Self-assembled Arrays Research Articles

Room-temperature resonant quantum tunneling transport of macroscopic systems.

A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (∼10(2) V cm(-1)) could be enhanced by three orders of magnitude (∼10(5) V cm(-1)) between the Ni QDA because of the higher permittivity of BaTiO3 and the 'hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (σ-T curves) construction.

Fabrication of servo-integrated template for 1.5 Teradot/inch2bit patterned media with block copolymer directed assembly

Directed self-assembly (DSA) of block copolymers (BCPs) proves to be a viable solution for the ultrahigh density bit-patterned media (BPM) application. However, servo design integration is still extremely challenging since the servo layouts require more complex patterns than the simple arrays naturally achieved by the DSA process. We present an integration scheme to create BPM servo patterns by utilizing the BCP dot-array patterns. This proposed method is based on an imprint guided two-step DSA process, combined with conventional optical lithography to define two separate zones. Both the data zone and servo zone consist of self-assembled hexagonal dot arrays: a regular pattern in the data zone and an arbitrary pattern in the servo zone. This method was successfully used to fabricate a servo-integrated BPM template with an areal density of 1.5 Teradot/inch2 (Td/in.2) (Lo=22.3 nm). Using the fabricated quartz template, CoCrPt BPM media has been successfully patterned by nanoimprint lithography and subsequent ion-beam etching process on a 2.5 in. disk. Further, using patterned-in servo wedges on 1.5 Td/in.2 patterned CoCrPt media, we are able to close the servo control loop for track-following on a spin-stand test. The standard deviation of repeatable run-out over the full revolution is calculated to be about 4% of the 38.6 nm track pitch. This method is currently being used to fabricate a template at a much higher density of 3.2 Td/in.2 (Lo=15.2 nm).

Asymmetrically Coupled Plasmonic Core and Nanotriplet Satellites

Here, we report asymmetrical multiple electromagnetic coupling of plasmonic core and nanotriplet satellites. Within the plasmonic core and nanotriplet satellites, an enhanced local field is generated which expands across the core due to multiple electromagnetic coupling between a core and nanotriplets. Based on 3D simulations of our plasmonic nanosystem, the overall local field enhancement reaches to over 104 times, compared with that of a single nanoparticle array. A strong local field distribution across the core to nanotriplets as well as the critical role of the plasmonic core is demonstrated through the 3D simulations. It is proposed that a self-assembled nanotriplet array is completed through two stages of dewetting of a gold thin film on an anodic aluminum oxide (AAO) template. Formation of the core–nanotriplet satellites is significantly influenced by geometrical parameters (i.e., the pore diameter and depth) of the AAO template. Our experimental results show that the local field of our plasmonic ...

Erratum: "Nature-like photosynthesis of water and carbon dioxide with femtosecond laser induced self-assembled metal nanostructures"

Large-scale replication of the natural process of photosynthesis is a crucial subject of storing solar energy and saving our environment. Here, we report femtosecond laser induced self-assembled metal nanostructure arrays, which are easily mass producible on earth-abundant metals, can directly synthesize liquid and solid hydrocarbon compounds from carbon dioxide, water, and sunlight at a production rate of more than 1 × 105 μL/(gh) that is significantly (103–106 times) higher than those in previous studies.1,2 The efficiency for storing solar energy of the photosynthesis is about 10% in the present simple experimental setup which can be further improved. Moreover, different from previous artificial photosynthesis works, this phenomenon presents a new mechanism that, through a surface-enhanced photodissociation process, nature-like photosynthesis can be performed artificially.

A family of vertically aligned nanowires with smooth, hierarchical and hyperbranched architectures for efficient energy conversion

A powerful full solution-based process was demonstrated to synthesize various vertically aligned TiO2 wires/rods self-assembled arrays nanostructures on conductive substrates via a simple hydrothermal growth system. Demonstrated samples included a family of high-quality and high-crystallinity anatase nanowire arrays with smooth, hierarchical or hyperbranched architectures, thanks to oriented attachment and crystallization as well as a self-assembly growth mechanism. The proposed hyperbranched arrays, consisting of long TiO2 nanowire trunks, short TiO2 nanorod branches as well as tiny TiO2 nanorod leaves (recall a tree with luxuriant foliage) and thus possessing a microscopic feature size, overcome typical shortages of insufficient dye adsorption for conventional 1D smooth nanowire arrays or prototype hierarchical nanowire arrays when applied to DSSC, which achieved for the first time similar dye uptakes (i.e. 90.10nmolcm−2vs 88.62nmolcm−2) as nanoparticle counterparts under the same thickness. Dye-sensitized solar cell fabricated with an ~8μm long novel hyperbranched nanowire arrays photoelectrode yields an impressive power conversion efficiency (PCE) of 8.11%, which was much greater than that of anatase TiO2 nanoparticle (20nm in diameter) counterpart due to synergistic effects of high dye uptakes and superior broadband light scattering for improved light harvesting as well as fast charge transport for efficient charge collection for the former.

Ordering of 6-nm-sized nanodot arrays with 10-nm-pitch using self-assembled block copolymers along electron beam-drawn guide-lines

We studied the possibility to form long-range ordering of self-assembled nanodot arrays with a dot size of 6nm and a dot pitch of 12nm using guide-line templates for ultrahigh-density patterned media. This was realized by using self-assembled block copolymers of polystyrene-poly dimethyl siloxane (PS-PDMS) and the templates made of hydrogen silsesquioxane (HSQ) negative electron beam (EB) resist. We have demonstrated that the method could possibly achieve a minimum pitch of about 10nm using PS-PDMS of molecular weight 7000–1500g/mol and EB-drawn guide lines. These results evidence the promising potential of a technology for achieving 5 Tbit/in2 magnetic storage devices.

Stress-induced nanoparticle crystallization.

We demonstrate for the first time a new mechanical annealing method that can significantly improve the structural quality of self-assembled nanoparticle arrays by eliminating defects at room temperature. Using in situ high-pressure small-angle X-ray scattering, we show that deformation of nanoparticle assembly in the presence of gigapascal level stress rebalances interparticle forces within nanoparticle arrays and transforms the nanoparticle film from an amorphous assembly with defects into a quasi-single crystalline superstructure. Our results show that the existence of the hydrostatic pressure field makes the transformation both thermodynamically and kinetically possible/favorable, thus providing new insight for nanoparticle self-assembly and integration with enhanced mechanical performance.

Self-assembled Au nanoparticle arrays on thiol-functionalized resin beads for sensitive detection of paraquat by surface-enhanced Raman scattering

Efficient, scalable, and cost-effective self-assembly of Au nanoparticles (NPs) into close-packed arrays on the surfaces of thiol-functionalized resin spheres under mild conditions was demonstrated. The resulting Au NPs–resin spheres possessed a structure in which the densely packed Au NPs monolayer and the resin bead are the shell and the core, respectively. Each Au NPs–resin sphere could be used as a surface-enhanced Raman scattering (SERS) substrate with high SERS-enhancing capacity and reproducibility. The SERS enhancement factor (EF) was estimated at 109–1011 by using thiophenol as the probe. The spatial and sphere-to-sphere variations in SERS EF were <18%. The SERS-enhancing capacity could be tuned by varying the Au NPs size. The detection limit of paraquat in water by SERS using the as-synthesized Au NPs–resin as active substrate was ∼10−12M. The fabrication method could be a promising alternative to the preparation of well-ordered NPs arrays for SERS-active substrates.

Self-assembled ultrathin nanotubes on diamond (100) surface.

Surfaces of semiconductors are crucially important for electronics, especially when the devices are reduced to the nanoscale. However, surface structures are often elusive, impeding greatly the engineering of devices. Here we develop an efficient method that can automatically explore the surface structures using structure swarm intelligence. Its application to a simple diamond (100) surface reveals an unexpected surface reconstruction featuring self-assembled carbon nanotubes arrays. Such a surface is energetically competitive with the known dimer structure under normal conditions, but it becomes more favourable under a small compressive strain or at high temperatures. The intriguing covalent bonding between neighbouring tubes creates a unique feature of carrier kinetics (that is, one dimensionality of hole states, while two dimensionality of electron states) that could lead to novel design of superior electronics. Our findings highlight that the surface plays vital roles in the fabrication of nanodevices by being a functional part of them.

Subwavelength imaging of self-assembled triangular array through a silver superlens

Superlens nanolithography is a promising technique for patterning nanoscale structures because of its ability to overcome the diffraction limit. In this paper, subwavelength imaging of triangular particle array through a silver superlens is investigated. The superlens structure was optimized by means of the transfer transmission matrix method. The triangular array was obtained by self-assembly of nanoscale polystyrene spheres (PSS) and was successfully replicated into the photoresist. Experimental results show that the superlens structure provides at least 50nm resolution, about 1/7 of the incidence wavelength.

A Supramolecular Photosynthetic Model Made of a Multi-Porphyrinic Array Constructed Around a C60 Core and a C60-Imidazole Derivative

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative (F1) with a multi-metalloporphyrin array constructed around a hexa-substituted fullerene core (F(ZnP)12 ) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12 . In contrast, upon axial coordination with the mono-substituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12 (F1)n] both in polar and non polar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around 930 nm suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12 (F1)n] when compared to a reference system lacking the pyrrolidino-fullerene unit. In benzonitrile, a long-lived charge separated state (τ = 0.3 μs) has been detected for the supramolecular adduct.ReferencesK. Yoosaf, J. Iehl, I. Nierengarten, M. Hmadeh, A.-M. Albrecht-Gary, J.-F. Nierengarten, N. Armaroli, Chem. Eur. J., 2014, in press

Non-Lithographic Growth of Core–Shell GaAs Nanowires on Si for Optoelectronic Applications

We demonstrated a nonlithographic method for integrating GaAs nanowire (NW) array-based light-emitting diodes (LEDs) on silicon (Si) substrates. A sub-100 nm hole array on a deposited SiO2 layer was patterned on an entire 2 in. Si wafer based on a sacrificed self-assembled InAs NW array. Then, a core–shell n–p junction GaAs NW array was grown on exposed Si windows via the selective-area growth method. The electrical properties of the core–shell n–p junction GaAs NW has been measured and compared to those of the core–shell junction NWs formed via the self-assembled growth method. Room temperature electroluminescence was successfully observed from the fabricated GaAs NW array-based LEDs. The core–shell junction III–V NW array epitaxially grown on a ubiquitous Si platform could be applied to future low-cost optical devices.

Ordering of self-assembled 5-nm-diameter poly(dimethylsiloxane) nanodots with sub-10 nm pitch using ultra-narrow electron-beam-drawn guide lines and three-dimensional control

We demonstrate the possibility of forming long-range ordered self-assembled arrays of 5-nm-diameter nanodots with pitch of 10 × 7.5 nm2 using guide line templates and low molecular weight (MW) (4700–1200 g/mol) poly(styrene)-poly(dimethylsiloxane) (PS-PDMS) for application in ultrahigh density patterned magnetic recording media. We propose a three-dimensional control which involves control of the height of the guide lines, the thickness of the PS-PDMS films, and the gap between the guide lines in order to produce 5-nm-diameter, sub-10 nm pitched nanodots with long-range order along the guide lines. Adopting a 13-nm-thick PS-PDMS film and 14-nm-high resist guide lines, the 5-nm-diameter and 10 × 7.5 nm2-pitched self-assembled nanodots were ordered in 4–7 dot arrays with long-range order. The experimental results demonstrate that the method is suitable for the production of patterned media with magnetic recording densities of 8.6 Tbit/in.2 using low MW PS-PDMS and slim guide lines.

Self-assembled nanowire array capacitors: capacitance and interface state profile

Direct characterization of the capacitance and interface states is very important for understanding the electronic properties of a nanowire transistor. However, the capacitance of a single nanowire is too small to precisely measure. In this work we have fabricated metal–oxide–semiconductor capacitors based on a large array of self-assembled Si nanowires. The capacitance and conductance of the nanowire array capacitors are directly measured and the interface state profile is determined by using the conductance method. We demonstrate that the nanowire array capacitor is an effective platform for studying the electronic properties of nanoscale interfaces. This approach provides a useful and efficient metrology for the study of the physics and device properties of nanoscale metal–oxide–semiconductor structures.

Efficiency improvement of InGaN light emitting diodes with embedded self-assembled SiO2 nanosphere arrays

In this study, the periodic SiO2 nanosphere nanopatterned sapphire substrate (SiO2-NPSS) was made using self-assembled SiO2 nanosphere monolayer template and inductively coupled plasma (ICP) etching. And the self-assembled SiO2 nanosphere monolayer was directly embedded into the GaN/sapphire interface by nanoscale epitaxial lateral overgrowth (NELOG). For comparison, a common nanopatterned sapphire substrate (C-NPSS) was also made through dry etching with the SiO2 nanospheres used as the mask. Compared with LEDs grown on C-NPSS and flat sapphire substrate (FSS), the external quantum efficiency of LEDs with SiO2 nanopheres (SiO2-NPSS) was increased by 30.7% and 81.9% under a driving current 350mA. The SiO2-NPSS not only improved the crystalline quality of GaN but also enhanced the light extraction efficiency (LEE) of LED. And the SiO2-NPSS LED also showed more light in vertical direction and more uniform light distribution. By finite-difference time-domain (FDTD) simulation, we confirmed that more light could be reflected from the GaN/SiO2 interface than the GaN/sapphire interface because the refractive index of SiO2 was lower than that of sapphire. Therefore, LED grown on the SiO2-NPSS showed superior light extraction efficiency compared to that on C-NPSS.

High Q factor propagating plasmon modes based on low-cost metals

A hybrid plasmonic–photonic crystal consisting of a low-cost metal (Al or Cu) covered by self-assembly polystyrene sub-micro sphere arrays is fabricated. The angle-resolved reflection spectra show the existence of propagating optical surface modes in the structure. Especially, under normal incidence, five surface modes can be observed clearly. With the help of theoretical calculation, the origin of surface resonance modes is confirmed. From both the experiment and simulation, the surface plasmon modes supported by this structure possess high Q factors, which are comparable with those of the modes based on noble metals. Moreover, with a dielectric layer deposited on the top of the structure, its potential application for surface plasma polariton sensors is proposed.

Novel Architecture of Plasmon Excitation Based on Self-Assembled Nanoparticle Arrays for Photovoltaics

An efficient approach to producing hexagonally self-assembled and well-dispersed gold (Au) nanoparticles (NPs) in the pores of porous anodic aluminum oxide (AAO) is reported. This approach is particularly useful for tuning the surface plasmon resonance frequency of Au NPs by varying the effective dielectric constant of AAO. A strongly enhanced Raman spectrum of dye molecule rhodamine 6G using these well-dispersed Au NPs revealed that such a self-assembled Au NP array can induce a strong plasmonic field. Furthermore, we demonstrated a new architecture of plasmon excitation in a bulk heterojunction (BHJ) inverted organic solar cell (IOSC) using the Au NP array with AAO. The optical response of an active layer poly(3-hexylthiophene):(6,6)-phenyl-C61-butyric acid methyl ester was enhanced by this strong plasmonic field associated a well-dispersed Au NP array. A comparative study of AAO with and without Au NPs confirmed plasmonic improvement of the BHJ IOSC. Simulation results showed that Au NPs concentrate the incoming light into a strongly localized field and enhance light absorption in a wide wavelength range.

Attempts to form the 10-nm-order pitch of self-assembled nanodots using PS-PDMS block copolymer

Block copolymer (BCP) self-assembly exhibits its ability to form various nanostructures with a size down to 3 nm, which is particularly attractive for emerging technologies such as bit patterned media (BPM). Poly(styrene-b-dimethyl siloxane) (PS-PDMS) has been acknowledged as the most promising block copolymer for self-assembly fabrication due to its possibility to form nanopattern with a fine pitch, high etching selectivity, and its characteristic of robustness for pattern transfer. Here, we attempt to form PS-PDMS self-assembled nanodot array with a 10-nm-order pitch in order to satisfy the demand of low cost technique to form ultrahigh density nanodot array for BPM, which is regarded as the next-generation magnetic recording media, and for quantum devices such as the third-generation quantum dot photovoltaic cell and future battery cell. In this study, self-assembled nanodot array on a large area with pitches of 11 nm ( σ = 2.08 nm) and 10 nm ( σ = 1.61 nm) was formed using PS-PDMS with molecular weights of 5600–1300 g/mol (minority block volume fraction f PDMS = 19.8%) and 4700–1200 g/mol (f PDMS = 21.4%), respectively. In experiments, it was shown that some critical parameters, such as the thickness of PS-PDMS film, the treatment of the substrate surface, and annealing condition, played crucial roles in forming 10-nm-order size of self-assembled nanodot array using PS-PDMS. The relationships between pitches of PS-PDMS nanodot array and the product of the total number of segments and the Flory-Huggins segmental interaction parameter (χN) obtained by calculations and experiments will be discussed. Based on the position of PS-PDMS on mean-field phase diagram for BCP melts, the possibility to form nanodot array with a pitch of less than 10 nm is described. This study promises to open way toward the fabrication of more than 7.45 Tbit/in. 2 storage devices and the application of quantum devices.

Double-degradable responsive self-assembled multivalent arrays – temporary nanoscale recognition between dendrons and DNA

This article reports self-assembling dendrons which bind DNA in a multivalent manner. The molecular design directly impacts on self-assembly which subsequently controls the way these multivalent nanostructures bind DNA--this can be simulated by multiscale modelling. Incorporation of an S-S linkage between the multivalent hydrophilic dendron and the hydrophobic units responsible for self-assembly allows these structures to undergo triggered reductive cleavage, with dithiothreitol (DTT) inducing controlled breakdown, enabling the release of bound DNA. As such, the high-affinity self-assembled multivalent binding is temporary. Furthermore, because the multivalent dendrons are constructed from esters, a second slow degradation step causes further breakdown of these structures. This two-step double-degradation mechanism converts a large self-assembling unit with high affinity for DNA into small units with no measurable binding affinity--demonstrating the advantage of self-assembled multivalency (SAMul) in achieving highly responsive nanoscale binding of biological targets.

Self-assembled zirconia nanotube arrays: fabrication mechanism, energy consideration and optical activity

We present a comprehensive roadmap for the precise control of the dimensions and optical properties of anodically fabricated zirconia nanotubes.