Discrete catalytic nanoparticles with diameters in the range of 1−2 nm and 3−5 nm respectively are obtained by placing controllable numbers of metal atoms into the cores of apoferritin, and used for growth of single-walled carbon nanotube (SWNTs) on substrates by chemical vapor deposition (CVD). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and micro-Raman spectroscopy are used to characterize isolated nanotubes grown from the discrete nanoparticles. The characterizations, carried out at single-tube and single-particle level, obtain clear evidence that the diameters of nanotubes are determined by the diameters of catalytic nanoparticles. With nanoparticles placed on ultrathin alumina membranes, isolated SWNTs are grown and directly examined by transmission electron microscopy. For the first time, both ends of an as-grown single-walled nanotube are imaged by TEM, leading to a microscopic picture of nanotube growth mechanism. It is shown that controlling the structures of catalytic nanoparticles allows the control of nanotube diameter, and could also enable the control of SWNT length and eventually chirality.

Single-walled carbon nanotubes (SWNT) are grown by a plasma enhanced chemical vapor deposition (PECVD) method at 600°C. The nanotubes are of high quality as characterized by microscopy, Raman spectroscopy, and electrical transport measurements. High performance field effect transistors are obtained with the PECVD nanotubes. Interestingly, electrical characterization reveals that nearly 90% of the nanotubes are semiconductors and thus highly preferential growth of semiconducting over metallic tubes in the PECVD process. Control experiments with other nanotube materials find that HiPco nanotubes consist of ∼61% semiconductors, while laser ablation preferentially grows metallic SWNTs (∼70%). The characterization method used here should also be applicable to assessing the degree of chemical separation of metallic and semiconducting nanotubes.Single-walled carbon nanotubes (SWNTs) have been established as ballistic metallic and semiconducting molecular wires potentially useful for future high performance electronics. 1-4 To realize this potential, it is necessary to achieve preferential growth of semiconducting versus metallic nanotubes or enable high degrees of separation 5-8 of the two types of nanotubes. Here, we present synthesis of high quality SWNTs by a plasma enhanced CVD method at 600°C, and an unexpected result that the PECVD method preferentially grows semiconducting nanotubes at a high percentage of ∼90%. The preferential growth has prompted us to investigate the percentages of semiconducting (s-SWNT) and metallic SWNTs (m-SWNT) in materials grown by other methods, both as control experiments and to elucidate these previously unknown parameters for some of the widely used nanotube materials. We conclude that the relative abundances of semiconducting and metallic nanotubes grown by various methods are different and do not necessarily follow the 2:1 ratio expected for random chirality distribution. Highly preferential growth of a certain type of SWNT can occur depending on the growth method. The results and characterization method presented here should also have implications to chemical separation of nanotubes.A home-built radio frequency (RF, 13.56 MHz) 4-in. remote PECVD system 9 was used for nanotube growth (Figure 1). The plasma discharge source consisted of a copper coil wound around the outside of the 4-in. quartz tube near the feed-gas entrance. We operated the plasma in capacitive mode with the interior furnace wall acting as an electrode and the coil acting as the counter electrode. This created a low-density plasma that propagated down the interior of the quartz tube and reached the sample placed at the center of the tube reactor, 40 cm away from the plasma coil. The

In nature, electrical signalling occurs with ions and protons, rather than electrons. Artificial devices that can control and monitor ionic and protonic currents are thus an ideal means for interfacing with biological systems. Here we report the first demonstration of a biopolymer protonic field-effect transistor with proton-transparent PdH x contacts. In maleic-chitosan nanofibres, the flow of protonic current is turned on or off by an electrostatic potential applied to a gate electrode. The protons move along the hydrated maleic-chitosan hydrogen-bond network with a mobility of ~4. . This study introduces a new class of biocompatible solid-state devices, which can control and monitor the flow of protonic current. This represents a step towards bionanoprotonics.

The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydrationdependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Current−voltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectroscopy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10 −4 −10 −3 S cm −1 ), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.

With a cut metallic SWNT (gap L ~ 5-6 nm) bridged by a pentacene nano-crystallite (Fig.1b&c), we observed clear semiconducting FET characteristics in the current vs. gate (I ds -V gs ) curve (Fig. 2a). The device exhibited a current modulation of I max /I min ~ 10 5 under gating at a fixed bias voltage of V ds = -0.5V. The drastic switching clearly differed from the original metallic SWNT device (lack of gate dependence, Fig. 2a inset). This corresponds to the formation of a pentacene FET with channel length L ~ 5-6 nm and width of w ~ 2 nm (i.e., the diameter of the SWNT) as charge transport via hopping between pentacene molecules should be mainly confined in a width on the order of the tube diameter. Notably, the subthreshold swing of the device is S ~ 400 mV/decade (Fig. 2a).Small organic molecules and conjugated polymers can be easily processed to afford functional electronics such as field effect transistors (FETs), 1a and in principle, scaling 1b to singlemolecule long devices could circumvent the low carrier mobility problem for these materials to afford high performance ballistic FETs 2,3 . For highly scaled molecular transistors with short channels however, it is crucial to develop novel device geometries to optimize gate electrostatics needed for ON/OFF switching. 4,5 It is shown here that single-walled carbon nanotubes (SWNT) can be used as quasi one-dimensional (1D) electrodes to construct organic FETs with molecular scale width (~2 nm) and channel length (down to 1-3 nm). The favorable gate electrostatics associated with the sharp 1D electrode geometry allows for room temperature conductance modulation by orders of magnitude for organic transistors that are only several-molecules in length, with switching characteristics superior to devices with lithographically patterned metal electrodes. We suggest that carbon nanotubes may prove to be novel electrodes for a variety of molecular devices.We first developed a reproducible method of cutting metallic SWNTs to form small gaps within the tubes and with control over the gap size down to L~2 nm. The cutting relied on electrical break-down 6 of individual SWNTs between two metal electrodes (Fig. 1a), and the size of the cut was found to be controllable by varying the lengths of the SWNTs (see Ref.6b and Supp. Info). Organic materials were then deposited to bridge the gap in the vapor (for pentacene) or solution phase (for regio-regular ploy (3-hexylthiophene), P3HT), forming the smallest organic FETs with effective channel length down to L~1-3 nm and width ~2 nm. b cWe varied the channel lengths L of SWNT-contacted pentacene FETs (L ~ 1-3 nm, L ~5-6 nm and L ~10-15 nm respectively) and observed length dependent transport properties at various temperatures. At T=300K, the devices exhibited on-current I max scaling approximately with ~1/L (under V ds =-1 V). This suggests

Proton conduction is essential in biological systems. Oxidative phosphorylation in mitochondria, proton pumping in bacteriorhodopsin, and uncoupling membrane potentials by the antibiotic Gramicidin are examples. In these systems, H+ hop along chains of hydrogen bonds between water molecules and hydrophilic residues – proton wires. These wires also support the transport of OH− as proton holes. Discriminating between H+ and OH− transport has been elusive. Here, H+ and OH− transport is achieved in polysaccharide- based proton wires and devices. A H+- OH− junction with rectifying behaviour and H+-type and OH−-type complementary field effect transistors are demonstrated. We describe these devices with a model that relates H+ and OH− to electron and hole transport in semiconductors. In turn, the model developed for these devices may provide additional insights into proton conduction in biological systems.

A transparent paper made of chitin nanofibers (ChNF) is introduced and its utilization as a substrate for flexible organic light-emitting diodes is demonstrated. Given its promising macroscopic properties, biofriendly characteristics, and availability of the raw material, the utilization of the ChNF transparent paper as a structural platform for flexible green electronics is envisaged.

Racemates often have lower solubility than enantiopure compounds, and mixing of enantiomers can enhance aggregation propensity of peptides. Amyloid β (Aβ) 42 is an aggregation-prone peptide, believed to play a key role in Alzheimer’s Disease. Soluble Aβ42 aggregation intermediates (oligomers) have emerged as particularly neurotoxic. We hypothesized that addition of mirror image (D-) Aβ42 should reduce the concentration of toxic oligomers formed by natural (L-) Aβ42. We synthesized L- and D-Aβ42 and found their equimolar mixing to lead to accelerated fibril formation. Confocal microscopy with fluorescently labeled analogs of the enantiomers showed their co-localization in racemic fibrils. Reflecting enhanced fibril formation propensity, racemic Aβ42 was less prone to form soluble oligomers. This resulted in protection of cells from toxicity of L-Aβ42 at concentrations ranging up to 50 µM. In summary, mixing of Aβ42 enantiomers induces accelerated formation of non-toxic fibrils.