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A simple and economical approach to the preparation of superhydrophilic and water-capturing surfaces is reported. In this method, a common polymer aqueous blend is drop-cast onto a substrate, and the natural drying of the aqueous drop allows for the formation of phase-segregated nanosegregants between the bulk film and substrate surface. The nanosegregant is then exposed by dissolving the bulk film using water. The nanosegregant is stable, water-insoluble and optically transparent, and exhibits superhydrophilicity with a minimum contact angle below 10°. It also displays strong water-attracting ability. The mechanism of superwettability and water-capturing behavior is discussed in terms of the self-organization and functional group of the nanosegregant.

This work reports a bias-assisted natural-drying method in film drop-casting for the formation of an interfacial layer inside the bulk organic film. The natural-drying facilitates phase segregation in the polymer blend, while the simultaneous substrate bias application induces host electronic states in the interfacial layer. Consequently, an embedded organic hetero-junction is formed between the interfacial layer and bulk film. The hetero-junction not only enhances the separation of photoexcited electron–hole ( e p - h p ) pairs, but also allows for the selective storage and extraction of photocarriers through the bias-induced host states. Unusual photocurrent with negative-differential-resistance (NDR) is thus obtained for the first time for organic optoelectronic devices. The typical peak-to-valley ratio of the NDR peak is ⩾500, and the NDR behavior is stable for prolonged photocurrent measurements. The bias-assisted natural-drying method is simple and cost-effective, and can be used as a new approach to the design and control of organic interfaces.

This work reports a series of distinct current density∼field (JE) characteristics of the poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) (or PDET:PSS) conducting polymer system. Symmetrical and asymmetrical negative differential resistance (NDR) behaviors are observed for metal/PEDT:PSS/metal sandwich devices, and these novel behaviors are related to hole injection and resonant tunneling, hole blockage and extraction, and ionic motion in the PEDT:PSS films. Both the PEDT:PSS/metal interface configuration and film thickness have strong effect on the manifestation of the NDR characteristic. It is proposed that phase segregation in μm-thick PEDT:PSS films could lead to the conversion of hole-dominated transport to ionic motion-dominated conduction, thus causing a drastic change in JE characteristics of films with different thickness. Our results highlight the important effect of PEDT:PSS/metal interface and PEDT:PSS film thickness on charge conduction, and broaden our current understanding of this model organic system with both electronic and ionic conducting components.

Size and ligand effects are the basis for the novel properties and applications of metallic nanoparticles (NPs) in nanoelectronics, optoelectronics, and biotechnology. This work reports the first observation of enhanced photoelectron emission from metallic Au NPs ligated by alkanethiols. The enhancement is based on a conceptually new mechanism: the AuNP provides electrons while the alkane ligand emits electrons due to its low or negative electron affinity. Moreover, the AuNP-ligand chemical bonding is found to significantly facilitate the transmission of photoexcited electrons from the AuNP to the ligand emitter. Consequently the smooth NP film, which is a typical low-aspect-ratio two-dimensional structure, exhibits strong and stable field emission behavior under photoillumination conditions. The photoenhanced field emission is related to the interband and surface plasmon transitions in AuNPs, and a photoenhancement factor of up to approximately 300 is observed for the AuNP-based field emission. This is highly remarkable because field emission is often based on one-dimensional, high-aspect-ratio nanostructures (e.g., nanotubes and nanowires) with geometrical field enhancement effect. The chemical linkage of electron-supplying AuNP and electron-emitting alkane ligand represents a fundamentally new mechanism for efficient photoexcitation and emission. Being low-temperature/solution processable, and inkjet printable, AuNPs may be a flexible material system for optoelectronic applications such as photodetection and photoenhanced field emission.

This work addresses the electric characteristics associated with the slow ionization relaxation in ionizable alkylthiols which are widely used as passivation ligands for gold nanoparticles (NPs). It is observed that reversible ionic motion under a cycling voltage induces highly transient current with strong hysteresis loop. The ionization and relaxation of alkanethiols is responsible for the buildup and reversal of an internal bias, and thus leads to capacitive and charge memory effect in the electric conduction of the molecules. The role of ligand ionization in the electric behavior of passivated gold NPs is also demonstrated. The slow ionic process allows for both capacitive and resistive conduction and can be used to regulate the charge transport through the Au NP film. Our results represent a novel charge conduction mechanism governed by ligands in the NP/molecule binary system and would find new applications in molecular electronics and NP-based memory and sensor devices.

Two coexisting mechanisms, i.e., electrohydrodynamic destabilization and electrostatic detachment, for polymer nanostructuring in field-assisted atomic force microscope nanolithography are presented. The electrohydrodynamic destabilization mechanism is based on the surface instability of molten polymer film in the form of surface waves, and it leads to the formation of well defined polymeric wave patterns. The electrostatic detachment mechanism is associated with nano-blister formation caused by pre-existing defects, such as buried cavities in the polymer, and is responsible for the creation of hollow pillar-like structures. Here, the coexistence and pattern formation probability of the two polymer patterning modes under similar nanolithographic conditions are discussed. It was found that the field strength and the efficiency of probe-induced joule heating can significantly change the flow property of the polymer, which eventually leads to the occurrence of the two modes. The results presented here are useful in obtaining a complete picture of the diverse behaviors of polymers in AFM nanolithographic operations.

Nanotechnology is vital to the fabrication of integrated circuits, memory devices, display units, biochips and biosensors. Scanning probe microscope (SPM) has emerged to be a unique tool for materials structuring and patterning with atomic and molecular resolution. SPM includes scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In this chapter, we selectively discuss the atomic and molecular manipulation capabilities of STM nanolithography. As for AFM nanolithography, we focus on those nanopatterning techniques involving water and/or air when operated in ambient. The typical methods, mechanisms and applications of selected SPM nanolithographic techniques in nanoscale structuring and fabrication are reviewed.

Nanoscale characterization is a key field in nanoscience and technology as it provides fundamental understanding of the properties and functionalities of materials down to the atomic and molecular scale. In this article, we review the development and application of scanning tunneling microscope (STM) techniques in nanoscale characterization. We will discuss the working principle, experimental setup, operational modes, and tip preparation methods of scanning tunneling microscope. Selected examples are provided to illustrate the application of STM in the nanocharacterization of semiconductors. In addition, new developments in STM techniques including spin-polarized STM (SP-STM) and multi-probe STM (MP-STM) are discussed in comparison with conventional non-magnetic and single tip STM methods.

In this work, an aqueous acidic thin-layer-based strategy for fabricating nanostructures on silicon by using atomic force microscopy (AFM) nanolithography is presented. The approach involves the formation of microscale droplets via dilute hydrofluoride (DHF) etching, the conversion of the droplets to acidic thin layers by AFM-probe scanning, and subsequent lithographic operations using a biased probe in the aqueous layers. By varying the concentration of the acidic DHF layers, the thin layers can facilitate the creation of both positive and negative patterns, such as oxide dots and Si pores, through anodic oxidation and dissolution. In particular, the anodic oxidation in the acidic media is associated with the field-enhanced nonequilibrium dissociation of the weak electrolyte. The Si pore structure formation is related to the field-assisted dissolution of anodic oxides and the Si substrate. The acidic-layer-based technique allows switching between different lithographic modes by changing the acidity of the DHF layers, and is complementary to bulk solution-based and local meniscus-based approaches in AFM nanolithography. In principle, this method can also be extended to other materials that have similar reactions with DHF.

This review article aims to provide an updated and comprehensive description on the development of atomic force microscopy (AFM) nanolithography for structuring and fabrication at the nanometer scale. The many AFM nanolithographic techniques are classified into two general groups of force-assisted and bias-assisted nanolithography on the basis of their mechanistic and operational principles. Force-assisted AFM nanolithography includes mechanical indentation and plowing, thermomechanical writing, manipulation and dip-pen nanolithography. Bias-assisted AFM nanolithography encompasses probe anodic oxidation, field evaporation, electrochemical deposition and modification, electrical cutting and nicking, electrostatic deformation and electrohydrodynamic nanofluidic motion, nanoexplosion and shock wave generation, and charge deposition and manipulation. The experimental procedures, pattern formation mechanisms, characteristics, and functionality of nanostructures and nanodevices fabricated by AFM nanolithography are reviewed. The capabilities of AFM nanolithography in patterning a large family of materials ranging from single atoms and molecules to large biological networks are presented. Emphasis is given to AFM nanolithographic techniques such as dip-pen nanolithography, probe anodic oxidation, etc. due to the rapid progress and wide applications of these techniques.

Formation of conical polymer structures by atomic force microscopy (AFM) nanolithography and the electrical-conduction mechanism involved in the AFM- probe-induced patterning process are reported. The current is dominated by water-bridge-assisted ionic conduction. Polymer phase transition and mass redistribution occur without modification or degradation of the poly(methyl methacrylate) (PMMA) material.

The kinetics and mechanism of probe-induced oxide growth on an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) passivated native-SiO2/Si surface have been investigated using atomic force microscopy (AFM). It was found that oxidation strongly depends on tip polarity and the local chemistry of OTS molecules. At negative tip voltage, oxide grows and the oxidation involves a decomposition and depletion of OTS SAM. While under positive tip bias, OTS molecules are partially degraded. The dielectrical properties of the oxide were characterized by I–V measurements using current sensing AFM. The barrier height of AFM grown oxide, in comparison with thermal oxide and OTS SAM, was determined. Current spikes relating to the release of single charge were also observed on the I–V curves of AFM oxide.

The initial stage adsorption of molecular oxygen on the 6H-SiC(0001)-3×3 surface has been studied using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy. STM filled-state imaging reveals the sequential appearances of dark sites upon initial oxygen exposure at room temperature, followed by the appearances of bright sites at higher oxygen exposures. The changes in the STM images are interpreted on the basis of changes in the local density-of-states of the silicon adatom cluster site following the sequential development of different oxygen chemisorption states, beginning with the attachment of oxygen on the dangling bond site to its subsequent insertion in the Si-Si back-bond. Periodic density functional theory calculations supported our interpretations because the most stable chemisorption site was found to occur on the reactive adatom cluster site, as opposed to the adlayer coplanar bonds. The interaction of atomic O beam with the 3 x 3 surface results in the formation of silicon oxide nanoclusters.

The atomic reconstruction and the adsorption of oxygen on 6H-SiC (0001) surfaces have been investigated by reflection high energy electron diffraction (RHEED) dynamic rocking beam analysis. The various possible chemisorption states on the surface following the adsorption of one, two, and three oxygen molecules have been studied using periodic density functional theory. RHEED rocking beam analysis provided insights into the atomic structure of 6H-SiC (0001) 3×3 in terms of vertical and lateral displacements, as well as the initial chemisorption state of oxygen on the reconstructed surface.

Silicon adatoms can occupy either the H3 or T4 site, corresponding to the hollow or on-top site of the hexagonal unit cell of the 6H–SiC(0001)−√3×√3R30° superstructure. Distinguishing these two possibilities is impossible with the one-beam calculation method in surface electron diffraction. We provide the experimental evidence to differentiate between these two possibilities using a dynamic, multiple rocking beam approach and demonstrate the sensitivity of this approach to the lateral displacement of atoms on the surface. Our study shows that the rocking curve based on the T4 model provides a more convincing fit to the experiment compared with the H3 model, with a metric distance as low as 7%. We also identify A-type termination to be the most likely bulk-truncated substrate face among the three possible truncated faces for the 6H–SiC polytype. Coverage dependence of the silicon adatoms on the profile of the rocking curve is also investigated.

The deposition of boron nitride nanomaterials and ultrathin films in high vacuum conditions (1×10 −6 –1×10 −3 Torr) using molecular borazine as well as pre-dissociated borazine has been investigated with the motivation of studying the nucleation efficiency of BN under high vacuum conditions. Molecular borazine displays negligible sticking probability on Si(1 1 1) 7×7 at room temperature. Pre-adsorbing the borazine on silicon at 140 K and subsequent annealing is effective in forming ultrathin hexagonal films on the sample. It is possible to nucleate BN nanomaterials on nickel-sputtered silicon with high efficiency if the borazine is first discharged in a radio-frequency plasma to form reactive radicals. High quality crystalline h-BN thin films, as well as BN nanotubes can be formed on nickel via this approach.

We present converged first-principles calculations for the atomic and electronic structure of the diamond(111) - (2 x 1) face adsorbed with C 2 or C 2 H 2 based on the periodic density functional theory (DFT) in the general gradient approximation. The unique geometry of the C( 111 )-(2 × 1 ) Pandey chain provides the ideal molecular template for the self-assembly of C 2 . Depending on the initial bonding configuration of the C 2 biradical on the Pandey chain, self-assembly via mutual interactions can result in different superstructures. The most stable C 2 binding site on the C( 111)-(2 x 1) surface is the straddled bridging site between adjacent Pandey chains. Van der Waals Epitaxy of graphite can proceed on the C( 111)-(2 x 1) template following the self-assembly of C 2 biradical, with consequent gain in surface energy. The self-assembly of C 2 H 2 on top of the Pandey chain results in the formation of polyethylene that follows the zigzag course of the chain. The adsorption of C 2 H 2 can passivate the surface states on C( 111)-(2 x 1 ) and result in an opening of the surface band gap.

Silicon oxide ultrathin films grown on silicon carbide (6H–SiC) by plasma hydrogenation have been studied using ultrashallow depth profiling with time–of–flight secondary ion mass spectrometry. Plasma hydrogenation gives rise to an epitaxial 3×3R30° silicate structure on 6H–SiC(0001) and 6H–SiC(0001). By selecting appropriate sputtering conditions, an ultrathin and atomically abrupt interface delineating the boundary between the silicate epilayer (SiO+,Si2O+, and SiO3−,SiO2−) and bulk silicon carbide (SiC+) was observed on both C(0001) and Si(0001) faces. Differences in the sputtering profile between the C and Si faces suggest an enrichment of the interface stoichiometry by Si and O on the Si face. Our results support the structural models of the silicate on the C and Si-face 6H–SiC(0001) proposed by Starke [Appl. Phys. Lett. 74, 1084 (1999); J. Vac. Sci. Technol. A 17, 688 (1999)].

The modification of the electron affinity of clean and oxygenated C(111) with cesium has been studied using ultra-violet photoelectron spectroscopy. Oxygenated C(111) shows strong valence emission features at 4.2 eV attributable to CO bonding orbital. Adsorption of cesium on the oxygenated diamond results in the formation of cesium oxide features at 4.2 eV and 8 eV and the condition of negative electron affinity (NEA). The cesium oxide adlayer is thermally stable to 500 °C and the NEA condition is not removed even at saturated O exposures, suggesting that cesium oxide-modified C(111) may act as a good photo-cathode. In order to evaluate the effect of oxygen atom adsorption on the surface states of C(111) 2×1 surface, the density of states of the O:C(111) surface adopting two different oxygen binding configurations have been calculated using the periodic density functional theory. The surface gap states on clean C(111) 2×1 surface are passivated by the adsorption of 1/2 monolayer oxygen in a bridging ‘epoxy’ fashion (C–O–C) across the carbon in the Pandey chain. At 1 monolayer oxygen coverage, the 2×1 reconstruction is lifted and an ‘on-top’ carbonyl (CO) binding mode results. Layered-resolved partial DOS calculation reveals that the surface band gap is closed with the adoption of the CO bonding configuration due to the introduction of quasi-continuous surface band states.

The exchange of radio-frequency plasma-excited atomic O with chemisorbed D, and vice versa, on single crystalline diamond (100) 2×1 has been investigated by elastic recoil detection analysis (ERDA), Rutherford backscattering spectrometry (RBS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was found that the O-D, as well as D-O, exchange processes were thermally activated by the diamond substrate. The surface D was only partially exchanged by atomic O at room temperature. At elevated temperatures, the replacement of D by O was greatly enhanced, with 80% substitution by O at 300 °C. It was also observed that the uptake of O proceeded more readily on the pre-deuterated surface compared to the clean surface. Ultra-shallow depth profiling revealed that atomic beam treatment of single crystalline samples at 800 °C resulted in only superficial uptake of D and O, with no surface incorporation within the shallow analysis depth. The replacement of pre-adsorbed O by RF-excited atomic D was also studied by TOF-SIMS. Pre-adsorbed O was relatively stable and resisted removal at 300 °C. D dosed onto the oxygenated surface was found to co-adsorb with O, possibly as surface bound OD species. Mechanisms for the O-D and D-O exchange processes were discussed in connection with the atomic structure of the C(100) surface.

Surface oxidation studies on pre-deuterated (1 0 0)-oriented single crystal diamond have been performed by oxidizing the diamond surfaces macroscopically using an oxygen atomic beam source as well as microscopically using local anodic oxidation by atomic force microscope (AFM). Oxygen-deuterium exchange on diamond (1 0 0) was investigated by X-ray photoelectron spectroscopy, elastic recoil detection and time-of-flight SIMS. Exchange of pre-adsorbed D by atomic O is thermally activated, with almost complete exchange of surface D by atomic O at 300 °C. At higher oxidation temperatures, oxidation states which are chemically shifted from the C 1s bulk peak by 3.2 eV was observed together with a disordering of the diamond surface. Micron-scale, localized oxygenation of the diamond surface at room temperature could be achieved with a biased AFM tip where we confirmed that the modified areas show a lower secondary electron yield and higher oxygen content. In addition, the electronic structure of the oxygenated diamond surface (on-top (OT) and bridging model) has been investigated by calculating the layered-resolved partial density of states using first principles plane wave ab initio pseudopotential method within the local density functional theory. For the oxygen OT model, sharp features due to occupied surface states in the valence band and unoccupied surface states in the gap exist. The increase in emission intensity near the valence band edge for oxygenated diamond (1 0 0) was verified by ultraviolet photoelectron spectroscopy study.

Using ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), and periodic density functional theory (DFT), we have investigated the oxidation chemistry of diamond (111) surface following its exposure to atomic oxygen generated from a remote radio frequency discharge. Partial O uptake occurs on the C(111) 2 × 1 surface at room temperature without lifting the surface reconstruction. A 2 × 1 → 1 × 1 transition and a full monolayer O coverage is only achieved following the oxygenation of the diamond surface at elevated temperatures (400 °C). Exchange of chemisorbed D by atomic O, and vice versa, is facile at room temperature. Desorption products originating from the reaction chemistry between O and D such as D2O were observed on the C(111) surface in addition to CO. The C(111) surface is readily graphitized following the desorption of CO from the surface. In addition, the structure and energetics of oxygenated C(111) 1 × 1 and C(111) 2 × 1 surfaces have been studied using perio...

The technique of reflection high energy electron diffraction (RHEED) has been applied to study the evolution of various superstructures on 6H–SiC (0 0 0 1) as a function of annealing temperature. Between the evolution of the stable 3×3 and √3×√3 R 30° phases on a silicon-enriched 6H–SiC (0 0 0 1), a mixed phase 3×3/2×2 reconstruction followed by a well-defined 6×6 reconstruction was observed by RHEED for the first time. The 6×6 reconstruction is distinct from the pseudo-periodic 6×6 structure suggested previously for graphite moire pattern on 6H–SiC (0 0 0 1) [Surf. Sci. 48 (1975) 463; Surf. Sci. 256 (1991) 354]. The mechanisms for the formation of these superstructures in the sequence of 3×3,6×6,√3×√3 R 30° and 6√3×6√3 R 30° between 800°C to 1200°C were discussed. The 6×6 structure is proposed to evolve directly from the 3×3 following the missing of consecutive Si clusters in the twisted silicon adlayer model. Annealing the 6×6 reconstructed surface to 1000°C gives rise to a √3×√3 R 30° reconstruction. From here, the segregation of carbon domains occurs readily and these form an incommensurate 6√3×6√3 R 30 epilayer at 1200°C. At the early stages of the annealing, the 6√3×6√3 R 30 RHEED pattern consists of a series of cluster satellite streaks superimposed on 1×1 SiC. Further annealing results in the appearance of graphite streaks with its basis vectors rotated 30° to SiC. Prolonged annealing of the graphitized surface results in the growth of single crystalline graphite multilayers on the 6H–SiC substrate.

A route for the regeneration of smooth √3×√3 R30 face on 6H-SiC(0001) by atomic hydrogen beam etching following the carbonization of the SiC surface at high temperatures had been investigated. The various stages during the segregation of carbonaceous super-structures at high temperatures as well as the layer-by-layer restructuring of the 6H-SiC(0001) surface by atomic H beam were studied by reflection high energy electron diffraction (RHEED). A smooth silicate-terminated √3×√3 R30 surface could be obtained after hydrogen-plasma beam treatment at 800°C. Annealing the √3×√3 R30 face to 900°C readily resulted in the segregation of 1×1 graphite islands on the surface, with the basis vectors of the graphite unit cell rotated 30° with respect to the bulk SiC. Further annealing to temperatures between 1000 and 1200°C resulted in the coalescence of the graphite islands to form an epitaxial layer, which adopted an incommensurate 6√3×6√3 R30-C structure with respect to the bulk. The epitaxial 6√3×6√3 R30-C layer acted as a template for the further growth of smooth single-crystalline graphite multilayers upon prolonged annealing. Atomic force microscopic (AFM) analysis revealed that the epitaxial graphite formed by this method was atomically smooth. Re-exposing the graphite-covered surface to a second hydrogen-plasma treatment readily converted the carbonized surface to a silicate-terminated √3×√3 R30 face. The layer-by-layer etching mechanism of the carbonized SiC by the atomic-H beam source constituted an effective route for the regeneration of the smooth silicon face.

We have observed the native oxide decomposition and local oxide growth on 6H-silicon carbide (0001) surface induced by atomic force microscopy (AFM). When the biased AFM probe was scanned over surface areas, native oxide was decomposed and assembled into protruded lines. The decomposition is accompanied by simultaneous graphitization of the scanned areas, leading to metal–semiconductor contact as evidenced in I–V characteristics. When the probe was immobilized and longer bias duration applied, direct oxidation of silicon carbide (SiC) surface was achieved. The dielectrical properties of AFM oxide on SiC were also investigated in terms of interface barrier height.

A 6×6 reconstruction consisting of a silicon-rich phase has been observed on 6H–SiC (0001) after annealing a silicon-enriched 3×3 6H–SiC (0001) surface at 900 °C. Our results show that the 6×6 reconstruction obtained is a long-range reconstruction and not a psuedoperiodic structure due to incommensurately adsorbed graphite honeycombs as suggested previously. We propose that the 6×6 structure arises from the absence of consecutive tetrahedral clusters in a tetrahedral cluster array with 3×3 periodicity. Annealing the 6×6 structure further at 1200 °C results in a carbon-rich 6√3×6√3R30 structure.

We report the creation of polymeric micro/nanostructures which exhibit distinct chemical and physical characteristics from the matrix poly(N-vinyl carbazole) (PVK). The structure formation is based on atomic force microscopy (AFM) facilitated cross-linking and oxygenation. The reaction of PVK with AFM lithographically induced nanoscale discharge produces raised structures in which bridge oxygen links neighboring carbazole groups. The cross-linking by bridge oxygen converts the initially insulating PVK matrix to chemically modified conducting patterns through the formation of extended pi-conjugations. A comprehensive AFM, PES (photoelectron spectroscopy), FTIR (Fourier transform infrared spectroscopy), and DFT (density functional theory) analysis is presented to address the chemophysical identity of the patterned structures. Our results demonstrate new capabilities of AFM nanolithography in generating heterogeneous functional structures in a polymer matrix.

We report a method to initiate and investigate electrical discharges of ambient air/water molecules in a nanometer-sized gap. Our methodology is based on a typical atomic force microscopy (AFM) setup, in which a cylinder discharge gap ofor =5 nm could be configured between the AFM probe and substrate. We observed highly localized stochastic nanoexplosions in which the discharge probability is dominated by the electric field, material-specific surface reactions, and humidity. AFM results, coupled with the boundary element method (BEM), finite element method (FEM), and method of characteristics (MOC) simulations, further revealed the generation of transient shock waves in the nanoscale discharge. The propagation of shock fronts significantly facilitates the radial expansion of the ionized particles, leading to the formation of microscale patterns on selected substrates. Our findings provide an initial understanding of nanoscale discharge and could be relevant to a few applications including nano/microstructuring, microelectronics, and plasma-assisted depositions.

We report, for the first time, the native oxide decomposition/etching and direct local oxide growth on 6H-SiC (0001) surface induced by atomic force microscopy (AFM). Surface native oxide was decomposed and assembled into protruded lines when the negatively biased AFM tip was scanned over surface areas. The mechanism of decomposition was found to be governed by the Fowler-Nordheim emission current enhanced by the negatively biased AFM tip. Direct oxide growth on the SiC surface was achieved when the AFM tip was immobilized and longer bias duration applied. In particular, the aspect ratio of oxide grown on SiC was found to be several times higher than that on the Si surface. The improved aspect ratio on SiC was attributed to the anisotropic OH(-) diffusion involved in vertical and lateral oxidation along the polar and nonpolar directions such as [0001] and [110] axis in SiC crystal. The electron transport in the above AFM grown oxide on SiC was further investigated by I-V characteristics. The dielectrical strength of AFM oxide against degradation and breakdown under electrical stressing was evaluated.

In this paper, we successfully demonstrated the fabrication of highly ordered and large-scale P3HT:PCBM nanowires via a slow-drying method, which allows for the convenient and cost-effective preparation of well-defined P3HT:PCBM nanostructures with large domains. The formation of the organic nanowires can be explained by the self-organization of polymer chains under favorable thermodynamic conditions in the slow-drying process. Furthermore, the C-V measurements revealed that the P3HT:PCBM nanowires possess high capacitance. This supercapacitive behavior of the nanowires is related to their large surface area and open structure, which can facilitate ion transport and accumulation. Owing to their extremely easy preparation and excellent capacitance performance, the P3HT:PCBM nanowires offer a promising electrode material for supercapacitor devices.

Electrical energy storage and management is an urgent issue due to climate change and energy shortage. Dielectric and double-layer capacitors are the two basic energy-storage devices currently available. However, the application of the dielectric capacitor is very limited due to its low capacitance, while the double-layer capacitor suffers from difficult scaling-up and high fabrication cost, even though its capacitance is high. In this work, we present the first energy-storage membrane which stores charge when simply sandwiched between two metal plates. With an ionic conductivity of 2.8 × 10−4 S cm−1, the membrane is highly polarizable, and its energy-storage mechanism is based on the condensation–decondensation of mobile cations in the membrane negative matrix. The capacitance of a 1.0 cm2 area membrane is 0.2 F cm−2, and it can be readily scaled up simply by using larger membrane pieces. In view of its extreme simplicity, excellent scalability and practical viability, the novel game-changing membrane reported here may provide a sustainable solution to energy storage.

Photocurrent generation and photodetection are usually based on semiconductor crystals including Si, CdS, and PbS. This work reports the enhanced photoabsorption and photodetection of close-packed metallic Au nanoparticles (NPs) in the UV-VIS (visible)-NIR (near infrared) region. Photoabsorption in the UV-VIS regions is associated with the interband transition and surface plasmon resonance of AuNPs, while the enhanced NIR absorption is due to the collective effect of interacting AuNPs in the close-packed network. Consequently, the AuNPs exhibits photodetection behavior in the wavelength range of 300–1500 nm. It is proposed that the inter-AuNP photoejection and delocalization of electron-hole pairs changes the carrier lifetime and transit dynamics in favor of photocarrier conduction, thus significantly facilitating photocurrent generation in the metallic AuNP close-pack. Moreover, due to the power-law conduction mechanism in AuNP networks, the quantum yield of AuNPs can be tuned from 10−6 to 10−1 photoelec...

This letter reports the negative differential resistance (NDR) behavior of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride films induced by aggregate formation in the film. It is observed that aggregate-states in the energy gap can by-pass the common charge conduction mode, and electron injection, trapping, and conduction through these states lead to the NDR characteristic. The rate-dependence of NDR is discussed in terms of the transit time and lifetime of the aggregates-states electrons. The quenching of NDR by photoillumination is also observed, and is attributed to the saturation of aggregates-states by photoelectrons.

This work reports a mechanism of negative differential resistance (NDR) observed for perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) films. The NDR is based on electron injection and extraction at the metal/PTCDA interface, and is governed by the joint effect of electronic and ionic components. Consequently, the NDR behavior exhibits a monotonous dependence on the voltage scan rate, and the number of NDR peaks is also sensitive to the work function of metal electrodes. The results provide further understanding on the diverse manifestation of NDR, and would be useful in organic electronic applications.

In this work, we address the spatiotemporal evolution of micro∕nanoscopic pattern formation on polymer films by atomic force microscope (AFM) assisted electrohydrodynamic (EHD) nanolithography. This patterning method combines the locality and site specificity of AFM and the surface wave amplification of EHD instability for pattern creation and is capable of generating a series of structures corresponding to the zeroth- to second-order wave patterns. Detailed simulations in the framework of nonlinear three-dimensional analysis are presented to elucidate the localized EHD pattern formation. The experimental and theoretical results are quantitatively compared to address the characteristics of the AFM-assisted EHD pattern formation. The impact of key experimental parameters such as the tip bias voltage and bias duration on the formation rate, morphology, and lateral dimension of the wave patterns are discussed. The AFM assisted EHD nanolithography would open new route to the fabrication of complex polymer nanostructures.

A probe-based nano-oxidation method for enhanced vertical oxide growth on silicon is presented. The technique involves cycling the tip biases between positive and negative polarities to produce high-aspect-ratio nano-oxides. Enhanced oxidation was observed to take place in the positive tip bias region as opposed to the negative tip voltage required for anodic oxidation. A model based on interface space charge accumulation and neutralization, OH− reactant mobilization, and diffusion is proposed to account for the oxidation enhancement observed under positive tip voltages. The proposed model is analogous to the transient charge pump effect which is at work when the polarity of a capacitor is switched. The results reveal the dynamical behavior of nano-oxidation under nonstatic fields which can be harnessed for fabricating oxide nanostructures with improved aspect ratios.