Gold Membrane Research Articles

Bulk-suppressed and surface-sensitive Raman scattering by transferable plasmonic membranes with irregular slot-shaped nanopores

Raman spectroscopy enables the non-destructive characterization of chemical composition, crystallinity, defects, or strain in countless materials. However, the Raman response of surfaces or thin films is often weak and obscured by dominant bulk signals. Here we overcome this limitation by placing a transferable porous gold membrane, (PAuM) on the surface of interest. Slot-shaped nanopores in the membrane act as plasmonic antennas and enhance the Raman response of the surface or thin film underneath. Simultaneously, the PAuM suppresses the penetration of the excitation laser into the bulk, efficiently blocking its Raman signal. Using graphene as a model surface, we show that this method increases the surface-to-bulk Raman signal ratio by three orders of magnitude. We find that 90% of the Raman enhancement occurs within the top 2.5 nm of the material, demonstrating truly surface-sensitive Raman scattering. To validate our approach, we quantify the strain in a 12.5 nm thin Silicon film and analyze the surface of a LaNiO3 thin film. We observe a Raman mode splitting for the LaNiO3 surface-layer, which is spectroscopic evidence that the surface structure differs from the bulk. These results validate that PAuM gives direct access to Raman signatures of thin films and surfaces.

Detection of available heavy metals in soil using gold nanoparticles-modified ion exchange membrane with laser-induced breakdown spectroscopy

The available heavy metals in soil can directly threaten food security and human health. However, traditional detection methods are often complicated and time-consuming. In this study, a novel method with nanoparticles-modified ion exchange membrane with laser-induced breakdown spectroscopy (NMIEM-LIBS) was proposed for the sensitive detection of available heavy metals in soil samples. Gold nanoparticles modified-ion exchange membrane was used to high-efficiency enrich lead (Pb) and cadmium (Cd) ions in soil solution and detected after separation. This method can realize the highly sensitive quantitative analysis of available Pb and Cd in soil, with the detection limits (LoDs) of 2.62 mg/kg and 0.24 mg/kg, respectively. Furthermore, the method was successfully applied to detect available Pb and Cd concentrations in three spiked soil samples, with recoveries of 87.02–115.79 % and 82.45–114.81 %, respectively. The developed method can provide a simple, rapid, and sensitive strategy for monitoring available heavy metals in environmental samples.

Design and preparation of an electromechanical implant prototype for an on-demand drug delivery

IntroductionA bio-implant is a drug-delivery system that is implanted in the human body for a period of more than 30 days. Electromechanical systems are one type of bio-implant that has recently been introduced as a new generation of targeted drug delivery methods. The overarching goal of utilizing these systems is to integrate electrical and mechanical features in order to benefit from the numerous applications of these two systems when used together.The current study aimed to design a prototype of an electromechanical system using Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and MultiJet Fusion (MJF) techniques for drug delivery that can release a specific drug dosage in the patient's body by connecting to a sensor or under the control of a signal sent by the physician. MethodsInitially, the implant chambers were created in the form of a hollow cylinder, closed at one end, using three different types of 3D printers: FDM, SLS, and MJF. Each implant was then filled with a model drug (pentoxifylline) and sealed with a thin gold membrane. To achieve the lowest voltage required to melt the gold membrane, an electric circuit with controllable DC voltage generator was designed.Finally, the mechanical resistance, drug release rate, and surface morphology of the designed implants were evaluated. ResultsThe MJF 3D printer, overally, had higher printing precision and repeatability than other printers; however, the implants printed by the FDM 3D printer were more accurate than other techniques (P value < 0.001), similar to the dimensions of the designed file. The mechanical resistance of the implants was also evaluated, and the polylactic acid implants printed by FDM had the highest value of Young's modulus in both the standard samples and the designed implants. During the 3-month drug leakage study, FDM 3D printed implant had a greater ability to store the desired drug load (P value < 0.001), Furthermore, the SEM micrographs revealed that the polylactic acid implants printed by FDM had minimal porosity in their structure and the layers were well adhered together. The gold membrane with a middle diameter of 2 mm required the lowest voltage of 6 V. As a result, the final electrical circuit was designed with smaller dimensions in order to achieve the voltage required to melt the gold membrane. ConclusionDue to the lack of drug leakage and other mechanical studies, the electromechanical implant produced by the FDM 3D printer was chosen as the optimal electromechanical implant in this study. Along with the designed small circuit, this implant can release a drug dosage in the patient's body at the physician's demand.

High sensitivity Fabry–Pérot interferometric magnetic sensor based on Fe3O4-doped PDMS composite thin film

A magnetic field sensor based on Fabry–Pérot interferometer (FPI) with soft gold magnetic composite film (GMCF) is proposed and demonstrated experimentally. GMCF is fabricated by Fe3O4-doped polydimethylsiloxane (PDMS) film and adhered thin gold membrane via van der Waals force. Applying an external magnetic field, GMCF can vibrate under magnetic forces and cause a change in the cavity length of FPI and hence modulates the interference spectra. Experimental results indicate that the sensor can achieve maximum sensitivity of 390 pm mT−1 under a linear magnetic field intensity ranging from 0 to 65 mT. The proposed sensor could help with magnetic field detection in complex environments.

Switch mode capacitive pressure sensors

Switch mode capacitive pressure sensors are proposed as a new class of microfabricated devices that transform pressure into a mechanically switching capacitance to form an analog-to-digital signal with zero power, high sensitivity, and a high signal-to-noise ratio. A pressure-sensitive gold membrane suspended over a capacitive cavity makes ohmic contact with patterned gold leads on the substrate, closing circuits to fixed on-chip capacitors outside the cavity and leading to significant step responses. This function is achieved by allocating the switch leads on the part of the counter electrode area, while the remaining area is used for touch mode analog capacitive sensing. The sensor microchip is prototyped through a novel design approach to surface micromachining that integrates micro-Tesla valves for vacuum sealing the sensor cavity, showing an unprecedented response to applied pressure. For a gauge pressure range of 0–120 mmHg, the sensor exhibits an increase of 13.21 pF with resultant switch events, each of which ranges from 2.53–3.96 pF every 12–38 mmHg, in addition to the touch mode linear capacitive increase between switches. The equivalent sensitivity is 80–240 fF/mmHg, which is 11–600× more than commercial and reported touch mode sensors operating in similar pressure ranges. The sensor is further demonstrated for wireless pressure tracking by creating a resonant tank with the sensor, showing a 32.5–101.6 kHz/mmHg sensitivity with frequency jumps led by the switch events. The developed sensor, with its promising performance, offers new application opportunities in a variety of device areas, including health care, robotics, industrial control, and environmental monitoring.

Freestanding high-aspect-ratio gold masks for low-energy, phase-based x-ray microscopy

High-resolution, x-ray phase contrast microscopy, a key technique with promising potential in biomedical imaging and diagnostics, is based on narrow-slit high-aspect-ratio gold gratings. We present the development, fabrication details, and experimental testing of the freestanding 10 μm thick gold membrane masks with an array of 0.9–1.5 μm void slit apertures for a novel low-energy x-ray microscope. The overall mask size is 4 mm × 4 mm, with a grating pitch of 7.5 μm, 6.0–6.6 μm wide gold bars are supported by 3 μm wide crosslinks at 400 μm intervals. The fabrication process is based on gold electroplating into a silicon mold coated with various thin films to form a voltage barrier, plating base, and sacrificial layer, followed by the mold removal to obtain the freestanding gold membrane with void slit apertures. We discuss key aspects for the materials and processes, including gold structures homogeneity, residual stresses, and prevention of collapsing of the grid elements. We further demonstrate the possibility to obtain high-resolution, high contrast 2D images of biological samples using an incoherent, rotating anode x-ray tube.

Direct Atomic Observation of Reversible Orientation Switch in Monoatomic-Layered Gold Membrane Conducted by Dynamic Vortex.

Controlling the material structure at an atomic scale to tune their physicochemical and nanoengineering properties is a major driving force of nanotechnology. However, manipulating the structural variation in monoatomic-layered metals remains a challenge, hindering the full application of their novel properties. Here, we show by experiments and simulations that a reversible orientation rotation of monoatomic-layered gold membrane embedded in the gold crystal is performed through dynamic vortexing that is comprised of the circular motion of atoms. A pair of dynamic vortices are successively generated and together span the entire gold membrane to accomplish the orientation switch. Density functional theory calculations demonstrate that the gold membrane exhibits a Rashba-type spin splitting, while the spin direction reversibly flips with the switching orientation of the gold membrane. The results provide a conceptual approach for constructing a novel electronic system with monoatomic-layered metals and the reversible spin-flip has inspiring applications for future spintronics.

Freestanding and Permeable Nanoporous Gold Membranes for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman spectroscopy (SERS) demands reliable, high-enhancement substrates in order to be used in different fields of application. Here we introduce freestanding porous gold membranes (PAuM) as easy-to-produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 nm thick PAuM that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to more than 3 bar and exhibit surface-enhanced Raman scattering with local enhancement factors from 104 to 105, which we demonstrate by wavelength-dependent and spatially resolved Raman measurements using graphene as a local Raman probe. Numerical simulations reveal that the enhancement arises from individual, nanoscale pores in the membrane acting as optical slot antennas. Our PAuM are mechanically stable, provide robust SERS enhancement for excitation power densities up to 106 W cm-2, and may find use as a building block in SERS-based sensing applications.

Multi-resonant absorptions in asymmetric step-shaped plasmonic metamaterials for versatile sensing application scenarios.

Plasmonic nanostructures have attracted remarkable attention in label-free biosensing detection due to their unprecedented potential of high-sensitivity, miniaturization, multi-parameter, and high throughput screening. In this paper, we propose a plasmonic metamaterial absorber consisting of an asymmetrical step-shaped slit-groove array layer and an opaque gold film, separated by a silica dielectric layer, which demonstrates three-resonant perfect absorption peaks at near-infrared frequencies in an air environment.This is equivalent to three reflection dips due to the opaque gold membrane underneath the structure. Originating from the coupling and hybridization of different plasmonic modes, these three absorption peaks show different linewidths and distinctive excellent sensing performance. The surface lattice resonance (SLR) at the short wavelength range enables an ultra-narrow absorption peak of merely 2 nm and a high bulk refractive index sensitivity of 1605 nm/RIU, but occurring with comparatively low surface sensitivity. Compared to the above-mentioned narrowband SLR mode, the other two absorption peaks, respectively stemming from the coupling between slit-cavity mode and the plasmon resonance of different orders, possess relatively broad linewidths and low bulk refractive index sensitivities, yet outstanding surface sensitivities. The complementary sensing performance among these absorption peaks presents opportunities for using the designed plasmonic metamaterial absorber for multi-parameter detection and various complex application scenarios.

A Gold Coating Nanoporous AAO Membrane as the Substrate for Rapid SERS Detection of Conjugated Cyanide in Fingertip Blood

A Gold Coating Nanoporous AAO Membrane as the Substrate for Rapid SERS Detection of Conjugated Cyanide in Fingertip Blood

Quantitative nanoscale imaging using transmission He ion channelling contrast: Proof-of-concept and application to study isolated crystalline defects

A newly developed microscope prototype, namely npSCOPE, consisting of a Gas Field Ion Source (GFIS) column and a position sensitive Delay-line Detector (DLD) was used to perform Scanning Transmission Ion Microscopy (STIM) using keV He+ ions. One experiment used 25 keV ions and a second experiment used 30 keV ions. STIM imaging of a 50 nm thick free-standing gold membrane exhibited excellent contrast due to ion channelling and revealed rich microstructural features including isolated nanoscale twin bands which matched well with the contrast in the conventional ion-induced Secondary Electron (SE) imaging mode. Transmission Kikuchi Diffraction (TKD) and Backscattered Electron (BSE) imaging were performed on the same areas to correlate and confirm the microstructural features observed in STIM. Monte Carlo simulations of the ion and electron trajectories were performed with parameters similar to the experimental conditions to derive insights related to beam broadening and its effect in the degradation of transmission image resolution. For the experimental conditions used, STIM imaging showed a lateral resolution close to30 nm. Dark twin bands in bright grains as well as bright twin bands in dark grains were observed in STIM. Some of the twin bands were invisible in STIM. For the specific experimental conditions used, the ion transmission efficiency across a particular twin band was found to decrease by a factor of 2.8. Surprisingly, some grains showed contrast reversal when the Field of View (FOV) was changed indicating the sensitivity of the channelling contrast to even small changes in illumination conditions. These observations are discussed using ion channelling conditions and crystallographic orientations of the grains and twin bands. This study demonstrates for the first time the potential of STIM imaging using keV He+ ions to quantitatively investigate channelling in nanoscale structures including isolated crystalline defects.

Upconversion nanoparticles coated organic photovoltaics for near infrared light controlled drug delivery systems

Abstract On-demand drug delivery systems (DDSs) have been widely investigated for spatiotemporally controlled therapy with greatly improved patient compliance. However, power systems to operate the DDSs are one of the serious unmet needs constraining their further applications. Here, we report implantable organic photovoltaic cells using upconversion nanoparticles (UCNPs) for on-demand controlled drug delivery. Although skin-penetrating near infrared (NIR) light cannot be used for flexible organic photovoltaic cells, UCNPs can convert NIR light to visible light for their operation after implantation to the body. The core-shell structured UCNPs coated on flexible organic photovoltaic cells generate current flow upon NIR irradiation for triggering on-demand drug delivery from microelectromechanical system (MEMS) drug reservoirs. Gold (Au) membrane sealing the reservoirs is dissolved to AuCl4− by the applied electrical current triggering the pulsatile drug release. The successful fabrication of NIR light triggered DDS by UCNPs coated organic photovoltaic cells is confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–vis spectroscopy, photoluminescence, current density–voltage characterization, and gold thin film dissolution tests. Furthermore, on-demand model drug release tests confirm the feasibility of the new paradigm light-triggered DDS and the relevant phototherapy.

Free-Standing Two-Dimensional Gold Membranes Produced by Extreme Mechanical Thinning.

Two-dimensional (2D) materials exhibit exceptional physical and chemical properties owing to their atomically thin structures. However, it remains challenging to produce 2D materials consisting of pure monoelemental metallic atoms. Here free-standing 2D gold (Au) membranes were prepared via in situ transmission electron microscopy straining of Au films. The applied in-plane tensile strain induces an extensive amount of out-of-plane thinning deformation in a local region of an Au thin film, resulting in the nucleation and growth of a free-standing 2D Au membrane surrounded by its film matrix. This 2D membrane is shown to be one atom thick with a simple-hexagonal lattice, which forms an atomically sharp interface with the face-centered cubic lattice of the film matrix. Diffusive transport of surface atoms, in conjunction with the dynamic evolution of interface dislocations, plays important roles in the formation of 2D Au membranes during the mechanical thinning process. These results demonstrate a top-down approach to produce free-standing 2D membranes and provide a general understanding on extreme mechanical thinning of metallic films down to the single-atom-thick limit.

Design and analysis of enhanced capacitive radio frequency MEMS switch based on Nb2O5 and HfO2 dielectric for satellite payload applications

AbstractAn innovative capacitive radio frequency MEMS shunt switch with a unique shaped spring is designed and analyzed using COMSOL Multiphysics 5.4. The proposed switch using Hafnium oxide (HfO2) and Niobium pentoxide (Nb2O5) as the dielectric material between the transmission line and the deflecting gold membrane provides certain advantageous benefits with respect to performance parameters such as low actuation voltage, less spring constant, good isolation, low insertion loss, small size, and high capacitance ratio compared to other designs. A combination of three‐turn meander and C‐ shaped spring having a spring constant of 0.186 N/m helps in achieving convenient actuation voltage. For 1, 1.5, and 2 μm air gaps, the actuation voltages required to bring the switch to ON mode are 1.77, 3.24, and 4.96 V respectively with Nb2O5 as the dielectric layer and 1.8, 3.28, and 5.01 V respectively with HfO2 as the dielectric layer respectively. At 2‐μm air gap, the capacitance ratio is 329 for Nb2O5 and 113 for HfO2. RF analysis using ANSYS HFSS software shows the isolation of −19.41 dB at 11 GHz and insertion loss as low as −0.27 dB at 15 GHz. The proposed switch operating within the range of 1 to 30 GHz gives optimum results compared to other devices and is suitable for wireless communication and satellite payload applications.

Imprint and transfer fabrication of freestanding plasmonic membranes

This paper reports an imprint and transfer approach for the rapid and inexpensive fabrication of the ultra-thin freestanding plasmonic membrane (FPM) that supports surface plasmon resonances. The imprint and transfer fabrication method involves the soft imprint lithography on an ultrathin polymer film, transfer of the perforated polymer film to a supporting frame, subsequent deposition of gold, and final removal of the polymer film. Without using any sophisticated lithography and etching processes, the imprint and transfer method can produce freestanding gold membranes with 2D arrays of submicrometer-sized holes that support plasmonic modes in the mid-wavelength infrared (mid-IR) range. Two FPM devices with an array constant of 4.0 and 2.5 μm have been simulated, fabricated, and measured for their transmittance characteristics. The fabricated FPMs exhibit surface plasmon polariton Bloch mode and extraordinary optical transmission (EOT) with the enhanced local field around the membrane. The effects of membrane thickness and angle dispersion on the FPM were investigated to show the tuning of EOT modes in IR. Furthermore, we demonstrated the refractometric sensing and enhanced IR absorption of the FPM device for its potential in chemical and biomolecule sensing applications.

Hybrid target design for imprint mitigation in direct-drive inertial confinement fusion.

A target design for mitigating the Rayleigh-Taylor instability is proposed for use in high energy density and direct-drive inertial confinement fusion experiments. In this scheme, a thin gold membrane is offset from the main target by several-hundred microns. A strong picket on the drive beams is incident upon this membrane to produce x rays which generate the initial shock through the target. The main drive follows shortly thereafter, passing through the ablated shell and directly driving the main target. The efficacy of this scheme is demonstrated through experiments performed at the OMEGA EP facility, showing a reduction of the Rayleigh-Taylor instability growth which scales exponentially with frequency, suppressing development by at least a factor of 5 for all wavelengths below 100 μm. This results in a delay in the time of target perforation by ∼40%.

In Situ Observations of Freestanding Single‐Atom‐Thick Gold Nanoribbons Suspended in Graphene

AbstractBulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period ≈40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single‐atom‐thick two‐dimensional (2D) metals exist. This work shows single‐atom‐thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single‐atom‐thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly.

Molecular Dynamics Simulations of Deformation Mechanisms in the Mechanical Response of Nanoporous Gold.

The mechanical behaviour of nanoporous gold has so far been the subject of studies for bicontinuous morphologies, while the load transfer between ligaments is the primary challenge for using nanoporous structures—especially membranes with nanopores—in single-molecule sensors. This work studies the pore shape effect on deformation mechanisms of nanoporous gold membranes through molecular dynamics simulations. Tension and compression tests are carried out for nanoporous gold with circular, elliptical, square and hexagonal pore shapes. A significant pore shape effect on the mechanical properties is observed with distinct load transfer capabilities. A uniform stress transfer between ligaments constitutes a distinguished set of mechanical responses for structures with the hexagonal pore shape under tension, while a unique stress distribution in nanoporous with the circular pore shape introduces a high strength and ductile structure under compression. Further to shed light on the existing experimental observations, this work provides a comprehensive study on load transfer capabilities in the mechanical behaviour of nanoporous gold for sensing applications.

Design and simulation of MEMS based capacitive pressure sensor for harsh environment

In this paper, we have designed and simulated a capacitive pressure sensor for harsh environment. The sensor is metal–insulator-metal type sensor in which the structure is designed using gold and the dielectric using silicon nitrate with thickness of 0.5 μm. The device achieves a linear characteristic response and high sensitivity. MIM consists of a circular clamped-edges gold membrane suspended over sealed cavity on the upper metal surface which is placed on the silicon substrate. The proposed MEMS capacitive pressure sensor is optimised and designed in COMSOL Multiphysics. The sensor illustrated with a proof mass 140 μm diameter, with air gap from 0.15 to 2 μm and pressure ranging from 200 to 1500Mpa.

Free-Standing Large-Area Nanoperforated Gold Membranes Fabricated by Hopping Electrodeposition

A room-temperature two-step cost-effective electrochemical technology is proposed for the preparation of free-standing Au nanomembranes. A thin Au film with the thickness less than 100 nm was deposited by pulsed electroplating on a GaAs substrate in the first step, while electrochemical etching was applied in the second technological step to introduce porosity into the GaAs substrate underneath the Au film. It has been shown that detachment of the film from the substrate occurs at optimized parameters of anodic etching. Scanning electron microscopy imaging of the deposited Au film revealed its nanoparticulate structure generated via the mechanism of hopping electrodeposition, i.e. the film proved to consist of a monolayer of Au nanoparticles with the mean diameter around 20–30 nm. It was found that nanoholes with the diameter controlled by the duration of negative voltage pulses can be introduced into the Au film during electroplating. The purity of the detached Au nanomembranes was demonstrated by the energy dispersive X-ray analysis. The flexibility, nanoparticulate structure along with possibilities to transfer the prepared nanomembranes to various substrates make them promising for new optical, plasmonic and electronic applications.