A. Rzhevskii, S. Chahid, R. Dulal, S. Teknowijoyo, A. Gulian
Thermo Fisher Scientific,
Keywords: Meissner effect, graphene, n-heptane, sulfur, Raman spectroscopy
Summary:Graphite and its derivatives such as graphene have demonstrated many interesting properties that are still under intense exploration and even more interesting properties are expected. Superconductivity is among them. Our research was motivated by the ideal diamagnetic screening reported previously in [Y. Kawashima, arXiv:cond-mat/1801.09376]. We explored magnetic screening of milligauss fields in a system comprised of single-layer graphene (on various substrates) wetted by n-heptane in the presence of a thin Fe-Ni foil parallel to the graphene layer. Some of our attempts resulted in signals similar to the reported ones. However, we encountered problems with reproducing these results on demand. One of the possible obstacles was variation in humidity at the location of the experimental setup. Thus, two research directions have been undertaken: 1) to perform experiments in the glovebox with Ar atmosphere and 2) to perform systematic studies of the influence of pristine graphene ageing and surface degradation vs. atmospheric conditions. Raman studies constituted an essential part of the latter studies and will be reported in detail. We used not only graphene but also pure graphite powders pulverized using the method suggested by Woltornist et.al., ACS Nano 7, 7062 (2013). On this way, we obtained promising results by pulverizing ultrapure graphite in water/n-heptane mixture to form continuous films on a glass substrate. Subsequent steps consist of studying specimens on different substrates and application of annealing (at 100o-600o, in air and in a vacuum) to vary physical properties of these films. These variations will be described in the presentation. We complemented Raman mapping by characterizing the morphology of films using scanning electron microscopy. Other instrumentation techniques have also been used to affect and study the physical properties of these films. These results allowed us to elevate the level of research aiming to reach reproducibility on demand with graphite/n-heptane/permalloy system. Studies of thin films also allowed us to improve the properties of the initial graphite powder via purification. Next, we apply the powders with improved properties to generate composite systems of graphite nanoparticles in sulfur. Magnetic susceptibility of this composition has been explored at different temperatures with the goal of revealing ideal diamagnetism. The properties of this composition have been analyzed with various techniques including Raman microscopy. This work was supported in part by the ONR Grants N00014-16-2269, N00014-17-1-2972, N00014-18-1-2636, and N00014-1901-2265.