Chemical evidence for the formation of an acidic Mo(100) surface by adsorbed oxygen

Walker, B. W.; Stair, Peter C.

doi:10.1016/0039-6028(80)90335-0

Cited by 21 publications

(4 citation statements)

References 13 publications

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“…For example, CO 2 adsorbs dissociatively on Fe(1 1 1), Fe(1 0 0) and Ni (1 1 0), but non-dissociativly on Fe(1 0 0) and Ni (1 1 1), while dissociativly and non-dissociativly on Ni(1 0 0) [50]. It also showed that CO 2 adsorbs dissociatively on clean Mo(1 0 0) [52] and polycrystalline Mo [53] at the lower temperature. It was believed that on Ni(1 1 0), Ni(1 0 0) and Fe(1 1 1) the chemisorbed CO dÀ 2 anionic species represents an intrinsic precursor for CO 2 dissociation into CO and atomic oxygen [54,55].…”

Section: Resultsmentioning

confidence: 82%

Density functional theory study into the adsorption of CO2, H and CHx (x=0–3) as well as C2H4 on α-Mo2C(0001)

et al. 2006

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Section: Resultsmentioning

confidence: 82%

Density functional theory study into the adsorption of CO2, H and CHx (x=0–3) as well as C2H4 on α-Mo2C(0001)

et al. 2006

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“…It is difficult with the current XPS orientation, θ = 0°, to determine the exact elemental ratio of the top few layers of the substrate. Previous work from our laboratory has explored the effects of chemisorbed oxygen on the structure, oxidation state, and acidity of Mo(100). ,− These early experiments used CO dissociation to calibrate the O(1s) signal to establish a metric for the expected intensity ratio of the Mo(3d 5/2 ) to the O(1s) peaks for increasing oxygen coverage ranging from 0.3 to 2 monolayers on a Mo(100) surface . For this work, the O/Mo ratios are 0.06, 0.15, and 0.14 for the base substrate in the 573, 473, and 373 K experiments, respectively.…”

Section: Resultsmentioning

confidence: 99%

Alternative Low-Pressure Surface Chemistry of Titanium Tetraisopropoxide on Oxidized Molybdenum

Johnson

Stair

2014

J. Phys. Chem. C

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Titanium tetraisopropoxide (TTIP) is a precursor utilized in atomic layer depositions (ALDs) for the growth of TiO 2 . The chemistry of TTIP deposition onto a slightly oxidized molybdenum substrate was explored under ultrahigh vacuum (UHV) conditions with X-ray photoelectron spectroscopy. Comparison of the Ti(2p) and C(1s) peak areas has been used to determine the surface chemistry for increasing substrate temperatures. TTIP at a gas-phase temperature of 373 K reacts with a MoO x substrate at 373 K but not when the substrate is at 295 K, consistent with a reaction that proceeds via a Langmuir−Hinshelwood mechanism. Chemical vapor deposition was observed for depositions at 473 K, below the thermal decomposition temperature of TTIP and within the ALD temperature window, suggesting an alternative reaction pathway competitive to ALD. We propose that under conditions of low pressure and moderate substrate temperatures dehydration of the reacted precursor by nascent TiO 2 becomes the dominant reaction pathway and leads to the CVD growth of TiO 2 rather than a self-limiting ALD reaction. These results highlight the complexity of the chemistry of ALD precursors and demonstrate that changing the pressure can drastically alter the surface chemistry. ■ INTRODUCTIONAtomic layer deposition (ALD) is a technique that relies on two sequential gas−surface reactions to grow materials in a layer-by-layer fashion. This method is employed in the semiconductor industry and is most commonly used to deposit metal oxides. 1 However, ALD has become an emerging technique for the fabrication of novel and complex catalytic systems and in the process has been extended to the growth of metal films and nanoparticles on catalytic supports. 2,3 ALD employs multiple cycles that are combined to build materials with precise thickness control. One ALD cycle is composed of two half cycles that result in the regeneration of the initial surface groups, providing new reactive sites for the following cycle. Given a finite number of surface reaction sites and steric constraints imposed by the ligands, only a finite number of precursor molecules can react, resulting in the selflimiting nature of the technique. 4 Reactive sites on oxides include hydroxyl groups, bridging oxygen atoms, and defect sites.There has been a significant amount of work directed toward elucidating ALD chemistry, utilizing techniques such as X-ray photoelectron spectroscopy (XPS), mass spectrometry, quartz crystal microbalance (QCM), temperature-programmed desorption (TPD), DFT, and ab initio calculations. 5,6 The most studied system is the deposition of Al 2 O 3 from trimethylaluminum (TMA) and H 2 O because it is widely used and considered an "ideal" deposition process. Significant work has been done to establish a mechanism for the reaction, identify the source of self-limiting behavior, and understand the reaction kinetics. 4,7,8 Many of these experiments are summarized in a dedicated review by Puurunen. 4 Studies of other ALD metal precursors and corresponding growth processes of...

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“…The chemistry of trimethylamine (TMA−(CH 3 ) 3 N) on Mo(100) was studied by means of LEED, XPS, AES, and TPD under UHV conditions. − The advantage in using TMA as the source of the methyl fragments is the particularly high density of initial methyl adsorbates on the surface, following parent molecule dissociation.…”

Section: Introductionmentioning

confidence: 99%

“…In these studies of TMA, its chemical reactivity was discussed in terms of Lewis acids and Lewis bases on different metal surfaces. − Dissociative adsorption of TMA molecules resulting in its respective fragments was recorded on a clean Mo surface by careful examination of the carbon Auger peak shapes. When the surface became partially passivated by the dissociation products, parent molecule desorption could be detected.…”

Section: Introductionmentioning

confidence: 99%

The Chemistry of Trimethylamine on Ru(001) and O/Ru(001)

Asscher

2007

Langmuir

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The interaction and reactivity of trimethylamine (TMA) has been studied over clean and oxygen-covered Ru(001) under UHV conditions, as a model for the chemistry of high-density hydrocarbons on a catalytic surface. The molecule adsorbs intact at surface temperature below 100 K with the nitrogen end directed toward the surface, as indicated from work function change measurements. At coverage less than 0.05 ML (relative to the Ru substrate atoms), TMA fully dissociates upon surface heating, with hydrogen as the only evolving molecule following temperature-programmed reaction/desorption (TPR/TPD). At higher coverage, the parent molecule desorbs, and its desorption peak shifts down from 270 K to 115 K upon completion of the first monolayer, indicating a strong repulsion among neighbor molecules. The dipole moment of an adsorbed TMA molecule has been estimated from work function study to be 1.4 D. Oxygen precoverage on the ruthenium surface has shown efficient reactivity with TMA. It shifts the surface chemistry toward the production of various oxygen-containing stable molecules such as H2CO, CO2, and CO that desorb between 200 and 600 K, respectively. TMA at a coverage of 0.5 ML practically cleans off the surface from its oxygen atoms as a result of TPR up to 1650 K, in contrast to CO oxidation on the O/Ru(001) surface. The overall reactivity of TMA on the oxidized ruthenium surface has been described as a multistep reaction mechanism.

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Chemical evidence for the formation of an acidic Mo(100) surface by adsorbed oxygen

Cited by 21 publications

References 13 publications

Density functional theory study into the adsorption of CO2, H and CHx (x=0–3) as well as C2H4 on α-Mo2C(0001)

Density functional theory study into the adsorption of CO2, H and CHx (x=0–3) as well as C2H4 on α-Mo2C(0001)

Alternative Low-Pressure Surface Chemistry of Titanium Tetraisopropoxide on Oxidized Molybdenum

The Chemistry of Trimethylamine on Ru(001) and O/Ru(001)

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