Space Charge Limited Transport and Time of Flight Measurements in Tetracene Single Crystals: a Comparative Study

We report on a systematic study of electronic transport in tetracene single crystals by means of space charge limited current spectroscopy and time of flight measurements. Both $I$-$V$ and time of flight measurements show that the room-temperature effective hole-mobility reaches values close to $\mu \simeq 1$ cm$^2$/Vs and show that, within a range of temperatures, the mobility increases with decreasing temperature. The experimental results further allow the characterization of different aspects of the tetracene crystals. In particular, the effects of both deep and shallow traps are clearly visible and can be used to estimate their densities and characteristic energies. The results presented in this paper show that the combination of $I$-$V$ measurements and time of flight spectroscopy is very effective in characterizing several different aspects of electronic transport through organic crystals.Comment: Accepted by J. Appl. Phys.; tentatively scheduled for publication in the January 15, 2004 issue; minor revisions compared to previous cond-mat versio

Effect of Impurities on Pentacene Thin Film Growth for Field-Effect Transistors

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material at number densities from 0.001 to 0.474 to quantify the relative effects of impurity content and grain boundary structure on transport in pentacene thin-film transistors. Atomic force microscopy (AFM) and electrical measurements of top-contact pentacene thin-film transistors have been employed to directly correlate initial structure and final film structures, with the device mobility as a function of added impurity content. The results reveal a factor four decrease in mobility without significant changes in film morphology for source PnQ number fractions below ~0.008. For these low concentrations, the impurity thus directly influences transport, either as homogeneously distributed defects or by concentration at the otherwise-unchanged grain boundaries. For larger impurity concentrations, the continuing strong decrease in mobility is correlated with decreasing grain size, indicating an impurity-induced increase in the nucleation of grains during early stages of film growth.Comment: 18 pages, 4 Figures, 1 Tabl

Oscillator strength of the strongly "forbidden" Pb 6p

The "forbidden"Pb $6p^2$ 3P$_0\to 6p^2$ 3P1 line at 1278.9 nm is measured by diode laser absorption in a resistively heated hot-pipe filled with a lead vapour and argon as buffer gas. The measurements performed at a temperature of 1170 K and a lead number density of $2.4 \times10^{15}$ cm-3 yield the oscillator strength $f_{\rm F} = (4.5 \pm 1.1)\times10^{-7}$ which corresponds to a radiative transition probability $A_{\rm F} = (6.1 \pm 1.5)$ s-1. Within the error bars, the result is in agreement with theoretical data published by different authors

Measurements of sulfur compounds in CO2 by diode laser atomic absorption spectrometry

International audienc

Energy pooling to the Ba 6s6p

The energy-pooling rate coefficient for the {\rm Ba}({\rm 6s5d}\;^3{\rm D}_J)+{\rm Ba}({\rm 6s5d}\;^3{\rm D}_J) \rightarrow~{\rm Ba (6s^{2\ 1}S_0) + } ${\rm Ba (6s6p ~ ^1{\rm P}_1^0)}$ process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination line and the metastable atoms in the 6s5d $^3{\rm D}_J$ state were produced due to radiative and collisional depopulation of the laser-excited 6s6p $^3{\rm P}^0_1$ state. The measurements were performed at $^{138}{\rm Ba}$ number densities of about $4\times 10^{10}\; {\rm cm}^{-3}$ and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to the triplet metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line 791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single mode ring dye laser. The rate coefficient was found to be $k = 1\times 10^{-10}\;{\rm cm^3 \; s^{-1}}\;{\rm at}\; T = 730 \;{\rm K}$