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The cover picture shows the mechanics of the tearing of a ribbon from a single-layer graphene sheet attached to an adhesive substrate, simulated using molecular dynamics with a first-principles-based reactive force field. The overlay shows the torn part of the sheet and the resulting rough edges at the atomic scale largely consist of characteristic armchair surface termination. The underlying color plot shows the out-of-plane deformation in the section of the sheet still attached to the substrate. The concentrated region of large deformation (red and blue color) right below the tearing flap in contrast to zero deformation in regions away from the flap (green color) causes large shear stresses, leading to shear rupture in the sheet. The tearing results in the formation of tapered nanoribbons, where the tapering angle can be controlled by adhesion strength to the substrate and number of graphene layers torn off. Considering graphene as a model 2D material, experiments, atomistic simulation, and theory provide fundamental insight into the energetics of tearing that can be extended to other 2D nanoscale thin films attached to substrates. For more information, please read the Full Paper “Tearing Graphene Sheets From Adhesive Substrates Produces Tapered Nanoribbons” by M. J. Buehler et al., beginning on page 1108.

The cover picture shows a new method to illuminate quantum dots (QDs) by radiation luminescence as an internal light source. Taking advantage of the radioactive luminescent light at the visible and NIR range, many different fluorophores such as QDs can be exited to emit fluorescence for optical imaging. Three CdSe/ZnS core/shell QDs are chosen and irradiated by a β⁻ emitter, ¹³¹I. The excited QDs can produce fluorescence for both in vitro and in vivo imaging. This study demonstrates an alternate strategy for the design of self-illuminating optical-imaging agents. Radiation-luminescence-excited fluorophores could also be readily adapted for dual-modality imaging. For more information, please read the Communication “Radiation-Luminescence-Excited Quantum Dots for in vivo Multiplexed Optical Imaging” by Z. Cheng et al., beginning on page 1087.

The controlled patterning of nanomaterials presents a major challenge to the field of nanolithography because of differences in size, shape, and solubility of these materials. Matrix-assisted dip-pen nanolithography and polymer-pen lithography provide a solution to this problem by utilizing a polymeric matrix that encapsulates the nanomaterials and delivers them to surfaces with precise control of feature size (see image).

Polymer-pen lithography is a scanning-probe contact-printing method that can control feature diameter from many micrometers to sub-100nm in a single writing operation as a result of force- and time-dependent ink transport. A quantitative model that relates the force between the elastomeric tips and the substrate to the feature edge length has been derived and experimentally confirmed (see image).

A new method to illuminate quantum dots (QDs) by radiation luminescence as an internal light source is reported. The excited QDs can produce fluorescence for both in vitro and in vivo imaging. This study provides an alternate strategy for the design of self-illuminated optical imaging agents. Radiation-luminescence-excited QDs can also be readily adapted for dual-modality imaging.

Peptide nanotubes are integrated with microfabricated transducer arrays for bacterial detection. On each microelectrode of the array, circulating antibody-modified peptide nanotubes agglutinate bacteria as pathogen catchers and generate an impedance signal on the transducer. The pathogen microarray can detect as few as 10² cells of E. coli or S. typhi within one hour and the sensor chip can be easily reused for multiple measurements.

Multi-walled TaS₂ nanotubes are synthesized from anodized Ta₂O₅ nanotube templates in a gas-phase reaction, with control over the length, diameter, and number of TaS₂ layers within a nanotube. TaS₂ nanotubes exhibit elevated superconducting transition temperatures and suppressed charge density wave transition temperatures compared to bulk, offering a straightforward method of characterizing other transition metal dichalcogenide materials in reduced dimensions.

A simple and scalable exfoliation approach is developed to produce high-quality single-layer graphene sheets without the use of toxic reduction agents of expensive solvents. Graphite powders are exfoliated in a water solution of pyrene derivatives, which act as dispersion agents, healing agents, and electric “glue” during the thermal annealing process.

Tearing of graphene layers from adhesive substrates, such as SiO₂ and poly(methyl methacrylate), leads to the formation of tapered ribbons, the angle of tapering increasing with adhesion strength. Being a truly two-dimensional material, the tearing mechanics are governed by the in-plane stretching energy of the graphene sheet, deviating from the behavior of macroscopic thin films.

Clusters of charged nanoparticles in the gas phase are selectively deposited onto electrically grounded surfaces. Similar to electroplating, the continued deposition of Au nanoparticles onto underlying traces increases the overall line conductivity. Alternatively, semiconducting ZnO and Ge nanomaterials can be sequentially deposited between interdigitated electrodes and serve as addressable sensor-active areas.

The chemical modification of graphene with diazonium chemistry is analyzed by confocal Raman spectroscopy. The reaction shows a clear selectivity between single- (1L) and bilayer (2L) graphene after ten minutes of reaction. The edge of the single-layer-graphene areas has an increased reactivity to the diazonium reagent and the local carbon hybridization changes from sp2 to sp3, altering the electronic properties of graphene.

Diverse nanostructures are formed by single-com ponent self-assembly of homoditopic 1,18-nucleotide-appended bolaamphiphiles and binary self-assembly with complementary single-stranded oligonucleotides. The self-assembled morphologies—nanosheets, nanofibers, nanorods, and nanoparticles—strongly depend both on the nature of the nucleobase moieties and DNA templates.

Monolithic diamond probes with integrated tips possessing small radii, smooth surfaces, and controlled geometry are fabricated by a wafer-level process. The tips have superior wear resistance to that of SiN_x tips under contact-mode scanning conditions at low and high humidity, and under stresses in the 2–8 GPa range.

Adenine nucleoside is physisorbed on the graphene supercell where the π orbitals of the base interact with the π orbitals of the graphene layer. Micro-Raman spectroscopy of the 2D band of pristine graphene and single-stranded DNA (ssDNA)/graphene systems indicates a shift of ≈4 cm⁻¹ as a result of ssDNA patterning. The ssDNA fragments act as negative-potential gating agents.