Graphene has emerged as a material with a vast variety of applications. The electronic, optical and mechanical properties of graphene are strongly influenced by the number of layers present in a sample. As a result, the dimensional characterization of graphene films is crucial, especially with the continued development of new synthesis methods and applications. A number of techniques exist to determine the thickness of graphene films including optical contrast, Raman scattering and scanning probe microscopy techniques. Atomic force microscopy (AFM), in particular, is used extensively since it provides three-dimensional images that enable the measurement of the lateral dimensions of graphene films as well as the thickness, and by extension the number of layers present. However, in the literature AFM has proven to be inaccurate with a wide range of measured values for single layer graphene thickness reported (between 0.4 and 1.7 nm). This discrepancy has been attributed to tip-surface interactions, image feedback settings and surface chemistry. In this work, we use standard and carbon nanotube modified AFM probes and a relatively new AFM imaging mode known as PeakForce tapping mode to establish a protocol that will allow users to accurately determine the thickness of graphene films. In particular, the error in measuring the first layer is reduced from 0.1–1.3 nm to 0.1–0.3 nm. Furthermore, in the process we establish that the graphene-substrate adsorbate layer and imaging force, in particular the pressure the tip exerts on the surface, are crucial components in the accurate measurement of graphene using AFM. These findings can be applied to other 2D materials.

As the most commonly used potential energy conversion and storage devices, lithium-ion batteries (LIBs) have been extensively investigated for a wide range of fields including information technology, electric and hybrid vehicles, aerospace, etc. Endowed with attractive properties such as high energy density, long cycle life, small size, low weight, few memory effects and low pollution, LIBs have been recognized as the most likely approach to be used to store electrical power in the future. This review will start with a brief introduction to charge–discharge principles and performance assessment indices. The advantages and disadvantages of several commonly studied anode materials including carbon, alloys, transition metal oxides and silicon along with lithium intercalation will be reviewed. The mechanism and synthesis methods, followed by strategies to enhance battery performance by virtue of interesting structural designs will be examined. Finally, a few issues needing further exploration will be discussed followed by a brief outline of the prospects and outlook for the LIB field.

A comprehensive review of current developments in flexible fluoropolymer-based piezoelectric generators for sustainable energy harvesting.