Indium Tin Oxide Film Characteristics for Cathodic Stripping Voltammetry

Abstract

The combination of conductivity, optical transparency, and wide anodic potential window has driven significant interest in indium tin oxide (ITO) as an electrode material for electrochemical measurements. More recently, ITO has been applied to the detection of trace metals using cathodic stripping voltammetry (CSV), specifically manganese (Mn). However, the optimization of ITO fabrication for a voltammetric method such as CSV is yet to be reported, nor have the microstructural properties of ITO been investigated for CSV. Furthermore, CSV does not require optical transparency, thereby allowing nontransparent substrates to be used for deposition. This enables microfabrication procedures to be expanded and simplified compared to glass or quartz. Combining this with the profound importance of sensitive, selective detection of toxic metal ions in environmentally and biologically relevant samples makes ITO especially attractive. In this work, we report a thorough investigation of ITO deposition and processing on silicon (Si) substrates for CSV analysis using Mn as the model analyte. Several ITO process parameters were examined such as heated deposition and post-process annealing. Each ITO film was characterized using a variety of surface, bulk (X-ray diffraction), and electrochemical measurements. Although each ITO film type showed electrochemical activity, the heated and annealed (HA) ITO fabrication process yielded superior results for Mn CSV; a limit of detection (LOD) of 0.1 ppb (1.8 nM) was obtained. This work exemplifies new applications of ITO as an electrode material while providing a baseline for trace detection of toxic metals and other contaminants amenable to detection by CSV.

Post‐Transition Metal Electrodes for Sensing Heavy Metal Ions by Stripping Voltammetry

“…It was also reported that ITO could also be utilized for sensing manganese (Mn) species by CSV. [116] In this case, the annealing process could increase the grain size and enhance the crystalline structure. After obtaining the stripping voltammograms, it was concluded that annealed ITO electrodes were an optimum option to determine Mn(II) with a detection limit of 0.1 ppb.…”

“…ITO electrode modified with Au nanoparticles [114] Hg(II): 0.03 Water and soil samples Hg(II): 0.1-10 µg L −1 DPASV, pH: 2.0, E d and t d : 0.30 V for 300 s, E step : 4 mV ITO chip sensor modified with Au nanoparticles [115] Hg(II): 0.11 Lake water samples Hg(II): 0.63-80 ppb DPASV combined with online flow system, pH: 4.3, E d and t d : 0.60 V for 180 s, E step : 4 mV ITO on Si substrate electrode [116] Mn(II): 0.1 Chemical reagents Mn(II): 1-50 ppb CSV, pH: 5.0, E d and t d : 1.20 V for 180 s, E step : 4 mV ITO coated with polystyrene-blockpoly(ethylene-ran-butylene)-blockpolystyrene-sulfonate (SSEBS) [117] Mn(II): 0.060 Water samples Mn(II): 18-1800 nm CSV, pH: 5.0, E d and t d : 1.20 V for 180 s, E step : 5 mV…”

Monitoring the Electrochemical Failure of Indium Tin Oxide Electrodes via Operando Ellipsometry Complemented by Electron Microscopy and Spectroscopy

“…Especially for the utilization in bioelectronics and photoelectrocatalysis purposes, contact with an electrolytic environment demands the characterization of an inert electrochemical potential window . Since ITO is already in an oxidized form, the positive potential window is large . However, multiple cathodic reduction pathways at negative potential are possible depending on the electrolyte specifications, where reductive degradation is promoted under acidic conditions and rather inhibited in a basic environment. − Acidic chemical degradation has been reported even at solid interfaces. , Typically, this leads to a visible darkening of the ITO layer caused by the reductive formation of metallic indium and tin nanoparticles and, finally, a loss of electrical conductivity.…”

Modulating Mechanism of the LSPR and SERS in Ag/ITO Film: Carrier Density Effect

“…17 Therefore, the ITO film exhibits a higher carrier density and a wider optical band gap (above 3.5 eV). 18 Doping of the foreign metal Ag into an ITO film can not only maintain the basic properties of the ITO film but also effectively tune the carrier density and improve some characteristics, such as electrical and optical characteristics. 19 Ag/ITO was cosputtered on a 2D ordered polystyrene (PS) template (a schematic of the preparation of the cosputtered Ag/ITO film is shown in Supporting Information (SI) Figure S1).…”

“…The introduction of defects forms a shallow donor or impurity level near the conduction band and provides free electrons . Therefore, the ITO film exhibits a higher carrier density and a wider optical band gap (above 3.5 eV) . Doping of the foreign metal Ag into an ITO film can not only maintain the basic properties of the ITO film but also effectively tune the carrier density and improve some characteristics, such as electrical and optical characteristics …”