As part of the UMass Summer ENGineering Institute (SENGI) for high school students, NETlab-ers Meenakshi, Arnab, and Prof. Aksamija taught a workshop on the principles of thermoelectric energy conversion. We all had loads of fun!
Our recent collaborative work with the Salehi-Khojin and Hersam groups at U. Illinois Chicago and Northwester, respectively, has been published in the Wiley journal “Small”. The article, titled “Direct Growth of High Mobility and Low-Noise Lateral MoS2–Graphene Heterostructure Electronics”, details our progress on the electronic properties of graphene/MoS2 heterojuctions for nanoelectronic device applications.
Congratulations to NETlab member and doctoral student Arnab Majee on his nomination for “Best Poster” award at the 2017 MRS Spring Meeting in Phoenix. Arnab presented his poster on ” Dynamical Thermal Conductivity in Single-Crystalline Graphene Ribbons” in the Nanoscale Heat Transfer session at MRS.
here is a link to the abstract
The paper “Interface Thermal Conductance of van der Waals Monolayers on Amorphous Substrates” with NETlab alum Ela Correa and Cameron Foss has been accepted for publication in IOP’s journal Nanotechnology (IF=3.5). In it, we discuss our model for interface thermal conductance (ITC) between 2-dimensional materials graphene and MoS2 and amorphous SiO2 substrates. We discover that the flexural acoustic branch in graphene plays a significant role in ITC, but gets modified by the van der Waals interaction with the substrate. The findings will have an impact on heat dissipation in 2-d nanoelectronics. The accepted article can be accessed via this DOI link: https://doi.org/10.1088/1361-6528/aa5e3d
Interface thermal conductance between a monolayer and amorphous SiO2 substrate for graphene as a function of temperature T (a) and with relation to the spring coupling constant K_a dependence at T=300 K (b). Similarly for MoS_2 as a function of temperature T (c) and as a function of coupling constant K_a at room temperature (d).
As dimensions of nanoelectronic devices become smaller, CPU hot spots become increasingly more difficult to manage. Applying mechanical strain in nanostructures provides an additional tuning mechanism for both electronic band structures and phonon dispersions that is independent of other methods such as alloying and dimensional confinement. By breaking crystal symmetry, strain increases anisotropy.
We present thermal conductivity calculations, performed in thin Si and Ge strained films, using first principles calculations of vibrational frequencies under biaxial strain, along with a phonon Boltzmann transport equation within the relaxation time approximation. We find that, while in-plane transport is not strongly dependent on strain, the cross-plane component of the thermal conductivity tensor shows a clear strain dependence, with up to 20% increase (decrease) at 4% compressive (tensile) strain in both Si and Ge. We also uncover that strain emphasizes the anisotropy between in-plane and cross-plane thermal conductivity across several orders of magnitude in film thickness. Read the article in J. Appl. Phys. here: http://dx.doi.org/10.1063/1.4971269
We fabricate, measure, and simulate ultrathin diamond membranes with large lateral dimensions for MALDI TOF MS of high-mass proteins. With a minimal thickness of 100 nm and cross sections of up to 400×400 μm sq., the membranes offer extreme aspect ratios. Ion detection is demonstrated in MALDI TOF analysis over a broad range from insulin to albumin. The resulting data and simulations show much enhanced resolution as compared to existing detectors, which can offer better sensitivity and overall performance in resolving protein masses.
The article is available in Physical Review Applied: https://doi.org/10.1103/PhysRevApplied.6.064031
The latest article on phonon superdiffusion in Si-Ge alloy nanowires has been published in Physical Review B: https://doi.org/10.1103/PhysRevB.94.174303
Being a good thermoelectric material is a balancing act between high electrical conductivity σ and low thermal conductivity κ, because both quantities depend directly on the flow of electrons. Fortunately, κ also depends on lattice phonons, so this contribution can be cut—for example, by scattering from randomly distributed heavy atoms. The authors’ calculations show that adding tin to alloys of silicon and germanium should yield quite good thermoelectrics, especially in thin-film systems.