Platinum Oxide Films Research Articles

Structural and electrical properties of Pt film fabricated by laser scanning and reduction of its oxide film

A thin platinum (Pt) oxide film was deposited on a polypropylene substrate, and a part of the film was removed and reduced by a laser scanning process using a commercially available apparatus. A Pt film that is electrically isolated from the surroundings was successfully obtained, and the potential of using it as a thermometer was demonstrated by measuring its resistance as a function of temperature in the vicinity of RT. The results indicate that a device structure (thermometer) can be prepared using a Pt oxide film, which is applicable when using a flexible substrate.

Post-annealing effect of thin platinum oxide film on tin oxide film for an application enhancing gas sensitivity

A thin platinum oxide film was stacked on a tin oxide film, a well-known gas-sensing semiconductor, to improve its gas sensitivity. The response property to ethanol gas was enhanced by about three times by the stacking annealed at 600 °C. Post-annealing, platinum oxide was reduced to platinum and tin oxide was in a polycrystalline state. The results indicate that applying platinum oxide is effective in improving sensitivity when annealing at a high temperature of 600 °C is required for the fabrication of gas sensors.

Influence of Chlorine Oxyacid on the Electrooxidation of Methanol in Strong Acid

An electrochemical oxidation of methanol in a strong acid solution was investigated at a polycrystalline platinum electrode in the presence of different concentrations of hypochlorite. The addition of a slight amount of hypochlorite brought about drastic increase in the oxidation current of methanol, because the presence of hypochlorite inhibited the formation of a platinum oxide film on platinum electrodes. However, the oxidation current of methanol decreased with increasing the concentration of coexisting hypochlorite. The result may be due to i) the enhancement of the methanol adsorption to the surface of platinum electrodes by the inhibition of the formation of oxide film, and ii) the inhibition of methanol adsorption on platinum electrodes by higher concentration of NaClO and chemical compounds generated by the chemical reaction between methanol and increased hypochlorite.

Preparation and electrocatalytic property of three‐dimensional nano‐dendritic platinum oxide film

Platinum oxide electrode, as an important part of hydrogen concentration monitoring sensor built in containment, needs to withstand extreme conditions such as high temperature, high humidity, and high irradiation and can still work normally even in the case of serious accidents, which puts forward higher requirements for its performance. In present study, platinum oxide film electrode was successfully prepared with three‐dimensional nano‐dendritic, uniform, and crack‐free on platinum substrate by reactive magnetron sputtering, and the influence of different substrate temperature and sputtering atmosphere on the composition, morphology, and electrocatalytic property of the film was investigated. The results show that platinum oxide film is composed of PtO and PtO2. As the temperature increases from room temperature (RT) to 200°C, the oxygen vacancies in the amorphous film are gradually repaired and convert to the crystalline state, which shows increasing PtO2 ratio, increasing electrochemical active area (ECSA), and improved stability. When the temperature is rising to 400°C, the film shows decreasing oxygen vacancies, increasing average grain size. Because PtO2 decomposes into PtO and Pt, and thus ECSA decreases, the stability and oxygen reduction activity of the films decreases gradually. At the same temperature, the crystalline film obtained in Ar/50%O2 has higher concentration of oxygen vacancies and smaller average grain size than that obtained in O2, resulting in larger ECSA and relatively good stability. By contrast, the platinum oxide film electrode prepared in Ar/50%O2 and 200°C has better stability and excellent electrocatalytic activity for oxygen reduction.

Performance-Enhanced Non-Enzymatic Glucose Sensor Based on Graphene-Heterostructure.

Non-enzymatic glucose sensing is a crucial field of study because of the current market demand. This study proposes a novel design of glucose sensor with enhanced selectivity and sensitivity by using graphene Schottky diodes, which is composed of graphene (G)/platinum oxide (PtO)/n-silicon (Si) heterostructure. The sensor was tested with different glucose concentrations and interfering solutions to investigate its sensitivity and selectivity. Different structures of the device were studied by adjusting the platinum oxide film thickness to investigate its catalytic activity. It was found that the film thickness plays a significant role in the efficiency of glucose oxidation and hence in overall device sensitivity. 0.8–2 μA output current was obtained in the case of 4–10 mM with a sensitivity of 0.2 μA/mM.cm2. Besides, results have shown that 0.8 μA and 15 μA were obtained by testing 4 mM glucose on two different PtO thicknesses, 30 nm and 50 nm, respectively. The sensitivity of the device was enhanced by 150% (i.e., up to 30 μA/mM.cm2) by increasing the PtO layer thickness. This was attributed to both the increase of the number of active sites for glucose oxidation as well as the increase in the graphene layer thickness, which leads to enhanced charge carriers concentration and mobility. Moreover, theoretical investigations were conducted using the density function theory (DFT) to understand the detection method and the origins of selectivity better. The working principle of the sensors puts it in a competitive position with other non-enzymatic glucose sensors. DFT calculations provided a qualitative explanation of the charge distribution across the graphene sheet within a system of a platinum substrate with D-glucose molecules above. The proposed G/PtO/n-Si heterostructure has proven to satisfy these factors, which opens the door for further developments of more reliable non-enzymatic glucometers for continuous glucose monitoring systems.

Optimization of Platinum dioxide properties by plasma oxidation of sputtered PtOx

We have previously used reactively sputtered Platinum oxide thin film as DNA sensing element. In this work, we subject the reactively sputtered Platinum oxide thin films to an additional RIE step for 3, 6 and 9 min and carry out a detailed comparative study of the material and electrical properties of these films. XRD and XPS analysis revealed that when the reactively sputtered Platinum oxide film was subjected to RIE step for longer periods of time, it became progressively α-PtO2 in nature. Activation energies of 0.24 eV, 0.26 eV, 0.29 eV and 0.31 eV were obtained for the as deposited film and the films subjected to RIE step for 3, 6 and 9 min respectively. The Hall mobility of the as deposited Platinum oxide film was found to be 32.15 cm2V−1s−1 at room temperature. However, when the as deposited film was subjected to RIE step for 9 min the mobility value rises to as high as 136.13 cm2V−1s−1 at room temperature.

Functionalization-Free Microfluidic Electronic Tongue Based on a Single Response.

Electronic tongues (e-tongues) are promising analytical devices for a variety of applications to address the challenges of quality control in water monitoring and industries of foods, beverages, and pharmaceuticals. A crucial drawback in the current e-tongues is the need to recalibrate the device when one or more sensing units (usually with modified surface) are replaced. Another downside is the necessity to perform subsequent surface modifications and analyses to each of the diverse sensing units, undermining the simplicity and velocity of the method. These features have prevented widespread commercial use of the e-tongues. In this paper, we introduce a microfluidic e-tongue that overcomes all such limitations. The key principle of global selectivity of the e-tongue was achieved by recording only a single response, namely, the equivalent admittance spectrum of an association of resistors in parallel. Such resistors consisted of five nonfunctionalized stainless steel microwires (sensing units), which were short-circuited and coated with gold, platinum, nickel, iron, and aluminum oxide films. The microwires were inserted in a chip composed of a single piece of polydimethylsiloxane (PDMS). Using impedance spectroscopy, the e-tongue was successfully applied in classification of basic tastes at a concentration below the threshold for the human tongue. In addition, our chip allowed the distinction of various chemicals used in oil industry. Finally, our cleanroom-free prototyping allows the mass production of chips with easily replaceable and reproducible sensing units. Hence, one can now envisage the widespread dissemination of e-tongues with fast and reproducible data.

A Polarity Switching Technique for the Efficient Production of Sodium Hypochlorite from Aqueous Sodium Chloride Using Platinum Electrodes

A novel, periodic polarity-switching technique is developed for the electrolytic production of sodium hypochlorite from aqueous sodium chloride. The technique employs a flow-through cell having two identical platinum electrodes. Polarities of these electrodes are periodically swapped. The main purpose of this step is to prevent the growth of platinum oxide film and thereby retain high initial activity of the electrodes throughout the operation. The performance of this mode of operation is evaluated using the cumulative productivity and current efficiency of the cell as indicators. Typical ranges of parameters used are as follows: concentration of Cl– ions, 0.1–0.5 M; switching frequency, 0.01–1 Hz; and current density, 100–700 A m–2. The productivity of the switching mode is 5–6 times higher and its current efficiency is 15%–20% higher than that of the DC mode. The switching frequency has a strong influence on both the cumulative production rate and the average current efficiency and an optimal switching ...

Study of the formation and quick growth of thick oxide films using platinum nanoelectrodes as a model electrocatalyst.

We report a study of the formation and quick growth of thick films of platinum oxide on platinum nanoelectrodes at low anodic potentials. Here, structurally well-defined platinum nanoelectrodes are used as a model platform for nanoscale platinum electrocatalysts. Platinum films are formed on the surface of the nanoelectrode upon application of a constant anodic potential in an acidic environment for an extended time period. A current spike is initially observed, which is attributed to capacitance charging, the oxidation of water, and the initial oxidation of the platinum surface. A finite residual current follows the initial current spike, which is composed of both water oxidation and the oxidation of platinum metal concealed beneath the growing oxide layer. These films are observed to be structurally irreversible, grow to be relatively thick, and protrude out of the glass insulating material encasing the nanoelectrode due to the added volume of the oxygen incorporated into the growing platinum oxide film. Once reduced, the platinum metal remains protruding out of the glass, and its presence is confirmed by both SEM imaging and cyclic voltammetry. Steady-state voltammetric data shows a finite increase in the diffusion-limited faradaic current of the nanoelectrode, relative to the initial steady-state current, after the oxidation/reduction of the platinum which is due to an increased area of the protruding platinum metal. A minimum apparent rate of ∼1.2 nm/min can be calculated for the growth of the platinum oxide film. The use of platinum nanoelectrodes has shown several distinct advantages in this study, including better control of the size and morphology of the individual electrocatalysts, the ability to image using electron microscopy, and the ability to use voltammetry to evaluate the geometry of the electrode quickly.

Amperometric Nitric Oxide Sensors with Enhanced Selectivity Over Carbon Monoxide via Platinum Oxide Formation Under Alkaline Conditions

An improved planar amperometric nitric oxide (NO) sensor with enhanced selectivity over carbon monoxide (CO), which represents a volatile interfering species for NO sensors that has been largely overlooked until recently, is described. Formation of an oxide film on the inner platinum working electrode via anodic polarization using an inner alkaline electrolyte solution provides the basis for improved selectivity. Cyclic voltammetry reveals that formation of an oxidized Pt film inhibits adsorption of CO to the electrode surface, which is a necessary initial step in the electrocatalytic oxidation of CO on Pt. Previous NO gas sensors that employ internal electrolyte solutions have been assembled using acidic internal solutions that inhibit the formation of a dense platinum oxide film on the working electrode surface. It is demonstrated herein that increasing the internal electrolyte pH promotes oxidized platinum film formation, resulting in improved selectivity over CO. Selectivity coefficients (log KNO,j) for sensors assembled with internal solutions at various pH values range from -0.08 at pH 2.0 to -2.06 at pH 11.7, with average NO sensitivities of 1.24 nA/μM and a limit of detection (LOD) of <1 nM.

Thermal decomposition and fractal properties of sputter-deposited platinum oxide thin films

Abstract

ChemInform Abstract: Early Stages of Growth of Hydrous Platinum Oxide Films

Abstract The growth of thin hydrous Pt oxide (β-oxide) films by the rapid potential cycling method has been examined in detail, β-oxide formation commences in only a few cycles of potential to an extent which is dependent on the sweep rate used during oxide growth. Its properties, as gauged by the shape and position of the reduction peak, vary significantly after ca. 20–30 cycles of potential and then become constant. The compact α-oxide, which is present along with the β-oxide at all times, can be reduced and reformed in potential sweep experiments, as well as thickened under potentiostatic conditions in the presence of the β-oxide film, exactly as at a bare Pt electrode surface. This confirms that the α-oxide lies beneath a porous β-oxide film. In addition, the kinetics of Fe 2+ oxidation at a β-oxide covered electrode has been investigated. The inhibition of this reaction by the oxide, as well as its other electrochemical properties, support the notion that the β-oxide is a solvent-filled, highly porous, polymer-like material.

Fabrication and characterization of implantable and flexible nerve cuff electrodes with Pt, Ir and IrOx films deposited by RF sputtering

This paper presents the fabrication and characterization of implantable and flexible nerve cuff electrodes for neural interfaces using the conventional BioMEMS technique. In order to fabricate a flexible nerve electrode, polyimide (PI) was chosen as the substrate material. Then, nerve electrodes were thermally re-formed in a cuff shape so as to increase the area in which the charges were transferred to the nerve. Platinum (Pt), iridium (Ir) and iridium oxide (IrOx) films, which were to serve as conducting materials for the nerve electrodes, were deposited at different working pressures by RF magnetron sputtering. The electrochemical properties of the deposited films were characterized by electrochemical impedance spectroscopy (EIS). The charge delivery capacities of the films were recorded and calculated by cyclic voltammetry (CV). The deposited films of Pt, Ir and IrOx have strong differences in electrochemical properties, which depend on the working pressure of sputter. Each film deposited at 30 mTorr of working pressure shows the highest value of charge delivery capacity (CDC). For the IrOx films, the electrochemical properties were strongly affected by the working pressure as well as the Ar:O2 gas ratio. The IrOx film deposited with an Ar:O2 gas ratio of 8:1 showed the highest CDC of 59.5 mC cm−2, which was about five times higher than that of films deposited with a 1:1 gas ratio.

Surface Ionization Gas Detection on Platinum and Metal Oxide Surfaces

Surface ionization (SI) gas detection experiments have been performed on platinum (Pt) and metal oxide (MOX) films. The probability of surface ion emission varies with temperature in an Arrhenius-type manner. Among all hydrocarbons studied so far those with amine functional groups exhibited the lowest activation energies allowing detection in the ppm concentration range at emitter operation temperatures of about 400degC. All other kinds of hydrocarbons could not be detected under these same conditions, not even if their concentrations were as high as 1% or 2%. Under high-temperature conditions (~800degC), this kind of selectivity breaks down and solid-state SI emitters start to behave in a similar way as flame ionization detectors, allowing detection of a much wider range of hydrocarbon species. Emitter materials with surface morphologies in the nanometer range were found to form much more efficient ion emitters than emitters with smooth surfaces.

Remote Plasma ALD of Platinum and Platinum Oxide Films

Platinum and platinum oxide films were deposited by remote plasma atomic layer deposition (ALD) from the combination of (methylcyclopentadienyl)trimethylplatinum precursor and plasma. A short plasma exposure (0.5 s) resulted in low resistivity , high density , cubic Pt films, whereas a longer plasma exposure (5 s) resulted in semiconductive films. In situ spectroscopic ellipsometry studies revealed no significant nucleation delay, different from the thermal ALD process with gas which was used as a benchmark. A broad temperature window for remote plasma ALD of Pt and was demonstrated.

Atomic Layer Deposition of Platinum Oxide and Metallic Platinum Thin Films from Pt(acac)2 and Ozone

Platinum oxide and platinum thin films have been grown by atomic layer deposition (ALD) using Pt(acac)2 (acac = acetylacetonato) and ozone as precursors. Amorphous platinum oxide thin films were deposited at 120 and 130 °C while metallic platinum films were obtained at 140 °C and above. The sublimation temperature of Pt(acac)2 set the low temperature limit for oxide film deposition. The platinum oxide films were successfully deposited on Al2O3 and TiO2 adhesion layers, soda lime glass, and silicon substrate with native oxide on top. Platinum films were grown on Al2O3 adhesion layer. The platinum oxide had good adhesion to all tested surfaces, whereas metallic platinum films did not pass the common tape test. Resistivities of 50−60 nm thick platinum oxide films were between 1.5 and 5 Ω cm at 130 °C and could be varied with both precursor pulse lengths. The resistivity of about 110 nm thick metallic film deposited at 140 °C was about 11 μΩ cm. The platinum films deposited at higher temperatures suffered from deterioration of thickness uniformity. The platinum oxide films can be reduced in 5% H2 gas under reduced pressure at room temperature to porous platinum structures.

Remote Plasma and Thermal ALD of Platinum and Platinum Oxide Films

Platinum and platinum oxide films were deposited using thermal and remote plasma ALD. The combination of MeCpPtMe3 precursor and O2 gas or a short (0.5 s) O2 plasma exposure resulted in high purity, low-resistivity (15 microOhm cm), high-density (21 g/cm3), cubic platinum films. The combination of MeCpPtMe3 precursor with a longer (5 s) O2 plasma exposure resulted in semi-conductive PtO2 films with a band gap of ~1.5 eV. The long nucleation delay observed with the thermal process could be overcome by using the remote plasma process where atomic oxygen is provided from the gas phase. The ALD process dependence on substrate temperature was investigated, where both the thermal and the remote plasma Pt process revealed a temperature window from 200 C to 300 C and the remote plasma PtO2 process had a temperature window from 100 C to 300 C.

Remote Plasma and Thermal ALD of Platinum and Platinum Oxide Films

not Available.

Internal Structure of a Molecular Junction Device: Chemical Reduction of PtO2 by Ti Evaporation onto an Interceding Organic Monolayer

We present a physical and chemical characterization study of molecular electronic junctions previously shown1,2 to display tunable hysteric electrical switching behavior useful for nanoscale memory and logic circuitry applications.3-6 X-ray photoelectron spectroscopy (XPS) data were acquired from the internal buried interfaces in a series of related device structures. This was accomplished using a new technique based on stripping (delaminating) the molecular device stacks at the molecular layer for XPS examination in ultrahigh vacuum (UHV). These data reveal that evaporative deposition of titanium onto the organic monolayers in these junctions results in the chemical reduction of the 2.5 nm platinum oxide film underlying the monolayers. This understanding allows us to construct an improved model for the internal chemical structure of these electrically well-studied molecular junctions, and to suggest a new model for how the evaporation of titanium as the top contact in molecular electronic devices prevent...

Plasma-produced ultra-thin platinum-oxide films for nanoelectronics: physical characterization

We present a detailed experimental characterization of ultra-thin platinum-oxide films formed on metallic Pt surfaces using O2 plasma treatment. A monotonic consumption of the metallic Pt by the O2 plasma is demonstrated by electrical resistance measurements of micron-wide, ultra-thin metallic Pt wires for the range of O2 plasma exposure times explored in this study. Conversely, angle-resolved X-ray photoelectron spectroscopy (AR-XPS) of the plasma-treated Pt reveals that the oxide layer formed on the Pt surface maintains a constant thickness over these exposure times. In combination, these data demonstrate that the O2 plasma treatment of Pt simultaneously forms and etches an ultra-thin platinum-oxide layer on the Pt surface. In addition, the AR-XPS data also reveals the oxide layer to be composed of two different platinum–oxygen compounds. Detailed analysis demonstrates a stratified structure for the ultra-thin platinum oxide, with the oxide ‘bulk’ being composed of PtO2, likely with PtO defects, and the exposed oxide surface being Pt(OH)y≈2 terminated after exposure to ambient conditions. The potential utility of using plasma oxidization to form ultra-thin platinum (or other metal) oxide films on nanoscale metal structures for nano- and molecular-electronic applications is discussed, along with other promising applications in technologies such as sensors and catalysts.