Noise spectroscopy

Busch, K.L. Chemical Noise in Mass Spectrometry. Part 11 - Effects of Choices in Ionization Methods on Chemical Noise. Spectroscopy 2003,18, 56-62. 

Flicker-noise spectroscopy — The spectral density of - flicker noise (also known as 1// noise, excess noise, semiconductor noise, low-frequency noise, contact noise, and pink noise) increases with frequency. Flicker noise spectroscopy (FNS) is a relatively new method based on the representation of a nonstationary chaotic signal as a sequence of irregularities (such as spikes, jumps, and discontinuities of derivatives of various orders) that conveys information about the time dynamics of the signal [i—iii]. This is accomplished by analysis of the power spectra and the moments of different orders of the signal. The FNS approach is based on the ideas of deterministic chaos and maybe used to identify any chaotic nonstationary signal. Thus, FNS has application to electrochemical systems (-> noise analysis). 

Refs. [i] Timashev SF (1993) Zh Fiz Khim 67 1755 [ii] Timashev SF (2001) Russ J Phys Chem 75 1742 [Hi] Timashev SF (2001) Flicker-noise spectroscopy as a tool for analysis of fluctuations in physical systems. In Bosman G (ed) Noise in physical systems and 1/f fluctuations. ICNF, World Scientific, New Jersey, pp 775-778 [iv] Timashev SF, Vstovskii GV (2003) Russ JElectrochem 39 141 [v] Parkhutik V, Patil R, Harima Y, Matveyeva E (2006) Electrochim Acta 51 2656 [vi]Parkhutik V, RayonE, FerrerC, TimashevS, Vstovsky G (2003) Phys Status Solidi A Applied Research 197 471... 

FNS - flicker-noise spectroscopy Formal potential - potential Foerster, Fritz... 

Wavelet analysis is a rather new mathematical tool for the frequency analysis of nonstationary time series signals, such as ECN data. This approach simulates a complex time series by breaking up the ECN data into different frequency components or wave packets, yielding information on the amplitude of any periodic signals within the time series data and how this amplitude varies with time. This approach has been applied to the analysis of ECN data [v, vi]. Since electrochemical noise is 1/f (or flicker) noise, the new technique of -> flicker noise spectroscopy may also find increasing application. 

We now turn to the case of noise spectroscopy and in particular consider the important issue of the number of sensors needed to analyze a mixture of different chemical species. It is first assumed that oidy one sensor is present. If the power density spectrum of the resistance fluctuations in this sensor has K different frequency ranges, in which the dependence of the response on the concentration of the chemical species is different from the response in the other ranges, one can write... 

The idea of noise spectroscopy is to determine for a measured 7(f) the average current, J = < 7(f) >, and also the temporary current correlation fimction. 

A sharp drop, by several orders of magnitude, of (f)llP with the change in concentration of CO in the air suggests the possibility of making a precise estimation of the gas content in air - that is, we can offer a new method of estimation of the concentration of gases in an environment and the noise spectroscopy (Figs 12.3 and 12.4). Su is the spectral density of the noise voltage. 

Reliability of electronic devices is caused predominantly by failures which result from the latent defects created during the manufacture processes or during the operating life of the devices. A search for new nondestructive methods to characterise quality and predict reliability of vast ensembles became a trend in the last four decades (Saveli etal. 1984), (Hartler et al. 1992), (Vandamme 1994), (Hashiguchi et al. 1998). The most promising methods to provide a non-destructive evaluation are an analysis of the electron transport parameters. Experiments are based on the measurements of device VA characteristics, nonlinearity using the non-linearity index (NLl), electronic noise spectroscopy, electro-ultrasonic spectroscopy and acoustic emission. These ones apply to both active and passive components, i.e., bipolar devices and MOS structures, on one hand, and resistors and capacitors on the other. 

Rarkhutik, V., Ratil, R., Harima, Y. and Matveyeva, E. (2006) Electrical conduction mechanism in conjugated polymers studied using flicker noise spectroscopy. Electrochimica Acta, 51, 2656-1661. 

Pulsed ENDOR offers several distinct advantages over conventional CW ENDOR spectroscopy. Since there is no MW power during the observation of the ESE, klystron noise is largely eliminated. Furthemiore, there is an additional advantage in that, unlike the case in conventional CW ENDOR spectroscopy, the detection of ENDOR spin echoes does not depend on a critical balance of the RE and MW powers and the various relaxation times. Consequently, the temperature is not such a critical parameter in pulsed ENDOR spectroscopy. Additionally the pulsed teclmique pemiits a study of transient radicals. 

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

The pyrolysis of CR NH (<1 mbar) was perfomied at 1.3 atm in Ar, spectroscopically monitoring the concentration of NH2 radicals behind the reflected shock wave as a fiinction of time. The interesting aspect of this experiment was the combination of a shock-tube experiment with the particularly sensitive detection of the NH2 radicals by frequency-modulated, laser-absorption spectroscopy [ ]. Compared with conventional narrow-bandwidth laser-absorption detection the signal-to-noise ratio could be increased by a factor of 20, with correspondingly more accurate values for the rate constant k T). 

Precision In absorption spectroscopy, precision is limited by indeterminate errors, or instrumental noise, introduced when measuring absorbance. Precision is generally worse with very low absorbances due to the uncertainty of distinguishing a small difference between Pq and and for very high absorbances when Px approaches 0. We might expect, therefore, that precision will vary with transmittance. 

Different analytical techniques are used for detection of the elemental composition of the solid samples. The simplest is direct detection of emission from the plasma of the ablated material formed above a sample surface. This technique is generally referred to as LIBS or LIPS (laser induced breakdown/plasma spectroscopy). Strong continuous background radiation from the hot plasma plume does not enable detection of atomic and ionic lines of specific elements during the first few hundred nanoseconds of plasma evolution. One can achieve a reasonable signal-to-noise ra-... 

Because the Raman cross-section of molecules is usually low, intense light sources and low-noise detectors must be used, and high sensitivities - as required for surface analysis - are difficult to achieve. Different approaches, singly and in combination, enable the detection of Raman spectroscopy bands from surfaces. 

Nitrophenyl groups covalently bonded to classy carbon and graphite surfaces have been detected and characterized by unenhanced Raman spectroscopy in combination with voltammetry and XPS [4.292]. Difference spectra from glassy carbon with and without nitrophenyl modification contained several Raman bands from the nitrophenyl group with a comparatively large signal-to-noise ratio (Fig. 4.58). Electrochemical modification of the adsorbed monolayer was observed spectrally, because this led to clear changes in the Raman spectrum. 

Are, H.A., Marum, P., "On the Effect of Calibration and the Accuracy ofNIR Spectroscopy with High Levels of Noise in the Reference Values", Appl. Spec. 1991 (45) 109-115. 

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