The issues related to Raman scattering characterization of the microstructure of diamond thin films are reviewed. The optical effects of the transparent/absorbing composite of sp2/sp3 bonded material is discussed. Then the dependence of the Raman spectra on the microcrystalline size is described. The comparison is made with crystalline Si, and the analysis is applied to a series a diamond films. Lastly micro-Raman scattering from the initial stages of diamond film growth are described, and the results are correlated with STM measurements of the nuclei. Surface enhanced Raman scattering is applied to examine the regions between diamond nuclei.
Diamond films grow on the anode of DC plasmas while only diamondlike carbon and graphite grow on the cathode. In situ plasma diagnostics were employed to investigate the plasma as a whole and the anode in particular. To this end, pure hydrogen and diamond-producing DC plasmas were studied with optical emission spectroscopy. The pure hydrogen plasmas were analyzed to determine the effect of critical deposition parameters on the visible structure of the plasma. Two methane/hydrogen plasmas were also examined, one of which produced a graphitic film, the other a diamond film. The visible structures of these plasmas differed in that the diamond-producing plasma exhibited evidence of an anode (substrate) glow while the graphite-producing plasma had no glow.
We report a high-resolution resonance Raman study of C60 films. We identify several peaks whose frequencies are in good agreement with the predictions of a first-principles quantum molecular dynamics calculation for an isolated C60 molecule having icosahedral symmetry. On the other hand, the depolarization ratios for most Raman peaks, some fine- structure features observed with high resolution, and the resonance photon energies suggest solid-state effects or the existence of C60 isomers of lower symmetry
Measurements of plasma generated amorphous carbon films (a:C-II and A:C) in our laboratory show that nitrogen doping of the carbon imparts infrared activity to the films. In particular, the Raman G and D bands which are infrared inactive in typical amorphous carbons become active when nitrogen is substituted for carbon. This increase in infrared activity is attributed to a symmetry breaking by the nitrogen centers. In this paper we show that this symmetry breaking also gives rise to increases infrared emission. We suggest this same mechanism may be relevant to the origin of diffuse interstellar infrared emission from carbonaceous dust.
Solid and hollow waveguides have been employed for spectroscopic and radiometric measurements. Hollow sapphire guides, with a transmission window from 10 - 17 micrometers , are used to detect 20% CO2 in N2. Hollow silica waveguides, with a transmission window from 7 -9 micrometers , are utilized for detecting 100% methane and also for low temperature radiometric measurements from 30 degree(s)C to 150 degree(s)C. The spectroscopic analysis was accomplished by passing the gas down the interior of the hollow guide for an extended pathlength absorption. The hollow silica guide measured the low temperature region with a minimum resolvable temperature difference of less than 1 degree(s)C.
Amorphous Materials serves as a source of high purity IR transmitting chalcogenide glasses. Based primarily on the element selenium, the glasses are used for optical elements in passive IR optical systems. However, because of their transparency in the IR combined with chemical inertness, the glasses can be used to fabricate ATR plates for chemical analysis. Addition of the element tellurium extends the long wavelength transparency of selenium glasses increasing their suitability for use as IR fiber materials. Uncoated fibers may be used in the same manner as ATR plates for chemical analysis. Production of glass and fibers are discussed.
Recent advances in mid-infrared (IR) transmitting fiber optic technology have opened up new opportunities in biomedical technology and biological research. A high sensitivity IR fiber optic sensor has been developed which can be used to monitor physiologically relevant concentrations of biological molecules. The use of fiber optics will allow sampling at locations that are remote from the spectrometer with a hand-held probe. The fiber can also be used as a low cost, disposable sensor.
The real-time in situ monitoring of the chemical states of epoxy and polyimide resins were investigated during cure using an embedded fiber optic sensor and a Fourier transform infrared spectrometer (FTIR). In this work a short length of sapphire fiber is used as the sensor for monitoring the cure of the epoxy, while for the polyimide resin, we use a chalcogenide fiber as the sensor. The cure of the epoxy resin/graphite fiber composite is monitored in an autoclave, while the cure of the polyimide resin/graphite fiber composite is monitored in a high temperature press. The sapphire sensor is connected to infrared transmitting zirconium fluoride optical fiber cables which penetrate the wall of the autoclave and interface to the FTIR spectrometer. The chalcogenide sensor connects to other chalcogenide fibers which act as a transmission link to the FTIR spectrometer. The results indicate that this equipment and sensors are suitable for monitoring the degree of cure of the laminates throughout the entire cure cycle.
Infrared spectroscopy (IR) is a vibrational spectroscopic technique used for the nondestructive identification of molecular species. It provides information about molecular structure by determining the frequency and intensity of light a compound absorbs in the infrared region. The resultant IR absorption spectrum is characteristic of the compound. This spectrum is considered one of the compound's physical properties, like its density or boiling point. However, unlike these other properties only optical isomers have identical infrared absorption spectra. Infrared spectroscopy can be performed on molecular species in any physical state. Therefore, gases, liquids, and solids can all be sampled. Generally, because of the high information content of the infrared spectra of organic molecules IR is most useful for the identification of organic materials. However, many inorganics also exhibit IR detectable molecular vibrations and therefore can be identified by this technique. The paper deals briefly with the use of infrared spectrometers coupled to microscopes, and methods of compressing spectral data by integrating absorbance intensity over a characteristic frequency range.
The chemical information obtained from a sample by the techniques of Fourier Transform Infrared (FTIR) microscopy and small spot Electron Spectroscopy for Chemical Analysis (ESCA) can be very complementary. The basics of both of these analytical techniques will be discussed and case studies showing how the data from these techniques can be combined to provide a powerful tool for industrial problem solving and materials characterization, will be presented.
A new objective lens for grazing angle FT-IR microscopy provides a means for the infrared analysis of monomolecular films in small (25 X 25 micrometers ) areas. Conventional grazing incidence reflection spectroscopy is an established technology for detecting and analyzing thin surface films on metals or highly reflecting materials. The grazing incidence objective extends these techniques to microscopic areas. Applications of grazing angle FT-IR microscopy (GAM) are illustrated by exemplar analyses. The analyses of thin film lubricants and contaminants are specially important.
Infrared and ultraviolet matrix-assisted laser desorption Fourier transform mass spectrometry is investigated using a number of different matrices. In common with previous reports, it is found that the most efficacious matrices, regardless of laser wavelength used, are those which absorb at the chosen wavelength. Effects of matrix/analyte ratio, laser power, and choice of matrix under low pressure Fourier transform mass spectrometry conditions are examined.
A surface analysis method called LITD/FTMS has been used to measure the rate constants and detect the reaction intermediates for the dehydrogenation of various hydrocarbons on platinum. Laser-induced thermal desorption (LITD) utilizes a pulsed laser beam to rapidly heat the surface and remove intact neutral molecular species. These are then ionized by an electron beam, trapped in a magnetic field, and detected by Fourier transform mass spectrometry (FTMS). FTMS has two advantageous features: high mass resolution and the ability to record all masses simultaneously from a single laser shot. LITD/FTMS is a highly sensitive and rapid method for identifying complex molecular species adsorbed on surfaces. Intermediates in catalytic reactions can be observed and rate constants for surface-catalyzed reactions can be measured.
Laser desorption followed by jet-cooling allows wavelength-selective as well as mass-selective detection of organic molecules desorbed from a surface without fragmentation. The absolute detection sensitivity is demonstrated with the perylene molecule. A two-color REMPI spectrum (400 wavelength points) of perylene is recorded using only 30 picogram of material. Rotational cooling to 5 - 10 K is demonstrated with laser-desorbed anthracene; vibrational cooling below 15 K is demonstrated with laser-desorbed diphenylamine. The ability to take a 'snapshot' of molecules on a surface is illustrated with the spectrum of benzoic acid monomers. Other applications are discussed, i.e. PABA dimer spectroscopy and detection of C60.
Fourier transform mass spectrometry (FT/MSR) has been recognized as a powerful analytical technique for the determination of elemental compositions and the molecular structure of materials. The simultaneous measurement of all species, produced in a single event, in a Fourier transform mass spectrometer provides a natural combination with pulsed lasers, where the pulsed laser is used to ablate and ionize a portion of a sample. This unique combination of lasers with FTMS provides elemental and molecular information from inorganic and organic materials and from surface layers and from bulk materials. Microanalysis of materials, allowing spatially-resolved high-resolution mass spectra to be obtained, is possible with small laser spot sizes and optical systems for viewing samples inside the mass spectrometer. The advantages of FTMS are reviewed, and several examples of laser probe FTMS are illustrated to demonstrate applications of the technique to industrial problem solving.
A method for the chemical analysis of individual aerosol particles on a real-time basis has been developed. This is accomplished by measuring their mass spectra. In this method, particles are directly introduced in the ion source of the mass spectrograph in the form of a beam. Volatilization and ionization of a particle in an ion source of the mass spectrograph is performed by using a pulsed high-energy Nd-YAG laser. Each particle, when hit by the laser pulse, produces a burst of ions of different masses. These ions are spatially separated according to their masses along the focal plane of a mass spectrograph and their intensities are measured simultaneously by an array detector. Some of the preliminary results on the mass spectral measurement of potassium biphthalate particles are presented. Volatilization and ionization of particles eliminate any possible substrate sample matrix interferences in the analysis. In order to preserve the real-time feature of the method for the analysis of particles present in low concentrations, the aerosol sample is concentrated by using a two-stage virtual impactor.
Laser induced thermal desorption (LITD) has proven to be an effective probe of reaction kinetics on single-crystal surfaces. The ability of LITD techniques to measure adsorption, decomposition and desorption kinetics will be illustrated by studies of SiCl4 and (CH3CH2)2 SiH2 on Si(111)7X7. Silicon tetrachloride, SiCl4, is important in silicon epitaxial growth and diethylsilane, (CH3CH2)2 SiH2, is a promising candidate for silicon atomic layer epitaxy. The desorption products, sticking coefficients and decomposition and desorption kinetics measured by these LITD investigations are important for an understanding of silicon epitaxy by chemical vapor deposition.
The application of cw lasers as powerful excitation sources for transient (triplet-) state spectroscopy is demonstrated. By focusing a cw laser beam on a sample with the aid of a lens, high triplet optical densities ODT((lambda) ) can be recorded. Using McClure's method, triplet extinction coefficients (epsilon) T((lambda) ) of many organic compounds are conveniently measured. To illustrate the method, we recorded (epsilon) T values on syn- (dimethoxyphosphinylmethyl,methyl) bimane. Exciting organic compounds with light causes various degrees of photodecomposition. We have developed a method to measure triplet optical densities ODT((lambda) ) in the presence of photodecomposition. The method is demonstrated on Coumarin 120. One records ODT((lambda) ) values as well as the accumulation of absorbing photoproducts as a function of time. Turning off the cw laser excitation, one records the accumulation of photoproducts only. Separating the two processes, one can determine how the triplet optical density declines as a function of time t. The decline curve can be expressed with an equation that is of second order in time. This equation allows one to extrapolate back to t equals 0 and recover ODT when there was no photodecomposition. Because the cw laser light is highly polarized, triplet-triplet (T-T) photoselection spectroscopy can be employed. The degree of polarization P of several syn- binanes was recorded, providing important insight on the polarization of T-T transitions. These data may be used to improve laser action properties of syn-bimanes by substitutions.
Second harmonic generation (SHG) has been used to characterise the chemical composition of an iron or mild steel electrode. SHG has then been used to follow the adsorption of a representative corrosion inhibitor, oleic imidazoline, onto the surface. Information about the adsorption kinetics and thermodynamics is obtained. Extension of these experiments to corrosive media is also discussed.
Laser excited fluorescence (LEF) and fluorescence probes have been used to observe bulk damage in aged cross-linked polyethylene (XLPE) insulation of power transmission cable. 'Water trees' in the shape of bow-ties (50 micrometers to 1 mm) and striations near the cable core were observed under a microscope when the aged XLPE samples were irradiated by an Argon-ion laser. Changes in the bulk fluorescence of samples subjected to various aging conditions were observed as well. XLPE samples could be bulk-stained by soaking them in solutions of fluorescent dyes such as rhodamine 6G, Acridine Yellow G, resorufin and Nile Red in order to probe and highlight defects under similar LEF conditions. Resorufin proved useful for preferential staining of the water-trees making them flagrantly visible. Rhodamine 6G and Acridine Yellow G soaked samples provided evidence of chemical and/or physical changes surrounding these trees: A halo arising from dye fluorescence quenching could be observed surrounding the trees. The chemical and spectroscopic properties of fluorescent probes may provide insight into chemical/physical features of observed defects.
In this paper, the lattice vibrations of barium metaborate ((beta) -BaB2O4) crystal are analyzed with the aid of group theory. The (beta) -BaB2O4 crystal belongs to space group C34 (R3) and approach space group C3v6 (R3C) very much. The vibration modes classified by the site-symmetry method. Their results of Infrared and Raman spectra have been given.
We have demonstrated a correlation between laser Raman scattering features and the octane rating of
gasolines and aromatic content of hydrocarbon fuels; our initial success measuring octane and
aromatic content is very encouraging and forms the basis for our proposed research program. It is
our aim to use this technology to develop an inexpensive, portable, field-deployable device that
would allow on-site testing and/or verification of octane labeling of gasoline products at the pump,
along with the environmentally significant properties, Reid vapor pressure and aromatic content.
Quantitative measurements of reflected optical second harmonic generation (SHG) versus the angle of polarization of the incident light from the interface between opaque silver films and several glasses are presented. And we also measured the reflected SHG from the surface of vacuum cold-evaporated thick silver film on a polycrystalline silver substrate in ultra-high vacuum (UHV) chamber before and after annealing the specimen. For comparison, the reflected SHG from 99.99% finely polished polycrystalline silver surface was detected in UHV. By calibrating the reflected SHG from the silver film to the transmitted SHG from a z- cut quartz, the value of normal current parameter a could be determined. We measured that the phenomenological normal current parameter a had a value of 2.1 for glass-silver interface and -9 for polycrystalline silver sample. And that a varied from 7 to -5 for the cold-evaporated silver film on a polycrystalline silver substrate with the sample annealed. The experimental result shows that the SHG signal is sensitive to the surface structure of the silver film. The electro-dynamic theory is used to fit the experimental results.
Amorphous 'hard carbon' and microcrystalline diamond films are being investigated and characterized using high-sensitivity and spatial-profiling Raman spectroscopy. The 'hard carbon' films have broad Raman spectra with no diamond line while higher quality diamond films show only a single sharp diamond line. Features in the Raman spectra of the amorphous 'hard carbon' films correlate with the rates of specific types of wear. Changes in the relative intensity of the Raman band near 1570 cm-1 (G-band) compared to the band near 1360 cm-1 (D-band) are related to the rate of abrasive wear. Shifts in the frequency of the G-band are related to the rate of tribochemical wear. The results are consistent with a structural model of amorphous carbon films in which small (< 20 angstrom) graphitic microcrystals comprised of sp2 bonded domains are cross-linked by sp3 carbon atoms. Profiles of Raman frequency and linewidth obtained from spatially resolved Raman spectroscopy across CVD-grown diamond thin films show that the Raman frequency and position are correlated in these films and that both change in regions of poorer film quality.