Raman Spectral Properties Research Articles

Facile co-precipitation synthesis of nano-molybdenum-doped BaO nanoparticles and their physical characterization

Alkaline metal oxides have received significant attention recently due to their abundance, inherent conductivity, optical absorption, and thermal stability. Here, a straightforward co-precipitation method was employed to obtain both undoped BaO and Mo-doped BaO nanoparticles. Various techniques were used to characterize the synthesized nanoparticles’ structural, Raman spectral, optical, thermal, and electrical properties. X-ray diffraction (XRD) results revealed that Mo was successfully doped into tetragonal nanocrystalline BaO. The W-H plot showed that as Mo doping increases from 2 % to 6 %, the crystallite size grows while the lattice structure remains well-ordered with even strain distribution. Scanning electron microscopy (SEM) was used to examine its surface features. The purity and crystalline character of the samples were further confirmed via Raman spectroscopy, which shows that the peak intensity of the spectra increases with the increase of particle size owing to the rise in the force constant. UV spectroscopy was used to observe the energy band gap, which is found to decrease from 4.2 eV to 3.8 eV, and then it drops to 3.4 eV as the Mo content increases. This is reasonable because of the size-dependent attraction between metallic ions and conduction electrons. PL spectra concluded that Mo doping leads to the enhancement of the optical characteristics of BaO. Adding Mo to BaO also modifies the material’s thermal properties, potentially affecting its suitability for applications that require thermal durability. This finding exhibits that even slight doping of Mo4+ into BaO can significantly impact their structural, thermal, optical, and electrical characteristics. It enriches the existing body of knowledge of BaO nanoparticles and lays the foundation for its future research.

Raman Spectra of Electrified Si-Water Interfaces: First-Principles Simulations.

We investigate the Raman spectra of liquid water in contact with a semiconductor surface using first-principles molecular dynamics simulations. We focus on a hydrogenated silicon-water interface and compute the Raman spectra from time correlation functions of the polarizability. We establish a relationship between Raman spectral signatures and structural properties of the liquid at the interface, and we identify the vibrational impacts of an applied electric field. We show that negative bias leads to a reduction of the number of hydrogen bonds (HBs) formed between the surface and the topmost water layer and an enhancement of the HB interactions between water molecules. Instead, positive bias leads to an enhancement of both the HB interactions between water and the surface and between water molecules, creating a semi-ordered interfacial layer. Our work provides molecular-level insights into electrified semiconductor/water interfaces and the identification of specific structural features through Raman spectroscopy.

Tunning carrier concentration and Fermi-level in substrate-supported graphene monolayers: Effect of laser power

Tunning the carrier concentration n and the position of Fermi-level EF in graphene monolayers has a great impact on the design and fabrication of next generation graphene-based devices. Raman spectral properties of graphene/SiO2/Si and graphene/Al2O3 are investigated over a wide range of laser power (PL= 1 to 25 mW). The increase in PL results in significant variations in position and half-width of the G-band, allowing the determination of n and EF using nonadiabatic fitting. The initially formed p-type graphene is converted to n-type with increasing PL due to charge transfer to/from graphene with the substrate interfacial defect states and/or redox interactions with environmental gas. Whereas n and EF of the graphene/SiO2/Si reach saturation at PL=12mW, those of graphene/Al2O3 exhibit a monotonic increase before saturating at PL>21mW. A noticeable enhancement in graphene quality concurrent with a decrease in defect density is observed at PL>17 mW and >20 mW for graphene/Al2O3 and graphene/SiO2/Si, respectively, which are attributed to thermal laser effects at high PL. This work provides a contactless easy approach to monitor EF and tune the doping state of graphene against unintentional environment or substrate doping and gives an insight to the significant role played by the supported substrate.

Non-linear pH responses of passivated graphene-based field-effect transistors

Graphene-based field-effect transistors (FETs) are suitable for pH sensors due to their outstanding surface chemical properties and its biocompatibility. To improve the devices' stability and pH sensitivity, different sets of dielectric passivation layers composed of monolayer hexagonal boron nitride with and without aluminum oxide layers were evaluated. Non-linearities of the pH response were observed. Heterostructure FETs were derived from subtractive manufacturing of commercially transferred two-dimensional materials on four-inch SiO2/Si wafers via stainless steel and polypropylene masking. Phosphate solutions (10 mM) of varying pH were incubated on bare devices, whereby liquid-gating elucidated linear changes in the Dirac voltage of hBN/graphene (−40 mV/pH) that was smaller than a device consisting only of monolayer graphene (−47 mV/pH). Graphene-based FETs were passivated with aluminum oxide nanofilms via electron beam or atomic layer deposition and were observed to have distinct Raman spectral properties and atomic force microscopy topologies corroborating the hypothesis that morphological differences of the deposited aluminum oxide influence the pH-dependent electrical properties. Atomic layer deposition of aluminum oxide on the 2D sensing areas resulted in non-linear shifting of the Dirac voltage with respect to pH that evolved as a function of deposition thickness and was distinct between graphene with and without hexagonal boron nitride as a capping monolayer. The non-linear response of varying thickness of AlxOy on graphene-based FETs was progressively reduced upon basic wet etching of the AlxOy. Overall, passivated graphene-based transistors exhibit deposition-dependent pH responses.

Thermal evolution of graptolite and solid bitumen properties at high maturity under natural and artificial conditions

To refine the use of graptolite and solid bitumen as thermal proxies at overmature conditions, we evaluated their evolution via Raman and infrared (IR) spectroscopies, reflectance, and geochemical screening using high-temperature pyrolysis experiments in comparison to naturally matured samples. Naturally matured samples included marine shales from the overmature Upper Ordovician Wufeng-Lower Silurian Longmaxi Formations (herein referred to as Wufeng-Longmaxi) of the Sichuan Basin, China. Immature samples for pyrolysis experiments included Mesoproterozoic (Ectasian) Xiamaling marine shale from Hebei, China (graptolite absent) and graptolite-bearing Ordovician (Tremadocian) Alum marine shale from Grönhögen, Sweden. Pyrolysis experiments at 360 °C for 10 days and 27 days (hydrous conditions), and 450 °C 3 days, 550 °C 3 days, and 550 °C 10 days (all anhydrous) created Xiamaling and Alum residues with solid bitumen and graptolite, respectively, of similar and higher maturity compared to the naturally matured Wufeng-Longmaxi samples. Compositional proxies from IR spectroscopy were inconclusive. Raman spectral properties including Raman band separation (RBS) and the full-width at half-maximum of the G-band (G-FWHM) exhibited robust positive and inverse relationships with increasing reflectance in pyrolysis residues, respectively. RBS values were systematically lower in artificially matured samples versus naturally matured samples with equivalent reflectance values, whereas G-FWHM values were systematically higher. This observation indicates that the limited duration or low internal reactor pressure of pyrolysis experiments is insufficient to allow alignment or ordering of aromatic carbon arrays in both organic matter types, relative to natural maturation occurring at geologic time scales. Reflectance of graptolite was typically higher than co-occurring solid bitumen in Wufeng-Longmaxi samples and the untreated Alum sample, suggesting inherently higher aromaticity. However, aromaticity in pyrolysis residues was systematically higher in solid bitumen compared to graptolite with equivalent reflectance values, indicating a higher kinetic barrier to molecular rearrangement in graptolite versus solid bitumen. These data further clarify differences in the molecular evolution of sedimentary organic matter in natural versus analogue laboratory environments and distinguish the properties of individual organic matter types in response to thermal stress.

Human Basal and Suprabasal Keratinocytes Are Both Able to Generate and Maintain Dermo-Epidermal Skin Substitutes in Long-Term In Vivo Experiments.

The basal layer of human interfollicular epidermis has been described to harbour both quiescent keratinocyte stem cells and a transit amplifying cell population that maintains the suprabasal epidermal layers. We performed immunofluorescence analyses and revealed that the main proliferative keratinocyte pool in vivo resides suprabasally. We isolated from the human epidermis two distinct cell populations, the basal and the suprabasal keratinocytes, according to the expression of integrin β4 (iβ4). We compared basal iβ4+ or suprabasal iβ4− keratinocytes with respect to their proliferation and colony-forming ability and their Raman spectral properties. In addition, we generated dermo–epidermal substitutes using freshly isolated and sorted basal iβ4+ or suprabasal iβ4− keratinocytes and transplanted them on immuno-compromised rats. We show that suprabasal iβ4− keratinocytes acquire a similar proliferative capacity as basal iβ4+ keratinocytes after two weeks of culture in vitro, with expression of high levels of iβ4 and downregulation of K10 expression. In addition, both basal iβ4+ and suprabasal iβ4− keratinocytes acquire authentic self-renewing properties during the in vitro 3D-culture phase and are able to generate and maintain a fully stratified epidermis for 16 weeks in vivo. Therefore, against the leading dogma, we propose that human suprabasal keratinocytes can retro-differentiate into true basal stem cells in a wound situation and/or when in contact with the basement membrane.

Theoretical insights into interaction energy, IR intensity and Raman activity enhancements of H2O adsorbed on Mg containing Zn3O3 nanoclusters: A computational study

Theoretical insights into H2O detection ability of Zn3O3 and Mg containing Zn3O3 nanoclusters are provided using density functional theory (DFT) based calculations. For this, the IR and Raman spectral properties of H2O adsorbed on Zn3O3, Zn2MgO3 (Mg as substituent) and Zn3O3Mg (Mg as interstitial atom) nanoclusters are investigated. All the species in study are optimized at B3LYP/6-31G(d,p) computational model. While Zn site of Zn3O3 is favorable for interaction of the water molecule, the site of Mg in both the Zn2MgO3 and Zn3O3Mg is preferential for interaction of H2O molecule. The complex geometry formed by H2O interacting with Mg site of Zn2MgO3 shows highest interaction energy and significant magnitudes of molecular orbital interactions. The IR intensity calculations on the stable geometries show that the symmetric mode of vibration of water molecule enhances significantly, and the predicted IR enhancement agrees with an experimental finding. The Raman activity enhancement for the symmetric vibrational mode of H2O is notable, when H2O interacts with Zn3O3Mg at Mg site. The observed IR and Raman enhancements are substantiated by the calculations on dipole moment and polarizability components of the complex geometries distorted along normal coordinates of H2O vibrational modes. The time dependent (TD) DFT calculations carried out at B3LYP/6-31G(d,p) computational model, envisages that Zn3O3Mg is a good SERS substrate for amplification of Raman spectral lines of H2O by surface plasmon resonance.

Raman spectral probed electron–phonon coupling and phonon lifetime properties of Ni-doped CuO nanoparticles

In the present report, optical and Raman spectral properties were extensively studied. Ni-doped CuO nanoparticles were prepared using the sol–gel method. X-ray diffraction patterns confirm that the prepared particles have the space group of C2h6 with monoclinic structure. Optical studies show that there is a broad absorption spectrum in the whole visible regime due to surface plasmon oscillations (SPR). Raman spectral measurements taken using 532 nm excitation found that three Raman peaks centred at 276 cm−1 (Ag), 330 cm−1 (Bg) and 616 cm−1 (Bg), respectively. Doping of Ni ions shows a redshift in Raman peak position. In the present work, the influence of Ni doping on electron–phonon coupling and phonon lifetimes has been studied extensively.

The effect of silicon doping on the geometrical structures, stability, and electronic and spectral properties of magnesium clusters: DFT study of SiMgn (n = 1‐12) clusters

AbstractUsing the density functional theory (DFT) method at the B3LYP /6−311G (D) level, we studied how silicon doping affects the geometrical structure, stability, and electronic and spectral properties of magnesium clusters. The stable isomers of SiMg n (n = 1‐12) clusters were calculated by searching numerous initial configurations using the CALYPSO program. The geometrical structure optimization shows that most stable SiMg n (n = 3‐12) clusters are three‐dimensional. In addition, geometrical structure growth patterns show that some structures of SiMg n clusters can be directly formed by replacing one Mg atom in the corresponding Mg n + 1 cluster with one silicon atom, such as SiMg8 and Mg9 clusters. The stability of SiMg n clusters is analyzed by calculating the average binding energy, fragmentation energy, and second‐order energy difference. The results show that SiMg n clusters with n = 5 and 8 are more stable than others. MO contents analysis show that the Si 3p‐orbitals and Mg 3s‐orbital are mainly responsible for the stability of these two clusters. The results of the natural charge population (NCP) and natural electronic configure (NEC) analysis of the electronic properties reveal that the charges in SiMgn (n = 1‐12) clusters transfer from magnesium atoms to silicon frame, and electronic charge distributions are primarily governed by s‐ and p‐orbital interactions. In addition, the Vertical ionization potential (VIP), vertical electron affinity (VEA), and chemical hardness of ground sates of SiMg n (n = 1‐12) clusters were studied in detail and compared with the experimental results. The conclusions show that the chemical hardness of most SiMg n clusters are lower than that of pure Mg n + 1 (n = 1‐12) clusters, except for n = 1 and 8. This indicates that the doping of silicon atom can always reduce the chemical hardness of pure magnesium clusters. Finally, the infrared and Raman spectral properties of SiMg5 and SiMg8 clusters were calculated and discussed in detail.

In vivo detection of changes in cutaneous carotenoids after chemotherapy using shifted excitation resonance Raman difference and fluorescence spectroscopy.

Various cutaneous toxicities under chemotherapy indicate a local effect of chemotherapy by secretion after systemic application. Here, changes in the fluorescence and Raman spectral properties of the stratum corneum subsequent to intravenous chemotherapy were assessed. Twenty healthy subjects and 20 cancer patients undergoing chemotherapy were included. Measurement time points in cancer patients were before the first cycle of chemotherapy (Tbase ) and immediately after intravenous application of the chemotherapy (T1 ). Healthy subjects were measured once without any further intervention. Measurements were conducted using an individually manufactured system consisting of a handheld probe and a wavelength-tunable diode laser-based 488nm SHG light source. Hereby, changes in both skin fluorescence and shifted excitation resonance Raman difference spectroscopy (SERRDS) carotenoid signals were assessed. Healthy subjects showed significantly (P<.001) higher mean concentrations of carotenoids compared to cancer subjects at Tbase . An increase in fluorescence intensity was detected in almost all patients after chemotherapy, especially after doxorubicin infusion. Furthermore, a decrease in the carotenoid concentration in the skin after chemotherapy was found. The SERRDS based noninvasive detection can be used as an indirect quantitative assessment of fluorescent chemotherapeutics. The lower carotenoid SERRDS intensities at Tbase might be due to cancerous diseases and co-medication.

Shift in the Raman symmetric stretching band of N2, CO2, and CH4 as a function of temperature, pressure, and density

AbstractThe Raman spectra of pure N2, CO2, and CH4 were analyzed over the range 10 to 500 bars and from −160°C to 200°C (N2), 22°C to 350°C (CO2), and −100°C to 450°C (CH4). At constant temperature, Raman peak position, including the more intense CO2 peak (ν+), decreases (shifts to lower wave number) with increasing pressure for all three gases over the entire pressure and temperature (PT) range studied. At constant pressure, the peak position for CO2 and CH4 increases (shifts to higher wave number) with increasing temperature over the entire PT range studied. In contrast, N2 first shows an increase in peak position with increasing temperature at constant pressure, followed by a decrease in peak position with increasing temperature. The inflection temperature at which the trend reverses for N2 is located between 0°C and 50°C at pressures above ~50 bars and is pressure dependent. Below ~50 bars, the inflection temperature was observed as low as −120°C. The shifts in Raman peak positions with PT are related to relative density changes, which reflect changes in intermolecular attraction and repulsion. A conceptual model relating the Raman spectral properties of N2, CO2, and CH4 to relative density (volume) changes and attractive and repulsive forces is presented here. Additionally, reduced temperature‐dependent densimeters and barometers are presented for each pure component over the respective PT ranges. The Raman spectral behavior of the pure gases as a function of temperature and pressure is assessed to provide a framework for understanding the behavior of each component in multicomponent N2‐CO2‐CH4 gas systems in a future study.

An efficient method for extracting microplastics from feces of different species

Concerns have been raised regarding the ingestion of microplastics (MPs) by numerous organisms including humans. However, no efficient and standardized methods are available for extracting MPs from feces. In this study, we introduce a novel approach with high digestion efficiency that involves using Fenton’s reagent and nitric acid to remove feces solids. Firstly, Fenton’s reagent was used to degrade small solids and decompose large solids into small pieces. Secondly, nitric acid was used to digest the remaining solids and filters. Furthermore, absolute ethyl alcohol was used to remove the mineral residues wrapped on the plastic surfaces and disperse MPs. By using this method, 97.78 % MPs can be recovered from human and chicken feces, and no significant changes were observed in the physical and Raman spectral properties of different polymer types of MPs. This method has also been verified by extracting MPs from field feces. Overall, the proposed method can efficiently digest feces solids and extract MPs with higher recovery rate, less intermediate steps and less damage, which can serve as an economical and feasible method for the detection of MPs in the feces of different species.

Indigo chromophores and pigments: Structure and dynamics

In this study, we explore the molecular mechanisms of the stability of indigo chromophores and pigments. Assisted with density functional theory, we compare visible, infrared and Raman spectral properties of model molecules, chromophores and pigments derived from living organisms. Using indigo carmine as a representative model system, we characterize the structure and dynamics of the chromophore in the first electronic excited state using femtosecond visible pump-infrared probe spectroscopy. Results of experiments and theoretical studies indicate that, while the trans geometry is strongly dominant in the electronic ground state, upon photoexcitation, in the Franck-Condon region, some molecules may experience isomerization and proton transfer dynamics. If this happens, however, the normal modes of the trans geometry of the electronic excited state are reconfirmed within several hundred femtoseconds. Supported by quantum theory, first, we ascribe stabilization of the trans geometry in the Franck-Condon region to the reactive character of the potential energy surface for the indigo chromophore when under the cis geometry in the electronic excited state. Second, we suggest that a conical intersection crossing, due to the high barrier along the isomerization pathway in the ground state, would provide for the effective relaxation and observed dominance of the trans geometry of the chromophore in the ground state. Planarity of the chromophore under the trans geometry assists effective dissipation of energy via a cascade of in-plane C-C, C-O⋯H-N stretchings and C-C-C bending modes delocalized over the molecular mainframe. The described mechanisms help to explain the remarkable photo-stability of indigo chromophores.

Quantitative evaluation of vitrinite reflectance and atomic O/C in coal using Raman spectroscopy and multivariate analysis

Vitrinite reflectance (VRo) is a standard petrographic method for assessing thermal maturity (rank) of coal. The vitrinite reflectance technique, however, requires significant petrographic experience, can be time-consuming, and may be biased by analyst subjectivity. Correlations between coal rank and Raman spectral properties are a promising alternative that can supplant some of the limitations inherent in the VRo protocol. The traditional peak-fitting methodologies for quantifying metrics from Raman spectra, however, also suffer from analyst subjectivity that can affect correlations between analyte and spectral properties.This research combines high-throughput Raman spectroscopy with multivariate analysis (MVA) to create calibration models for the prediction of coal rank though VRo and atomic O/C ratio. MVA techniques eliminate the ambiguous subjectivity prevalent in peak-fitting methods by evaluating the full Raman spectrum, then identifying the integral vibrational modes for constructing accurate models. Partial least squares (PLS) regression models were developed using Raman spectra and VRo values (0.23–5.23%) for 68 geographically diverse coal samples. The calibration set was validated using one-half of the samples to rigorously assess the model’s predictive accuracy. The root mean standard error of prediction was 0.19 for the VRo model and 0.014 for the atomic O/C model. Both models exhibited linear correlations, with coefficients of determination (R2) for the validation set of 0.99 (VRo) and 0.93 (atomic O/C), despite the geographic and rank diversity of the samples. This study demonstrates the applicability and power of using PLS models for the prediction of both the VRo and atomic O/C ratio from Raman spectra. The quantitative MVA protocol contained herein provides a Raman alternative to the VRo industry benchmark for coal rank that is not subject to the limitations and subjectivity of peak-fitting methods.

Experimental study and Ab-initio calculations on the molecular structure, infrared and Raman spectral properties of dinitroimidazoles

Abstract The structural and vibrational properties of 1,4-dinitroimidazole, 2,4-dinitroimidazole and 1-methyl-2,4-dinitroimidazole have been explored both experimentally and theoretically. The N1-N6, C2-NO 2 , C4-NO 2 , N1-CH 3 lengths were found to be varied with the levels of theory and the calculated values were over estimated compared with those of experimental values. The experimental vibrational frequencies were compared with those values calculated at the HF/6–311 ++G(d,p), B3P86/6–311 ++G(d,p), B3LYP/6–311 ++G(d,p) and B3LYP/aug-cc-pVDZ levels. The calculated frequencies were in good agreement with the experimental values and the relative mean deviations between the measured and calculated vibrational frequencies were smaller than 1% for all molecules. The discrepancies in the bond lengths bond angles and harmonic frequencies are confined to the relative positions of NO 2 groups that present a great deviation from the planarity of the molecule. Nevertheless the structural parameters and harmonic vibrational frequencies of nitroimidazoles calculated at the B3LYP/aug-cc-pVDZ level are superior compared with those values computed from other levels of calculation.

Raman spectroscopy and TEM characterization of solid particulate matter emitted from soot generators and aircraft turbine engines

To obtain reliable mass concentrations of solid particulate matter (PM) in the exhaust emissions from engines using optical instruments, it is essential that the solid PM used for instrument calibration has similar optical properties to the solid PM emitted from the engines being tested. The solid PM emitted from combustion engines is predominantly soot. The optical properties of soot are dictated by its chemical structure, size, and morphology. In this work, the chemical bond structure, primary-particle diameters, aggregate sizes, and morphological parameters of the soot emitted from two laboratory soot generators, widely used for calibrating instruments, are compared to those of soot emitted from three aircraft turbine engines using Raman spectroscopy and transmission electron microscopy. The Raman spectral properties, size, and morphology of soot emitted from aircraft engines are distinctly different from the properties of soot emitted from the soot generators operating under globally near-stoichiometric and fuel-rich conditions. These differences can be attributed to the variations in the size and orientation of the graphitic crystallites, amorphous-carbon content, amount of polyacetylene compounds, deposition of organic material, and extent of oxidation. Conversely, general agreement is observed between the chemical structure, size, and morphology of soot emitted from aircraft engines and the soot emitted from the soot generators operating at globally fuel-lean conditions. The findings of this investigation can be useful for identifying suitable soot particles for the calibration of instruments to measure the mass concentration of solid PM emissions from engines, and for other types of soot.Copyright © 2017 Crown Copyright

Raman characterization of synthetic magnesian calcites

Magnesian calcites are important components of sediments and biominerals. Although Raman spectra of calcite, dolomite, and magnesite are well known, those of magnesian calcites deserve further investigation. Nineteen syntheses of magnesian calcites covering the range 0–50 mol% MgCO_3 have been carried out at high pressure and temperature (1–1.5 GPa, 1000–1100 °C). The crystalline run products have been characterized by μ-Raman spectroscopy. For all lattice and internal modes (L, T, ν_1, ν_4, 2ν_2) but ν_3, wavenumbers align closer to the calcite– dolomite line than the calcite–magnesite line. The compositional dependence is strong and regression curves with high correlation coefficients have been determined. Full-width at half maximum (FWHM) plot along parabolas that depart from the calcite–dolomite or calcite–magnesite lines. The limited data dispersion of both shifts and FWHM allow using Raman spectral properties of magnesian calcites to determine the Mg content of abiotic calcites. A comparison with Raman data from the literature obtained on synthetic magnesian amorphous calcium carbonate (Mg ACC) shows that the wavenumber position of the ACC ν1 mode is systematically shifted toward lower values, and that their FWHM are higher than those of their crystalline counterparts. The FWHM parameters of crystalline and amorphous materials do not overlap, which allows a clear-cut distinction between crystalline and amorphous materials. In synthetic magnesian calcites, the shift and FWHM of Raman bands as a function of magnesium can be interpreted in terms of changes of metal-O bond lengths resulting from the replacement of calcium by magnesium. The facts that the wavenumber of magnesian calcites are close to the calcite–dolomite line (not calcite-magnesite), that the FWHM of the T, L, and ν4 modes reach a maximum around 30 ±5 mol% MgCO_3, and that a peak specific to dolomite at 880 cm^(−1) is observed in high-magnesian calcites indicate that dolomite-like ordering is present abov ~10 mol% MgCO_3. Mg atom clustering in cation layers combined with ordering in successive cation basal layers may account for the progressive ordering observed in synthetic magnesian calcites.

Highly sensitive visible to infrared MoTe2 photodetectors enhanced by the photogating effect

Two-dimensional materials are promising candidates for electronic and optoelectronic applications. MoTe2 has an appropriate bandgap for both visible and infrared light photodetection. Here we fabricate a high-performance photodetector based on few-layer MoTe2. Raman spectral properties have been studied for different thicknesses of MoTe2. The photodetector based on few-layer MoTe2 exhibits broad spectral range photodetection (0.6–1.55 μm) and a stable and fast photoresponse. The detectivity is calculated to be 3.1 × 109 cm Hz1/2 W−1 for 637 nm light and 1.3 × 109 cm Hz1/2 W−1 for 1060 nm light at a backgate voltage of 10 V. The mechanisms of photocurrent generation have been analyzed in detail, and it is considered that a photogating effect plays an important role in photodetection. The appreciable performance and detection over a broad spectral range make it a promising material for high-performance photodetectors.

Microscale organic maturity determination of graptolites using Raman spectroscopy

Organic maturity is a key property for assessment of hydrocarbon potential and generation of black shales. Early Paleozoic strata are usually void of terrestrial organic matter such as vitrinite, thus evading conventional, reflectance based maturity analysis. To overcome this, graptolites in samples from the basal hot shales of the Silurian Qusaiba Formation, with known, reflectance based vitrinite equivalent maturities from 0.54 to 1.76 VRE%, were analyzed with Raman spectroscopy to establish a spectroscopic maturity scale. All samples provided spectra showing the Disorder (D) peak and the Graphite (G) peak typical for organic carbons. Systematic variation of these peaks with sample maturity is used to quantify the relationship of reflectance with the graptolites molecular condition. Several spectral properties were tested for use as maturity indicators. The most reliable maturity tracers are the variation of position of the G peak between 1570 and 1610cm−1 and the widening band distance (Δ(G-D)) between the G peak and D peak position at 1320 to 1370cm−1. Comparison of the mean and modal maxima of peak positions showed that the mean of G peak position and Δ(G-D) provide the best fit of Raman and optical reflectance determinations with R2 of 0.884 and 0.935, respectively. Algorithms for the calculation of vitrinite equivalent reflectance from the Raman spectral properties were developed based on best fit exponential regressions, with a linear cross correlation of the measured and calculated values at R2=0.9178 for the mean of Δ(G-D). Raman based maturity measurements on graptolites provide a welcome alternative method for on particles as small as 3μm diameter.

Deep-UV Resonance Raman Spectral Properties of Membrane Proteins

Deep-UV resonance Raman (λex < 210 nm) spectroscopy has proven a valuable tool for assessing secondary structure content in globular proteins. Recent studies have shown that predominantly α-helical transmembrane proteins have a much stronger amide I feature, when compared to their globular counterparts due to desolvation of the peptide backbone. Although β-sheet transmembrane proteins are less common, β-barrel proteins are a major class of membrane proteins. Comparison of the amide I band of the globular protein Aurocyanin and the membrane protein OmpA, show a modest increase in the intensity of this feature. Although, it appears that the mode remains solvent sensitive, the β-barrel structure may result in greater exposere of the protein backbone to solvent versus multi-helix bundles. Aromatic amino acids, phenylalanine and tyrosine also have strong features in the deep-UVRR spectra of proteins. Using a model leucine-alanine peptide with either a single tyrosine or phenylalanine residue, we investigated the effect of the membrane environment on the deep-UVRR spectral features of these amino acids. As expected, the intensity of the aromatic features increased in lipid and surfactant environments with respect to aqueous environments. Additionally, the 7a’ band (C-O str), which typically has two features at ∼1235 (proton-accepting) and ∼1265 cm-1 (weakly or non-hydrogen bonded), exhibited only the higher feature in DLPG liposomes. A small increase in the intensity at ∼1235 cm-1 was observed in DDM micelles, indicating that the peptide is more solvent exposed in the surfactant environment.