Showing papers on "Raman spectroscopy published in 2005"
TL;DR: The use of Raman spectroscopy to reveal the remarkable structure and the unusual electronic and phonon properties of single wall carbon nanotubes (SWNTs) is reviewed comprehensively in this article.
3,835 citations
TL;DR: In this article, experimental conditions and mathematical fitting procedures for the collection and analysis of Raman spectra of soot and related carbonaceous materials have been investigated and optimised with a Raman microscope system operated at three different laser excitation wavelengths (514, 633, and 780 nm).
3,304 citations
TL;DR: The electromagnetic theory of surface-enhanced Raman spectroscopy (SERS), despite its simplicity, can account for all major SERS observations, including: the need for a nanostructured material as the SERS-active system; the observation that some metals form good SERS active systems while others do not; the observed polarization sensitivity shown by nanoparticle aggregates; and the optical behavior of nanostructure materials in the absence of a molecular adsorbate as mentioned in this paper.
Abstract: The electromagnetic theory of surface-enhanced Raman spectroscopy (SERS), despite its simplicity, can account for all major SERS observations, including: the need for a nanostructured material as the SERS-active system; the observation that some metals form good SERS-active systems while others do not; the observation that strongly interacting metal nanoparticles result in very much more effective SERS-active systems; the observed polarization sensitivity shown by nanoparticle aggregates; and the optical behavior of nanostructured metals in the absence of a molecular adsorbate. By extending the ideas inherent in the electromagnetic model one can also understand the seminal features reported for single-molecule SERS, including the puzzling observation that only a few silver ‘particles’ in an ensemble are ‘hot’ (they are appropriately structured nanoparticle clusters) and that for a hot particle, once one is able to observe SERS, adding more adsorbate does not significantly alter the intensity (once the electromagnetic hot spot is occupied, adding adsorbate to other sites on the nanoparticle cluster will not add greatly to the observed intensity). However, the electromagnetic model does not account for all that is learned through SERS. Molecular resonances, charge-transfer transitions and other processes such as ballistic electrons transiently probing the region where the molecule resides and then modulating electronic processes of the metal as a result certainly contribute to the rich information SERS reports; and by virtue of the fact that these contributions will vary from molecule to molecule, they will constitute the most interesting aspects reported by SERS. But, the overall reason why SERS produces such inordinate enhancements is largely an electromagnetic property of nanostructures. Copyright © 2005 John Wiley & Sons, Ltd.
1,644 citations
Book•
26 Jan 2005
TL;DR: In this paper, the authors present a comprehensive overview of Raman Spectroscopy and its application in the field of data processing, including a discussion of the basic theory of RAMAN SPECTROSCOPY.
Abstract: Preface. Acknowledgements. CHAPTER 1: INTRODUCTION, BASIC THEORY AND PRINCIPLES. 1.1 Introduction. 1.2 Basic Theory. 1.3 Molecular Vibrations. 1.4 Summary. CHAPTER 2: THE RAMAN EXPERIMENT - RAMAN INSTRUMENTATION, SAMPLE PRESENTATION, DATA HANDLING AND PRACTICAL ASPECTS OF INTERPRETATION. 2.1 Introduction. 2.2 Choice of Instrument. 2.3 Visible Excitation. 2.4 NIR Excitation. 2.5 Raman Sample Preparation and Handling. 2.6 Sample Mounting Accessories. 2.7 Microscopy. 2.8 Calibration. 2.9 Data Handling, Manipulation and Quantitation. 2.10 Approach to Qualitative Interpretation. 2.11 Summary. CHAPTER 3: THE THEORY OF RAMAN SPECTROSCOPY. 3.1 Introduction. 3.2 Absorption and Scattering. 3.3 States of a System and Hooke's Law. 3.4 The Nature of Polarizability and the Measurement of Polarization. 3.5 The Basic Selection Rule. 3.6 Number and Symmetry of Vibrations. 3.7 Symmetry Elements and Point Groups. 3.8 The Mutual Exclusion Rule. 3.9 The Kramer Heisenberg Dirac Expression. 3.10 Lattice Modes. 3.11 Conclusions. CHAPTER 4: RESONANCE RAMAN SCATTERING. 4.1 Introduction. 4.2 Theoretical Aspects. 4.3 Practical Aspects. 4.4 Examples of the Use of Resonance Raman Scattering. 4.5 Conclusions. CHAPTER 5: SURFACE-ENHANCED RAMAN SCATTERING AND SURFACE-ENHANCED RESONANCE RAMAN SCATTERING. 5.1 Introduction. 5.2 Theory. 5.3 Electromagnetic and Charge Transfer Enhancement. 5.4 Selection Rules. 5.5 Applications of SERS. 5.6 Applications of SERRS. 5.7 The Basic Method. CHAPTER 6: APPLICATIONS. 6.1 Introduction. 6.2 Inorganics and Minerals. 6.3 Art and Archaeology. 6.4 Polymers and Emulsions. 6.5 Colour. 6.6 Electronics Applications. 6.7 Biological and Pharmaceutical Applications. 6.8 Forensic Applications. 6.9 Plant Control and Reaction Following. 6.10 Summary. CHAPTER 7: MORE ADVANCED RAMAN SCATTERING TECHNIQUES. 7.1 Flexible Optics. 7.2 Tuneable Lasers, Frequency Doubling and Pulsed Lasers. 7.3 Spatially Resolved Systems. 7.4 Nonlinear Raman Spectroscopy. 7.5 Time Resolved Scattering. 7.6 Raman Optical Activity. 7.7 UV Excitation. 7.8 Conclusions. Index.
1,013 citations
TL;DR: Three vibrational modes of benzenethiol are studied simultaneously on one substrate, and it is demonstrated that the smaller Raman shifted peak shows a maximum enhancement closer to the LSPR lambda(max) than that of a larger Raman shift peak, in agreement with the predictions of the electromagnetic enhancement mechanism of SERS.
Abstract: A detailed wavelength-scanned surface-enhanced Raman excitation spectroscopy (WS SERES) study of benzenethiol adsorbed on Ag nanoparticle arrays, fabricated by nanosphere lithography (NSL), is presented. These NSL-derived Ag nanoparticle array surfaces are both structurally well-characterized and extremely uniform in size. The WS SERES spectra are correlated, both spatially and spectrally, with the corresponding localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays. The surface-enhanced Raman scattering (SERS) spectra were measured in two excitation wavelength ranges: (1) 425−505 nm, and (2) 610−800 nm, as well as with the 532-nm line from a solid-state diode-pumped laser. The WS SERES spectra have line shapes similar to those of the LSPR spectra. The maximum SERS enhancement factor is shown to occur for excitation wavelengths that are blue-shifted with respect to the LSPR λmax of adsorbate-covered nanoparticle arrays. Three vibrational modes of benzenethiol (1575, 1081, and 1009 ...
906 citations
TL;DR: Measurements of the elastic modulus of tunicate cellulose using a Raman spectroscopic technique show that the tunicate sample is a two-dimensional in-plane random network of fibers, and the modulus is very high, at about 143 GPa.
832 citations
TL;DR: In this paper, the characterization methods of carbon nanotubes which are most employed today are reviewed and the most interesting features of each technique are indexed for each technique, including the most important features of the most used techniques.
Abstract: Carbon nanotubes due to their specific atomic structure have interesting chemical and physical properties according to those of graphite and diamond. This review covers the characterization methods of carbon nanotubes which are most employed today. The structure of carbon nanotubes is first briefly summarized followed by a description of the characterization methods such as STM, TEM, neutron diffraction, X-ray diffraction, X-ray photoelectron spectroscopy, infrared and Raman spectroscopy. The most interesting features are indexed for each technique.
787 citations
TL;DR: In this article, the authors review recent developments in Kα and Kβ spectroscopy and show how the chemical sensitivity of the fluorescence lines can be exploited for selective X-ray absorption studies.
775 citations
TL;DR: In this paper, a new method based on optical microscopy is proposed for the determination of MWCNT solubility in concentrated aqueous-suspensions, which is found to correlate well with the area ratio of the G and D bands from the Raman spectrum.
726 citations
TL;DR: In this paper, the authors investigated the relationship between the particle size and the Raman bands of TiO 2 nanoparticles using transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES), extended Xray absorption fine structure (EXAFS), and Raman spectroscopy.
642 citations
TL;DR: As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
Abstract: We demonstrate a convenient and cost-effective chemical approach for fabricating highly ordered Au nanoparticle arrays with sub-10-nm interparticle gaps. Near-field enhancements inside the interparticle gaps create uniform periodic arrays of well-defined “hot spots” exploitable for large surface-enhanced Raman spectroscopy (SERS) enhancements. A cetyltrimethylammonium bromide (CTAB) bilayer surrounding each individual nanoparticle upon array crystallization is responsible for this periodic gap structure; displacement of the CTAB by smaller thiolated molecules does not affect the structural integrity of the arrays. As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
TL;DR: This surface enhanced Raman scattering (SERS) geometry offers large surface enhancements for molecules adsorbed onto planar substrates and could be quite useful for determining chemical information for poor Raman scatterers from assays on 2-D substrates.
Abstract: Surface enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid (4-MBA) self-assembled monolayers (SAMs) on gold substrates is presented for SAMs onto which gold nanoparticles of various shapes have been electrostatically immobilized. SERS spectra of 4-MBA SAMs are enhanced in the presence of immobilized gold nanocrystals by a factor of 107−109 relative to 4-MBA in solution. Large enhancement factors are a likely result of plasmon coupling between the nanoparticles (localized surface plasmon) and the smooth gold substrate (surface plasmon polariton), creating large localized electromagnetic fields at their interface, where 4-MBA molecules reside in this sandwich architecture. Moreover, enhancement factors depend on nanoparticle shape and vary by a factor of 102. This SERS geometry offers large surface enhancements for molecules adsorbed onto planar substrates and could be quite useful for determining chemical information for poor Raman scatterers from assays on 2-D substrates.
TL;DR: The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates.
Abstract: The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.
TL;DR: The spectral evolution of the vibrational features from 200 femtoseconds to 1 picosecond after photon absorption reveals the temporal sequencing of the geometric changes in the retinal backbone that activate this receptor.
Abstract: The primary event that initiates vision is the light-induced 11-cis to all-trans isomerization of retinal in the visual pigment rhodopsin. Despite decades of study with the traditional tools of chemical reaction dynamics, both the timing and nature of the atomic motions that lead to photoproduct production remain unknown. We used femtosecond-stimulated Raman spectroscopy to obtain time-resolved vibrational spectra of the molecular structures formed along the reaction coordinate. The spectral evolution of the vibrational features from 200 femtoseconds to 1 picosecond after photon absorption reveals the temporal sequencing of the geometric changes in the retinal backbone that activate this receptor.
TL;DR: In this paper, the authors measured nonresonant and resonant Raman-scattering spectra from ZnO nanocrystals with an average diameter of 20nm.
Abstract: We have measured nonresonant and resonant Raman-scattering spectra from ZnO nanocrystals with an average diameter of 20nm. Based on our experimental data and comparison with the recently developed theory, we show that the observed shifts of the polar optical-phonon peaks in the resonant Raman spectra are not related to the spatial phonon confinement. The very weak dispersion of the polar optical phonons in ZnO nanocrystals does not lead to any noticeable redshift of the phonon peaks for 20-nm nanocrystals. The observed phonon shifts have been attributed to the local heating effects. We have demonstrated that even the low-power ultraviolet laser excitation, required for the resonant Raman spectroscopy, can lead to the strong local heating of ZnO nanocrystals. The latter causes significant (up to 14cm−1) redshift of the optical-phonon peaks compared to their position in bulk crystals. Nonresonant Raman excitation does not produce noticeable local heating. The obtained results can be used for identification ...
TL;DR: In this article, the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon present in arc-derived SWNT soot was studied.
Abstract: IR and Raman spectroscopy has been used to study the evolution of the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon present in arc-derived SWNT soot. We have carried out a systematic study to define the different outcomes stemming from the purification protocol (e.g., DO, DO/HCl, DO/HNO3, H2O2, H2O2/HCl), where dry oxidation (DO) or refluxing in H2O2 was used in a first purification step to remove amorphous carbon. The second step involves acid reflux (HCl or HNO3) to remove the residual growth catalyst (Ni−Y). During strong chemical processing, it appears possible to create additional defects where carbon atoms are eliminated, the ring structure is now open, localized CC bonds are created, and O-containing groups can be added to this defect to stabilize the structure. Evolution of SWNT skeletal disorder obtained via chemical processing was studied by Raman scattering. Higher intensity ratios of R...
TL;DR: The surface enhanced Raman scattering (SERS) of a number of species and strains of bacteria obtained on novel gold nanoparticle covered SiO(2) substrates excited at 785 nm is reported, showing the potential of SERS for detection and identification of bacterial pathogens with species and strain specificity on these gold particle covered glassy substrates.
Abstract: The surface enhanced Raman scattering (SERS) of a number of species and strains of bacteria obtained on novel gold nanoparticle (∼80 nm) covered SiO2 substrates excited at 785 nm is reported. Raman cross-section enhancements of >104 per bacterium are found for both Gram-positive and Gram-negative bacteria on these SERS active substrates. The SERS spectra of bacteria are spectrally less congested and exhibit greater species differentiation than their corresponding non-SERS (bulk) Raman spectra at this excitation wavelength. Fluorescence observed in the bulk Raman emission of Bacillus species is not apparent in the corresponding SERS spectra. Despite the field enhancement effects arising from the nanostructured metal surface, this fluorescence component appears “quenched” due to an energy transfer process which does not diminish the Raman emission. The surface enhancement effect allows the observation of Raman spectra of single bacterial cells excited at low incident powers and short data acquisition times....
TL;DR: A simple methodology for the effective retrieval of Raman spectra of subsurface layers in diffusely scattering media, providing an effective noninvasive means of screening for bone degeneration, other skeletal disease diagnosis, and dermatology studies, as well as materials and catalyst research.
Abstract: We describe a simple methodology for the effective retrieval of Raman spectra of subsurface layers in diffusely scattering media. The technique is based on the collection of Raman scattered light from surface regions that are laterally offset away from the excitation laser spot on the sample. The Raman spectra obtained in this way exhibit a variation in relative spectral intensities of the surface and subsurface layers of the sample being investigated. The data set is processed using a multivariate data analysis to yield pure Raman spectra of the individual sample layers, providing a method for the effective elimination of surface Raman scatter. The methodology is applicable to the retrieval of pure Raman spectra from depths well in excess of those accessible with conventional confocal microscopy. In this first feasibility study we have differentiated between surface and subsurface Raman signals within a diffusely scattering sample composed of two layers: trans-stilbene powder beneath a 1 mm thick over-layer of PMMA (poly(methyl methacrylate)) powder. The improvement in contrast of the subsurface trans-stilbene layer without numerical processing was 19 times. The potential applications include biomedical subsurface probing of specific tissues through different overlying tissues such as assessment of bone quality through skin, providing an effective noninvasive means of screening for bone degeneration, other skeletal disease diagnosis, and dermatology studies, as well as materials and catalyst research.
TL;DR: Theoretical calculations of the Raman intensities and the simulated Raman spectra of platinum(II) complexes were presented in this article, where the clear-cut assignment of the Pt-ligand vibrations in the analyzed compounds has been made on the basis of the calculated potential energy distribution.
TL;DR: In this paper, surface-enhanced Raman scattering (SERS) by time-dependent evolution in the intermediate anionic state of the adsorbate is analogous to intramolecular Franck-Condon resonance Raman scatterings.
Abstract: The model of surface-enhanced Raman scattering (SERS) by time-dependent evolution in the intermediate anionic state of the adsorbate is analogous to intramolecular Franck–Condon resonance Raman scattering. For adsorbates with a π* state, the residence time of some femtoseconds (10−15 s) in the anionic state leads to a separation of electron (e) and hole (h), which quenches SERS at a smooth surface. At so-called SERS-active sites, the residence time of the hole is enhanced and therefore there is no final e–h pair and the excitation of only a molecular vibration leads to SERS. In contrast, for molecules with only high-energy σ* states, the residence time in the anionic state is <1 fs (analogous to the impulse mechanism in electron scattering), and the creation of e–h pairs is less likely. This leads to first-layer electronic Raman scattering, especially by CH stretch vibrations with an average enhancement of about 30–40-fold. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, a surface-enhanced Raman spectroscopy (SERS) substrate consisting of silver nanorod arrays with an irregular surface lattice (i.e., random nucleation sites) and with varying rod lengths was fabricated by an oblique angle vapor deposition method.
Abstract: Substrates consisting of silver nanorod arrays with an irregular surface lattice (i.e., random nucleation sites) and with varying rod lengths were fabricated by an oblique angle vapor deposition method. These arrays were evaluated as potential surface-enhanced Raman spectroscopy (SERS) substrates using trans-1,2-bis(4-pyridyl)ethene as a reported molecule. SERS activity was shown to depend upon the length of the nanorods. The Ag nanorods with average lengths of 508.29±44.86nm, and having aspect ratios of 5.69±1.49 exhibited the maximum SERS enhancement factors of greater than 108. Theoretical calculations indicate that this large SERS enhancement may be partially explained by the shape, density, and lateral arrangement of the Ag nanorod arrays.
TL;DR: Well-aligned stripe patterns with tunable orientation, thickness and periodicity at the micrometre scale were obtained by transferring nanoparticles from a floating film onto a substrate in a dip-coating fashion.
Abstract: Significant advancement has been made in nanoparticle research, with synthetic techniques extending over a wide range of materials with good control over particle size and shape1,2,3,4,5,6. A grand challenge is assembling and positioning the nanoparticles in desired locations to construct complex, higher-order functional structures. Controlled positioning of nanoparticles has been achieved in pre-defined templates fabricated by top–down approaches7,8. A self-assembly method, however, is highly desirable because of its simplicity and compatibility with heterogeneous integration processes. Here we report on the spontaneous formation of ordered gold and silver nanoparticle stripe patterns on dewetting a dilute film of polymer-coated nanoparticles floating on a water surface. Well-aligned stripe patterns with tunable orientation, thickness and periodicity at the micrometre scale were obtained by transferring nanoparticles from a floating film onto a substrate in a dip-coating fashion. This facile technique opens up a new avenue for lithography-free patterning of nanoparticle arrays for various applications including, for example, multiplexed surface-enhanced Raman substrates and templated fabrication of higher-order nanostructures.
TL;DR: It is shown here that many of the features of the Raman spectrum that are considered to be hallmarks of a multistate system, including the asymmetric band profile, the isosbestic (temperature invariant) point, and van't Hoff behavior, actually result from a continuous distribution.
Abstract: The unique chemical and physical properties of liquid water are a direct result of its highly directional hydrogen-bond (HB) network structure and associated dynamics. However, despite intense experimental and theoretical scrutiny spanning more than four decades, a coherent description of this HB network remains elusive. The essential question of whether continuum or multicomponent (“intact,” “broken bond,” etc.) models best describe the HB interactions in liquid water has engendered particularly intense discussion. Most notably, the temperature dependence of water's Raman spectrum has long been considered to be among the strongest evidence for a multicomponent distribution. Using a combined experimental and theoretical approach, we show here that many of the features of the Raman spectrum that are considered to be hallmarks of a multistate system, including the asymmetric band profile, the isosbestic (temperature invariant) point, and van't Hoff behavior, actually result from a continuous distribution. Furthermore, the excellent agreement between our newly remeasured Raman spectra and our model system further supports the locally tetrahedral description of liquid water, which has recently been called into question [Wernet, P., et al. (2004) Science 304, 995-999].
TL;DR: Raman spectroscopy has become a versatile tool in protein science and biotechnology as discussed by the authors, and examples of use in protein structural biology and selected industrial applications are discussed in Section 2.1.
Abstract: Raman spectroscopy has become a versatile tool in protein science and biotechnology. Recent advances in spectral assignments and vibrational theory, examples of use in structural biology and selected industrial applications are discussed. New insights into protein folding, assembly and aggregation were obtained by classical Raman spectroscopy. Raman spectroscopy has been used to characterize intrinsically unstructured proteins. The improved instrument sensitivity made it possible to use Raman difference spectroscopy to characterize enzyme–substrate interactions. Specifically, Raman crystallography has been instrumental in the delineation of protein–ligand interactions with a resolution surpassing that of x-ray diffraction. Numerous applications of Raman spectroscopy to protein analysis in biotechnology and food industry have been facilitated by the new generation of commercial Raman instruments. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: Thermogravimetric analysis indicated that the polymer-functionalized SWNTs consisted of 45% polymer, amounting to approximately one polymer chain for every 200-700 carbons of the nanotubes, depending on polymer molecular weight.
Abstract: Covalent functionalization of alkyne-decorated SWNTs with well-defined, azide-terminated polystyrene polymers was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. This reaction was found to be extremely efficient in producing organosoluble polymer-nanotube conjugates, even at relatively low reaction temperatures (60 °C) and short reaction times (24 h). The reaction was found to be most effective when a CuI catalyst was employed in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive. IR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the SWNTs, and Raman spectroscopy evidenced the conversion of a high proportion of sp2 carbons to sp3 hybridization during alkyne introduction. Thermogravimetric analysis indicated that the polymer-functionalized SWNTs consisted of 45% polymer, amounting to approximately one polymer chain for every 200−700 carbons of the nanotubes, depending on polymer molecular weight. Transmission electron microscopy an...
TL;DR: A detailed interpretations of the infrared and Raman spectra of 5-bromo-2-nitropyridine is reported on the basis of the calculated potential energy distribution (PED).
TL;DR: Collagen-CNT composite matrices may have utility as scaffolds in tissue engineering, or as components of biosensors or other medical devices, and Scanning electron microscopy showed physical interactions between CNT and collagen matrix.
Abstract: Carbon nanotubes (CNT) are attractive for use in fiber-reinforced composite materials due to their very high aspect ratio, combined with outstanding mechanical and electrical properties. Composite materials comprising a collagen matrix with embedded CNT were prepared by mixing solubilized Type I collagen with solutions of carboxylated single-walled carbon nanotubes (SWNT) at concentrations of 0, 0.2, 0.4, 0.8, and 2.0 weight percent. Living smooth muscle cells were incorporated at the time of collagen gelation to produce cell-seeded collagen-CNT composite matrices. Constructs containing 2.0 wt % CNT exhibited delayed gel compaction, relative to lower concentrations that compacted at the same rate as pure collagen controls. Cell viability in all constructs was consistently above 85% at both Day 3 and Day 7, whereas cell number in CNT-containing constructs was lower than in control constructs at Day 3, though statistically unchanged by Day 7. Scanning electron microscopy showed physical interactions between CNT and collagen matrix. Raman spectroscopy confirmed the presence of CNT at the expected diameter (0.85-1.30 nm), but did not indicate strong molecular interactions between the collagen and CNT components. Such collagen-CNT composite matrices may have utility as scaffolds in tissue engineering, or as components of biosensors or other medical devices.
TL;DR: In this paper, the size-dependent changes to the Raman spectrum are best explained in terms of three-dimensional confinement of phonons in finite-sized nanocrystalline anatase.
Abstract: The Raman scattering behavior of anatase nanocrystals with average diameters of 4, 8, 20, and 34 nm has been compared with bulk crystal data in order to establish size-dependent changes to the phonon spectrum at ambient conditions. Further, the high-pressure behavior of the anatase nanocrystals was examined at room-temperature using in situ Raman scattering data obtained in diamond-anvil cells to a maximum pressure of 41 GPa. The size-dependent changes to the Raman spectrum are best explained in terms of three-dimensional confinement of phonons in finite-sized nanocrystalline anatase. The difference in slopes obtained for the pressure shifts of Raman modes between nanocrystalline and single crystal anatase is in conformity with the observed size-dependent bulk modulus values. The metastability of anatase as a function of pressure is demonstrated to be size dependent, with smaller crystallites preserving the structure to higher pressures. Three size regimes have been recognized for the pressure-induced phase transition of anatase at room temperature: an anatase-amorphous transition regime at the smallest crystallite sizes, an anatase-baddeleyite transition regime at intermediate crystallite sizes, and an anatase--$\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$ transition regime comprising large nanocrystals to macroscopic single crystals. This size-dependent phase selectivity of anatase at high pressures explains the recent contradictory experimental data. A semiquantitative phase diagram for anatase metastability as a function of size and pressure at room temperature is proposed.
TL;DR: Room-temperature piranha treatments have the capability of cutting existing damage sites with minimal carbon loss, slow etch rates, and little sidewall damage and combined with a method of introducing controlled amounts of damage sites have the potential to yield an efficient means of creating short, cut nanotubes.
Abstract: The oxidation reaction of piranha solutions with purified HiPco carbon nanotubes was measured as a function of temperature. At high temperatures, piranha is capable of attacking existing damage sites, generating vacancies in the graphene sidewall, and consuming the oxidized vacancies to yield short, cut nanotubes. Increased reaction time results in increasingly shorter nanotubes. However, significant sidewall damage occurs as well as selective etching of the smaller diameter nanotubes. On the other hand, room-temperature piranha treatments show the capability of cutting existing damage sites with minimal carbon loss, slow etch rates, and little sidewall damage. Combined with a method of introducing controlled amounts of damage sites, these room-temperature piranha solutions have the potential to yield an efficient means of creating short, cut nanotubes.