Y-Ba-Cu-oxides are deposited by MOCVD in a hot-wall reactor using the well known copper-and yttrium-Bdiketonate precursors, Cu(thd), and Y(thd),, and the novel barium precursor, Ba(hfa),-tetraglyme. This novel barium precursor is thermally stable, non-hygroscopic and highly volatile. Depositions are performed on single-crystalline (100)-oriented MgO substrates. Depositions performed at 800°C and 900°C show smooth c-axis-oriented YBa$h30,4 layers, with CuO precipitates. At 900°C also Y,BaCuO, and barium oxide crystals are present.
Preparation of RuO, from Ru04, as well as from in situ generated 'ruthenium hydroxide' or ruthenate ions, followed by calcination a t 400 O C , reproducibly affords active catalysts generally without noxious oxidation of the CdS support, whereas impregnation of RuCI3.3H20 and subsequent annealing yields poor materials; in the latter procedure the CdS is irretrievably damaged.
The basic photoelectrochemical behavior of tetragonal p‐type
α‐ZnP2
has been investigated for the first time. The photoinduced current as a function of applied voltage and the spectral distribution of the photoresponse were measured in alkaline solutions (pH 13). Photosensitivity up to 580 nm in the visible range of the spectrum has been observed. From a linear Mott‐Schottky relation, an approximate value of the flatband potential
false(VFB=−0.7±0.05 VSCEfalse)
at pH 13 for monoclinic
β‐ZnP2
has been determined. As a function of pH,
VFB
shows Nernstian behavior. For tetragonal
α‐ZnP2
,
VFB
could not be determined. The onset of the cathodic photocurrent (
≈−0.4 VSCE
at pH 13) indicates, however, a somewhat more positive
VFB
for
α‐ZnP2
. Upon illumination with visible light, hydrogen evolution from alkaline EDTA solutions containing
ZnP2
powders loaded with a catalyst is very efficient. For
α‐ZnP2
loaded with 0.5 weight percent of
RuO2
, a formal quantum efficiency of 12% is found at 470 nm.
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