Functional polyelectrolyte nanospaced MoS2 multilayers for enhanced photoluminescence.

Molybdenum disulfide (MoS2) multilayers with functional polyelectrolyte nanospacing layers are presented. Taking advantage of the facile method of layer-by-layer (LbL) assembly, individual chemically exfoliated MoS2 layers are not only effectively isolated from interlayer coupling but also doped by functional polymeric layers. It is clearly demonstrated that MoS2 nanosheets separated by polymeric trilayers exhibit a much larger increase in photoluminescence (PL) as the number of layers is increased. The enhanced PL has been correlated to the ratio of excitons to trions with the type of polymeric spacers. Because uniform heterogeneous interfaces can be formed between various transition metal dichalcogenides and other soft materials, LbL assembly offers possibilities for further development in the solution-processable assemblies of two-dimensional materials.

Transparent conducting films based on reduced graphene oxide multilayers for biocompatible neuronal interfaces.

Among the most critical components in neuronal interfaces is the implanted electrode which requires the long-term stability of its electrical performance and biocompatibility of electrode material in contact with live neuronal cells. Reduced graphene oxide (rGO) renowned for its high electrical conductivity and optical transparency has shown great potential for a variety of applications such as transparent conducting electrodes and biosensors, and might be a potential candidate material for the next-generation neuronal interfaces. However, there have been only few systematic studies on graphene-based neuronal interfaces in terms of electrical conductivity and biocompatibility. In this report, we maintained rat hippocampal neurons on top of the rGO multilayers and observed that the viability of neurons is minimally affected and comparable to those grown on a glass substrate up to 30 days in vitro. These results implicate that rGO multilayer can be utilized for excellent neuronal interfaces with its high electrical conductivity and biocompatibility.

Optical switching of the Dirac point in graphene multilayer field-effect transistors functionalized with spiropyran.

A facile method for achieving optical switching of the Dirac point and conductance in reduced graphene oxide multilayer FETs that are non-covalently functionalized with a photo-responsive spiropyran derivative is presented. The photoresponsive transition from spiropyran to merocyanine induces the reversible optical switching in graphene based FETs.

Highly tunable charge transport in layer-by-layer assembled graphene transistors.

We demonstrate a controlled, systematic method to tune the charge transport in graphene field-effect transistors based on alternating layer-by-layer assembly of positively and negatively charged graphene oxide followed by thermal reduction. Surprisingly, tuning the number of bilayers of thermally reduced graphene oxide multilayer films allowed achieving either ambipolar or unipolar (both n- and p-type) transport in graphene transistors. On the basis of X-ray photoemission spectroscopy, Raman spectroscopy, time-of-flight secondary ion mass spectrometry, and temperature-dependent charge transport measurements, we found that nitrogen atoms from the functional groups of positively charged graphene oxide are incorporated into the reduced graphene oxide films and substitute carbon atoms during the thermal reduction. This nitrogen-doping process occurs in different degrees for graphene multilayers with varying numbers of bilayers and thereby results in the interesting transition in the electrical behavior in graphene multilayer transistors. We believe that such a versatile method to control the charge transport in graphene multilayers will further promote their applications in solution-processable electronic devices based on graphene.

Carbon-based layer-by-layer nanostructures: from films to hollow capsules.

Over the past years, the layer-by-layer (LbL) assembly has been widely developed as one of the most powerful techniques to prepare multifunctional films with desired functions, structures and morphologies because of its versatility in the process steps in both material and substrate choices. Among various functional nanoscale objects, carbon-based nanomaterials, such as carbon nanotubes and graphene sheets, are promising candidates for emerging science and technology with their unique physical, chemical, and mechanical properties. In particular, carbon-based functional multilayer coatings based on the LbL assembly are currently being actively pursued as conducting electrodes, batteries, solar cells, supercapacitors, fuel cells and sensor applications. In this article, we give an overview on the use of carbon materials in nanostructured films and capsules prepared by the LbL assembly with the aim of unraveling the unique features and their applications of carbon multilayers prepared by the LbL assembly.