A High-Throughput Screening System for Thermoelectric Material Exploration Based on a Combinatorial Film Approach

Abstract

In conjugated organic molecules, the difference between the HOMO and LUMO Kohn-Sham eigenvalues is significantly smaller than the transport gap measured experimentally. We discuss here, within a local-orbital formulation of DFT, how this problem can be corrected using appropriate hybrid potentials, that add a fraction of Hartree-Fock exchange interaction in the DFT calculation. We illustrate this approach presenting calculations for two simple systems: H 2 and C 6 H 6 ; then, we discuss how to implement this hybrid approach in a general local-orbital calculation, adjusting the hybrid contribution to yield the correct experimental HOMO/LUMO energy gap for the molecule. We also consider the case of an organic molecule on a metal and analyze the effect of the molecule-metal interaction on the organic energy gap. In particular, we discuss how to introduce in this hybrid-potential scheme the effect of the image potential, and present results for the organic molecules PTCDA, TTF, benzene and pentacene on the metal surfaces Au(111), Ag(111) and Cu(111).

Probing thermopower on the microscale

“…Basically, many works employed constructional variants of known principles, using different probe designs or sensor concepts for mapping of transport properties; applied to different material systems while sometimes constructional adapted to either thin film 27–31 or bulk 24, 32, 33 samples and thus differently exposed to specific measurement errors. On the other hand several works addressed completely new spatially resolving approaches, which were inspired by classic bulk or thin film measurement techniques and partly enabled by new developments on miniaturised electronic drives and the availability of suitable commercial sensors or components thereof.…”

Fulfilling the promise of the materials genome initiative with high-throughput experimental methodologies

“…Further, high-throughput measurements of thermal effusivity, from which thermal conductivity can be derived, have also been carried out, using either time domain 54 or frequency domain thermoreflectance. 55 Thus, ZT can be obtained through HTE techniques; however, the power factor, equal to S 2 r, is also a suitable figure of merit and can be obtained more readily because it does not require measuring thermal conductivity. Figure 2, illustrating research performed on the Ca 3 Co 4 O 9 system, 56 shows the compositions on the library film that exhibit the highest power factors.…”

“…HTE approaches have been applied in the search for new thermoelectric materials by diffusion annealing of bulk materials, 57 unidirectional solidification, 58 and the use of compositionally graded thin films. 51,53,55,59 Thus far, only a limited number of pseudo-binary and -ternary thermoelectric systems have been investigated using HTE: (Zn,Al)O, 51 Ca 3 Co 4 O 9 , 56 Co-Ce-Sn, 55 PbTe Energy storage materials such as in Li ion batteries represent another opportunity for the HTE approach. The exponential growth of computer processing power, combined with the laws of physics expressed through quantum mechanics, has made it possible to design new materials from first principle physics using supercomputers.…”

Applications of high throughput (combinatorial) methodologies to electronic, magnetic, optical, and energy-related materials

“…The Sr and La substituted Ca 3 Co 4 O 9 system, (Ca 1ÀxÀy Sr x La y ) 3 Co 4 O 9 , where x varied continuously between 0 and approximately 0.35, has also been studied combinatorially. 229,230 PLD was used to deposit the ternary film library, and a four point screening probe, with one heated leg, Fig. 58, was used to measure both the Seebeck coefficient and the electrical resistivity.…”

“…230 In this case, thermal effusivity, b, equal to (jcq) 1/2 (where j is the thermal conductivity, c is the specific heat, and q is the density), was measured on a metal coated oxide film, with a ten micrometer spot size. The authors were able to obtain a thermal effusivity calibration curve using various bulk samples, i.e., SiO 2 , SrTiO 3 , LaAlO 3 , Al 2 O 3 , and Si.…”