An extension of Shockley–Read–Hall kinetics is presented for interface states at grain boundaries in silicon. The emission of majority carriers by these states is generalized to include thermionic field emission (TFE), which is shown to be important in many practical cases. Comparison is made with experimental results obtained on studies of isolated grain boundaries in silicon. One of the principal results is that energy distributions of interface states deduced from electrical characteristics of grain boundaries must be interpreted using a model which includes TFE. The importance of TFE increases with the doping concentration of the silicon N and the voltage applied across the grain boundary V and decreases with temperature. It is legitimate to neglect TFE from the interface states and consider pure thermal emission only for NV≲1016 cm−3 V at a temperature of 300 K, or NV≲1015 cm−3 V for 130 K.

Transition frequencies were determined for transitions in Ra in an atomic beam and for reference lines in Te2 molecules in a vapor cell. The absolute frequencies were calibrated against a GPS stabilized Rb-clock by means of an optical frequency comb. The 7s 2 1 S0(F = 1/2)-7s7p 1 P1(F = 3/2) transition in 225 Ra was determined to be 621 042 124(2) MHz. The measurements provide input for designing efficient and robust laser cooling of Ra atoms in preparation of a search for a permanent electric dipole moment in Ra isotopes. PACS numbers: 31.30.jp, 11.30.Er, 42.62.Fi, Radium (Ra) is the heaviest alkaline earth metal and it offers unique possibilities for measuring parity and time reversal symmetry violation. The particular atomic and nuclear [1][2][3][4][5][6][7][8] structure in Ra isotopes cause the largest enhancement for permanent electric dipole moments (EDMs) [9] in any atom. This arises from the close proximity of the 7s7p 3 P 1 and 7s6d3 D 2 states [1]. The exploitation of the enhancement from this 5 cm −1 separation requires precise knowledge of Ra atomic properties such as the absolute frequencies of transitions that are relevant for laser cooling and state manipulation (see Fig. 1). Many isotopes of Ra are available from radioactive sources such as 229 Th [10-13], or at online isotope production facilities such as ISOLDE, CERN, Switzerland [14,15].A sensitive search for EDMs requires efficient collection of the atoms in an optical trap because of the low abundance of Ra isotopes. A strategy for efficient laser cooling and trapping has been developed with the chemical homologue barium (Ba). Exploiting the strong 6s 2 1 S 0 -6s6p 1 P 1 transition [16,17] resulted in an efficiency of ∼1% for slowing and capturing Ba from an atomic beam, whereas capture efficiencies of below 10 −6 were reported for Ra when using the weak intercombination transition 7sThe optical spectrum of Ra was first studied by Rasmussen [18]. This identified Ra as an alkaline earth metal. Hyperfine splittings and isotope shifts were determined for the 7s 2 1 S 0 -7s7p 1,3 P 1 transitions by collinear laser spectroscopy [14,15] with intense Ra ion beams at ISOLDE, lifetimes of low lying states were determined in ANL, USA [9,19]; no absolute frequencies are quoted.Here we report on a laser spectroscopy measurement of the frequency of the strong 7s 2 1 S 0 -7s7p

SYNOPSISThis is the second part of a two-part study of the NH,NH,SCN cellulose solvent system. Quasielastic light scattering was used to determine the diffusion coefficients of cellulose in solution and the effective hydrodynamic radius of the dissolved molecules. Additionally, the system was studied using light microscopy to determine the minimum critical volume fraction or liquid crystal formation. Very little change was found in the diffusion coefficients with change in cellulose concentration indicating little interaction between the chains in solution. Values of 7.69 and 2.66 X 10' cmz/s were measured for samples having a degree of polymerization of 153 and 969. The value of the coefficient relating the hydrodynamic volume to the radius of gyration was found to be in the range of 0.33 to 0.53, indicating an extended coil conformation according to the Kirkwood-Riseman theory. The minimum critical volume fractions necessary for liquid crystal formation, u ; , were 0.039, 0.038, and 0.048 for the three solvent compositions studied. The values calculated for u; based on the measured persistence lengths were much larger than the predicted values, indicating strong deviation from theory or possible aggregation in the system.

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