Manipulation of the long-range organization of nanomaterials plays a key role in expanding their applications. Specifically for carbon nanomaterials, the ordering of fullerenes, which have a defined molecular structure, has been extensively studied. However, for the members which are polydisperse in size and shape, such as carbon nanotubes, graphene and the newly discovered carbon dots (C dots), the control of their supramolecular organization becomes highly challenging. In this work, we prepared alkylated C dots by mild pyrolysis of aliphatic amines in chlorobenzene, which can be further sorted based on their polarity through silica gel chromatography. These C dots have tiny, planar cores surrounded by peripheral alkyl chains, and can self-organize into highly ordered crystals or soft crystals with lamellar arrangements in a solvent-free state. As a typical example of applications, the nonlinear optical response of the C dots was investigated in the film state without any other additive. Reverse saturable absorption behavior has been found, and the nonlinear absorption coefficient is closely related to the content of the carbon nitride inside the C dots, revealing that their nonlinear optical response is governed by the higher absorption cross section of the excited-state induced by the π-conjugated structure. These new C dots could find applications in laser protection as they can be used for making flexible and even wearable thin films. In addition, other potential applications could also be envisaged, such as being new candidates for the production of high-quality carbon fibers.

Cr doped MoS₂ films were deposited by magnetron sputtering. The tribological properties of Cr doped MoS₂ films under vacuum (VC) and air (AR) environments were investigated. The results show that Cr doped MoS₂ film with Cr target power of 0.2 A (0.2 A Cr:MoS₂ film) exhibits low friction coefficient and long wear life under both VC and AR environments. The chemical compositions of the films were analyzed by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). With the increases of Cr target power, the content of Cr increases. The cross-sectional FESEM morphologies show that the structure of the films changed from granular particles to column when the Cr target power increases from 0.2A to 0.4A. The wear mechanism has also been discussed based on the characteristics of worn surface. The 0.4 A Cr:MoS₂ film has the lowest wear volume among these films, which can be attributed to the compact microstructure. The bandgap of Cr doped MoS₂ films were measured by XPS and the tribological performance of the film is found to be best when there is a modest bandgap. It can be speculated that the tribological performance of Cr doped MoS₂ films are closely related to the width of bandgap.