Trimethyl Platinum Research Articles

Chemical mechanism for nucleation enhancement in atomic layer deposition of Pt by surface functionalization

Atomic layer deposition (ALD) of metals on oxide substrates often yields islandlike growth, undesirable toward conductor applications. Thus, enhancement of initial nucleation of metal ALD is of great importance. One potential solution reported is to functionalize the substrate surface with small molecules, such as trimethylaluminum (TMA) and aluminum chloride (AlCl3) before metal ALD, so that nucleation delay is reduced, and the coverage and conformality are enhanced. In this study, density functional theory calculations are utilized to elucidate the chemical mechanism toward a change of the reactivity of the surface toward metal ALD upon functionalization by TMA or AlCl3. Surface adsorption of a typical Pt ALD precursor, trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3), on an OH-terminated SiO2 surface is compared to its adsorption on AlCH3-terminated and AlCl-terminated surfaces. Considering rate-limiting steps on each surface, greater rates for adsorption of Pt are found for the organometallic-functionalized surfaces than the bare SiO2 surface, confirming the chemical enhancement effect by functionalization.

Novel Strategy to Evaluate Platinum Photocatalysts for Hydrosilation-Curable Silicones

UV-activated catalytic hydrosilation is a low-temperature crosslinking process that has attracted attention for its high efficiency and lower energy demand relative to thermal curing. In this study, formulations comprising industrially relevant model silanes and Pt photocatalysts trimethyl(methylcyclopentadienyl)platinum(IV) and trimethyl(pentamethylcyclopentadienyl)platinum(IV) (MeCpPtMe3 and Cp*PtMe3, respectively) were prepared with and without a photosensitizer (PS) and assessed for catalytic performance by a novel strategy. Photopolymerizations were initiated using different wavelengths from LEDs and monitored in real-time using an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) “well” strategy to track the degree of cure in ultra-thin films by consumption of hydride via the disappearance of the Si-H bending absorption band at 915 cm−1. Irradiation of formulations with 365 nm excitation showed higher conversions relative to 400 nm light and improvements to calculated initial reaction rates by incorporation of a PS suggested increased sensitization to 365 nm irradiation. To the best of our knowledge, this is the first study to report catalytic performance, electronic absorption spectroscopic data, and the crystal structure of Cp*PtMe3.

Nonoxidative dehydrogenation of propane using boron-incorporated silica-supported Pt Sites synthesized by atomic layer deposition.

Nonoxidative dehydrogenation of propane to propylene using Pt-based supported catalysts is an active research area in catalysis because catalyst attributes of Pt sites can be controlled by careful design of active sites. One way to achieve this is by the addition of a second metal that may impart a change in the electron density of active sites, which in turn affects catalytic performance. In this study, bimetallic Pt and B sites were deposited on powder SiO2 using atomic layer deposition (ALD). Boron was first deposited on SiO2 via half-cycle ALD using triisoproplyborate as the B source. Following calcination, Pt deposition was performed via half-cycle ALD using trimethyl(methylcyclopentadienyl)platinum(IV) as the Pt source. The synthesized catalysts were reduced under H2 at 550 °C and characterized using inductively coupled plasma optical emission spectroscopy for elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO to examine the properties of Pt, and time-resolved X-ray absorption near edge structure spectroscopy to examine the changes in the reducibility of Pt sites. The samples were then tested for nonoxidative dehydrogenation of propane at 550 °C using a fixed-bed plug-flow reactor to examine the role of B on the catalytic performance. Characterization results showed that the addition of B imparted an increase in electron density and affected the reducibility of Pt sites. In addition, incorporating B on SiO2 created anchoring sites for Pt ALD. The amount of Pt deposited on B/SiO2 was 2.2 times that on SiO2. Catalytic activity results revealed the addition of B did not change the initial activity of Pt sites significantly, but improved propylene selectivity from 80% to 87% and stability almost threefold. The enhanced selectivity and stability of PtB/SiO2 is most presumably due to favored desorption of propylene and mitigating coke formation under reaction conditions, respectively.

In vacuo studies on reaction mechanisms in ALD processes of ruthenium and platinum films

Noble metal ALD processes with organometallic precursors together with oxygen have been developed extensively. Reaction mechanisms in this family of processes involve combustion of the ligands of the metal precursor by the O2 counter reactant. The ligands are oxidized and form gaseous CO2 and H2O as byproducts. Simultaneously the metallic center is reduced and a noble metal film is deposited. The overall reaction mechanism is fairly well-known, however details regarding the carbonaceous intermediates on the surface at different states of an ALD cycle and the nature of the active surface oxygen are still lacking. In this work, these details are studied mainly with in vacuo X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) for platinum and ruthenium processes. Trimethyl(methylcyclopentadienyl) platinum(IV) (MeCpPtMe3) and bis(cyclopentadienyl) ruthenium(II) RuCp2 are used as precursors together with O2.

Effect of Nitrogen Doping and Oxidation of Graphene on the Deposition of Platinum from Trimethyl(methylcyclopentadienyl)platinum(IV)

Effect of Nitrogen Doping and Oxidation of Graphene on the Deposition of Platinum from Trimethyl(methylcyclopentadienyl)platinum(IV)

Synthesis of ZIF-69-derived Electrocatalyst with Low loading Platinum for Oxygen Reduction Reaction

Here, we report a facile preparation of a low-platinum catalyst derived from ZIF-69 denoted as Pt@ZC-69. Nitrogen-abundant ZIF-69 could act as a support to efficiently encapsulate trimethyl (methylcyclopentadienyl) platinum (IV) (MeCpPtMe3@ZIF-69) precursor. After high-temperature reduction, Pt@ZC-69 with uniform Pt-loading was obtained. In the acidic medium, the Pt@ZC-69 presented a desirable performance, the half-wave potential could reach 0.845 V vs. RHE, while the Pt content is less than 10% of the commercial 20 wt.% Pt/C. Moreover, Pt@ZC-69 also possessed robust stability (40 mV decays after 20000 cycles).

Formation of silica-supported platinum nanoparticles as a function of preparation conditions and boron impregnation.

Preparation of supported metal nanoparticles for catalytic applications often relies on an assumption that the initially prepared wet-impregnated support material is covered with approximately a monolayer of adsorbed species that are shaped into the target nanoparticulate material with a desired size distribution by utilizing appropriate post-treatments that often include calcination and reduction schemes. Here, the formation and evolution of surface nanoparticles were investigated for wet-chemistry deposition of platinum from trimethyl(methylcyclopentadienyl)platinum (IV) precursor onto flat silica supports to interrogate the factors influencing the initial stages of nanoparticle formation. The deposition was performed on silicon-based substrates, including hydroxylated silica (SiO2) and boron-impregnated hydroxylated silica (B/SiO2) surfaces. The deposition resulted in the immediate formation of Pt-containing nanoparticles, as confirmed by atomic force microscopy and x-ray photoelectron spectroscopy. The prepared substrates were later reduced at 550 °C under H2 gas environment. This reduction procedure resulted in the formation of metallic Pt particles. The reactivity of the precursor and dispersion of Pt nanoparticles on the OH-terminated silica surface were compared to those on the B-impregnated surface. The size distribution of the resulting nanoparticles as a function of surface preparation was evaluated, and density functional theory calculations were used to explain the differences between the two types of surfaces investigated.

ToF-SIMS Investigation of the Initial Stages of MeCpPt(CH3)3 Adsorption and Decomposition on Nickel Oxide Surfaces: Exploring the Role and Location of the Ligands

The chemistry of trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPt(CH3)3), a platinum organometallic compound often used for the chemical deposition of Pt films, on nickel oxide surfaces was in...

UV‐activated hydrosilylation of (Me‐Cp)Pt(Me)3: Enhanced photocatalytic activity, polymerization kinetics, and photolithography

ABSTRACTHydrosilylation is commonly known as a thermally induced addition reaction between unsaturated bonds and SiH bonds to synthesize or crosslink organosilanes and organosilicones, while it has emerged that it can also be activated under the coaction of UV irradiation and specific platinum catalyst. For higher photopolymerization conversion, excessive platinum catalyst is always required; however, this inevitably causes the significant increase of production cost and decrease of operation time. In this study, traces of trimethyl(methylcyclopentadienyl) platinum (IV) (Me‐Cp)Pt(Me)3 catalysts is combined with different photosensitizers (PSs) to efficiently promote the UV‐activated hydrosilylation. Naphthalene is found to be the most applicable PS, because it improves the photopolymerization conversion from about 70 to 100% for the crosslinking of silicone rubbers. This UV‐activated hydrosilylation is more likely to follow the first‐order reaction kinetics, and its activation energy is 30.9 kJ mol−1. The mechanical properties and thermostability of UV‐crosslinked silicone rubbers are also enhanced with the incorporation of naphthalene. Moreover, this UV‐activated hydrosilylation of silicone rubbers reveals a potential role to prepare complicated geometry shapes by photolithography. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48251.

Application of time-of-flight secondary ion mass spectrometry to the detection of surface intermediates during the first cycle of atomic layer deposition (ALD) of platinum on silica surfaces

Abstract Atomic layer deposition (ALD) has become the method of choice for many applications requiring the controlled growth of thin films on solid surfaces. However, the use of metalorganic precursors typical in these depositions adds significant complexity to the chemistry involved. Unfortunately, it is difficult to obtain direct information about the surface species that participate in the reaction mechanisms of ALD. Here we illustrate the value of using time-of-flight secondary ion mass spectrometry (ToF-SIMS) for this purpose. A particular example is provided, a study of the first cycle of deposition of platinum using trimethyl(methylcyclopentadienyl)platinum (IV), or MeCpPt(CH3)3, on silicon oxide surfaces. In previous investigations of this process, we have determined that the low reactivity of the MeCpPt(CH3)3 precursor, which hinders fast deposition, can be partially overcome by gas-phase electron-impact activation. What has not been clear is what chemical species form on the solid surface as a result of such activation. Here we show that the MeCp ligand is quite stable and that it remains intact and coordinated to the Pt atoms upon adsorption on the surface. It was also established that some of the methyl groups may remain bound to the Pt center: the main species detected on the silicon oxide surfaces were MeCpPt and MeCpPt(CH3). On the other hand, it appears that no Pt intermediates without MeCp ligands are formed during this initial adsorption. Finally, O2 treatment of these surfaces at elevated temperature to complete the first ALD cycle leads to the complete removal of all the organic ligands: no evidence for MeCp or methyl groups is seen in the ToF-SIMS traces from the final samples.

Atomic layer deposition of Pt@CsH2PO4 for the cathodes of solid acid fuel cells

Atomic layer deposition (ALD) has been used to apply continuous Pt films on powders of the solid acid CsH2PO4 (CDP), in turn, used in the preparation of cathodes in solid acid fuel cells (SAFCs). The film deposition was carried out at 150 °C using trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3) as the Pt source and ozone as the reactant for ligand removal. Chemical analysis showed a Pt growth rate of 0.09 ± 0.01 wt%/cycle subsequent to an initial nucleation delay of 84 ± 20 cycles. Electron microscopy revealed the contiguous nature of the films prepared using 200 or more cycles. The cathode overpotential (0.48 ± 0.02 V at a current density of 200 mA/cm2) was independent of Pt deposition amount beyond the minimum required to achieve these continuous films. The cell electrochemical characteristics were moreover extremely stable with time, with the cathode overpotentials increasing by no more than 10 mV over a 100 h period of measurement. Thus, ALD holds promise as an effective tool in the preparation of SAFC cathodes with high activity and excellent stability.

Platinum atomic layer deposition on metal substrates: A surface chemistry study

The surface chemistry associated with the atomic layer deposition (ALD) of platinum films on metallic nickel substrates using trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3) and oxygen was characterized by using X-ray photoelectron spectroscopy (XPS). The uptake of the MeCpPtMe3 ALD precursor was found to be self-limiting between 525 and 625 K, but to lead to multilayer deposition at 675 K. The adsorbed species display a C:Pt ratio of approximately 5:1, suggesting that all methyl moieties are lost upon activated bonding to the surface but that the methylcyclopentadienyl group remains coordinated to the adsorbed Pt atoms. Oxygen treatment of that surface leads to the complete removal of the carbon-containing species from the surface and to the formation of a thin NiO film. Further dosing with MeCpPtMe3, in the next ALD cycle, fully reduces that NiO film to metallic Ni(0) and adds more Pt to the surface. However, no Pt film buildup was seen after several ALD cycles. Angle-resolved XPS data suggested that the deposited Pt migrates below the NiO that forms during the O2 exposures and possibly alloys with the metallic Ni substrate at that stage.

On the Activity Enhancing Role of Iron Oxide for Noble Metal Oxidation Catalysts: A CVD-Based Study with Differently Structured Combinations of Pt and FeOx Coatings on Al2O3

With regard to the catalysis of oxidation reactions by noble metals, the addition of FeOx to an Al2O3-supported Pt catalyst is known to be energetically more favorable compared to only Pt. In this work, different process routes for the preparation of such Fe-promoted Pt/Al2O3 catalysts via atmospheric chemical vapor deposition (CVD) in a fluidized bed were explored. Specifically, the question of whether it would be advantageous to deposit the Fe before, along with, or after the Pt was addressed, and new information was obtained about the optimum FeOx–Pt interface and mixing ratio. Vapors of Trimethyl(methylcyclopentadienyl)platinum(IV) and/or Ethyl-ferrocene were injected into the bed from the top, permitting a quasi-lossless precursor operation and a very good control of the deposited metal, and hence of the catalyst structure. Samples could be extracted from the top while CVD was ongoing to obtain time-resolved data. The catalytic activity was determined through CO oxidation. The Fe-Pt mixing ratio was then varied for the most active deposition sequence, in order to identify an activity optimum generated by the minimum amount of Pt catalyst. When compared to pure Pt/Al2O3, the optimum catalyst consistently showed superior performance even after thermal stress.

From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder.

A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (PO2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high PO2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high PO2 .

Dynamics and fragmentation mechanism of (C5H4CH3)Pt(CH3)3 on SiO2 surfaces

The interaction of trimethyl(methylcyclopentadienyl)platinum(IV) ((C5H4CH3)Pt(CH3)3) molecules on fully and partially hydroxylated SiO2 surfaces, as well as the dynamics of this interaction were investigated using density functional theory (DFT) and finite temperature DFT-based molecular dynamics simulations. Fully and partially hydroxylated surfaces represent substrates before and after electron beam treatment and this study examines the role of electron beam pretreatment on the substrates in the initial stages of precursor dissociation and formation of Pt deposits. Our simulations show that on fully hydroxylated surfaces or untreated surfaces, the precursor molecules remain inactivated while we observe fragmentation of (C5H4CH3)Pt(CH3)3 on partially hydroxylated surfaces. The behavior of precursor molecules on the partially hydroxylated surfaces has been found to depend on the initial orientation of the molecule and the distribution of surface active sites. Based on the observations from the simulations and available experiments, we discuss possible dissociation channels of the precursor.

Electron-driven and thermal chemistry during water-assisted purification of platinum nanomaterials generated by electron beam induced deposition.

Focused electron beam induced deposition (FEBID) is a versatile tool for the direct-write fabrication of nanostructures on surfaces. However, FEBID nanostructures are usually highly contaminated by carbon originating from the precursor used in the process. Recently, it was shown that platinum nanostructures produced by FEBID can be efficiently purified by electron irradiation in the presence of water. If such processes can be transferred to FEBID deposits produced from other carbon-containing precursors, a new general approach to the generation of pure metallic nanostructures could be implemented. Therefore this study aims to understand the chemical reactions that are fundamental to the water-assisted purification of platinum FEBID deposits generated from trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3). The experiments performed under ultrahigh vacuum conditions apply a combination of different desorption experiments coupled with mass spectrometry to analyse reaction products. Electron-stimulated desorption monitors species that leave the surface during electron exposure while post-irradiation thermal desorption spectrometry reveals products that evolve during subsequent thermal treatment. In addition, desorption of volatile products was also observed when a deposit produced by electron exposure was subsequently brought into contact with water. The results distinguish between contributions of thermal chemistry, direct chemistry between water and the deposit, and electron-induced reactions that all contribute to the purification process. We discuss reaction kinetics for the main volatile products CO and CH4 to obtain mechanistic information. The results provide novel insights into the chemistry that occurs during purification of FEBID nanostructures with implications also for the stability of the carbonaceous matrix of nanogranular FEBID materials under humid conditions.

Independent tuning of size and coverage of supported Pt nanoparticles using atomic layer deposition

Synthetic methods that allow for the controlled design of well-defined Pt nanoparticles are highly desirable for fundamental catalysis research. In this work, we propose a strategy that allows precise and independent control of the Pt particle size and coverage. Our approach exploits the versatility of the atomic layer deposition (ALD) technique by combining two ALD processes for Pt using different reactants. The particle areal density is controlled by tailoring the number of ALD cycles using trimethyl(methylcyclopentadienyl)platinum and oxygen, while subsequent growth using the same Pt precursor in combination with nitrogen plasma allows for tuning of the particle size at the atomic level. The excellent control over the particle morphology is clearly demonstrated by means of in situ and ex situ X-ray fluorescence and grazing incidence small angle X-ray scattering experiments, providing information about the Pt loading, average particle dimensions, and mean center-to-center particle distance.

Plasma enhanced atomic layer deposited platinum thin film on Si substrate with TMA pretreatment

Benefiting from the good etching and patterning feasibilities and excellent electrical properties, platinum silicide attracts renewed attention as a suitable candidate for the next generation complementary metal-oxide-semiconductor (CMOS) technologies recently. This work focuses on the effects of the trimethylaluminum (TMA) pretreatment on the Plasma Enhanced Atomic Layer Deposition (PEALD) growth of Platinum (Pt) film on silicon substrate by using (methylcyclopentadienyl)-trimethyl platinum (MeCpPtMe3) and ammonia plasma as precursors. The incubation period of PEALD Pt was shortened by TMA pretreatment, and the saturation growth rate reached 0.21 Å/cycle. X-ray diffraction showed that as-deposited films have strongly preferred orientation along the (111) plane. The resistivity of the as-deposited Pt film can be approached to 15 μΩ cm. At last, an optimized PEALD Pt process was put forward. Our research provides an effective strategy for the fabrication of high-quality Pt thin films on Si substrate. The findings are important to obtain well defined silicide films which would be used in the advanced CMOS source and drain technology.

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.

Direct observation of hydrogenation and dehydrogenation of a zirconium alloy

The hydrogenation and dehydrogenation behaviors of a zirconium alloy were in-situ studied by scanning electron microscopy and transmission electron microscopy. The zirconium alloy can absorb hydrogen to form Zr hydride which is enhanced by the relaxation of inner stress in the alloy. The hydrogen is generated from an ion/electron beam stimulated decomposition of an organometallic precursor, trimethyl (methylcyclopentadienyl) platinum (IV), in a scanning electron microscope and focused ion beam system. The formed δ-type zirconium hydride that has a face centered cubic structure was observed to grow as preferentially oriented platelets in the zirconium alloy matrix. The platelets have a common crystallographic relationship of [010]α//[1-10]δ, (001)α//(111)δ. The dehydrogenation of the zirconium hydride was in-situ investigated in a transmission electron microscope by heating the materials. It was found that the δ-ZrH1.5–1.66 hydride transformed into ζ-ZrH0.25 at 450 °C even at a longer heating time. The experiment demonstrates a new way for in-situ study of hydrogenation behaviors of other hydrogen storage alloys.