Platinum Thin Films Research Articles

Voltammetric determination of iron(III) using sputtered platinum thin film

A sputtered platinum thin film was fabricated by using photolithography, sputtering, and a lift-off method. The sputtered Pt grains were uniformly dispersed in the film as observed from FE-SEM images to form a compact film with fairly homogeneous size. Square wave voltammetry was used to directly detect Fe(III) with this electrode, typically at a working potential of 0.63 V (vs. Ag/AgCl). The method had a 90 ppb detection limit and worked in the 0.3–5 ppm concentration range. This value meets the requirements set by the World Health Organization. In addition, the stability and reproducibility of the electrode were superior (with RSDs of 3.363% for 5 repetitive measurements). For real tap and well water samples, the electrode gave the well-defined peak for Fe(III) without showing any enrichment in Fe(III). The results from real water analyses were in agreement with those obtained by the UV–Vis method.

Formation of Highly Ordered Platinum Nanowire Arrays on Silicon via Laser-Induced Self-Organization

Laser-induced periodic surface structures (LIPSS) provide an elegant solution for the generation of highly ordered periodic patterns on the surface of solids. In this study, LIPSS are utilized for the formation of periodic platinum nanowire arrays. In a process based on laser-stimulated self-organization, platinum thin films, sputter-deposited onto silicon, are transformed into nanowire arrays with an average periodicity of 538 nm. The width of the platinum nanowires is adjustable in a range from 20 nm to 250 nm by simply adjusting the thickness of the initial platinum thin films in a range from 0.3 nm to 4.3 nm. With increasing width, platinum nanowires show a rising tendency to sink into the surface of the silicon wafer, thus indicating alloying between platinum and silicon upon LIPSS-formation by a nanosecond-pulsed laser. The Pt/silicon wires may be etched away, leaving a complementary nanostructure in the silicon surface.

Electroreduction of oxygen on Nafion®-coated thin platinum films in acid media

Electrocatalytic oxygen reduction reaction (ORR) kinetics on vacuum-evaporated thin platinum films in sulfuric acid solution is thoroughly investigated employing the rotating disc electrode (RDE) method. The nominal thickness of the Pt films is varied from 0.25 to 20nm and the effect of applied Nafion® layer on the ORR activity in 0.5M H2SO4 solution is evaluated. The electroactive surface area of Pt and the corresponding overall ORR activity decreases with the nominal film thickness. An increase in the hydrogen peroxide yield and a decrease of the ORR specific activity of Pt with decreasing the film thickness is also observed. The Nafion® coating slightly increases the hydrogen peroxide production, but does not affect the electrocatalytic activity of Pt. The results obtained with the model system employed herein are important for elucidating the influence of Nafion® layer on the ORR kinetics on Pt-based electrocatalysts.

Electrochemical Stability of Thin-Film Platinum as Suitable Material for Neural Stimulation Electrodes.

Only thin-film technology can satisfy the requirements of high spatial selectivity at high-channel-count electrode array designs by simultaneously good conformability to the targeted tissue through mechanical flexibility enriching future applications of functional neural stimulation. However, caused by the high impact of the microstructure on the mechanical and electrochemical film properties, varying fabrication processes of the same thin-film makes the difference between acute and chronic long-term stable electrodes. The influence of standard clinical electrical pulsing on flexible polyimide-based thin-film platinum electrodes for neuroprostheses, either sputter deposited or evaporated, and different diameters was assessed and compared. The electrochemical and morphological analysis showed a higher corrosion susceptibility and electrochemical degradation for the sputter deposited platinum electrodes with even total failures of smaller diameters. In contrast, the evaporated thin-films provided itself as more stable and reliable metallization with also smaller electrodes keeping their film integrity intact over the experimental period, -appearing to be the preferable material for improving thin-film electrodes' longevity.

Design, Fabrication, and Characterization of a Compact Hierarchical Manifold Microchannel Heat Sink Array for Two-Phase Cooling

High-heat-flux removal is critical for the next-generation electronic devices to reliably operate within their temperature limits. A large portion of the thermal resistance in a traditional chip package is caused by thermal resistances at interfaces between the device, heat spreaders, and the heat sink; embedding the heat sink directly into the heat-generating device can eliminate these interface resistances and drastically reduce the overall thermal resistance. Microfluidic cooling within the embedded heat sink improves the heat dissipation, with two-phase operation offering the potential for dissipation of very high heat fluxes while maintaining moderate chip temperatures. To enable multichip stacking and other heterogeneous packaging approaches, it is important to densely integrate all fluid flow paths into the device; volumetric heat dissipation emerges as a performance metric in this new heat sinking paradigm. In this paper, a compact hierarchical manifold microchannel design is presented that utilizes an integrated multilevel manifold distributor to feed coolant to an array of microchannel heat sinks. The flow features in the manifold layers and microchannels are fabricated in silicon wafers using deep reactive-ion etching. The heat source is simulated via Joule heating using thin-film platinum heaters. The on-chip spatial temperature measurements are made using four-wire resistance temperature detectors. The individual manifold layers and the microchannel-bearing wafers are diced and bonded into a sealed stack via thermocompression bonding using gold layers at the mating surfaces. Thermal and hydrodynamic testing is performed by pumping the dielectric fluid HFE-7100 through the device at a known flow rate, temperature, and pressure at different levels of chip heat input. A volumetric heat density of up to 2870 W/cm3 is dissipated at a chip temperature less than 112 °C and microchannel pressure drop less than 27 kPa. The overall pressure drop is governed by flowing through the manifold, rather than the microchannels, in this compact heat sink that occupies envelope of 5 mm $\times 5$ mm $\times2.3$ mm including all the functional flow features.

Oxidative addition of 1,4‐dichloro‐2‐butyne to an organoplatinum complex: A new precursor for synthesis of ultrasmall Pt nanoparticles thin film at liquid/liquid interface as the electrocatalyst in methanol oxidation reaction

In this study, the usage of ClCH2CCCH2Cl alkyne as a reagent for the oxidative addition reaction with organoplatinum‌(II) complex [PtMe2(bipy)] (1), in which bipy = 2,2′‐bipyridine to give a mixture including of trans‐[PtClMe2(CH2CCCH2Cl)(bipy)] (2a) and a cis‐[PtClMe2(CH2CCCH2Cl)(bipy)] (2b) complexes is reported. Kinetic study was investigated by monitoring the disappearance of the metal‐to‐ligand charge transfer (MLCT) band in the UV–Vis spectra. 1H NMR experimental results confirmed that trans isomer (2a) is more stable than its corresponding cis isomer. A liquid–liquid planar interface has been employed as a template for self‐assembly of platinum nanoparticles. The as prepared complex was applied for the synthesis of platinum thin film that characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy dispersive analysis of X‐rays (EDAX), field emission‐scanning electron micrographs (FE‐SEM) and elemental mapping. The electrocatalytical activity of Pt thin film was investigated in methanol oxidation reaction.

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 µm diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

Water-mediated photo-induced reduction of platinum films.

Platinum thin films activated ex situ by oxygen plasma become reduced by the combined effect of an intense soft X-ray photon beam and condensed water. The evolution of the electronic structure of the surface has been characterized by near-ambient-pressure photoemission and mimics the inverse two-step sequence observed in the electro-oxidation of platinum, i.e. the surface-oxidized platinum species are reduced first and then the adsorbed species desorb in a second step leading to a surface dominated by metallic platinum. The comparison with measurements performed under high-vacuum conditions suggests that the reduction process is mainly induced by the reactive species generated by the radiolysis of water. When the photon flux is decreased, then the reduction process becomes slower.

Rapid antibiotic susceptibility testing by resazurin using thin film platinum as a bio-electrode

Traditional antibiotic susceptibility testing methods take several days to confirm and start disease treatment. The lack of new antibiotics or drugs warrants a need for optimization of current diagnostic tools for immediate antibiotic susceptibility testing. We present a rapid screening method to evaluate the response of bacteria to antibiotics based upon the electrochemical measurement of live bacterial cell metabolic activity using an electroactive redox dye, resazurin. A thin film of Pt deposited over a glass substrate using the direct current sputtering technique was used as a working bio-electrode for electrochemical readouts. X-ray diffraction and scanning electron microscopy was carried out to characterize the Pt thin film. We tested the efficacy of the method using two different strains, Klebsiella pneumoniae (ATCC-700603) and Escherichia coli (ATCC-25922), against ampicillin, kanamycin and tetracycline. The dye, on incubation with viable bacteria, undergoes reduction and lowers the corresponding peak current value. However, in the presence of an effective antibacterial agent, reduction did not occur due to bacterial cell death and absence of a reducing environment. The electrochemical changes in peak current values were monitored using the differential pulse voltammetry technique and interpretation of the results obtained was based upon changes in peak current values. Our results depict a new methodology where a concentration of 104 cells/mL cells can be detected in less than 4 h. The results were also compared with the conventional disc diffusion method for susceptibility testing which has a bacterial incubation time of 18–24 h. The method can potentially be used for monitoring the susceptibility of bacterial strains towards existing antibacterial agents in an easy, rapid, reliable and inexpensive manner without any pre-cultivation of bacteria.

Fabrication of Piezoelectric Platforms for Studying Strain in Electrocatalysis

The fabrication of piezoelectric supports for straining thin film electrodes using standard photolithography, sputter coating, and atomic layer deposition is detailed. An interdigitated array on the back of single crystal lithium niobate piezoelectric substrates allows large electric fields to be applied to strain thin films on the front of the device. A thin metal oxide insulating layer prevents electronic communication between the electrode of interest and the underlying piezoelectric. Platinum thin films (<10 nm) can be sputtered and annealed to produce quality electrodes. Microelectrode arrays can be patterned on the electrode via another oxide layer or insulating resist. The various challenges of fabricating and testing these devices as well as future prospects are discussed.

Piezoelectric Electric Supports Modulate the Reactivity of Platinum Thin Films

The oxygen reduction reaction (ORR) is at the heart of many renewable energy technologies. This kinetically slow reaction requires large overpotentials even on the best catalysts like platinum and its alloys. Numerous studies have employed strained platinum surfaces to change oxygen adsorbate binding energies and lower the ORR overpotential, though strain is often convoluted with electronic effects from alloying with other metals. Additionally, discrete samples offer only one static strain condition, making testing of multiple surface configurations costly. We present a piezoelectric platform capable of generating dynamic strain on thin film platinum catalysts without unwanted electronic effects due to alloying. Application of various voltages to an interdigitated array on the piezoelectric drives the mechanical deformation of the platinum thin film, resulting in significant increases in ORR activity and up to 10 mV lower overpotentials. The applied mechanical strain is reversible, and reactivity changes are not resultant from electronic communication between the piezoelectric and electrode, temperature increases, or local field effects. This new analytical platform opens new opportunities for studying strain effects in electrocatalysis.

(Invited) Stationary Phase Coatings for a Microfabricated GC Column Integrated with Low Power Ion Trap Mass Spectrometer for Analysis of Volatile Organic Compounds

Miniature gas chromatography (GC) columns of length 6m were fabricated in silicon using eutectic bonding to achieve a column with improved temperature control. The micro GC column includes an integrated platinum thin film heater and temperature sensors for closed loop temperature programing. In order to achieve low power operation the GC column was mounted inside the vacuum chamber of an ion-trap mass spectrometer. This approach provides much lower power consumption than a laboratory instrument. The ion trap electronics were miniaturized and operate at lower power, to demonstrate a portable instrument able to operate at with less than 25W, including vacuum pumps. This instrument will have a range of applications from environmental monitoring, to food safety and medical diagnostics, including breath analysis. Static coating of the stationary phase in the microfabricated column was carried out by injection using a solvent and extraction at reduced pressure to improve resolution. This paper reports the results of different stationary phases investigated to separate mixtures of volatile organic compounds, specifically OV-1 and OV-215. The properties of the stationary phases where characterized using a novel probe mixture for microcolumn evaluation and six McReynolds probes to identify the Kovats indices and the polarity of the column. The dependence of polarity on the coating technique and temperature of the column during analysis was also investigated. Results are presented with both an FID and ion-trap mass spectrometer to achieve rapid temperature programmed analysis of mixtures of up to 18 organic compounds.

Sandwiched Platinum Thin Film TCD for 3-Omega Technique for Detection of Ammonia Gas

Over the past few decades, sensor technology has been revolutionized by exploring the disciplines of nanotechnology and nanofabrication process. As a result, environmental sensors including gas sensors have been miniaturized and become more advanced in the terms of sensitivity and accuracy. Todays, gas sensors can cover a broader range of volatile compounds with a limit of detection (LOD) as low as single ppm. Despite these advances, ammonia sensing is still challenging because of its corrosive nature. The chemical-based gas sensors for ammonia are not reliable due to several factors such as slow recovery time, sensor base-line drifting, vulnerability to degradation and false alarm [1]. On the other hand, physical-based ammonia sensing approaches have the advantage of fast response time and long-term durability [2]. The Thermal Conductivity Detector (TCD) limit of detection has been improved to 30 ppm by making use of the 3-omega measurement technique, however the sensor requires a robust geometrical design, and careful material selection to withstand the higher temperature during operation [3,4]. To enhance LOD further, a new design including design elements which eliminates the shortcomings in the current cantilever design. The temperature difference in the deposition process for Al203 and platinum layer causes the sensor to bend away from the silicon wafer surface, and be vulnerable to fluid velocity. Hence a supporting platinum layer has been added underneath of Al2O3 layer so that thermal stresses introduced during fabrication, and generated in operation are compensated. The new design of micro wire TCD also includes optimized shape to bear the high thermal stresses caused by continuous current needed for the 3-omega measurement technique, and a higher stability of the temperature coefficient of resistance with platinum film to improve reproducibility of response. [1] Azad, A. M., Akbar, S. A., Mhaisalkar, S. G., Birkefeld, L. D., & Goto, K. S. (1992). Solid‐state gas sensors: A review. Journal of the Electrochemical Society, 139(12), 3690-3704. [2] Mahdavifar, A., Navaei, M., Hesketh, P. J., Dimandja, J. D., Stetter, J. R., & McMurray, G. (2015). Implementation of a polysilicon micro electro-thermal detector in gas chromatography system with applications in portable environmental monitoring. ECS Journal of Solid State Science and Technology, 4(10), S3062-S3066. [3]Lotfi, Ardalan, Milad Navaei, and Peter J. Hesketh. "A Platinum Cantilever-Based TCD for 3-Omega Sensing of Gas Mixtures." ECS Transactions 86.16 (2018): 79-86. [4] Lotfi, A., Mahdavifar, A., Struk, D., Stetter, J. R., Navaei, M., & Hesketh, P. (2017). Ultimate Sensitivity of Physical Sensor for Ammonia Gas Detection Exploiting Full Differential 3-Omega Technique. ECS Transactions, 80(10), 1571-1578 Figure 1

Electro-mechanical properties of multilayered aluminum nitride and platinum thin films at high temperatures

In this study, the electro-mechanical properties of multilayered thin films consisting of 10 bi-layers of 7 nm aluminum nitride (AlN) and 3 nm platinum (Pt) are investigated in the as deposited state and after different post deposition annealing steps. The multilayers are deposited using direct current magnetron sputtering on thermally oxidized silicon wafers or sapphire substrates and are annealed in Ar atmosphere at 800, 900 and 1000 °C up to 24 h. The electro-mechanical properties are characterized from room temperature up to 500 °C using Van-der-Pauw as well as gauge factor measurements. Furthermore, transmission electron microscopy and energy dispersive X-ray analyses are used to investigate the microstructure and the chemical composition of the multilayers before and after thermal loading. The influence of the annealing on the crystalline structure is examined by X-ray diffraction analyses. Annealing in this high temperature range causes an intermixture of the individual Pt and AlN sub-layers as well as a recrystallization of the Pt thin films. Annealing the multilayered thin film system at 900 °C for 1 h in Argon atmosphere results in a multilayer which is electrically stable up to 500 °C in air and which exhibits a 3 times lower temperature coefficient of resistance at a similar gauge factor when compared to pure Pt thin films.

Rapid, Low-Temperature Growth of Sub-10 nm Silica Nanowires through Plasma Pretreatment for Antireflection Applications

Silica nanowires were rapidly grown at the Pt–Si eutectic temperature (830 °C) through active oxidation. Because a silica source with a high amount of SiO is required for high solubility in a small droplet, we developed a plasma treatment that was conducted on a platinum thin film prior to nanowire growth to incorporate a high amount of silica source into the droplets. After the samples were pretreated with hydrogen and argon plasma, sub-10 nm silica nanowires were successfully grown through 1.8 nm Pt thin films on silicon wafers. This is an effective method to grow thin nanowires on nanopillars with low surface reflection at low temperatures.

Synthesis and utilization of platinum(II) dialkyldithiocarbamate precursors in aerosol assisted chemical vapor deposition of platinum thin films as counter electrodes for dye-sensitized solar cells

A facile and cost effective AACVD procedure for the synthesis of platinum thin films has been reported using newly synthesized Pt-dialkyldithiocarbamate complexes, [Pt(S2CNR2)] (where R = isobutyl, iBu (1); benzyl, Bz (2)), as single source precursors. The structural characterization of the dithiocarbamate complexes has been performed by single crystal X-ray diffraction, 1H and 13C NMR, FT-IR and thermogravimetric analysis. The structure, composition, and morphology of the resulting Pt-films is established through XRD, XPS, EDX and FE-SEM analyses. The catalytic performance of the as-synthesized Pt-films is evaluated by using them as counter electrodes in dye sensitized solar cells as an example application. The efficiency of the AACVD produced electrodes is found to be better than conventionally used Pt-counter electrodes made from the doctor blade’s method. It is also demonstrated that films having a well-connected and defect free surface topography show better catalytic performance, which is due to their high conductivity and reflectivity. Thus a simple and low cost method employing dithiocarbamate precursors is manifested to be immensely efficient in generating Pt-films and electrodes of tremendous applicability.

Electrical Properties of Ultrathin Platinum Films by Plasma-Enhanced Atomic Layer Deposition

The ability to deposit thin and conformal films has become of great importance because of downscaling of devices. However, because of nucleation difficulty, depositing an electrically stable and thin conformal platinum film on an oxide nucleation layer has proven challenging. By using plasma-enhanced atomic layer deposition (PEALD) and TiO2 as a nucleation layer, we achieved electrically continuous PEALD platinum films down to a thickness of 3.7 nm. Results show that for films as thin as 5.7 nm, the Mayadas–Shatzkes (MS) model for electrical conductivity and the Tellier–Tosser model for temperature coefficient of resistance hold. Although the experimental values start to deviate from the MS model below 5.7 nm because of incomplete Pt coverage, the films still show root mean square electrical stability better than 50 ppm over time, indicating that these films are not only electrically continuous but also sufficiently reliable for use in many practical applications.

Dynamic calibration of temperature sensors from light rays for transient measurement

Measurement of transient heat fluxes in the applications involving very short duration of a heating environment which has been promised for the candidate by measurement of surface heating rates with thin film gauges (TFG). They are basically resistance temperature detectors having to measure in a very short duration of time. In the present study, a platinum based TFG has been fabricated and dynamically calibrated (radiation based) in the laboratory with a view to assessing the performance of platinum thin film gauges (PTFG) in the dynamic environment. These examinations are focusing to explore the probability of using TFG for small duration transient measurements with pure radiation mode of heat transfer. Radiation based heat flux is applied on the gauge by using the halogen bulb in a square box and its response is obtained through measured transient temperature. Subsequently, the surface heat fluxes are estimated by using radiation-based heat transfer. The purpose of this work is to statically calibrate each handmade heat transfer gauges by using quartz as substrate material deposited on platinum paste. This experiment has been carried out by oil bath based experimental technique. The similar experimental environment is also studied to observe the transient temperature response by using numerical simulation. The experiments are carried out by exposing the platinum TFG to various known step heat load of known input wattage, for the duration of 10 seconds. Then, the voltage signals are recorded due to change in temperature of air-flow past the TFG. The numerical simulation (ANSYS-Fluent v. 14.5) is performed in the similar experimental environmental conditions, for the same heating loads. Experimentally recorded temperature signals from the gauges are compared with simulated temperature histories obtained through finite element analysis. Cubic spline methods of the 1-D heat conduction equation are used to predict surface heat flux and compared with input heat loads. The presently developed calibration set-up is seen to very useful for radiation-based measurements of TFG.

Photoinduced Hall Effect for Low-Temperature Magnetic Sensing

Some low-temperature magnetic sensors are based on the Hall effect in thin metallic films. However, their sensitivity is more than one order of magnitude smaller than that of silicon-based Hall sensors operating at room temperature. Furthermore, in order to avoid significant Joule heating, only very small bias currents can be injected at low temperatures. Here, we show that a sensor based on a photoinduced Hall effect, in which charge is photogenerated in a semiconductor and injected into an adjacent metallic layer, can be used as a bias-free, cryogenic sensor. The system consists of a platinum thin film deposited on intrinsic-silicon substrate. The film forms a Schottky interface with the semiconductor. At room temperature, carriers photogenerated in the semiconductor are injected into the metal, because of rounding-off of the Schottky barrier, and are deflected by a magnetic field applied in the film plane. At cryogenic temperatures, and well below the freeze-out temperature for silicon, the photogenerated electrons can tunnel through the barrier, and the sensor recovers the same sensitivity as that obtained at room temperature.

Piezoresistive granular metal thin films of platinum–boron nitride and platinum–alumina at higher strain levels

Granular metal thin films have a strain sensitivity much larger than continuous metal films. Experiments at high strain can help reveal their piezoresistive mechanisms. We deposit films of platinum nanoparticles in boron nitride (Pt:BN) as well as platinum particles in aluminum oxide (Pt:Al2O3) on polyimide foil as strain gauges. Under low strain of 0.1%, the films exhibit enhanced gauge factors, k=23 for Pt:BN and k=6 for Pt:Al2O3. Toward higher strain of 1.5%, Pt:BN shows reproducible and linear resistance-strain curves. In contrast, Pt:Al2O3 exhibits anomalies: The resistance-strain curves are highly nonlinear with an increasing slope before reaching saturation. The differential gauge factor versus strain increases from 9 to 9500, and the return curve shows large hysteresis. With scanning electron microscopy unstrained and in situ strained films are compared, Pt:BN shows no changes, whereas in Pt:Al2O3, large cracks develop. The relatively soft BN is less prone to cracks than the hard and brittle Al2O3. Hence, the gauge factor in Pt:BN can still be attributed to an electron tunneling mechanism, whereas Pt:Al2O3 becomes dominated by the influence of cracks. A model is presented, and we argue that the reproducible opening and closing of these cracks leads to the gigantic resistance increases at high strain.