Multiple trap and release models

Several models can explain the carrier transport in organic semiconductors. However, none of them can be independently employed to explain the carrier transport phenomena and the mechanism at the same time. Among the theoretical models, the most often used models are the band transport model (Warta and Karl, 1985 Pemstich et al., 2008 Karl et al., 1991), polaron transport model (Holstein, 1959 Emin and Holstein, 1969 Marcus, 1960), hopping transport model (Vissenberg and Matters, 1998), and multiple trapping and release model (Horowitz et al., 1995 Le Comber and Spear, 1970). 

At a phenomenological level, the effect of shallow traps on the channel conductivity can be described by the multiple trap and release (MTR) model [27,77]. According to this model, which helps to illustrate the distinction between intrinsic ... 

In the context of the multiple trapping and release (MTR) model, the decrease in transistor current upon introduction of vapor results from an increase in the density of traps due to the electrostatic properties of the analyte molecules, which introduce additional trap states in the material. As a result, the ratio of mobile charges to total charges decreases, causing a decrease in the measured mobility. Physically, the analyte molecule acts as an electrostatic... 

Steinberg et al. (1987) studied the persistence of 1,2-dibromoethane (EDB) in soils and found that low amounts of the organic were released with time, particularly if EDB had not been freshly added to the soil (Fig. 6.3). They suggested that the slow release rate was due to EDB being trapped in soil micropores where release is influenced by extreme tortuosity and/or steric restrictions. It was estimated that based on a radial diffusion model, 23 and 31 years would be required for a 50% equilibrium in EDB release to occur from two Connecticut soils. The previous studies point out that while sorption of pesticides is usually rapid and often reversible in the laboratory, extraction from field soils is extremely slow and often requires multiple extractions or even chemical dissolution of the soil matrix. 

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