Test of the thermal equilibration model for persistent photoconductivity in doping-modulated amorphous silicon.
The persistent photoconductivity effect in doping modulated amorphous silicon is compared to the light-induced conductivity changes in compensated amorphous silicon. The recent proposal that the defect structure of doped amorphous silicon is in metastable thermal equilibrium is able to account for the metastable excess conductivity in both systems, and for the several orders of magnitude difference in exposure times needed.
Influence of Light-Soaking in Undoped Polycrystalline Silicon Films from SiCl4/H2
The stability of pc-Si films under long-time illumination was studied. The films were fabricated at low temperature of 250degC by plasma-enhanced chemical vapor deposition technology from SiCl4 /H2. The light soaking for 720 min in vacuum was carried out using white light of an intensity of 100 mW/cm2. The light-induced effects were monitored by measuring the changes in the photoconductivity and dark conductivity. The experimental results indicate that light-soaking degradation phenomenon doesn't exit in the pc-Si films, which almost appears in all a-Si films. During long-term light irradiation, the photoconductivity is increasing all along until saturation. The phenomenon is similar to the persistent photoconductivity effect observed in the a-Ge films. Furthermore, the light-induced changes of conductivity depend on hydrogen dilution ratio. The persistent photoconductivity effect appeared in pc-Si films maybe relate to the material microstructure. Comparing with amorphous silicon films, pc-Si films have high crystallinity. Besides, we think chlorine element plays a important role
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.