Combinatorial Particle Patterning

The unique properties of solid particles make them a promising element of micro‐ and nanostructure technologies. Solid particles can be used as building blocks for micro and nanostructures, carriers of monomers, or catalysts. The possibility of patterning different kinds of particles on the same substrate opens the pathway for novel combinatorial designs and novel technologies. One of the examples of such technologies is the synthesis of peptide arrays with amino acid particles. This review examines the known methods of combinatorial particle patterning via static electrical and magnetic fields, laser radiation, patterning by synthesis, and particle patterning via chemically modified or microstructured surfaces.     

Electrostatically Templated Self‐Assembly of Polymeric Particles: The Role of Friction and Shape Complementarity

Conductive electrodes held at kV potentials and patterned with non‐conductive circular islands can drive templated self‐assembly (TSA) of millimeter‐sized polymeric particles. It is found, however, that the complementarity of the shapes of the “capturing” islands and the projected shapes of the “adsorbing” particles is insufficient to produce high quality assemblies. For instance, while spherical particles center onto circular islands and form highly regular arrays, disk‐shaped particles remain off‐centered on the same islands. These effects are due to frictional effects that compete with electrostatic forces during TSA. A finite‐element model is used to quantify the forces acting in the system and suggests heuristic rules that guide the design of islands capturing particles of desired shapes and sizes.     

Assembling components with behavioural contracts

Component based design is a new paradigm to build distributed systems and applications. The problem of compositional verification of such systems is however still open. We investigate methods and concepts for the provision of “sound” assemblies. We define a behavioural interface type language endowed with a (decidable) set of interface compatibilty and subtyping rules. We define an abstract, dynamic, multi-threaded, component model, encompassing both client/server and peer to peer communication patterns. Based on the notion of compliance of components to their interfaces, we define the concepts of “contract” and “contract satisfaction”. This leads to sound assemblies of components, which possess interesting properties, such as “external deadlockfreeness” and “message consumption”.     

Analysis of radiation forces in laser trapping and laser-guideddirect writing applications

Radiation forces allow the remote manipulation of physical objects. Two radiation force-based systems have been used, in particular: 1) laser trapping, which uses a strongly convergent beam to form a micrometer-sized focal point in which particles can be trapped and manipulated in three dimensions, and 2) laser guidance, which uses a weakly convergent beam to achieve radial confinement of particles about the beam axis coupled with pushing along the beam axis, which allows the high precision delivery of particles over hundreds of micrometers. Biological applications of laser trapping include high-precision molecular motor force measurement, and those of laser guidance include the direct writing of living cells in two and three dimensions for tissue engineering applications. The results presented here show that a general electromagnetic theory, the Generalized Lorenz-Mie Theory, is able to accurately predict experimental results for both schemes without any assumptions regarding the size of the particle relative to the wavelength of the radiation. In addition, radial forces are found to be directly correlated to the dimensionless particle size (a/w) where the particle radius (a) is normalized over the beam radius (w). The dimensionless particle size can be used to theoretically estimate radiation forces in any arbitrary setup, and facilitate the design of radiation force-based systems for a variety of applications in biology and medicine     

Particle‐Stabilized Materials: Dry Oils and (Polymerized) Non‐Aqueous Foams

Oil (liquids with low surface tension and practically immiscible with water) drops can be dispersed in air if relatively oleophobic particles are available. However, such particles with oil‐repellent surfaces cannot simply be prepared by controlling the particle surface chemistry alone. Herein the preparation of oil‐in‐air materials (oil marbles, dry oils) by changing the wetting behavior of particles by tuning the oil properties, which allows the formation of the metastable Cassie–Baxter wetting state of particle assemblies on oil drop surfaces, is presented. The oil‐in‐air materials can be converted to air‐in‐oil materials (non‐aqueous foams) by tailoring the oil properties, as the robustness of the metastable Cassie–Baxter state of the particle assemblies critically depends on the particle wettability. This conversion implies the phase inversion of dispersed systems consisting of air and oils. It is also shown that particle‐stabilized non‐aqueous foams can be utilized as template to produce macroporous polymers.     

“Layer‐Filter Threshold” Technique for Near‐Infrared Laser Ablation in Organic Semiconductor Device Processing

Although conventional laser ablation (CLA) method has widely been used in patterning of organic semiconductor thin films, its quality control still remains unsatisfied due to the ambiguous photochemical and photothermal processes. Based on industrial available near‐infrared laser source, herein, a novel “layer‐filter threshold” (LFT) technique is proposed, which involves the decomposition of targeted “layer‐filter” and subsequent explosive evaporation process to purge away the upper layers instead of layer‐by‐layer ablation. For photovoltaic device with structure of metal/blend/PEDOT:PSS/ITO/glass, the PEDOT:PSS layer as the “layer‐filter” is first demonstrated to be effective, and then the merged P1–P2 line and metal electrode layer are readily patterned through the “self‐aligned” effect and regulation of ablation direction, respectively. The correlation between laser fluence and explosive ablation efficacy is also investigated. Finally, photovoltaic modules based on classical P3HT:PC₆₁BM and low‐bandgap PBDT‐TFQ:PC₇₁BM systems are separately fabricated following the LFT technique. It is found that over 90% of geometric fill factor is achieved while device performances maintain in a limited change with increased number of series cells. In comparison to conventional laser ablation methods, the LFT technique does not require sophisticated instruments but reaches comparable processing accuracy, which shows promising potential in the fabrication and commercialization of organic semiconductor thin‐film devices.     

Stimuli‐Responsive Liquid Marbles: Controlling Structure,Shape, Stability,and Motion

“Liquid marbles” are liquid‐in‐gas dispersed systems stabilized by hydrophobic solid particles adsorbed at the gas‐liquid interface. The structure, stability and movement of these liquid marbles can be controlled by external stimuli such as pH, temperature, light, magnetic and electric fields, ultrasonic, mechanical stress and organic solvents. Stimuli‐responsive modes can be categorized into five classes: (i) liquid marbles whose stability can be controlled by adsorption/desorption of solid particles to/from liquid surfaces, (ii) liquid marbles that can open and close their particle‐coated surface by moving particles to and from the gas‐liquid surface, (iii) liquid marbles that can move, (iv) liquid marbles that can change their shape and (v) liquid marbles that can be split. As a result of these stimuli‐responsive characteristics, liquid marbles offer potential in the areas of controlled encapsulation, delivery and release.     

Interface and interconnection stresses in electronic assemblies – A critical review of analytical solutions

The closed-form solutions for the interfacial stresses in assemblies constituting of two relatively stiff adherends sandwiching a relatively compliant adhesive layer are reviewed. The closed-form solutions are categorised into the “non-free edge solutions” that do not satisfy the nil-shear stress condition at the free edge of the adhesive and the “free edge solutions” that do. Being strength of material solutions, the non-free edge solutions are significantly simpler in form. On the other hand, the solutions tend to grossly underestimate the magnitude of the peeling stress at the free edge. Almost all classical “non-free edge solutions” suffer from two setbacks: (i) assumed σ_a = 0, thus severely underestimating the magnitude of the peeling stress; and (ii) neglected the thickness of the adhesive in their formulation of the x-compliance of assemblies and the evaluation of the effective bending strain on adherends; the former leads to overestimation while the latter leads to gross underestimation of the shear stress (and hence, σ_a(l)). These are demonstrated in a numerical exercise in which two widely followed “non-free edge solutions” and a simplified “free edge solutions” are benchmarked against the finite element analysis.     

Design of Multiresponsive Hydrogel Particles and Assemblies

In the realm of soft nanotechnology, hydrogel micro‐ and nanoparticles represent a versatile class of responsive materials. Over the last decade, our group has investigated the synthesis and physicochemical properties of a variety of synthetic hydrogel particles. From these efforts, several particle types have emerged with potentially enabling features for biological applications, including nanogels for targeted drug delivery, microlenses for biosensing, and coatings for biomedical devices. For example, core/shell nanogels have been used to encapsulate and deliver small interfering RNA to ovarian cancer cells; nanogels used in this fashion may improve therapeutic outcomes for a variety of macromolecular therapeutics. Microgels arranged as multilayers on implantable biomaterials greatly minimize the host inflammatory response to the material. Furthermore, the triggered release of drugs (i.e., insulin) has been demonstrated from similar assemblies. The goal of this feature article is to highlight developments in the design of responsive microgels and nanogels in the context of our recent efforts and in relation to the community that has grown up around this fascinating class of materials.     

Discovery and Optimization of New ZnO‐Based Phosphors Using a Combinatorial Method

The combinatorial method, which was exclusively employed for the drug discovery until recently, has invaded the field of inorganic materials and is becoming a key technology in materials science today. Phosphors, with their diversity of possible mechanisms of luminescence, represent a typical example of a field where the combinatorial approach promises to be especially fruitful. Here, we present the results of systematic combinatorial exploration of different binary and ternary ZnO:dopant systems, which resulted in identification of bright luminescence in ZnO:(Y,Eu), ZnO:V, ZnO:W, and ZnO:(W,Mg) systems. Careful “zooming in”, i.e., fabrication and screening of more detailed libraries near the identified promising compositions, allowed us to find optimum phosphor compositions for the above‐mentioned systems. The efficiency of the new phosphors in low‐voltage cathodoluminescence is high and promises their prospective use in advanced flat panel display and lighting applications.     

Microtribology of Aqueous Carbon Nanotube Dispersions

The tribological behavior of carbon nanotubes (CNTs) in aqueous humic acid (HA) solutions was studied using a surface forces apparatus (SFA) and shows promising lubricant additive properties. Adding CNTs to the solution changes the friction forces between two mica surfaces from “adhesion controlled” to “load controlled” friction. The coefficient of friction with either single‐walled (SW) or multi‐walled (MW) CNT dispersions is in the range 0.30–0.55 and is independent of the load and sliding velocity. More importantly, lateral sliding promotes a redistribution or accumulation, rather than squeezing out, of nanotubes between the surfaces. This accumulation reduced the adhesion between the surfaces (which generally causes wear/damage of the surfaces), and no wear or damage was observed during continuous shearing experiments that lasted several hours even under high loads (pressures ～10 MPa). The frictional properties can be understood in terms of the Cobblestone Model where the friction force is related to the fraction of the adhesion energy dissipated during impacts of the nanoparticles. We also develop a simple generic model based on the van der Waals interactions between particles and surfaces to determine the relation between the dimensions of nanoparticles and their tribological properties when used as additives in oil‐ or water‐based lubricants.     

Interfacial Self‐Assembly of Amphiphilic Dual Temperature Responsive Actuating Janus Particles

Amphiphilic Janus particles feature the combination of two different functional materials in one single colloid, as well as the possibility of self‐assembly at interfaces into complex superstructures. In this article, the self‐assembly of dual temperature responsive amphiphilic Janus particles at liquid–liquid interfaces and their subsequent conversion into an actuating layer‐shaped surface are presented. These microparticles are produced in a capillaries based continuous flow microfluidic device by photoinitiated radical polymerization. The hydrophobic part of the Janus particles contains a liquid crystalline elastomer (LCE), which performs a strong actuation up to 95% during the nematic–isotropic phase transition. The other side consists of a p(NIPAAm) hydrogel, which features volumetric expansions up to 280% below the lower critical solution temperature. A multistep molding process is developed to uniformly align the Janus particles at a toluene/water boundary surface and to embed the particles into a hydrogel matrix. A particle covered hydrogel layer is obtained, which features a collective actuation of the rod‐like LCE parts on the surface and a bundling of the resulting forces during the phase transition.     

“Clinging‐Microdroplet” Patterning Upon High‐Adhesion,Pillar‐Structured Silicon Substrates

The rapidly increasing research interest in nanodevices, including nanoelectronics, nano‐optoelectronics, and sensing, requires the development of surface‐patterning techniques to obtain large‐scale arrays of nanounits (mostly nanocrystals and/or nanoparticles) on a silicon substrate. Herein, we demonstrate a “clinging‐microdroplet” method to fabricate patterning crystal arrays based on the employment of high‐adhesion, superhydrophobic, pillar‐structured silicon substrates. Different from the previous hydrophilic/hydrophobic patterned self‐assembly monolayer technique, this method provides a novel strategy to fabricate patterning crystal arrays upon pillar‐structured silicon substrates of homogenous superhydrophobicity and high adhesion, which greatly simplifies the modification process of the supporting substrates. Ordered crystal arrays with a tunable size and distribution density were successfully generated, and individual crystals grew on the top of each micropillar. Besides soluble inorganic materials, protein microspheres and suspending Ag‐nanoparticle or polystyrene‐microsphere aggregations could also be patterned in regular arrays, showing the wide adaptation of such an adhesive patterning technique. This novel and low‐cost technique for patterning crystal arrays upon silicon substrates could yield breakthroughs in areas ranging from nanodevices to nanoelectronics.     

Reconfigurable Anisotropic Coatings via Magnetic Field‐Directed Assembly and Translocation of Locking Magnetic Chains

A method for the generation of remotely reconfigurable anisotropic coatings is developed. To form these coatings, locking magnetic nanoparticles (LMNPs) made of a superparamagnetic core and a two‐component polymer shell are employed. Two different polymers form phase‐separated coaxial shells. The outer shell provides repulsive interactions between the LMNPs while the inner shell exerts attractive forces between the particles. Applying a non‐uniform magnetic field, one gathers the particles together, pushing them to come in contact when the internal shells could effectively hold the particles together. When the magnetic field is turned off, the particles remain locked due to these strong interactions between internal shells. The shells are thus made stimuli‐responsive, so this locking can be made reversible and the chains can be disintegrated on demand. In a non‐uniform magnetic field, the assembled chains translocate, bind to the solid substrate and form anisotropic coatings with a “locked” anisotropic structure. The coatings can be constructed, aligned, realigned, degraded, and generated again on demand by changing the magnetic field and particle environment. The mechanism of the coating formation is explained using experimental observations and a theoretical model.     

Influence of Electron Acceptor and Electron Donor on the Photophysical Properties of Carbon Dots: A Comparative Investigation at the Bulk‐State and Single‐Particle Level

Carbon dots (CDs) are extensively studied to investigate their unique optical properties such as undergoing electron transfer in different scenarios. This work presents an in‐depth investigation to study the ensemble‐averaged state/bulk state and single‐particle level photophysical properties of CDs that are passivated with electron‐accepting (CD‐A) and electron‐donating molecules (CD‐D) on their surface. The bulk‐state experiments reveal that in a mixture of these CDs, CD‐A dominates the overall photophyiscal properties and eventually leads to formation of at least two associated geometries, which is dependent on time, concentration, intramolecular electron/charge transfer, and hydrogen bonding. Single‐particle studies, however, do not reveal an “acceptor‐dominating” scenario based on analysis of instantaneous intensity, bleaching kinetics, and photoblinking, indicating that the direct interaction of these CDs may affect their photophysical properties in the bulk state due to formation of hierarchical structural assemblies. Here it is anticipated that these fundamental results will further provide insights toward the understanding of the complex mechanism associated with CD emission, which is one of the key contributors to their successful application. As an immediate application of these functional CDs, it is shown that they can be used as a sensing array for metal ions and serve as a powerful toolbox for their technological applications.     

Direct Patterning of Metal Chalcogenide Semiconductor Materials

Lithography is one of the most widely used methods for cutting‐edge research and industrial applications, mainly owing to its ability to draw patterns in the micro and even nanoscale. However, the fabrication of semiconductor micro/nanostructures via conventional electron or optical lithography technologies often requires a time‐consuming multistep process and the use of expensive facilities. Herein, a low‐cost, high‐resolution, facile, and versatile direct patterning method based on metal–organic molecular precursors is reported. The ink‐based metal–organic precursors are found to operate as negative resists, with the material exposed by different methods (electron‐beam/laser/heat/ultraviolet (UV)) to render them insoluble in the development process. This technical process can deliver metal chalcogenide semiconductors with arbitrary 2D/3D patterns with sub‐50 nm resolution. Electron beam lithography, two‐photon absorption lithography, thermal scanning probe lithography, and UV photolithography are demonstrated for the direct patterning process. Different metal chalcogenide semiconductor nanodevices, such as photoconductive selenium‐doped Sb₂S₃ nanoribbons, p‐type PbS single‐nanowire field‐effect transistors, and p‐n junction CdS/Cu₂S nanowire solar cells, are fabricated by this method. This direct patterning technique is a versatile and simple micro/nanolithography technology with considerable potential for “lab‐on‐a‐chip” preparation of semiconductor devices.     

基于用几何光学和米散射法的球形粒子前向散射特性计算研究

分别用几何光学(GOM)、Lorenz-Mie散射方法计算了0.55 m波段球形粒子的散射特性,并对两种计算方法的准确性进行了分析。研究了粒子尺度参数、折射率虚部对粒子0散射相函数的影响。结果表明:在粒子尺度参数大于60时,GOM计算的球形粒子的散射特性与Mie非常接近。在粒子尺度参数小于1 000时,两种方法得到的前向散射相函数与粒子尺度参数均成二次方关系,且计算结果基本一致;随着粒子尺度参数的增大,前向散射与尺度参数之间将逐步失去二次方关系。当粒子尺度参数大于10 000时,采用GOM方法得到的结果要比Mie散射方法的结果偏大;当粒子尺度一定时, 0散射相函数与折射率虚部之间呈先增大后减小的规律。     

Exploring Exchange Bias Coupling in Fe3−δO4@CoO Core–Shell Nanoparticle 2D Assemblies

Core‐shell ferro(i)magnetic@antiferromagnetic (F(i)M@AFM) nanoparticles exhibiting exchange bias coupling are very promising to push back the superparamagnetic limits. However, their intrinsic magnetic properties can be strongly affected by interparticle interactions. This work reports on the collective properties of Fe_3–dO₄@CoO core‐shell nanoparticles as function of the structure of their assembly. The structure of nanoparticle assembly is controlled by a copper (I) catalyzed alkyne–azide cycloaddition (CuAAC) “click” reaction between complementary functional groups located at the surface of both substrates and nanoparticles. 2D arrays of nanoparticles with tunable sizes ranging from clusters of few nanoparticles to a dense and homogenous monolayer were prepared. The spatial arrangement of nanoparticles strongly influences the exchange bias coupling which is significantly enhanced for large 2D nanoparticle assemblies and, even more in 3D assemblies such as powder, which favour weak and random dipolar interactions.     

Pad effects on material-removal rate in chemical-mechanical planarization

The role of a porous pad in controlling material-removal rate (MRR) during the chemical-mechanical planarization (CMP) process has been studied numerically. The numerical results are used to develop a phenomenological model that correlates the forces on each individual abrasive particle to the applied nominal pressure. The model provides a physical explanation for the experimentally observed domains of pressure-dependent MRR, where the pad deformation controls the load sharing between active-abrasive particles and direct pad-wafer contact. The predicted correlations between MRR and slurry characteristics, i.e., particle size and concentration, are in agreement with experimentally measured trends reported by Ouma¹ and Izumitani.²     

Comprehensive defect analysis methodology for nano imprint lithography

Because of the non traditional elements involved in both the manufacture of nano imprint lithography (NIL) templates [T. DiBiase, J. Maltabes, B. Reese, M. Ahmadian, SPIE 6151 (2006)] and the resulting features printed on substrates, methods and procedures for effectively locating, tracking and identifying defect mechanisms need to be modified and refined from the traditional methods employed by the semiconductor industry [I. Peterson, G. Thompson, T. DiBiase, S. Ashkenaz, R. Pinto, Yield Management Solutions, KLA-Tencor Spring, (2000)].Since NIL involves pattern structures defined at 1× magnification, there is no defect “forgiveness” such as with conventional 4× optical reduction lithography. In addition, NIL is performed with the patterning tooling (template) in full contact with the casting material (in this case, UV curable monomer) used to define the final features on the substrate of interest. Surface chemistry and substrate interactions quickly become obvious crucial factors in defect formation mechanisms.This article describes a few non-traditional approaches to working with the extreme dynamic range of defect types found in the step and repeat NIL process.