Direct Surface Patterning from Solutions: Localized Microchemistry Using a Focused Laser

A method for creating microscale‐patterned surfaces by direct‐write lithography is described. A tightly focused, low‐power infrared laser beam is applied to a homogeneous precursor solution containing soluble reagents. When the laser is focused directly at a glass–solution interface, it initiates the local precipitation of a solid product that attaches firmly to the substrate. Operating the laser momentarily forms isolated spots, whereas moving the microscope stage or the laser spot draws continuous lines. The method has been demonstrated for metallic silver and gold, for oxidized copper, and for molybdenum disulfide, suggesting a broad range of suitable materials. Silver patterns were further modified by chemical reactions. Their morphology and physical properties can be altered during deposition by the use of capping agents, which may provide an onset for further functionalization.     

A Room‐Temperature High‐Conductivity Metal Printing Paradigm with Visible‐Light Projection Lithography

Fabricating electronic devices require integrating metallic conductors and polymeric insulators in complex structures. Current metal‐patterning methods such as evaporation and laser sintering require vacuum, multistep processes, and high temperature during sintering or postannealing to achieve desirable electrical conductivity, which damages low‐temperature polymer substrates. Here reports a facile ecofriendly room‐temperature metal printing paradigm using visible‐light projection lithography. With a particle‐free reactive silver ink, photoinduced redox reaction occurs to form metallic silver within designed illuminated regions through a digital mask on substrate with insignificant temperature change (<4 °C). The patterns exhibit remarkably high conductivity achievable at room temperature (2.4 × 10⁷ S m^?1, ≈40% of bulk silver conductivity) after simple room‐temperature chemical annealing for 1–2 s. The finest silver trace produced reaches 15 µm. Neither extra thermal energy input nor physical mask is required for the entire fabrication process. Metal patterns were printed on various substrates, including polyethylene terephthalate, polydimethylsiloxane, polyimide, Scotch tape, print paper, Si wafer, glass coverslip, and polystyrene. By changing inks, this paradigm can be extended to print various metals and metal–polymer hybrid structures. This method greatly simplifies the metal‐patterning process and expands printability and substrate materials, showing huge potential in fabricating microelectronics with one system.     

Nanolaminates Utilizing Size‐Dependent Homogeneous Plasticity of Metallic Glasses

Homogeneous plasticity in metallic glasses is generally only observed at high temperatures or in very small structures (less than ≈100 nm), so their applications for structural performance have been very limited. Here, nanolaminates with alternating layers of Cu₅₀Zr₅₀ metallic glass and nanocrystalline Cu are synthesized and it is found that samples with an optimal composition of 112‐nm‐thick metallic‐glass layers and 16‐nm‐thick Cu layers demonstrate a maximum strength of 2.513 GPa, a value 33% greater than that predicted by the rule‐of‐mixtures and 25% better than that of pure Cu₅₀Zr₅₀ metallic glass. Furthermore, ≈4% strain at fracture is achieved, suppressing the instantaneous catastrophic failure often associated with metallic glasses. It is postulated that this favorable combination of high strength and deformability is caused by the size‐dependent deformation‐mode transition in metallic glasses, from highly localized plasticity, leading to immediate failure in larger samples to homogeneous extension in the smaller ones.     

Optimizing Single‐Walled‐Carbon‐Nanotube‐Based Saturable Absorbers for Ultrafast Lasers

The application of single‐walled carbon nanotubes (SWCNTs) as saturable absorbers (SA) in a Nd:glass femtosecond laser is verified as a promising alternative to traditional semiconductor saturable‐absorber mirrors (SESAMs). The shortest laser pulses achieved with a SWCNT‐SA fabricated by the slow‐evaporation method are reported herein. Nearly Fourier‐limited 288 fs pulses are obtained with negative‐dispersion soliton mode‐locking. The importance of the properties of the starting material, such as the degree of purity and the chirality, and the successive slow‐evaporation deposition method is proven by using a multitechnique approach based on X‐ray diffractometry, scanning electron microscopy, and μ‐Raman spectroscopy. The high degree of nanotube alignment on the glass substrate and also the slight metallic character due to electron transfer between the glass matrix and the nanotubes themselves are identified as the main features responsible for the good laser response.     

激光诱导银纳米颗粒薄膜和微结构

利用可见激光诱导化学沉积方法在玻璃基底上制备纳米银薄膜和微结构。玻璃样品池中装满柠檬酸钠和硝酸银的混合透明溶液,当一束可见连续激光正入射样品池一段时间后,在辐照区域的玻璃内壁上便可以形成一层光亮的银膜。银膜沉积的速度受到激光功率密度、激光波长、辐照时间以及混合溶液的浓度等条件的影响。利用X射线衍射、原子力显微镜和拉曼光谱仪等手段对制备的薄膜的成分、表面形貌和拉曼活性等性质进行了表征和分析。利用此方法制备的银膜具有良好的表面增强拉曼散射活性。同时,利用双光束干涉的方法在玻璃基底上诱导出不同周期的银纳米颗粒光栅。     

Concurrent Formation of Metallic Glass During Laser Forward Transfer 3D Printing

In recent years, bulk metallic glasses (BMGs) have drawn much research attention and are shown to be of industrial interest due to their superior mechanical properties and resistance to corrosion. In spite of the interest in harnessing MG for microelectromechanical systems devices, there are limitations in manufacturing such micrometer‐scale structures. A novel approach for the fabrication of 3D MG structures using laser‐induced forward transfer (LIFT) is demonstrated. Inherent tremendous cooling rates associated with the metal LIFT process (≈10¹⁰ k s^?1) make the formation of a variety of BMGs accessible, including also various binary compositions. In this work, it is demonstrated that LIFT printing of ZrPd‐based metallic glass microstructures can also be performed under ambient conditions. X‐ray diffraction analysis of the printed structures reveals > 95% of amorphous metal phase. Taking advantage of the properties of BMG, high quality printing of high aspect ratio BMG pillars, and microbridges are demonstrated. It is also shown how a composite, amorphous‐crystalline metal structure with a required configuration can be fabricated using multimaterial LIFT printing. The inherent high resolution of the method combined with the noncontact and multimaterial printing capacity makes LIFT a valuable additive manufacturing technique to produce metallic glass‐based devices.     

Suppression of Catastrophic Failure in Metallic Glass–Polyisoprene Nanolaminate Containing Nanopillars

One considerable concern in metallic glass is enhancing ductility by suppressing catastrophic failure by the instantaneous propagation of shear bands. Compressed nanopillars with alternating CuZr metallic glass and polyisoprene nanolaminates exhibit >30% enhancement in plastic flow, as compared with monolithic glass, without sacrifice of strength. A suppression of stochastic strain burst signature in these metallic glass‐polymer composites is reported, which is an undesirable characteristic ubiquitously present in monolithic metallic glass and in metallic glass‐metal composites. The intermittent stochastic signature is quantified in each metallic glass‐containing nanolaminate system by constructing histograms of burst size distributions and provide theoretical foundation for each behavior. The exceptional mechanical properties emergent in these MG‐polymer nanolaminate composites are attributed to the combination of nanometer size‐induced shear band suppression in metallic glasses and the damping capability of the polyisoprene layers.     

Silver Nanoparticles Deposited Layered Double Hydroxide Nanoporous Coatings with Excellent Antimicrobial Activities

Simple and facile processes to produce silver nanoparticles deposited layered double hydroxide (Ag‐LDH) coatings are reported. High quality nanoporous LDH coatings are obtained under hydrothermal conditions via an improved in situ growth method by immersing the substrates in LDH suspensions after removal of free electrolytes. Different types of substrates including metal, ceramics, and glass with planar and non‐planar surfaces can all be coated with the oriented LDH films with strong adhesion. The pore size can be easily tuned by changing the metal:NaOH ratio during the precipiation process of LDH precursors. In the presence of LDH coatings, silver ions can be readily reduced to metallic silver nanoparticles (Ag NPs) in aqueous solutions. The resulting Ag NPs are incorporated evenly on LDH surface. The Ag‐LDH coating exhibits excellent and durable antimicrobial activities against both Gram‐negative (E. Coli and P. Aeruginosa) and Gram‐positive (B. Subtilis and S. Aureus) bacteria. Even at the 4th recycled use, more than 99% of all types of bacteria can be killed. Moreover, the Ag‐LDH coating can also effectively inhibit the bacterial growth and prevent the biofilm formation in the nutrient solutions. These newly designed Ag‐LDH coatings may offer a promising antimicrobial solution for clinical and environmental applications.     

3D Microfluidic Surface‐Enhanced Raman Spectroscopy (SERS) Chips Fabricated by All‐Femtosecond‐Laser‐Processing for Real‐Time Sensing of Toxic Substances

A novel all‐femtosecond‐laser‐processing technique is proposed for the fabrication of 2D periodic metal nanostructures inside 3D glass microfluidic channels, which have applications to real‐time surface‐enhanced Raman spectroscopy (SERS). In the present study, 3D glass microfluidic channels are fabricated by femtosecond‐laser‐assisted wet etching. This is followed by the space‐selective formation of Cu‐Ag layered thin films inside the microfluidic structure via femtosecond laser direct writing ablation and electroless metal plating. The Cu‐Ag films are subsequently nanostructured by irradiation with linearly polarized beams to form periodic surface structures. This work demonstrates that a double exposure to laser beams having orthogonal polarization directions can generate arrays of layered Cu‐Ag nanodots with dimensions as small as 25% of the laser wavelength. The resulting SERS microchip is able to detect Rhodamine 6G, exhibiting an enhancement factor of 7.3 × 10⁸ in conjunction with a relative standard deviation of 8.88%. This 3D microfluidic chip is also found to be capable of the real‐time SERS detection of Cd²⁺ ions at concentrations as low as 10 ppb in the presence of crystal violet. This technique shows significant promise for the fabrication of high performance microfluidic SERS platforms for the real‐time sensing of toxic substances with ultrahigh sensitivity.     

Cover Picture: Fabrication and Characterization of Three‐Dimensional Silver‐Coated Polymeric Microstructures (Adv. Funct. Mater. 13/2006)

Kuebler and co‐workers report on p. 1739 a method for preparing conductive and optically reflective silver‐coated polymeric microstructures having virtually any 3D form. Shown are reflection images of a silvered five‐layer simple‐cubic lattice having a period of 2.4 μm (background) and a macroscopic silvered polymer film (inset). To prepare metallopolymeric microstructures, 3D polymeric scaffolds are first created by multiphoton direct laser writing, then functionalized with gold particles, and metallized using nucleated electroless silver deposition. A method is reported for fabricating complex 3D silver‐coated polymeric microstructures. The approach is based on the creation of a crosslinked polymeric microscaffold via patterned multiphoton‐initiated polymerization followed by surface‐nucleated electroless deposition of silver. The conductivity and reflectivity of the resulting silver–polymer composites and the nanoscale morphology of the deposited silver are characterized. Sub‐micrometer thick layers of silver can be controllably deposited onto surfaces, including those of 3D microporous forms without occluding the interior of the structure. The approach is general for silver coating crosslinked polymeric structures based on acrylate, methacrylate, and epoxide resins and provides a new path to complex 3D micrometer‐scale devices with electronic, photonic, and electromechanical function.     

Elastic Fluctuations and Structural Heterogeneities in Metallic Glasses

Suppressing crystallization of a metallic melt results in a disordered solid, also known as a metallic glass. One may conclude that a metallic glass is free of defined structural length scales beyond some atomic‐scale value that characterizes short‐ and medium‐range order. While it is well known from atomistic modeling that a metallic glass is structurally heterogeneous, heterogeneities at such a small length scale can hardly be resolved in experiments. This review highlights experimental insights into elastic fluctuations and structural heterogeneities that emerge at scales between a few nanometers and tens to hundreds of micrometers. It distinguishes between structural and property fluctuations in as‐cast metallic glasses, and heterogeneities introduced by elastic and inhomogeneous plastic deformation. As‐cast glasses reveal elastic fluctuations across 3 orders of magnitude, suggesting a hierarchy of length scales that can be tuned by thermomechanical processing. Similarly, nanoscale strain localization into shear bands drives the formation of structural and elastic heterogeneities at both the nano‐ and the microscale. It is proposed that both types of fluctuations will allow one to quantitatively define structure–property relationships via measurable length scales—an approach that has largely contributed to the engineering success of crystalline metals.     

锆基非晶合金与不锈钢激光焊接的接头特性

为了优化非晶合金与晶体金属的激光焊接工艺,运用最大平均功率300 W脉冲红外激光焊接锆基非晶合金Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀与440、304、17-4PH不锈钢。采用材料分析手段和力学测试方法对实验焊接接头的材料微观组织、成分组成以及力学性能进行了表征,取得了合适的激光偏移量焊接工艺参数、焊接接头微观组织特性数据及其力学性能数据。结果表明,激光焦点往不锈钢侧偏移0.2 mm～0.3 mm可以使焊接熔化均匀并有效提高抗弯强度,通过合适的焊接工艺使非晶合金与17-4PH接头抗弯强度达339 MPa;非晶合金与3种不锈钢的激光焊接接头主要分为熔化混合区与热影响区,熔化混合区中发现了呈树枝状与颗粒状的结晶组织,焊后通过低温退火可使抗弯强度提升14%～48%。此研究结果对扩大锆基非晶合金在各个领域的应用具有指导意义。     

Direct Ink‐Jet Printing of Ag–Cu Nanoparticle and Ag‐Precursor Based Electrodes for OFET Applications

The field of organic electronics has seen tremendous progress over the last years and all‐solution‐based processes are believed to be one of the key routes to ultra low‐cost roll‐to‐roll device and circuit fabrication. In this regard a variety of functional materials has been successfully designed for inkjet printing. While orthogonal‐solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field‐effect transistors (OFET) and their curing concepts. Two metallic inkjet‐printable materials are studied: i) a silver‐copper nanoparticle based dispersion and ii) a soluble organic silver‐precursor. Photoelectron spectroscopy reveals largely metallic properties of the cured materials, which are compared with respect to OFET performance and process‐related issues. Contact resistance of the prepared metal electrodes is significantly larger than that of evaporated top‐contact gold electrodes. As direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 μm, the influence of contact resistance is rather small, however, and overall device performance is comparable.     

光热折变玻璃的研究进展

光热折变玻璃是一种光敏硅酸盐玻璃,主成分为Na2O–ZnO–Al2O3–SiO2,并掺有Ag、Ce和F等成分,其折射率在紫外曝光并热处理后发生改变,具有在可见光以及红外光谱范围内损耗小,激光破坏阈值高,热稳定性好等特点,可用于制备衍射效率高,光谱选择性和角度选择性好的体Bragg光栅,可用于光谱窄化,相干耦合,谱合成等,在激光与光通信领域以及其他光学系统中有广阔的应用前景。分析了光热折变玻璃的折射率改变机制,讨论了光热折变玻璃的吸收特性,结构转变及激光破坏特性等光学特性。     

Silver Doped with Acidic/Basic Polymers: Novel,Reactive Metallic Composites

We report the preparation and properties of metallopolymeric composites with acidic and basic properties. The composites are prepared via the recently developed method of entrapping organic molecules within metals. Specifically, we describe the entrapment of the polyacid Nafion or the polybase poly(vinylbenzyltrimethylammonium hydroxide) within silver. The resulting acidic or basic metallic composites decrease or increase, respectively, the pH of water through an ion‐exchange process. Furthermore, silver doped with Nafion can be employed as an acid catalyst, as shown for the pinacol–pinacolone rearrangement and for the dehydration of an alcohol. Characterization of these novel materials via microscopy and adsorption studies reveals a three‐level hierarchical structure: clusters of ≈ 10 μm in size built from ≈ 1 μm aggregates of ≈ 100 Å silver crystals. Thermogravimetric analysis of the entrapped polymers reveals a catalytic effect of the metal on this process. The two polymers are entrapped differently, and the differences are discussed. Applications ranging from ion‐exchange electrodes to bifunctional catalysts are envisaged.     

Genetically Engineered Phage Fibers and Coatings for Antibacterial Applications

Multifunctionality can be imparted to protein‐based fibers and coatings via either synthetic or biological approaches. Here, potent antimicrobial functionality of genetically engineered, phage‐based fibers and fiber coatings, processed at room temperature, is demonstrated. Facile genetic engineering of the M13 virus (bacteriophage) genome leverages the well‐known antibacterial properties of silver ions to kill bacteria. Predominant expression of negatively charged glutamic acid (E3) peptides on the pVIII major coat proteins of M13 bacteriophage enables solution‐based, electrostatic binding of silver ions and subsequent reduction to metallic silver along the virus length. Antibacterial fibers of micrometer‐scale diameters are constructed from such an E3‐modified phage via wet‐spinning and glutaraldehyde‐crosslinking of the E3‐modified viruses. Silverization of the free‐standing fibers is confirmed via energy dispersive spectroscopy and inductively coupled plasma atomic emission spectroscopy, showing ～0.61 µg cm^?1 of silver on E3–Ag fibers. This degree of silverization is threefold greater than that attainable for the unmodified M13–Ag fibers. Conferred bactericidal functionality is determined via live–dead staining and a modified disk‐diffusion (Kirby–Bauer) measure of zone of inhibition (ZoI) against Staphylococcus epidermidis and Escherichia coli bacterial strains. Live–dead staining and ZoI distance measurements indicate increased bactericidal activity in the genetically engineered, silverized phage fibers. Coating of Kevlar fibers with silverized E3 phage exhibits antibacterial effects as well, with relatively smaller ZoIs attributable to the lower degree of silver loading attainable in these coatings. Such antimicrobial functionality is amenable to rapid incorporation within fiber‐based textiles to reduce risks of infection, biofilm formation, or odor‐based detection, with the potential to exploit the additional electronic and thermal conductivity of fully silverized phage fibers and coatings.     

UV‐vis‐Induced Vitrification of a Molecular Crystal

A charge‐transfer complex of 2,5‐dimethyl‐N,N′‐dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)₂, defined as α) is irreversibly transformed by UV‐vis illumination. Depending on the illumination conditions, three new types of solids (defined as γ, δ, and ?) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid‐state, high‐resolution, cross‐polarization magic angle spinning (CP‐MAS) ¹³C NMR, elemental analysis (EA), mass spectrometry (MS), X‐ray absorption fine structure (XAFS), and powder X‐ray diffraction (XRD). The CP‐MAS, EA, MS, and XAFS results indicate that compound γ is a glass state of Ag(DM)₂. The transformation from crystalline (α) to amorphous (γ) solid Ag(DM)₂ is an irreversible exothermic glass transition (glass‐transition temperature 155.2 °C; ΔH = –126.8 kJ mol^–1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound δ (Ag(DM)_1.5) consists of silver nanoparticles (diameter (7 ± 2) nm ) dispersed in a glassy matrix of neutral DM molecules. The ?N–CN–Ag coordination bonds of the α form are not maintained in the δ form. Decomposition of α by intense illumination results in a white solid (?), identified as being composed of silver nanoparticles (diameter (60 ± 10) nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both δ and ? are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver.     

Ovonic Memory Switching in Multimaterial Fibers

We demonstrate the first rewritable memory in thermally drawn fibers. A high tellurium‐content chalcogenide glass, contacted by metallic electrodes internal to the fiber structure, is drawn from a macroscopic preform. An externally applied voltage is utilized to switch between a high resistance (OFF) and a low resistance (ON) state; this in turn allows the fibers to function as a memory device reminiscent of the ovonic switch. The difference between the ON and OFF states is found to be four orders of magnitude. The glass–crystal phase transition is localized to micrometer‐wide filaments, whose position can be optically controlled along the fiber axis. An architecture that enabled the encoding of multiple bits per fiber is described.     

Laser-induced implantation of silver particles into poly(vinyl alcohol) films and its application to electronic-circuit fabrication on encapsulated organic electronics

In this study, we propose a new laser-induced implantation based approach for embedding electronic interconnects in this study. Direct implantations of silver particles, vaporized by a pulsed laser from a silver film initially pre-coated on a transparent glass substrate, into poly(vinyl alcohol) (PVA)-encapsulated organic electronic devices as electronic conducting circuits are demonstrated. Two test carriers are the devices of organic thin-film transistors and polymeric light-emitting diodes. Device property characterizations indicate the implanted circuits can work smoothly. The implantation process is driven by the high-energy ejected particles that soften and melt the PVA layer and penetrate into it until their momentums are totally lost. The penetration depth increases with the number of laser pulses and is becoming saturated as the pulse number is getting high. A conducting circuit, with length of 2 μm, can be completely embedded within 3 laser pulses. Due to its flexibility in embedding metals into an encapsulated device, this technique can be used for repairing internal circuit damage. Besides, all steps can be executed in the ambient environment and at room temperature that is suitable for plastic substrate processing.     

Lead‐free on‐laminate laser soldering: a new module assembling concept

We demonstrate lead‐free laser soldering of standard industrial solar cells. The laser‐soldered contacts stay stable for more than 240 accelerated ageing cycles by humidity–freeze test and withstand peel forces in excess of 10 N/cm. Laser soldering is demonstrated while the cells are lying on the ethylene vinyl acetate (EVA) foil. This permits to connect the solar cells to the lead‐free tinned copper ribbons directly on the lamination materials. We also demonstrate soldering on the bottom side by lasering through the glass and the non‐polymerized EVA. With the aid of a pick and place robot it thus becomes possible to avoid all string handling. On‐laminate laser soldering (OLLS) technique, which permits a high level of automation and process control, induces little thermal and mechanical stress, reduces the handling and should thus be of particular advantage for assembling modules with very thin cells at a high yield. Copyright © 2007 John Wiley & Sons, Ltd.