Fabrication Of Metallic Electrodes Research Articles

Nondestructive Evaluation of Detuned Wavelength for As-Grown VCSEL Epi-Wafer

We propose a nondestructive method to estimate the peak wavelength of the active quantum well (QW) region of an as-grown vertical-cavity surface-emitting laser (VCSEL) epi-wafer based on room temperature electroluminescence (EL) measurements. Contacts for the electrical excitation are established using flexible conductive materials on the epilayers without the fabrication of metal electrodes. The angle dependence of the EL properties is investigated to analyze the detuned wavelength of the active QW region for the VCSEL structure. The wavelength offset caused by detuning obtained from the as-grown epi-wafer correlates with the laser threshold properties of the VCSEL chips fabricated from the epi-wafer. The results show the possibility of a nondestructive evaluation method without metal electrodes for as-grown VCSEL epi-wafers, particularly the active QW region, which has been challenging to optically analyze from completed VCSEL epi-structures.

Fully metallic copper 3D-printed electrodes via sintering for electrocatalytic biosensing

3D printing is a very useful manufacturing method for the fabrication of electrochemical devices. Typically, accessible fused filament fabrication (FFF) is the most used method; but it is limited to the materials of use, mainly to carbon/polylactic acid blend. The use of metal 3D printed devices produced by FFF would offer very useful combination of advantages such as robustness, and electrocatalytic surfaces at a low cost. Here, 3D printed copper electrodes were successfully prepared by FFF followed by a sintering step. The physical and electrochemical properties of FFF 3D printed copper electrodes were characterised using various complementary techniques, while the electrochemical performance was evaluated for the non-enzymatic sensing of glucose as a first demonstration of applicability. Such low-cost 3D-printing method for fabrication of metallic electrodes will be further applicable for a wide variety of devices.

Giant Dielectric Constant and Superior Photovoltaic Property of the Mechanochemically Synthesized Stable CH3NH3PbBr3 in a Hole Transporter-Free Solar Cell

Hybrid organic inorganic perovskites (HOIPs) have emerged as the most promising next-generation photovoltaic (PV) materials. However, syntheses of HOIPs not only require a controlled environment but also their long term stability is a major challenge. Herein, we report mechanochemical synthesis of highly stable CH₃NH₃PbBr₃ (MAPbBr₃) powder under an open atmosphere that undergoes no phase change even after 6 months. The MAPbBr₃ exhibits a large dielectric constant of >10⁴ in the frequency regime of 1 Hz to 10⁶ Hz and in a wide temperature range of 300–475 K because of its inherent charge carrier, which is contended for the low exciton binding energy in HOIPs, leading to superior PV performance as compared to the solution-based synthesized MAPbBr₃. The excitonic activation energy measured from the ac conductivity study in the same temperature range is 5 meV, which suggests facile exciton separation and generation of free charge carrier upon irradiation. The PV performance of the as-synthesized MAPbBr₃ is investigated by fabricating two thin-film based device architectures without the hole-transporter layer, that is, FTO/MAPbBr₃/Ag and FTO/TiO₂/MAPbBr₃/Ag, exhibiting a photo conversion efficiency of 4.2 and 7.31%, respectively. In contrast to the thermally evaporated metal counter electrode (e.g., Au and Ag), the spin-coated Ag film from solution is used as top contact here, thereby improving the cost-effectiveness and metal-electrode fabrication impediments.

Large array fabrication of high performance monolayer MoS2 photodetectors

Large array fabrication of high quality photodetectors derived from synthetically grown monolayer transition metal dichalcogenides is highly desired and important for a wide range of nanophotonic applications. We present here large array fabrication of monolayer MoS2 photodetectors on sapphire substrates through an efficient process, which includes growing large scale monolayer MoS2 via chemical vapor deposition (CVD) and multi-step optical lithography for device patterning and high quality metal electrode fabrication. In every measured device, we observed the following universal features: (i) negligible dark current (Idark≤10 fA), (ii) sharp peaks in photocurrent at ∼1.9 eV and ∼2.1 eV attributable to the optical transitions due to band edge excitons, and (iii) a rapid onset of photocurrent above ∼2.5 eV peaked at ∼2.9 eV due to an excitonic absorption originating from the van Hove singularity of MoS2. We observe a low (≤300%) device-to-device variation of photoresponsivity. Furthermore, we observe a very fast DC time response of ∼0.5 ms, which is two orders of magnitude faster than other reported CVD grown 1L-MoS2 based photodetectors. The combination of large-array device fabrication, high sensitivity, and high speed offers great potential for applications in photonics.

Coating and functionalization of high density ion track structures by atomic layer deposition

In this study flexible TiO2 coated porous Kapton membranes are presented having electron multiplication properties. 800nm crossing pores were fabricated into 50 μm thick Kapton membranes using ion track technology and chemical etching. Consecutively, 50nm TiO2 films were deposited into the pores of the Kapton membranes by atomic layer deposition using Ti(iOPr)4 and water as precursors at 250°C. The TiO2 films and coated membranes were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray reflectometry (XRR). Au metal electrode fabrication onto both sides of the coated foils was achieved by electron beam evaporation. The electron multipliers were obtained by joining two coated membranes separated by a conductive spacer. The results show that electron multiplication can be achieved using ALD-coated flexible ion track polymer foils.

Contactless analysis of electric dipoles at high-k/SiO2 interfaces by surface-charge-switched electron spectroscopy

The continuous development of silicon devices has been supported by fundamental understanding of the two interfaces that predict the device properties: high-dielectric oxide (high-k)/SiO2 and SiO2/Si. In the absence of metal electrode fabrication, it is challenging to use spectroscopic approaches to deduce the electric dipoles in these interfaces for the prediction of electrical characteristics such as the leakage current and threshold voltage. Here, we propose a method to analyze the permanent dipole at the high-k/SiO2 interface by surface-charge-switched electron spectroscopy (SuCSES). An electron flood gun was used to switch the electrical polarity at the insulating surface to extract the interface-dipole contribution from the macroscopic dielectric polarization in the high-k/SiO2/Si stack structure. TaO3− nanosheet (TaNS) crystallites, which are a family of high-k tantalate materials deposited on the SiO2/Si substrates, were annealed to prepare a nanoscale model interface. The properties of this interface were examined as a function of annealing temperature across the crystalline-to-amorphous transition. Macroscopic dielectric polarization of the TaNS/SiO2/Si gate stack was found to exhibit a gradual decay that depended upon the quantum tunneling processes of induced carriers at the SiO2/Si interface. Additionally, the dipole at the high-k/thin-SiO2 interface abruptly changed by ∼0.4 eV before and after annealing at 400 °C, which may be the result of a decrease in conduction-band offsets at the high-k/Si interface. Thus, SuCSES can aid in determining the inherent valence-band offsets in dielectric interfaces by using X-ray photoelectron spectroscopy with high accuracy and precision. Furthermore, SuCSES can determine whether dielectric polarization, including the interfacial dipole, affects the experimental value of the band offsets.

Facile 3D Metal Electrode Fabrication for Energy Applications via Inkjet Printing and Shape Memory Polymer

This paper reports on a simple 3D metal electrode fabrication technique via inkjet printing onto a thermally contracting shape memory polymer (SMP) substrate. Inkjet printing allows for the direct patterning of structures from metal nanoparticle bearing liquid inks. After deposition, these inks require thermal curing steps to render a stable conductive film. By printing onto a SMP substrate, the metal nanoparticle ink can be cured and substrate shrunk simultaneously to create 3D metal microstructures, forming a large surface area topology well suited for energy applications. Polystyrene SMP shrinkage was characterized in a laboratory oven from 150-240°C, resulting in a size reduction of 1.97-2.58. Silver nanoparticle ink was patterned into electrodes, shrunk, and the topology characterized using scanning electron microscopy. Zinc-Silver Oxide microbatteries were fabricated to demonstrate the 3D electrodes compared to planar references. Characterization was performed using 10M potassium hydroxide electrolyte solution doped with zinc oxide (57g/L). After a 300s oxidation at 3Vdc, the 3D electrode battery demonstrated a 125% increased capacity over the reference cell. Reference cells degraded with longer oxidations, but the 3D electrodes were fully oxidized for 4 hours, and exhibited a capacity of 5.5mA-hr/cm2 with stable metal performance.

Fabrication of metal electrodes on flexible substrates by controlled deposition of conductive nano-ink

In this study, a novel process was developed for the fabrication of ultrafine electrodes on flexible substrates. Conductive fine electrodes using silver nano-ink on polyimide (PI) film were obtained by means of plasma-enhanced superhydrophobic technology. The plasma etching conditions were optimized for the formation of a superhydrophobic layer on the surface of the PI film. A micro-trench on the hydrophobic PI film was then formed by mechanical scratching, thus imparting hydrophilic properties only to the trench area. Finally, the fine electrode was realized by the selective deposition of aqueous silver nano-ink on the trench region. The electrical properties of the conductive electrodes fabricated using silver nano-ink with an average particle size of 50 or 200nm were investigated and the microstructure of the electrodes was observed using an electron microscope at sintering temperatures ranging from 150 to 400°C. In addition, the addition effect of silver nanowire to silver nano-ink was examined to assess the improvement on the conductive properties of electrode.

Cleaning organized single-walled carbon nanotube interconnect structures for reduced interfacial contact resistance

A method is presented for significantly reducing the interfacial contact resistance of single-walled carbon nanotube (SWCNT) interconnects test-structures. Conventional lithographic cleaning steps are insufficient for complete removal of lithographic residues in SWCNT networks, leading to large interfacial contact resistance. Using improved purification procedures and controlled developing time, the interfacial contact resistance between SWCNTs and contact electrodes of Ti/Au were found to reach values below 2% of the overall resistance in two-probe test-structures of SWCNTs, demonstrating the importance of cleaning lithographic residues from the surface of SWCNTs before the fabrication of metal electrodes. These low-resistance contacts are quite stable over a large temperature range, and represent a step towards the implementation of SWCNTs as future interconnects.

Fabrication of Metal Electrodes Based on the Self-Differentiation Technique Using the Novel High-and-Low Strategy

In this study, a strategic analysis of the most successful printing techniques in terms of their capability to make high resolution patterns, i.e., the laser transfer and reverse offset printing techniques, is conducted and a novel self-differentiation technique is introduced on the basis of the modified strategy. The proposed self-differentiation technique is based on the high resolution subtractive patterning of a cheap material coated on a substrate and the subsequent low-resolution additive patterning of metallo-organic silver ink. The novelty of this self-differentiation technique lies in its capability to convert metallo-organic silver ink to either conductive or nonconductive patterns, as intended. With the proposed self-differentiation technique, conductive and nonconductive patterns were successfully self-differentiated, no matter where the metallo-organic silver ink was applied, and the line resistance of the self-patterned metal electrode, as fine as 190.1±0.3 μm in line width, was as low as 24.8±0.2 Ω/cm.

All‐Carbon Electronic Devices Fabricated by Directly Grown Single‐Walled Carbon Nanotubes on Reduced Graphene Oxide Electrodes

Being free from the harsh post-growth treatments in strong acids, long time sonication, etc., directly grown single-walled carbon nanotubes (SWCNTs) preserve their pristine structures and intrinsic properties, which make them ideal for highperformance electronic devices. [ 1–9 ] Integration of directly grown SWCNTs into such addressable devices is a crucial step and requirement for both fundamental studies and applications. Two strategies, i.e., fabrication of metal electrodes on CNTs [ 5 , 7 , 10 ] and direct growth of CNTs between the pre-fabricated electrodes, [ 3 , 4 , 11 ] are normally used to fabricate the directly grown CNT-based devices. Although the fi rst strategy is popular and commonly used, the shadow mask and/or the use of photoresist may contaminate or destroy CNTs, leading to a low performance or even failure of devices. [ 3 ] The second strategy possesses some advantages, such as no CNT purifi cation and no photolithography required. This could be a better choice to produce clean and high-performance CNT-based devices, since the pristine structures and intrinsic properties of the grown CNTs are preserved. Despite the fact that many attempts have been reported, [ 3 , 4 , 9 , 11 ]

Self-patterned Metal Electrodes by the Fusion Control of Silver Nanoclusters for Inkjet Printing Process

The opportunity of inkjet printing for the fabrication of metal electrodes in electronics applications has been explored for years but the direct fabrication of fine metal electrodes in the scale of tens of micrometers and less has suffered from its limited resolution and reliability. Moreover, the imperfect wetting control of silver ink has caused the short circuit formation between adjacent electrodes, even with a surface energy patterning technique. In this study, a novel self-patterning technique is introduced, which has the capability to convert metallo-organic silver ink to either conductive or non-conductive patterns, as intended. It is found that polyaniline allows the infiltration of metallo-organic silver ink into the voids among polyaniline granules and inhibits the formation of networked silver nanoclusters after a thermal process. With the fusing control layer of polyaniline, conductive and non-conductive patterns were successfully self-differentiated, no matter where metallo-organic silver ink lied down, and the line resistance of the self-patterned metal electrode as fine as 96 μm in line width and 27 μm in line space was as low as 27.55±0.62 Ω/cm.

Simple Patterning via Adhesion between a Buffered‐Oxide Etchant‐Treated PDMS Stamp and a SiO2 Substrate

AbstractA very simple polydimethylsiloxane (PDMS) pattern‐transfer method is devised, called buffered‐oxide etchant (BOE) printing. The mechanism of pattern transfer is investigated, by considering the strong adhesion between the BOE‐treated PDMS and the SiO2 substrate. PDMS patterns from a few micrometers to sub‐micrometer size are transferred to the SiO2 substrate by just pressing a stamp that has been immersed in BOE solution for a few minutes. The patterned PDMS layers work as perfect physical and chemical passivation layers in the fabrication of metal electrodes and V2O5 nanowire channels, respectively. Interestingly, a second stamping of the BOE‐treated PDMS on the SiO2 substrate pre‐patterned with metal as well as PDMS results in a selective transfer of the PDMS patterns only to the bare SiO2. In this way, the fabrication of a device structure consisting of two Au electrodes and V2O5 nanowire network channels is possible; non‐ohmic semiconducting I–V characteristics, which can be modeled by serially connected percolation, are observed.

Cover Picture: Fabrication of Stable Metallic Patterns Embedded in Poly(dimethylsiloxane) and Model Applications in Non-Planar Electronic and Lab-on-a-Chip Device Patterning (Adv. Funct. Mater. 4/2005)

A composite image is shown that highlights examples of device architectures that either incorporate or exploit polymer-embedded metallic microstructures. In work reported by Nuzzo and co-workers on p. 557, new applications of soft lithography, in conjunction with advanced forms of multilayer metallization, are used to construct these exceptionally durable structures. They are suitable for use in non-planar lithographic patterning, and as device components finding applications ranging from microelectronics to Lab-on-a-Chip analytical systems. This article describes the fabrication of durable metallic patterns that are embedded in poly(dimethylsiloxane) (PDMS) and demonstrates their use in several representative applications. The method involves the transfer and subsequent embedding of micrometer-scale gold (and other thin-film material) patterns into PDMS via adhesion chemistries mediated by silane coupling agents. We demonstrate the process as a suitable method for patterning stable functional metallization structures on PDMS, ones with limiting feature sizes less than 5 μm, and their subsequent utilization as structures suitable for use in applications ranging from soft-lithographic patterning, non-planar electronics, and microfluidic (lab-on-a-chip, LOC) analytical systems. We demonstrate specifically that metal patterns embedded in both planar and spherically curved PDMS substrates can be used as compliant contact photomasks for conventional photolithographic processes. The non-planar photomask fabricated with this technique has the same surface shape as the substrate, and thus facilitates the registration of structures in multilevel devices. This quality was specifically tested in a model demonstration in which an array of one hundred metal oxide semiconductor field-effect transistor (MOSFET) devices was fabricated on a spherically curved Si single-crystalline lens. The most significant opportunities for the processes reported here, however, appear to reside in applications in analytical chemistry that exploit devices fabricated using the methods of soft lithography. Toward this end, we demonstrate durably bonded metal patterns on PDMS that are appropriate for use in microfluidic, microanalytical, and microelectromechanical systems. We describe a multilayer metal-electrode fabrication scheme (multilaminate metal–insulator–metal (MIM) structures that substantially enhance performance and stability) and use it to enable the construction of PDMS LOC devices using electrochemical detection. A polymer-based microelectrochemical analytical system, one incorporating an electrode array for cyclic voltammetry and a microfluidic system for the electrophoretic separation of dopamine and catechol with amperometric detection, is demonstrated.

Fabrication of Stable Metallic Patterns Embedded in Poly(dimethylsiloxane) and Model Applications in Non-Planar Electronic and Lab-on-a-Chip Device Patterning

This article describes the fabrication of durable metallic patterns that are embedded in poly(dimethylsiloxane) (PDMS) and demonstrates their use in several representative applications. The method involves the transfer and subsequent embedding of micrometer-scale gold (and other thin-film material) patterns into PDMS via adhesion chemistries mediated by silane coupling agents. We demonstrate the process as a suitable method for patterning stable functional metallization structures on PDMS, ones with limiting feature sizes less than 5 μm, and their subsequent utilization as structures suitable for use in applications ranging from soft-lithographic patterning, non-planar electronics, and microfluidic (lab-on-a-chip, LOC) analytical systems. We demonstrate specifically that metal patterns embedded in both planar and spherically curved PDMS substrates can be used as compliant contact photomasks for conventional photolithographic processes. The non-planar photomask fabricated with this technique has the same surface shape as the substrate, and thus facilitates the registration of structures in multilevel devices. This quality was specifically tested in a model demonstration in which an array of one hundred metal oxide semiconductor field-effect transistor (MOSFET) devices was fabricated on a spherically curved Si single-crystalline lens. The most significant opportunities for the processes reported here, however, appear to reside in applications in analytical chemistry that exploit devices fabricated using the methods of soft lithography. Toward this end, we demonstrate durably bonded metal patterns on PDMS that are appropriate for use in microfluidic, microanalytical, and microelectromechanical systems. We describe a multilayer metal-electrode fabrication scheme (multilaminate metal–insulator–metal (MIM) structures that substantially enhance performance and stability) and use it to enable the construction of PDMS LOC devices using electrochemical detection. A polymer-based microelectrochemical analytical system, one incorporating an electrode array for cyclic voltammetry and a microfluidic system for the electrophoretic separation of dopamine and catechol with amperometric detection, is demonstrated.

A Controllable Electrochemical Fabrication of Metallic Electrodes with a Nanometer/Angstrom‐Sized Gap Using an Electric Double Layer as Feedback

A Controllable Electrochemical Fabrication of Metallic Electrodes with a Nanometer/Angstrom‐Sized Gap Using an Electric Double Layer as Feedback

A Controllable Electrochemical Fabrication of Metallic Electrodes with a Nanometer/Angstrom‐Sized Gap Using an Electric Double Layer as Feedback

Potential feedback: Metallic electrodes with controlled gap widths ranging from about 10 nm down to several angstroms (as determined by SEM measurements) can be fabricated electrochemically by using a simple potential feedback system with a unique electrode configuration (see picture). The working principle is based on the potential distribution in the electric double-layer. The process is simple, controllable, and reproducible.

Fabrication of nanometer-spaced electrodes using gold nanoparticles

A simple and highly reproducible technique is demonstrated for the fabrication of metallic electrodes with nanometer separation. Commercially available bare gold colloidal nanoparticles are first trapped between prefabricated large-separation electrodes to form a low-resistance bridge by an ac electric field. A large dc voltage is then applied to break the bridge via electromigration at room temperature, which consistently produces gaps in the sub-10 nm range. The technique is readily applied to prefabricated electrodes with separation up to 1 μm, which can be defined using optical lithography. The simple fabrication scheme will facilitate electronic transport studies of individual nanostructures made by chemical synthesis. As an example, measurement of a thiol-coated gold nanoparticle showing a clear Coulomb staircase is presented.

Fabrication of metallic electrodes with nanometer separation by electromigration

A simple yet highly reproducible method to fabricate metallic electrodes with nanometer separation is presented. The fabrication is achieved by passing a large electrical current through a gold nanowire defined by electron-beam lithography and shadow evaporation. The current flow causes the electromigration of gold atoms and the eventual breakage of the nanowire. The breaking process yields two stable metallic electrodes separated by ∼1 nm with high efficiency. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by fabricating single-electron transistors based on colloidal cadmium selenide nanocrystals.

Controlled fabrication of metallic electrodes with atomic separation

We report a technique for fabricating metallic electrodes on insulating substrates with separations on the 1 nm scale. The fabrication technique, which combines lithographic and electrochemical methods, provides atomic resolution without requiring sophisticated instrumentation. The process is simple, controllable, reversible, and robust, allowing rapid fabrication of electrode pairs with high yield. We expect the method to prove useful in interfacing molecular-scale structures to macroscopic probes and electronic devices.