Micro‐ and Nanopatterning of Functional Organic Monolayers on Oxide‐Free Silicon by Laser‐Induced Photothermal Desorption

The photothermal laser patterning of functional organic monolayers, prepared on oxide‐free hydrogen‐terminated silicon, and subsequent backfilling of the laser‐written lines with a second organic monolayer that differs in its terminal functionality, is described. Since the thermal monolayer decomposition process is highly nonlinear in the applied laser power density, subwavelength patterning of the organic monolayers is feasible. After photothermal laser patterning of hexadecenyl monolayers, the lines freed up by the laser are backfilled with functional acid fluoride monolayers. Coupling of cysteamine to the acid fluoride groups and subsequent attachment of Au nanoparticles allows easy characterization of the functional lines by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Depending on the laser power and writing speed, functional lines with widths between 1.1 μm and 250 nm can be created. In addition, trifluoroethyl‐terminated (TFE) monolayers are also patterned. Subsequently, the decomposed lines are backfilled with a nonfunctional hexadecenyl monolayer, the TFE stripes are converted into thiol stripes, and then finally covered with Au nanoparticles. By reducing the lateral distance between the laser lines, Au‐nanoparticle stripes with widths close to 100 nm are obtained. Finally, in view of the great potential of this type of monolayer in the field of biosensing, the ease of fabricating biofunctional patterns is demonstrated by covalent binding of fluorescently labeled oligo‐DNA to acid‐fluoride‐backfilled laser lines, which—as shown by fluorescence microscopy—is accessible for hybridization.     

A Hierarchically Ordered TiO2 Hemispherical Particle Array with Hexagonal‐Non‐Close‐Packed Tops: Synthesis and Stable Superhydrophilicity Without UV Irradiation

A hierarchical TiO₂ ordered hemispherical particle array with hexagonal‐non‐close‐packed (hncp) tops is prepared by pulsed laser deposition (PLD) using a polystyrene colloidal monolayer as a template. Compared with conventional lithography, the route presented has the advantage of low cost for producing hncp nanostructured arrays. This hierarchical particle array exhibits excellent superhydrophilicity with a water contact angle of 0° without further UV irradiation. The superhydrophilic property originates from oxygen defects or vacancies on the surface of the TiO₂ nanoparticles produced by PLD and the increased roughness of the hierarchical particle arrays. More importantly, this property is very stable for half a year and could be used in self‐cleaning surfaces and microfluidic devices.     

Interplay between Short‐ and Long‐Ranged Forces Leading to the Formation of Ag Nanoparticle Superlattice

Nanoparticle (NP) superlattices have attracted increasing attention due to their unique physicochemical properties. However, key questions persist regarding the correlation between short‐ and long‐range driving forces for nanoparticle assembly and resultant capability to predict the transient and final superlattice structure. Here the self‐assembly of Ag NPs in aqueous solutions is investigated by employing in situ liquid cell transmission electron microscopy, combined with atomic force microscopy‐based force measurements, and theoretical calculations. Despite the NPs exhibiting instantaneous Brownian motion, it is found that the dynamic behavior of NPs is correlated with the van der Waals force, sometimes unexpectedly over relatively large particle separations. After the NPs assemble into clusters, a delicate balance between the hydration and van der Waals forces results in a distinct distribution of particle separation, which is ascribed to layers of hydrated ions adsorbed on the NP surface. The study demonstrates pivotal roles of the complicated correlation between interparticle forces; potentially enabling the control of particle separation, which is critical for tailoring the properties of NP superlattices.     

Reversible Size‐Tuning of Self‐Assembled Silver Nanoparticles in Phospholipid Membranes via Humidity Control

A monolayer of 5‐nm‐sized Ag nanoparticles embedded in a liquid‐crystalline lipid membrane undergoes a reversible morphological change during hydration and dehydration of the lipid membrane. High mobility of the encapsulating lipid molecules, chemically bound to the Ag atoms, induces redistribution of metal particles to produce significant and optically detectable changes in nanoparticle morphology. The morphological change occurs on a time scale that enables the Ag‐nanoparticle‐embedded membrane to be used as a convenient visual sensor for moisture and other organic solvents, as well as for biosensing by virtue of the biocompatibility of the lipid molecules. The mechanism demonstrated here can also be extended to construct guided nanostructures based on self‐assembled nanoparticles.     

Preparation of monodisperse Ni nanoparticles and their assembly into 3D nanoparticle superlattices

Monodisperse Ni nanoparticles with sizes varying from 4.8 to 11.3 nm are prepared via a one-pot reaction that involves the reduction of nickel(II) acetylacetonate in oleylamine in the presence of trioctylphosphine and 1,2-hexadecanediol. Reaction parameters such as temperature and the concentration of capping agent and metal precursor are critical for the adjustment of particle size. The decrease of crystallinity is observed for the samples with smaller particle sizes, which significantly affects the magnetic properties. Three-dimensional (3D) superlattices that are composed of Ni nanoparticles with different sizes are obtained on different substrates by a facile self-assembly process, and are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and small-angle X-ray diffraction (SAXRD). The Ni nanoparticle superlattices formed on carbon-coated TEM copper grids exhibit a dominant hexagonal close-packed (hcp) symmetry, although local fcc packing is also occasionally observed. The formation of 3D nanoparticle superlattice structures on Si substrates is confirmed from the SAXRD measurements. The method revealed in this study for the preparation of 3D superlattices composed of Ni nanoparticles with tunable sizes offers the potential to explore their interesting collective properties for multiple applications.     

Palladium and gold nanoparticle array films formed by using self-assembly of block copolymer

The well-arrayed Pd and Au nanoparticle thin films were successfully prepared by making use of self-assembled PS-b-P4VP block copolymer (BCP) as a mask for the reduction of PdCl2 deposited on glass substrate. The films consisted of spherialcal nanoparticles with an average diameter of about 45 nm. For monitoring the size, shape and array formation of Pd nanopaticle films, this procedure was proved better to the conventional process in which PdCl2 impregnated in the channels of self assembled BCP film is reduced to form nanoparticle array. This observations of Pd nanoparticle array film formation is supported by the AFM and UV-VIS studies of Au nanoparticle array films formed by conventional method.     

Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets

Highly ordered arrays of nanoparticles exhibit many properties that are not found in their disordered counterparts. However, these nanoparticle superlattices usually form in a far-from-equilibrium dewetting process, which precludes the use of conventional patterning methods owing to a lack of control over the local dewetting dynamics. Here, we report a simple yet efficient approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their dewetting process. This approach can provide rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures with high degrees of internal order, including single-particle-width corrals, single-particle-thickness microdiscs and submicrometre-sized 'supra-crystals'. Remarkably, these features could be addressed by micropatterned electrode arrays, suggesting potential applications in bottom-up nanodevices.     

Bimetallic Nanostructures as Active Raman Markers: Gold‐Nanoparticle Assembly on 1D and 2D Silver Nanostructure Surfaces

It is demonstrated that bimetallic silver–gold anisotropic nanostructures can be easily assembled from various nanoparticle building blocks with well‐defined geometries by means of electrostatic interactions. One‐dimensional (1D) silver nanowires, two‐dimensional (2D) silver nanoplates, and spherical gold nanoparticles are used as representative building blocks for bottom‐up assembly. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle‐to‐particle interaction that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. The Raman activity of the bimetallic nanostructures is compared with that of the individual nanoparticle blocks by using rhodamine 6G solution as the model analyte. The Raman intensity of the best‐performing silver–gold nanostructure is comparable with the dense array of silver nanowires and silver nanoplates that were prepared by means of the Langmuir–Blodgett technique. An optimized design of a single‐nanostructure substrate for surface‐enhanced Raman spectroscopy (SERS), based on a wet‐assembly technique proposed here, can serve as a compact and low‐cost alternative to fabricated nanoparticle arrays.     

Transport Gap of Nanoparticle‐Passivated Silicon Substrates

The transport gap of nanoparticle‐passivated Si substrates is measured by scanning tunneling microscopy. Passivation is achieved using a monolayer of CdSe nanoparticles. It is shown that the transport gap and conduction‐band edge of the system change upon passivation. The size of the nanoparticles that passivate the Si substrate is varied to study its effect on the transport gap of the system. Plots of the tunneling current versus voltage show that the transport gap of the system can be tuned by the binding of just a monolayer of suitable nanoparticles. From the normalized density of states, it is shown that the conduction‐band edge of the system responds to the size of the nanoparticles. Here, a monolayer of the nanoparticles, which were capped with suitable functional groups, has been formed via electrostatic adsorption with the substrate.     

Electron Mobility of 24 cm2 V−1 s−1 in PbSe Colloidal‐Quantum‐Dot Superlattices

Colloidal quantum dots (CQDs) are nanoscale building blocks for bottom‐up fabrication of semiconducting solids with tailorable properties beyond the possibilities of bulk materials. Achieving ordered, macroscopic crystal‐like assemblies has been in the focus of researchers for years, since it would allow exploitation of the quantum‐confinement‐based electronic properties with tunable dimensionality. Lead‐chalcogenide CQDs show especially strong tendencies to self‐organize into 2D superlattices with micrometer‐scale order, making the array fabrication fairly simple. However, most studies concentrate on the fundamentals of the assembly process, and none have investigated the electronic properties and their dependence on the nanoscale structure induced by different ligands. Here, it is discussed how different chemical treatments on the initial superlattices affect the nanostructure, the optical, and the electronic‐transport properties. Transistors with average two‐terminal electron mobilities of 13 cm² V^?1 s^?1 and contactless mobility of 24 cm² V^?1 s^?1 are obtained for small‐area superlattice field‐effect transistors. Such mobility values are the highest reported for CQD devices wherein the quantum confinement is substantially present and are comparable to those reported for heavy sintering. The considerable mobility with the simultaneous preservation of the optical bandgap displays the vast potential of colloidal QD superlattices for optoelectronic applications.     

Chemically synthesized L1/sub 0/-type FePt nanoparticles and nanoparticle arrays via template-assisted self-assembly

Chemically ordered L1/sub 0/-type FePt nanoparticle agglomerates were synthesized directly by the co-reduction of Fe(III) and Pt(II) acetylacetonates in tetraethylene glycol at 300/spl deg/C in the absence of surfactants. These nanoparticles could be dispersed in n-hexane by coating with oleic acid and oleylamine. However, the dispersed particles exhibited only chemically disordered fcc phase and superparamagnetic behavior. The FePt nanoparticle film composed of dispersed particles and stabilized using amino-silane began to structurally transform to ordered L1/sub 0/ phase at 600/spl deg/C, which is lower compared to that prepared by the hot soap method. Rotational hysteresis loss measurement suggested that the ordering was incomplete at 600/spl deg/C and the nanoparticle film had the distribution of magnetocrystalline anisotropy field values. The FePt nanoparticle array was fabricated using the template-assisted self-assembly technique. To produce periodic dots on a substrate, positive-biased pulse voltage was applied to the substrate coated with octadecyltrichlorosilane monolayer by using a conducting cantilever used in a scanning probe microscope. This process induced electrochemical modification of -CH/sub 3/ groups into polar ones. The resulting template had well-aligned sub-100-nm dot arrays with sub-100-nm periodicity. The FePt nanoparticles were fixed on the patterned areas selectively.     

Dipole-dipole interactions in nanoparticle superlattices

Nanoparticles often self-assemble into hexagonal-close-packed (hcp) structures although it is predicted to be less stable than face-centered-cubic (fcc) packing in hard-sphere models. In addition to close-packed fcc and hcp superlattices, we observe formation of nonclose-packed simple-hexagonal (sh) superlattices of nearly spherical PbS, PbSe, and gamma-Fe2O3 nanocrystals. This surprisingly rich phase diagram of monodisperse semiconducting nanoparticles is explained by considering the interactions between nonlocal dipoles of individual nanoparticles. By calculating the total electrostatic and dispersive energies, we explain stability of the hcp and sh nanoparticle superlattices, introduce the superlattice phase diagram, and predict antiferroelectric ordering in dipolar nanoparticle superlattices.     

Synthetically programmable nanoparticle superlattices using a hollow three-dimensional spacer approach

Crystalline nanoparticle arrays and superlattices with well-defined geometries can be synthesized by using appropriate electrostatic, hydrogen-bonding or biological recognition interactions. Although superlattices with many distinct geometries can be produced using these approaches, the library of achievable lattices could be increased by developing a strategy that allows some of the nanoparticles within a binary lattice to be replaced with 'spacer' entities that are constructed to mimic the behaviour of the nanoparticles they replace, even though they do not contain an inorganic core. The inclusion of these spacer entities within a known binary superlattice would effectively delete one set of nanoparticles without affecting the positions of the other set. Here, we show how hollow DNA nanostructures can be used as 'three-dimensional spacers' within nanoparticle superlattices assembled through programmable DNA interactions. We show that this strategy can be used to form superlattices with five distinct symmetries, including one that has never before been observed in any crystalline material.     

Tuning the Intensity of Metal‐Enhanced Fluorescence by Engineering Silver Nanoparticle Arrays

It is demonstrated that silver nanoparticle (SNP) arrays fabricated by combining nanoimprint lithography and electrochemical deposition methods can be used as substrates for metal‐enhanced fluorescence, which is widely used in optics, sensitive detection, and bioimaging. The method presented here is simple and efficient at controlling the nanoparticle density and interparticle distance within one array. Furthermore, it is found that the fluorescence intensity can be tuned by engineering the feature size of the SNP arrays. This is due to the different coupling efficiency between the emission of the fluorophores and surface plasmon resonance band of the metallic nanostructures.     

二氧化硅纳米颗粒的反应离子刻蚀及其在硅纳米针尖制备中的应用

系统地研究了硅衬底上二氧化硅纳米颗粒的反应离子刻蚀（R IE）过程,并在此基础上制备了可用于场发射的硅纳米针尖阵列.首先,采用改进的蒸发法在硅衬底上实现二氧化硅纳米颗粒的单层密排结构,再采用典型的刻蚀二氧化硅的RIE技术同时刻蚀硅衬底和二氧化硅纳米颗粒,在对纳米颗粒尺寸随刻蚀进行而改变的电镜照片分析的基础上,获得了相应的二氧化硅纳米颗粒刻蚀模型,计算得到横向和纵向的刻蚀速率;当刻蚀后的二氧化硅纳米颗粒从衬底上脱落后,进一步对硅衬底的刻蚀可以得到锐利的硅纳米针尖阵列,初步的实验结果表明,所制备的硅纳米针尖具有较好的场发射特性.     

Colloid‐Interface‐Assisted Laser Irradiation of Nanocrystals Superlattices to be Scalable Plasmonic Superstructures with Novel Activities

High‐efficient charge and energy transfer between nanocrystals (NCs) in a bottom‐up assembly are hard to achieve, resulting in an obstacle in application. Instead of the ligands exchange strategies, the advantage of a continuous laser is taken with optimal wavelength and power to irradiate the film‐scale NCs superlattices at solid–liquid interfaces. Owing to the Au‐based NCs' surface plasmon resonance (SPR) effect, the gentle laser irradiation leads the Au NCs or Au@CdS core/shell NCs to attach each other with controlled pattern at the interfaces between solid NCs phase and liquid ethanol/ethylene glycol. A continuous wave 532 nm laser (6.68–13.37 W cm^?2), to control Au‐based superlattices, is used to form the monolayer with uniformly reduced interparticle distance followed by welded superstructures. Considering the size effect to Au NCs' melting, when decreasing the Au NCs size to ≈5 nm, stronger welding nanostructures are obtained with diverse unprecedented shapes which cannot be achieved by normal colloidal synthesis. With the help of facile scale‐up and formation at solid–liquid interfaces, and a good connection of crystalline between NCs, the obtained plasmonic superstructured films that could be facilely transferred onto different substrates exhibit broad SPR absorption in the visible and near‐infrared regime, enhanced electric conductivities, and wide applications as surface enhanced Raman scattering (SERS)‐active substrates.     

High‐Throughput Near‐Field Optical Nanoprocessing of Solution‐Deposited Nanoparticles

The application of nanoscale electrical and biological devices will benefit from the development of nanomanufacturing technologies that are high‐throughput, low‐cost, and flexible. Utilizing nanomaterials as building blocks and organizing them in a rational way constitutes an attractive approach towards this goal and has been pursued for the past few years. The optical near‐field nanoprocessing of nanoparticles for high‐throughput nanomanufacturing is reported. The method utilizes fluidically assembled microspheres as a near‐field optical confinement structure array for laser‐assisted nanosintering and nanoablation of nanoparticles. By taking advantage of the low processing temperature and reduced thermal diffusion in the nanoparticle film, a minimum feature size down to ≈100 nm is realized. In addition, smaller features (50 nm) are obtained by furnace annealing of laser‐sintered nanodots at 400 °C. The electrical conductivity of sintered nanolines is also studied. Using nanoline electrodes separated by a submicrometer gap, organic field‐effect transistors are subsequently fabricated with oxygen‐stable semiconducting polymer.     

Recent Advances in Chemical Synthesis,Self‐Assembly,and Applications of FePt Nanoparticles

This paper reviews recent advances in chemical synthesis, self‐assembly, and potential applications of monodisperse binary FePt nanoparticles. After a brief introduction to nanomagnetism and conventional processes of fabricating FePt nanoparticles, the paper focuses on recent developments in solution‐phase syntheses of monodisperse FePt nanoparticles and their self‐assembly into nanoparticle superlattices. The paper further outlines the surface, structural, and magnetic properties of the FePt nanoparticles and gives examples of three potential applications in data storage, permanent magnetic nanocomposites, and biomedicine.     

Bionanosphere Lithography via Hierarchical Peptide Self‐Assembly of Aromatic Triphenylalanine

A nanolithographic approach based on hierarchical peptide self‐assembly is presented. An aromatic peptide of N‐(t‐Boc)‐terminated triphenylalanine is designed from a structural motif for the β‐amyloid associated with Alzheimer's disease. This peptide adopts a turnlike conformation with three phenyl rings oriented outward, which mediate intermolecular π–π stacking interactions and eventually facilitate highly crystalline bionanosphere assembly with both thermal and chemical stability. The self‐assembled bionanospheres spontaneously pack into a hexagonal monolayer at the evaporating solvent edge, constituting evaporation‐induced hierarchical self‐assembly. Metal nanoparticle arrays or embossed Si nanoposts could be successfully created from the hexagonal bionanosphere array masks in conjunction with a conventional metal‐evaporation or etching process. Our approach represents a bionanofabrication concept that biomolecular self‐assembly is hierarchically directed to establish a straightforward nanolithography compatible with conventional device‐fabrication processes.     

Spray‐Dried Nanoparticle‐in‐Microparticle Delivery Systems (NiMDS) for Gene Delivery,Comprising Polyethylenimine (PEI)‐Based Nanoparticles in a Poly(Vinyl Alcohol) Matrix

Nucleic acid‐based therapies rely on efficient formulations for nucleic acid protection and delivery. As nonviral strategies, polymeric and lipid‐based nanoparticles have been introduced; however, biological efficacy and biocompatibility as well as poor storage properties due to colloidal instability and their unavailability as ready‐to‐use systems are still major issues. Polyethylenimine is the most widely explored and promising candidate for gene delivery. Polyethylenimine‐based polyplexes and their combination with liposomes, lipopolyplexes, are efficient for DNA or siRNA delivery in vitro and in vivo. In this study, a highly potent spray‐dried nanoparticle‐in‐microparticle delivery system is presented for the encapsulation of polyethylenimine‐based polyplexes and lipopolyplexes into poly(vinyl alcohol) microparticles, without requiring additional stabilizing agents. This easy‐to‐handle gene delivery device allows prolonged nanoparticle storage and protection at ambient temperature. Biological analyses reveal further advantages regarding profoundly reduced cytotoxicity and enhanced transfection efficacies of polyethylenimine‐based nanoparticles from the nanoparticle‐in‐microparticle delivery system over their freshly prepared counterparts, as determined in various cell lines. Importantly, this nanoparticle‐in‐microparticle delivery system is demonstrated as ready‐to‐use dry powder to be an efficient device for the inhalative delivery of polyethylenimine‐based lipopolyplexes in vivo, as shown by transgene expression in mice after only one administration.