement using a white light (21) and a spectrograph (22) The frequency-domain data are acquired at a few selected wavelengths using laser diodes (13) and an avalanche photodiode unit (16) Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest, The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values

Trends in the Carbonyl Core (C 1S, O 1S) → π*C=O Transition in the Near-Edge X-ray Absorption Fine Structure Spectra of Organic Molecules

Abstract: Carbonyl core (C 1s, O 1s) → π*CO transitions are distinctive in the near-edge X-ray absorption fine structure (NEXAFS) spectra of species containing carbonyl groups. These features are used for the chemical microanalysis of organic materials using X-ray microscopy. We have explored the chemical sensitivity of these features in C 1s and O 1s NEXAFS spectra for a series of polymers containing the carbonyl group in a range of different bonding environments. Ab initio calculations are used to explain the origin of the observed trends and to explore the effect that orbital interactions have on the energy of these core (C 1s, O 1s) → π*CO features. The differences between the experimental and the calculated carbonyl core (C 1s, O 1s) → π*CO transition energies are systematic and can be used to develop a semiempirical method for predicting the absolute (experimental) transition energies from the calculated transition energies. This relationship is applied to a large body of calculated transition energy data to ...

Optical properties of CH3NH3PbX3 (X = halogen) and their mixed-halide crystals

Abstract: Thin films of microcrystalline CH3NH3PbX3 (X = halogen) as well as their mixed-halide crystals were fabricated by the spin-coating technique, and their optical properties were investigated. X-ray diffraction investigation revealed that CH3NH3PbBr3 − x Cl x (x = 0–3) were successfully formed on glass substrate self-assembly and oriented with the a-axis. Owing to due to their large exciton binding energy, these materials showed clear exciton absorption and free-exciton emission in the visible region at room temperature. Replacing Br with CI made it possible to control the band structure of these materials. As a result, the peak position of the exciton band shifted continuously towards blue region with increasing the CI content in the films.

Oxygen contribution on Li-ion intercalation-deintercalation in LiCoO2 investigated by O K-edge and Co L-edge X-ray absorption spectroscopy

Abstract: To investigate the electronic structure of the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co L I I , I I I -edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, we made a binder-free LiCoO 2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li 1 - x CoO 2 shows more effective spectral change with respect to Li-ion content than the Co L I I , I I I -edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co L I I , I I I -edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deintercalation is due to rehybridization between Co and O atoms under the local structural distortion of CoO 6 octahedra, which is also confirmed by the formation of two additional absorption peaks below the threshold energy corresponding to the oxygen 2p hole state hybridized with the 3d orbital of Co ion in the distorted CoO 6 octahedral site. In the O K-edge XAS spectra for the deintercalated Li 1 - x CoO 2 film, the shoulder absorption peak in the energy region higher than the threshold energy could be assigned to the higher oxidation state of the oxygen site on Li deintercalation. From the Co L I I , I I I -edge and O K-edge XAS results for the Li-ion deintercalated Li 1 - x CoO 2 film, it is concluded that the charge compensation for the Li-ion deintercalation process could be achieved mainly in the oxygen site and Co metal atomic site simultaneously. O K-edge and Co L I I , I I I -edge XAS results for cycled LiCoO 2 film show that the capacity fading of the LiCoO 2 system is related to the decrease of Co-O bond covalency by the local structural distortion of CoO 6 octahedra remaining in the cycled LiCoO 2 .

Electrochromic modulation of excited-state intramolecular proton transfer: the new principle in design of fluorescence sensors.

Abstract: Internal Stark effect (or internal electrochromy) consists of the shift of light absorption and emission bands under the influence of electric field produced by proximal charges. In the studies of 3-hydroxyflavone (3HF) derivatives exhibiting the excited-state intramolecular proton transfer (ESIPT), we describe a new phenomenon − a very strong internal electrochromic modulation of this reaction. Fluorescence spectra of 3HF derivatives with charged groups attached to the chromophore from the opposite sides without π-electronic conjugation, N-[(4‘-diethylamino)-3-hydroxy-6-flavonyl]methyl-N,N-dimethyloctylammonium bromide and 4-{4-[4‘-(3-hydroxyflavonyl)]piperazino}-1-(3-sulfopropyl)pyridinium, were compared with those of their neutral analogues in a series of representative solvents. The introduction of the proximal charge results in shifts of absorption spectrum and of both normal (N*) and tautomer (T*) emission bands, which correspond to initial and phototautomer states of the ESIPT reaction. The observe...

Modification of thiol-derived self-assembling monolayers by electron and x-ray irradiation: Scientific and lithographic aspects

Abstract: This article reviews recent experiments on the modification of thiol-derived self-assembling monolayers (SAMs) by electron and x-ray irradiation. Several complementary experimental techniques such as near-edge x-ray absorption fine structure spectroscopy, x-ray photoelectron spectroscopy and microscopy, and infrared reflection absorption spectroscopy were applied to gain a detailed knowledge on the nature and extent of irradiation-induced damage in these systems. The reaction of a SAM to electron and x-ray irradiation was found to be determined by the interplay of the damage/decomposition and cross-linking processes. Ways to adjust the balance between these two opposing effects by molecular engineering of the SAM constituents are demonstrated. The presented data provide the physical–chemical basis for electron-beam patterning of self-assembled monolayers to extend lithography down to the nanometer scale.