Bond Dissociation Energies of Tungsten Molecules: WC, WSi, WS, WSe, and WCl

Sevy, Andrew; Huffaker, Robert F.; Morse, Michael D.

doi:10.1021/acs.jpca.7b09704

Cited by 42 publications

(18 citation statements)

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“…Furthermore, since WS 2 crystals are only van der Waals bonded to the starting surface, the surface mobility of WS 2 crystals is anticipated to be higher compared to chemisorbed species. In addition, the W–S bond is relatively strong (476.15 kJ/mol), rendering single atom detachment from WS 2 crystal (i.e., Ostwald ripening) less probable at these deposition temperatures . Irrespective of the type of diffusion mechanism during the PEALD process, the development of the peak on the right-hand side of the GSD illustrates that WS 2 PEALD is a diffusion-mediated process, which enables the WS 2 crystals to grow in the lateral direction by incorporating mobile adsorbed surface species at the reactive edges of the WS 2 crystals (Figure ).…”

Section: Resultsmentioning

confidence: 99%

Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism

et al. 2018

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When two-dimensional (2D) group-VI transition metal dichalcogenides such as tungsten disulfide (WS2) are grown by atomic layer deposition (ALD) for atomic growth control at low deposition temperatures (< 450 °C), they often suffer from a nanocrystalline grain structure limiting the carrier mobility. The crystallinity and monolayer thickness control during ALD of 2D materials is determined by the nucleation mechanism, which is currently not well understood. Here, we propose a qualitative model for the WS2 nucleation behavior on dielectric surfaces during plasma-enhanced (PE-) ALD using WF6, H2 plasma and H2S based on analyses of the morphology of the WS2 crystals. The WS2 crystal grain size increases from ~20 nm to 200 nm by lowering the nucleation density. This is achieved by lowering the precursor adsorption rate on the starting surface using an inherently less reactive starting surface, by decreasing the H2 plasma reactivity, and by enhancing the mobility of the adsorbed species at higher 2 deposition temperature. Since SiO2 is less reactive than Al2O3, and diffusion and crystal ripening is enhanced at higher deposition temperature, WS2 nucleates in an anisotropic island-like growth mode with preferential lateral growth from the WS2 crystal edges. This work emphasizes that increasing the crystal grain size while controlling the basal plane orientation is possible during ALD at low deposition temperatures, based on insight in the nucleation behavior, which is key to advance the field of ALD of 2D materials. Moreover, this work demonstrates the conformal deposition on 3D structures, with WS2 retaining the basal plane orientation along topographic structures.

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Section: Resultsmentioning

confidence: 99%

Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism

et al. 2018

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“…Finally, it should be noted that these 5d transition metal borides are subject to strong spin–orbit effects, which are neglected in all of these computational treatments. Computing the atomic spin–orbit stabilization as described in ref leads to reductions in the computed BDEs of LaB, HfB, TaB, and WB of 0.08, 0.34, 0.44, and 0.55 eV, respectively, due to the lowering of the ground separated atom asymptote. Stabilization of the molecular ground state leads to an increase in the computed BDE by an amount that depends strongly on the molecular ground state and is estimated by first order perturbation theory, as described in ref , as 0.21 eV for the 5 Δ state of TaB.…”

Section: Discussionmentioning

confidence: 99%

“…Computing the atomic spin–orbit stabilization as described in ref leads to reductions in the computed BDEs of LaB, HfB, TaB, and WB of 0.08, 0.34, 0.44, and 0.55 eV, respectively, due to the lowering of the ground separated atom asymptote. Stabilization of the molecular ground state leads to an increase in the computed BDE by an amount that depends strongly on the molecular ground state and is estimated by first order perturbation theory, as described in ref , as 0.21 eV for the 5 Δ state of TaB. The first-order stabilization of the calculated ground states of LaB, HfB, and WB is zero, because these are all Σ states with no first-order spin–orbit splitting.…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the observation of a sharp predissociation threshold can be used to assign the BDE for a molecule with R2PI spectroscopy. This technique has been previously employed to precisely measure the BDEs for transition metal boride, aluminide, , carbide, ,− silicide, ,,, nitride, oxide, sulfide, − ,− selenide, ,,− and chloride diatomics. In this article, we report ten highly precise BDEs for early transition metal borides using the same spectroscopic method.…”

Section: Introductionmentioning

confidence: 99%

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Chemical Bonding and Electronic Structure of the Early Transition Metal Borides: ScB, TiB, VB, YB, ZrB, NbB, LaB, HfB, TaB, and WB

et al. 2021

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The predissociation thresholds of the early transition metal boride diatomics (MB, M = Sc, Ti, V, Y, Zr, Nb, La, Hf, Ta, W) have been measured using resonant two-photon ionization (R2PI) spectroscopy, allowing for a precise assignment of the bond dissociation energy (BDE). No previous experimental measurements of the BDE exist in the literature for these species. Owing to the high density of electronic states arising from the ground and low-lying separated atom limits in these open d-subshell species, a congested spectrum of vibronic transitions is observed as the energy of the ground separated atom limit is approached. Nonadiabatic and spin−orbit interactions among these states, however, provide a pathway for rapid predissociation as soon as the ground separated atom limit is reached, leading to a sharp decrease in signal to background levels when this limit is reached. Accordingly, the BDEs of the early transition metal borides have been assigned as D 0 (ScB) 1.72(6) eV, D 0 (TiB) 1.956( 16) eV, D 0 (VB) 2.150( 16) eV, D 0 (YB) 2.057(3) eV, D 0 (ZrB) 2.573(5) eV, D 0 (NbB) 2.989(12) eV, D 0 (LaB) 2.086(18) eV, D 0 (HfB) 2.593(3) eV, D 0 (TaB) 2.700(3) eV, and D 0 (WB) 2.730(4) eV. Additional insight into the chemical bonding and electronic structures of these species has been achieved by quantum chemical calculations.

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“… a This compilation only includes values measured in the Morse group. b Not yet published. Final published value may differ slightly from this report. c Ref . d Ref . e Ref . f Ref . g Ref . h Ref . i Ref . …”

Section: Bond Energies Of Transition Metalmain Group Moleculesmentioning

confidence: 99%

Predissociation Measurements of Bond Dissociation Energies

Morse

2018

Acc. Chem. Res.

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CONSPECTUS: A fundamental need in chemistry is understanding the chemical bond, for which the most quantitative measure is the bond dissociation energy (BDE). While BDEs of chemical bonds formed from the lighter main group elements are generally well-known and readily calculated by modern computational chemistry, chemical bonds involving the transition metals, lanthanides, and actinides remain computationally extremely challenging. This is due to the simultaneous importance of electron correlation, spin−orbit interaction, and other relativistic effects, coupled with the large numbers of low-lying states that are accessible in systems with open d or f subshells. The development of efficient and accurate computational methods for these species is currently a major focus of the field. An obstacle to this effort has been the scarcity of highly precise benchmarks for the BDEs of M−X bonds. For most of the transition metal, lanthanide, or actinide systems, tabulated BDEs of M−X bonds have been determined by Knudsen effusion mass spectrometric measurements of high-temperature equilibria. The measured ion signals are converted to pressures and activities of the species involved in the equilibrium, and the equilibrium constants are then analyzed using a van't Hoff plot or the third-law method to extract the reaction enthalpy, which is extrapolated to 0 K to obtain the BDE. This procedure introduces errors at every step and ultimately leads to BDEs that are typically uncertain by 2−20 kcal mol −1 (0.1−1 eV). A second method in common use employs a thermochemical cycle in which the ionization energies of the MX molecule and M atom are combined with the BDE of the M + −X bond, obtained via guided ion beam mass spectrometry, to yield the BDE of the neutral, M−X. When accurate values of all three components of the cycle are available, this method yields good resultsbut only rarely are all three values available. We have recently implemented a new method for the precise measurement of BDEs in molecules with large densities of electronic states that is based on the rapid predissociation of these species as soon as the ground separated atom limit is exceeded. When a sharp predissociation threshold is observed, its value directly provides the BDE of the system. With this method, we are able in favorable cases to determine M−X BDEs to an accuracy of ∼0.1 kcal mol −1 (0.004 eV). The method is generally applicable to species that have a high density of states at the ground separated atom limit and has been used to measure the BDEs of more than 50 transition metal−main group MX molecules thus far. In addition, a number of metal−metal BDEs have also been measured with this method. There are good prospects for the extension of the method to polyatomic systems and to lanthanide and actinide-containing molecules. These precise BDE measurements provide chemical trends for the BDEs across the transition metal series, as well as crucial benchmarks for the development of efficient and accurate computational methods for the d-and f-block elem...

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Bond Dissociation Energies of Tungsten Molecules: WC, WSi, WS, WSe, and WCl

Cited by 42 publications

References 64 publications

Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism

Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism

Chemical Bonding and Electronic Structure of the Early Transition Metal Borides: ScB, TiB, VB, YB, ZrB, NbB, LaB, HfB, TaB, and WB

Predissociation Measurements of Bond Dissociation Energies

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Bond Dissociation Energies of Tungsten Molecules: WC, WSi, WS, WSe, and WCl

Cited by 42 publications

References 64 publications

Two-Dimensional Crystal Grain Size Tuning in WS2 Atomic Layer Deposition: An Insight in the Nucleation Mechanism

Two-Dimensional Crystal Grain Size Tuning in WS2 Atomic Layer Deposition: An Insight in the Nucleation Mechanism

Chemical Bonding and Electronic Structure of the Early Transition Metal Borides: ScB, TiB, VB, YB, ZrB, NbB, LaB, HfB, TaB, and WB

Predissociation Measurements of Bond Dissociation Energies

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Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism

Two-Dimensional Crystal Grain Size Tuning in WS₂ Atomic Layer Deposition: An Insight in the Nucleation Mechanism