Graphene materials have entered a phase of maturity in their development that is characterized by their explorative utilization in various types of applications and fi elds from electronics to biomedicine. Herein, we describe the recent advances made with graphene-related materials in the biomedical fi eld and the challenges facing these exciting new tools both in terms of biological activity and toxicological profi ling in vitro and in vivo.
Graphene has unique mechanical, electronic, and optical properties, which researchers have used to develop novel electronic materials including transparent conductors and ultrafast transistors. Recently, the understanding of various chemical properties of graphene has facilitated its application in high-performance devices that generate and store energy. Graphene is now expanding its territory beyond electronic and chemical applications toward biomedical areas such as precise biosensing through graphene-quenched fluorescence, graphene-enhanced cell differentiation and growth, and graphene-assisted laser desorption/ionization for mass spectrometry.
A simple method that uses graphene to fabricate nanotopographic substrata was reported for stem cell engineering. Graphene-incorporated chitosan substrata promoted adhesion and differentiation of human mesenchymal stem cells (hMSCs). In addition, we proposed that nanotopographic cues of the substrata could enhance cell?cell and cell?material interactions for promoting functions of hMSCs.
Donor?acceptor-blended bulk-heterojunction (BHJ) solar cells fabricated by low-cost printing technology offer a number of advantages: They are robust, lightweight, and flexible and can be produced in large area by roll-to-roll manufacturing.[1?4] During recent years, there have been significant improvements in power conversion efficiency (PCE) in BHJ solar cells because of the synthesis of specific polymers and small molecules, the achievement of improved nanomorphology through process control (by processing additives), and the use of new architectures (e.g., the inverted structure with specific transport layers).
Even weak van der Waals (vdW) adhesion between two-dimensional solids may perturb their various materials properties owing to their low dimensionality. Although the electronic structure of graphene has been predicted to be modified by the vdW interaction with other materials, its optical characterization has not been successful. In this report, we demonstrate that Raman spectroscopy can be utilized to detect a few percent decrease in the Fermi velocity (vF) of graphene caused by the vdW interaction with underlying hexagonal boron nitride (hBN). Our study also establishes Raman spectroscopic analysis which enables separation of the effects by the vdW interaction from those by mechanical strain or extra charge carriers.
A uniform polymer thin layer of controllable thickness was bar-coated onto a chemical vapor deposition (CVD) grown monolayer graphene surface. The effects of this coating layer on the optical, electric, and tribological properties were then investigated. The thin polymer coating layer did not reduce the optical transmittance of the graphene films. The variation in the sheet resistance of the graphene films after the coating depended on the interaction between polymer and graphene.
We present polarized optical transmission study of uniaxially strained large scale graphene in THz/ far-infrared (IR) frequency region. Graphene was supported on stretchable polyethylene substrate and they were elongated up to 20% (DL/Lo¼ 0.2) by applying tensile force.
Graphene has attracted much attention because of its exceptional physical properties such as an anomalous quantum hall effect[1,2] and Klein tunneling originating from a chiral fermion. In addition, graphene-based electronic devices have been designed to exhibit high carrier mobility, ultrahigh speed,[5,6] large scale flexibility,[7,8] and fast DNA sequencing.
The possibility of fabricating a full graphene device was investigated by utilizing atomic layer etching (ALET) technology. By using O2 ALET which functions by oxygen radical adsorption followed by the removal of the oxygen chemisorbed on carbon, the removal of exactly one graphene layer per ALET cycle was detected through the increase of the transmittance by 2.3% after one ALET cycle and by the decrease of the G peak in the Raman spectra.
Although graphene films have a strong potential to replace indium tin oxide anodes in organic light-emitting diodes (OLEDs), to date, the luminous efficiency of OLEDs with graphene anodes has been limited by a lack of efficient methods to improve the low work function and reduce the sheet resistance of graphene films to the levels required for electrodes
Recently, graphene-based organic light emitting diodes (OLEDs) were successfully demonstrated using graphene as anodes. However, the graphene electrodes have not been utilized for polymer light emitting diodes (PLEDs) yet, although the simpler device structure and the solution-based fabrication process of PLEDs are expected to be more advantageous in terms of time and cost.
It is known that low-field mobility of graphene depends largely on the substrate material on which it is transferred. We measured Drude optical conductivity oh graphene on various substrates and determined the carrier density and carrier scattering rate. The carrier density varies widely depending on the substrate material.
Large-area monolayer graphene, synthesized by chemical vapor deposition, was transferred to a 1-in. quartz substrate. The high-quality monolayer graphene has been subject to characterization of the nonlinear properties near 1 lm and was successfully applied as saturable absorber for passive mode-locking of a femtosecond Yb:KLuW laser.
For the application of graphene quantum dots (GQDs) to optoelectronic nanodevices, it is of critical importance to understand the mechanisms which result in novel phenomena of their light absorption/emission. Here, we present size-dependent shape/edge-state variations of GQDs and visible photoluminescence (PL) showing anomalous size dependences.
The first micrometer-sized graphene flakes extracted from graphite demonstrated outstanding electrical, mechanical and chemical properties, but they were too small for practical applications. However, the recent advances in graphene synthesis and transfer techniques have enabled various macroscopic applications such as transparent electrodes for touch screens and light-emitting diodes (LEDs) and thin-film transistors for flexible electronics in particular.
The total thickness of a graphene sample depends upon the number of individually stacked graphene layers. The 13 corresponding surface plasmon resonance (SPR) reflectance alters the SPR angle, depending on the number of gra- 14 phene layers. Thus, the correlation between the SPR angle shift and the number of graphene layers allows for a 15 nonintrusive, real-time, and reliable counting of graphene layers. A single-layer graphene (SLG) is synthesized 16 by means of chemical vapor deposition, followed by physical transfer to a thin gold film (48 nm) repeatedly, so 17 that multilayer graphene samples with one, three, and five layers can be prepared. Both the measured SPR angles 18 and the entire reflectance curve profiles successfully distinguish the number of graphene layers.
We develop two simple methods?the dip coat stamping and lift-off methods?to transfer large area, high quality graphene films onto the top and side faces of the polymer optical fiber. The graphene films can be synthesized using chemical vapor deposition method on large Cu foils. After synthesis, the graphene films are characterized by scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The polymer optical fiber probe with the transferred graphene film can be used as a chemical sensor for the detection of various organic aerosols.
This article reviews recent advances in the large-area synthesis of graphene sheets and the applications of such sheets to graphene-based transistors. Graphene is potentially useful in a wide range of practical applications that could benefit from its exceptional electrical, optical, and mechanical properties. Tremendous effort has been devoted to overcoming several fundamental limitations of graphene, such as a zero band gap and a low direct current conductivity-to-optical conductivity ratio.
Successful application of graphene requires development of various tools for its chemical modification. In this paper, we present a Raman spectroscopic investigation of the effects of UV light on single layer graphene with and without the presence of O2 molecules. The UV emission from a low pressure Hg lamp photolyzes O2 molecules into O atoms, which are known to form epoxy on the basal plane of graphene.
We demonstrate low-temperature growth and direct transfer of graphene?graphitic carbon films (G?GC) onto plastic substrates without the use of supporting materials. In this approach, G?GC films were synthesized on copper layers by using inductively coupled plasma enhanced chemical vapor deposition, enabling the growth of few-layer graphene (G) on top of Cu and the additional growth of graphitic carbon (GC) films above the graphene layer at temperatures as low as 300 ?C. The patterned G?GC films are not easily damaged or detached from the polymer substrates during the wet etching and transfer process because of the van der Waals forces and π?π interactions between the films and the substrates.
Graphene films grown on metal substrates by chemical vapor deposition (CVD) method have to be safely transferred onto desired substrates for further applications. Recently, a roll-to-roll (R2R) method has been developed for large-area transfer, which is particularly efficient for flexible target substrates. However, in the case of rigid substrates such as glass or wafers, the roll-based method is found to induce considerable mechanical damages on graphene films during the transfer process, resulting in the degradation of electrical property.
High-performance, flexible all graphene-based thin film transistor (TFT) was fabricated on plastic substrates using a graphene active layer, graphene oxide (GO) dielectrics, and graphene electrodes. The GO dielectrics exhibit a dielectric constant (3.1 at 77 K), low leakage current (17 mA/cm2 ), breakdown bias (1.5 × 106 V/cm), and good mechanical flexibility.
Graphene has exceptional optical, mechanical, and electrical properties, making it an emerging material for novel optoelectronics, photonics, and flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constraint for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using nonvolatile ferroelectric polymer gating. In this hybrid structure, largescale graphene is heavily doped up to 3 1013 cm2 by nonvolatile ferroelectric dipoles, yielding a low sheet resistance of 120 Ω/0 at ambient conditions.
We present the photon induced conductivity of 2D DNA lattices with and without graphene and demonstrate the switching current responses controlled by light irradiation. The conductivity in the DNA lattices with protein streptavidin controlled by blue and white lights shows significant enhancement with the addition of graphene. An optical pulse response of a graphene immobilized DNA lattice is encouraging and may lead to various bio-sensing applications such as immunological assays, DNA forensics, and toxin detection.
Graphene?CdS nanowire (NW) hybrid structures with high-speed photoconductivity were developed. The hybrid structure was comprised of CdS NWs which were selectively grown in specific regions on a single-layer graphene sheet. The photoconductive channels based on graphene?CdS NW hybrid structures exhibited much larger photocurrents than graphene-based channels and much faster recovery speed than CdS NW network-based ones.
The near explosion of attention given to graphene has attracted many to its research field. As new studies and findings about graphene synthesis, properties, electronic quality control, and possible applications simultaneous burgeon in the scientific community, it is quite hard to grasp the breadth of graphene history. At this stage, graphene’s many fascinating qualities have been amply reported and its potential for various electronic applications are increasing, pulling in ever more newcomers to the field of graphene.
The efficient passive mode-locking of a Ti:sapphire laser with a monolayer graphene saturable absorber is demonstrated for the first time. Highquality and large-area (1 in.) monolayer graphene, synthesized by chemical vapor deposition, exhibits ultrafast recovery times and excellent nonlinear absorption behavior for bulk solid-state laser mode-locking near 800 nm. The continuous-wave mode-locked Ti:sapphire laser generates 63-fs pulses with output powers up to 480 mW under stable operation at 99.4 MHz.
We present polarized optical transmission study of uniaxially strained large scale graphene in THz/ far-infrared (IR) frequency region. Graphene was supported on stretchable polyethylene substrate and they were elongated up to 20% (DL/Lo¼ 0.2) by applying tensile force.
The technical breakthrough in synthesizing graphene by chemical vapor deposition methods (CVD) has opened up enormous opportunities for large-scale device applications. To improve the electrical properties of CVD graphene grown on copper (Cu-CVD graphene), recent efforts have focused on increasing the grain size of such polycrystalline graphene films to 100 μm and larger.
Since the first isolation of graphene in 2004 by mechanical exfoliation from graphite, many people have tried to synthesize large-scale graphene using various chemical methods. In particular, there has been a great number of advances in the synthesis of graphene using chemical vapor deposition (CVD) on metal substrates such as Ni and Cu. Recently, a method to synthesize ultra-large-scale (∼30 inch) graphene films using roll-to-roll transfer and chemical doping processes was developed that shows excellent electrical and physical properties suitable for practical applications on a large scale.
The pre-treatment (catalyst reduction with H2) time effect on the carbon nanotube (CNT) growth is reported. The total CNT height, the initial growth rate, the diameter, the number of walls, and the alignment in the CNT forests change with the catalyst reduction time. Densely packed, vertically super-aligned, double-walled CNT (DWCNT) forests with 9 mm height were synthesized in 10 hrs.
We demonstrated that the structural formation of vertically aligned carbon nanotube (CNT) forests is primarily affected by the geometry-related gas flow, leading to the change of growth directions during the chemical vapor deposition (CVD) process. By varying the growing time, flow rate, and direction of the carrier gas, the structures and the formation mechanisms of the vertically aligned CNT forests were carefully investigated.
We fabricated a highly oxidized large-scale graphene platform using chemical vapor deposition (CVD) and UV/ozone-based oxidation methods. This platform offers a large-scale surface-enhanced Raman scattering (SERS) substrate with large chemical enhancement in SERS and reproducible SERS signals over a centimeter-scale graphene surface. After UV-induced ozone generation, ozone molecules were reacted with graphene to produce oxygen-containing groups on graphene and induced the p-type doping of the graphene.
We demonstrate high-performance, flexible, transparent heaters based on large-scale graphene films synthesized by chemical vapor deposition on Cu foils. After multiple transfers and chemical doping processes, the graphene films show sheet resistance as low as ∼43 Ohm/sq with ∼89% optical transmittance, which are ideal as low-voltage transparent heaters.
With the emergence of human interface technology, the development of new applications based on stretchable electronics such as conformal biosensors and rollable displays are required. However, the difficulty in developing semiconducting materials with high stretchability required for such applications has restricted the range of applications of stretchable electronics. Here, we present stretchable, printable, and transparent transistors composed of monolithically patterned graphene films.
High-quality monolayer graphene as large as 1:2 × 1:2 cm2 was synthesized by chemical vapor deposition and used as a transmitting saturable absorber for efficient passive mode-locking of a femtosecond bulk solid-state laser. The monolayer graphene mode-locked Cr:forsterite laser was tunable around 1:25 μm and delivered sub-100 fs pulses with output powers up to 230 mW.
Organic materials [1,2] and amorphous fi lms  have long been studied for foldable and wearable mobile devices since the devices must be fabricated on a fl exible plastic fi lm. However, higher device performance is expected using a singlecrystalline inorganic compound semiconductor, such as gallium nitride (GaN), because of its high radiative recombination rate and mobility, as well as its excellent thermal and mechanical characteristics.
We study ultrafast modulations of absorption spectra for both monolayer and multilayer graphene, by performing time-resolved transmission measurements with tuning probe photon energy. While reduced absorptions by photo-excited carriers are observed in monolayer graphene irrespective of the probe energy, multilayer graphene shows increased absorption at around 0.6 eV, which is explained by the optical transitions between subband states.
To use human neural stem cells (hNSCs) for brain repair and neural regeneration, it is critical to induce hNSC differentiation that is directed more towards neurons than glial cells. [1?5] However, most previous studies report that hNSCs, without biochemical motifs or co-culturing, differentiated more towards glial cells than neurons.
We study the effect of extended charge defects in electronic transport properties of graphene. Extended defects are ubiquitous in chemically and epitaxially grown graphene samples due to internal strains associated with the lattice mismatch. We show that at low energies these defects interact quite strongly with the 2D Dirac fermions and have an important effect in the DC-conductivity of these materials.
We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples.
Hydrophobic self-assembled monolayers (SAMs) with alkyl chains of various lengths were inserted between CVD-grown graphene layers and their SiO2 substrates (figure). As the SAM alkyl chain length increased, substrate-induced doping was suppressed by the ordered close-packed structure of SAMs with long alkyl chains.
High mobility of massless Dirac fermion plays critical role in high-speed electronic device application of graphene. In free-standing graphene electron mobility as high as = 250 000 cm2 /V s is reported at room temperature.
Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation into muscles, bones, and cartilages.
Selective n-type doping of graphene is developed by utilizing patternable gold nanoparticles functionalized with photoreactive cinnamate moieties. The gold nanoparticles can be regularly patterned on the graphene by UV-induced cross-linking of cinnamate, which provides a convenient method to control the optical and electrical properties of graphene site-specifically.
We have devised a method to optimize the performance of organic field-effect transistors (OFETs) by controlling the work functions of graphene electrodes by functionalizing the surface of SiO2 substrates with self-assembled monolayers (SAMs). The electron-donating NH2-terminated SAMs induce strong n-doping in graphene, whereas the CH3-terminated SAMs neutralize the p-doping induced by SiO2 substrates, resulting in considerable changes in the work functions of graphene electrodes.
Preparing graphene and its derivatives on functional substrates may open enormous opportunities for exploring the intrinsic electronic properties and new functionalities of graphene. However, efforts in replacing SiO2 have been greatly hampered by a very low sample yield of the exfoliation and related transferring methods. Here, we report a new route in exploring new graphene physics and functionalities by transferring large-scale chemical-vapor deposition singlelayer and bilayer graphene to functional substrates.
We have measured optical transmission and reflection spectra of large scale graphene grown by chemical vapor deposition technique over the extensive frequency range from far-IR to uv 4 meV?6.2 eV. Large scale graphene exhibits an excitonic absorption peak in the uv-region = 4.6 eV and the constant interband absorption with 1=e2 /4 in the IR-visible region, respectively.
There has been much interest in graphene-based electronic devices because graphene provides excellent electrical, optical, and mechanical properties. [ 1 ] In this sense, organic electronic devices using graphene electrodes have attracted considerable attention, and several reports have described the use of graphene source/drain electrodes in organic fi eld-effect transistors (OFETs).
Organic electronic devices that use graphene electrodes have received considerable attention because graphene is regarded as an ideal candidate electrode material. Transfer and lithographic processes during fabrication of patterned graphene electrodes typically leave polymer residues on the graphene surfaces. However, the impact of these residues on the organic semiconductor growth mechanism on graphene surface has not been reported yet.
A novel graphene-on-organic film fabrication method that is compatible with a batch microfabrication process was developed and used for electromechanically driven microactuators. A very thin layer of graphene sheets was monolithically integrated and the unique material characteristics of graphene including negative thermal expansion and high electrical conductivity were exploited to produce a bimorph actuation.
In this paper we present a transparent and stretchable dielectric elastomer actuator(DEA). The device, called "active skin" is under development as a new means of human interfaces. The active skin consists of elastomeric films sandwiched between compliant patterned electrodes. Thus, depending on the properties of the elastomer or electrodes, it is possible to realize a wide variety of implementations as transducers.
Recently, many studies have been focused on the development of fiber optic sensor systems for various gases and vapors. In the present study, an intrinsic polymer optical fiber (POF) sensor using graphene is described for the purpose of acetone vapor sensing for the first time. Observations on the continuous measurement of acetone vapor in dehydrated air are presented. The principle of operation of sensor transduction relies on the dependence of the reflectance on the optical and geometric properties of the sensitive over layered when the vapor molecules are adsorbed on the graphene film.
A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 ( 57 and 91 ( 50 cm2 /(V·s), respectively, at a drain bias of -1 V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility.
We developed means to produce wafer scale, high-quality graphene films as large as 3 in. wafer size on Ni and Cu films under ambient pressure and transfer them onto arbitrary substrates through instantaneous etching of metal layers. We also demonstrated the applications of the large-area graphene films for the batch fabrication of field-effect transistor (FET) arrays and stretchable strain gauges showing extraordinary performances.
The outstanding electrical1 , mechanical2,3 and chemical4,5 properties of graphene make it attractive for applications in flexible electronics6?8. However, efforts to make transparent conducting films from graphene have been hampered by the lack of effi- cient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications.
This paper reports a mechanically flexible, transparent thin film transistor that uses graphene as a conducting electrode and single-walled carbon nanotubes (SWNTs) as a semiconducting channel. These SWNTs and graphene films were printed on flexible plastic substrates using a printing method. The resulting devices exhibited a mobility of ∼2 cm2 V?1 s?1, On/Off ratio of ∼102, transmittance of ∼81% and excellent mechanical bendability.
We report substantially enhanced photoluminescence (PL) from hybrid structures of graphene/ZnO films at a band gap energy of ZnO ( 3:3 eV=376 nm). Despite the well-known constant optical conductivity of graphene in the visible-frequency regime, its abnormally strong absorption in the violet-frequency region has recently been reported. In this Letter, we demonstrate that the resonant excitation of graphene plasmon is responsible for such absorption and eventually contributes to enhanced photoemission from structures of graphene/ZnO films when the corrugation of the ZnO surface modulates photons emitted from ZnO to fulfill the dispersion relation of graphene plasmon.
This work demonstrates a large-scale batch fabrication of GaN light-emitting diodes (LEDs) with patterned multi-layer graphene (MLG) as transparent conducting electrodes. MLG films were synthesized using a chemical vapor deposition (CVD) technique on nickel films and showed typical CVD-synthesized MLG film properties, possessing a sheet resistance of ∼620 / with a transparency of more than 85% in the 400?800 nm wavelength range. T
Raman spectra of a single layer graphene sheet placed in different gold substrates were obtained and are discussed in the context of surface enhanced Raman scattering (SERS). The gold substrates were composed of a combination of a thermally deposited gold film and a close-packed gold nanosphere layer. The SERS effects were negligible when the excitation wavelength was 514 nm, while the Raman signals were enhanced 3- to 50-fold when the excitation wavelength was 633 nm.
Since the discovery of microscale single-layer graphene in 2004, graphene and related materials have received intensive attention as promising materials for nanoelectronics because of their fascinating electrical, mechanical, and chemical properties.[5,6] In addition, the recent large-scale synthesis of highquality graphene films enables their use in bendable and/or stretchable transparent electrodes for solar cells, sensors, and displays. Surface grafting on graphene of functional materials will be an indispensable technique for these applications....
To understand the self-assembly process of the transition metal (TM) nanoclusters and nanowires self-synthesized by hydroquinone (HQ) and calixhydroquinone (CHQ) by electrochemical redox processes, we have investigated the binding sites of HQ for the transition-metal cations TMn+=Ag+, Au+, Pd2+, Pt2+, and Hg2+ and those of quinone (Q) for the reduced neutral metals TM0, using ab initio calculations. For comparison, TM0?HQ and TMn+?Q interactions, as well as the cases for Na+ and Cu+(which do not take part in self-synthesis by CHQ) are also included. In general, TM?ligand coordination is controlled by symmetry constraints imposed on the respective orbital interactions. ....
The edge-to-face interactions for either axially or facially substituted benzenes are investigated by using ab initio calculations. The predicted maximum energy difference between substituted and unsubstituted systems is ∼0.7 kcal/mol (∼1.2 kcal/mol if substituents are on both axially and facially substituted positions). In the case of axially substituted aromatic systems, the electron density at the para position is an important stabilizing factor, and thus the stabilization/destabilization by substitution is highly correlated to the electrostatic energy....
We introduced a simple chemical method to synthesize semimetal bismuth nanoparticles in N,Ndimethylformamide (DMF) by reducing Bi3+ with sodium borohydride (NaBH4) in the presence of poly- (vinylpyrroldone) (PVP) at room temperature. The size and dispersibility of Bi nanoparticles can be easily controlled by changing the synthetic conditions such as the molar ratio of PVP to BiCl3 and the concentration of BiCl3. The UV-visible absorption spectra of Bi nanoparticles of different diameters are systematically studied.....
For the first time, we introduced a simple method of synthesizing segregated thin antimony nanowires based on the principle that nanoparticles can spontaneously self-assemble into crystalline nanowires (∼20 nm) in the absence of any rigid templates at room temperature. By collecting electron energy loss spectra from individual Sb nanowires with different diameters, we investigated the effect of nanowire diameter on plasmon excitations in Sb nanowires. As the diameter of Sb nanowire decreases, we find that the peak energy of surface plasmon shifts toward the lower energy....
The equilibrium structures and binding energies of the benzene complexes of p-benzoquinones (PBQ) and its negatively charged anionic species (PBQ(-) and PBQ(2-)) have been investigated theoretically using second-order Moller-Plesset calculations. While neutral p-benzoquinone-benzene clusters (PBQ-Bz) prefer to have a parallel displaced geometry (P-c), CH...pi interactions (T-shaped geometries) prevail in the di-anionic PBQ-benzene (PBQ(2-)-Bz) complexes (T-e(2-)). Studies on dianionic p-benzoquinone-benzene clusters showed that two nonbonded intermolecular interactions compete in the most stable conformation....
The mechanism of electrochemical reduction of calixquinones (CQs) is of vital importance, as their reduction products, calixhydroquinones (CQH8s), are known to self-assemble organic nanotubes, which in turn selfassemble novel metal nanostructures by a self-synthetic process of electrochemical reduction of solvated metals. We therefore conducted detailed studies of electrochemical reduction of CQ in rigorously dried acetonitrile (CH3CN) and in CH3CN containing varied amounts of water as well as perchloric acid.....
We use first principles calculations to investigate the structure and electronic properties of ultrathin silver (Ag) nanowires self-synthesized in organic calixhydroquinone (CHQ) nanotubes. The insulating CHQ nanotubes get transformed to semiconducting calixdiquinone-dihydroquinone (CQHQ) tubes in the presence of Ag. These encapsulated nanowires have linear crystalline structure. The electron density around the Fermi level is localized on the Ag nanowire. This indicates that the organic tubes act as shields between Ag nanowires, and the quantum confinement is possible in the encapsulated Ag nanowires like in quantum dots.....
Using the computer-aided molecular design approach, we recently reported the synthesis of calixhydroquinone (CHQ) nanotube arrays self-assembled with infinitely long one-dimensional (1-D) short hydrogen bonds (H-bonds) and aromatic-aromatic interactions. Here, we assess various calculation methods employed for both the design of the CHQ nanotubes and the study of their assembly process....
A new molecular system, 2,11-dithio[4,4]metametaquinocyclophane containing a quinone moiety, was designed and synthesized. As the quinone moiety can readily be converted into an aromatic π-system (hydroquinone) upon reduction, the nanomechanical molecular cyclophane system exhibits a large flapping motion like a molecular flipper from the electrochemical redox process. The conformational changes upon reduction and oxidation are caused by changes of nonbonding interaction forces (devoid of bond formation/breaking) from the edge-to-face to faceto-face aromatic interactions and vice versa, respectively....
Protein folding is a fundamental problem in life sciences. It is generally known that nonlocal interactions determine the folding conformation to the context of the folding process.1,2 As the most common regular secondary conformation in proteins, the helix has been an important ingredient of the protein folding problem.3 In particular alanine-based polypeptides are widely studied to identify the helix-folding process in that the alanine amino acid is known to have one of the highest helix propensities....
We have studied [n,n]metaparacyclophanessmodel compounds exhibiting edge-to-face and displaced stacked aromatic-aromatic interactionssusing semiempirical calculations for n ) 2-5 and ab initio calculations for n ) 2-4. For n ) 2 and 3, the strain energies govern the conformational preference, while for n ) 4 and 5 the aromatic-aromatic and strain energies are equally important. The 3,12- dithio[4,4]metaparacyclophanes exhibit edge-to-face aromatic-aromatic intereactions, while the [4,4]metaparacyclophanes and 2,11-dithio[4,4]metaparacyclophanes exhibit displaced stacked aromatic-aromatic interactions.....
It is well known that a lens-based far-field optical microscope cannot resolve two objects beyond Abbe’s diffraction limit. Recently, it has been demonstrated that this limit can be overcome by lensing effects driven by surface-plasmon excitation1?3, and by fluorescence microscopy driven by molecular excitation4 . However, the resolution obtained using geometrical lens-based optics without such excitation schemes remains limited by Abbe’s law even when using the immersion technique5 , which enhances the resolution by increasing the refractive indices of immersion liquids.....
Problems associated with large-scale pattern growth of graphene constitute one of themain obstacles to using thismaterial in device applications1. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chem-ically derived from graphite crystals and graphene oxides2,3 . However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two differentmethods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of 280Vper square, with 80 per cent optical transparency......
We present an experimental investigation on the scaling of resistance in individual single walled carbon nanotube devices with channel lengths that vary four orders of magnitude on the same sample. The electron mean free path is obtained from the linear scaling of resistance with length at various temperatures. The low temperature mean free path is determined by impurity scattering, while at high temperature the mean free path decreases with increasing temperature, indicating that it is limited by electron-phonon scattering. An unusually long mean free path at room temperature has been experimentally confirmed. Exponentially increasing resistance with length at extremely long length scales suggests anomalous localization effects.
Owing to outstanding mechanical and electrical properties of carbon nanotubes (CNTs), intense research efforts have been made to synthesize aligned long CNTs. Chemical vapor deposition(CVD) methods using transition metal nanoparticle catalysts have been widely used to produce long single-walled nanotubes(SWNTs). The growth of ultralong CVD SWNTs, whose lengths are up to 4 cm, has been reported in the literature. On the other hand, the multi-walled nanotubes (MWNTs) have great potential for nanomechanical and nanoelectrical applications, employing their excellent mechanical properties and hierarchal structures. However, the scale and diversity of the MWNT structures have been limited because of short lengths of available isolated MWNTs.
We report a simple but powerful method for engineering multi-walled carbon nanotubes (MWNTs) by using manipulation by an atomic-force microscope. The successive shell-by-shell extraction process of ultralong MWNTs allows the exposure of the innermost single-walled carbon nanotubes (SWNTs),which have diameters as small as 0.4 nm. The inner-shell extraction process changes the electrical characteristics of the MWNTs. Whereas the outer hol-lowed-out nanotubes show either metallic or semiconducting character, the innermost SWNTs of small diameter exhibit predom-inantly metallic transport properties....
Recent interest in nanotechnology leads to a dramatic upsurge in the quest for tubular organic/inorganic nanotubes. However, few organic nanotubes exhibit interesting useful electrochemical/photochemical properties. Therefore, we have designed, synthe-sized, and characterized self-assembled organic nanotube arrays composed of nontubular subunits of electrochemically/photo-chemically active calix hydroquinones (CHQ)....
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