Some photoelectric properties of the nucleic acid bases in thin layers

The current-voltage characteristics of dark-conductivity and photoconductivity, the lux-ampere characteristics, the spectral dependence of photoconductivity and the relative quantum efficiency of vacuum deposited layers of adenine, thymine, uracil and cytosine were investigated at room temperature. The following values of photoconductivity thresholdE _th were obtained: 3·81 ±± 0·1 eV for adenine; 3·69±0·1 eV for thymine; 3·80±0·1 eV for uracil; 3·77 ± 0·1 eV for cytosine.It may be shown thatE _th is most probably the threshold value for intrinsic photoconductivity of NA bases and, consequently, corresponds to the first electron conductivity levelE _c or at leastE _c >E_th. The possible energy diagram of the NA bases is evaluated.     

Thermoluminescence of (ZnS∶CdS∶Ag∶Ni∶Co) phosphors

The doping of (ZnSCdSAgNi) phosphors with cobalt impurity results in new phosphors with thermoluminescence curves showing five distinct peaks. Four of these peaks are associated with chlorine, cadmium, cobalt and nickel impurities and have energy depths of 0·26 eV, 0·52 eV, 0·53 eV and 0·78 eV respectively. The fifth peak, appearing at high cobalt concentrations, has an energy depth of 1·09 eV and is attributed to the formation of (Co⁺⁺ - Ag^–) associates. The emitted thermoluminescence consists of two bands: one in the yellow and the other in the red spectral region. The yellow band subsumes the chlorine, cadmium and cobalt peaks and is due to recombination processes occurring through silver centres. The red band, on the other hand, includes the nickel and the (Co⁺⁺-Ag^–) peaks. The appearance of the nickel peak in the red band is explained by recombination processes at energy levels created by the nickel impurity centres.     

The density of quenched gold

A precision hydrostatic differential method for measuring small density differences of solid bodies was used to determine the activation energy of vacancy formation and migration in quenched gold. The values were found to beE _f =0·76 eV, andE _m =0·51 eV.E _f is substantially lower than the well established value 0·96 eV, whereasE _m is close to the value 0·56 eV determined by Jeannette and Machlin for oxygen-free gold.The concentration of vacancies determined from our measurement is of the same order as the absolute calorimetric determination by DeSorbo.A short communication was read at the Conference on Point Defects in Quenched Metals, ANL, June 1964.     

The dependence of the neutron temperature on the geometric parameter for water and loose diphenyl

The dependence of the neutron temperatureT _n on the geometric parameterB ² was measured by the pulse method in water and loose diphenyl. The measurements were made on a moderator poisoned by cadmium sulphate, a substance whose absorption cross-section is non 1/v.The following results were obtained: For waterT _n [eV]=–(0·00391±0·00045)B ² [cm^–2]+(0·02537±0·00035) for loose diphenyl:T _n [eV]=–(0·01014±0·00152)B ² [cm^–2]+(0·02518±0·00054).We are indebted to J. Jirou and J. Jadavan for their assistance in the measurements, the accelerator operation and electronic apparatus maintenance.     

Birefringence in YA1O3∶Nd between 2–4·7 eV

The paper presents original spectra of the birefringence of the orthorhombic YAlO₃Nd single crystal in the region from 2 to 4·7 eV, describes a reflection method of null ellipsometry which was used for the measurement of the spectra and, in conclusion, makes a comparison between the measured spectra and the values predicted from the values measured over the region of lower energies 1·1 – 2·2 eV.The authors are grateful to J. Kvapil for samples preparation.     

The electrical properties and growth conditions of CdS crystals

Large crystals of cadmium sulphide have been grown in various partial pressures of cadmium and sulphur vapour. The concentration and ionisation energy of the shallow donors in the different crystals have been determined by measuring the Hall coefficient and electrical conductivity of semiconducting samples, and by comparing the magnitudes of the drift and Hall mobilities in photoconducting (semi-insulating) samples. The variation of the donor and acceptor content can be explained in broad terms in relation to the parameters of crystal growth. Hall measurements indicate that the ionisation energy of the shallow donors is 0·021 ± 0·002eV. The drift mobility experiment suggests that two shallow traps are present with energy depths of 0·015 and 0·037 eV. The variation of Hall mobility with temperature over the range 30–300°K can be explained in terms of polar optical mode, piezoelectric and ionised impurity scattering. The best value of effective mass obtained was 0·19m.     

Transport of an excess electron in molecular solids: Effect of the dynamical self-consistency of the polarization

In a simple model, the influence of formation of the electronic polaron on the form of the electronic dispersion law in molecular systems is calculated in a way which treats the electronic polarization self-consistently with respect to the electronic motion. Corrections to the polarization energy in the Lyons model calculated using the microelectrostatic approach are found which are of the order of the experimental half-band-width (0·1 eV) in current molecular crystals.     

Relaxation during short-range-ordering in Cu-30% Zn alloy

The internal friction measured in a vacuum torsion pendulum has been used to determine the kinetics of short range ordering in an Cu-30% Zn alloy. Curves of relative internal friction (Q^–1/Q ₀ ^–1 ) against annealing time have been determined for various annealing temperatures. Average activation energy of 1·7 eV was found for the ordering process, which equals to that derived for zinc diffusion in coarse grained copper.     

On the mechanism of the induced anisotropy of magnesium ferrites in the range of higher temperatures

A simple mechanism explaining not only the magnitude but also the type of induced anisotropy on the magnesium ferrite Mg_0·78 Fe_2·22 O_4·026 in the temperature range from 400 to 500°K has been designed. The experimentally estimated values of the microscopic bond energyl _p 7×10^–16 erg of the configuration contributing to theF-type anisotropy and the activation energy _exp = 1·1 eV are in good correspondence with the valuesl _d1·6×10^–16erg and _cal = 1·1₅ eV which have been calculated theoretically.Dedicated to Professor Dr. Jaromír Bro on his sixtieth birthday.The author would like to express his thanks to Dr. S. Krupika for valuable discussions and his interest in this paper.     

Optical,photoelectric and electric properties of single-crystalline Sb2Se3

Measurements of absorption coefficient in the region of the absorption edge, of spectral distribution of photoconductivity and dependence of electrical conductivity upon temperature on Sb₂Se₃ single crystals are given. The absorption of light was proved to correspond to indirect forbidden transitions. The value of optical gapE _g ^opt =(1·11±0·02) eV forE a andE c was determined. From photoconductivity and conductivity measurements the values of the gaps areE _g ^opt =1·11 eV andE _g ^el =1·04 eV. The anisotropy of the electrical conductivity parallel and perpendicular to the cleavage plane is 2·2.     

Diffuse reflectance spectra of Pb(Zr0·60RTi0·40) O3 solid solutions doped with Fe2O3, Cr2O3 and MnO2

Measurements of diffuse reflectance spectra in the range of 400, 2500 nm were used for study of the effect of doping with iron oxide, chromium oxide and manganese oxide on the properties of polycrystalline Pb(Zr_0.60Ti_0.4) O₃ solid solution. On the basis of analysis of experimental results it is concluded that mentioned oxides in the amount of 2 at.% interact at 1000 °C with perovskite crystal lattice of studied solid solution, creating local level in its forbidden gap. The values of charge carrier excitation energy found from these levels are 2·48 eV in the case of iron oxide doping, 1·68 eV in the case of chromium oxide and 1·44 eV in the case of manganese doping.     

The effect of X-rays on ruby

The formation of colour centres was studied in ruby irradiated by X-rays containing 0·01–1·0% Cr. The absorption spectrum exhibits new bands at 450 and 380 m. It was found that the highest number of colour centres is formed at a concentration of 0·2% Cr. The nature of these centres is discussed on the basis of optical, thermoluminescent and phosphorescent measurements.     

Change of absolute thermoelectric power of gold and platinum due to lattice defects

The temperature dependence of the extra-thermoelectric power of gold and platinum after quenching or after plastic deformation was measured in the temperature range from –190°C to 20°C. It was found that dislocations raise the absolute thermoelectric power of gold, whereas vacancies reduce it. In platinum both kinds of defects reduce the absolute value of the thermoelectric power in the whole range of temperatures.Gold was quenched from different temperatures into water and the change of electrical resistivity and of thermoelectric power was simultaneously measured. The extra-thermoelectric powerS varies directly with the concentration of vacancies. Its value is given by the relationS/c=–1·08 V/(grad at. % vac.) The activation energy of the formation of lattice vacancies in gold wasE _F =(0·93±0·14) eV.The analysis of the experimental results was carried out at this institute.     

Ionic conductivity and cation selfdiffusion in NaCl crystals doped with calcium or cadmium

Measurements of the concentration dependences of dc conductivity and Na⁺ diffusion in NaCl + CaCl₂ and NaCl + CdCl₂ monocrystals have shown that the heats of association of both divalent admixtures into complexes with cation vacancies are very close (0·28±0·02 eV.) The Stasiw-Teltow model of association has been found suitable for concentrations of calcium not exceeding 0·1 mole-% within the whole temperature range of 150 to 720°C. This model gave the value of 0·284 eV for the enthalpy of association of Ca⁺⁺-complexes, the value of 0·74 eV for the enthalpy of migration of free vacancies and a negligibly low entropy of association of these complexes. The observed contribution of the complexes to selfdiffusion was in accordance with the model of association into tightly bound complexes. The contribution was, however, higher than could be expected for simple rotation of the associated vacancy round the admixture in the nearest neighbour positions.     

Coupled-static calculations of the partial and total cross sections of positron-lithium inelastic scattering

The inelastic scattering of positrons by lithium atoms has been investigated in details using a combination of the frozen-core and coupled-static approximations. The ground state of the target has been described by Walters' wave functions. The partial cross sections corresponding to 8 values of the total angular momentuml (0l7) are determined for 21 values of the incident energy lying between 0·1 and 1000 eV. Our results illustrate the stability of the iterative numerical technique employed. They demonstrate the role played by each partial wave in the total cross sections and emphasize the argument that the effect of positronium formation on the total collisional cross sections diminishes when the incident energy is larger than 30 eV.     

Thermally stimulated depolarization of a phosphate glass

Thermally stimulated depolarization (TSD) of phosphate glass of the composition 72·9% P₂O₅, 8·5% Al₂O₃, 18·6% CaO, 0·23% MnO has confirmed the existence of two types of slow relaxation. Migration polarization leads to TSD maximum near 0 °C, while the high temperature TSD maximum at 113 °C probably corresponds to space charge polarization. An analysis of the high temperature maximum shows that it is formed by a spectrum of relaxations with a single activation energy 1·0 eV, distributed over the dipole frequency factors with the most probable value ₀ 10¹⁰ sec^–1. Strong dispersion of permittivity points to the space charge polarization, though it is found that the effect is linear and independent of the sample geometry.The authors thank Dr. A.Bohun for the samples and for valuable advice.     

Plasma formation and sustainment by a multijunction grill on the CASTOR tokamak

Radiofrequency power up to 40 kW injected into the vacuum chamber of the CASTOR tokamak by a multijunction grill was used for plasma formation during the ramp-up phase of the toroidal magnetic field. When electron cyclotron resonance (ECR) appears inside the tokamak chamber for a given pumping frequency (f=1·25 GHz) a plasma with a density greater than 2×10¹⁸ m^–3 and temperatureTine=10 ÷ 40 eV is produced. The plasma is sustained at some lower value of the density during the whole RF pulse. Simultaneously, a toroidal current up to 0·2 kA is generated. The energy confinement time is estimated to be about 30 s during the ECR breakdown.It is a pleasure to acknowledge very useful discussions with Dr. R. Klíma.     

Synthesis and characterization of zinc oxide nanoparticles by laser ablation of zinc in liquid

We report formation of colloidal suspension of zinc oxide nanoparticles by pulsed laser ablation of a zinc metal target at room temperature in different liquid environment. We have used photoluminescence, atomic force microscopy and X-ray diffraction to characterize the nanoparticles. The sample ablated in deionized water showed the photoluminescence peak at 384 nm (3.23 eV), whereas peaks at 370 nm (3.35 eV) were observed for sample prepared in isopropanol. The use of water and isopropanol as a solvent yielded spherical nanoparticles of 14-20 nm while in acetone we found two types of particles, one spherical nanoparticles with sizes around 100 nm and another platelet-like structure of 1 μm in diameter and 40 nm in width. The absorption peak of samples prepared in deionized water and isopropanol are seen to be substantially blue shifted relative to that of the bulk zinc oxide due to the strong confinement effect. The technique offers an alternative for preparing the nanoparticles of active metal.     

Synthesis and properties of single crystals of nickel zinc ferrite

A method for growing single crystals of nickel zinc ferrite using PbO-PbF₂ as a flux under a gas pressure of 15 atmospheres of argon mixture is described.The magnetic properties indicate that with the addition of zinc oxideK ₁/M decreases in absolute value. TheH increases with zinc content. Theg value decreases and reaches 2·05 forx=0·8.The author wishes to thank Dr. Braginski and Dr. Krishnan for friendly cooperation and for valuable discussion, Mr. Duclos and Mrs. Enaud for performing the chemical analysis and Mr. Sanz for technical assistance in preparing the single crystals.     

X-ray photoelectron (XPS) and Auger (XAES) spectroscopy study of rhodium dispersed on carbon substrate

Photoelectron 3d_5/2 binding and Auger M₅VV kinetic energies of dispersed rhodium have been measured. For the smallest deposition of Rh the shifts 0·6 eV and -2·5 eV of 3d_5/2 and M₅VV lines respectively have been found. Electron core level energy, Auger kinetic energy and Fermi edge shifts have been interpreted by a model based on electrostatic relaxation mechanism in metal particles and initial state contribution of surface atoms. Intensity and background height analysis indicate only surface distribution of Rh.I wish to express my gratitude to Dr. Zdenk Bastl for helpful discussions.