This report demonstrates a simple, but efficient method to print highly ordered nanopillars without the use of sacrificial templates or any expensive equipment. The printed polymer structure is used as a scaffold to deposit electrode material (manganese dioxide) for making supercapacitors. The simplicity of the fabrication method together with superior power density and energy density make this supercapacitor electrode very attractive for the next-generation energy storage systems.

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The formation and structure of 2,2‘-bipyridine (22BPY) and 4,4‘-bipyridine (44BPY) monolayers on Au(111) substrate have been studied as a function of the substrate potential. At high potentials, both molecules adsorb onto the substrate and stand vertically with their nitrogen atoms facing the Au(111). The vertically standing molecules stack, like rolls of coins, into polymer-like chains which pack closely in parallel to form ordered monolayers. Decreasing the potential to a critical value, the 22BPY chains become randomly oriented via a reversible order−disorder phase transition. The phase transition, as revealed by scanning tunneling microscopy, is driven by a potential dependent attractive force between the chains. The attractive force is believed to be a substrate-mediated effective force which arises as an adsorbed 22BPY perturbs its surrounding local surface potential and thus the nearby molecules. This hypothesis is supported by a quantitative investigation of the local surface potential using a self-consistent density functional method. In contrast to 22BPY, the 44BPY chains dissolve instead of becoming randomly oriented at low potentials. This behavior may be due to that 44BPY is not as strongly adsorbed on the surface as 22BPY because it has only one nitrogen facing the surface.

Two-dimensional (2D) barcodes ubiquitously used to label, track and authenticate objects face increasing challenges of being damaged, altered and falsified. The past effort in nanomaterials has paved the way for controlled synthesis of nanomaterials with desired size, shape and function. Due to their extremely small sizes, these nanomaterials are promising as next generation barcodes that can be added into or mixed with objects of interest without being noticed. These barcodes can be effectively read owing to their physical properties by manufacturers, law enforcement and security agencies. Meanwhile, nanomaterial-based barcodes are hard to reverse-engineer or imitate without advanced knowledge and technical expertise. This review describes how nanomaterials can be used as barcodes, discusses advantages and limitations of each type of nanomaterial-based barcode, and points out ways that could help design and prepare better nanomaterial-based barcodes.

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