Electrochemical Quartz Crystal Microbalance Measurements Research Articles

The use of EQCM for setting the optimum conditions of the determination of Pd2+ ions via its palladium–histidine complex

Electrochemical quartz crystal microbalance (EQCM) was used as a novel approach for the determination of palladium–histidine complex formation on an amalgam film gold based electrode. We have demonstrated the applicability of an amalgam-modified gold QCM substrate to monitor histidine adsorption and palladium ions complexation under electrochemical control. The results of EQCM measurements revealed that adsorption of histidine on amalgam film gold based electrode is dependent on the potential, indicating that the electrosorption occurs which depends on the charge on the gold–mercury surface and the charge of the histidine ions. The interactions of palladium ions with the adsorbed layer of histidine at open circuit potential results in the removal of histidine from mercury surface, indicating stronger bonds between histidine and palladium than between histidine and mercury. On the other hand, by applying the potential of −200 mV upon the introduction of palladium ions it is possible to obtain histidine-palladium complex adsorbed on the mercury surface. This phenomenon was used for the determination of Pd using adsorptive stripping voltammetry (AdSV). Application of the deposition potential indicated by EQCM led to well defined analytical signals increasing with standard addition.

Influence of Acetic Acid on the Integrity and Protectiveness by an Iron Carbonate (FeCO3) Corrosion Product Layer

The effect of undissociated acetic acid on the integrity of an iron carbonate (FeCO3) layer formed on platinum and X65 steel substrates is investigated. Experiments were conducted using buffered solutions with 0.8 mM to 5 mM undissociated acetic acid. For the platinum substrates, changes in the FeCO3 layer were monitored via in situ electrochemical quartz crystal microbalance (EQCM) measurements. This investigation was supported by performing electrochemical experiments, under comparable conditions, on the X65 steel specimens, linking the integrity of FeCO3 layer to its corrosion protection effect. The EQCM measurements revealed that the addition of acetic acid, at all concentrations tested here, caused partial dissolution of the FeCO3 layer. The dissolution occurred selectively, with the outer layer dissolving first, leaving behind an inner FeCO3 layer at the end of the immersion experiment. The electrochemical results revealed that introducing the acetic acid caused a sudden increase in the corrosion rate, which over time returned to a lower value similar in magnitude to that seen before addition of the acetic acid. This was attributed to the protection provided by the inner FeCO3 layer, which was only mildly affected by the addition of acetic acid and was able to repair over time. It was proven that the dissolution of the protective FeCO3 layer in the presence of acetic acid was not due to a small pH change but rather due to the formation of ferrous acetate complexes and changes in ionic strength, which decreases the FeCO3 saturation values.

Passivation Behavior of Aluminum in a Carbonate-Free Electrolyte Based on Lithium Bis(fluorosulfonyl)imide and Sulfolane

Carbonate-free electrolytes comprising lithium bis(fluorosulfonyl)imide (LiFSI) and sulfolane (SL) (LiFSI/SL) with medium concentrations show excellent cycle stabilities with high Coulombic efficiencies. The high Coulombic efficiencies indicate that there is no corrosion of aluminum current collectors despite the absence of LiPF6. X-ray photoelectron spectroscopy and electrochemical quartz crystal microbalance measurements show that the passivation layer on the aluminum current collector in LiFSI/SL consists of LiF and sulfurous species. The study findings will expand the applicability range of lithium-ion batteries, the current mainstay of sustainable energy sources.

Electrodeposition of a Novel Ternary Fe–W–Zn Alloy: Tuning Corrosion Properties of Fe–W Based Alloys by Zn Addition

Herein, we report the electrodeposition of a novel ternary Fe–W–Zn alloy. Ternary alloys with compositions of Fe–(29.08–35.96 at.%) W–(1.73–8.16 at.%) Zn were prepared by potentiostatic deposition in citrate–ammonia aqueous solution equipped with an anode chamber. The electrodeposition behavior of the ternary Fe–W–Zn alloys and the effect of the Zn addition were analyzed by cyclic voltammetry and in situ electrochemical quartz crystal microbalance measurements. Ternary alloys with glossy appearances and smooth surface morphologies were fabricated, with a maximum current efficiency of approximately 43%. Incorporating Zn into the Fe–W alloy structure transformed the alloy structure into an amorphous-like nanocrystalline structure and refined the crystal size to a minimum of 1.45 nm. Potentiodynamic polarization test results showed that the corrosion resistance of the ternary Fe–W–Zn alloy with approximately 2 at.% Zn was distinctly improved compared to the binary Fe–W alloy, both in 1 M H2SO4 solution and neutral 3 mass% NaCl solution. Notably, the corrosion resistance was even better than Ni–W alloy in 1 M H2SO4 solution, with its unique passivation behavior. The incorporation of Zn was found to be effective for tuning the corrosion properties of Fe–W alloys.

Towards Estimating the Effect of SO3- Adsorption on the ORR in Pt (111)

Optimizing proton exchange membrane fuel cells (PEMFC) performance is crucial in order to attain sustainable commercialization. A major part of the issue involves understanding the role of Nafion in the catalyst layer. Nafion’s behavior on bulk mode has been extensively reported in the literature, though on ultra-thin layer mode (<20nm) its structural arrangement which dictates the transport properties highly depends on the type of substrate interfacing [1]. In PEMFC catalyst layers, Nafion covers carbon-supported platinum aggregates on ultra-thin layer mode. In these composite layers, Nafion works as a binder for the aggregates, at the same time as it is meant to ensure pathways for protons and let arrive to the catalyst surface.At high current densities, a steep performance drop is usually observed in PEMFC operation. A part of this drop is reported to be due to activation losses as a doubling of the Tafel slope is observed [2]. The origin of this Tafel slope doubling has been subject of multiple studies. Understanding the causes requires understanding the phenomena occurring at the electrode/electrolyte interface. A technique which is commonly employed is cyclic voltammetry (CV) as it can provide insights regarding these interactions.Comparative CV studies on monocrystalline platinum Pt (111) in a PFSI solution and solution exhibit distinct features, where oxide formation appears to be inhibited at the beginning of this range for PFSI [3]. These CV studies coupled with electrochemical quartz crystal microbalance (EQCM) measurements showed that when extending the potential range to 1.4V and holding the potential at 1.1V (place-exchanged oxide formation range) a large mass gain at 0.5V emerges. The origin of these features is found to be due to strongly adsorbed sulfonate groups on the platinum surface. Other works validate this behavior [4], where sulfonate groups are found to be adsorbed in both the double layer region (0.4-0.5V) and in the hydroxyl adsorption region (0.6-0.85V).In this work, the continuum model proposed by Huang et al. [5] is coupled with a reaction framework comprising multistep mechanism [6]. The adsorption of SO3- is expected to follow a Langmuirian behavior [7], indicating that the oxygen reduction reaction (ORR) is hindered through site blocking. For the adsorption of on Pt(111) a single electron transfer mechanism is assumed [8]. Kinetic parameters are obtained by fitting the model’s response to experimental data as in [6].The simulations allow quantifying the adsorption of sulfonate groups on the platinum surface and estimating its impact on the ORR.

(Invited) Molecular Models for Electrodeposition Inhibitors, Suppressors, and Anti-Suppressors

We evaluate the effect of chain length for a series of alkyl sulfonic acid additives on Cu electrodeposition by using a combination of electrochemical and Raman spectroscopic methods. The combination of these methods suggests that effective Cu electrodeposition acceleration processes require: 1) direct tethering of mercaptoalkylsulfonate species to the electrode, 2) partial desolvation of Cu2+ by the sulfonate group to minimize its solvent reorganization energy, and 3) stabilization of Cu+ adjacent to the electrode surface by addition of halide. Finally, we use the cis-trans ratio idea developed for SPS to examine the effect of inhibitors on SPS activity.We also investigate the behavior of Cu plating bath suppressor additives poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) using normal Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and electrochemical quartz crystal microbalance (QCM) measurements. Raman and SERS show a clear spectroscopic trend of increased intensity in higher wavenumber modes in the CH stretching region as the environment is changed from pure material to solution to surface for both PEG and PPG. The spectral changes associated with PEG are larger than those associated with PPG, suggesting that the relatively more hydrophilic PEG undergoes more conformational changes upon surface association relative to the more hydrophobic PPG. In the presence of Cl-, PPG forms a denser surface layer compared to PEG on a Cu underpotential deposition (UPD) layer on Au. These differences are consistent with the increased hydrophobicity of PPG relative to PEG.

An electrically switched ion exchange film with molecular coupling synergistically-driven ability for recovery of Ag+ ions from wastewater

An electrically switched ion exchange film with molecular coupling synergistically-driven ability for the selective recovery of Ag+ ions is developed by coupling a conducting polypyrrole (PPy) with a 2, 2ʹ-dithiosalicylic acid (DTSA) at molecular scale. The rapid and selective uptake/release of Ag+ ions by this hybrid film was found to be realized by the electrochemical circulation of the PPy ↔ PPyn+ as well as the disulfide ↔ dithiolate and the recognition ability of the carboxyl groups and disulfide bonds of DTSA. As a result, the recovery of Ag+ ions can be handily achieved by adjusting the operating potential applied on the hybrid film coated electrode. The electrochemical quartz crystal microbalance measurements combined with the cyclic voltammetric technique, X-ray photoelectron spectroscopy and density functional theory computations were performed to identify the uptake/release mechanism of the hybrid film. Furthermore, the uptake capacity of the hybrid film maintained almost invariable after 10 consecutive uptake/release cycles, and the regeneration rate of Ag+ ions remained over 80% in each cycle. It is expected that such an electroactive hybrid film can be applied for the recovery of Ag+ ions from various industrial discharges.

Investigation on inhibition of ruthenium corrosion by glycine in alkaline sodium hypochlorite based solution

Removal of Ru by etching in alkaline sodium hypochlorite (NaClO) based solution is carried out. The glycine on the corrosion of Ru in NaClO based solution is systematically investigated. The results show that in the alkaline NaClO solution, glycine is a good corrosion inhibitor for Ru. Through electrochemical measurements, electrochemical quartz crystal microbalance (EQCM) and X-Ray photoelectron microscopy (XPS) measurements, it is found that the glycine adsorption isotherm on the Ru surface follows TEMKIN’s model. Glycine can not only adsorb on the Ru surface to inhibit the corrosion of Ru, but also promote the dissolution of the formed oxide layer through complexing action. Finally, we use glycine and NaClO for chemical mechanical polishing (CMP) of the Cu/Ru interconnect structure and the removal rate selectivity of Cu and Ru can be adjusted to 1:1.

Deuterium Isotope Effects Upon the Redox‐switching of the Viscosity of DNA Layers Observed by Electrochemical Quartz Crystal Micro‐balance

AbstractWe report on H/D isotope effects observed upon quick redox‐switching of the viscoelasticity of self‐assembled monolayers of single‐stranded DNA (ssDNA‐SAM) observed by electrochemical quartz‐crystal micro‐balance (EQCM) of three redox‐active small molecules that travel through the DNA layer on gold electrodes. We have recently reported hexammine cobalt(III) (CoHex) to have the largest voltammetric isotope effect while hexammine ruthenium(III) (RuHex) does not show this effect. Daunomycin, on the other hand showed a significant redox potential shift up to −80 mV. A thin‐layer model may explain this voltammetric behavior. RuHex covers the negatively charged DNA strand and provides considerable conductivity, while CoHex and daunomycin do not. Latest results regarding the reproducible frequency responses indicate considerable isotope effects also in EQCM measurements depending on the redox molecule interacting with the ssDNA‐SAM. These effects will provide new opportunities in drug screening and studies of DNA damage by toxic chemicals.

Electrochemical reduction mechanism of NbF5 and NbCl5 in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate

The electrochemical reduction mechanism of niobium was studied in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][OTf]) containing niobium halides (NbCl5 and NbF5). The influence of the electrolyte composition, temperature, and nature of the substrate were systematically investigated. In situ electrochemical techniques, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical quartz crystal microbalance (EQCM) and rotating ring disc electrode (RRDE), were used, besides the ex situ characterization techniques scanning electron microscopy (SEM) and vibrational spectroscopy. The number of transferred electrons was estimated from the half width of the cathodic peaks in the DPV measurements. Furthermore, the product of the diffusion coefficient and the number of transferred electrons at the power of 3/2 were evaluated from RRDE measurements to be approx. 3 × 10−10 m2/s. Thicker and better adherent niobium-based deposits were obtained from NbCl5 in [BMP][OTf] than from NbF5 in [BMP][OTf]. EQCM measurements combined with DPV indicated the potential region where niobium-based deposits could be obtained as well as their stoichiometry.Vibrational spectroscopy reveals that NbF5 and NbCl5 interact differently with [BMP][OTf]. The spectra show that in the case of NbF5 – [BMP][OTf] only niobium(V) anionic species [NbF6A]2- and [NbF5A]- (where A = [OTf]-) are formed, while in NbCl5 – [BMP][OTf] both niobium(V) and niobium(IV) anionic species are present. At low NbCl5 concentrations, [NbCl4A2]2- and [NbCl4A2]- are obtained, while at high NbCl5 concentration, [NbCl5A]2- and [NbCl5A]- are found. The electrochemical niobium reduction mechanism depends on temperature and on the anionic species that are involved in the reduction process. In the case of NbCl5 – [BMP][OTf], at high cathodic potentials the formation of subvalent Nb-clusters (possibly Nb6Cl14) was observed.

Effects of transition metal cation additives on the passivation of lithium metal anode in Li–S batteries

The effect of additives of transition metal cations (Zn2+, Cu2+, Co2+, Ni2+, and Mn 2+) on the passivation of lithium metal anode in Li–S batteries was investigated. The effects of transition cation additives on improving rate capability and Coulombic efficiency were observed in the following order: Zn2+ > Cu2+ > Co2+ > Ni2+ > Mn2+ > no salt. With Zn additives, less-accumulation of sulfur and smoother surfaces were observed using Scanning Electron Microscope (SEM) compared to that without additives. The result is consistent with Electrochemical Quartz Crystal Microbalance (EQCM) measurement, where less increase in mass changes of the anode for Zn additive as compared to Cu and no additive. The findings can be attributed to transition metal sulfides deposited on lithium surface cooperate with lithium sulfide and electrolyte decomposition product resulting in a smoother and more robust solid electrolyte interphase (SEI) films. The enhanced homogeneity of passivation layer greatly hinders the parasitic reactions between lithium metal and polysulfides as well as organic electrolyte, reducing the loss of active material and improving Coulombic efficiency. On the other hand, the uniform and mechanically strong SEI film introduces less undesired lithium plating and further accumulation on active sites, which significantly enhance the long-term stability due to improved surface morphology and chemistry. The results of this study provide a facile method of in-situ chemical formation of passivation layer protecting the lithium metal in batteries.

Label-free electrochemical immunosensor for quick detection of anti-hantavirus antibody

This report describes the preparation and evaluation of an immunosensor based on chemical modification of gold surface with hantavirus (strain Araucaria) antigen/protein and the antibody detection by electrochemical analysis. The viral nucleoprotein was immobilized onto gold by SAM formation with 3-mercaptopropionic acid (MPA) followed by activation of the surface using N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and N-Hydroxysuccinimide (EDC/NHS). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM) measurements were used for evaluation of each step involved in the construction of the proposed immunosensor. Several experimental conditions were studied and after optimization of immobilization parameters, the device showed good stability within 21days and selectivity for a qualitative detection of specific antibody (IgG) directed against hantavirus Araucaria. The proposed sensor had shown a linear response for concentration varying between 0.400 and 300μgmL−1 allowing its application in spiked serum samples for detection of specific antibody of hantavirus Araucaria based on a cutoff value. The immunosensor showed a sensitive response to the spiked samples and can be employed as an alternative for the qualitative diagnosis of hantavirus infections.

Tuning Charge Storage Properties of Supercapacitive Electrodes Evidenced by In Situ Gravimetric and Viscoelastic Explorations.

Revealed by an integrated electrogravimetric and viscoelastic method, slightly electrochemically reduced graphene oxide (ERGO) presents an anion preference for charge storage and delivery, while with the progressive removal of oxygen functionalities on its basal planes, cations begin to predominate in charge compensation. This "anion-to-cation" evolution in neutral aqueous media can not only affect the electrochemical charge storage, but also play an important role in electrode's viscoelasticity. It was demonstrated that oxygen functionalities could modify the interactions between graphene layers and even contribute to pseudocapacitances. However, the role of oxygen functionalities in species transfer and viscoelastic variations still remains poorly understood. Herein, a combined methodology of electrochemical quartz crystal microbalance (EQCM), ac-electrogravimetry and electroacoustic impedance measurements was proposed for characterizing the electrochemical and viscoelastic responses of graphene oxides with various degree of electrochemical reduction. With the removal of oxygen containing functional groups, ERGO electrode exhibits ( i) a gradually enhanced specific capacitance ( Cs) with increased flexibility (decreased storage moduli, G'); ( ii) a dehydration process of cations (i.e., from Na+·2H2O to Na+·H2O); and ( iii) a potential-dependent "stiffened-softened" behavior. These results open the door for a suitable design of GO-based materials for electrochemical energy storage and shed light on electronic devices where ion-selective behavior plays a key role.

Suppression of Copper Electrodeposition by PEG in Methanesulfonic Acid Electrolytes

We investigate the suppression behavior of poly(ethylene glycol) (PEG) in methanesulfonic acid (MSA) Cu plating baths using electrochemical methods, normal Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and electrochemical quartz crystal microbalance (QCM) measurements. Suppression of Cu electrodeposition by PEG in H2SO4 electrolytes only occurs in the presence of Cl−, whereas Cl− is not required in MSA electrolytes. SERS measurements of MSA electrolytes without PEG at a Cu surface show MSA molecules undergo a re-orientation at ca. −0.15 V vs. Ag/AgCl, as evidenced by potential-dependent symmetry changes. The re-orientation of MSA in MSA + PEG electrolyte does not occur until −0.3 V vs. Ag/AgCl. At potentials negative of −0.3 V, MSA re-orients and PEG leaves the surface, in coordination with onset of Cu reduction current, suggesting the suppression interaction of PEG at a Cu surface is facilitated by MSA. QCM measurements demonstrate a similar departure of PEG mass at potentials negative of the MSA re-orientation.

The Critical Role of pH Gradient Formation in Driving Superconformal Cobalt Deposition

Conventional damascene electroplating uses a combination of organic additives, namely, a suppressor, an accelerator, and a leveler, to achieve superconformal fill of interconnects. This work demonstrates an alternative mechanism that produces bottom-up cobalt deposition through a combination of pH and suppressor gradient formation within the patterned features. The fill mechanism was investigated using voltammetric and electrochemical quartz crystal microbalance measurements. The results show that local pH affects both the deposition rate and the current efficiency for cobalt deposition, which, combined with the kinetic effects of suppressor-type additives, drive a plating rate differential between the field and the feature-bottom. By appropriately selecting solution concentrations, organic additives, the waveform, and the mass transport conditions, void-free superconformal cobalt fill can be achieved in a variety of features.

The incorporation of drug molecules with poor water solubility into polypyrrole as dopants: Indomethacin and sulindac

There is considerable interest in the development of polypyrrole–based drug delivery systems. However, it is not possible to incorporate drugs with limited water solubility into polypyrrole from the usual aqueous–based electropolymerisation solutions. In this study, two drugs with poor solubility in water, sulindac and indomethacin, were incorporated within polypyrrole films as dopants from an ethanol–containing electropolymerisation solution to give PPyIndo and PPySul. An organic perchlorate salt was added to the electropolymerisation solution and the resulting perchlorate dopant anions were released initially on reducing the PPyIndo and PPySul at −0.70 V vs SCE. The drug molecules were then re–doped in the absence of the perchlorate salt. On reduction of the polymer films the sulindac and indomethacin were released into an aqueous saline solution, giving approximately 0.12 mg cm−2 of sulindac and 0.29 mg cm−2 of indomethacin over a 60 min release period. The greater amounts of indomethacin released from PPyIndo were explained in terms of higher doping levels. The doping levels of indomethacin and sulindac were estimated at 0.28 and 0.10, respectively, using electrochemical quartz crystal microbalance measurements.

On the Contrasting Effect Exerted by a Thin Layer of CdS against the Passivation of Silver Electrodes Coated with Thiols

The passivation of metal electrodes covered by self-assembled monolayers of long-chain thiols is well known. The disappearance of the voltammetric peak of redox species in solution is a classical test for the formation of full layers of thiols. Similar studies on semiconductors are still very limited. We used silver surfaces covered by an ultrathin layer of CdS as substrate for self-assembling of n-hexadecanethiol (C16SH), and we compared the experimental results with those obtained by using the bare silver surface as substrate. The strong insulating effect of C16SH deposited on Ag(III) is shown by the inhibition of the voltammetric peak of Ru(NH3)63+/2+. On the contrary, the voltammogram obtained on CdS-covered Ag(III) is very similar to that obtained on the bare Ag(III) electrode, thus suggesting that the presence of CdS exerts a contrasting effect on the passivation of the silver electrode. A crucial point of our work is to demonstrate the effective formation of C16SH monolayers on Ag(III) covered by CdS. The formation of full layers of C16SH was strongly suggested by the inhibition of the stripping peak of Cd from the CdS deposit covered by C16SH. The presence of C16SH was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements as well as by Auger electron spectroscopy (AES) analysis.

Interaction of 3D Conductive Polymer-Reticulated Vitreous Carbon Composites in Ionic Liquid As Energy Storage Material

Energy storage technologies, which combine high specific energy and power with sustainability and low costs, are fundamental drivers for an energy sustainable society. Conductive polymers in highly stable and non-toxic ionic liquid (IL) electrolytes have been proposed as possible systems that combine these advantages. Recently, it has been demonstrated that poly(3,4-ethylenedioxythiophene) (PEDOT) can undergo a redox reaction like in a battery and at the same time perform the characteristics of a capacitor by being doped/charged (de-doped/discharged) by anions from the IL. The storable amount of charges depends on the generated doping/de-doping sites in the polymer, which is a function of the electrode potential. These so called “hybrid-battery-capacitor” system combines the faradaic and capacitive properties in a single electrode [1,2], providing the possibility to improve cell voltages and energy densities. High surface area materials such as three-dimensional conductive reticulated vitreous carbon (RVC) substrate, provide large surface area for electro-polymerisation of a thin film nano/micro-porous PEDOT active material (“footprint-area” [3]). The resulting composite has large capacitance supported by the rigid carbon substrate which helps to stabilise the typical swelling/contraction process observed in conducting polymers during the electrochemical charge/discharge process. This study focuses on the synthesis and characterisations of thin electro-active PEDOT films on RVC substrates by electro-polymerisation in IL. The polymer synthesis produced a uniform film on the RVC with a high number of doping/de-doping sites in Lewis neutral 1-ethyl-3-methylimidazolium chloride aluminum chloride (EMImCl-AlCl3) IL with AlCl4 - as doping/de-doping anion. The interaction of the conductive polymer films with the ionic liquid electrolyte are characterised by combined in-operando atomic force microscopy (AFM) and electrochemical quartz crystal microbalance measurements (EQCM), distinguishing the predominant battery or capacitor behaviour per doping/de-doping site and the correlated changes of the polymer structure as function of the electrode potential. [1] Chemical Reviews 110 (2010) 4724–4771. [2] Chemical Society Reviews 44 (2015) 1777–1790. [3] Advanced Materials 26 (2014) 2440–2445. Graphical abstract: (A-C) PEDOT electro-polymerised on RVC and (D) schematic illustration of the three-dimensional RVC-PEDOT composite, which is doped (charged) and de-doped (discharged) with AlCl4 - anions of a chloroaluminate ionic liquid. Figure 1

Anion-Dependent Doping and Charge Transport in Organic Electrochemical Transistors

We study the effects of different electrolyte anions on the mixed ionic/electronic transport properties of organic electrochemical transistors (OECTs) based on poly(3-hexylthiophene-2,5-diyl). We show that the transport properties depend on the anion present in the electrolyte, with greater source-drain currents resulting from the use of molecular anions such as hexafluorophosphate and trifluoromethanesulfonylimide than from the use of smaller atomic anions such as fluoride or chloride. Using spectroelectrochemistry, we show the maximum doping level that can be achieved in an aqueous environment is also anion-dependent. Furthermore, we find that the average electronic carrier mobility at a given doping level depends on the chemistry of the compensating counterion. We further investigate this dependence by electrochemical quartz crystal microbalance measurements, showing the solvation of the dopant anions within the polymer is drastically different depending on the choice of the anion. Surprisingly, we fin...

In Situ Atomic Force Microscopy and Electrochemical Quartz Crystal Microbalance Studies on the Electrodeposition and Oxidation of Silicon

In this paper, we investigated how the anion of an ionic liquid (IL) affects nanostructure of electrode/electrolyte interface and subsequently the deposition process of silicon. For this purpose, ILs with the same cation 1-butyl-1-methylpyrrolidinium and various anions, namely, tris(pentafluoroethyl) trifluorophosphate ([Py1,4]FAP), bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSA), and bis(fluorosulfonyl)amide ([Py1,4]FSA) were chosen. Cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) were used to study the electrochemical processes. Raman spectroscopy and in situ atomic force microscopy (AFM) were used to evaluate the changes in the ILs on addition of SiCl4 and to probe the changes in the Au (111)/electrolyte interface, respectively. From cyclic voltammetry and EQCM measurements, it was found that the electrochemical processes changed significantly on changing the anion. However, from Raman spectroscopy a few spectral changes related to vibrational modes of the employed anions were...