MEASUREMENT OF THE HALL MOBILITY AND OF THE TIME-OF-FLIGHT MOBILITY IN LIQUID TETRAMETHYLSILANE AND NEOPENTANE
Abstract
The Hall mobility (mu)(,H) and the time of flight mobility (mu)(,TOF) have been measured in the same sample of two different liquids: tetramethylsilane (TMS) and neopentane. In the former, the results at room temperature (21(DEGREES)C) are (mu)(,H) = 187 (+OR-) 21 cm('2)/V-sec, (mu)(,TOF) = 97 (+OR-) 5 cm('2)/V-sec. The value of (mu)(,H) in TMS is somewhat uncertain; the value of (mu)(,TOF) is in good agreement with results published by others. In the latter, the measurement of (mu)(,H) and (mu)(,TOF) was carried out between -10(DEGREES)C and 160(DEGREES)C along the liquid-vapor coexistence line (in neopentane, the triple point is 256.6 K and the critical point is 433.75 K). The measured (mu)(,TOF) in neopentane is in good agreement with the results published by Freeman and coworkers. The mobility ratio r (TBOND) (mu)(,H)/(mu)(,TOF) in neopentane exhibits a remarkable temperature dependence: it is 1.8 near the triple point, it decreases linearly to a minimum of 1.4 at (TURN) 408 K and increases again to 5.8 at the critical point. The minimum in r occurs at the same temperature (density) at which the minimum of the position of the bottom of the conduction band V(,0) occurs, as determined by measurements performed by Cipollini and Holroyd in neopentane, along the liquid-vapor coexistence line. The Hall mobility (mu)(,H) is determined by scattering processes only, while the time of flight mobility (mu)(,TOF) is sensitive to both scattering and trapping processes. The coincidence between the temperature at which the minimum in V(,0) occurs and that at which r = (mu)(,H)/(mu)(,TOF) attains its minimum value and, particularly, the drastic increase in r close to the critical point, suggest the onset of electron localization in potential wells which are deep enough and wide enough to contain at least one bound state. These potential wells result from local fluctuations in V(,0) induced by density fluctuations. Such states may keep the electron localized for times short compared with the measurement time; they are consistent with the conceptual framework developed by Basak and Cohen, to explain the motion of electrons in liquid Ar.
Degree
Ph.D.
Subject Area
Radiation
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