Editor's Pick in RSI: Pawan and Maheswar's shadow mask technique to measure thin film Seebe

Organics, hybrid (inorganic-organic), PLD, MBE, sputtering, evaporation - you name it! No matter how you make your films, we can measure the transport properties including Seebeck, four-probe electrical conductivity and Hall to characterize your film! Pawan and Maheswar calibrated the technique with PEDOT:PSS as well as Nickel and we are now routinely using this in our lab for measurements on organic, hybrid, semiconducting films with <1% error bars! Anas and Wu Jing are now working on the AC version of this technique - should be greatly useful for smaller size samples... Congratulations folks!

Yunshan's paper on Low thermal conductivity in Single Crystalline Porous Silicon Nanowires publi

We measure the porosity and thermal conductivity of electrolessly-etched single-crystalline silicon nanowires by means of an electron-beam heating technique. Upon irradiating the nanowire with a focused electron beam, the power absorbed by the nanowire scales with the cross-sectional area, thus allowing us to ascertain the material porosity. Such porous silicon nanowires exhibit extremely low thermal conductivity (as low as 0.33 W/m-K at 300K for 43% porosity), even lower than that of amorphous silicon.

See the paper here!

Dimensionality and Thermoelectrics in 2D MoS2: Hong Kuan et. al. in JAP, 121, 204303 (2017)

It has been an experimental challenge to show that electronic confinement is actually better for thermoelectrics. In our work published in Physical Review B (Jan 2017), we showed that high powerfactors are indeed possible in semiconducting 2D MoS2. In that work, we didn't analyze in detail what the exact benefits of 2D over 3D are.

In this work, Hong Kuan presents that two-dimensional (2D) bilayer molybdenum disulfide (MoS2) does indeed exhibit an enhanced Seebeck coefficient over its three-dimensional (3D) counterpart arising from dimensionality confinement. In this work, he extensively studies the Seebeck coefficient, S, the electrical conductivity, σ, and the thermoelectric powerfactor, S2σ of 2D monolayer and bilayer MoS2 using theoretical Boltzmann Transport Equation calculations and compares the results to well-characterized experimental data. We concluded that dimensional confinement indeed gives a Seebeck coefficient by up to ∼50% larger in 2D bilayer MoS2 over 3D MoS2 under similar doping concentrations because of the discretization of density of states. We also consider electrical conductivity with various energy-dependent scattering rates considering charged-impurities and acoustic phonon mediated scattering, and comment on a theoretical comparison of the powerfactor to the best-case scenario for 3D MoS2. More details can be found here.

Hopefully in the future, we can measure highly doped bulk (3D) MoS2 samples that can corroborate our estimations...