Probing Single and Bilayer Graphene Field Effect Transistors By Raman Spectroscopy

This article is a review of our work related to Raman studies of single layer and bilayer graphenes as a function Fermi level shift achieved by electrochemically top gating a field effect transistor. Combining the transport and in situ Raman studies of the field effect devices, a quantitative understanding is obtained of the phonon renormalization due to doping of graphene. Results are discussed in the light of time dependent perturbation theory, with electron phonon coupling parameter as an input from the density functional theory. It is seen that phonons near and Gamma and K points of the Brillouin zone are renormalized very differently by doping. Further, Gamma-phonon renormalization is different in bilayer graphene as compared to single layer, originating from their different electronic band structures near the zone boundary K-point. Thus Raman spectroscopy is not only a powerful probe to characterize the number of layers and their quality in a graphene sample, but also to quantitatively evaluate electron phonon coupling required to understand the performance of graphene devices.

Sensitivity map of laser tweezers Raman spectroscopy for single-cell analysis of colorectal cancer

Raman spectroscopy on single, living epithelial cells captured in a laser trap is shown to have diagnostic power over colorectal cancer. This new single-cell technology comprises three major components: primary culture processing of human tissue samples to produce single-cell suspensions, Raman detection on singly trapped cells, and diagnoses of the cells by artificial neural network classifications. it is compared with DNA flow cytometry for similarities and differences. Its advantages over tissue Raman spectroscopy are also discussed. In the actual construction of a diagnostic model for colorectal cancer, real patient data were taken to generate a training set of 320 Raman spectra and, a test set of 80. By incorporating outlier corrections to a conventional binary neural classifier, our network accomplished significantly better predictions than logistic regressions, with sensitivity improved from 77.5% to 86.3% and specificity improved from 81.3% to 86.3% for the training set and moderate improvements for the test set. Most important, the network approach enables a sensitivity map analysis to quantitate the relevance of each Raman band to the normal-to-cancer transform at the cell level. Our technique has direct clinic applications for diagnosing cancers and basic science potential in the study of cell dynamics of carcinogenesis. (C) 2007 Society of Photo-Optical Instrumentation Engineers.

Study of the effect of alcohol on single human red blood cells using near-infrared laser tweezers Raman spectroscopy

The effect of alcohol solution on single human red blood Cells (RBCs) was investigated using near-infrared laser tweezers Raman spectroscopy (LTRS). In our system, a low-power diode laser at 785 nm was applied for the trapping of a living cell and the excitation of its Raman spectrum. Such a design could simultaneously reduce the photo-damage to the cell and suppress the interference from the fluorescence on the Raman signal. The denaturation process of single RBCs in 20% alcohol solution was investigated by detecting the time evolution of the Raman spectra at the single-cell level. The vitality of RBCs was characterized by the Raman band at 752 cm(-1), which corresponds to the porphyrin breathing mode. We found that the intensity of this band decreased by 34.1% over a period of 25 min after the administration of alcohol. In a further study of the dependence of denaturation on alcohol concentration, we discovered that the decrease in the intensity of the 752 cm(-1) band became more rapid and more prominent as the alcohol concentration increased. The present LTRS technique may have several potential applications in cell biology and medicine, including probing dynamic cellular processes at the single cell level and diagnosing cell disorders in real time. Copyright (c) 2005 John Wiley T Sons, Ltd.

Diagnosis of colorectal cancer using Raman spectroscopy of laser-trapped single living epithelial cells

A single-cell diagnostic technique for epithelial cancers is developed by utilizing laser trapping and Raman spectroscopy to differentiate cancerous and normal epithelial cells. Single-cell suspensions were prepared from surgically removed human colorectal tissues following standard primary culture protocols and examined in a near-infrared laser-trapping Raman spectroscopy system, where living epithelial cells were investigated one by one. A diagnostic model was built on the spectral data obtained from 8 patients and validated by the data from 2 new patients. Our technique has potential applications from epithelial cancer diagnosis to the study of cell dynamics of carcinogenesis. (c) 2006 Optical Society of America.

Sensitivity map of laser tweezers Raman spectroscopy for single-cell analysis of colorectal cancer

Raman spectroscopy on single, living epithelial cells captured in a laser trap is shown to have diagnostic power over colorectal cancer. This new single-cell technology comprises three major components: primary culture processing of human tissue samples to produce single-cell suspensions, Raman detection on singly trapped cells, and diagnoses of the cells by artificial neural network classifications. it is compared with DNA flow cytometry for similarities and differences. Its advantages over tissue Raman spectroscopy are also discussed. In the actual construction of a diagnostic model for colorectal cancer, real patient data were taken to generate a training set of 320 Raman spectra and, a test set of 80. By incorporating outlier corrections to a conventional binary neural classifier, our network accomplished significantly better predictions than logistic regressions, with sensitivity improved from 77.5% to 86.3% and specificity improved from 81.3% to 86.3% for the training set and moderate improvements for the test set. Most important, the network approach enables a sensitivity map analysis to quantitate the relevance of each Raman band to the normal-to-cancer transform at the cell level. Our technique has direct clinic applications for diagnosing cancers and basic science potential in the study of cell dynamics of carcinogenesis. (C) 2007 Society of Photo-Optical Instrumentation Engineers.

Optical spectroscopy of Yb3Al5O12 single crystal

Yb3Al5O12 single crystal has been grown by Czochralski (CZ) method. The absorption spectrum was investigated at low temperature and the electronic energy levels for F-2(5/2) multiplet of Yb3+ in YbAG was proposed. The up-conversion emission of the crystal under 940 nm diode pumping and the X-ray excited luminescence (XEL) features of the crystal were also studied. (c) 2005 Elsevier B.V. All rights reserved.

Investigation of native defects and property of bulk ZnO single crystal grown by a closed chemical vapor transport method

Hall effect, Raman scattering, photoluminescence spectroscopy (PL), optical absorption (OA), mass spectroscopy, and X-ray diffraction have been used to study bulk ZnO single crystal grown by a closed chemical vapor transport method. The results indicate that shallow donor impurities (Ga and Al) are the dominant native defects responsible for n-type conduction of the ZnO single crystal. PL and OA results suggest that the as-grown and annealed ZnO samples with poor lattice perfection exhibit strong deep level green photoluminescence and weak ultraviolet luminescence. The deep level defect in as-grown ZnO is identified to be oxygen vacancy. After high-temperature annealing, the deep level photoluminescence is suppressed in ZnO crystal with good lattice perfection. In contrast, the photoluminescence is nearly unchanged or even enhanced in ZnO crystal with grain boundary or mosaic structure. This result indicates that a trapping effect of the defect exists at the grain boundary in ZnO single crystal. (C) 2007 Elsevier B.V. All rights reserved.

Surface-enhanced resonant Raman spectroscopy (SERRS) of single-walled carbon nanotubes absorbed on the Ag-coated anodic aluminum oxide (AAO) surface

In this paper, we developed a new kind of substrate, the silver-coated anodic aluminum oxide (AAO), to investigate the characters of surface-enhanced resonant Raman scattering (SERRS) of the dilute single-walled carbon nanotubes. Homogeneous Ag-coated AAO substrate was obtained by decomposing the AgNO3 on the surface of AAO. single-walled carbon nanotubes (SWNTs) were directly grown onto this substrate through floating catalyst chemical vapor deposition method (CVD). SERRS of SWNTs was carried out using several different wavelength lasers. The bands coming from metallic SWNTs were significantly enhanced. The two SERRS mechanisms, the "electromagnetic" and "chemical" mechanism, were mainly responsible for the experiment results. (c) 2005 Elsevier B.V. All rights reserved.

Native deep level defects in ZnO single crystal grown by CVT method - art. no. 68410I

Hall effect, photoluminescence (PL), infrared absorption, deep level transient spectroscopy (DLTS), and Raman scattering have been used to study property and defects of ZnO single crystal grown by a chemical vapor transport method (CVT). As-grown ZnO is N type with free electron density Of 10(16)-10(17)cm(-3). It has a slight increase after 900 degrees C annealing in oxygen ambient. The DLTS measurement revealed four deep level defects with energy at 0.30eV, 0.50eV, 0.68eV and 0.90eV in the as-grown ZnO sample, respectively. After the high temperature annealing, only the 0.5eV defect survive and has a concentration increase. PL results of the as-grown and annealed ZnO indicate that the well-known green emission disappear after the annealing. The result suggests a correlation between the 0.68eV defect and the green PL peak. Results of P-doped ZnO were also compared with the undoped ZnO sample. The nature of the defects and their influence on the material property have been discussed.

Luminescence spectroscopy of ion implanted AlN bulk single crystal

High concentrations of Si and Zn were implanted into (0001) AlN bulk crystal grown by the self-seeded physical vapor transport (PVT) method. Cathode luminescence (CL) and photoluminescence (PL) spectroscopy were used to investigate the defects and properties of the implanted AlN. PL spectra of the implanted AlN are dominated by a broad near-band luminescence peak between 200 and 254 nm. After high temperature annealing, implantation induced lattice damages are recovered and the PL intensity increases significantly, suggesting that the implanted impurity Si and Zn occupy lattice site of Al. CL results imply that a 457 nm peak is Al vacancy related. Resistance of the AlN samples is still very high after annealing, indicating a low electrical activation efficiency of the impurity in AlN single crystal.

Morphology-controllable synthesis and characterization of single-crystal molybdenum trioxide

Molybdenum trioxide nanobelts and prism-like particles with good crystallinity and high surface areas have been prepared by a facile hydrothermal method, and the morphology could be controlled by using different inorganic salts, such as KNO3, Ca(NO3)(2), La(NO3)(3), etc. The possible growth mechanism of molybdenum trioxide prism-like particles is discussed on the basis of the presence of HI and the modification of metal cations. The as-prepared nanomaterials are characterized by means of powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and ultraviolet and visible spectroscopy (UV-vis). TEM and HRTEM micrographs show that the molybdenum trioxide nanobelts and prism-like particles have a relatively high degree of crystallinity and uniformity. BET specific surface areas of the as-prepared molybdenum trioxide nanocrystals are 67-79 m(2)g(-1). XPS analysis indicates that the hexavalent molybdenum is predominant in the nanocrystals. UV-vis spectra reveal that the direct band gap energy of the annealed molybdenum trioxide prism-like particles shows a pronounced blue shift compared to that of bulk MoO3 powder.

Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di-amino acid peptide cyclo(L-Glu-L-Glu)

Cyclo(L-Glu-L-Glu) has been crystallised in two different polymorphic forms. Both polymorphs are monoclinic, but form 1 is in space group P21 and form 2 is in space group C2. Raman scattering and FT-IR spectroscopic studies have been conducted for the N,O-protonated and deuterated derivatives. Raman spectra of orientated single crystals, solid-state and aqueous solution samples have also been recorded. The different hydrogen-bonding patterns for the two polymorphs have the greatest effect on vibrational modes with N&bond;H and C&dbond;O stretching character. DFT (B3-LYP/cc-pVDZ) calculations of the isolated cyclo(L-Glu-L-Glu) molecule predict that the minimum energy structure, assuming C2 symmetry, has a boat conformation for the diketopiperazine ring with the two L-Glu side chains being folded above the ring. The calculated geometry is in good agreement with the X-ray crystallographic structures for both polymorphs. Normal coordinate analysis has facilitated the band assignments for the experimental vibrational spectra. Copyright © 2009 John Wiley & Sons, Ltd.

Label-Free Detection of Single-Base Mismatches in DNA by Surface-Enhanced Raman Spectroscopy

Singles only: DNA sequences can be induced to spontaneously adsorb to the surfaces of Ag colloids through their nucleotide side chains (see picture). The SERS spectra of these nonspecifically bound strands are sufficiently reproducible that they can be used to identify single-base mismatches in short (25-mer and 23-mer) strands. Subtracting the spectra of different DNA sequences results in difference spectra that contain features corresponding to the exchanged nucleotides.