Optical absorption properties of NaxSi136 clathrate studied by diffuse reflection spectroscopy

Thin film of guest-free type-II silicon clathrate on Si(111) wafer

“…1(c) shows the Raman spectrum of the film in region A. The spectrum was assigned as being from NaxSi136 by comparing the spectra of Na2.5Si136, Na6.1Si136, and Na13Si136 powders [22] shown in the top panel. The 520 cm -1 peak from the Si wafer was clearly observed.…”

“…The guest-free type-II Si clathrate (Si136) and Ge clathrate (Ge136) have been obtained experimentally [4,[7][8][9][10]18]. However, there has been no report on their practical application to optoelectronic devices despite many studies on the type-II clathrates of Si [4,[7][8][9][10][19][20][21][22][23][24], Ge [18], and…”

High-Pressure Melting Curve of Zintl Sodium Silicide Na4Si4 by In Situ Electrical Measurements

“…[5][6][7][8][9][10][11][12][13] NaxSi46 (x ≤ 8) and NaxSi136 (x ≤ 24) (type-I and type-II clathrates, respectively) consisting of Si cages encapsulating Na have been reported from Na4Si4 decomposition. [14][15][16][17] Empty Si46 and Si136 frameworks also provide tunable band gap for thermoelectrics and photovoltaics with Si136 exhibiting a quasi-direct bandgap of ~2 eV. 15,18 Recently Na4Si4 has been used as precursor to design a new high-pressure synthetic route to the narrow-bandgap silicon allotrope Si-III.…”

Thin-film formation of Si clathrates on Si wafers

“…The latter property is important for applications in thermoelectric devices. On the other hand, clathrates without guest atoms, known as guest-free clathrates, exhibit semiconductor properties [12][13][14][15][16][17][18][19]. For type II, guest-free Si 136 and Ge 136 clathrates have been experimentally obtained, and the reported band-gap energy of Si 136 is in the visible region (~1.8 eV) [13].…”

“…For type II, guest-free Si 136 and Ge 136 clathrates have been experimentally obtained, and the reported band-gap energy of Si 136 is in the visible region (~1.8 eV) [13]. In addition, semiconducting properties of clathrate materials are also investigated using Na x Si 136 with a reduction in concentrations x of Na guest atoms [17,18]. Such a visible band gap of Si-related materials has attracted the interest of many material scientists, especially those researching band-gap engineering for solar cells [15].…”