Nitrogen-doped carbon quantum dots (NCQDs) were prepared from chitosan through a hydrothermal reaction. When ethanol precipitation was used as the purification method, a high product yield of 85.3% was obtained. A strong blue fluorescence emission with a high quantum yield (QY) of 6.6% was observed from the NCQD aqueous solution. Physical and chemical characteristics of the NCQDs were carefully investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and transient fluorescence spectra. Experimental results showed that diameters of the NCQDs were in the range of 2–10 nm. The carbon quantum dots possess good water dispersibility and precipitation by ethanol. When used for metal ion detection, the detection limit of the NCQDs for Fe3+ was as low as 1.57 μM. This work proposed a facile method to synthesize NCQDs from chitosan with high yield and demonstrated that carbon quantum dots derived from chitosan were promising for ion detection.

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For the fabrication of high performance graphene devices, the transfer process with clean surface without too many PMMA residues is of paramount importance in that it is has great impact on graphene interface. In this paper, a graphene heat-free-transfer process is proposed for the first time in order to get a decently clean surface. The evaluation of PMMA residues as a function of baking temperature is carried out. Experimental results clearly show that baking at higher temperature leads to more PMMA residues on graphene. In order to reduce these residues on graphene, a heat-free-transfer process is presented, in which the baking step is skipped. Thanks to both the step of anisole recoating and the abolishment of DI water rinsing, this heat-free-transfer overcomes the crack issue occurred to transferred graphene. It has been proven that, by adopting this heat-free-transfer process, the PMMA residues are notably reduced and the surface roughness of transferred graphene is improved, which in turn improves the interface of graphene. This improved interface is ought to be beneficial for the fabrication of high performance graphene devices.