Smooth Metal Surfaces Research Articles

Molybdenum Disulfide‐Based Tubular Microengines: Toward Biomedical Applications

2D molybdenum disulfide (MoS2) is herein explored as an advanced surface material in the fabrication of powerful tubular microengines. The new catalytic self‐propelled open‐tube bilayer microengines have been fabricated using a template electrodeposition and couple the unique properties of sp2 hybridized MoS2 with highly reactive inner granular Pt catalytic structures. The MoS2/metal microengines display extremely efficient bubble propulsion, reflecting the granular structure of the inner catalytic platinum or gold layers (compared to the smooth metal surfaces of common micromotors). The efficient movement of functionalized MoS2 micromotors can address challenges imposed by slow mass transport processes involved in various applications of MoS2. The delocalized electron network of the MoS2 outer layer facilitates π–π stacking interactions and endows the tubular microengines with a diverse array of capabilities. These are demonstrated here for efficient loading and release of the drug doxorubicin, and rapid and sensitive “OFF–ON” fluorescent detection of important nucleic acids (miRNA‐21) and proteins (thrombin) using microengines modified with dye‐labeled single‐stranded DNA and aptamer, respectively. Such coupling of the attractive capabilities of 2D‐MoS2 nanosheets with rapidly moving microengines provides an opportunity to develop multifunctional micromachines for diverse biomedical applications ranging from efficient drug delivery to the detection of important bioanalytes.

Effect of new adhesion promoter and mechanical interlocking on bonding strength in metal-polymer composites

There are various opportunities to improve the adhesion between polymer and metal in metal-plastic composites. The addition of a bonding agent which reacts with both joining components at the interfaces of the composite can enhance the bonding strength. An alternative method for the adjustment of interfaces in metal-plastic composites is the specific surface structuring of the joining partners in order to exploit the mechanical interlock effect. In this study the potential of using an adhesion promoter based on twin polymerization for metal-plastic composites in combination with different methods of mechanical surface treatment is evaluated by using the tensile shear test. It is shown that the new adhesion promoter has a major effect when applied on smooth metal surfaces. A combination of both mechanical and chemical surface treatment of the metal part is mostly just as effective as the application of only one of these surface treatment methods.

Dependence of Q Factor on Surface Roughness in a Plasmonic Cavity

We investigated surface-roughness-dependent optical loss in a plasmonic cavity consisting of a semiconductor nanodisk/silver nanopan structure. Numerical simulations show that the quality factors of plasmonic resonant modes significantly depend on the surface roughness of the dielectric-metal interface in the cavity structure. In the transverse-magnetic-like whispering-gallery plasmonic mode excited in a structure with disk diameter of 1000 nm, the total quality factor decreased from 260 to 130 with increasing root-mean-square (rms) surface roughness from 0 to 5 nm. This quantitative theoretical study shows that the smooth metal surface plays a critical role in high-performance plasmonic devices.

Direct Observation of Confinement-Induced Charge Inversion at a Metal Surface.

Surface interactions across water are central to areas from nanomedicine to colloidal stability. They are predominantly a combination of attractive but short-ranged dispersive (van der Waals) forces, and long-ranged electrostatic forces between the charged surfaces. Here we show, using a surface force balance, that electrostatic forces between two surfaces across water, one at constant charge while the other (a molecularly smooth metal surface) is at constant potential of the same sign, may revert smoothly from repulsion to attraction on progressive confinement of the aqueous intersurface gap. This remarkable effect, long predicted theoretically in the classic Gouy-Chapman (Poisson-Boltzmann) model but never previously experimentally observed, unambiguously demonstrates surface charge reversal at the metal-water surface. This experimental confirmation emphasizes the implications for interactions of dielectrics with metal surfaces in aqueous media.

Geometric tools for exploring manifolds of light transport paths

Photorealistic images created using physical simulations of light have become a ubiquitous element of our everyday lives. The most successful techniques for producing such images replicate the key physical phenomena in a detailed software simulation, including the emission of light by sources, transport through space, and scattering in the atmosphere and at the surfaces of objects. Mathematically, this computation involves the approximation of many high-dimensional integrals, one for each pixel of the image, usually using Monte Carlo methods. Although a great deal of progress has been made on rendering algorithms, so that physically based rendering is now routinely used in many applications, commonly occurring situations can still cause these algorithms to become impractically slow, forcing users to make unrealistic scene modifications to obtain satisfactory results. Light transport is complex because light can flow along a great variety of different paths through a scene, though only a subset of these makes relevant contributes to the final image. The simulation becomes ineffective when it is difficult to find the important paths. Commonly occurring materials like smooth metal or glass surfaces can easily lead to such situations, where only very few lighting paths participate, leading to spiky integrands and poor convergence. How to efficiently handle such cases in general has been a long-standing problem.<!-- END_PAGE_1 --> In this paper, we provide a geometric solution to this problem by representing light paths as points in an abstract high-dimensional configuration space that is defined by a system of constraint equations. This configuration space is a differentiable manifold, which can be locally parameterized in the neighborhood of an existing path. Building on this framework, we propose Manifold Exploration, a rendering technique that efficiently explores the integration domain by taking geometrically informed steps on the manifold of light paths.

(Invited) Nano-Controlled Etching of Polycrystalline Metals - a Key Enabler for Future Technologies

As Moore's law continues its relentless march, defying odds of its predicted demise well in to more than a decade, innovations are required to enable 10 nm and beyond technology nodes. The capability to etch polycrystalline metals with an unprecedented nanometer scale control offers unique challenges at the forefront of mechanistic and structural understanding of chemical reactivity and kinetics. Since the advent of Cu-based interconnects embedded in low-k dielectrics, the landscape of BEOL cleans has focused on development of process technologies that were aimed at enhancing metal compatibility in highly corrosive media. Fluorocarbon plasma-based etches and ashes needed to pattern interlayer vias leave behind a chemically-susceptible dielectric, surface modified metals, locally corrosive environments and copious amounts of etch polymer. Advanced formulations for BEOL via cleans incorporated metal corrosion inhibitors, buffering agents for precise pH control, additives for surface tension control and carefully selected solvent systems for precisely tuned viscosity control. Removal of post-plasma-etch residues with metal compatibility remained a finely tuned balancing act between clean wafers and undamaged wiring. Capping of the interconnect wires by selective metal growth as shown in Figure 1 has been extensively researched. While its benefits and limitations are beyond the scope of discussion here, two critical yield impactors, nodules of non-selective metal growth and protrusions of capping metal beyond the CD of the patterned line, are shown schematically in Figure 1. The scheme shown in Figure 2 relies on nano-controlled wet etching of the polycrystalline Cu in the line to create a recessed cavity which may be capped with a metal of choice followed by polishing to yield a capped metal flush with the dielectric. This scheme has the potential to realize benefits of metal capping without the yield-limiting defects shown in Figure 1. In this paper, we describe the development of a liquid phase chemical solution to etch a solid polycrystalline metal line composed of grains with potentially different sizes, orientations, phases, textures and inherently anisotropic grain boundaries with nanometer scale precision to yield a non-pitted and smooth metal surface with a RMS roughness of ~ 1.2 nm. Rates and mechanisms of metal dissolution reactions, in both acidic and basic media, are highly sensitive to dissolved oxygen concentration and the mass-transport of reactants and products. Development of etchant chemistry involved optimization of the chemistry components along with tool parameters to yield the process on a 300 mm wafer with < 3 nm center to edge etch depth uniformity (shown in Figure 3). Use of dopants to improve electromigration (EM) performance of Cu-interconnects has been a fairly standard practice in the semiconductor industry. Within the context of understanding dissolution of Cu lines with added EM-dopant, we observed somewhat expectedly, drastic differences in etch rates and profiles using the same chemical etch solution. The barrier metal, in direct contact with the Cu line, was also found to influence the mechanism and profile of metal etching. While Ta-based barriers yielded uniform etch rates in the middle of the Cu line relative to the edges, Ru-based barriers showed effects of galvanically-accelerated etching at contacted interfaces (Figure 4). Fundamental studies in the nature of metal etching at grain boundaries as a function of grain size, phase, orientation and texture are critically needed. The reaction mechanisms and equilibriums leading to oxidation, nature of transient oxides and their dissolution in the etchant as well as chelation-based stabilization of the dissolved metal to prevent re-deposition are not well characterized. While the application of nano-controlled etching to enable metal-capping for better EM performance and LWR control as described, is quite specific, it is neither unique nor exhaustive. Enhanced ability to selectively and controllably etch different metals may enable multiple innovations that will be needed at the 10 nm node and beyond to drive Moore's law. Fig 1. Metal capping by selective metal deposition: a) marginality in growth selectivity poses a shorting risk; b) cap growth typical produces an overhang which reduces dielectric CD and negatively impacts line width roughness (LWR) Fig 2. Nano-controlled etch of polycrystalline metal allows for deposition of a metal cap in the recessed cavity. Fig 3. Nano-controlled etch of Cu lines with a Ta-based barrier Fig 4. a) Nano-controlled Cu etch with a Ta-based barrier b) Nano-controlled Cu etch with a Ru-based barrier Figure 1

Wear rate and fracture toughness of porous particle-filled phenol composites

We experimentally investigated the effects of filler volume fraction of the phenol composites filled with porous particles on the fracture toughness and the wear rate against a smooth metal surface under multi-pass condition. Porous particles, made from rice husks, of various volume fractions from 0 to 0.5 were added to phenol resin as carbon filler. For the reported results of adhesive wear under multi-pass condition, we correlated the bulk parameters associated with the fracture toughness to the wear rate. We found an empirical power–law relation between the reciprocal of the product of stress and strain at rupture in bending test and the wear rate with various filler volume fractions. We also proposed the modified mixture law of the wear rate by taking account of the area fraction of transfer layer, which can provide a good prediction of the filler volume fraction dependence.

2091543 Wooden Toothpick with Two Sharp Tips Pierced the Gallbladder: A Very Rare Clinical Case Report

ObjectivesGastrointestinal foreign bodies is a common problem in clinical practice and multiple complications were reported such as peritonitis from gastrointestinal tract perforation, bladder perforation, vessel perforation, liver abscess, ... However, the gallbladder perforation by foreign bodies was rarely reported and we have not found any reports about the gallbladder was pierced by wooden toothpick.MethodsWe report a clinical case, 43-year-old male patient, history foreign body in the liver about two months, current upper abdominal pain like stomach syndrome. No history of abdominal trauma and inhaling sharp of food. We have conducted an abdominal ultrasound examination.ResultsAbdominal ultrasound detected edema of gallbladder wall, 7mm thickness. There was a straight, echogenic foreign body, 2.5mm in width, 60mm in length, slight shadowing pierced the gallbladder which we think this is a wooden toothpick. One tip was inside the gallbladder and the other tip outside the gallbladder, toward the duodenum, in the fluid 20mm, surrounded by omentum, mild pain when pressed. Blood tests show increased WBC 14,540/uL and Neutrophil 10,160/uL.Upper endoscopy and X-ray were unremarkable.MDCT was done at the moment and had similar results.The patient underwent surgery, removed the gall bladder with abscess and confirm the wooden toothpick pierced of the gallbladder.Then, some small trials have been done we showed that ultrasound provides difference pictures between foreign bodies such as wood, smooth surface metal and rough surface metal.ConclusionsThis is a case of abdominal foreign bodies is extremely rare, unknown intrusion time, vague symptoms. Ultrasound has helped detect and provide accurate diagnosis with stunning visuals and characteristic mages. ObjectivesGastrointestinal foreign bodies is a common problem in clinical practice and multiple complications were reported such as peritonitis from gastrointestinal tract perforation, bladder perforation, vessel perforation, liver abscess, ... However, the gallbladder perforation by foreign bodies was rarely reported and we have not found any reports about the gallbladder was pierced by wooden toothpick. Gastrointestinal foreign bodies is a common problem in clinical practice and multiple complications were reported such as peritonitis from gastrointestinal tract perforation, bladder perforation, vessel perforation, liver abscess, ... However, the gallbladder perforation by foreign bodies was rarely reported and we have not found any reports about the gallbladder was pierced by wooden toothpick. MethodsWe report a clinical case, 43-year-old male patient, history foreign body in the liver about two months, current upper abdominal pain like stomach syndrome. No history of abdominal trauma and inhaling sharp of food. We have conducted an abdominal ultrasound examination. We report a clinical case, 43-year-old male patient, history foreign body in the liver about two months, current upper abdominal pain like stomach syndrome. No history of abdominal trauma and inhaling sharp of food. We have conducted an abdominal ultrasound examination. ResultsAbdominal ultrasound detected edema of gallbladder wall, 7mm thickness. There was a straight, echogenic foreign body, 2.5mm in width, 60mm in length, slight shadowing pierced the gallbladder which we think this is a wooden toothpick. One tip was inside the gallbladder and the other tip outside the gallbladder, toward the duodenum, in the fluid 20mm, surrounded by omentum, mild pain when pressed. Blood tests show increased WBC 14,540/uL and Neutrophil 10,160/uL.Upper endoscopy and X-ray were unremarkable.MDCT was done at the moment and had similar results.The patient underwent surgery, removed the gall bladder with abscess and confirm the wooden toothpick pierced of the gallbladder.Then, some small trials have been done we showed that ultrasound provides difference pictures between foreign bodies such as wood, smooth surface metal and rough surface metal. Abdominal ultrasound detected edema of gallbladder wall, 7mm thickness. There was a straight, echogenic foreign body, 2.5mm in width, 60mm in length, slight shadowing pierced the gallbladder which we think this is a wooden toothpick. One tip was inside the gallbladder and the other tip outside the gallbladder, toward the duodenum, in the fluid 20mm, surrounded by omentum, mild pain when pressed. Blood tests show increased WBC 14,540/uL and Neutrophil 10,160/uL. Upper endoscopy and X-ray were unremarkable. MDCT was done at the moment and had similar results. The patient underwent surgery, removed the gall bladder with abscess and confirm the wooden toothpick pierced of the gallbladder. Then, some small trials have been done we showed that ultrasound provides difference pictures between foreign bodies such as wood, smooth surface metal and rough surface metal. ConclusionsThis is a case of abdominal foreign bodies is extremely rare, unknown intrusion time, vague symptoms. Ultrasound has helped detect and provide accurate diagnosis with stunning visuals and characteristic mages. This is a case of abdominal foreign bodies is extremely rare, unknown intrusion time, vague symptoms. Ultrasound has helped detect and provide accurate diagnosis with stunning visuals and characteristic mages.

Theoretical analysis of micro-vibration between a high moisture content rape stalk and a non-smooth surface of a reciprocating metal cleaning screen matrix

Because rape stalk has a high water content, rape materials easily adhere to the cleaning screens of combine harvesters leading to a high screen loss. Inspired by friction-reducing research on bionic non-smooth metal surfaces, a special rape cleaning screen with non-smooth surface was developed and compared with a standard screen in field experiment. It showed good anti-adhesion performance to rape components. To understand the mechanism, a reciprocating friction test between a rape stalk and non-smooth metal surface was carried out. The result was consistent with the findings of a field experiment. In the test, a vertical micro-vibration was discovered between rape stalk and the non-smooth metal surface. This did not exist in the case of a common smooth metal surface and was considered as an important factor in the mechanism. In this paper, a theoretical analysis was proposed to explain how the vertical micro-vibrations occurred during a horizontal reciprocating translation of non-smooth units. Firstly, according to the case of friction test, a geometry contact model and a dynamic equation were established. Then computing methods of vertical impact force and its action time were respectively deduced. Finally, a simulation was produced with a time-scale factor of two. The result from the simulation was consistent with basic trend of test data. Although the theoretical analysis requires improvement for further investigation, it could still provide the basis of a theoretical model and the foundation for further friction-reducing research for non-smooth surfaces.

Insights into the superhydrophobicity of metallic surfaces prepared by electrodeposition involving spontaneous adsorption of airborne hydrocarbons

Electrochemical fabrication of micro/nanostructured metallic surfaces with superhydrophobicity has recently aroused great attention. However, the origin still remains unclear why smooth hydrophilic metal surfaces become superhydrophobic by making micro/nanostructures without additional surface modifications. In this work, several superhydrophobic micro/nanostructured metal surfaces were prepared by a facile one-step electrodeposition process, including non-noble and noble metals such as copper, nickel, cadmium, zinc, gold, and palladium with (e.g. Cu) or without (e.g. Au) surface oxide films. We demonstrated by SEM and XPS that both hierarchical micro/nanostructures and spontaneous adsorption of airborne hydrocarbons endowed these surfaces with excellent superhydrophobicity. We revealed by XPS that the adsorption of airborne hydrocarbons at the Ar+-etched clean Au surface was rather quick, such that organic contamination can hardly be prevented in practical operation of surface wetting investigation. We also confirmed by XPS that ultraviolet-O3 treatment of the superhydrophobic metal surfaces did not remove the adsorbed hydrocarbons completely, but mainly oxidized them into hydrophilic oxygen-containing organic substances. We hope our findings here shed new light on deeper understanding of superhydrophobicity for micro/nanostructured metal surfaces with and without surface oxide films.

300-GHz Step-Profiled Corrugated Horn Antennas Integrated in LTCC

This paper presents 300-GHz step-profiled corrugated horn antennas, aiming at their integration in low-temperature co-fired ceramic (LTCC) packages. Using substrate integrated waveguide technology, the cavity inside the multi-layer LTCC substrate and a surrounding via fence are used to form a feeding hollow waveguide and horn structure. Owing to the vertical configuration, we were able to design the corrugations and stepped profile of horn antennas to approximate smooth metallic surface. To verify the design experimentally, the LTCC waveguides and horn antennas were fabricated with an LTCC multi-layer process. The LTCC waveguide exhibits insertion loss of 0.6 dB/mm, and the LTCC horn antenna exhibits 18-dBi peak gain and 100-GHz bandwidth with more than 10-dB return loss. The size of the horn antenna is only 5×5×2.8 mm 3 , which makes it easy to integrate it in LTCC transceiver modules.

Anchor-free NEMS non-volatile memory cell for harsh environment data storage

This work demonstrates a novel anchor-free nano-electromechanical (NEMS) based non-volatile memory cell, suitable for high temperature (T ≤ 300 °C) and radiation prone harsh environment applications. The anchor-free circular metal beam is actuated by electrostatic force and is held in one of the bi-stable memory states by adhesion force between two smooth metal surfaces in contact. Smooth metal layers form strong van der Waals stiction between two surfaces in contact and memory detection (Logic-‘1’ / Logic-‘0’) is obtained by detecting the conductance between two fixed contacts. This anchor-free design offers highest density (9F2 footprint) compared to other mechanical memory devices reported to date.

“Seeing” the Resonant SPP Modes Confined in Metal Nanocavity via Cathodoluminescne Spectroscopy

ABSTRACT:Surface plasmon polaritons (SPPs), which are coupled excitations of electrons bound to a metal-dielectric interface, show great potential for application in future nanoscale photonic systems due to the strong field confinement at the nanoscale, intensive local field enhancement, and interplay between strongly localized and propagating SPPs. The fabrication of sufficiently smooth metal surface with nanoscale feature size is crucial for SPPs to have practical applications. A template stripping (ST) method combined with PMMA as a template was successfully developed to create extraordinarily smooth metal nanostructures with a desirable feature size and morphology for plasmonics and metamaterials. The advantages of this method, including the high resolution, precipitous top-to bottom profile with a high aspect ratio, and three-dimensional characteristics, make it very suitable for the fabrication of plasmonic structures. By using this ST method, boxing ring-shaped nanocavities have been fabricated and the confined modes of surface plasmon polaritons in these nanocavities have been investigated and imaged by using cathodoluminescence (CL) spectroscopy, which has been turned out to be a powerful means to characterize the resonant SPPs modes confined in metal nanocavities [1∼5] . The mode of the out-of-plane field components of surface plasmon polaritons dominates the experimental mode patterns, indicating that the electron beam locally excites the out-of-plane field component of surface plasmon polaritons. Quality factors can be directly acquired from the spectra induced by the ultrasmooth surface of the cavity and the high reflectivity of the silver (Ag) reflectors. Because of its three-dimensional confined characteristics and the omnidirectional reflectors, the nanocavity exhibits a small modal volume, small total volume, rich resonant modes, and flexibility in mode control. Numerous applications, such as plasmonic filter, nanolaser, and efficient light-emitting devices, can be expected to arise from these developments.

The Abrasion Behavior and Mechanisms of a Superhydrophobic Surface Comprising Styrene Butadiene Rubber

The microprotuberances of superhydrophobic surfaces are easily destroyed during a friction cycle, resulting in invalidation of superhydrophobicity, because they are then loaded with pressure and shearing stress. Thus, the abrasion-resistance of superhydrophobic surfaces is the main barrier preventing their wide application. Elastic microprotuberances will be compressed and collapsed by elastic deformation to avoid being broken during a friction cycle, and the deformation will rebound to renew the original surface structure when the load is withdrawn. A superhydrophobic surface comprising styrene butadiene rubber (SBR) was fabricated via template replication in the research described here, with a water contact angle up to 160°. Friction testing was then used to characterize the abrasion resistance of the surface; the contact angle remained more than 139° even after being loaded with 4.4 KPa or 6.87 KPa and rubbed by a smooth metal surface at 18 cm/s for 10,000 times. Scanning electron microscopy was used t...

Development and application of the in situ radiotracer thin gap method for the investigation of corrosion processes. I. Adaptation of the thin gap method for the application of porous surfaces

The electrode lowering method of the in situ radiotracer technique provides a unique opportunity for the understanding of both the kinetics and the mechanism of contamination, corrosion and electrocatalytic phenomena. The advanced version of the technique, the thin gap method was originally developed for the investigation of sorption phenomena on smooth metal surfaces. This fact greatly limits the applicability of the method both with species of low specific activity and in case of surfaces of industrial specimens. As the first part of an article series the adaptation of the original method for the investigation of compact, porous surfaces with high surface roughness is demonstrated. The basic equations of the improved method are described, with the help of which the description of sorption phenomena on rough surfaces can be characterized. The optimized preparation parameters of the porous platinum black layer for detection of 36Cl labelled chloride ions are given. It is shown that the sensitivity of the in situ thin gap radiotracer method was substantially increased by the application of porous electrodes.

Effects of Sputter Deposition Sequence and Sulfurization Process of Cu, Zn, Sn on Properties of Cu2ZnSnS4 Solar Cell Material

The effect of a sputter deposition sequence of Cu, Zn, and Sn metal layers on the properties of <TEX>$Cu_2ZnSnS_4$</TEX> (CZTS) was systematically studied for solar cell applications. The set of Cu/Sn/Zn/Cu multi metal films was deposited on a Mo/<TEX>$SiO_2$</TEX>/Si wafer using dc sputtering. CZTS films were prepared through a sulfurization process of the Cu/Sn/Zn/Cu metal layers at <TEX>$500^{\circ}C$</TEX> in a <TEX>$H_2S$</TEX> gas environment. <TEX>$H_2S$</TEX> (0.1%) gas of 200 standard cubic centimeters per minute was supplied in the cold-wall sulfurization reactor. The metal film prepared by one-cycle deposition of Cu(360 nm)/Sn(400 nm)/Zn(400 nm)/Cu(440 nm) had a relatively rough surface due to a well-developed columnar structure growth. A dense and smooth metal surface was achieved for two- or three-cycle deposition of Cu/Sn/Zn/Cu, in which each metal layer thickness was decreased to 200 nm. Moreover, the three-cycle deposition sample showed the best CZTS kesterite structures after 5 hr sulfurization treatment. The two- and three-cycle Cu/Sn/Zn/Cu samples showed high-efficient photoluminescence (PL) spectra after a 3 hr sulfurization treatment, wheres the one-cycle sample yielded poor PL efficiency. The PL spectra of the three-cycle sample showed a broad peak in the range of 700-1000 nm, peaked at 870 nm (1.425 eV). This result is in good agreement with the reported bandgap energy of CZTS.

Electromagnetic particle-in-cell (PIC) method for modeling the formation of metal surface structures induced by femtosecond laser radiation

The particle in cell (PIC) method coupled to the finite-difference time-domain (FDTD) method is used to model the formation of laser induced periodic surface structures (LIPSS) at the early stage of femtosecond laser irradiation of smooth metal surface. The theoretical results were analyzed and compared with experimental data taken from the literature. It was shown that the optical properties of the target are not homogeneous and the ejection of electrons is such that ripples in the electron density were obtained. The Coulomb explosion mechanism was proposed to explain the ripples formation under the considered conditions.

Rarefied gas flow through nanoscale tungsten channels

The aim of this work is to investigate argon flow behaviors through the channels with three types of boundary conditions. Current work deals with numerical simulations of rarefied gas flow through nano-channels using the Molecular Dynamics method. Taking into account that this method is very time consuming, we implemented all the simulations using CUDA capable graphic cards. We found that the well-known and relatively simple Maxwell model of boundary conditions is able to reproduce gas flow through a tungsten channel with irregularities and roughness, while it results in a significant error in the case of a smooth metal surface. We further found that the flow rate through a relatively short channel correlates nonlinearly with the channel's length. This finding is in contrast with the results available in extant literature. Our results are important for both numerical and theoretical analyses of rarefied gas flow in micro- and nano-systems where the choice of boundary conditions significantly influences flow.

Interactions and visualization of bio-mimetic membrane detachment at smooth and nano-rough gold electrode surfaces

Non-specific physical and specific chemical interactions of cells, bacteria, and biomembranes with non-biological target surfaces (e.g., metallic and metal oxides) are crucial in determining the interfacial behavior (interaction forces, adhesion, local deformations and structuring) of many bio- and nano-inspired materials. Knowledge of the governing interactions provides physicochemical understanding of biological systems, and enables engineering of new nano-systems for biomaterials or biomedical benefit. We have directly measured and visualized membrane adhesion and detachment at nanoscopic and extended rough gold electrode surfaces through a multi-scale approach: interactions and contact mechanics measured by surface forces apparatus (SFA) are in quantitative agreement with atomic force microscopy (AFM) measurements, both of which show that membranes can strongly adhere to rough gold surfaces and asperities via specific amine–gold binding and non-specific hydrophobic interactions. The results give insights into membrane interactions at smooth and rough metallic surfaces, and provide a basis for improved design of nanoparticle and extended surface biomaterials.

Broadband and broadangle SPP antennas based on plasmonic crystals with linear chirp

Plasmonic technology relies on the coupling of light to surface electromagnetic modes on smooth or structured metal surfaces. While some applications utilise the resonant nature of surface polaritons, others require broadband characteristics. We demonstrate unidirectional and broadband plasmonic antennas with large acceptance angles based on chirped plasmonic gratings. Near-field optical measurements have been used to visualise the excitation of surface plasmon polaritons by such aperiodic structures. These weakly aperiodic plasmonic crystals allow the formation of a trapped rainbow-type effect in a two-dimensional geometry as surface polaritons of different frequencies are coherently excited in different locations over the plasmonic structure. Both the crystal's finite size and the finite lifetime of plasmonic states are crucial for the generation of broadband surface plasmon polaritons. This approach presents new opportunities for building unidirectional, broadband and broad-angle plasmonic couplers for sensing purposes, information processing, photovoltaic applications and shaping and manipulating ultrashort optical pulses.