Metallic Nanopore Research Articles

Electrical Resistivity Modification of Electrodeposited Mo and Mo–Co Nanowires for Interconnect Applications

Achieving historically anticipated improvement in the performance of integrated circuits is challenging, due to the increasing cost and complexity of the required technologies with each new generation. To overcome this limitation, the exploration and development of novel interconnect materials and processes are highly desirable in the microelectronics field. Molybdenum (Mo) is attracting attention as an advanced interconnect material due to its small resistivity size effect and high cohesive energy; however, effective processing methods for such materials have not been widely investigated. Here, we investigate the electrochemical behavior of ions in the confined nanopores that affect the electrical properties and microstructures of nanoscale Mo and Mo–Co alloys prepared via template-assisted electrodeposition. Additives in an electrolyte allow the deposition of extremely pure metal materials, due to their interaction with metal ions and nanopores. In this study, boric acid and tetrabutylammonium bisulfate (TBA) were added to an acetate bath to inhibit the hydrogen evolution reaction. TBA accelerated the reduction of Mo at the surface by inducing surface conduction on the nanopores. Metallic Mo nanowires with a 130 nm diameter synthesized through high-aspect-ratio nanopore engineering exhibited a resistivity of (63.0 ± 17.9) μΩ·cm. We also evaluated the resistivities of Mo–Co alloy nanowires at various compositions toward replacing irreducible conventional barrier/liner layers. An intermetallic compound formed at a Mo composition of 28.6 at%, the resistivity of the Mo–Co nanowire was (58.0 ± 10.6) μΩ·cm, indicating its superior electrical and adhesive properties in comparison with those of conventional barriers such as TaN and TiN. Furthermore, density functional theory and non-equilibrium Green’s function calculations confirmed that the vertical resistance of the via structure constructed from Mo-based materials was 21% lower than that of a conventional Cu/Ta/TaN structure.

Imbibition and rheology of polymer-matrix nanoporous metal composites: Towards extrusion-based 3D printing

When combined with additive manufacturing, nanoporous metals can be shaped into multifunctional and interdigitated 3D circuits with hierarchical diffusional pathways, critical for optimizing electrochemical storage devices. In an attempt to develop a method for extrusion-based additive manufacturing of nanoporous metals and their composites, this paper examines a new polymer matrix composite reinforced with spherical nanoporous copper powders (PMC-NP-Cu) synthesized by dealloying at high fill fractions (>45 vol%), that can be integrated with fused filament fabrication (FFF). The role of capillary imbibition of the polymer into the metal's nanopores was investigated by examining their wettability, rheology, and density as a function of polymer's molecular weight (MW) particularly for a range of radius of gyration (Rg) between 2 and 20 nm comparable to its average pore size (22 nm). It was found that the melt viscosity of PMC-NP-Cu with the shortest Mw departed from classical viscosity scaling (i.e., η ∞ MW1) which is attributed to the polymer imbibition into nanopores and composite densification. For molecular weights equal to 5 and 200 kg/mol, it was found that the volume fraction of the reinforcing phase was 16% and 8% higher respectively when imbibition was accounted for, resulting in an increase of two orders of magnitude in its zero-shear viscosity. These results correlated to the extrudability tests of PMC-NP-Cu filaments at higher packing factors (i.e., 47 vol%) for FFF. The insight of this study might be beneficial to integrate nanoporous metals into binder-based 3D printing technology to fabricate interdigitated battery electrodes and multifunctional 3D printed electronics.

Plasmonic Photochemistry as a Tool to Prepare Metallic Nanopores with Controlled Diameter for Optimized Detection of Single Entities

AbstractPlasmonic solid‐state nanopores with tunable hole diameters can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic (EM) field inside a metallic ring on top of a dielectric nanotube. Under white light illumination, the plasmon‐enhanced EM‐field induces a site‐selective metal nucleation and growth within the ring. This approach is used to prepare Au and bimetallic Au–Ag nano‐rings and demonstrate the reduction of the initial inner diameter of the nanopore down to 4 nm. The tunability of the nanopore diameter can be used to enable optimized detection of single entities with different sizes. As a proof‐of‐concept, single object detection of double stranded DNA (dsDNA) and Au nanoparticles (AuNPs) with a diameter down to 15 nm is performed. Numerical simulations provide insights into the EM‐field distribution and confinement, showing that a field intensity enhancement of up to 104 can be achieved inside the nanopores. This localized EM‐field can be used to perform enhanced optical measurements and generate local heating, thereby modifying the properties of the nanopore. Such a flexible approach also represents a valuable tool to investigate plasmon‐driven photochemical reactions, and it can represent an important step toward the realization of new plasmonic devices.

Flexible Nanoarchitectonics for Biosensing and Physiological Monitoring Applications (Small 9/2023)

Flexible Mesoporous Electronics In article number 2204946, Hoang-Phuong Phan, Yusuke Yamauchi, Tuan-Khoa Nguyen, Mostafa Kamal Masud, and co-workers develop flexible mesoporous architectures using selective electrochemical deposition. Soft metallic nanopores formed on thin polyimide films offer excellent mechanical bendability, high sensitivity for glucose sensing, and low impedance that facilitates detection of neural activities. These features suggest the promise of soft mesoporous material systems for biomedical applications.

Electroreduction of Carbon Dioxide in Metallic Nanopores through a Pincer Mechanism.

Metallic catalysts with nanopores are advantageous on improving both activity and selectivity, while the reason behind that remains unclear all along. In this work, porous Zn nanoparticles (P-Zn) were adopted as a model catalyst to investigate the catalytic behavior of metallic nanopores. In situ X-ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and density functional theory (DFT) analyses reveal that the concave surface of nanopores works like a pincer to capture and clamp CO2 and H2 O precursors simultaneously, thus lowering the energy barriers of CO2 electroreduction. Resultantly, the pincer mechanism endows P-Zn with a high Faradic efficiency (98.1 %) towards CO production at the potential of -0.95 V vs. RHE. Moreover, DFT calculation demonstrates that Co and Cu nanopores exhibit the pincer behavior as well, suggesting that this mechanism is universal for metallic nanopores.

Electroreduction of Carbon Dioxide in Metallic Nanopores through a Pincer Mechanism

AbstractMetallic catalysts with nanopores are advantageous on improving both activity and selectivity, while the reason behind that remains unclear all along. In this work, porous Zn nanoparticles (P‐Zn) were adopted as a model catalyst to investigate the catalytic behavior of metallic nanopores. In situ X‐ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and density functional theory (DFT) analyses reveal that the concave surface of nanopores works like a pincer to capture and clamp CO2 and H2O precursors simultaneously, thus lowering the energy barriers of CO2 electroreduction. Resultantly, the pincer mechanism endows P‐Zn with a high Faradic efficiency (98.1 %) towards CO production at the potential of −0.95 V vs. RHE. Moreover, DFT calculation demonstrates that Co and Cu nanopores exhibit the pincer behavior as well, suggesting that this mechanism is universal for metallic nanopores.

Ising models of charge storage in multifile metallic nanopores

Ising type models of charging of conductive nanopores with ions have already been proposed and investigated for single file cylindrical or single layer slit nanopores. In such pores, the state of ions, the coulombic interactions of which are exponentially screened by their images in pore walls, was named superionic. In the present work we extend the analysis of the superionic state to nanopores that can accommodate multiple rows of ions. By grouping multiple charges in the same row into ‘supercharges’, we map the arrangement of ions in polarised electrodes on a multi-row Ising model in an external field. We investigate one-, two- and three-row cases, which we solve exactly, using a purpose-built semi-numerical transfer matrix method. For pores of different radii, which can accommodate the corresponding number of ion rows, we calculate the dependence of the electrical capacitance and stored energy density on electrode potential. As in charging the single file pores, we find that in narrower pores higher energy densities can be achieved at low applied potentials, while wider pores perform better as the voltage is increased.

Probing Local Potentials inside Metallic Nanopores with SERS and Bipolar Electrochemistry

It is essential to understand the local potential distribution of solid‐state nanopores in nanofluidic systems. However, applying gate voltage or adding external electrical probes tends to disturb the electric field and/or flow patterns. To solve this problem, an approach is described to monitor the local potential using electrochemical surface enhanced Raman spectroscopy (EC‐SERS) in two types of nanocavity pores: doubled‐sided gold nanopores (MM nanopores) and single‐sided gold nanopores with a dielectric passivation layer on the backside (MD nanopores). Numerical simulations predict an electrical polarization reversal in the two nanopore geometries. Consequently, the redox SERS changes of Nile Blue A on the two gold nanopores are found to be reversed, which is consistent with the variation of polarizations. The driving voltage of metallic nanopore devices is about an order of magnitude lower than that of microfluidic bipolar devices. Our method will not only prove valuable for the design of metallic nanopores, but also will find applications in the measurement of contactless metallized nanofluidic devices.

Nanopore sensing at ultra-low concentrations using single-molecule dielectrophoretic trapping.

Single-molecule techniques are being developed with the exciting prospect of revolutionizing the healthcare industry by generating vast amounts of genetic and proteomic data. One exceptionally promising route is in the use of nanopore sensors. However, a well-known complexity is that detection and capture is predominantly diffusion limited. This problem is compounded when taking into account the capture volume of a nanopore, typically 108–1010 times smaller than the sample volume. To rectify this disproportionate ratio, we demonstrate a simple, yet powerful, method based on coupling single-molecule dielectrophoretic trapping to nanopore sensing. We show that DNA can be captured from a controllable, but typically much larger, volume and concentrated at the tip of a metallic nanopore. This enables the detection of single molecules at concentrations as low as 5 fM, which is approximately a 103 reduction in the limit of detection compared with existing methods, while still maintaining efficient throughput.

Asymmetric plasmonic induced ionic noise in metallic nanopores.

We present distinct asymmetric plasmon-induced noise properties of ionic transport observed through gold coated nanopores. We thoroughly investigated the effects of bias voltage and laser illumination. We show that the potential drop across top-coated silicon nanocavity pores can give rise to a large noise asymmetry (∼2-3 orders of magnitude). Varying the bias voltage has an appreciable effect on the noise density spectra, typically in the Lorentzian components. The laser power is found to strongly affect the ionic noise level as well as the voltage threshold for light-induced noise generation. The asymmetric noise phenomenon is attributed to plasmon-induced interfacial reactions which promote light-induced charge fluctuation in the ion flow and allow voltage modulation of photo-induced carriers surmounting over such Schottky junctions. We further compare the ionic noise performances of gold nanocavities containing different material stacks, among which thermal oxide passivation of the silicon successfully mitigates the light-induced noise and is also fully CMOS-compatible. The understanding of the described noise characteristics will help to foster multiple applications using related structures including plasmonic-based sensing or plasmon-induced catalysis such as water splitting or solar energy conversion devices.

ChemInform Abstract: Applications of Metal Nanopore Catalysts in Organic Synthesis

AbstractReview: [129 refs.

Applications of Metal Nanopore Catalysts in Organic Synthesis

Reducing the size of bulk metals to nanometer scale can result in the display of extraordinary physical and chemical properties. Typically, metal nanoparticles (MNPs) are prepared from metal atoms or metal salts and show remarkable catalytic properties. Metal nanopores (MNPores) are prepared through a totally reverse approach (from bulk metal to nanosized metal): alloy M¹M² is fabricated from metal M¹ and metal M², and then dealloying of M² results in a nanoporous framework of metal M¹. This account summarizes MNPore-catalyzed reactions developed in our group, and their comparison with other representative catalytic reactions. 1 Introduction 1.1 Fabrication and Structural Characteristics of Nanoporous Gold 2 Oxidation Reactions 2.1 Oxidation of Alcohols 2.2 Synthesis of Formamides Through Oxidative Coupling of Methanol with Amines 2.3 Oxidation of Silanes 3 Reduction Reactions 3.1 Semihydrogenation of Alkynes 3.2 Reduction of Quinoline 3.3 Reduction of Imines and Reductive Amination of Carbonyls 3.4 Reduction of α,β-Unsaturated Aldehydes 3.5 1,4-Hydrosilylation of Cyclic Enones 4 Formation of C–Si, C–B, and C–C Bonds Using Alkynes 4.1 Hydrosilylation of Alkynes 4.2 Diboration of Alkynes 4.3 Benzannulation Reaction 5 CuNPore-Catalyzed Click Reaction 6 Suzuki, Negishi and Heck Coupling Reactions 7 Concluding Remarks

Self-supported metallic nanopore arrays with highly oriented nanoporous structures as ideally nanostructured electrodes for supercapacitor applications.

Self-supported metallic nanopore arrays with highly oriented nanoporous structures are fabricated and applied as ideally nanostructured electrodes for supercapacitor applications. Their large specific surface area can ensure a high capacitance, and their highly oriented and stable nanoporous structure can facilitate ion transport.

Switchable imbibition in nanoporous gold.

Spontaneous imbibition enables the elegant propelling of nano-flows because of the dominance of capillarity at small length scales. The imbibition kinetics are, however, solely determined by the static host geometry, the capillarity, and the fluidity of the imbibed liquid. This makes active control particularly challenging. Here we show for aqueous electrolyte imbibition in nanoporous gold that the fluid flow can be reversibly switched on and off through electric potential control of the solid–liquid interfacial tension, that is, we can accelerate the imbibition front, stop it, and have it proceed at will. Simultaneous measurements of the mass flux and the electrical current allow us to document simple scaling laws for the imbibition kinetics, and to explore the charge transport in the metallic nanopores. Our findings demonstrate that the high electric conductivity along with the pathways for fluid/ionic transport render nanoporous gold a versatile, accurately controllable electrocapillary pump and flow sensor for minute amounts of liquids with exceptionally low operating voltages.

Fabrication of nanopore on pyramid

There have been tremendous interests about the fabrication of metallic nanopore due to the ultrafast genome sequencing biosensor capability. In this report, the fabrication of the nanopore on the Au coated SiO2 pyramid has been examined using various high energy electron beam irradiation and focused ion beam (FIB) milling techniques. The microfabricated Au nano-apertures on pyramid were irradiated with various high energy electron beam and FIB techniques. The formation of the nanopore dependent on the probe current was also examined using electron probe micro-analysis (EPMA). The nanopore on the Au coated SiO2 pyramid is found to be an AuSi mixture. The Au nanopore on the crater type hole was also fabricated using FIB Ga ion beam scanning. The shrinking rate was found to be the fastest compared with those fabricated with the other electron beam techniques.

Interionic Interactions in Conducting Nanoconfinement

Interionic interactions in conducting nanopores determine how counterions may be packed in the pores subject to the applied voltage. In ideal metals, interactions are exponentially screened by metallic electrons. However, modern nanoporous electrodes are predominantly made of carbon materials. To what extent is this screening affected by a different mode of dielectric response in such materials? To answer this question we study Coulomb interaction of charges in cylindrical and slit pores that allow finite electric field penetration into the pore walls, as well as the Coulomb interaction in a nanogap between two thin walls of graphene modeled by a non-local dielectric function. In all cases studied the screening was found to be subtly different than in metallic nanopores, but still strong enough to support realization of the so called superionic state in such pores.

Rapid Ultrasensitive Single Particle Surface-Enhanced Raman Spectroscopy Using Metallic Nanopores

Nanopore sensors embedded within thin dielectric membranes have been gaining significant interest due to their single molecule sensitivity and compatibility of detecting a large range of analytes, from DNA and proteins, to small molecules and particles. Building on this concept we utilize a metallic Au solid-state membrane to translocate and rapidly detect single Au nanoparticles (NPs) functionalized with 589 dye molecules using surface-enhanced resonance Raman spectroscopy (SERRS). We show that, due to the plasmonic coupling between the Au metallic nanopore surface and the NP, signal intensities are enhanced when probing analyte molecules bound to the NP surface. Although not single molecule, this nanopore sensing scheme benefits from the ability of SERRS to provide rich vibrational information on the analyte, improving on current nanopore-based electrical and optical detection techniques. We show that the full vibrational spectrum of the analyte can be detected with ultrahigh spectral sensitivity and a rapid temporal resolution of 880 μs.

Active control of surface forces via nanopore structures

Understanding the effects of electrical potential on nanoscale contacts is critically needed for design and development of nanodevices. In the present letter, we characterize the metallic nanopore structure of nickel using an atomic force microscope. The morphology, phase distribution, and tribological behavior were studied under an applied electrical potential. It was found that the increase in electrical potential resulted in reduction of friction and pull-off force (adhesion), which is attributed to the real contact area change. Results indicated that the nanoporous structured Ni enables the control of friction and adhesion, which is beneficial for the design of nanoelectromechanical systems.

Characterization of Electronic States inside Metallic Nanopores

Previous work has shown that unusual chemistry can be induced inside metallic slit nanopores. This phenomenon has been attributed to the presence of an enhanced electronic density within the pore. Here we use ab initio density functional theory and post-Hartree–Fock correlated methods to characterize the electronic density in the gap defined by two parallel metallic surfaces. In the first part of this work, the electronic density of states of several transition metal nanopores is calculated for different pore sizes (i.e., surface–surface separations). Results show the existence of a critical surface–surface separation below which electronic states corresponding to the gap between surfaces become populated at energies below the Fermi level of the metal, leading to the presence of electrons in the pore. Further reduction in the nanopore size increases the number of states corresponding to the gap, which agrees with the increasingly higher electronic densities found in the gap for smaller surface–surface sep...

Harnessing Plasmon-Induced Ionic Noise in Metallic Nanopores

The ionic properties of a metal-coated silicon nanopore were examined in a nanofluidic system. We observed a strong increase of the ionic noise upon laser light illumination. The effect appeared to be strongly mediated by the resonant excitation of surface plasmons in the nanopore as was demonstrated by means of ionic mapping of the plasmonic electromagnetic field. Evidence from both simulations and experiments ruled out plasmonic heating as the main source of the noise, and point toward photoinduced electrochemical catalysis at the semiconductor-electrolyte interface. This ionic mapping technique described is opening up new opportunities on noninvasive applications ranging from biosensing to energy conversion.