Growth of n-alkane films on a single-crystal substrate

Wu, Zhenyu; Ehrlich, Steven N.; Matthies, B.; Herwig, K. W.; Dai, Pengcheng; Volkmann, U.G.; Hansen, Flemming Yssing; Taub, H.

doi:10.1016/s0009-2614(01)01147-2

Cited by 31 publications

(29 citation statements)

References 14 publications

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“…The mean free path of the photoelectrons during the UPS measurements is approximately 0.5 nm, [44] which is similar to the thickness of a complete n-butane monolayer coverage reported on various surfaces {0.41 nm on MgO (100) [62] and Ag (111) [63] }. The saturation of the  state, which occurs at d/l e  1, thus corresponds to the completion of a monolayer.…”

Section: Interpretation Of Isobarssupporting

confidence: 74%

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

Lloyd

Hansen

Ranke

et al. 2011

Applied Catalysis A: General

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Nanocrystalline thin films of the alkane skeletal isomerisation catalyst sulfated zirconia were successfully deposited on a silicon substrate in order to allow the application of surface science techniques. Thermal treatment of the films was optimised to chemically mimic the powder preparation process, resulting in films possessing the essential features (including tetragonal phase, nanocrystallinity and sulfur content of ~3 atomic %) of active powder catalysts. The n-butane adsorption-desorption equilibrium under isobaric conditions (10 -8 to 10 -6 hPa) over the temperature range 300-100 K was monitored by photoelectron spectroscopy. Analysis of the isobars revealed strong and weak n-butane chemisorption sites, releasing heats of between 59-40 and 47-34 kJ/mol, corresponding to 5 and 25% of a monolayer coverage, respectively. The total amount of chemisorbed n-butane coincides with the estimated number of surface sulfate groups. An increase in adsorption heat was observed between coverages of ~5-8% of a monolayer, indicating adsorbate-adsorbate interactions. It follows that adjacent sites are present and isomerisation by a bimolecular surface reaction is feasible. Physisorption on the films generates heats of ~28 kJ/mol, for coverages from 30% up to a complete monolayer. Multilayer adsorption results in the formation of an electrically insulating adsorbate structure. It is proposed that the strong chemisorption sites correspond to an interaction with a minority disulfate species.

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Section: Interpretation Of Isobarssupporting

confidence: 74%

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

Lloyd

Hansen

Ranke

et al. 2011

Applied Catalysis A: General

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“…Previous experiments with alkane adsorption on graphite ͑0001͒, 3,19 Cu͑111͒, 20 Au͑111͒, 20 Ag͑111͒, 21 and Pt͑111͒ 22 surfaces, using a wide variety of techniques, have always indicated a first layer in which the long molecular axis is parallel to the surface. In addition, molecular dynamics ͑MD͒ simulations of intermediate-length alkanes adsorbed on Au͑001͒ 23 and graphite basal plane surfaces 24 show the molecules in the first layer to be parallel to the surface.…”

Section: Discussionmentioning

confidence: 99%

High-resolution ellipsometric study of an n-alkane film, dotriacontane, adsorbed on a SiO2 surface

Volkmann

Pino

Altamirano

et al. 2002

The Journal of Chemical Physics

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Using high-resolution ellipsometry and stray light intensity measurements, we have investigated during successive heating-cooling cycles the optical thickness and surface roughness of thin dotriacontane (n-C 32 H 66 ) films adsorbed from a heptane (n-C 7 H 16 ) solution onto SiO 2 -coated Si͑100͒ single-crystal substrates. Our results suggest a model of a solid dotriacontane film that has a phase closest to the SiO 2 surface in which the long-axis of the molecules is oriented parallel to the interface. Above this ''parallel film'' phase, a solid monolayer adsorbs in which the molecules are oriented perpendicular to the interface. At still higher coverages and at temperatures below the bulk melting point at T b ϭ341 K, solid bulk particles coexist on top of the ''perpendicular film.'' For higher temperatures in the range T b ϽTϽT s where T s ϭ345 K is the wetting temperature of the bulk phase, the coexisting bulk particles melt into droplets; and for TϾT s , a uniformly thick fluid film wets to the parallel film phase. This structure of the alkane/SiO 2 interfacial region differs qualitatively from that which occurs in the surface freezing effect at the bulk alkane fluid/vapor interface. In that case, there is again a perpendicular film phase adjacent to the air interface but no parallel film phase intervenes between it and the bulk alkane fluid. Similarities and differences between our model of the alkane/SiO 2 interface and one proposed recently will be discussed. Our ellipsometric measurements also show evidence of a crystalline-to-plastic transition in the perpendicular film phase similar to that occurring in the solid bulk particles present at higher coverages. In addition, we have performed high-resolution ellipsometry and stray-light measurements on dotriacontane films deposited from solution onto highly oriented pyrolytic graphite substrates. After film deposition, these substrates proved to be less stable in air than SiO 2 .

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“…In general, these peaks can be observed to a higher wave vector transfer Q than is possible with x-ray diffraction where the effect of the molecular form factor attenuates the scattering at high Q. 15,23,[29][30][31][32] We conducted our neutron diffraction experiments on C24 and C32 monolayers on the two-axis diffractometer located at the C-port of the University of Missouri Research Reactor Facility. The neutron beam with wavelength of 4.35 Å scattered from the sample placed in a transmission geometry before reaching a five-detector data acquisition system.…”

Section: B Neutron Diffractionmentioning

confidence: 99%

Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

Diama

Matthies

Herwig

et al. 2009

The Journal of Chemical Physics

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We present evidence from neutron diffraction measurements and molecular dynamics ͑MD͒ simulations of three different monolayer phases of the intermediate-length alkanes tetracosane ͑n-C 24 H 50 denoted as C24͒ and dotriacontane ͑n-C 32 H 66 denoted as C32͒ adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered ͑RC͒ structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its ͓110͔ direction such that the distance between molecular rows in a lamella is 4.26 Å = ͱ 3a g , where a g = 2.46 Å is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a "smectic" phase in which the inter-row spacing within a lamella expands by ϳ10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

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Growth of n-alkane films on a single-crystal substrate

Cited by 31 publications

References 14 publications

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

High-resolution ellipsometric study of an n-alkane film, dotriacontane, adsorbed on a SiO2 surface

Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

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