Assembly and alignment of metallic nanorods on surfaces with patterned wettability

Orientational ordering and correlation in quasi-one-dimensional hard-body fluids due to close-packing degeneracy

We study the orientational ordering properties of some quasi-one-dimensional hard-body fluids, where the anisotropic particles are confined to a straight line, while they are free to rotate in a plane. We examine a class of models where the close-packing structure is degenerate, i.e., the highest possible density can be realized with different orientational ordering. We find that the close-packing degeneracy always gives rise to a diverging orientational correlation, which can be a marker of phase transition, glass formation, and jamming. In the case of isotropic or partially ordered phases at the close-packing density, the diverging orientational correlation indicates a tendency for being a strongly ordered nematic phase. However, the orientational divergence in the perfect nematic phase shows that the particles must rotate in concert to go from one closely packed structure to another.

Fabrication of Oriented Polycrystalline MOF Superstructures

The field of metal-organic frameworks (MOFs) has progressed beyond the design and exploration of powdery and single-crystalline materials. A current challenge is the fabrication of organized superstructures that can harness the directional properties of the individual constituent MOF crystals. To date, the progress in the fabrication methods of polycrystalline MOF superstructures has led to close-packed structures with defined crystalline orientation. By controlling the crystalline orientation, the MOF pore channels of the constituent crystals can be aligned along specific directions: these systems possess anisotropic properties including enhanced diffusion along specific directions, preferential orientation of guest species, and protection of functional guests. In this perspective, we discuss the current status of MOF research in the fabrication of oriented polycrystalline superstructures focusing on the specific crystalline directions of orientation. Three methods are examined in detail: the assembly from colloidal MOF solutions, the use of external fields for the alignment of MOF particles, and the heteroepitaxial ceramic-to-MOF growth. This perspective aims at promoting the progress of this field of research and inspiring the development of new protocols for the preparation of MOF systems with oriented pore channels, to enable advanced MOF-based devices with anisotropic properties.

Ordering properties of anisotropic hard bodies in one-dimensional channels

The phase behavior and structural properties of hard anisotropic particles (prisms and dumbbells) are examined in one-dimensional channels using the Parsons-Lee (PL) theory, and the transfer-matrix and neighbor-distribution methods. The particles are allowed to move freely along the channel, while their orientations are constrained such that one particle can occupy only two or three different lengths along the channel. In this confinement setting, hard prisms behave as an additive mixture, while hard dumbbells behave as a non-additive one. We prove that all methods provide exact results for the phase properties of hard prisms, while only the neighbor-distribution and transfer-matrix methods are exact for hard dumbbells. This shows that non-additive effects are incorrectly included into the PL theory, which is a successful theory of the isotropic-nematic phase transition of rod-like particles in higher dimensions. In the one-dimensional channel, the orientational ordering develops continuously with increasing density, i.e., the system is isotropic only at zero density, while it becomes perfectly ordered at the close-packing density. We show that there is no orientational correlation in the hard prism system, while the hard dumbbells are orientationally correlated with diverging correlation length at close packing. On the other hand, positional correlations are present for all the systems, the associated correlation length diverging at close packing.

In-plane aligned assemblies of 1D-nanoobjects: recent approaches and applications

One-dimensional (1D) nanoobjects have strongly anisotropic physical properties which are averaged out and cannot be exploited in disordered systems. We reviewed the in plane alignment approaches and potential applications with perspectives shared.

Molecular Transport Junctions Created By Self-Contacting Gapped Nanowires

Molecular transport junctions (MTJs) are important components in molecular electronic devices. However, the synthesis of MTJs remains a significant challenge, as the dimensions of the junction must be tailored for each experiment, based on the molecular lengths. A novel methodology is reported for forming MTJs, taking advantage of capillary and van der Waals forces.

A Robust Epoxy Resins @ Stearic Acid-Mg(OH)2 Micronanosheet Superhydrophobic Omnipotent Protective Coating for Real-Life Applications

Superhydrophobic coating has extremely high application value and practicability. However, some difficult problems such as weak mechanical strength, the need for expensive toxic reagents, and a complex preparation process are all hard to avoid, and these problems have impeded the superhydrophobic coating's real-life application for a long time. Here, we demonstrate one kind of omnipotent epoxy resins @ stearic acid-Mg(OH)2 superhydrophobic coating via a simple antideposition route and one-step superhydrophobization process. The whole preparation process is facile, and expensive toxic reagents needed. This omnipotent coating can be applied on any solid substrate with great waterproof ability, excellent mechanical stability, and chemical durability, which can be stored in a realistic environment for more than 1 month. More significantly, this superhydrophobic coating also has four protective abilities, antifouling, anticorrosion, anti-icing, and flame-retardancy, to cope with a variety of possible extreme natural environments. Therefore, this omnipotent epoxy resins @ stearic acid-Mg(OH)2 superhydrophobic coating not only satisfies real-life need but also has great application potential in many respects.

Electrically robust silver nanowire patterns transferrable onto various substrates

We report a facile technique for patterning and transferring silver nanowires (AgNWs) onto various substrates. By employing only UV/O3 and vapor treatment of hexamethyldisilazane (HMDS), we are able to accurately manipulate the surface energy via alternating the terminal groups of a polydimethylsiloxane (PDMS) substrate, so as to assist selective formation and exfoliation of AgNW films. A simple UV/O3 treatment on PDMS enables uniform, well-defined, and highly conductive patterns of AgNWs after spin-coating. A vapor treatment of HMDS lowers the surface energy of the oxidized PDMS so that the patterned AgNWs embedded in an epoxy resin (EPR) are cleanly transferred from the PDMS to the target substrate. It is found that the AgNW-EPR composite on polyethylene glycol terephthalate (PET) exhibits remarkable durability under the bending test, tape test, ultrasonic treatment in water, and immersion of chemical solvents. In addition, we demonstrate that the AgNW-EPR composite work well as conductive patterns on the oxidized PDMS, polyvinyl alcohol (PVA), paper, and curved glass. The facile technique extends the applicability of AgNWs in the field of electronics, and it is potentially applicable to other nanomaterials.

Hydrodynamic confinement and capillary alignment of gold nanorods

Controlling the alignment and orientation of nanorods on various surfaces poses major challenges. In this work, we investigate hydrodynamic confinement and capillary alignment of gold nanorod assembly on chemically stripe-patterned substrates. The surface patterns consist of alternating hydrophilic and hydrophobic micrometer wide stripes; a macroscopic wettability gradient enables controlling the dynamics of deposited suspension droplets. We show that drying of residual liquid on the hydrophilic stripes gives rise to spatially localized deposition and alignment of the nanorods. Moreover, a universal relation between the extent of order within the single layers of nanoparticles and the lateral dimension of the deposits is presented and discussed.

Wettability gradient-induced alignment of peptide nanotubes as templates for biosensing applications

Peptide nanotubes coated with silver nanoparticles and aligned using wettability-patterned substrates provide improved Raman intensity for biosensing applications.

Bioinspired super-wettability from fundamental research to practical applications

Engineered wettability is a traditional, yet key issue in surface science and attracts tremendous interest in solving large-scale practical problems. Recently, different super-wettability systems have been discovered in both nature and experiments. In this Review we present three types of super-wettability, including the three-dimensional, two-dimensional, and one-dimensional material surfaces. By combining different super-wettabilities, novel interfacial functional systems could be generated and integrated into devices for use in tackling current and the future problems including resources, energy, environment, and health.

Assembling single gold nanorods into large-scale highly aligned nanoarrays via vacuum-enhanced capillarity

We report a simple, straightforward, and efficient approach to assemble single gold nanorods (AuNRs) into highly aligned arrays, via a unique vacuum-enhanced capillarity. The assembled AuNR arrays demonstrate both an excellently unidirectional ordering and a wonderful single-rod resolution. The key role of vacuum in this approach enables high-aspect-ratio (10 to 22) AuNR alignment and efficiently facilitates large-area alignment. Further investigation of one- and two-dimensional AuNR arrays would undoubtedly be beneficial to their potential applications.

Self-assembly and hierarchical patterning of aligned organic nanowire arrays by solvent evaporation on substrates with patterned wettability

The controlled growth and alignment of one-dimensional organic nanostructures at well-defined locations considerably hinders the integration of nanostructures for electronic and optoelectronic applications. Here, we demonstrate a simple process to achieve the growth, alignment, and hierarchical patterning of organic nanowires on substrates with controlled patterns of surface wettability. The first-level pattern is confined by the substrate patterns of wettability. Organic nanostructures are preferentially grown on solvent wettable regions. The second-level pattern is the patterning of aligned organic nanowires deposited by controlling the shape and movement of the solution contact lines during evaporation on the wettable regions. This process is controlled by the cover-hat-controlled method or vertical evaportation method. Therefore, various new patterns of organic nanostructures can be obtained by combing these two levels of patterns. This simple method proves to be a general approach that can be applied to other organic nanostructure systems. Using the as-prepared patterned nanowire arrays, an optoelectronic device (photodetector) is easily fabricated. Hence, the proposed simple, large-scale, low-cost method of preparing patterns of highly ordered organic nanostructures has high potential applications in various electronic and optoelectronic devices.

Aligned growth of gold nanorods in PMMA channels: parallel preparation of nanogaps

We demonstrate alignment and positional control of gold nanorods grown in situ on substrates using a seed-mediated synthetic approach. Alignment control is obtained by directing the growth of spherical nanoparticle seeds into nanorods in well-defined poly(methyl methacrylate) nanochannels. Substrates with prepatterned metallic electrodes provide an additional handle for the position of the gold nanorods and yield nanometer-sized gaps between the electrode and nanorod. The presented approach is a novel demonstration of bottom-up device fabrication of multiple nanogap junctions on a single chip mediated viain situ growth of gold nanorods acting as nanoelectrodes.

High-performance, all-solution-processed organic nanowire transistor arrays with inkjet-printing patterned electrodes

Organic nanowire (NW) transistor arrays with a mobility of as high as 1.26 cm(2)·V(-1)·S(-1) are fabricated by combining the dip-coating process to align the NW into arrays with the inkjet printing process to pattern the source/drain electrodes. A narrow gap of ~20 μm has been obtained by modifying the inkjet process. The all-solution process is proven to be a low-cost, high-yield, simple approach to fabricating high-performance organic NW transistor arrays over a large area.

Templating of self-alignment patterns of anisotropic gold nanoparticles on ordered SWNT macrostructures

We report a simple and versatile technique for oriented assembly of gold nanorods on aligned single-walled carbon nanotube (SWNT) macrostructures, such as thin nanotube films and nanotube fibers. The deposition and assembly is accomplished via drop drying of dilute gold nanorod suspensions on SWNT macrostructures under ambient conditions. Guided by anisotropic interactions, gold nanorods, and polygonal platelets spontaneously align with SWNTs, resulting in macroscopic arrays of locally ordered nanorods supported on aligned SWNT substrates. SEM reveals that the scalar order parameter of rods relative to the local average SWNT alignment is 0.7 for rods on SWNT films and 0.9 for rods on SWNT fibers. This self-alignment is enabled by anisotropic gold nanoparticle-SWNT interactions and is observed for a wide range of nanoparticles, including nanorods with aspect ratios ranging from 2-35, thin gold triangular and other polygonal platelets. The plasmonic properties of aligned gold nanorods together with superior electronic, chemical and mechanical properties of SWNTs make these hybrid nanocomposites valuable for the design of self-assembled multifunctional optoelectronic materials and optical metamaterials.

Role of diffusion in scaling of polymer chain aggregates found in vapor deposition polymerization

Polymer chain aggregates grown by (1+1)-dimensional Monte Carlo simulations of vapor deposition polymerization (VDP) were studied. The dynamic scaling behavior of polymer chain length distribution n(s)(t) was studied as a function of chain length (s), deposition time (t), and the ratio G=D/F of deposition rate (F) and free monomer diffusion (D). The dynamic scaling approach was employed to highlight the dependence of n(s)(t) on t, s, and G. With an increase in t, we found a power law increase in n(s)(t) and total number of polymer chains N(total)(t), given by N(total)(t)~t(ω) and n(s)(t)~t(ω) with exponent ω=1.01(2) that was invariant for a range of G=10 to 10^{4}. For small s and t=10^{3}, 5×10^{3}, and 10^{4}, n_{s}(t) decreased according to n(s)(t)~s(-τ) with τ=0.58(2). As G was increased from 10 to 10(4), we observed a systematic influence of G on the rescaled n(s)(t) data that prevented the manifestation of unique scaling function for polymer chain aggregates. The dependence of scaling functions of n(s)(t) on G elucidates the sensitivity of polymer chain aggregates to G and is thought to be a characteristic of VDP.

Applications of bio-inspired special wettable surfaces

In this review we focus on recent developments in applications of bio-inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio-inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.

A solution process for size-controlled growth and transfer of organic nanostructures with manufacture scalability

A simple and robust process has been developed to control the growth of the organic nanowires in situ self-assembled in a polymer matrix, lift off the nanostructure/polymer composite film from the mother substrate for storage and transfer, and remove the polymer host prior to usage. Every step was completed through a solution process, which ensured the process's simplicity and low cost. The realization of large-sized nanowire/polymer composite film demonstrated the necessary process scalability required by the industrial roll-to-roll manufacturing.

Solution-processed, high-performance n-channel organic microwire transistors

The development of solution-processable, high-performance n-channel organic semiconductors is crucial to realizing low-cost, all-organic complementary circuits. Single-crystalline organic semiconductor nano/microwires (NWs/MWs) have great potential as active materials in solution-formed high-performance transistors. However, the technology to integrate these elements into functional networks with controlled alignment and density lags far behind their inorganic counterparts. Here, we report a solution-processing approach to achieve high-performance air-stable n-channel organic transistors (the field-effect mobility (mu) up to 0.24 cm(2)/Vs for MW networks) comprising high mobility, solution-synthesized single-crystalline organic semiconducting MWs (mu as high as 1.4 cm(2)/Vs for individual MWs) and a filtration-and-transfer (FAT) alignment method. The FAT method enables facile control over both alignment and density of MWs. Our approach presents a route toward solution-processed, high-performance organic transistors and could be used for directed assembly of various functional organic and inorganic NWs/MWs.

Non-adhesive PEG hydrogel nanostructures for self-assembly of highly ordered colloids

In this paper, we report on the effect of patterned non-adhesive hydrogel nanosurfaces on the self-assembly of highly ordered colloids. Polyethylene glycol (PEG) hydrogel is employed as the substrate material in the study, for its desired non-adhesive property, and biocompatibility as well as photopatternability. Ultrafine PEG features are photopatterned onto glass substrates with minimal feature resolution of 500 nm using ultraviolet or deep ultraviolet exposure. By simply controlling the colloidal concentration of the nanoassembly solutions and the dimensions of the wells, a range of highly organized nanocolloidal patterns are formed inside the PEG wells. Unlike the traditional surface modification techniques, ours takes advantage of the unique non-adhesive property of PEG hydrogels to achieve extremely high selectivity in the pattern-assisted nanoassembly. Our experiments show that with oxygen plasma treatment, the non-adhesive property of the PEG surface deteriorates significantly, leading to non-selective assembly with complete surface coverage of nanocolloidal beads under the same processing condition. Therefore, benefiting from the unique non-adhesive surface property, the pattern-assisted nanoassembly method enables a highly predictable and robust process for colloidal nanofabrication, and the obtained nanocolloidal arrays with well organized patterns could potentially find applications in photonic crystal fabrication, biological sensing and analytical detection.

Biomineralization nanolithography: combination of bottom-up and top-down fabrication to grow arrays of monodisperse gold nanoparticles along peptide lines

From top to bottom: Peptide lines were formed in trenches in the self-assembled monolayer (SAM) on an Au substrate. Combination of the top-down (peptide nanolithography) and the bottom-up fabrications (biomineralization) yielded arrays of monodisperse Au nanoparticles assembled on the peptide lines (see picture). The number of nanoparticles on the lines was simply determined by the width of the peptide pattern.

Finite-size effect on magnetic properties in iron sulfide nanowire arrays

We report the size effect on the magnetic properties in Fe(7)S(8) nanowire arrays. Samples with diameters in the range of 50-200 nm have been prepared by electrodeposition with AAO films. The Mössbauer measurement results show that four parameters (hyperfine fields, isomer shift, quadrupole splitting, full width at half-maximum) increased with decreasing the diameter of the nanowires. The magnetic properties were investigated. The hysteresis loop shape and the magnetization are dependent on the diameter of the nanowires. The thermomagnetic measurements on the as-synthesized nanowire samples and the corresponding bulk display a mixed-type curve and a Weiss-type curve, respectively.

Crossbar assembly of antibody-functionalized peptide nanotubes via biomimetic molecular recognition

Previously, a large scale assembly of nanowires in a parallel array configuration has been demonstrated, and one type of nanowire could interconnect two electrodes in the high-wire density. However, to assemble nanowires into practical logic-gate configurations in integrated circuits, we need more than the parallel assembly of nanowires. For example, when the assembling nanowires are monopolar semiconductors, logic gates such as AND, OR and NOR are to be assembled necessarily from two types of semiconducting nanowires, n-type and p-type, and some of these nanowires must cross perpendicularly to form a crossbar geometry for the logical operation. In this paper, the crossbar assembly of antibody-functionalized peptide nanotubes was demonstrated by a new biomimetic bottom-up technique. Molecular recognition between antigens and antibodies enabled two types of the antibody-functionalized bionanotubes to place them onto targeted locations on substrates, where their complementary antigens were patterned. When two rectangular pads of antigens, human IgG and mouse IgG, were patterned perpendicularly on an Au substrate by nanolithography and then the antihuman IgG nanotubes and the antimouse IgG nanotubes were incubated on this substrate in solution, these bionanotubes were attached onto corresponding locations to form the crossbar configuration.

Monte Carlo simulation of two-dimensional hard rectangles: confinement effects

We use orientational-bias Monte Carlo simulations to examine the phase behavior of two-dimensional hard rectangles in the bulk and under confinement by hard walls. For all of the rod aspect ratios and area fractions studied, we find that confinement increases the degree of nematic ordering over the bulk, as confined rods tend to align their long axes parallel to the confining walls. The extent of nematic ordering increases as the separation between the confining walls decreases. If the aspect ratio of the rectangles is sufficiently large, they exhibit nematic ordering in both the bulk and under confinement, where the nematic director is set by the walls. Rods with a small aspect ratio are isotropic in the bulk and exhibit weak tetratic tendencies for sufficiently high densities. From studies of density profiles, angular distributions, and orientational correlation functions for confined, low-aspect-ratio rods, it is apparent that they align their long axes parallel to the wall in the near-wall region, where layering occurs for sufficiently high rod densities. However, confined rods with low aspect ratios still exhibit weak tetratic (isotropic) tendencies near the center of the confined region for all but the smallest wall separations. We note that although our studies probe the ordering of hard rectangles, the entropic tendencies that we observe here will be present for rods with energetic interactions. Thus, these studies serve as a general starting point for understanding and controlling the assembly of rods in two-dimensional confining geometries.