Recent Publications

A comparison of small-angle scattering with electron microscopy techniques to characterize low volume fractions of heterogeneously distributed precipitates in alloys
Honaramooz, Mohammad Taha, MSc / SyNergy_Mat Lab

The characterization of Zr-containing dispersoids in aluminum alloys is challenging due to their broad size distribution, low volume fraction, and heterogeneous distribution within the grains. In this work, small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) were compared to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) regarding their capability to characterize Zr-containing dispersoids in aluminum alloys. It was demonstrated that both scattering techniques are suitable tools to characterize dispersoids in a multiphase industrial aluminum alloy. While SAXS is more sensitive than SANS due to the high electron density of Zr, SANS has the advantage of being able to probe a much larger sample volume. The combination of SAXS and SANS allows for the verification that the dispersoids can be separated from other precipitate phases. The size distribution obtained from SAXS, SANS and TEM showed good agreement. The SEM-derived size distributions were, however, found to significantly deviate from those of the other techniques, which can be explained by considering the resolution-limited restrictions of the different techniques

Single Crystalline 2D Material Nanoribbon Networks for Nanoelectronics

Muhammad Awais Aslam / Matkovic's Lab

The last decade has seen a flurry of studies related to graphene nanoribbons owing to their potential applications in the quantum realm. However, little experimental work has been reported towards nanoribbons of other 2D materials due to the absence of synthesis routes. Here, we propose a universal approach to synthesize high-quality networks of nanoribbons from arbitrary 2D materials while maintaining high crystallinity, sufficient yield, narrow size distribution, and straight-forward device integrability. The wide applicability of this technique is demonstrated by fabricating MoS2, WS2, WSe2, and graphene nanoribbon field effect transistors that inherently do not suffer from interconnection resistances. By relying on self-assembled and self-aligned organic nanostructures as masks, we demonstrate the possibility of controlling the predominant crystallographic direction of the nanoribbon’s edges. Electrical characterization shows record mobilities and very high ON currents for various TMDCs despite extreme width scaling. Lastly, we explore decoration of nanoribbon edges with plasmonic particles paving the way towards the development of nanoribbon-based plasmonic sensing and opto-electronic devices.

A universal substrate for the nanoscale investigation of two-dimensional materials

T.H. Tran, Applied Surface Science 604, 154585, 2022/ Matkovics Lab
Since discovering two-dimensional materials, there has been a great interest in exploring, understanding, and taking advantage of their unique properties. Si/SiO2 is one of the most used substrates for the deposition and characterization of 2D materials due to its availability and optical contrast. This work goes beyond the conventional substrate and introduces highly-ordered pyrolytic graphite (HOPG) as universal support for investigating two-dimensional materials due to several unique properties such as chemical and temperature stability, intrinsic high flatness, reusability, electrical conductivity, ease of use, availability, and enhanced adhesion of two-dimensional materials. We demonstrate this by analyzing several 2D materials with advanced atomic force microscopy methods, Raman and photoluminescence spectroscopy with hyperspectral imaging, and scanning electron microscopy with elementary analysis imaging. The strong adhesion to HOPG allowed the instant deposition of different two-dimensional materials GaSe, MoS2, Zn2In2S5, talc, and h-BN. This feat is hard to accomplish on the conventional SiO2 substrate without polymer-assisted transfer. Moreover, this strong interaction can strain 2D materials deposited on HOPG, giving localized changes in reactivity, optical, and electronic properties. This effect is explored for selective Ag deposition on strained regions of 2D materials to activate photocatalytic reactions.

Coffee Waste-Derived Nanoporous Carbons for Hydrogen Storage
Sebastian Stock  ACS Applied Energy Materials /  SyNergy_Mat Lab

Biological waste such as residues from the food and beverage industry provides a valuable and abundant resource to be used as a precursor for the synthesis of activated carbons that can be subsequently employed as adsorbents for, e.g., hydrogen storage. Materials with a large specific surface area and pores of appropriate size are necessary to achieve reasonable hydrogen adsorption capacity. Here, we present the repeatable synthesis of activated carbons from coffee waste, i.e., spent coffee grounds and coffee silver skins, on the basis of two independently synthesized batches. The carbonization process under nitrogen gas flow followed by chemical activation with solid potassium hydroxide results in microporous carbons with bimodal pore size distribution and specific surface area up to 3300 and 2680 m2/g based on Brunauer–Emmett–Teller and density functional theory methods, respectively. The materials exhibit excellent hydrogen adsorption performance under cryogenic conditions (77 K), reaching high and fully reversible excess gravimetric hydrogen uptake values of up to 5.79 wt % at 37 bar, and total capacities exceeding 9 wt % at 100 bar.