Atomic Layer Deposition Of Platinum Research Articles

Near-perfect broadband metamaterial absorbers of truncated nanocones using colloidal lithography

Broadband optical absorbers are significant for applications in solar energy harvesting, thermal emitters, and infrared detection. Broadband solar absorbers should have the advantages of broad solar spectrum utilization, good thermal stability, easy large-area fabrication, polarization independence, and insensitivity to incident angle. In this work, the ultra-broadband absorption of metallic truncated nanocones in the ultraviolet–visible–near-infrared spectral region is reported. The average absorptivity in the wavelength range of 100–2500 nm is 96.11%, and greater than 96% absorptivity can be continuously maintained in the range of 160–1470 nm. The results of a finite-difference time-domain simulation using air mass 1.5 show that the metallic truncated nanocones have an average solar absorptivity of 94.22% between 280 and 2500 nm. The absorptivity in the wide oblique angle range of 0–70° along all polarizations is higher than 80%. The effect of the geometric parameters of the metallic truncated nanocones on broadband absorption is discussed. The interaction of local surface plasmonic resonance, Fabry-Perot cavity resonance, and magnetic polarization resonance in the truncated nanocones leads to the high absorption performance. The feasibility of fabricating the truncated nanocones was verified using self-assembled monolayer colloidal crystal-assisted ultraviolet light lithography followed by atomic layer deposition of platinum. The average absorptivity of 74.82% presented from photoresist and platinum arrays is close to that of the simulated data.

Highly Conductive Collagen by Low-Temperature Atomic Layer Deposition of Platinum.

In modern biomaterial-based electronics, conductive and flexible biomaterials are gaining increasing attention for their wide range of applications in biomedical and wearable electronics industries. The ecofriendly, biodegradable, and self-resorbable nature of these materials makes them an excellent choice in fabricating green and transient electronics. Surface functionalization of these biomaterials is required to cater to the need of designing electronics based on these substrate materials. In this work, a low-temperature atomic layer deposition (ALD) process of platinum (Pt) is presented to deposit a conductive thin film on collagen biomaterials, for the first time. Surface characterization revealed that a very thin ALD-deposited seed layer of TiO2 on the collagen surface prior to Pt deposition is an alternative for achieving a better nucleation and 100% surface coverage of ultrathin Pt on collagen surfaces. The presence of a pure metallic Pt thin film was confirmed from surface chemical characterization. Electrical characterization proved the existence of a continuous and conductive Pt thin film (∼27.8 ± 1.4 nm) on collagen with a resistivity of 295 ± 30 μΩ cm, which occurred because of the virtue of TiO2. Analysis of its electronic structures showed that the presence of metastable state due to the presence of TiO2 enables electrons to easily flow from valence into conductive bands. As a result, this turned collagen into a flexible conductive biomaterial.

Surface mobility and impact of precursor dosing during atomic layer deposition of platinum: in situ monitoring of nucleation and island growth.

The increasing interest in atomic layer deposition (ALD) of Pt for the controlled synthesis of supported nanoparticles for catalysis demands an in-depth understanding of the nucleation controlled growth behaviour. We present an in situ investigation of Pt ALD on planar Si substrates, with native SiO2, by means of X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS), using a custom-built synchrotron-compatible high-vacuum ALD setup and focusing on the thermal Pt ALD process, comprising (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O2 gas at 300 °C. The evolution in key scattering features provides insights into the growth kinetics of Pt deposits from small nuclei to isolated islands and coalesced worm-like structures. An analysis approach is introduced to extract dynamic information on the average real space parameters, such as Pt cluster shape, size, and spacing. The results indicate a nucleation stage, followed by a diffusion-mediated particle growth regime that is marked by a decrease in average areal density and the formation of laterally elongated Pt clusters. Growth of the Pt nanoparticles is thus not only governed by the adsorption of Pt precursor molecules from the gas-phase and subsequent combustion of the ligands, but is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Moreover, the influence of the Pt precursor dose on the particle nucleation and growth is investigated. It is found that the precursor dose influences the deposition rate (number of Pt atoms per cycle), while the particle morphology for a specific Pt loading is independent of the precursor dose used in the ALD process. Our results prove that combining in situ GISAXS and XRF provides an excellent experimental strategy to obtain new fundamental insights about the role of deposition parameters on the morphology of Pt ALD depositions. This knowledge is vital to improve control over the Pt nucleation stage and enable efficient synthesis of supported nanocatalysts.

Clamping effects on mechanical stability and energy dissipation in nanoresonators based on carbon nanotubes

With continuous downscaling of resonators, clamping is expected to significantly impact the mechanical stability as well as the energy dissipation mechanisms, especially at the nanoscale. To understand the clamping effects at the nanoscale, we here report on an experimental investigation of a same nanotube based resonator subjected to two different clamping configurations. We investigate clamping associated stability and damping mechanisms by pushing the resonator into the nonlinear regime. The nanotube was first dry-transferred and suspended between source-drain palladium electrodes resulting in a bottom clamped configuration. A selective top-metallization process by platinum atomic layer deposition applied later resulted in a top-bottom clamped configuration. Large nanotube motional amplitude leading to a nonlinear Duffing response initiated small slippage of the nanotube. This instability in clamping was seen in both clamping configurations and was measured as an irreversible resonance frequency downshift. For the measured resonator devices, a gate induced nanotube tension in the range of 58–71 pN was estimated to overcome clamping forces and initiate slipping. In terms of energy dissipation, the top-metallization process was accompanied by a reduction in amplitude dependent nonlinear damping and Q-factor enhancement. Subjecting the same nanotube to both clamping configurations allowed for a direct comparison of clamping and quantification of nonlinear damping. In the present case, nonlinear damping was observed at an estimated nanotube motional amplitude of 11 nm (and higher), being dominant in bottom clamped configuration, suggesting the origin of this nonlinear damping to partially stem from external mechanisms in addition to other possible internal dissipation paths reported such as viscoelastic effects.

Initial reaction mechanism on the atomic layer deposition of platinum on a graphene surface: A density functional theory study

The atomic layer deposition (ALD) of platinum on carbon supports has been studied extensively due to the wide potential application in microelectronics and catalysis. The initial reaction mechanism of atomic layer deposited platinum on a hydroxylated graphene surface has been investigated using density functional theory (DFT). Methylcyclopentadienyl trimethylplatinum (MeCpPtMe3) and molecular oxygen were adopted as precursors. In addition, finite temperature calculations were performed to investigate the effect of process conditions. The free energies were calculated at temperatures 200°C and 300°C with pressure of 1Pa. The results obtained from the simulations were compared and correlated with available literature.

Proton Exchange Membrane Fuel Cell Flooding Caused by Residual Functional Groups after Platinum Atomic Layer Deposition

Proton exchange membrane fuel cell (PEMFC) catalysts manufactured using atomic layer deposition (ALD) on unmodified and functionalized carbon were compared to a commercial catalyst in half- and whole-cell tests. Half-cell tests showed the ALD catalyst performed better or comparable to a commercial catalyst. Conversely, whole-cell tests revealed flooding in the ALD catalyst produced on functionalized carbon. Residual functional groups had reduced the hydrophobicity, and rendered this catalyst impractical for use in whole-cell PEMFC applications. However, the ALD catalyst produced on unmodified carbon performed better than the commercial catalyst, which illustrates the power of ALD on appropriate catalyst supports.

Low temperature platinum atomic layer deposition on nylon-6 for highly conductive and catalytic fiber mats

Low temperature platinum atomic layer deposition (Pt-ALD) via (methylcyclopentadienyl)trimethyl platinum and ozone (O3) is used to produce highly conductive nonwoven nylon-6 (polyamide-6, PA-6) fiber mats, having effective conductivities as high as ∼5500–6000 S/cm with only a 6% fractional increase in mass. The authors show that an alumina ALD nucleation layer deposited at high temperature is required to promote Pt film nucleation and growth on the polymeric substrate. Fractional mass gain scales linearly with Pt-ALD cycle number while effective conductivity exhibits a nonlinear trend with cycle number, corresponding to film coalescence. Field-emission scanning electron microscopy reveals island growth mode of the Pt film at low cycle number with a coalesced film observed after 200 cycles. The metallic coating also exhibits exceptional resistance to mechanical flexing, maintaining up to 93% of unstressed conductivity after bending around cylinders with radii as small as 0.3 cm. Catalytic activity of the as-deposited Pt film is demonstrated via carbon monoxide oxidation to carbon dioxide. This novel low temperature processing allows for the inclusion of highly conductive catalytic material on a number of temperature-sensitive substrates with minimal mass gain for use in such areas as smart textiles and flexible electronics.

Mechanistic studies for depositing highly dispersed Pt nanoparticles on carbon by use of trimethyl(methylcyclopentadienyl)platinum(IV) reactions with O2 and H2

A fundamental understanding is developed for the chemical reaction mechanism that underlies platinum atomic layer deposition (ALD) on a carbon support, XC72R, for use as a fuel cell catalyst. Specifically, trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) was fed as the 1st reactant for ALD on high surface area particles using a well-instrumented fluidized bed reactor equipped with an in-line mass spectrometer. The precursor’s organic ligands were removed by reaction with the 2nd reactant, either oxygen or hydrogen. These experiments were performed on both unmodified and functionalized XC72R. Carbon modification involved reflux with nitric acid, which oxygenated the XC72R. Platinum weight loading, average particle size, and particle dispersion depended on carbon treatment and on the reactant used for ligand removal (oxygen or hydrogen). Deposited platinum particle sizes ranged from 2.6 to 6.7 nm. Transmission electron microscopy, chemisorption, and diffuse reflectance infrared Fourier transform spectroscopy were used to characterize the Pt deposition and carbon support functionalization. More discrete and non-agglomerated platinum nanoparticles were produced using hydrogen, rather than oxygen, as a reactant and when deposition was conducted on functionalized, rather than unmodified, XC72R carbon. The platinum nanoparticles are stabilized by the underlying oxygen added during substrate functionalization and the avoidance of carbon substrate combustion when using hydrogen, instead of oxygen, as the 2nd reactant to remove residual ligands.

Atomic layer deposition of platinum with enhanced nucleation and coalescence by trimethylaluminum pre-pulsing

Conformal coating of metal layers on three-dimensional structures is essential for advanced electronic devices such as storage elements, transistors, and sensors. The quality of atomic layer deposited platinum on oxide surfaces was enhanced by adding pre-deposition pulses of trimethylaluminum (TMA) for improved wetting. With an optimal number of TMA pre-pulses, a 6 nm thick Pt film was perfectly coalesced in contrast to only Pt island formation without TMA pre-pulses. A Pt gate all around Ge/Si nanowire field effect transistor was realized highlighting the potential of this approach for efficient deposition of Pt on 3D nanoelectronic devices.

Influence of Oxygen Exposure on the Nucleation of Platinum Atomic Layer Deposition: Consequences for Film Growth, Nanopatterning, and Nanoparticle Synthesis

Control of the nucleation behavior during atomic layer deposition (ALD) of metals is of great importance for the deposition of metallic thin films and nanoparticles, and for nanopatterning applications. In this work it is established for Pt ALD, that the exposure to O2 during the O2 pulse of the ALD process is the key parameter controlling the nucleation behavior. The O2 dependence of the Pt nucleation is explained by the enhanced diffusion of Pt species in the presence of oxygen, and the resulting faster aggregation of Pt atoms in metal clusters that catalyze the surface reactions of ALD growth. Moreover, it is demonstrated that the O2 exposure can be used as the parameter to tune the nucleation to enable (i) deposition of ultrathin films with minimal nucleation delay, (ii) preparation of single element or core/shell nanoparticles, and (iii) nanopatterning of metallic structures based on area-selective deposition.

Synthesis and Electrochemical Characterization of Carbon Supported Platinum Grown by Template Assisted Gas Phase Deposition

Platinum catalysts remain one of the primary cost and durability concerns for polymer electrolyte fuel cells. The most common approach to produce Pt/C catalysts is to deposit Pt nanoparticles onto carbon supports. In this study, we first synthesize Pt particles on a sacrificial template and subsequently backfill with a carbon support. We utilize an anodized aluminum oxide (AAO) template in conjunction with atomic layer deposition of platinum and chemical vapor deposition to achieve this process in an all gas-phase synthesis. Following platinum deposition, carbon is deposited into the AAO pores via chemical vapor deposition to support the platinum nanoparticles and to provide electrical continuity, creating a uniquely stabilized Pt particle on carbon. These materials are then recovered from the template by dissolution of the AAO and characterized by microscopy and electrochemical measurements. The initial results from these studies show promising performance metrics and suggest further development of these materials.

In Vacuo Photoemission Studies of Platinum Atomic Layer Deposition Using Synchrotron Radiation.

The mechanism of platinum atomic layer deposition using (methylcyclopentadienyl)trimethylplatinum and oxygen is investigated with in vacuo photoemission spectroscopy at the Stanford Synchrotron Radiation Lightsource. With this surface-sensitive technique, the surface species following the Pt precursor half cycle and the oxygen counter-reactant half cycle can be directly measured. We observed significant amounts of carbonaceous species following the Pt precursor pulse, consistent with dehydrogenation of the precursor ligands. Significantly more carbon is observed when deposition is carried out in the thermal decomposition temperature region. The carbonaceous layer is removed during the oxygen counter reactant pulse, and the photoemission spectrum shows that a layer of adsorbed oxygen remains on the surface as previously predicted.

Catalytic Combustion and Dehydrogenation Reactions during Atomic Layer Deposition of Platinum

Atomic layer deposition (ALD) processes of noble metals are gaining increasing interest for applications in catalysis and microelectronics. Platinum ALD from (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe3) and O2 gas has been considered as a model system for noble metal ALD. However, many questions about the underlying reaction mechanisms remain. In this work, the insight into the Pt ALD reaction mechanisms is extended by considering the catalytic nature of the Pt film. It is evaluated which surface reactions are likely to take place during Pt ALD on the basis of surface science results on the interaction of the Pt surface with O2 and hydrocarbon species, combined with previously reported Pt ALD mechanistic studies. In analogy to the reactions of hydrocarbon species on catalytic Pt, it is proposed that, in addition to combustion-like reactions, dehydrogenation of precursor ligands plays a role in the mechanism. The formation of CH4 during the MeCpPtMe3 exposure pulse is explained by hydrogenation of...

Fabrication of tin dioxide nanowires with ultrahigh gas sensitivity by atomic layer deposition of platinum

Gas-sensing properties of SnO2 nanowires were investigated before and after their surface functionalization by the atomic layer deposition (ALD) of Pt nanoparticles. The morphology, size, and concentration of Pt particles on SnO2 nanowires can be controlled by varying the number of ALD reaction cycles, and therefore, the gas-sensing properties of the nanowires can be altered via the Pt catalyst effect and the modification of Schottky barrier junctions on the nanowire surface in the vicinity of Pt nanoparticles. The Pt-decorated SnO2 nanowires obtained after 200 ALD reaction cycles exhibited an ultrahigh gas sensitivity (S = Ig/Ia) of ∼8400 to 500 ppm ethanol vapor at 200 °C. This provides an efficient route for strongly enhancing the gas sensitivity of semiconducting nanostructures and fabricating gas sensors that are highly sensitive and responsive.

Atomic Layer Deposition of Platinum onto Functionalized Aligned MWNT Arrays for Fuel Cell Application

High aspect ratio materials, such as carbon nanotubes (CNTs), provide unique opportunities and advantages as catalyst support materials in fuel cells. In particular, CNTs are highly conductive and corrosion resistant; properties which represent limitations for current carbon supports. While most advanced catalysts research focuses on the production of small nanoparticles to increase the percent of surface accessible Pt; here, we specifically attempt to conformally coat Pt in thin layers onto CNT arrays. We present our work on modifying CNT surfaces inside high-density, surface-bound aligned CNT arrays (aspect ratio ~1:750) with non-toxic gas phase chemistries. The number of nucleation sites and the onset of growth of Pt by ALD can be tuned by using Ar plasma, O2 plasma and chemical functionalization. This, in turn, affects the uniformity of the Pt ALD coating down the length of the tubes within the CNT array.

Atomic Layer Deposition of Platinum onto Functionalized Aligned MWNT Arrays for Fuel Cell Application

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Genesis and Evolution of Surface Species during Pt Atomic Layer Deposition on Oxide Supports Characterized by in Situ XAFS Analysis and Water−Gas Shift Reaction

Platinum atomic layer deposition (ALD) using MeCpPtMe3 was employed to prepare high loadings of uniform-sized, 1−2 nm Pt nanoparticles on high surface area Al2O3, TiO2, and SrTiO3 supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe3 adsorption yielded smaller particles due to reduced thermal decomposition. A 300 °C air treatment of the adsorbed MeCpPtMe3 leads to PtO. In subsequent ALD cycles, the MeCpPtMe3 reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 °C H2 treatment of the adsorbed MeCpPtMe3 leads to the formation of 1−2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe3 adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed...

Enhancing the Photon-Sensing Properties of ZnO Nanowires by Atomic Layer Deposition of Platinum

Platinum nanoparticles were uniformily deposited on ZnO nanowires for photon-sensing applications. The morphology, size, and concentration of Pt particles on the ZnO nanowires can be controlled by varying the number of atomic layer deposition reaction cycles. The Pt-decorated ZnO nanowires exhibit much faster photon response and recovery speeds than the pristine ZnO nanowires. This provides an efficient route for strongly enhancing the photon-sensing properties of nanostructured metal oxides and fabricating photodetectors with fast response and recovery speeds.

Photochemical Covalent Attachment of Alkene-Derived Monolayers onto Hydroxyl-Terminated Silica

The functionalization of optically transparent substrates is of importance, for example, in the field of biosensing. In this article, a new method for modification of silica surfaces is presented that is based on a photochemical reaction of terminal alkenes with the surface. This yields highly hydrophobic surfaces, which are thermally stable up to at least 400 degrees C. The formed monolayer provides chemical passivation of the underlying surface, according to studies showing successful blocking of platinum atomic layer deposition (ALD). The reaction is photochemically initiated, requiring light with a wavelength below 275 nm. X-ray photoelectron spectroscopy and infrared spectroscopy studies show that the alkenes initially bind to the surface hydroxyl groups in Markovnikov fashion. At prolonged reaction times (>5 h), however, oligomerization occurs, resulting in layer growth normal to the surface. The photochemical nature of the reaction enables the use of photolithography as a tool to constructively pattern silica surfaces. Atomic force microscopy shows that the features of the photomask are well transferred. The newly developed method can complement existing patterning methods on silica that are based on soft lithography.

Application of Atomic Layer Deposition of Platinum to Solid Oxide Fuel Cells

In this study, atomic layer deposition (ALD) was used to deposit Pt thin films as an electrode/catalyst layer for solid oxide fuel cells. I−V measurements were performed to determine the dependence of the fuel cell performance on the Pt film thickness at different operating temperatures. The measured fuel cell performance revealed that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the platinum loading relative to dc-sputtered Pt anodes. The Pt films fabricated by dc sputtering and ALD had different microstructure, which accounted for the difference in their performance as a fuel cell anode. In addition to the continuous electrocatalyst layer, a micropatterned Pt structure was fabricated via area-selective ALD and used as a current collector grid/patterned catalyst for the fuel cells. An improvement of the fuel cell performance by a factor of 10 was observed using the Pt current collector grid/patterned catalyst integrated onto cathodic La0.6Sr0.4Co0.2Fe0.8O3-δ. The study suggests the potential to achieve improved performance and/or lower loadings using ALD for catalysts in fuel cells.