A thin film of a type II Ge clathrate epitaxially grown on a Ge substrate

Abstract

A thin film of a type II Ge clathrate, Na x Ge 136 , was epitaxially grown on a (111) substrate of Ge with a diamond structure (α-Ge). A Zintl phase NaGe film was synthesized in advance by a reaction of the substrate surface with Na vapor under an Ar atmosphere, and was highly oriented such that the NaGe(100) planes were parallel to the Ge(111) surface. The NaGe film was transformed to the Na x Ge 136 film by heat treatment under dynamic vacuum. XRD measurements demonstrated that the prepared film consisting of twin crystals with a (111) twin plane was epitaxially grown with the <111> direction normal to the substrate surface. It was also suggested that the lattice mismatch between Na x Ge 136 and the Ge substrate is relaxed by a buffer layer of α-Ge having a triple-period superlattice. The electrical resistivity of the Na x Ge 136 film was estimated from the I-V measurements to be in the order of 10 1 -10 2 Ω m. ExperimentalFrequently, type II clathrates are synthesized from Zintl alloys of alkali elements and Si or Ge. 1,3,12,16,20,21 Fig. 1(b) shows 5630

Reactivity and Controlled Redox Reactions of Salt‐like Intermetallic Compounds in Imidazolium‐Based Ionic Liquids

“…This value is consistent with the composition deduced from Rietveld refinement, and conclusively only slightly smaller than the one observed for Na 23.0(5) Ge 136 ( a =15.4412(7) Å), which was obtained only recently by an electrochemical oxidation at 280 °C [17] . As well, the value is close to other Na‐rich compositions reported for that phase [26–29] . Remarkably, the temperature of 340 °C found to be optimal for the yield of Na 24– δ Ge 136 is somewhat lower than the temperature range for a maximal yield of Na 24– δ Ge 136 by rapid thermal degradation of bulk samples of Na 4 Ge 4 at dynamic vacuum conditions (350 °C–380 °C) [26,30] .…”

Experimental and Computational Study of the Lithiation of Ba8AlyGe46–y Based Type I Germanium Clathrates

“…A similar observation was made in epitaxially grown Ge clathrate, where only the Ge oxide signals were seen in the Ge 2p XPS spectrum taken from the surface. 50 The high-resolution XPS profile for Al 2p (Figure S2b) showed a single peak at 75.44 and 75.07 eV for BM-Al16 and HG-Al16, respectively. These binding energies are in the range for aluminum oxide.…”

An Electrochemical Approach toward the Metastable Type II Clathrate Germanium Allotrope

“…Thermal degradation of epitaxially grown Na 4 Ge 4 at suitably low temperature has provided access only to thin films of that phase. 44 Higher temperatures and rapid conversion applied to prepare bulk products favored the formation of the more temperature-stable Na 4 Ge 13 , which, however, rapidly degraded to α-Ge rather than to Na 24−δ Ge 136 . 42 On the other hand, although gas–solid oxidation of Na 12 Ge 17 at 280 °C may lead to small amounts of Na 24−δ Ge 136 after short reaction times, 43 the method does not provide sufficient control of the redox potential to hinder Na depletion of the clathrate during bulk conversion.…”

“…However, so far Na 24−δ Ge 136 has never been conserved as the main product. Thermal degradation of epitaxially grown Na 4 Ge 4 at suitably low temperature has provided access only to thin films of that phase . Higher temperatures and rapid conversion applied to prepare bulk products favored the formation of the more temperature-stable Na 4 Ge 13 , which, however, rapidly degraded to α-Ge rather than to Na 24−δ Ge 136 .…”