Single‐molecule surface‐enhanced Raman scattering of fullerene C60

We achieved single‐molecule surface‐enhanced Raman scattering (SM‐SERS) spectra from ultralow concentrations (10⁻¹⁵ M) of fullerene C₆₀ on uniformly assembled Au nanoparticles. It was found that resonant excitation at 785 nm is a powerful tool to probe SM‐SERS in this system. The appearance of additional bands and splitting of some vibrational modes were observed because of the symmetry reduction of the adsorbed molecule and a relaxation in the surface selection rules. Time‐evolved spectral fluctuation and ‘hot spot’ dependence in the SM‐SERS spectra were demonstrated to result from the single‐molecule Raman behavior of the spherical C₆₀ on Au nanoparticles. Copyright © 2010 John Wiley & Sons, Ltd.     

Tunable n‐ and p‐type doping of single‐layer graphene by engineering its interaction with the SiO2 support

We report a technique to tune the excess charge concentration in single‐layer graphene from p‐ to n‐type up to densities of |n | ～ 1.2 × 10¹³ cm^–2, corresponding to a displacement electric field of ～2.5 V/nm. The tuning is achieved by engineering the interaction between graphene and the underlying Si/SiO₂ substrate with an amino group‐terminated self‐assembled monolayer, and subsequent rinsing in aqueous solutions at controlled pH. Raman spectroscopy and electrical measurements on treated graphene devices confirm the occurrence of doping. Interestingly, we found the field‐effect mobility not to be significantly affected by the procedure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mobility Enhancement of P3HT‐Based OTFTs upon Blending with Au Nanorods

The mobility enhancement of organic thin‐film transistors based on poly(3‐hexylthiophene) (P3HT) by incorporating gold nanorods (Au NRs) is reported. Through varying the doping concentration and surface modifier of the Au NRs in P3HT matrix, the P3HT/Au composite with 0.5 mg mL^?1 pyridine‐capped Au NRs exhibits a hole mobility of 0.059 cm² V^?1 s^?1, this value is seven times higher than that of pristine P3HT. This remarkable improvement of mobility originates from the enhanced crystallinity and optimized orientation of P3HT after doping with Au NRs. In addition, the appropriate surface modification can produce more‐efficient hole conduction of Au NRs.     

Trapping intermediates and comparing relative reactivities: a DFT M06‐2X study on Diels–Alder cycloadditions of butadiene to C60 and C70

All possible types of Diels–Alder cycloadditions of 1,3‐cis‐butadiene to C₆₀ (2 in total) and to C₇₀ (8 in total) were theoretically investigated by the M06‐2X density functional method in gas phase and solutions. An intermediate between the reactant and the transition state was located for each reaction. These intermediates except one have not been experimentally or theoretically reported before. The reactivities of the 10 reactions in both the gas phase and solutions were systematically compared based on the calculated results. The present conclusion agrees with the experimental observations and partly disagrees with the previously theoretical conclusion. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel X‐ray diffractometer for studies of liquid–liquid interfaces

The study of liquid–liquid interfaces with X‐ray scattering methods requires special instrumental considerations. A dedicated liquid surface diffractometer employing a tilting double‐crystal monochromator in Bragg geometry has been designed. This diffractometer allows reflectivity and grazing‐incidence scattering measurements of an immobile mechanically completely decoupled liquid sample, providing high mechanical stability. The available energy range is from 6.4 to 29.4 keV, covering many important absorption edges. The instrument provides access in momentum space out to 2.54 Å^?1 in the surface normal and out to 14.8 Å^?1 in the in‐plane direction at 29.4 keV. Owing to its modular design the diffractometer is also suitable for heavy apparatus such as vacuum chambers. The instrument performance is described and examples of X‐ray reflectivity studies performed under in situ electrochemical control and on biochemical model systems are given.     

Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C60) interface and mobility improvement

We studied various aspects relating to surface charge‐transfer‐induced doping at an organic/organic interface using in situ electrical measurements with a field‐effect transistor (FET) during the formation of the electron donor/acceptor interface. Adsorption of the electron‐accepting molecules (C₆₀) on top of the electron donating molecules (α‐6T) led to an increase in the FET hole mobility in an α‐6T film. Under illumination, the FET hole mobility in the α‐6T film with C₆₀ deposition was significantly increased in comparison with that in the dark due to exciton dissociation at the C₆₀/α‐6T interface, resulting in a large threshold voltage shift. The origin of the mobility increase is explained by the multiple trapping and release (MTR) model in which the mobility is determined by the carrier density. Various phenomena relevant to charge transfer and charge transport at the organic/organic interface are reported and their origins are discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally‐activated post‐growth dewetting of fullerene C60 on mica

Understanding and controlling the growth and stability of molecular thin films on solid surfaces is necessary to develop nanomaterials with well‐defined physical properties. As a prominent model system in organic electronics, we investigate the post‐growth dewetting kinetics of the fullerene C₆₀ on mica with real‐time and in situ X‐ray scattering. After layer‐by‐layer growth of C₆₀, we find a thermally‐activated post‐growth dewetting, where the smooth C₆₀‐layer breaks up into islands. This clearly shows that growth is kinetically limited before the system moves over an activation barrier into an energetically favored configuration. From the temperature‐dependent dewetting kinetics we find an effective activation barrier of 0.33 eV, which describes both the temperature‐dependent macroscopic changes in the surface morphology and the microscopic processes of inter‐ and intralayer diffusion during dewetting.

     

A DFT study on Diels–Alder cycloadditions of trans‐1,3‐butadiene to C60 and C70

Investigation of the relative reactivity of bonds in fullerenes will provide fundamental theory for the design of fullerene‐based materials. We have theoretically investigated the reactivity of the Diels–Alder (DA) cycloaddition of cis‐1,3‐butadiene to all types of bonds in C₆₀ and C₇₀ using the M06‐2X hybrid density functional theory (DFT) calculations (J. Phys. Org. Chem. 2012, 25 850–855) and have pointed out that the DA cycloadditions of cis and trans forms of 1,3‐butadiene to ethylene have a specially intimate relationship (J. Phys. Org. Chem. 2014, 27 652–660). For the aim of telling a whole story of the DA cycloaddition concerning C₆₀ and C₇₀, the DA cycloadditions of trans‐1,3‐butadiene to all types of bonds in C₆₀ and C₇₀ were explored at the same theoretical level as those of the cis‐1,3‐butadiene. The calculated results related with the trans‐ and cis‐1,3‐butadienes were compared. The potential energy curves of DA cycloadditions of trans‐ and cis‐1,3‐butadiene to C₆₀ and C₇₀ were discussed. The distortion–interaction energy model was employed to elucidate the origin of different reactivity of all kinds of C?C bonds. The solvent effects were examined using the continuum solvent model. These current results, along with our previous research, will help to obtain an overall view of the DA cycloadditions of 1,3‐butadiene to C₆₀ and C₇₀. Copyright © 2014 John Wiley & Sons, Ltd.     

Liquid‐Crystal‐Mediated Self‐Assembly of Porous α‐Fe2O3 Nanorods on PEDOT:PSS‐Functionalized Graphene as a Flexible Ternary Architecture for Capacitive Energy Storage

A novel aqueous‐based self‐assembly approach to a composite of iron oxide nanorods on conductive‐polymer (CP)‐functionalized, ultralarge graphene oxide (GO) liquid crystals (LCs) is demonstrated here for the fabrication of a flexible hybrid material for charge capacitive application. Uniform decoration of α‐Fe₂O₃ nanorods on a poly(3,4‐ethylene‐dioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐functionalized, ultralarge GO scaffold results in a 3D interconnected layer‐by‐layer (LBL) architecture. This advanced interpenetrating network of ternary components is lightweight, foldable, and possesses highly conductive pathways for facile ion transportation and charge storage, making it promising for high‐performance energy‐storage applications. Having such structural merits and good synergistic effects, the flexible architecture exhibits a high specific discharge capacitance of 875 F g^?1 and excellent volumetric specific capacitance of 868 F cm^?3 at 5 mV s^?1, as well as a promising energy density of 118 W h kg^?1 (at 0.5 A g^?1) and promising cyclability, with capacity retention of 100% after 5000 charge–discharge (CD) cycles. This synthesis method provides a simple, yet efficient approach for the solution‐processed LBL insertion of the hematite nanorods (HNR) into CP‐functionalized novel composite structure. It provides great promise for the fabrication of a variety of metal‐oxide (MO)‐nanomaterial‐based binder and current collector‐free flexible composite electrodes for high‐performance energy‐storage applications.     

Large scale synthesis of pinhole‐free shell‐isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) as a new member of Raman technique garnered great attention among scientific community. In this work, we used an improved experimental setup to float the bare silver nanoparticles in air with the help of extraneous airflow, and used atomic layer deposition (ALD) method to coat ultra‐thin inert shell without pinholes. Under optimal conditions, we successfully prepared three kinds of SHINERS NPs (Ag@Al₂O₃, Ag@SiO₂ and Ag@TiO₂) in large quantity without pinholes. The ultra‐thin inert shell maintains the SERS activity of silver nanoparticles for long period of time. Transmission electron microscopy (TEM) images confirm the uniform coating of shell material on silver nanoparticles. Finally, the as‐prepared SHINs have been applied to detect various samples to demonstrate the applications. The presented ALD method offers a unique way to coat ultrathin shell (1–10 nm) on metal nanoparticles in large quantity (1–10 g) for practical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Complex concentration dependence of SERS and UV–Vis absorption of glycine/Ag‐substrates because of glycine‐mediated Ag‐nanostructure modifications

Complex concentration‐dependence of surface‐enhanced Raman scattering (SERS) and UV–Vis absorption of Ag‐nanoparticles (AgNPs) mixed with Gly has been observed. Surprisingly, with decreasing Gly concentration, a new band in UV–Vis absorption of AgNPs/Gly mixtures is found to red‐shift with increasing intensity, until a turning point at a critical concentration. Further diluting Gly, the new band blue‐shifts with decreasing intensity. Similarly, the SERS intensities of Gly bands at 615 and 905 cm^–1 consistently increase with decreasing Gly concentrations, reaching maxima at the critical concentration. This agrees consistently with the variation in position and intensity of the new developing plasmon absorption band. Interestingly, transmission electron microscopy (TEM) revealed Gly‐induced modifications of AgNPs, including a reassembling and increasing aspect ratio with deceasing Gly concentration. The concentration‐dependent behavior of UV–Vis absorption, SERS, and TEM of AgNPs/Gly mixtures could be due to the complex nature of Gly‐AgNPs interaction depending on the molecular density, as supported by TEM images. Copyright © 2012 John Wiley & Sons, Ltd.     

In vivo study on the protection of indole‐3‐carbinol (I3C) against the mouse acute alcoholic liver injury by micro‐Raman spectroscopy

Micro‐Raman spectroscopy (MRS) was utilized for the first time to evaluate the effect of indole‐3‐carbinol (I3C) on acute alcoholic liver injury in vivo. In situ Raman analysis of tissue sections provided distinct spectra that can be used to distinguish alcoholic liver injury as well as ethanol‐induced liver fibrosis from the normal state. Sixteen mice with liver diseases including acute liver injury and chronic liver fibrosis, and eight mice with normal liver tissues, and eight remedial mice were studied employing the Raman spectroscopic technique in conjunction with biomedical assays. The biochemical changes in mouse liver tissue when liver injury/fibrosis occurs such as the loss of reduced glutathione (GSH), and the increase of collagen (α‐helix protein) were observed by MRS. The intensity ratio of two Raman peaks (I₁₄₅₀/I₆₆₆) and in combination with statistical analysis of the entire Raman spectrum was found capable of classifying liver tissues with different pathological features. Raman spectroscopy therefore is an important candidate for a nondestructive in vivo screening of the effect of drug treatment on liver disease, which potentially decreases the time‐consuming clinical trials. Copyright © 2008 John Wiley & Sons, Ltd.     

Air stability of PTCDI‐C13‐based n‐OFETs on polymer interfacial layers

This Letter reports the novel use of poly(9‐vinylcarbazole) (PVK) as a dielectric interfacial layer for n‐type organic field‐effect transistors (n‐OFETs). With PVK, both the air stability and electron mobility of N,N′‐ditridecylperylene‐3,4,9,10‐tetracarboxylic diimide (PTCDI‐C13)‐based OFETs were improved. Among the PVKs with different weight‐average molecular weight (M_w), PVK with high M_w showed good performance. The high glass transition temperature of PVK enabled thermal post annealing of the active layer, which resulted in a high electron mobility of 0.61 cm²/Vs. This mobility was maintained at 90% and 59% after 4 days and 105 days in air, respectively. The PVK interfacial layer reduced the trapped charges in the PTCDI‐C13‐based n‐OFET for air‐exposure and caused a decrease in the threshold voltage shift.

     

Quantitative,comparable coherent anti‐Stokes Raman scattering (CARS) spectroscopy: correcting errors in phase retrieval

Coherent anti‐Stokes Raman scattering (CARS) microspectroscopy has demonstrated significant potential for biological and materials imaging. To date, however, the primary mechanism of disseminating CARS spectroscopic information is through pseudocolor imagery, which explicitly neglects a vast majority of the hyperspectral data. Furthermore, current paradigms in CARS spectral processing do not lend themselves to quantitative sample‐to‐sample comparability. The primary limitation stems from the need to accurately measure the so‐called nonresonant background (NRB) that is used to extract the chemically sensitive Raman information from the raw spectra. Measurement of the NRB on a pixel‐by‐pixel basis is a nontrivial task; thus, surrogate NRB from glass or water is typically utilized, resulting in error between the actual and estimated amplitude and phase. In this paper, we present a new methodology for extracting the Raman spectral features that significantly suppresses these errors through phase detrending and scaling. Classic methods of error correction, such as baseline detrending, are demonstrated to be inaccurate and to simply mask the underlying errors. The theoretical justification is presented by re‐developing the theory of phase retrieval via the Kramers–Kronig relation, and we demonstrate that these results are also applicable to maximum entropy method‐based phase retrieval. This new error‐correction approach is experimentally applied to glycerol spectra and tissue images, demonstrating marked consistency between spectra obtained using different NRB estimates and between spectra obtained on different instruments. Additionally, in order to facilitate implementation of these approaches, we have made many of the tools described herein available free for download. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Reactivity of C4‐indolyl substituted 1,4‐dihydropyridines toward superoxide anion (O2•) in dimethylsulfoxide

Reactivity of two new C4‐indolyl substituted 1,4‐dihydropyridines (1,4‐DHPs) toward superoxide anion (O₂^? ) in dimethylsulfoxide (DMSO) is reported. Reactivity was followed by electrochemical and spectroscopic techniques. Gas chromatography‐mass spectrometry (GC–MS) was used to identify the final products of the reaction. C4 indolyl‐substituted‐1,4‐DHPs reacted toward O₂^? at significant rates, according to the calculated kinetic rate constants. Results are compared with 4‐phenyl‐DHP and the commercial 1,4‐DHPs, nimodipine, nisoldipine, and amlodipine. Indolyl‐substituted 1,4‐DHPs were more reactive than the commercial derivatives. The direct participation of proton of the 1‐position of the secondary amine in the quenching of O₂^? was demonstrated. Copyright © 2008 John Wiley & Sons, Ltd.     

Rapid atto‐molar level detection of surface‐enhanced Raman spectroscopy technique based on glycidyl methacrylate–ethylene dimethacrylate (GMA–EDMA) porous material

A novel miniature device for rapid ultra‐sensitive surface‐enhanced Raman scattering (SERS) detection was developed in the present study. The device was made of a syringe, a piece of filter, and a Teflon tube. Therefore, it was with advantages of simplicity, miniaturization, and easy operability. The tube was filled in advance with the glycidyl methacrylate‐ethylene dimethacrylate powder porous material which has been proved to increase the sensitivity of normal SERS dramatically, then the mixture solution containing the analyte, silver colloid, and NaCl solution passed through the porous material by the action of the syringe. SERS signals were collected from the surface of the material. Rhodamine 6G (R6G), p‐aminothiophenol (PATP), and thiabendazole (TBZ) were employed as the probe molecules in the present work. R6G at microlitre‐scale can be detected at an extremely low concentration of 10^–18 mol/l, and the relative standard deviation of spot to spot is 14.16% at the intensity of the band at 609 cm⁻¹. The concentrations of PATP and TBZ that can be detected with the method are 10⁻¹¹ mol/l and 1.3 × 10⁻⁶ mol/l, respectively. This method not only has achieved the ultra‐sensitive detection of dye and pesticide but also realized the simple, rapid, and small sample quantity requirement detection, and it is of great potential use for lots of analytes. Copyright © 2013 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and DFT calculations of di‐amino acid peptides: α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu in the solid state

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di‐amino acid peptide derivatives α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3‐LYP correlation functional and the cc‐pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di‐amino acid peptide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of serum albumins: an effect of proton‐ and γ‐irradiation

Raman spectroscopy was applied to analyse structural changes in serum albumins (bovine serum albumin, BSA; human serum albumin, HSA) following proton and γ‐irradiation (0.5, 5 and 50 Gy). Characteristic Raman bands of both polypeptide backbone and amino acid residues were sensitive to irradiation. Significant damage of HSA/BSA was observed only at the highest dose (50 Gy). Raman spectra confirmed radiation‐induced denaturation, destruction of helical structures and aggregation of serum albumins. The differences in the dose‐dependent effects of proton and γ‐radiation on studied proteins are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Identification of minerals and organic materials in Middle Eocene ironstones from the Bahariya Depression in the Western Desert of Egypt by means of micro‐Raman spectroscopy

The Middle Eocene ironstones of the Bahariya Depression consist of four iron ore types: manganiferous mud‐ironstone, fossiliferous ironstone, stromatolitic ironstone and nummulitic–ooidal–oncoidal ironstone. The upper surfaces of these sequences were subjected to subaerial weathering and a lateritic iron ore type was formed. The chemical composition of these ironstone types was investigated by means of micro‐Raman spectroscopy. Various closely related iron‐containing and manganese‐containing minerals were detected by means of the above‐mentioned approach. The high spatial resolution and sensitivity of this method allowed us to identify minerals that could not be detected by other techniques. Well‐preserved organic materials were observed in one type of ironstones. Therefore, using Raman spectroscopy, we were able to provide evidence that the formation of some of the investigated rocks was biologically mediated. The application of Raman spectroscopy is considered a powerful technique for the identification of both organic and inorganic substances in the studied iron ore deposits. Copyright © 2011 John Wiley & Sons, Ltd.