Spectroscopy mass, laser-induced

Brands proposed a calculation method in the case of segregation A special type of inhomogeneous, particulate objects is the surface analysis by microscopic techniques e.g. analytical electron sj troscopy, laser induced mass spectroscopy or proton-induced X-ray emission. Here the minimum sample size can be translated into the minimum number of specific sample points in the specimen under investigation. 

This presentation will summarize developments in laser ablation with emphasis on LIBS (laser induced breakdown spectroscopy) and inductively coupled plasma mass spectrometry (ICPMS) as analytical tools for real time chemical analysis (Fig. 1) (Russo et al. 

Figure 7. Schematic diagram of the supersonic beam apparatus which combines laser-induced fluorescence spectroscopy with time-of-flight mass spectrometry. Reproduced with permission from Ref [92a].

Jockusch, R.A. Bian, Q. Talbot, F.O. Forbes, M.W. Development and characterization of laser induced fluorescence spectroscopy coupled with ion trap mass spectrometry, Proc. 56th ASMS Conf. on Mass Spectrometry and Allied Topics, Denver, CO 2008. 

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

Spectral methods based on UV-visible spectrophotometry, laser-induced breakdown spectroscopy (LIBS), infrared (IR), Raman, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), thermoanalytical and chromatographic methods, especially liquid chromatography (LC) or gas chromatography (GC) combined with pyrolysis are most common. 

Laser desorption and ionization laser-induced breakdown spectroscopy, matrix-assisted laser desorption and ionization, and aerosol time-of-flight mass spectrometry... 

Laser-induced plasma spectroscopy Time-of-flight secondary ion mass spectrometry... 

Surface analysis techniques such as secondary ion mass spectrometry (SIMS), laser induced mass analysis (LIMA) and X-ray photoelectron spectroscopy (XPS) are used for failure diagnosis work associated with such things as poor bonding to substrates and for surface characterisation work. 

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

The industrial application of Plasma Induced Chemical Vapour Deposition (PICVD) of amorphous and microcrystalline silicon films has led to extensive studies of gas phase and surface processes connected with the deposition process. We are investigating the time response of the concentration of species involved in the deposition process, namely SiH4, Si2H6, and H2 by relaxation mass spectroscopy and SiH2 by laser induced fluorescence. 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

Marijnissen, J., B. Scarlett, and P. Verheijen, Proposed On-Line Aerosol Analysis Combining Size Determination, Laser-Induced Fragmentation, and Time-of-Flight Mass Spectroscopy, ./. Aerosol Sci., 19, 1307-1310(1988). 

The pump and probe pulses employed may be subjected to a variety of nonlinear optical mixing processes they may be prepared and characterized by intensity, duration, spectral band width, and polarization. They may arrive in the reaction chamber at a desired time difference, or none. The probe pulse may lead to ionizations followed by detections of ions by mass spectrometry, but many alternatives for probing and detection have been used, such as laser-induced fluorescence, photoelectron spectroscopic detection, absorption spectroscopy, and the like. 

---