Electric-field dependent electron mobility in anthracene single crystals

We observed the electric-field dependence of electron drift velocity in the c′ direction of anthracene single crystals at low temperature and found out that it tends to almost constant value above the electric-field of 1.8 × 10⁵ V cm^-1 at 140 K deviating from the linear proportionality to the field below this value. This result may be regarded as an experimental verification for the recent theoretical prediction by Sumi.     

Characteristic electron energy losses in germanium

The characteristic electron energy loss spectrum of germanium was studied in a transmission type experiment as a function of the changes in structure due to electron bombardment. The structure of the material was characterized by electron micrograph and diffraction techniques. The electron energy loss spectrum of germanium was studied up to 45 eV, and loss peaks were observed at 15.7 eV and 31.6 eV as well as a 6 eV carbon loss. The positions of the most intense characteristic energy loss peak at 15.7 eV and its first multiple were constant for a large variation in the lattice parameters for the individual films.     

An electron energy loss study of aluminum single crystals exposed to carbon monoxide

Aluminum single crystals of orientations {111}, {110}, and {100} were exposed at room temperature to carbon monoxide. The electron energy loss spectra of the exposed surfaces (> 20000 L) were essentially the same as those of clean surfaces. Since such spectra are very sensitive to small amounts of absorbate (e.g., 0.001 to 0.01 monolayer of oxygen), it is inferred that carbon monoxide does not adsorb on these clean low-order faces at room temperature. Similar results were obtained on polycrystalline and evaporated film samples. This finding contrasts with previous work on aluminum exposed to carbon monoxide.     

Surface morphologies of anthracene single crystals grown from vapor phase

The morphologies and lattice structures of anthracene single crystals grown from the vapor phase were investigated using optical microscopy, phase contrast microscopy, atomic force microscopy (AFM), and X-ray diffraction analysis. Common morphologies with hexagonal large planes were observed irrespective of crystal size. The observation of certain surface morphologies with a phase contrast microscopy revealed that the spiral steps originated from screw dislocations present on the (0 0 1) planes. Moreover, the center and edge of the (0 0 1) planes had large curvatures, similar to hills. Resultantly, quarter-monolayer (ML) steps were observed on the large and flat planes between both hills.     

Optical study of anthracene molecules doped in fluorene single crystals

Properties of two luminescence centers, which are observed in anthracene-doped fluorene crystal as concentration increases, have been investigated to clarify their origin. Excitation spectra and concentration dependence of absorption spectra were measured and two types of luminescence are attributed to anthracene molecule pair centers with weak and strong interaction. Dipole-dipole interactions between two anthracence molecules of various configurations are estimated and possible configuration for two types of luminescence is proposed.     

Effect of electron irradiation of ZnGeP2 single crystals on terahertz losses in a wide temperature range

Physics of the Solid State - The reflection and transmission spectra of ZnGeP2 single crystals irradiated with 4-MeV electrons have been measured in the frequency range of 5-5000 cm−1 at...     

Intersystem crossing mechanisms and single molecule fluorescence: Terrylene in anthracene crystals

Single molecule spectroscopy requires molecules with low triplet yields and/or short triplet lifetimes. The intersystem crossing (ISC) rate may be dramatically enhanced by the host matrix. Comparing the fluorescence intensity of single terrylene molecules in para-terphenyl, naphthalene, and anthracene crystals, we found a reduction of the saturation intensity by three orders of magnitude in the latter case. The fluorescence autocorrelation function indicates that the bottleneck state is the terrylene triplet. We propose a ping-pong mechanism between host and guest. This intermolecular ISC mechanism, which can open whenever the host triplet lies lower than the guest singlet, was overlooked in previous single molecule investigations.     

Track structure in dielectric and semiconductor single crystals irradiated by heavy ions with high level of inelastic energy losses

The phenomenological model of the track formation processes during a heavy ion passing through materials is discussed. This model is based on the scanning tunneling and electronic microscopy investigations of diamond single crystals and stainless steel subjected to ⁴⁰Ar, ⁸⁴Kr and ¹²⁹Xe ion irradiation with energies in the MeV region. The energy and temperature criteria when crater formation on the surface during the heavy ion irradiation takes place are introduced.     

Phase transition and triplet exciton mobility in anthracene—tetracyanobenzene charge-transfer single crystals

Triplet-Excitons in a mixed 1 : 1 anthracene—tetracyanobenzene single crystal are established by ESR-spectrocopy. These excitons (lifetime 0.5 msec) are characterized by a hopping frequency of v = 1.3 × 10⁶ K at 300K. The temperature dependence of the ESR line shape indicates a phase transition of the crystal at T_t = 205K. Above and below the phase transition the exciton mobility is nearly temperature independent.     

Space-charge-limited-trap-limited-currents in anthracene crystals

Space-charge-limited-trap-limited hole currents in anthracene crystals are interpreted in terms of a trap distribution which starts at a discrete trap level at 0·6–0·8 eV and in which the trap density falls off exponentially with energy relative to this level. It is suggested that exponential hole trap distributions are produced by physical perturbations of the crystal lattice introduced by the same impurities which give rise to the discrete hole trap level at 0·6–0·8 eV (revealed by thermally stimulated current studies). The results indicate that a perturbed molecule is introduced for every 10,000 impurity molecules and the total number of perturbed molecules is constant at 10¹⁷ m^?3 for melt-grown and vapor-grown crystals. The parameter kT_c varies from crystal to crystal, indicating that the relative contributions of highly perturbed and slightly perturbed molecules is influenced by crystal growth conditions.     

Optical properties of solid benzene derived from electron energy losses

From energy loss measurements of fast electrons on polycrystalline benzene films the energy loss function Im(?1/?) and the dielectric constants ?=?₁+i?₂ are calculated up to 40 eV. The results are discussed in terms of ?₂ and are compared with the corresponding ?₂-spectrum of benzene vapour.     

Impedance and electron diffraction studies on single crystals of BINIVOX

Single crystals of the nominal composition Bi₂V_0.9Ni_0.1O_5.35 were prepared. They were studied by TGA/DTA, impedance spectroscopy and electron diffraction. The impedance of the crystals with Pt electrodes was measured in two directions: parallel and perpendicular to the layers of the intergrowth structure in the frequency range 10⁻²−10⁷ Hz at temperatures between 300 and 940 K. Arrhenius type plots for both directions show two linear regions with different activation energies. In the low temperature region the conductivity in the direction parallel to the layers was by a factor of about 1000 larger than in the perpendicular direction. In the high temperature region the ratio of conductivities was about 100. A time dependence of the conductivity in the perpendicular direction was observed during heating and cooling in limited temperature ranges. The electron diffraction experiments gave evidence that the superlattice spots present in the diffraction patterns at low temperature, disappear reversibly at temperatures higher than 650 K. The transition temperatures observed in the DTA and in the electron diffraction experiments correspond to the temperature of changes of the activation energy. An order-disorder transition of oxygen ions is considered to be responsible for this phenomenon. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

FMR linewidth and eddy-current losses in Ag-doped CdCr2Se4 single crystals

We report FMR linewidth data on Ag-doped CdCr₂Se₄ single crystals, with 0.1, 0.75 and 5.4% of Ag doping, in the range 70 K < T < 170 K. The contribution of eddy-current losses to the linewidth is analyzed for samples of spherical and slab shapes. Together with two-magnon scattering due to surface and volume pits, these losses explain the observed linewidths. The microwave conductivities obtained are consistent with the model for conduction and the results for n-type CdCr₂Se₄ and EuO.     

Synchrotron reflectivity spectrum, characteristic electron losses, and electronic structure of TlCl crystals

Spectra of two complete sets of TlCl fundamental optical functions are obtained in the energy range 0–25 eV using experimental reflectivity and characteristic electron loss spectra. The ?₂ and-Im?^?1 spectra are decomposed into components, and their main features are determined. The bands, ?₂, and the localization of transitions in the Brillouin zone are calculated. The experimental and theoretical transitions are compared with theoretical data on the electronic structure of a TlCl crystal.     

Anisotropy of the excitation probability of electron energy losses in silicon

The elastic and inelastic intensity (17 eV volume plasma loss) of electrons (50 keV) having transmitted a monocrystal of silicon are registered. The elastic intensity (I_e1) changes rapidly if the crystal is tilted, the inelastic intensity (I_ine1) changes similarly. The quotient Q = I_ine1/I_e1 varies in strong correlation with both intensities which is unexpected.     

Low energy ion reflection from metal single crystals

Energy and angular distributions of ions reflected from metal single crystals have been computed. The neutralisation process is involved in the computing model. The result indicates a strong dependence on the surface trajectories of the reflected particles.     

Plasma losses of electron energy and secondary electrons of discrete energies in aluminum

Discrete energy' loss is examined for electrons of energy 30–116 V. The losses due to excitation of three types of plasma wave are found; these plasmons have energies of 15.5, 9.5, and 7 eV. The energy distribution curves for the secondary electrons contain groups with discrete energies, which in aluminum coincide with the plasma energies, and so arise by decomposition of plasmons.     

The kinetics of the sensitized flourescence of naphthalene single crystals doped with 2-methylnaphthalene and anthracene

The kinetics of the sensitized flourescence in naphthalene crystals doped with 2-methylnaphthalene (2-MN) and anthracene (A) was studied as a function of the temperature. These experiments yield singlet exciton diffusion constants of (2 ± 1) × 10^-4cm²s^-1 at 4.2 K and roughly 10^-5 cm² s^-1 at 300 K. The exciton trapping radii can be estimated to be of the order of 60 Å for A and 10 Å for 2-MN. At temperatures below 40 K a partially coherent exciton motion can be inferred, above 40 K the exciton motion appears to be purely incoherent.