Andrey Turchanin

Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors

carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Nitrogen-Doped Graphene and Its Iron-Based Composite As Efficient Electrocatalysts for Oxygen Reduction Reaction

The high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has hindered the practical application of fuel cells. Thanks to its unique chemical and structural properties, nitrogen-doped graphene (NG) is among the most promising metal-free catalysts for replacing platinum. In this work, we have developed a cost-effective synthesis of NG by using cyanamide as a nitrogen source and graphene oxide as a precursor, which led to high and controllable nitrogen contents (4.0% to 12.0%) after pyrolysis. NG thermally treated at 900 °C shows a stable methanol crossover effect, high current density (6.67 mA cm(-2)), and durability (∼87% after 10,000 cycles) when catalyzing ORR in alkaline solution. Further, iron (Fe) nanoparticles could be incorporated into NG with the aid of Fe(III) chloride in the synthetic process. This allows one to examine the influence of non-noble metals on the electrocatalytic performance. Remarkably, we found that NG supported with 5 wt % Fe nanoparticles displayed an excellent methanol crossover effect and high current density (8.20 mA cm(-2)) in an alkaline solution. Moreover, Fe-incorporated NG showed almost four-electron transfer processes and superior stability in both alkaline (∼94%) and acidic (∼85%) solutions, which outperformed the platinum and NG-based catalysts.

Layer-by-Layer Assembled Heteroatom-Doped Graphene Films with Ultrahigh Volumetric Capacitance and Rate Capability for Micro-Supercapacitors

Highly uniform, ultrathin, layer-by-layer heteroatom (N, B) co-doped graphene films are fabricated for high-performance on-chip planar micro-supercapacitors with an ultrahigh volumetric capacitance of ∼488 F cm(-3) and excellent rate capability due to the synergistic effect of nitrogen and boron co-doping.

One Nanometer Thin Carbon Nanosheets with Tunable Conductivity and Stiffness

Atomically thin (similar to 1 nm) carbon films and membranes whose electrical behavior can be tuned from insulating to conducting are fabricated by a novel route. These films present arbitrary size and shape based on molecular self-assembly, electron irradiation, and pyrolysis, and their technical applicability is demonstrated by their incorporation into a microscopic pressure sensor.

A Universal Scheme to Convert Aromatic Molecular Monolayers into Functional Carbon Nanomembranes

Free-standing nanomembranes with molecular or atomic thickness are currently explored for separation technologies, electronics, and sensing. Their engineering with well-defined structural and functional properties is a challenge for materials research. Here we present a broadly applicable scheme to create mechanically stable carbon nanomembranes (CNMs) with a thickness of ~0.5 to ~3 nm. Monolayers of polyaromatic molecules (oligophenyls, hexaphenylbenzene, and polycyclic aromatic hydrocarbons) were assembled and exposed to electrons that cross-link them into CNMs; subsequent pyrolysis converts the CNMs into graphene sheets. In this transformation the thickness, porosity, and surface functionality of the nanomembranes are determined by the monolayers, and structural and functional features are passed on from the molecules through their monolayers to the CNMs and finally on to the graphene. Our procedure is scalable to large areas and allows the engineering of ultrathin nanomembranes by controlling the composition and structure of precursor molecules and their monolayers.

Extreme ultraviolet interference lithography at the Paul Scherrer Institut

We review the performance and applications of an extreme ultraviolet interference lithography (EUV-IL) system built at the Swiss Light Source of the Paul Scherrer Institut (Villigen, Switzerland). The interferometer uses fully coherent radiation from an undulator source. 1-D (line/space) and 2-D (dot/hole arrays) patterns are obtained with a transmission-diffraction-grating type of interferometer. Features with sizes in the range from one micrometer down to the 10-nm scale can be printed in a variety of resists. The highest resolution of 11-nm half-pitch line/space patterns obtained with this method represents a current record for photon based lithography. Thanks to the excellent performance of the system in terms of pattern resolution, uniformity, size of the patterned area, and the throughput, the system has been used in numerous applications. Here we demonstrate the versatility and effectiveness of this emerging nanolithography method through a review of some of the applications, namely, fabrication of metallic and magnetic nanodevice components, self-assembly of Si/Ge quantum dots, chemical patterning of self-assembled monolayers (SAM), and radiation grafting of polymers. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3116559]

Conversion of Self-Assembled Monolayers into Nanocrystalline Graphene: Structure and Electric Transport

Graphene-based materials have been suggested for applications ranging from nanoelectronics to nanobiotechnology. However, the realization of graphene-based technologies will require large quantities of free-standing two-dimensional (2D) carbon materials with tunable physical and chemical properties. Bottom-up approaches via molecular self-assembly have great potential to fulfill this demand. Here, we report on the fabrication and characterization of graphene made by electron-radiation induced cross-linking of aromatic self-assembled monolayers (SAMs) and their subsequent annealing. In this process, the SAM is converted into a nanocrystalline graphene sheet with well-defined thickness and arbitrary dimensions. Electric transport data demonstrate that this transformation is accompanied by an insulator to metal transition that can be utilized to control electrical properties such as conductivity, electron mobility, and ambipolar electric field effect of the fabricated graphene sheets. The suggested route opens broad prospects toward the engineering of free-standing 2D carbon materials with tunable properties on various solid substrates and on holey substrates as suspended membranes.

High thermal stability of cross-linked aromatic self-assembled monolayers: Nanopatterning via selective thermal desorption

An extremely high thermal stability of electron cross-linked biphenyl self-assembled monolayers (SAMs) is reported. The authors found that pristine biphenylthiol SAMs desorb at ∼400K from gold surfaces, which is induced by a breaking of C–S bonds. Despite of a similar bond cleavage in cross-linked SAMs, these remain on the surface up to 1000K, which is the highest temperature reported for a SAM. When patterns of pristine and cross-linked SAMs are heated, the pristine regions desorb, and the cross-linked regions remain on the surface. The authors show that this thermal desorption lithography can be utilized for the fabrication of molecular surface nanostructures.

Cooperative self-assembly of discoid dimers: hierarchical formation of nanostructures with a pH switch.

Derivatives of the self-complementary 2-guanidiniocarbonyl pyrrole 5-carboxylate zwitterion (1) (previously reported by us to dimerize to 1•1 with an aggregation constant of ca. >10(10) M(-l) in DMSO) aggregate in a diverse manner depending on, e.g., variation of concentration or its protonation state. The mode of aggregation was analyzed by spectroscopic (NMR, UV) and microscopic (AFM, SEM, HIM, and TEM) methods. Aggregation of dimers of these zwitterions to higher supramolecular structures was achieved by introduction of sec-amide substituents at the 3-position, i.e., at the rearward periphery of the parent binding motif. A butyl amide substituent as in 2b enables the discoid dimers to further aggregate into one-dimensional (rod-like) stacks. Quantitative UV dilution studies showed that this aggregation is strongly cooperative following a nucleation elongation mechanism. The amide hydrogen seems to be essential for this rod-like aggregation, as neither 1 nor a corresponding tert-amide congener 2a form comparable structures. Therefore, a hydrogen bond-assisted π-π-interaction of the dimeric zwitterions is suggested to promote this aggregation mode, which is further affected by the nature of the amide substituent (e.g., steric demand), enabling the formation of bundles of strands or even two-dimensional sheets. By exploiting the zwitterionic nature of the aggregating discoid dimers, a reversible pH switch was realized: dimerization of all compounds is suppressed by protonation of the carboxylate moiety, converting the zwitterions into typical cationic amphiphiles. Accordingly, typical nanostructures like vesicles, tubes, and flat sheets are formed reversibly under acidic conditions, which reassemble into the original rod-like aggregates upon readjustment to neutral pH.

Dry-cleaning of graphene

Studies of the structural and electronic properties of graphene in its pristine state are hindered by hydrocarbon contamination on the surfaces. Also, in many applications, contamination reduces the performance of graphene. Contamination is introduced during sample preparation and is adsorbed also directly from air. Here, we report on the development of a simple dry-cleaning method for producing large atomically clean areas in free-standing graphene. The cleanness of graphene is proven using aberration-corrected high-resolution transmission electron microscopy and electron spectroscopy.