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 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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.