Vibrational properties of surface hydroxyls: Nonempirical model calculations including anharmonicities

Mix, Hartmut; Sauer, Joachim; Schröder, K.-P.; Merkel, A.

doi:10.1135/cccc19882191

Cited by 37 publications

(17 citation statements)

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“…The computed frequencies of 600 (438) cm −1 for Si2a–H(D) and 621 (422) cm −1 for the Si1a–H(D) modes agree with experiments within the accuracy of vibrational modes obtained by density functional theory (DFT)–generalized gradient approximation and the harmonic approximation. In fact, anharmonicities can change frequencies upto ~80 cm −1 for groups such as surface silanols40, which provides an indication of the accuracy of the present calculations. As evident from Table 1, the largest difference between experimental and theoretical values is 37 cm −1 , with the theoretical value always lower than the experimental one, indicating the systematic nature of this error.…”

Section: Resultsmentioning

confidence: 78%

Hydrogen-induced nanotunnel opening within semiconductor subsurface

et al. 2013

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One of the key steps in nanotechnology is our ability to engineer and fabricate low-dimensional nano-objects, such as quantum dots, nanowires, two-dimensional atomic layers or three-dimensional nano-porous systems. Here we report evidence of nanotunnel opening within the subsurface region of a wide band-gap semiconductor, silicon carbide. Such an effect is induced by selective hydrogen/deuterium interaction at the surface, which possesses intrinsic compressive stress. This finding is established with a combination of ab-initio computations, vibrational spectroscopy and synchrotron-radiation-based photoemission. Hydrogen/deuterium-induced puckering of the subsurface Si atoms marks the critical step in this nanotunnel opening. Depending on hydrogen/deuterium coverages, the nanotunnels are either metallic or semiconducting. Dangling bonds generated inside the nanotunnel offer a promising template to capture atoms or molecules. These features open nano-tailoring capabilities towards advanced applications in electronics, chemistry, storage, sensors or biotechnology. Understanding and controlling such a mechanism open routes towards surface/interface functionalization.

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Section: Resultsmentioning

confidence: 78%

Hydrogen-induced nanotunnel opening within semiconductor subsurface

et al. 2013

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“…At a bulk NHJNH4+ ratio between 0 and approximately 1, at least five types of ammonium species may exist for samples 3 and 4. We assign the signal at 6 = 6.9 to ammonium ions located in a supercage, since this signal is also observed for sample 1 where the ammonium ions are located in the supercages only.…”

Section: Resultsmentioning

confidence: 99%

Interaction of ammonia with Broensted acid sites in different cages of zeolite Y as studied by proton MAS NMR

Jacobs¹,

Haan²,

Ven³

et al. 1993

J. Phys. Chem.

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. (1993). Interaction of ammonia with Broensted acid sites in different cages of zeolite Y as studied by proton MAS NMR. Journal of Physical Chemistry, 97(40), 10394-10402. DOI: 10.1021/j100142a022General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Ammonia adsorption onto acidic Y zeolites is studied with 'H MAS N M R (at 295-320 K). The influence of the amount of adsorbed ammonia is investigated in the presence of sodium or cesium as exchangeable cations and for different framework compositions (Si/Al= 2.4-12). The B r~n s t e d sites in unloaded or partially loaded zeolites are observed near 6 = 3.9 for protons in supercages and near 6 = 4.6 for protons in sodalite cages.Ammonium ions under condition of no proton-exchange resonate at 6 = 8.1. These species are detected as such only in the sodalite cages. In the supercages, a signal at 6 = 6.9 is observed, which is ascribed to an exchange involving NH4+ (6 = 8,1), H + (6 = 3.9), and NH3 (6 = 0.8). Furthermore, in the sodalite cages, a signal at 6 = 6.5 is observed, which is ascribed to an exchange involving NH4+ (6 = 8.1), H+ (6 = 4.6), and NHs (6 = 0.8), but with different relative residence times. Additionally, ammonium-ammonia signals are found at 6 = 5.3-5.9 and at a position determined by the NH3/NH4+ ratio in the zeolite (6 = 7-1). For the ammoniumammonia species proton-exchange between ammonium and ammonia is fast compared to the time scale of the N M R experiment. For at least two ammonium species proton-exchange with the Br~nsted protons is fast, and consequently the lines are shifted to 6 = 6.9 and 6.5. This implies that ammonium ions observed at 6 = 8.1 have the lowest basicity and the ammonium ions at 6 = 6.5 have the highest basicity. However, for the temperature range used, ammonia reacts statistically with the Bransted sites of different acid strength.

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“…In an ab initio study by Mix et al 48 the of the free zeolitic OH groups was found to be equal to -4 cm-'. This shows the contribution to the potential curve of the bending vibration from the H bonding to be harmonic with high precision.…”

Section: Resultsmentioning

confidence: 99%