S. Maruno

Dextran-magnetite complex: conformation of dextran chains and stability of solution.

Three kinds of dextran-magnetite (DM) complexes were prepared using alkali-treated dextrans with molecular weights of 1900, 4200 and 9600, respectively. The number of dextrans binding to a magnetite core was determined. The number was proportional to the area of core surface and the area occupied by a dextran was 2.5 nm2 for molecular weight of 1900, 2.8 for 4200 and 3.8 for 9600. The binding of dextrans to core may be conditioned by the conformation of dextran chains in water (possibly by the steric hindrance between dextrans covering core). Stability of the DM solution was examined at 80 °C. Aggregation and/or precipitation of DM particles were observed within two weeks. The stability of DM solution was found to increase with increasing molecular weight of dextran. The dissociation of dextran from the core may cause the aggregation and subsequent precipitation of DM particles (the dissociation constant at 20 °C, 3.7 x 10 -6 for a molecular weight of 1900 and 5.4 x 107 for 9600).

Compositional dependence of the photoinduced surface deposition of metallic silver in AgAsS glasses

Abstract Photoinduced surface deposition (PSD) of metallic Ag for the Ag x As 60− x S 40 system has been quantitatively studied using bulk glasses with x = 35, 37.5, 40, 42.5, and 45 to determine the compositional dependence of the PSD phenomenon in the AgAsS system. The glasses were found to be homogeneous in the range 40 ≤ x ≤ 45 but phase-separated at 35 ≤ x ≤ 37.5 based upon compositional trends of physical properties such as Vickers hardness. The minimum Ag content for the appearance of the PSD phenomenon was evaluated as 38 at% in the AgAsS system by taking phase separation into consideration. The PSD properties of the homogeneous glasses suggested that the photosensitivity (amount of the photodeposited Ag) and the mean radius of the Ag particles increase with an increase in the Ag content but the number of the Ag particles decreases markedly. The origin of this compositional dependence can be accounted for by the combined effects of diffusivity and insolubility of Ag + ions in the Ag-rich glasses. This idea can also explain the temperature dependence of the PSD properties.

Photoelectro-ionic processes in photoinduced surface deposition of metallic silver on a chalcogenide glass

Abstract To understand the mechanism of Ag+ migration in the phenomenon of photoinduced surface deposition (PSD) of metallic silver, the photoelectro-ionic properties of glasses showing the PSD phenomenon have been studied using Ag-rich AgAsS glasses. From the Dember and photovoltaic effects of the glasses, it is suggested that the glasses are p-type semiconductors and that the photoexcited electrons can be trapped by the Ag particles deposited by the PSD phenomenon. The depth profile of the Ag concentration after photodeposition was examined by electron-probe microanalysis to determine the consumption of Ag at the illuminated surface. The profile was found to be almost constant from the illuminated surface to the deep interior of the glass, suggesting that Ag+ ions deeper than 1 μm can migrate in counterflow to the hole motion. Accordingly, Ag− migration in the PSD phenomenon can be accounted for both by the Coulomb force induced by the trapped electrons and coupled ion-hole motions deep inside the glass.

Optical and electrical properties of amorphous Cu-rich CuGeS films: Photoinduced and thermally induced phenomena

Photoinduced and thermally induced phenomena in Cu-rich CuGeS amorphous alloys were examined. (Ge0.3S0.7)100-xCux (0 ≤ x ≤ 65) films were prepared by co-evaporation of Ge30S70 glass and metallic Cu. Amorphous, homogeneous films were obtained up to Cu contents of 62 at.%. Photoinduced and thermal bleaching of the optical absorption were observed in the composition range 0 ≤ x < 40. Both types of bleaching decrease with increasing Cu content and become negligible at around 40 at.%. The photoinduced surface deposition (PSD) of metal phenomenon was not observed even for the Cu-rich film of x = 62. Optical and electrical properties of the films were also examined as a function of Cu content and compared with the data for amorphous (Ge0.3S0.7)100-xAgx (0 ≤ x ≤ 67) films. A difference between the Cu and Ag systems is noticeable at metal contents above 25 at.%. It was found that the Cu-rich films did not exhibit ionic conduction of Cu. The absence of the PSD phenomenon in the Cu-rich films can be accounted for by this lack of ionic conduction of Cu.

De Haas-van Alphen effect in ytterbium and uranium compounds

Abstract We have measured the de Haas-van Alphen (dHvA) effects of YbSn 3 , YbZn 11 and UGa 2 in the 4 He temperature range up to 15 T. The results for YbSn 3 show that the dHvA frequencies range from 60 to 3000 T and the cyclotron masses from 0.13 m 0 to 0.44 m 0 , where m 0 is the free electron mass. For YbZn 11 the dHvA frequencies range from 200 to 11 000 T and the cyclotron masses are nearly the same as those of YbSn 3 . These results indicate that YbSn 3 is a compensated metal and Yb ions in YbSn 3 and YbZn 11 are divalent. The dHvA frequencies of UGa 2 range from 20 to 1300 T. The observed cyclotron masses range from 0.3 m 0 to 3.3 m 0 , which are larger than those of YbSn 3 and YbZn 11 by a factor of ten. Field dependence of the dHvA frequency is observed in the lowest frequency oscillations in UGa 2 . These results indicate that the 5 f electrons in UGa 2 hybridize appreciably with the conduction electrons.

Photoinduced surface deposition of metallic silver in AgAsS glasses: effect of addition of other elements

Abstract The effect of the addition of several elements (Cu, Au, Tl, and Se) on the phenomenon of photoinduced surface deposition (PSD) of metallic Ag has been investigated using an Ag 45 As 15 S 40 bulk glass as the host sample to examine enhancement of the PSD effect, especially the formation of Ag nuclei in the PSD process. The addition of a small amount of Au (between 0.1 and 0.5 wt%, and between 0.037 and 0.185 at.%) was found to increase the nucleus density by at least two orders of magnitude. A latent image consisting of a large number of Ag nuclei has been successfully obtained using a sample with 0.5 wt% Au. We suggest that the incorporated Au atoms form Au clusters in the AgAsS network structure of the host glass, and that the Au clusters can enhance the formation of Ag nuclei. On the other hand, the addition of Cu and Se had a negative effect on the PSD phenomenon and no change was observed on the addition of Tl.

De Haas-van Alphen effect in LuAl3

We have measured the de Haas-van Alphen (dHvA) effect in LuAl3 at temperatures between 1.3 K and 4.2 K in magnetic fields up to 13 T. Observed frequencies range from 400 T to 23 kT. The highest one corresponds to a cyclotron orbit with an area equal to a square face of the Brillouin zone. The angular dependence of the frequencies suggests that the Fermi surfaces are composed of a nearly spherical closed sheet and multiple connected open sheet. The observed cyclotron effective masses for the closed Fermi surface are about 0.7 and those for open Fermi surface range from 0.3 to 1 in units of the free electron mass. A band structure calculation was carried out by a full potential linearized APW method. The gross feature of the observed results was explained by the calculation

EFFECT OF ADDITION OF AU ON THE PHYSICAL, ELECTRICAL AND OPTICAL PROPERTIES OF BULK GLASSY AS2S3

Bulk glasses in the (As0.4S0.6)100−xAux system have been prepared by melt‐quenching in air. Homogeneous glasses were limited in composition up to 0.5 at. % Au and precipitation of pure Au particles was observed above 0.5 at. %. The physical properties have been studied and compared with those of Ag‐doped bulk glasses. The compositional trends of the density, Vickers hardness, and glass‐transition temperature were found to be significantly different between the Au and Ag systems. The optical gap and activation energy of the Au‐doped glasses were less than those of the Ag‐doped glasses with the same dopant concentration. The Au atoms incorporated into As2S3 glass are suggested to be located in and/or between the As–S network and behave as neutral atoms or form some weak bond with surrounding S atoms, in contrast to Ag atoms that break up the network through the formation of Ag—S ionic bonds. An increase in the randomness of the As–S network structure with the addition of Au may mainly affect the electronic ...

Magnetic properties and de Haas-van Alphen effect of GdGa2

Abstract Thermal, magnetic, and transport properties of single-crystalline GdGa2 were investigated. We have observed an antiferromagnetic transition at TN = 23.6 K and a second magnetic phase transition at Tt = 5 K. We have also measured the de Haas-van Alphen effect and found that the Fermi surface of GdGa2 is very similar to that of LaGa2.

De Haas-van Alphen effect and magnetic properties of antiferromagnetic SmGa2 and PrGa2

Abstract We have measured the de Haas-van Alphen effect up to 15T on SmGa 2 and PrGa 2 . It was found that angular dependances of low frequency branches for both compounds are very similar to that of LaGa 2 while high frequency branches in SmGa 2 are completely different from that of LaGa 2 . Magnetization has also measured up to 28T at 1.8K on SmGa 2 and PrGa 2 . The metamagnetic phase transitions were observed for field H //the c-axis for SmGa2 and H //the a-axis for PrGa 2 . The magnetic moment at 27T is about 85% of the gJ values for Sm 3+ ion whereas that of PrGa 2 reaches nearly the value of Pr 3+ ion at about 3T.