22 research outputs found
Direct Imaging, Three-dimensional Interaction Spectroscopy, and Friction Anisotropy of Atomic-scale Ripples on MoS
Theory predicts that two-dimensional (2D) materials may only exist in the
presence of out-ofplane deformations on atomic length scales, frequently
referred to as ripples. While such ripples can be detected via electron
microscopy, their direct observation via surface-based techniques and
characterization in terms of interaction forces and energies remain limited,
preventing an unambiguous study of their effect on mechanical characteristics,
including but not limited to friction anisotropy. Here, we employ
high-resolution atomic force microscopy to demonstrate the presence of
atomic-scale ripples on supported samples of few-layer molybdenum disulfide
(MoS). Three-dimensional force / energy spectroscopy is utilized to study
the effect of ripples on the interaction landscape. Friction force microscopy
reveals multiple symmetries for friction anisotropy, explained by studying
rippled sample areas as a function of scan size. Our experiments contribute to
the continuing development of a rigorous understanding of the nanoscale
mechanics of 2D materials.Comment: 22 pages including 4 figures in the main text, 2 figures in the
supplemental informatio
Inverse Layer Dependence of Friction on Chemically Doped MoS_{2}
We present the results of atomic-force-microscopy-based friction measurements
on Re-doped molybdenum disulfide (MoS2). In stark contrast to the seemingly
universal observation of decreasing friction with increasing number of layers
on two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits an
anomalous, i.e. inverse dependency on the number of layers. Raman spectroscopy
measurements revealed signatures of Re intercalation, leading to a decoupling
between neighboring MoS2 layers and enhanced electron-phonon interactions, thus
resulting in increasing friction with increasing number of layers: a new
paradigm in the mechanics of 2D materials.Comment: 15 pages incl. Supplemental Material, 5 figure