Charge modulation spectroscopy

Despite the potential significance of shallow traps in the operational degradation of OLED devices, there are no established general techniques for their effective detection and measurement in such an environment. The application of methods, such as electron spin resonance [43], electrically detected magnetic resonance [44], and charge modulation spectroscopy [45,46], is hindered by their limited sensitivities and selectivities in operationally degraded OLED devices. 

The inhomogeneity of the micellar aggregate also affords assisted spin trapping and the exploitation of magnetic field effects on the charge separated ion pairs [48]. Optical modulation spectroscopy can be used, for example, to follow the decay of radicals formed in homogeneous solution and in SDS micelles. Enhancements of a factor of about 50 in the lifetimes and the steady state concentrations of the radical were observed in the micelle, and a kinetic analysis led to a value of 2 x 103 s 1 for the exit rate constant from the micelle [49]. 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

In this chapter we will review a powerful type of modulation spectroscopy electroabsorption (EA) spectroscopy. Such technique is particularly interesting, since it enables probing of completed and operational devices for the determination of (a) the internal fields that arise either from application of an external bias, from equilibration of the Fermi energy, or from fixed or injected charges, and their accumulation at trap sites or at heterointerfaces, and (b) the evolution of the injection barrier... 

Petrozza A, Groves C, Snaith HJ (2008) Electron transput and recombination in dye-sensitized mesoporous Ti02 probed by photo induced charge-conductivity modulation spectroscopy with Monte Carlo modeling. J Am Chem Soc 130 12912-12920... 

M. G. Harrison, R. H. Friend, F. Gamier and A. Yassar, A study of the charged excitations in thin-films of alpha-sexithiophene by voltage-modulation spectroscopy and photoimpedance measurements, Molec. Cryst. Liq. Cryst. Sci. Technology Section A - Molec. Cryst. Liq. Cryst., 1994, 252, 165. 

The prototype DSCs used liquid electrolytes, typically L/I2 in an organic solvent such as propylene carbonate. The electron generation/collection problem in this cell has been discussed analytically with the help of intensity-modulated photocurrent and photovoltage spectroscopy [314]. A particularly challenging issue has been the replacement of the liquid electrolyte with a solid charge-transport material... 

A consistent picture for dynamics of heterogeneous ET has been emerging in the last 5 years with the development of new experimental approaches. Techniques such as AC impedance, modulated and time-resolved spectroscopy, SECM, and photoelectrochemical methods have extended our knowledge of charge-transfer kinetics to a wide range of time scales. This can be exemplified by comparing impedance analysis, which is limited to k of... 

Chronocoulometry and photon polarization modulation infrared reflec-tion/absorption spectroscopy have been employed [311] to study the fusion of dimyristoylphosphatidylcholine vesicles onto an Au(lll) electrode. The fusion was controlled either by the electrode potential, or charge. Film characteristics was also potential dependent. After removing the film from the electrode surface (negative potential), phospholipid molecules remained in its close proximity, in the ad-vesicle state. Several electrochemical and nonelec-trochemical methods have been applied [312, 313] to investigate the spreading of small unilamellar vesicles onto Au(lll) electrode. Vesicles fused onto the surface at > —0.5 V (versus SSCE), to form defected bilayers in contact with the metal surface. At more negative potentials, the film was removed from the electrode surface, but it still remained in its close proximity. 

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