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PbTe, is a narrow bandgap (E_g = 0.31 eV at 300 K) semiconductor material that is among the most efficient materials known for thermoelectric power generation. In this application, PbTe is valued because of its excellent thermal stability which permits power generation at operating temperatures up to 1000K. The fraction of the Carnot efficiency that is recoverable as power from a thermoelectric element is determined by its dimensionless figure-of-merit, ZT:
ZT =sTS²/k Eq. (1)
where s is the electrical conductivity of the thermoelement, S is its thermoelectric power or Seebeck coefficient, k is its thermal conductivity, and T is the mean absolute temperature. PbTe has a ZT of 0.45 at 300 K and 0.85 at 700 K.

Shrinking conductors composed of thermoelectric materials to the nanometer scale is predicted to increase S and depress k both of these effects leading, via Eq. 1, to an elevation in ZT. Motivated by these predictions, tremendous effort has been devoted to the synthesis of PbTe nanomaterials. Harman et al. reported that the ZT at 300 K could be doubled from 0.45 to 0.9 for PbTe quantum dot superlattices and PbSeTe/PbTe quantum well superlattices prepared by molecular beam epitaxy (MBE). Their success has further stimulated experimental efforts to develop methods for synthesizing PbTe-based nanomaterials that, unlike MBE, are cheap and scalable.

We have developed a method for patterning polycrystalline PbTe nanowires over wafer-scale areas on glass or silicon surfaces. This method is an adaptation of the lithographically patterned nanowire electrodeposition (LPNE) method that we have previously demonstrated for the preparation of metal nanowires on glass and silicon surfaces. In LPNE, photolithography is used to pattern a nickel nanoband electrode that is recessed into a horizontal trench that is several hundred nanometers in width. This patterned electrode is then immersed into an aqueous synthesis solution and the metal of interest is electroplated into this trench using the nickel nanoband as an electrode. Because the nanowire is formed by electrodeposition, a technique applicable to the deposition of a wide variety of materials, LPNE has tremendous versatility for the fabrication of nanowires having different compositions but we have reported mainly on the fabrication of metal nanowires in our prior work. In our papers on this subject, we provide a complete description of the synthesis of PbTe nanowires using LPNE, we disclose data for the structural and compositional characterization of these nanowires, and we present the results of electrical conductivity measurements and a simultaneous x-ray photoelectron spectroscopy (XPS) investigation carried out as an oxide surface layer is formed in ambient air.

In summary, our work supports the following conclusions:

1. The LPNE Method can be adapted to produce single phase, cubic PbTe nanowires on glass surfaces.
   
2. Growth of PbTe involves the electrodeposition of PbTe using a cyclic electrodeposition-stripping method in which lead-rich PbTe is first electrodeposited, and excess lead is then anodically stripped from the nascent nanowire. By skewing the mole ratio of Pb:Te strongly in favor of Pb (100:1), the electrodeposition of elemental Te is avoided during this process. Repeating this cyclic electrodeposition/stripping process allows near stoichiometric PbTe nanowires to be built up in 60-80 nm increments.
3. These PbTe nanowires have a rectangular cross-section with height and width dimensions that are independently adjustable, down to minimum values of 20 nm and 70 nm, respectively.
4. These nanowires are polycrystalline with a mean grain diameter of 10-20 nm.
5. "Portable" nanowire arrays, consisting of PbTe nanwires entrained in an ultra-thin photoresist layer, can be prepared by rinsing a photoresist-supported PbTe array with acetone. These arrays are suspended in the recovered wash solution and they can be transferred (e.g. onto a TEM grid) using a Pasteur pipette.
6. Wire surfaces are initially tellurium rich but oxidation in laboratory air more rapidly produces PbO₂ (1.3 nm in 24 hrs) relative to TeO₂ (0.3 nm in 24 hrs).
7. Commensurate with wire oxidation is a progressive loss in the electrical conductivity of PbTe nanowires of up to 60% for wires with a thickness of 20 nm. We hypothesize that this loss in conductivity derives from the progressive and compensative p-doping of initially n-type PbTe nanowires.