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- Semiconductors
- Superconductors
- New Techniques, Instrumentation, and Detectors
- Polymers, Pharmaceuticals, and Biological Molecules
- Pollution and Medical Analytical Instrumentation
- Analytical Applications of Surface-Enhanced Raman Scattering
- Superconductors
Semiconductors
Light scattering from electrons in semiconductor microstructures: two-dimensional electron gas
Show abstract
We present a review of our recent resonant inelastic light scattering research of the ultra-high
mobility two-dimensional electron gas in GaAs quantum wells. Spectroscopy of intersubband
excitations shows that exchange interactions are larger than previously anticipated. Light scattering
by large wavevector inter-Landau-level excitations displays the excitonic binding and roton minima
in the mode dispersions that are predicted by Hartree-Fock theories.
Raman-scattering characterization of atomic layer semiconductor superlattices
Show abstract
Raman spectroscopy is a widely applied technique for investigating the dynamical and structural properties of atomic-layer
semiconductor superlawces. The low-frequency acoustic phonons in such structures are influenced by the average lattice
properties, the overall periodicities within the structure, and the boundary conditions, whereas the optic phonons are sensitive
to the local structure, the nature of the interfaces, and the intralayer strain. Examples taken from recent studies of phonons in
thin layer superlattices composed of GaAS/AlAS, InAs/GaSb and SilGe are used to demonstrate the usefulness of the Raman
technique.
Raman spectroscopy of the II-V vacancy ordered semiconductor Zn3As2
Gerardo I. Pangilinan,
R. Sooryakumar,
Bhanu Chelluri,
et al.
Show abstract
We report evidence of a new long-range order in singleS-crystal
Zn3As2 grown epitaxially on lattice-inisinatched InP and GaAs. The
Raman activity of the layers confirm, in contrast to the bulk C4,'2
syirmietry, a space group of D4h'5 for the epilayers. Thermodynamic
considerations show that the dependence of the free energy on the
lattice parameters of this 11-V compound may be sufficient to
account for the stability of the new structure. Such preferential
stability in these ordered defect, single crystalline materials is
not unlike the occurrence of long range order reported recently in
several III-'V and IV-IV semiconductor alloys grown on bulk
substrates. We identify a process analogous to stress induced Zener
relaxation that could yield the new order.
Advances in semiconductor physics through spectroscopy
Anant K. Ramdas
Show abstract
Spectroscopic techniques have been and continue to be extremely fruitful in discovering arid
delineating novel phenomena exhibited by semiconductors and in characterizing their properties. In
turn, discoveries in semiconductor physics made with spectroscopic techniques have led to some of
the most sensitive infrared detectors and highly monochromatic single frequency as well as tunable
solid state lasers; spectroscopy under high resolution is inconceivable in their absence.
Frequencies of confined longitudinal-optical phonon modes in short-period strained semiconductor superlattices
Show abstract
The theories describing the dispersion of longitudinal-optical (LO) phonon
modes and electron-LO-phonon interactions are generalized to include the effects
of both strain and confinement in semiconductor superlattices and semiconductor
microstructures. In particular, the effects of strain and confinement on LO
phonon frequencies are analyzed for short-period strained-layer superlattices as
well as for semiconductor microstructures where effective force constants are
altered near heterojunction interfaces.
Raman spectroscopy of shallow impurities in semiconductor quantum-well structures
Show abstract
A brief review is given of Raman scattering from bound electrons and holes in semiconductor
superlattices. The experiments on Si (donor)-doped and Be (acceptor)-doped
GaAs/AlGaAs quantum-well structures include studies of the dependence of the energy levels
on the position of the impurity in the well and the well-width, and as a function of temperature,
magnetic field and uniaxial stress. The data, showing reasonable agreement with
theoretical predictions, reveal most of the expected features of quantum confinement effects
on the impurity spectra. An extensive list of references to theoretical and related experimental
work is included.
Superconductors
Raman scattering from spin fluctuations in the cuprates
K. B. Lyons,
Paul A. Fleury,
R. P. Singh,
et al.
Show abstract
Raman scattering experiments on cuprate materials, both insulating and metallic, have provided insights on the
role of magnetic phenomena in the properties of these materials. Light scattering in fact provides the most
convenient measure of the superexchange interaction in the insulating materials, where we find that modification
of existing theories is required to obtain a quantitative description for the spin half case. In the metallic and
superconducting materials we find evidence that short wavelength spin excitations coexist with the
superconducting material.
Superconducting La2CuO4+x prepared by oxygenation at high pressure: a Raman-scattering study
Kevin F. McCarty,
J. E. Schirber,
S.-W. Cheong,
et al.
Show abstract
Superconducting crystals of La2CuO4+ prepared by high-pressure oxygenation have been
analyzed by Ramán spectroscopy. A direct comparison of the role of excess oxygen was made by
examining the same crystals with and without excess oxygen. La2CuO4+, like non-superconducting
La2CuO4.O, is found to have a soft phonon that drives an orthorhombic to tetragonal phase transition.
In both its tetragonal and orthorhombic forms, La2CuO4+ has a phonon peak at 630 cm1 that is
absent in La2CuO4.O. The frequency of this peak is suggestive of a peroxide-like species in
La2CuO4+. Surprisingly, the Ag phonons of La2CuO4.O and La2CuO4+ occur at essentially the
same frequency. While La2CuO4.O has a well-defined peak from double-magnon scattering, no welldefined
double-magnon scattering is observed in La2CuO4+, even in its phase-separated form.
Detailing of the "123" Raman continuum
Francis Slakey,
Miles V. Klein,
D. Reznik,
et al.
Show abstract
Raman investigations on several of the high temperature superconductors have revealed an unusual background
continuum. In the YBa2Cu3O' material ('123'), the continuum can be separated into two unique symmetries each having
distinct normal state and superconducting state characteristics. To elucidate the intrinsic qualities of the normal state
continuum we present Raman specira on '123' single crystals with critical temperatures in the range T =OK to T = 90K,
and introduce a model which accurately describes the normal state temperature dependent trend of the response functions of
Aig and Big symmetry for the 90K compound. To illustrate the superconducting state qualities, we present a comparison of
the lowest temperature spectra for the 60K and 90K phases and show the temperature evolution of the Big spectra of the 60K
sample.
Systematic Raman study on Tl-based superconductors with Tc variation due to oxygen deficiency
Kiyoto Matsuishi,
Y. Q. Wang,
Y. Y. Sun,
et al.
Show abstract
Using a Raman microprobe technique, we have measured the Raman spectra of singile
crystaillites of Ti2Ba2Ca-lCu02fl+4-d (n1,2 and 3) with Tc varied by oxygen removal
or addition. It is found in Ti2Ba2CuO6-d that the phonon modes associated with the
vibrations of bridging 02 in Ba-0 planes (-"485 cnr') and 03 in 11-0 pianes (--600
cm ' ) increase i n frequency and become broader as the Ic increases from 0 to 70 K
with oxygen removai, whiie the Ba and TIE vibration modes do not change appreciabily.
The observations are attributed to the vallence change of TI., resuilting from a change
in the charge transfer between H and (Cu-Ol), and to the distortion and/or disorder
in 11-0 planes due to the oxygen removal.. In TI2Ba2CaCu2O8d and TlI2Ba2Ca2Cu3OlOd,
the frequencies of 02 and 03 vibration modes increase with Tc raised by oxygen addition,
while the Iow-frequency modes do not change. There is a ciear correlEation
between Tc and phonon frequencies in fl-based superconductors. We suggest that a
change in charge distribution in (Cu-01)-02-(fl-03) complexes is responsibEe for the
phonon frequency shifts observed in 02 and 03 vibration modes.
Raman-scattering characterization of oxygen isotope substituted YBa2Cu3O7-x
Show abstract
Th Raman spectrum of YBa2Cu3O7 contains three phonon modes at 502, 435, and
337 cm that arise from the vibrations of oxyn atoms only. These lines are
consequently shifted when 0 is substituted for 0 and the measured shifts can 11e
compared with theoretical1 predictions and used to determine the degree of 0
substitution. The 502 cm phonon, which involves the moti?i of the 0(4) bridging
atoms has been observed to be broadened significantly by 0 substitution. This
broadening has been attributed to disorder induced by incomplete substitution at the
0(4) site. To test this hypothesis the equations of motion for a randomly
substituted linear chain have been solved numerically and the solutions have been
. . . . . 18 used to obtain the linewidth and frequency shift for various degrees of 0
substitution. Good agreement is obtained with the experimental data and the results
are discussed in the context of proosed mechanisms6for oxygen exchange. The
temperature dependence of the 502 cm mode in both 0 samples and 0-exchanged
samples has been carefuly investigated and the measured linewidth has been found to
decrease by about 3 cm at T a1nd then increase again at lower temperatures. The
possible coupling of the 502 cm mode to charge transfer excitations is discussed.
New Techniques, Instrumentation, and Detectors
Recent developments in Hadamard transform Raman spectrometry
Robert M. Hammaker,
Allan P. Bohlke,
John M. Jarvis,
et al.
Show abstract
An introduction to Hadamard transform spectrometry in general and Hadamard transform Raman spectrometry in
particular is presented. Two generations of Hadamard encoding masks are described. Experimental details are provided
for the operation of a Hadamard transform Raman spectrometer utilizing the Hadamard encoding masks described.
Near-infrared Hadamard transform Raman spectra are presented to illustrate spectral subtraction, the multiplex
advantage and a selective multiplex technique. With the second generation of Hadamard encoding masks available, the
Hadamard transform Raman technique is now ready to begin its testing in the analytical world.
Fluorescence-free Raman spectra of polymers
Francis J. Purcell,
Job M. Bello
Show abstract
Raman spectroscopy has provided a large body of information
on the characterization of polymers. It supplies molecular data
on properties such as identity, isomerization, branching and
conformation. Raman spectroscopy has however, suffered from the
problem of fluorescence interference, which has limited its
usefulness as a general analytical tool for the characterization
of polymers. The fluorescence is generated by a number of
sources like plasticizers, coloring agents, • sizings and
impurities. Two recent technical developments have effectively
eliminated this problem. Both of these developments are based on
near-IR excitation outside the fluorescence absorption band. The
first, uses a cw Nd:YAG laser as the source and an interferometer
to analyze the scattered light. The other utilizes excitation
between 700 and 800 nm from a krypton, diode or solid state
tunable laser as the source and a charge-coupled device detector.
Both of these techniques enjoy a multiplex advantage, either from
the interferometer or the detector, to overcome the loss of Raman
scattering efficiency on moving into the infrared. This paper
will compare the benefits and disadvantages of these two
techniques and discuss their applications to materials like
polyimides, polyetheretherketone and other packaging materials
and fibers such as polyethylene terephthalate.
Recent advances in the development of a fiber-optic-based instrument for on-line Raman analysis
Show abstract
The measurement of composition of chemical process streams at multiple points is a critical problem in many
industrial environments. We are developing an instrument, based on laboratory Raman spectroscopy, to measure
composition of multiple components in a distillation column. A Nd:YAG laser is used to excite the sample and an
interferometer is used to detect the Raman spectrum. The light from the laser is routed to the measurement points
through a fiber optic probe which also gathers the light generated in the column by the Raman effect. A multiplexer
is introduced to allow sharing of the expensive components of the system among several measurement points. The instrunient
will initially be applied to distillation columns, but should be applicable to analysis of many liquid mixtures
of commercial interest. The response time is approximately three minutes per measurement. The composition
measurement range is from approximately 5% to 100% with an average error of less than 2% RMS. Progress in the
implementation of the instrument will be discussed, with particular emphasis on losses due to optical fiber lengths up
to 35 meters.
Two-dimensional encoding of Raman emission for detection with a charge-coupled device
Michael J. Pelletier
Show abstract
This report investigates the performance of a CCD-echelle spectrograph designed
for Raman spectroscopy. A holographic band-reject filter is used to reject
elastically scattered light without seriously reducing the instrument
throughput. The capabilities of this instrument are demonstrated by a
cyclohexane spectrum collected in 300 milliseconds with 12 milliwatts of laser
power, and by a spectrum of 1% L-phenylalanine in water.
Index Headings: Raman spectroscopy, Charge-coupled device, Echelle, Holographic
filter
Capabilities of a charge-coupled device with enhanced red responsivity for use in Raman spectroscopy
Robert B. Bilhorn,
Nancy S. Ferris
Show abstract
The performance of a slow-scan camera system using a silicon CCD fabricated specifically to have good
performance in th near-rn a detector for Raman spectroscopy is described. The capabilities of the red-enhanced
CCD for producing high-quality spectra with red excitation wavelengths at moderate laser powers and relatively short
integration times are demonstrated using benzoic acid. The SNR performance is compared to a conventional CCD
and an intensified photodiode array. Utility of the red-enhanced CCD system for a variety of applications is
demonstrated with near-JR examples of resonance Raman, SERS, and conventional Raman with a low-power source.
Problems associated with the sensitivity of CCDs in general, and the red-enhanced CCD in particular, to highenergy
particles are described. Methods for minimizing the problem by adding shielding, using only the illuminated
part of the detector, using multiple exposures, and using the minimum amount of binning necessary are presented.
High-gain GaAs photoconductor arrays for multichannel spectroscopy detectors
Monique T. Constant
Show abstract
The purpose of this paper is to introduce a new linear array of GaAs planar
photoconductors for use as new detector in multichannel spectroscopic systems.
After a description of the device and its technology, a complete analysis of its
electrical and optical properties is given. The results obtained are reviewed in
terms of static and dynamic responsivities, noise figures and specific
detectivity. Then, examples of the application of the array in a multichannel
Raman detection system are presented.
Polymers, Pharmaceuticals, and Biological Molecules
Raman microprobe spectroscopy of polyethylene terephthalate fibers: separation by band fitting of amorphous-oriented and crystalline components
Show abstract
Polarized Raman micrbprobe spectra of spin-oriented, as well as spun
and drawn, single filaments of polyethylene terephthalate have demonstrated
the development of both orientation and crystallization with take-up speed
(TUS) and conditions of drawing1-. Careful examination of those spectra
indicated the presence of overlapping bands in the carbonyl and glycol
regions. By using commercially available band-fitting software2 we have
succeeded in separating carbonyl band components and correlating them with
different atomic arrangements of the polymer.
Recent developments in multidimensional fluorescence-detected circular dichroism
Cynthia K. Williamson,
Jonathan A. Tarr,
Thilivhali T. Ndou,
et al.
Show abstract
A multidimensional fluorescence-detected circular dichroism
spectrometer has been modified for improved performance. The
hardware and software which control the spectrometer were updated.
The optical layout of the spectrometer was also redesigned in order
to minimize spectral artifacts.
Ultraviolet resonance Raman and fluorescence studies of growth hormones
Thomas J. Thamann,
Henry A. Havel,
E. W. Kauffman,
et al.
Show abstract
Ultraviolet resonance Raman and fluorescence spectroscopy have been used to study acid-induced
structural alterations in growth hormones from three species. Resonance Raman data for porcine (pGH),
bovine (bGH) and human (hGH) growth hormones using 222 am laser excitation show strong enhancement
of aromatic residues (phenylalanine (Phe), tryptophan (Trp) and tyrosine (Tyr)). Proline (Pro) vibrations
are also enhanced. Protein amide backbone and non-aromatic amino acid vibrations are only enhanced
slightly, thus they contribute little to electronic absorption at 222 nm. Resonance Raman results indicate
that Pro is present in both cis and trans configurations over the pH 8 to 2 range. Vibrational intensities
due to the single Trp (observed at 756 and 1557 cm1) increase dramatically when bGH or pGH is partially
unfolded in acid. Trp vibrational intensities for hGH change little at acidic pH, and are comparable to the
intensities for partially unfolded bGH and pGH. Fluorescence quantum yields and lifetimes from the single
Trp in bGH and pGH increase at low pH in a similar manner to the Trp vibrational intensity increase,
while the bGH quantum yields and lifetimes do not change at low pH. Since fluorescence intensity
changes for bGH as a function of pH appear indistinguishable from the resonance Raman intensity
changes, Trp Raman and fluorescence properties are probably influenced by the same molecular
interactions. A pK. of 3.7 for the resonance Raman and fluorescence spectral changes indicates that acidic
groups (aspartic or glutamic acids) are involved in the structural alterations. The possible roles of disulfide
bridges, lysines, and histidines in decreasing Trp vibrational and fluorescence intensities in native bGH
and pGH are examined.
Use of Raman spectroscopy to study the interaction of antitumor drugs and DNA
Douglas J. Minick,
M. Cory,
T. A. Fairley,
et al.
Show abstract
The binding of two isomeric 2-[(chysenylmethyl)amino]-2-methyl- 1 ,3-propanediols
(AMAPs) to the biopolymer poly(dG-dC)•poly(dG-dC) was studied using Raman spectroscopy.
The Raman spectra of the bound AMAPs were obtained by subtracting the Raman spectrum of the
biopolymer in buffered aqueous solution from those recorded for the AMAP-DNA binary
complexes. The difference method applied here has been used in other studies to obtain spectra
of small molecules bound to macromolecules of biological origin (Yue, K.T. et al., J. Raman
Spectrosc., 20, 541-545, 1989, and references therein). Due to the extremely low number of
Raman active lines observed in the spectra of these AMAPs, it was also possible to study
perturbations in the Raman spectrum of the complexed biopolymer.
Spectroscopic data indicated that both AMAPs intercalate with DNA, in agreement with
viscometric measurements for these compounds; however, some differences were observed in the
Raman spectra of DNA complexed with these drugs, suggesting that the specific AMAP-DNA
binding interactions are different.
Raman spectra of crystalline 4Zn, 2Zn, and Na insulin
Lowell G. Tensmeyer,
J. E. Shields
Show abstract
Normal Raman spectra were obtained for three crystalline forms of human
insulin: 4Zn, 2Zn, and Zn-free or Na, from 1800-200 cm1. The extraction of a large
number of component bands from the heavily overlapped Raman bands was accomplished
by Fourier Self Deconvolution and bandfitting. Bands considered to be indicative
of protein conformation, including Amide I, Amide III, tyrosine, 5-5, and C-S bands,
and some which are relatively insensitive to protein structure, such as
phenylalanine and histidine, are compared. The published x-ray structures of 4Zn
and 2Zn insulins are used to help interpret the corresponding parameters of the
extracted Raman bands, and to suggest structures in the as yet unpublished Na/human
insulin crystals.
Pollution and Medical Analytical Instrumentation
Optimization of a Fourier transform infrared spectrometer during on-site pollution analysis
Martin L. Spartz,
Mark R. Witkowski,
Jonathan H. Fateley,
et al.
Show abstract
The field transportable Fourier transform infrared (FT-IR) spectrometer system developed at Kansas State University
is now finishing the testing stage. The testing stage consisted of three parts: the measurements of (1) controlled
releases of volatile organic compounds (VOC), (2) uncontrolled VOC releases at well documented sites, and (3)
uncontrolled VOC releases at complex sites with little or no precharacterization1. Some measurements have been
acquired in all three categories with most of the data acquisition taking place in the first two categories, which are
discussed in these proceedings. These tests were developed to validate the qualitative and quantitative capabilities
while enhancing the versatility and detection limits of the spectrometer system.
The controlled VOC releases, for the most part, took place at the University of Kansas (KU). The KU tests utilized
a co-monitoring technique, evacuated stainless steel canisters followed by GC/FID analysis, during the acquisition of
the infrared data. The ability to monitor the concentrations of the released plume with another technique allowed for
the comparison and examination of how varying parameters can affect the infrared spectrometer technique. The
varying parameters that were addressed were wind, path length, temperature, barometric pressure, water and carbon
dioxide concentration, and air borne particulates.
One set of uncontrolled releases occurred at an active production facility. A list of the possible compounds that might
be observed from the facility directly due to production was obtained. Infrared measurements were acquired at two
different setup geometries down wind and one setup geometry up wind. The three path lengths were 390 meters, 500
meters, and 412 meters respectively. During these measurements two series of canister samples were obtained down
wind and one series of canister samples were obtained up wind. The analyses of these canisters, on-going at this
writing, is being performed by GC/FT-IR (matrix isolation). When the analysis from this method is complete the
results will be compared.
These two different data acquisitions have led to much insight into the capabilities of the spectrometer system and how
varying parameters can affect the FT-IR spectrometer's performance. Preliminary analysis of the spectroscopic data
from both data acquisitions will be discussed.
Commercial anesthetic-respiratory gas monitor utilizing Raman spectroscopy
Donald E. Gregonis,
Richard A. Van Wagenen,
D. Coleman,
et al.
Show abstract
A commercial gas monitor which utilizes Raman Spectroscopy has
been developed to monitor anesthetic and respiratory gases in the
hospital operating room. The instrument measures all molecular
gases administered by the anesthesiologist in real time with fast
response of breath waveform. These gases include carbon dioxide,
nitrous oxide, oxygen, nitrogen and various volatile halogenated
organic anesthetics, e.g. halothane, isoflurane, enflurane,
sevoflurane and desflurane. The key feature of this instrument
which allows it to produce adequate Raman signals with a low cost
argon ion laser is measuring these gases inside the laser resonant
cavity.
Advances in surface-enhanced Raman spectroscopy for hazardous waste monitoring
Show abstract
Surface-enhanced Raman spectroscopy is being evaluated for use as an advanced method for detecting
organic contaminants in groundwater during field-screening of environmental samples. The SERS technique
offers attractive and unique capabilities for detecting a wide range of organic contaminants in aqueous
environments at ppm to ppb levels. An inexpensive computer-controlled portable spectrometer system coupled
to a fiberoptic probe has been developed for rapid on-site and in situ determination of organic contamination
in groundwater. Applications of recent advances in substrate fabrication for use with environmental samples
are discussed, and critical issues pertaining to substrate durability, repeatability, sensitivity, selectivity and
universality are addressed.
Analytical Applications of Surface-Enhanced Raman Scattering
Surface-enhanced Raman spectroscopy of thiols and disulfides
Robin L. Garrell,
Cory Szafranski,
Weslene Tanner
Show abstract
Aromatic and alkyl thiols adsorb on gold surfaces from ethanol to form stable monolayers.
Surface-enhanced Raman spectroscopy (SERS) has been used to characterize the interactions of thiols and
disulfides with gold surfaces immersed in aqueous solution. SERS provides the first direct evidence that
thiols such as benzenethiol (thiophenol), benzenemethanethiol (benzylthiol), and
4-cyanobenzenemethanethiol adsorb dissociatively on gold, and interact with gold through the sulfur atom.
The adlayers are quite robust, being stable between the potential required for the reduction of water and that
required for oxidation of the gold substrate. Generation of hydrogen at the surface results in the formation of
regions of low thiol coverage that are spectroscopically distinct from the high coverage regions that form
spontaneously when the electrode is immersed in a thiol solution. The SER spectra of adsorbed aromatic
thiols and the analogous disulfides are identical, indicating that the disulfide bond cleaves upon adsorption.
SERS reveals that 4-bromobenzenethiol and 4-chlorobenzenethiol are reduced to benzenethiol at -1000 mV
vs. SCE on gold. The corresponding 4-halo-benzenemethanethiols are reduced less readily, and
4-fluorobenzenethiol not at all. These reactions afford the possibility of preparing mixed thiol monolayers,
and of subsequently modifying thiol monolayers in situ.
Surface-enhanced fluorescence of aggregates in Langmuir-Blodgett monolayers
Show abstract
The geometry of the molecular organization in monolayers seems to be a key factor
in the formation of aggregates. In the present work, monolayers of perylene
tetracarboxylic derivatives have been fabricated under conditions leading to different
molecular orientations in the film. Monolayers of the neat dye material, and mixed
monolayers, were prepared at different pH values of the subphase and transferred to
glass slides at constant pressure. Monolayers were also transferred to glass
substrates at various points in the surface pressure-area isotherm. Steady state
surface-enhanced fluorescence measurements were used to characterize the aggregate
formation. Surface-enhanced resonant Raman scattering (SERRS) was observed and used
as an internal reference in the fluorescence measurements.
Surface-enhanced Raman spectroscopy for remote sensing
Show abstract
Conventional Raman spectroscopy is often limited by its low sensitivity due to the
inherently weak Raman cross section of organic chemicals. A relatively new detection
technique, Surface-Enhanced Raman Scattering (SERS) spectroscopy is based on recent
experimental observations, which have indicated enhancement of the Raman scattering
efficiency by factors of up to 106 when a compound is adsorbed on rough metallic surfaces
that have submicron-scale protrusions. In this report we discuss the development of the
SERS technique as a tool for monitoring hazardous chemical emissions and its application
to in situ remote sensing.
Surface-enhanced Raman detection of RNA and DNA bases following flow-injection analysis or HPLC separation
Therese M. Cotton,
Rong-Sheng Sheng,
Fan Ni
Show abstract
The goal of this study is to develop Surface-enhanced Raman scattering (SERS) detection
methods for flow injection analysis (FIA) and high performance liquid chromatography (HPLC).
Nucleic acid bases have been chosen for analysis because of their importance in life processes. The
advantages to the use of SERS-based detection include its sensitivity, specificity and versatility.
With the development of improved methodology, the detection limits should be comparable to UV
spectroscopy. However, the specificity is considerably superior to that obtained with electronic
spectroscopy in that the Raman spectrum provides a molecular fingerprint of the individual
analytes. Raman spectroscopy is very versatile: aqueous samples, gases and solids can be analyzed
with equal facility.
The results presented here demonstrate that SERS can be used as a detection method for both
FIA and HPLC detection. In the following experiments Ag sols have been used as the active
substrate. The effect of various parameters such as temperature, pH, flow rate, and the nature of
the interface between the HPLC system and the Raman spectrometer have been examined. One
of the most significant findings is that the temperature of the Ag sol/HPLC effluent mixture has
a dramatic effect on the SERS intensities. This effect is a result of increased colloid aggregation
at higher temperatures. Aggregation is known to produce greater enhancement in SERS and
proceeds much more rapidly at elevated temperatures. An increase in the temperature of the Ag
sol enables SERS detection under flowing conditions and in real time. This is a substantial
improvement over many of the previous attempts to interface SERS detection to FIA or HPLC.
In most of the previous studies, it was necessary to stop the flow as the analyte eluted from the
chromatogram and measure the SERS spectra under static conditions.
Superconductors
Raman spectra of bismuth cuprate high-Tc superconductors doped with thulium and lead
Leonilda A. Farrow,
R. Ramesh,
J. M. Tarascon,
et al.
Show abstract
Raman spectra of and Bi2PbSr2Ca2Cu3O are presented as a function of increasing x.
For the period of superstructure modulation decreases somewhat and oxygen content in the
Bi-O planes increases as x increases; for Bi2PbSr2Ca2Cu3O, more lead (increasing x) has the opposite effect of
increasing the modulation period and decreasing the oxygen content of the Bi-O layers. More modes are seen in these
spectra than are predicted from an analysis based on the space group of the undistorted cell; these extra modes are
discussed in terms of group theory predictions of a commensurate supercell with dimensions 4 or 5 times the basic
lattice spacing. Extra oxygen in causes the high frequency mode, associated with vibration of
oxygen in the Bi-O layers, gradually to broaden and then split. At higher lead additions to Bi2Sr2Ca2Cu3O, spectra
are consistent with formation of a new phase due to limits on lead solubility; the low frequency modes all but disappear
while the high frequency mode is strongly shifted down. Other details of the spectra confirm the necessity of
considering the superstructure as well as the symmetry of the undistorted unit cell.