Absorption and reflection spectra of β-Ga2O3 are measured with polarized light in the wavelength region near its absorption edge. The crystals of β-Ga2O3 are grown by using a Ga/HCl/O2/Ar vapor reaction system. The platelike crystals of β-Ga2O3 have (100), (010), and (001) surfaces, and the major surface is (100). The energies of the absorption edge are observed to be 4.90 eV for E//b, 4.54 eV for E//c, and 4.56 eV for E⊥b&c at room temperature. The energies for E//b and for E//c at 77 K are larger than those at room temperature by 40 meV and 220 meV, respectively. Reflection minima are observed at 5.06 eV and 5.30 eV for E//b, and at 4.63 eV and 5.30 eV for E//c at room temperature.
Elevating the charging voltage of lithium-ion batteries with a
LiCoO2
cathode is investigated to develop them toward high capacity and energy density. Three countermeasures are found to be essential to overcome side reactions with subsequent cycle degradations caused by higher cathode potential:
(i)
limiting the charging cut-off potential below
4.5V
vs
Li∕Li+
for the
LiCoO2
cathode,
(ii)
modification of
LiCoO2
particles with
Zr
element, and
(iii)
controlling the ratio of ethylene carbonate in electrolyte, which is found to be a major cause of cycle degradation in an elevated charging potential condition. It is suggested that ethylene carbonate is oxidized and dissolves cobalt on the surface of the
LiCoO2
cathode, degrading cycle performance especially at high potentials. Raising the charging voltage up to 4.4 from
4.2V
for a
650mAh
class test cell demonstrates 10% higher cell capacity with 20% higher
LiCoO2
capacity of
190mAhnormalg−1
and practical cycle performance up to 500 cycles.
The photoluminescence and optical absorption properties of Zn-doped GaS crystals prepared by the iodine vapor transport method are reported. Undoped GaS crystals are also used for comparison. Zn substituted for a Ga site acts as an acceptor having a deep energy level and forms a complex with the iodine coactivator, which can be the luminescence center. When increasing the charged amount of Zn, the near-blue emission band of 2.47 eV at 97 K becomes dominant, while the 2.17-eV emission band due to the Ga vacancies, which is dominant in the undoped crystals, gradually vanishes because of the reduction of the Ga vacancies. It is thus described that Zn is a promising dopant in GaS for near-blue-light-emitting devices.
Three lifetime components, one of which is extremely long (25±2 ns), have been observed in experimental studies of positron annihilation in porous silicon, made by anodization in hydrofluoric acid. The Doppler-broadened spectrum of the porous silicon is sharp compared with that of crystal silicon and becomes even narrower in an applied magnetic field. The positronium yield in the porous silicon therefore is concluded from the long lifetime, narrow Doppler spectrum and its narrowing in a magnetic field. The porous structure is the cause of positronium formation.
Porous silicons (PSs) were prepared from a lightly doped (boron; 7
× 1014/cm3) crystal silicon (c-Si)
wafer
by anodization in an aqueous hydrofluoric acid (HF) solution of
different concentrations (25−55%). The
porosity of these PSs was examined by nitrogen adsorption at 77 K.
The relationship between the pore
structure and the HF concentration upon anodization was examined.
All the PSs investigated showed the
type IV isotherm with a type H2 desorption hysteresis, indicating
mesoporosity. The pore size distribution
was derived from nitrogen adsorption isotherms with the BJH method.
The total pore volume of the PSs
decreased gradually with increasing HF concentration, but the specific
surface area increased with
concentration above 37 wt %. The pore size distribution varied
with the HF concentration. The profile
of the distribution became sharper and shifted to a smaller size with
the increase in the HF concentration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.