Micro/nano-machining (MNM) is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures (3D-MNS) in ultra-large scale integrated circuits, microelectromechanical systems, miniaturized total analysis systems, precision optics, and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micro/nano-machining (EC-MNM) has an irreplaceable role in MNM. This comprehensive review presents the state-of-art of EC-MNM techniques for direct writing, surface planarization and polishing, and 3D-MNS fabrications. The key point of EC-MNM is to confine electrochemical reactions at the micro/nano-meter scale. This review will bring together various solutions to “confined reaction” ranging from electrochemical principles through technical characteristics to relevant applications.

•A tip current/positioning close-loop mode is designed for scanning electrochemical microscopy.•The motion trail of SECM tip can be pre-programmed by this positioning mode.•The SECM mode is verified powerful to fabricate arbitrary 3D microstructures.Scanning electrochemical microscopy (SECM) has been approved as a prospective electrochemical micromachining (ECMM) technique soon after its birth. However, it still remains challenge for SECM to fabricate arbitrary three-dimensional (3D) microstructures because of the limitation of positioning system. To solve this problem, we proposed a tip current signal/positioning close-loop mode in which the tip current signal is fed back to the positioning system in order to program the motion trial of SECM tip. Both the triedge-cone and sinusoidal microstructures were obtained by the close-loop positioning mode. The static-state etching process was demonstrated not to be disturbed by the slow motion rate of SECM tip. The unique positioning mode would be significant for both ECMM and electrochemical imaging.

Scanning probe is the key issue for the electrochemical scanning probe techniques (EC-SPM) such as EC-scanning tunnel microscopy (STM), EC-atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM), especially the insulative encapsulation of the nanoelectrode probe for both positioning and electrochemical feedbacks. To solve this problem, we develop a novel fabrication method of the gold nanoelectrodes: firstly, a micropipette with nanomter-sized orifice was prepared as the template by a laser puller; secondly, the inside wall of micropipette apex was blocked by compact and conic Au nano-piece through electroless plating; thirdly, the Au nano-piece was grown by bipolar electroplating and connected with a silver wire as a current collector. The fabricated Au nanoelectrode has very good voltammetric responses for the electrodic processes of both mass transfer and adsorption. The advantage lies in that it is well encapsulated by a thin glass sealing layer with a RG value lowered to 1.3, which makes it qualified in the SECM-STM coupling mode. On one hand, it can serve as STM tip for positioning which ensures the high spatial resolution; on the other hand, it is a high-quality nanoelectrode to explore the local chemical activity of the substrate. The nanofabrication method may promote the SPM techniques to obtain simultaneously the physical and chemical images with nanoscale spatial resolution, which opens a new approach to tip chemistry in electrochemical nanocatalysis and tip-enhanced spectroscopy.

The functional three dimensional micro-nanostructures (3D-MNS) play crucial roles in integrated and miniaturized systems because of the excellent physical, mechanical, electric and optical properties. Nanoimprint lithography (NIL) has been versatile in the fabrication of 3D-MNS by pressing thermoplastic and photocuring resists into the imprint mold. However, direct nanoimprint on the semiconductor wafer still remains a great challenge. On the other hand, considered as a competitive fabrication method for erect high-aspect 3D-MNS, metal assisted chemical etching (MacEtch) can remove the semiconductor by spontaneous corrosion reaction at the metal/semiconductor/electrolyte 3-phase interface. Moreover, it was difficult for MacEtch to fabricate multilevel or continuously curved 3D-MNS. The question of the consequences of NIL meeting the MacEtch is yet to be answered. By employing a platinum (Pt) metalized imprint mode, we demonstrated that using electrochemical nanoimprint lithography (ECNL) it was possible to fabricate not only erect 3D-MNS, but also complex 3D-MNS with multilevel stages with continuously curved surface profiles on a gallium arsenide (GaAs) wafer. A concave microlens array with an average diameter of 58.4 μm and height of 1.5 μm was obtained on a ∼1 cm2-area GaAs wafer. An 8-phase microlens array was fabricated with a minimum stage of 57 nm and machining accuracy of 2 nm, presenting an excellent optical diffraction property. Inheriting all the advantages of both NIL and MacEtch, ECNL has prospective applications in the micro/nano-fabrications of semiconductors.

Although metal assisted chemical etching (MacEtch) has emerged as a versatile micro-nanofabrication method for semiconductors, the chemical mechanism remains ambiguous in terms of both thermodynamics and kinetics. Here we demonstrate an innovative phenomenon, i.e., the contact electrification between platinum (Pt) and an n-type gallium arsenide (100) wafer (n-GaAs) can induce interfacial redox reactions. Because of their different work functions, when the Pt electrode comes into contact with n-GaAs, electrons will move from n-GaAs to Pt and form a contact electric field at the Pt/n-GaAs junction until their electron Fermi levels (EF) become equal. In the presence of an electrolyte, the potential of the Pt/electrolyte interface will shift due to the contact electricity and induce the spontaneous reduction of MnO4− anions on the Pt surface. Because the equilibrium of contact electrification is disturbed, electrons will transfer from n-GaAs to Pt through the tunneling effect. Thus, the accumulated positive holes at the n-GaAs/electrolyte interface make n-GaAs dissolve anodically along the Pt/n-GaAs/electrolyte 3-phase interface. Based on this principle, we developed a direct electrochemical nanoimprint lithography method applicable to crystalline semiconductors.

In the past several decades, electrochemical machining (ECM) has enjoyed the reputation of a powerful technique in the manufacturing industry. Conventional ECM methods can be classified as electrolytic machining and electroforming: the former is based on anodic dissolution and the latter is based on cathodic deposition of metallic materials. Strikingly, ECM possesses several advantages over mechanical machining, such as high removal rate, the capability of making complex three-dimensional structures, and the practicability for difficult-to-cut materials. Additionally, ECM avoids tool wear and thermal or mechanical stress on machining surfaces. Thus, ECM is widely used for various industrial applications in the fields of aerospace, automobiles, electronics, etc.Nowadays, miniaturization and integration of functional components are becoming significant in ultralarge scale integration (ULSI) circuits, microelectromechanical systems (MEMS), and miniaturized total analysis systems (μ-TAS). As predicted by Moore’s law, the feature size of interconnectors in ULSI circuits are down to several nanometers. In this Account, we present our perseverant research in the last two decades on how to “confine” the ECM processes to occur at micrometer or even nanometer scale, that is, to ensure ECM with nanoscale accuracy. We have been developing the confined etchant layer technique (CELT) to fabricate three-dimensional micro- and nanostructures (3D-MNS) on different metals and semiconductor materials since 1992. In general, there are three procedures in CELT: (1) generating the etchant on the surface of the tool electrode by electrochemical or photoelectrochemical reactions; (2) confining the etchant in a depleted layer with a thickness of micro- or nanometer scale; (3) feeding the tool electrode to etch the workpiece. Scavengers, which can react with the etchant, are usually adopted to form a confined etchant layer. Through the subsequent homogeneous reaction between the scavenger and the photo- or electrogenerated etchant in the electrolyte solution, the diffusion distance of the etchant is confined to micro- or nanometer scale, which ensures the nanoscale accuracy of electrochemical machining.To focus on the “confinement” of chemical etching reactions, external physical-field modulations have recently been introduced into CELT by introducing various factors such as light field, force field, hydrodynamics, and so on. Meanwhile, kinetic investigations of the confined chemical etching (CCE) systems are established based on the finite element analysis and simulations. Based on the obtained kinetic parameters, the machining accuracy is tunable and well controlled. CELT is now applicable for 1D milling, 2D polishing, and 3D microfabrication with an accuracy at nanometer scale. CELT not only inherits all the advantages of electrochemical machining but also provides advantages over photolithography and nanoimprint for its applicability to different functional materials without involving any photocuring and thermoplastic resists. Although there are some technical problems, for example, mass transfer and balance, which need to be solved, CELT has shown its prospective competitiveness in electrochemical micromachining, especially in the semiconductor industry.

The adsorption and mobility of oxygen adspecies on platinum (Pt) surface are crucial for the oxidation of surface-absorbed carbon monoxide (CO), which causes the deactivation of Pt catalyst in fuel cells. By employing nanoelectrode and ultramicroelectrode techniques, we have observed the surface mobility of oxygen adspecies produced by the dissociative adsorption of H2O and the surface reaction between the oxygen adspecies and the preadsorbed CO on the Pt surface. The desorption charge of oxygen adspecies on a Pt nanoelectrode has been found to be in proportion to the reciprocal of the square root of scan rate. Using this information, the apparent surface diffusion coefficient of oxygen adspecies has been determined to be (5.61 ± 0.84) × 10–10 cm2/s at 25 °C. During the surface oxidation of CO, two current peaks are observed, which are attributed to CO oxidation at the Pt/electrolyte interface and the surface mobility of the oxygen adspecies on the adjacent Pt surface, respectively. These results demonstrate that the surface mobility of oxygen adspecies plays an important role in the antipoisoning and reactivation of Pt catalyst.

Can isotropic wet chemical etching be controlled with a spatial resolution at the nanometer scale, especially, for the repetitive microfabrication of hierarchical 3D μ-nanostructures on the continuously curved surface of functional materials? We present an innovative wet chemical etching method called “electrochemical buckling microfabrication”: first, a constant contact force is applied to generate a hierarchical 3D μ-nanostructure on a mold electrode surface through a buckling effect; then, the etchant is electrogenerated on-site and confined close to the mold electrode surface; finally, the buckled hierarchical 3D μ-nanostructures are transferred onto the surface of a GaxIn1−xP coated GaAs wafer through WCE. The concave microlens, with a Fresnel structure, has an enhanced photoluminescence at 630 nm. Comparing with energy beam direct writing techniques and nanoimprint lithography, this method provides an electrochemical microfabrication pathway for the semiconductor industry, with low cost and high throughput.

Quantum dots (QDs) are considered as the alternative of dye sensitizers for solar cells. However, interfacial construction and evaluation of photocatalytic nanomaterials still remains challenge through the conventional methodology involving demo devices. We propose here a high-throughput screening and optimizing method based on combinatorial chemistry and scanning electrochemical microscopy (SECM). A homogeneous TiO2 catalyst layer is coated on a FTO substrate, which is then covered by a dark mask to expose the photocatalyst array. On each photocatalyst spot, different successive ionic layer adsorption and reaction (SILAR) processes are performed by a programmed solution dispenser to load the binary PbxCd1–xS QDs sensitizers. An optical fiber is employed as the scanning tip of SECM, and the photocatalytic current is recorded during the imaging experiment, through which the optimized technical parameters are figured out. To verify the validity of the combinatorial SECM imaging results, the controlled trials are performed with the corresponding photovoltaic demo devices. The harmonious accordance proved that the methodology based on combinatorial chemistry and SECM is valuable for the interfacial construction, high-throughput screening, and optimization of QDSSCs. Furthermore, the PbxCd1–xS/CdS QDs cosensitized solar cell optimized by SECM achieves a short circuit current density of 24.47 mA/cm2, an open circuit potential of 421 mV, a fill factor of 0.52, and a photovoltaic conversion efficiency of 5.33%.

•A correlation between the nanostructure and performance of hematite as a photocatalyst is discovered.•The catalytic performance of hematite is crystal-facet dependent.•The improved catalytic performance of 2D hematite nanoplates is caused by separate electron and hole transport on facets {110} and {001}, respectively.•Crystal facet engineering plays a crucial role in the design of nanocatalysts.Physical structure determines nanocatalytic performance. A comparative study was performed using scanning electrochemical microscopy (SECM) in imaging mode and electrochemical impedance spectroscopy (EIS), demonstrating that crystal facets play an important role in the action of hematite as a photocatalyst for water splitting. The mass specific activity of the facets was found to be in the order {110} > {012} > > {001}, regardless of whether the hematite was sensitized by cadmium sulfide quantum dots (CdS QDs). However, the photocatalytic performance of 2D nanoplates with {001} and {110} facets improved dramatically on sensitization with CdS QDs. This was attributed to spatially separated transport of photogenerated charges on different facets, as shown by the selective deposition of CdS QDs and platinum clusters on the {110} facet. The work demonstrates the importance of crystal facet engineering in nanocatalysis.

The physicochemical principle of photocorrosion and photoetching is the internal photoelectric effect of semiconductors. However, the kinetic investigation of interfacial charge transfer induced by this phenomenon has been seldom reported due to its microdomain bipolarity. GaAs is a direct band gap semiconductor with high saturated electron velocity and high electron mobility. Once the photogenerated electrons on a n-type GaAs surface are removed by Fe3+ in the solution, it will dissolve due to the residual positive holes; i.e., the photoetching process will occur. By employing scanning electrochemical microscopy (SECM), the photoetching rates of n-type GaAs are obtained about ∼10–4 mol·m–2·s–1 with Fe3+ cation as electron acceptor. The rate-determining step (rds) is proved as the charge separation process at low illuminating intensity, and the mass transfer of Fe3+ in the solution at high illuminating intensity. Moreover, the photoetching process is developed as a controllable micromachining method for semiconductor materials.

Here we emphasise the importance of the dielectric environment on the electron transfer behavior in interfacial electrochemical systems. Through doping cobalt hexacyanide (Co(CN)63−) into single microcrystals of sodium chloride (NaCl), for the first time, we obtained the direct electrochemical behavior of Co(CN)63− which is hardly ever obtained in either aqueous or conventional nonaqueous solutions. DFT calculations elucidate that, as the Co(CN)63− anions occupy the lattice units of NaCl65− in the NaCl microcrystal, the redox energy barrier of Co(CN)63−/4− is decreased dramatically due to the low dielectric constant of NaCl. Meanwhile, the low-spin Co(CN)64− anions are stabilized in the lattices of the NaCl microcrystal. The results also show that the NaCl microcrystal is a potential solvent for solid-state electrochemistry at ambient temperature.

We report synergetic effect enhanced photoelectrocatalysis, in which Fe3+ and Br− are used as the acceptors of photogenerated charges on TiO2 nanoparticles. The kinetic rate of interfacial charge transfer is promoted from (4.0 ± 0.5) × 10−4 cm s−1 (TiO2/(O2, Br−)) to (1.5 ± 0.5) × 10−3 cm s−1 (TiO2/(Fe3+, Br−)). The synergetic effect provides a valuable approach to the design of photoelectrocatalytic systems.

Cuprous sulfide (Cu2S) is a direct band-gap p-type semiconductor with excellent ionic/electronic hybrid conductivity. Although Cu/Cu2S/sulfide or polysulfide system is adopted as counter electrode of quantum-dots-sensitized solar cells (QDSSC), the electrode process is seldom reported. Here, the electrochemical growth of Cu2S film on a copper (Cu) surface, the redox behaviors of sulfide and polysulfide, and the all-in-solid charge-transfer properties of Cu2S film are investigated. It is clarified that the copper electrode simultaneously undergoes an activated process, a membrane growth process, and a redox phase transformation process. The solid charge-transfer capability of Cu2S is quantified with a high exchange-current density of 2.27 A/cm2, which elucidates that the Cu/Cu2S electrode is a qualified material for counter electrodes of QDSSC. These results aid understanding of the physicochemical mechanism of QDSSC with a polysulfide electrolyte and Cu/Cu2S counter electrode.

Improving electrochemical activity of graphene is crucial for its various applications, which requires delicate control over its geometric and electronic structures. We demonstrate that precise control of the density of vacancy defects, introduced by Ar+ irradiation, can improve and finely tune the heterogeneous electron transfer (HET) rate of graphene. For reliable comparisons, we made patterns with different defect densities on a same single layer graphene sheet, which allows us to correlate defect density (via Raman spectroscopy) with HET rate (via scanning electrochemical microscopy) of graphene quantitatively, under exactly the same experimental conditions. By balancing the defect induced increase of density of states (DOS) and decrease of conductivity, the optimal HET rate is attained at a moderate defect density, which is in a critical state; that is, the whole graphene sheet becomes electronically activated and, meanwhile, maintains structural integrity. The improved electrochemical activity can be understood by a high DOS near the Fermi level of defective graphene, as revealed by ab initio simulation, which enlarges the overlap between the electronic states of graphene and the redox couple. The results are valuable to promote the performance of graphene-based electrochemical devices. Furthermore, our findings may serve as a guide to tailor the structure and properties of graphene and other ultrathin two-dimensional materials through defect density engineering.

We demonstrate that the solvation effect can be the driving force for ion transfer across the water/1,2-dichloroethane interface. Voltammetric behaviours of facilitated Li+ ion transfer by the solvents of lithium-based batteries are investigated, which is valuable for the dual-electrolyte Li–air batteries, but also for the ion detection, separation and extraction.

Solar energy is the most abundant nature resource and plays important roles in the sustainable developments of energy and environment. Scanning photoelectrochemical microscopy provides a high-throughput screening method by introducing the combinatorial technique to prepare the substrate with photoelectrochemical catalyst array. However, the signal/noise (S/N) ratio suffers from the background current of indium–tin oxide or fluorine-doped tin oxide itself, including a transient charge–discharge current of electric double layer and a steady-state photocatalytic current. Here we adopt a facile microfabrication method to isolate the substrate area other than the catalyst array from not only the electrolyte solution but also the light illumination. Consequently, the imaging quality has been promoted dramatically due to suppressed background current. This method provides a high S/N ratio screening method, which will be valuable for the high-throughput optimization of the photoelectrocatalytic system.

Confined etchant layer technique (CELT) has been proved an effective electrochemical microfabrication method for both 3D microstructures and a supersmooth surface. From a physical chemistry viewpoint, the confined etching system of n-GaAs includes an etchant generation reaction from Br– to Br2 (E) followed by two parallel reactions: the confining reaction between Br2 and l-cystine (C1), and the etching reaction between Br2 and n-GaAs (C2). In this paper, the homogeneous EC1 process is investigated first through the tip generation/substrate collection (TG/SC) mode of scanning electrochemical microscopy (SECM), and the reaction rate of C1 is determined as (8.0 ± 1.0) × 103 dm3 mol–1 s–1; second, the heterogeneous EC2 process is investigated through the feedback mode of SECM, and the reaction rate of C2 is determined as (3.2 ± 0.5) × 10–2 cm s–1; third, a deformed geometry finite element model is established to simulate the etching topography coupling E(C1∥C2) processes by using the obtained data. The theoretical profiles of pits etched at different concentrations of scavenger, l-cystine, are analyzed and compared with experimental results. This model allows the prediction of spatial resolution of CELT as a function of reaction rates of C1 and C2 but also of the concentration of scavenger.

Substrate leveling is an essential but neglected instrumental technique of scanning electrochemical microscopy (SECM). In this technical note, we provide an effective substrate leveling method based on the current feedback mode of SECM. By using an air-bearing rotary stage as the supporter of an electrolytic cell, the current feedback presents a periodic waveform signal, which can be used to characterize the levelness of the substrate. Tuning the adjusting screws of the tilt stage, substrate leveling can be completed in minutes by observing the decreased current amplitude. The obtained high-quality SECM feedback curves and images prove that this leveling technique is valuable in not only SECM studies but also electrochemical machining.

•EC-WETS works on aluminum workpiece in an up-down mode.•Potential-pulse methods promote the mass balance and the micromachining quality.•Machining tolerance lower than 200 nm and removal rate higher than 210 nm/min.We proposed an up–down working mode of electrochemical wet stamping technique (EC-WETS) for three dimensional (3D) micromachining on aluminum (Al) surface. 3D microstructures on a Si mold were transferred on to an agarose hydrogel containing 15% NaNO3, 2% MgF2, 1% NaOH and 5% glycerin, which acted as the quasi-solid electrolyte for the electrochemical micromachining. The transferred 3D microstructures on agarose hydrogel were then duplicated onto Al surface through anodic dissolution. The micromachining quality was improved by pulse-potential method dramatically with a machining tolerance lower than 200 nm and an average removal rate of 210 nm min− 1 in the Z direction. This method was proved to be a highly efficient, low cost and green method for 3D micromachining on active metal surface, which would be valuable for the manufacture of microelectromechanical system (MEMS).

•A photoelectrochemical method is proposed for the synthesis of AgTCNQ microrods.•A bipolar mechanism involves cooperative effect or coupling processes.•No external circuit makes the photoelectrochemical system simpler.Silver-7, 7, 8, 8-tetracyanoquinodimethane (AgTCNQ) microrods are synthesized through the photoelectrochemical catalysis of TiO2 nanoparticles. When illuminated by UV light, Ag nanoclusters deposit on TiO2 nanoparticles dispersed in the AgNO3/alcohol solution. When illuminated by visible light, the metallic Ag on TiO2 nanoparticles will dissolve in the solution as Ag+ while the released electron will be accepted by TCNQ to form TCNQ−. Consequently, AgTCNQ microrods are obtained through a photoinduced bipolar mechanism, which is valuable in the chemical synthesis involving cooperative effect or coupling processes.

High-quality products come from high-quality instrument. We present here an optimized instrument for electrochemical micromachining, in which a granite bridge base, a macro–micro dual driven positioning stage and a force-displacement sensing module are combined to promote dramatically the tool–workpiece alignment, in-situ monitoring and product quality. As a testing experiment, a polymethylmethacrylate (PMMA) microlens array with a diameter of 110 μm and a height of 3.5 μm has been transferred successfully onto the surface of an n-GaAs wafer by the confined etchant layer technique (CELT). The machining tolerance is about 3.4 nm and the surface roughness is lower than 8.0 nm. Moreover, the presented techniques have significance in the precise electrochemical instruments for not only micromachining but also scanning electrochemical probe techniques.Highlights► High-quality GaAs microlens array is fabricated with a tolerance of 3.4 nm and a surface roughness of 8.0 nm. ► New mechanical designs are adopted to promote tool-workpiece alignment, in-situ monitoring and product quality.

The facilitated transfer of alkali metal ions (Li+ and Na+) across the water/1,2-dichloroethane (W/1,2-DCE) interface was studied by using a series of crown ethers as ionophores: 4′-ethynylbenzo-15-crown-5-ether (L1), 3′,6′-diethynylbenzo-15-crown-5-ether (L2) and 4′,5′-diethynylbenzo-15-crown-5-ether (L3). Cyclic voltammetry was employed to study the electrochemical behaviour of the facilitated ion transfer across the W/1,2-DCE interface supported at the tip of a micropipette. The diffusion coefficients of the ionophores in the 1,2-DCE phase were determined, while the metal–ligand complexes formed by these ions with all the ionophores were obtained to be in a 1:1 stoichiometric ratio. The association constants, log β°, for complexes LiL1+, LiL2+, LiL3+, NaL1+, NaL2+ and NaL3+ were calculated to be 3.3, 4.2, 4.0, 2.1, 3.5 and 2.2, respectively. The theoretical calculations have shown that the conjugated constituent groups on the benzene ring have an essential effect on the spatial structures of the crown ether rings, which determine the supramolecular interaction between the ions and ionophores.

Scanning electrochemical cell microscopy (SECCM) was proven to be a prospective microfabrication method for the in situ synthesis and multiscale assembly of functional nanomaterials into microdevices. Nanostructured ZnO thin film was synthesized and assembled by SECCM, which has excellent electrochemical capacitance and electronic I–V properties.

Solid-state solution with excellent ionic conductivity and redox activity has potential applications in electrochemical microdevices, such as transistors, switches, sensors, and actuators, due to its controllable assembly, integration, and package in microchips. In this paper, we present an electrochemical method to synthesize single microcrystals of an iron hexacyanides/NaCl solid solution and to assemble them into microdevices based on scanning electrochemical cell microscopy. The redox behaviors of the single microcrystals were investigated systematically, especially in the “all-in-solid-state”, that is, without exposure to any external liquid environment. The unique metal/solid solution interface has similar electrochemical properties as the conventional metal/liquid solution interface. The apparent concentration of ion hexacyanides (1.05 × 10–3 mol/L), the diffusion coefficient of the counterion Na+ (8.05 × 10–8 cm2/s), and the electron transfer rate in the lattice (1.22 × 10–4 cm/s) were evaluated from the data obtained through all-in-solid-state cyclic voltammetry and electrochemical impedance. All the results are comparable to the conventional metal/solution theory of electrochemistry.

Here we report a novel generation/collection operation mode of scanning electrochemical microscopy, in which a theta micropipette was employed to support two adjacent water/1,2-dichloroethane interfaces separated by the thin central glass wall: one acts as the generator while the other as the collector. The generation current, collection current and collection efficiency were enhanced significantly when the tip approached to an insulate substrate.

•The contact electrification between Pt and an n-type Si (111) wafer can induce electrochemical corrosion of the latter.•Based on this principle, an electrochemical nanoimprint lithography method is developed.•Electrochemical nanoimprint lithography offers the possibility of imprinting directly on semiconductors.Here we report spontaneous redox reactions at the Pt/Si/electrolyte three-phase interface and propose an electrochemical method for nanoimprint lithography on a crystalline Si wafer that does not require thermoplastic and photocuring resists. When the Pt metallized imprint mold is compacted on the n-type Si (111) wafer, electrons will transfer from the n-type Si to Pt due to their different electron work functions. At equilibrium, the Fermi levels of the electrons in each phase become equal, resulting in an electric field and a contact potential at the Pt/Si interface. When immersed in an electrolyte solution, the potentials of the Pt/electrolyte interface and the Si/electrolyte interface are observed to shift in opposite directions. Hydrogen peroxide is spontaneously reduced on the Pt surface. Meanwhile, the electrons in Si will tunnel to Pt and the residual holes will oxidize Si along the three-phase interface. In this way, the micro-/nanostructures on the Pt metallized imprint mold are transferred to the Si wafer.

Here we emphasise the importance of the dielectric environment on the electron transfer behavior in interfacial electrochemical systems. Through doping cobalt hexacyanide (Co(CN)63−) into single microcrystals of sodium chloride (NaCl), for the first time, we obtained the direct electrochemical behavior of Co(CN)63− which is hardly ever obtained in either aqueous or conventional nonaqueous solutions. DFT calculations elucidate that, as the Co(CN)63− anions occupy the lattice units of NaCl65− in the NaCl microcrystal, the redox energy barrier of Co(CN)63−/4− is decreased dramatically due to the low dielectric constant of NaCl. Meanwhile, the low-spin Co(CN)64− anions are stabilized in the lattices of the NaCl microcrystal. The results also show that the NaCl microcrystal is a potential solvent for solid-state electrochemistry at ambient temperature.

Scanning electrochemical cell microscopy (SECCM) was proven to be a prospective microfabrication method for the in situ synthesis and multiscale assembly of functional nanomaterials into microdevices. Nanostructured ZnO thin film was synthesized and assembled by SECCM, which has excellent electrochemical capacitance and electronic I–V properties.

Although metal assisted chemical etching (MacEtch) has emerged as a versatile micro-nanofabrication method for semiconductors, the chemical mechanism remains ambiguous in terms of both thermodynamics and kinetics. Here we demonstrate an innovative phenomenon, i.e., the contact electrification between platinum (Pt) and an n-type gallium arsenide (100) wafer (n-GaAs) can induce interfacial redox reactions. Because of their different work functions, when the Pt electrode comes into contact with n-GaAs, electrons will move from n-GaAs to Pt and form a contact electric field at the Pt/n-GaAs junction until their electron Fermi levels (EF) become equal. In the presence of an electrolyte, the potential of the Pt/electrolyte interface will shift due to the contact electricity and induce the spontaneous reduction of MnO4− anions on the Pt surface. Because the equilibrium of contact electrification is disturbed, electrons will transfer from n-GaAs to Pt through the tunneling effect. Thus, the accumulated positive holes at the n-GaAs/electrolyte interface make n-GaAs dissolve anodically along the Pt/n-GaAs/electrolyte 3-phase interface. Based on this principle, we developed a direct electrochemical nanoimprint lithography method applicable to crystalline semiconductors.

Micro/nano-machining (MNM) is becoming the cutting-edge of high-tech manufacturing because of the increasing industrial demand for supersmooth surfaces and functional three-dimensional micro/nano-structures (3D-MNS) in ultra-large scale integrated circuits, microelectromechanical systems, miniaturized total analysis systems, precision optics, and so on. Taking advantage of no tool wear, no surface stress, environmental friendliness, simple operation, and low cost, electrochemical micro/nano-machining (EC-MNM) has an irreplaceable role in MNM. This comprehensive review presents the state-of-art of EC-MNM techniques for direct writing, surface planarization and polishing, and 3D-MNS fabrications. The key point of EC-MNM is to confine electrochemical reactions at the micro/nano-meter scale. This review will bring together various solutions to “confined reaction” ranging from electrochemical principles through technical characteristics to relevant applications.

We demonstrate that the solvation effect can be the driving force for ion transfer across the water/1,2-dichloroethane interface. Voltammetric behaviours of facilitated Li+ ion transfer by the solvents of lithium-based batteries are investigated, which is valuable for the dual-electrolyte Li–air batteries, but also for the ion detection, separation and extraction.

We report synergetic effect enhanced photoelectrocatalysis, in which Fe3+ and Br− are used as the acceptors of photogenerated charges on TiO2 nanoparticles. The kinetic rate of interfacial charge transfer is promoted from (4.0 ± 0.5) × 10−4 cm s−1 (TiO2/(O2, Br−)) to (1.5 ± 0.5) × 10−3 cm s−1 (TiO2/(Fe3+, Br−)). The synergetic effect provides a valuable approach to the design of photoelectrocatalytic systems.

Can isotropic wet chemical etching be controlled with a spatial resolution at the nanometer scale, especially, for the repetitive microfabrication of hierarchical 3D μ-nanostructures on the continuously curved surface of functional materials? We present an innovative wet chemical etching method called “electrochemical buckling microfabrication”: first, a constant contact force is applied to generate a hierarchical 3D μ-nanostructure on a mold electrode surface through a buckling effect; then, the etchant is electrogenerated on-site and confined close to the mold electrode surface; finally, the buckled hierarchical 3D μ-nanostructures are transferred onto the surface of a GaxIn1−xP coated GaAs wafer through WCE. The concave microlens, with a Fresnel structure, has an enhanced photoluminescence at 630 nm. Comparing with energy beam direct writing techniques and nanoimprint lithography, this method provides an electrochemical microfabrication pathway for the semiconductor industry, with low cost and high throughput.

The facilitated transfer of alkali metal ions (Li+ and Na+) across the water/1,2-dichloroethane (W/1,2-DCE) interface was studied by using a series of crown ethers as ionophores: 4′-ethynylbenzo-15-crown-5-ether (L1), 3′,6′-diethynylbenzo-15-crown-5-ether (L2) and 4′,5′-diethynylbenzo-15-crown-5-ether (L3). Cyclic voltammetry was employed to study the electrochemical behaviour of the facilitated ion transfer across the W/1,2-DCE interface supported at the tip of a micropipette. The diffusion coefficients of the ionophores in the 1,2-DCE phase were determined, while the metal–ligand complexes formed by these ions with all the ionophores were obtained to be in a 1:1 stoichiometric ratio. The association constants, log β°, for complexes LiL1+, LiL2+, LiL3+, NaL1+, NaL2+ and NaL3+ were calculated to be 3.3, 4.2, 4.0, 2.1, 3.5 and 2.2, respectively. The theoretical calculations have shown that the conjugated constituent groups on the benzene ring have an essential effect on the spatial structures of the crown ether rings, which determine the supramolecular interaction between the ions and ionophores.