Surface oxidation and thermoelectric properties of indium-doped tin telluride nanowires

Abstract

The recent discovery of excellent thermoelectric properties and topological surface states in SnTe-based compounds has attracted extensive attention in various research areas. Indium doped SnTe is of particular interest because, depending on the doping level, it can either generate resonant states in the bulk valence band leading to enhanced thermoelectric properties, or induce superconductivity that coexists with topological states. Here we report on the vapor deposition of In-doped SnTe nanowires and the study of their surface oxidation and thermoelectric properties. The nanowire growth is assisted by Au catalysts, and their morphologies vary as a function of substrate position and temperature. Transmission electron microscopy characterization reveals the formation of amorphous surface in single crystalline nanowires. X-ray photoelectron spectroscopy studies suggest that the nanowire surface is composed of In 2 O 3 , SnO 2 , Te and TeO 2 which can be readily removed by argon ion sputtering. Exposure of the cleaned nanowires to atmosphere yields rapid oxidation of the surface within only one minute. Characterizations of electrical conductivity σ, thermopower S, and thermal conductivity κ were performed on the same In-doped nanowire which shows suppressed σ and κ but enhanced S yielding an improved thermoelectric figure of merit ZT than the undoped SnTe.2

Te Nanoneedles Induced Entanglement and Thermoelectric Improvement of SnSe

“…For the Te 3d region, the binding energies at ~584.0 (Te 3d3/2) and 573.5 eV (Te 3d5/2) are observed. The binding energy values of the Sn, Se, and Te agree well with the previously reported values[21,24,25], further demonstrating the successful fabrication of the Te nanoneedles/SnSe composites.…”

Thermoelectrics of Nanowires

“…The size effect on thermal transport in materials that are conventionally known as good bulk thermoelectric materials is generally weak, and the ZT enhancement in NWs compared to bulk is not evident as shown in reports for individual NWs of Bi 2 Te 3 , , InSb, PbTe, Si 0.73 Ge 0.27 , Bi 0.5 Sb 1.5 Te 3 , InSb, CsSnI 3 , SnTe, Bi/Te, and SnSe . However, the reported ZT data for NWs (Figure b) still demonstrate a trend of higher ZT values for smaller diameter NWs.…”

“…Reported thermoelectric figures of merit ( ZT ) of representative nanowires at room temperature, (a) in chronological order and (b) as a function of wire diameter. The investigated individual nanowires include Bi 0.54 Te 0.46 , CrSi 2 , Si, PbSe, Bi 2 Te 3 , , InSb, IGZO, PbTe, Si 0.73 Ge 0.27 , Bi 0.5 Sb 1.5 Te 3 , InSb, CsSnI 3 , SnTe, Bi/Te, and SnSe . The investigated nanowire arrays and composite materials include Si NW arrays, ,, Te/Bi core/shell composites, Te NW-PEDOS:PSS hybrid, Bi 2 Te 3 composites, β-Zn 4 SB 3 , Te-Bi 2 Te 3 , AgTe 2 -Bi 2 Te 3 , PbTe, La 0.9 Sr 0.1 CoO 3 , Bi 2 (Te,Se) 3 , PbTe-Ag 2 Te, Bi 2 Te 3 -graphene, Bi 2 Te 2.7 Se 0.3 alloys, Sb 2 Se 3 NW bundles, Bi 2 Te 2.5 Se 0.5 , PbTe 0.66 Se 0.33 , and (Sb,Bi) 2 Te 3 .…”

“…On the other hand, top-down approaches, which rely on lithographic methods and etching processes, are well-suited for integrating with three-dimensional (3D) systems, hierarchical assemblies, and large-scale implementation. Si NWs created by both metal-assisted chemical etching (MACE) 33 and super- 31 CrSi 2 , 38 Si, 33 PbSe, 27 Bi 2 Te 3 , 44,45 InSb, 46 IGZO, 53 PbTe, 47 Si 0.73 Ge 0.27 , 43 Bi 0.5 Sb 1.5 Te 3 , 32 InSb, 48 CsSnI 3 , 49 SnTe, 50 Bi/Te, 51 and SnSe. 52 The investigated nanowire arrays and composite materials include Si NW arrays, 35,36,39 Te/Bi core/shell composites, 54 Te NW-PEDOS:PSS hybrid, 55 Bi 2 Te 3 composites, 28 β-Zn 4 SB 3 , 56 Te-Bi 2 Te 3 , 57 AgTe 2 -Bi 2 Te 3 , 58 PbTe, 29 La 0.9 Sr 0.1 CoO 3 , 59 Bi 2 (Te,Se) 3 , 60 PbTe-Ag 2 Te, 30 Bi 2 Te 3 -graphene, 61 Bi 2 Te 2.7 Se 0.3 alloys, 62 Sb 2 Se 3 NW bundles, 63 Bi 2 Te 2.5 Se 0.5 , 64 PbTe 0.66 Se 0.33 , 65 and (Sb,Bi) 2 Te 3 .…”

Physicochemical Properties of SnTe Thin Films Dependent on Compositional Ratios

“…[41][42][43] The Te 3d 5/2 peaks were deconvoluted into three peaks: Te bound with Sn (Te 2À ) at 572.5 AE 0.2 eV, Te 0 at 573.5 AE 0.3 eV, and oxidized Te (Te 4þ ) at 576.4 AE 0.3 eV. [44][45][46] As the content of Te increased, the percentage of Sn 0 species was roughly constant while the percentage of Sn 4þ species decreased and the percentage of Sn 2þ species increased. Therefore, the overall oxidation states of Sn were reduced.…”