Electrochemical Reduction Of Diazonium Salts Research Articles

Covalent Grafting of Dielectric Films on Cu(111) Surface via Electrochemical Reduction of Aryl Diazonium Salts.

Covalent grafting of dielectric films containing polyhedral oligomeric silsesquioxane (POSS) on the surface of Cu(111) is performed by a one-step electrochemical reduction of diazonium salts. This method is efficient and economic and performs in a proton-polar solvent of deionized water and tetrahydrofuran (THF), where the monomer employs an octavinylsilsesquioxane (OVS) containing a POSS core. The eight vinyl bonds contained in OVS are used to participate in aryl radical-initiated polymerization reactions to form films. The formed film is dense and covers the copper surface completely and uniformly. The thickness of the film can be controlled by adjusting the reaction time. The components of the films are mainly polynitrophenyl (PNP) or polyaminophenyl (PAP) as well as poly(octavinylsilsesquioxane) (POVS), and the POVS content could be adjusted by the applied voltage. The introduction of POSS prevents the copper surface from being oxidized and often gives the film good properties such as good dielectric properties, mechanical properties, and thermal properties. In addition, the presence of Cu-O-C and Cu-C bonds between the film and copper interface is confirmed at different film thicknesses by X-ray photoelectron spectroscopy (XPS), which allowed the construction of covalent bonds between metal and nonmetal, further enhancing the bonding between the film and copper. Organic films prepared by electrochemical reduction of diazonium salts using OVS as a monomer will have potential significance for the future development of the electronics industry.

The Surface Potential of Zero Charge Controls the Kinetics of Diazonium Salts Electropolymerization

AbstractOne of the central fundamental properties of solid/liquid interfaces is the potential of zero charge (pzc), where no excess charge prevails at the electrode surface. Applying potential on either side of the pzc can control adsorption of molecules on surfaces and is paramount for any interfacial process. However, the impact of pzc on electrode processes has been only demonstrated for reactions involving the adsorption of inorganic ions and gases. Here, the direct relationship between the pzc and electropolymerization rate of a small organic molecule was reported. The electrochemical reduction of diazonium salts, which are the most commonly used molecules to form thin films of molecules on electrode surfaces, was tested. The kinetics of the surface reaction and the reduction potential in electrochemical measurements depended on the pzc of the surface following the order of gold>platinum>carbon>indium‐tin‐oxide>fluorine‐doped tin‐oxide>silicon hydride. The immediate consequence of this finding was that the concentration of the diazonium salt molecules became critical in defining the electrochemical reduction mechanism. At higher concentrations, the mechanism was pzc‐controlled adsorption‐dominated inner‐sphere electron transfer whereas at lower concentrations, diffusion‐based outer‐sphere electron transfer dominated.

Electro-polymerization rates of diazonium salts are dependent on the crystal orientation of the surface

Electro-polymerization of diazonium salts is widely used for modifying surfaces with thin organic films. Initially this method was primarily applied to carbon, then to metals, and more recently to semiconducting Si. Unlike on other surfaces, electrochemical reduction of diazonium salts on Si, which is one of the most industrially dominant material, is not well understood. Here, we report the electrochemical reduction of diazonium salts on a range of silicon electrodes of different crystal orientations (111, 211, 311, 411, and 100). We show that the kinetics of surface reaction and the reduction potential is Si crystal-facet dependent and is more favorable in the hierarchical order (111) > (211) > (311) > (411) > (100), a finding that offers control over the surface chemistry of diazonium salts on Si. The dependence of the surface reaction kinetics on the crystal orientation was found to be directly related to differences in the potential of zero charge (PZC) of each crystal orientation, which in turn controls the adsorption of the diazonium cations prior to reduction. Another consequence of the effect of PZC on the adsorption of diazonium cations, is that molecules terminated by distal diazonium moieties form a compact film in less time and requires less reduction potentials compared to that formed from diazonium molecules terminated by only one diazo moiety. In addition, at higher concentrations of diazonium cations, the mechanism of electrochemical polymerization on the surface becomes PZC-controlled adsorption-dominated inner-sphere electron transfer while at lower concentrations, diffusion-based outer-sphere electron transfer dominates. These findings help understanding the electro-polymerization reaction of diazonium salts on Si en route towards an integrated molecular and Si electronics technology.

In Memoriam of Jean‐Michel Savéant (1933–2020)

In Memoriam of Jean‐Michel Savéant (1933–2020)

Development of a label-free electrochemical aptasensor based on diazonium electrodeposition: Application to cadmium detection in water

In this study we have developed a new aptasensor for cadmium (Cd2+) detection in water. Gold electrode surface has been chemically modified by electrochemical reduction of diazonium salt (CMA) with carboxylic acid outward from the surface. This was used for amino-modified cadmium aptamer immobilization through carbodiimide reaction. Chemical surface modification was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This latter was also used for Cd2+ detection. The aptasensor has exhibited a good linear relationship between the logarithm of the Cd2+ concentration and the impedance changes in the range from 10−3 to 10−9 M with a correlation R2 of 0.9954. A high sensitivity was obtained with a low limit of detection (LOD) of 2.75*10−10 M. Moreover, the developed aptasensor showed a high selectivity towards Cd2+ when compared to other interferences such as Hg2+, Pb2+ and Zn2+. The developed aptasensor presents a simple and sensitive approach for Cd2+detection in aqueous solutions with application for trace Cd2+ detection in spring water samples.

Long-Range Charge Transport in Diazonium-Based Single-Molecule Junctions.

Thin layers of cobalt and ruthenium polypyridyl-oligomers with thicknesses between 2 and 8 nm were deposited on gold by electrochemical reduction of diazonium salts. A scanning tunneling microscope was used to create single-molecule junctions (SMJs). The charge transport properties of the Au-[Co(tpy)2]n-Au (n = 1-4) SMJs do not depend markedly on the oligomer length, have an extremely low attenuation factor (β ∼ 0.19 nm-1), and do not show a thickness-dependent transition between two mechanisms. Resonant charge transport is proposed as the main transport mechanism. The SMJ conductance decreases by 1 order of magnitude upon changing the metal from Co to Ru. In Au-[Ru(tpy)2]n-Au and Au-[Ru(bpy)3]n-Au SMJs, a charge transport transition from direct tunneling to hopping is evidenced by a break in the length-dependent β-plot. The three different mechanisms observed are a clear molecular signature on transport in SMJs. Most importantly, these results are in good agreement with those obtained on large-area molecular junctions.

(Invited) Electro/Electroless Grafting of Organic Dielectric Film on Silicon Surface and Its Application on through Silicon Via

With the rapid development of electronic industry, the packaging technology requires higher density and integration, which is a great challenge for semiconductor manufacturing. In order to continue the acknowledged “Moore's law”, the three-dimensional through silicon via (TSV) packaging of stacked chips has become the focus of attention, providing fresh ideas for the industry. The preparation of insulators is one of the key technologies for TSV. However it is difficult for conventional methods to prepare SiO2 insulators with high coverage in TSV with small size and high aspect ratio. In addition, higher performance of TSV proposes a big challenge for SiO2. Organic polymers can replace SiO2 used as an insulator for TSV, because their lower dielectric constant can greatly improve the properties of TSV. Electrografting is a novel technology for polymer film preparation, which has the advantages of being simple, low cost and does not required special equipment.. In recent years, the modification of the Si surface with the electrochemical reduction of diazonium salts has become attractive because it can be performed in aqueous media, which is more acceptable for industrial applications. In the best understood reaction, a diazonium salt with an electrolyte such as tetrabutylammonium cations is reduced by an externally applied potential, typically at around −1 V versus the saturated calomel electrode. In our study, the electrografting technology is used to graft polymer film onto a Si surface, and its mechanism and the effects of pulsed voltage and composition of the solution are investigated. In the process of electrografting, 4-nitrobenzene diazonium (NBD) tetrafluoroborate is reduced by electrons provided by an electric source, forming nitrophenyl radicals. These radicals covalently bond to the Si surface to form a polynitrophenyl (PNP) primer layer, and initiate the polymerization of vinyl monomers. The radical-terminated polyvinyl chains formed in the solution and nitrophenyl radicals are then added to the aromatic rings of the primer layer to form the expected polyvinyl film. Consequently the grafted film is composed of PNP and the polymer of monomers. Furthermore, we propose an easier chemical grafting method based on the finding that diazonium salt can be spontaneously reduced at the Si surface when HF is present in the aqueous solution even without an externally applied potential., and study the influence factors of structure, morphology and component of the polymer film. This process is conducted in acidic aqueous media containing HF. From the mechanistic point of view, Si atoms at the Si surface are oxidized by HF, providing electrons for the reduction of NBD cations at the open circuit potential. The mechanism of the grafting of the polymer of monomers is the same as that of an electrografting process. The polymer films prepared by either the electrografting or chemical grafting methods have good adhesion, dielectric properties and thermal properties. Then the polymer film is applied in TSV. As far as we know, insufficient film thickness and low coverage are still serious problems for plasma-enhanced chemical vapor deposition methods. However, both electrografting and chemical grafting overcome these problems. In addition, the narrow diameter and high aspect ratio (≥1:10) are not limitations for grafting methods. Poly(methyl methacrylate) film has a coverage of 76%, while poly(acrylic acid) film has a coverage as high as 100%.

In Situ Spectroelectrochemical Studies into the Formation and Stability of Robust Diazonium-Derived Interfaces on Gold Electrodes for the Immobilization of an Oxygen-Tolerant Hydrogenase.

Surface-enhanced infrared absorption spectroscopy is used in situ to determine the electrochemical stability of organic interfaces deposited onto the surface of nanostructured, thin-film gold electrodes via the electrochemical reduction of diazonium salts. These interfaces are shown to exhibit a wide electrochemical stability window in both acetonitrile and phosphate buffer, far surpassing the stability window of thiol-derived self-assembled monolayers. Using the same in situ technique, the application of radical scavengers during the electrochemical reduction of diazonium salts is shown to moderate interface formation. Consequently, the heterogeneous charge-transfer resistance can be reduced sufficiently to enhance the direct electron transfer between an immobilized redox-active enzyme and the electrode. This was demonstrated for the oxygen-tolerant [NiFe] hydrogenase from the "Knallgas" bacterium Ralstonia eutropha by relating its electrochemical activity for hydrogen oxidation to the interface properties.

Phenylamide-oxime and phenylamide nanolayer covalently grafted carbon via electroreduction of the corresponding diazonium salts for detection of nickel ions

This study focuses on the covalent grafting of thin organic layers on a glassy carbon electrode by aryl diazonium salts containing functional groups capable of complexing Ni(II) ions. The goal was to develop a modified electrode for the detection of Ni(II) ions in aqueous media. The glassy carbon electrode (GCE) surface was modified by electrochemical reduction of diazonium salts synthesized in-situ in aqueous acid medium from 4-amino-benzamide (4-AB) and 4-amino-benzamide-oxime (4-ABO). XPS, AFM, ellipsometry and cyclic voltammetry were used for surface characterization of the grafted GCE. The barrier properties of the grafted layer were determined and compared by cyclic voltammetry, using Fe(CN)63−/4−, Ru(NH3)63+/2+ and dopamine redox probes in different pH media. The adsorptive properties of the grafted glassy carbon were compared for Pb(II), Cu(II) and Ni(II) cations. The ability of these modified GCE to detect Ni(II) ions was then explored using a two-step method: i) complexation of Ni(II) by the grafted layer, followed by ii) electroreduction of the complexed Ni(II) and then its analysis by anodic square wave voltammetry. The 4-ABO grafted glassy carbon electrodes were able to detect Ni(II) in micro-molar concentration. The presence of ions such as Pb2+, Mg2+, Ca2+, K+ and Na+ did not interfere with the Ni(II) quantification. The phenyl-oxime functionalized electrodes showed good robustness during more than fifty electroanalysis.

Direct on-chip DNA synthesis using electrochemically modified gold electrodes as solid support

DNA microarrays have propelled important advancements in the field of genomic research by enabling the monitoring of thousands of genes in parallel. The throughput can be increased even further by scaling down the microarray feature size. In this respect, microelectronics-based DNA arrays are promising as they can leverage semiconductor processing techniques with lithographic resolutions. We propose a method that enables the use of metal electrodes for de novo DNA synthesis without the need for an insulating support. By electrochemically functionalizing gold electrodes, these electrodes can act as solid support for phosphoramidite-based synthesis. The proposed method relies on the electrochemical reduction of diazonium salts, enabling site-specific incorporation of hydroxyl groups onto the metal electrodes. An automated DNA synthesizer was used to couple phosphoramidite moieties directly onto the OH-modified electrodes to obtain the desired oligonucleotide sequence. Characterization was done via cyclic voltammetry and fluorescence microscopy. Our results present a valuable proof-of-concept for the integration of solid-phase DNA synthesis with microelectronics.

Surface modification of CoCr alloys by electrochemical reduction of diazonium salts.

Tailoring the surface chemistry of CoCr alloys is of tremendous interest in many biomedical applications. In this work, we show that CoCr can be modified by diazonium electrografting provided the surface is not homogeneously covered with an oxide layer. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) show the electrografting of a poly(aminophenylene) (PAP) layer on CoCr when treated at a reductive potential (CoCr−0.5 V), whereas no PAP film was formed on CoCrOCP and CoCr1 V, treated at open circuit and anodic potentials respectively. Based on XPS results, we attributed the electrografting to the formation of carbide bonds between PAP and the inhomogeneous thin oxide layer of CoCr−0.5 V. We then show an example of application of PAP coatings on CoCr and prove that the presence of a PAP coating on CoCr−0.5 V results in a 5-fold increase of the adherence of poly methyl methacrylate (PMMA) to PAP-coated CoCr compared to uncoated samples; this is of prime significance to improving the long-term stability of dental prostheses. These findings support the importance of reducing the oxide layer for effective functionalization of metal oxides with aryl diazonium salts and suggest a promising surface modification approach for biomedical applications.

Multiplexed site-specific electrode functionalization for multitarget biosensors

Multitarget biosensors hold great promise to improve point-of-care diagnostics as they enable simultaneous detection of different biomolecular markers. Multiplexed detection of different markers, like genes, proteins, or a combination of both, propels advancement in numerous fields such as genomics, medical diagnosis and therapy monitoring. The functionalization of these biosensors, however, necessitates patterned immobilization of different bioreceptors, which remains challenging and time-consuming. We demonstrate a simple method for the patterned multiplexing of bioreceptors on a multi-electrode chip. By using the lithographically defined electrodes for surface functionalization, additional patterning steps become obsolete. Using the electrodes for self-aligned immobilization provides a spatial resolution that is limited by the electrode patterning process and that cannot be easily obtained by alternative dispensing or coating techniques. Via electrochemical reduction of diazonium salts combined with click chemistry, we achieved site-specific immobilization of two different ssDNA probes side by side on a single chip. This method was experimentally verified by cyclic voltammetry (CV), Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), and specific target recognition was visualized by fluorescence microscopy. The combination of the electroaddressability of electrografting with the chemoselectivity of click chemistry, offers a versatile platform for highly efficient site-specific functionalization of multitarget biosensors.

Electrografting and Controlled Surface Functionalization of Carbon Based Surfaces for Electroanalysis

AbstractThe basic concepts of electrografting on carbon surfaces are reviewed with the emphasis on the prospects of achieving robust, well‐defined compositions and structures of electrode interfaces. The surface functionalization allows tuning the interfacial properties which play an important role in various electrochemical applications, such as sensors and biosensors. Covalent attachment of organic compounds can be achieved by means of the electrochemical reduction of diazonium salts, and oxidation of amine or carboxylate. This review also demonstrates that the electrografting followed by a post‐functionalization is an interesting approach in the designs of well‐defined interface for electrochemical (bio)sensing.

Electrografted P4VP as Dielectric in High Aspect Ratio TSV: Surface Preparation and Thermomechanical Consideration

A challenge to most 3D integration approaches is the deposition of the Through-Silicon-Via (TSV) dielectric layer. A TSV is traditionally electrically insulated from the silicon substrate by a thin SiO2 film. As TSV aspect ratio gets higher, conformal SiO2 dielectric deposition becomes much more challenging. Alchimer has proposed as dielectric, the use of a highly conformal organic (poly-4-vinylpyridine, P4VP) as dielectric, electrografted through electrochemical reduction of diazonium salts in aqueous media. Surface cleaning prior to electrografting process is a challenge, especially in via last approach. Moreover, the thermomechanical behavior of P4VP coated TSVs remains unknown. This information is most relevant for the layout optimization of 3D integrated microsystems. We will discuss the TSV surface preparation challenge prior to the electrografting process and present the first measurements of the stress induced in the silicon substrate around TSV insulate by P4VP.

Grafting π-Conjugated Oligomers Incorporating 3,4-Ethylenedioxythiophene (EDOT) and Thiophene Units on Surfaces by Diazonium Electroreduction

The electrochemical reduction of diazonium salts, generated in situ, from 2-(4-aminophenyl)-3,4-ethylenedioxythiophene and two new amino functionalized π-conjugated oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) and thiophene units, has been investigated. It coats the electrodes (glassy carbon (GC), gold or ITO) with an ultrathin organic layer (less than 10 nm thickness). The X-ray photoelectron spectroscopy (XPS) investigations confirm the presence of the starting oligomers deposited on the surface. As an important result, EDOT-based oligomer grafting was achieved on those surfaces which may be of general use as adhesion primer layers in all devices using PEDOT type materials. Furthermore, the coating is electroactive and the electrochemical investigations exhibit redox signal at potentials close to that obtained for short oligoEDOT in solution. The electrochemical responses of the modified GC electrodes were further studied in the presence of various reversible redox probes, showing that the ...

Electrografted P4VP as Dielectric in High Aspect Ratio TSV: Surface Preparation and Thermomechanical Consideration

A key to most 3D integration approaches is the deposition of the Through-Silicon-Via (TSV) dielectric layer. A TSV is traditionally electrically insulated from the silicon substrate by a thin SiO2 film. As TSV aspect ratio is getting higher, conformal SiO2 dielectric deposition is getting harder. Alchimer has proposed a high conformal organic (poly-4-vinylpyridine, P4VP) as dielectric. This polymer is electrografted through electrochemical reduction of diazonium salts in aquous media. Although the electrografting process is well described in the literature [1, 2], electrical and thermomechanical properties of such material grafted onto silicon structure remain incomplete. This information is mandatory in order to optimize 3D integrated processor’s layout. Since electrografting mechanism is initiated from the surface [2], P4VP material properties and kinetic growth can vary with the surface preparation of the TSV. Results obtained on TSVs, with various surface preparations, insulated by electrografted P4VP suggest that the polymer is not only a good dielectric, but could allow a reduction of the Keep Out Zone (KOZ) size for a higher integration density. Furthermore, as P4VP is a viscoelastic material, its Young’s modulus is temperature dependent and dramatically drops down above its glass transition temperature. Such a material is particularly interesting to reduce stress as it can act as a buffer stress layer.We will present the study of electrical and thermomechanical properties of the electrografted P4VP dielectric realized on high aspect ratio TSV. We will discuss the impact of TSV surface preparation on the electrografting process and on the material properties of the P4VP grafted layer. Results will be compared to more conventional approaches based on a silicon oxide insulator. Acknowledgement Université de Sherbrooke, Natural Sciences and Engeeniring Research Council of Canada (NSERC), Institut National de la Recherche Scientifique (INRS), Teledyne Dalsa and Alchimer are gratefully acknowledged for their help and their financial support. Figure 1

New Method for Super Hydrophobic Treatment of Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells Using Electrochemical Reduction of Diazonium Salts.

The purpose of this article is to report a new method for the surface functionalization of commercially available gas diffusion layers (GDLs) by the electrochemical reduction of diazonium salt containing hydrophobic functional groups. The method results in superhydrophobic GDLs, over a large area, without pore blocking. An X-ray photoelectron spectroscopy study based on core level spectra and chemical mapping has demonstrated the successful grafting route, resulting in a homogeneous distribution of the covalently bonded hydrophobic molecules on the surface of the GDL fibers. The result was corroborated by contact angle measurement, showing similar hydrophobicity between the grafted and PTFE-modified GDLs. The electrochemically modified GDLs were tested in proton exchange membrane fuel cells under automotive, wet, and dry conditions and demonstrated improved performance over traditional GDLs.

Synthesis of conducting azopolymers by electrochemical grafting of a diazonium salt at polypyrrole electrodes

In this paper we report a new strategy for obtaining conducting azopolymers having pendant azobenzene moieties via functionalization of polypyrrole by electrochemical reduction of 4-[(4′-nitrophenyl)azo]benzenediazonium tetrafluoroborate (NABDBF4−). The functionalization of polypyrrole films with 4′-nitroazobenzene (NAB) groups has been evaluated by cyclic voltammetry and by spectroscopic techniques such as XPS, Raman and UV–vis spectroscopy. Moreover, the third-order nonlinear optical response of NAB-functionalized polypyrrole has been investigated using the optical third-harmonic generation technique. All these investigations confirmed the presence at the polymeric films surface of the functional groups introduced by the electrochemical reduction of diazonium salt. The versatility of this methodology allows not only the functionalization of polypyrrole-type materials with chromophore groups, but can also be successfully applied to other conjugated polymer systems in order to create various photoresponsive materials.

Post-Polymerization Electrochemical Functionalization of a Conducting Polymer: Diazonium Salt Electroreduction at Polypyrrole Electrodes

In this paper we report the functionalization of conductive polypyrrole (PPY) films via electrochemical reduction of the aryl diazonium salts in a manner that is similar to the one employed for other conductive surfaces. To understand the general trends of the grafting behavior of diazonium salts and to establish the optimal conditions for the covalent functionalization of the PPY films, we have compared the grafting behavior of four p-substituted phenyldiazonium salts: p-nitrophenyl diazonium tetrafluoroborate (PNBDBF4−), p-tolyl diazonium tetrafluoroborate (TDBF4−), p-fluorophenyl diazonium tetrafluoroborate (FPDBF4−) and 4-diazo-N,N-dimethylaniline tetrafluoroborate (DDMABF4−). The selection of the molecules to be grafted was done both for their electroactivity after grafting and the contrasted electronegativityof the substituents at the benzene ring. For all investigated diazonium salts, a linear relationship between their reduction potential at the PPY electrodes and Hammett substituent constants was obtained, suggesting a similar electrochemical reaction mechanism. The functionalization of the polypyrrole films has been evaluated using electrochemical methods like EQCM, CV and EIS. The presence at the polymeric films surface of the functional groups introduced by the electrochemical reduction of diazonium salts was evidenced also by XPS. This approach enables new functionalities on PPY that could otherwise not withstand the polymerization conditions.

Piezoelectric tuning fork probe for atomic force microscopy imaging and specific recognition force spectroscopy of an enzyme and its ligand

Piezoelectric quartz tuning fork has drawn the attention of many researchers for the development of new atomic force microscopy (AFM) self-sensing probes. However, only few works have been done for soft biological materials imaging in air or aqueous conditions. The aim of this work was to demonstrate the efficiency of the AFM tuning fork probe to perform high-resolution imaging of proteins and to study the specific interaction between a ligand and its receptor in aqueous media. Thus, a new kind of self-sensing AFM sensor was introduced to realize imaging and biochemical specific recognition spectroscopy of glucose oxidase enzyme using a new chemical functionalization procedure of the metallic tips based on the electrochemical reduction of diazonium salt. This scanning probe as well as the functionalization strategy proved to be efficient respectively for the topography and force spectroscopy of soft biological materials in buffer conditions.