Electrochemical Transparency of Graphene

In the present study, we used the electrochemical transparency of graphene to show that the direct intercalation of alkali-metal cations is not a prerequisite for the redox reaction of Prussian blue (PB). PB thin films passivated with monolayer graphene still underwent electrochemical redox reactions in the presence of alkali-metal ions (K+ or Na+) despite the inability of the cations to penetrate the graphene and be incorporated into the PB. Graphene passivation not only preserved the electrochemical activity of the PB but also substantially enhanced the stability of the PB. As a proof of concept, we showed that a transparent graphene electrode covering PB can be used as an excellent hydrogen peroxide transducer, thereby demonstrating the possibility of realizing an electrochemical sensor capable of long-term measurements

Graphene Quantum Dots as Nucleants for Protein Crystallization

Structural analysis of proteins using X-ray crystallography is crucial for discovering their biochemical functionalities. However, growing X-ray-quality crystals of proteins is often a challenging task that requires complicated and tedious processes, especially for the formation of crystalline seeds in the early stage of the process. In the present study, graphene quantum dots (GQDs) were investigated as a nanomaterial nucleant for protein crystallization in the aspects of the process accelerations and their possible underlying mechanisms, where lysozyme was employed for a model system. Compared to that without GQDs, dramatically faster formation of crystalline seeds was observed in the presence of GQDs within 2 h of incubation. The hydrodynamic size of lysozyme increased by about 30% when GQDs were included according to dynamic light scattering measurements, implying a possible binding of GQDs to the protein. X-ray diffraction analysis of lysozyme crystals also implies the possible binding of GQDs to the protein by showing reduced thermal B-factors when GQDs were included, suggesting flexibility reducing interactions of GQDs with random coil sites. In spite of the prevalent existence of GQDs in the crystal, the X-ray structural analysis cell parameters of lysozyme grown with GQDs showed negligible differences compared to those grown without GQDs, suggesting that GQDs might be an ideal nucleant for protein crystallization

Simple Interface Engineering of Graphene Transistors with Hydrophobizing Stamps

We demonstrate a simple surface engineering method for fabricating graphene transistors by using hydrophobizing stamps. By simply contact-printing hydrophobizing stamp that is made with polydimethylsiloxane (PDMS) on a standard silicon substrate for a certain contact-time, it was possible to control the contact angle of the substrate and electrical characteristics of the graphene transistors supported on the substrate. Moreover, graphene transistors supported on the engineered silicon substrate showed improved performances, including an increase in carrier mobility and loss of hysteresis. As a proof-of-concept experiment, a simple logic gate operation was demonstrated by connecting a pristine graphene device with an interface-engineered device

Lattice Transparency of Graphene

Here, we demonstrated the transparency of graphene to the atomic arrangement of a substrate surface, i.e., the “lattice transparency” of graphene, by using hydrothermally grown ZnO nanorods as a model system. The growth behaviors of ZnO nanocrystals on graphene-coated and uncoated substrates with various crystal structures were investigated. The atomic arrangements of the nucleating ZnO nanocrystals exhibited a close match with those of the respective substrates despite the substrates being bound to the other side of the graphene. By using first-principles calculations based on density functional theory, we confirmed the energetic favorability of the nucleating phase following the atomic arrangement of the substrate even with the graphene layer present in between. In addition to transmitting information about the atomic lattice of the substrate, graphene also protected its surface. This dual role enabled the hydrothermal growth of ZnO nanorods on a Cu substrate, which otherwise dissolved in the reaction conditions when graphene was absent

Selective Suppression of Conductance in Metallic Carbon Nanotubes

We show that different electrophilic molecules can be used for selective electronic structure control of single-walled carbon nanotubes (SWNT). Electrical transport properties of SWNT field-effect transistors (SWNT-FETs) treated with four electrophilic molecules revealed that these electrophilic molecules have higher selectivity toward metallic SWNTs than toward semiconducting SWNTs. One-third of the nondepletable SWNT-FETs treated with the electrophilic molecules turned into depletable devices, while devices that originally had depletable conductance showed negligible changes after treatment. AFM images showed that treatment with nitronium ions induced complete disintegration of the nanotube sidewalls

“Atomic Force Masking” Induced Formation of Effective Hot Spots along Grain Boundaries of Metal Thin Films

We present an interesting phenomenon, “atomic force masking”, which is the deposition of a few-nanometer-thick gold film on ultrathin low-molecular-weight (LMW) polydimethylsiloxane (PDMS) engineered on a polycrystalline gold thin film, and demonstrated the formation of hot spot based on SERS. The essential principle of this atomic force masking phenomenon is that an LMW PDMS layer on a single crystalline grain of gold thin film would repel gold atoms approaching this region during a second cycle of evaporation, whereas new nucleation and growth of gold atoms would occur on LMW PDMS deposited on grain boundary regions. The nanostructure formed by the atomic force masking, denoted here as “hot spots on grain boundaries” (HOGs), which is consistent with finite-difference time-domain (FDTD) simulation, and the mechanism of atomic force masking were investigated by carrying out systematic experiments, and density functional theory (DFT) calculations were made to carefully explain the related fundamental physics. Also, to highlight the manufacturing advantages of the proposed method, we demonstrated the simple synthesis of a flexible HOG SERS, and we used this substrate in a swabbing test to detect a common pesticide placed on the surface of an apple

Three-Dimensional Layer-by-Layer Anode Structure Based on Co₃O₄ Nanoplates Strongly Tied by Capillary-like Multiwall Carbon Nanotubes for Use in High-Performance Lithium-Ion Batteries

A layer-by-layer (LBL) structure composed of Co₃O₄ nanoplates and capillary-like three-dimensional (3D) multiwall carbon nanotube (MWCNT) nets was developed as an anode with simultaneous high-rate and long-term cycling performance in a lithium-ion battery. As the current density was increased to 50 A g^–1, the LBL structure exhibited excellent long-term cycling and rate performance. Thus, the Co₃O₄ nanoplates were in good electrical contact with the capillary-like 3D MWCNT nets under mechanically severe strain during long-term, high-rate cyclic operation

Oriented Immobilization of Antibody Fragments on Ni-Decorated Single-Walled Carbon Nanotube Devices

We herein demonstrate that Ni-decorated single-walled carbon nanotube field effect transistors (SWNT-FETs) combined with antibody fragments can be used as effective biosensing platforms. Nanoscales Ni particles 20 to 60 nm in diameter were formed on the sidewalls of SWNT-FETs using an electrochemical method. Carcinoembryonic antigen (CEA)-binding single chain variable fragments (scFvs) with a hexahistidine tag [(his)6] were synthesized using genetic engineering, and ordered immobilization of anti-CEA ScFvs on Ni nanoparticles was achieved by exploiting the specific interaction between hexahistidine and Ni. Whereas randomly oriented anti-CEA scFvs did not impart a noticeable change of conductance upon addition of CEA, a clear increase in conductance was observed using Ni-decorated SWNT-FETs functionalized with engineered scFvs

Interface Charge Induced p-Type Characteristics of Aligned Si_1−<i>x</i>Ge_<i>x</i> Nanowires

This study reports the electrical transport characteristics of Si1−xGex (x = 0−0.3) nanowires. Nanowires with diameters of 50−100 nm were grown on Si substrates. The valence band spectra from the nanowires indicate that energy band gap modulation is readily achievable using the Ge content. The structural characterization showed that the native oxide of the Si1−xGex nanowires was dominated by SiO2; however, the interfaces between the nanowire and the SiO2 layer consisted of a mixture of Si and Ge oxides. The electrical characterization of a nanowire field effect transistor showed p-type behavior in all Si1−xGex compositions due to the Ge−O and Si−O−Ge bonds at the interface and, accordingly, the accumulation of holes in the level filled with electrons. The interfacial bonds also dominate the mobility and on- and off-current ratio. The large interfacial area of the nanowire, together with the trapped negative interface charge, creates an appearance of p-type characteristics in the Si1−xGex alloy system. Surface or interface structural control, as well as compositional modulation, would be critical in realizing high-performance Si1−xGex nanowire devices

Three-Dimensional Layer-by-Layer Anode Structure Based on Co₃O₄ Nanoplates Strongly Tied by Capillary-like Multiwall Carbon Nanotubes for Use in High-Performance Lithium-Ion Batteries

A layer-by-layer (LBL) structure composed of Co₃O₄ nanoplates and capillary-like three-dimensional (3D) multiwall carbon nanotube (MWCNT) nets was developed as an anode with simultaneous high-rate and long-term cycling performance in a lithium-ion battery. As the current density was increased to 50 A g^–1, the LBL structure exhibited excellent long-term cycling and rate performance. Thus, the Co₃O₄ nanoplates were in good electrical contact with the capillary-like 3D MWCNT nets under mechanically severe strain during long-term, high-rate cyclic operation