scholarly journals Nitrile versus isonitrile adsorption at interstellar grain surfaces

2017 ◽  
Vol 608 ◽  
pp. A50 ◽  
Author(s):  
M. Bertin ◽  
M. Doronin ◽  
X. Michaut ◽  
L. Philippe ◽  
A. Markovits ◽  
...  
Keyword(s):  
Density Functional ◽  
Surface Defects ◽  
High Vacuum ◽  
Solid Support ◽  
Ultra High Vacuum ◽  
Structural Defects ◽  
Adsorption Energies ◽  
The Difference ◽  
Temperature Programmed ◽  
Open Question

Context. Almost 20% of the ~200 different species detected in the interstellar and circumstellar media present a carbon atom linked to nitrogen by a triple bond. Of these 37 molecules, 30 are nitrile R-CN compounds, the remaining 7 belonging to the isonitrile R-NC family. How these species behave in their interactions with the grain surfaces is still an open question. Aims. In a previous work, we have investigated whether the difference between nitrile and isonitrile functional groups may induce differences in the adsorption energies of the related isomers at the surfaces of interstellar grains of various nature and morphologies. This study is a follow up of this work, where we focus on the adsorption on carbonaceous aromatic surfaces. Methods. The question is addressed by means of a concerted experimental and theoretical approach of the adsorption energies of CH3CN and CH3NC on the surface of graphite (with and without surface defects). The experimental determination of the molecule and surface interaction energies is carried out using temperature-programmed desorption in an ultra-high vacuum between 70 and 160 K. Theoretically, the question is addressed using first-principle periodic density functional theory to represent the organised solid support. Results. The adsorption energy of each compound is found to be very sensitive to the structural defects of the aromatic carbonaceous surface: these defects, expected to be present in a large numbers and great diversity on a realistic surface, significantly increase the average adsorption energies to more than 50% as compared to adsorption on perfect graphene planes. The most stable isomer (CH3CN) interacts more efficiently with the carbonaceous solid support than the higher energy isomer (CH3NC), however.

Studies of Ge/Si(100) and Observation of Atomic Steps on Si(100) using Biassed Secondary Electron Imaging in a UHV STEM

1990 ◽  
Vol 48 (1) ◽  
pp. 308-309
Author(s):  
Mohan Krishnamurthy ◽  
Jeff S. Drucker ◽  
John A. Venablest
Keyword(s):  
Secondary Electron ◽  
Critical Thickness ◽  
Surface Defects ◽  
Film Growth ◽  
Growth Parameters ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Surface Steps ◽  
Epitaxial Crystal Growth ◽  
Electron Imaging

Secondary Electron Imaging (SEI) has become a useful mode of studying surfaces in SEM[1] and STEM[2,3] instruments. Samples have been biassed (b-SEI) to provide increased sensitivity to topographic and thin film deposits in ultra high vacuum (UHV)-SEM[1,4]; but this has not generally been done in previous STEM studies. The recently developed UHV-STEM ( codenamed MIDAS) at ASU has efficient collection of secondary electrons using a 'parallelizer' and full sample preparation system[5]. Here we report in-situ deposition and annealing studies on the Ge/Si(100) epitaxial system, and the observation of surface steps on vicinal Si(100) using b-SEI under UHV conditions in MIDAS.Epitaxial crystal growth has previously been studied using SEM and SAM based experiments [4]. The influence of surface defects such as steps on epitaxial growth requires study with high spatial resolution, which we report for the Ge/Si(100) system. Ge grows on Si(100) in the Stranski-Krastonov growth mode wherein it forms pseudomorphic layers for the first 3-4 ML (critical thickness) and beyond which it clusters into islands[6]. In the present experiment, Ge was deposited onto clean Si(100) substrates misoriented 1° and 5° toward <110>. This was done using a mini MBE Knudsen cell at base pressure ~ 5×10-11 mbar and at typical rates of 0.1ML/min (1ML =0.14nm). Depositions just above the critical thickness were done for substrates kept at room temperature, 375°C and 525°C. The R T deposits were annealed at 375°C and 525°C for various times. Detailed studies were done of the initial stages of clustering into very fine (∼1nm) Ge islands and their subsequent coarsening and facetting with longer anneals. From the particle size distributions as a function of time and temperature, useful film growth parameters have been obtained. Fig. 1 shows a b-SE image of Ge island size distribution for a R T deposit and anneal at 525°C. Fig.2(a) shows the distribution for a deposition at 375°C and Fig.2(b) shows at a higher magnification a large facetted island of Ge. Fig.3 shows a distribution of very fine islands from a 525°C deposition. A strong contrast is obtained from these islands which are at most a few ML thick and mottled structure can be seen in the background between the islands, especially in Fig.2(a) and Fig.3.

Deposition of Iron on Si(111)-(7×7): Photo- and Electron-Assisted Decomposition of Fe(CO)5

1986 ◽  
Vol 75 ◽  
Author(s):  
J. R. Swanson ◽  
C. M. Friend ◽  
Y. J. Chabal
Keyword(s):  
Auger Electron ◽  
Silicon Crystal ◽  
High Vacuum ◽  
Low Frequency ◽  
Temperature Programmed Desorption ◽  
Thermal Reaction ◽  
Ultra High Vacuum ◽  
Temperature Programmed ◽  
Ultraviolet Photons ◽  
Induced Decomposition

AbstractLaser- and electron-assisted deposition of Fe on Si(111)-(7×7) surfaces using decomposition of Fe(CO)5 has been investigated with multiple internal reflection Fourier transform infrared, Auger electron and temperature programmed desorption spectroscopies and low energy electron diffraction under ultra-high vacuum conditions. No thermal reaction was apparent in temperature programmed desorption experiments: only molecular Fe(CO)5 desorption was observed at temperatures of 150 and 170 K, corresponding to desorption energies in the range of 7–10 kcal./mole. Fe(CO)5 decomposition could be induced using either incident 1.6 keV electrons or ultraviolet photons. Significant amounts of carbon were deposited from the electron induced decomposition, consistent with earlier reports on the Si(100) surface. In contrast, ultraviolet photolysis did not result in any detectable incorporation of carbon or oxygen into the iron deposits. No partially decarbonylated Fe(CO)x, x<5, fragments were detected subsequent to exposure to photons using infrared spectroscopy. However, a new, unresolved low frequency shoulder did appear in the infrared spectrum after exposing the Fe(CO)5 covered Si(111)-(7×7) crystal to the electron beam. Iron photodeposition was evident in the Auger electron spectra obtained subsequent to photolysis and annealing of the surface to either 300 K or 1000 K in order to desorb unreacted Fe(CO)5. These data suggest that there are no surface stable Fe(CO)x, x<5, species in the photodeposition process. Instead, photolysis yields Fe atoms directly, even at low temperatures. Annealing to temperatures on the order of 1000 K subsequent to iron deposition resulted in a significant decrease in the Fe:Si ratio as measured by Auger electron spectroscopy. In addition, CO could not be readsorbed on a surface where the Fe(CO)5 had been decomposed. This is attributed to dissolution of Fe into the bulk silicon crystal.

Hydridization and catalysis by lanthanide films

1984 ◽  
Vol 393 (1805) ◽  
pp. 257-276 ◽  
Keyword(s):  
Activation Energy ◽  
High Vacuum ◽  
Deuterium Atom ◽  
Ultra High Vacuum ◽  
Gas Uptake ◽  
Metal Sublattice ◽  
Hydrogen Deuterium ◽  
Higher Temperature ◽  
Temperature Programmed ◽  
Interstitial Hydrogen

Hydrogen absorption to give the dihydrides MH 2+1 containing interstitial hydrogen H i has been studied for the metals Gd, Dy, Er, Yb and Lu in the form of films deposited in ultra-high vacuum on glass. Film areas were determined by Kr adsorption, and hydrogen content, in particular inter­stitial hydrogen H i , characterized by gas uptake, temperature programmed desorption, electrical conductivity and work function measurements by the diode method. The catalytic activity of the dihydride films for the H 2 + D 2 → 2HD reaction was studied at a pressure of 1.1 Torr over 175-579 K, and at 273 K over 0.19-6.2 Torr. Arrhenius plots for the rate con­stant show a low temperature low activation energy region changing over at a temperature T c to a higher temperature higher activation energy régime, with T c on average for the five metals about 50 K below the tem­perature T max at which the interstitial hydrogen H i has disappeared. The suggested mechanisms are T < T c : D 2 + H i □ s → (D 2 H i )□ s → □ s D i + HD, (1) T > T c : D 2 + H 2 + 4□ s → 2(D i □ s ) (H i □ s ) → 4□ s + 2HD, (2) where H i □ s , D i □ s , denotes a hydrogen, deuterium, atom held on a surface octahedral site in the f. c. c. metal sublattice. These mechanisms agree with the observed approximate first-order pressure dependency down to 77 K. The rate constants at both 273 K (under T c ) and 573 K (over T c ) decrease over Gd, Dy, Er, to Yb, and rise again to Lu, and this is discussed in terms of the metal-hydrogen, H i □ s or D i □ s bond strength.

scholarly journals How to Extract Adsorption Energies, Adsorbateadsorbate Interaction Parameters, and Saturation Coverages from Temperature Programmed Desorption Experiments

2021 ◽  
Author(s):  
Sudarshan Vijay ◽  
Henrik Høgh Kristoffersen ◽  
Yu Katayama ◽  
Yang Shao-Horn ◽  
Ib Chorkendorff ◽  
...  
Keyword(s):  
Adsorption Energy ◽  
Density Functional ◽  
Configurational Entropy ◽  
Density Functional Theory Calculations ◽  
Temperature Programmed Desorption ◽  
Functional Theory ◽  
Interaction Terms ◽  
Saturation Coverage ◽  
Adsorption Energies ◽  
Temperature Programmed

<p>We present a simple scheme to extract the adsorption energy, adsorbate interaction parameter and the saturation coverage from temperature programmed desorption (TPD) experiments. We propose that the coverage dependent adsorption energy can be fit using a functional form including the configurational entropy and linear adsorbate-adsorbate interaction terms. As one example of this scheme, we analyze TPD spectra of desorption on Au(211) and Au(310) surfaces. We determine that under atmospheric pressure, the <i>steps</i> of both facets adsorb between 0.4-0.9 ML coverage of CO*. We show this result to be consistent with density functional theory calculations of adsorption energies with the BEEF-vdW functional. <b></b></p>

scholarly journals Effect of H Adsorption on the Magnetic Properties of an Fe Island on a W(110) Surface

2019 ◽  
Author(s):  
Marko Melander ◽  
Hannes Jonsson
Keyword(s):  
Magnetic Properties ◽  
Data Storage ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Low Dimensional ◽  
Low Dimensional Materials

<p>Low-dimensional materials, such as ultrathin films, nanoislands and wires, are actively being researched due to their interesting magnetic properties and possible technological applications for example in high density data storage. Results of calculations of an Fe nanoisland on a W(110) support are presented here with particular focus on the effect of hydrogen adsorption on its magnetic properties. This is an important consideration since hydrogen is present even under ultra-high vacuum conditions. The calculations are based on density functional theory within the generalized gradient approximation. The adsorption of H atoms is found to strongly decrease the magnetic moment of the Fe atoms they are bound to, down to less than a half in some cases as compared with the clean Fe island. The results show that it may be important to take the presence of hydrogen into account in measurements of magnetic properties of nanoislands.</p>

The influence of surface defects on the catalytic reaction of submonolayer films observed by photoemission electron microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 268-269
Author(s):  
M. Mundschau ◽  
M. E. Kordesch ◽  
B. Rausenberger ◽  
W. Engel ◽  
A. M. Bradshaw ◽  
...  
Keyword(s):  
Active Sites ◽  
Surface Defects ◽  
Co Adsorption ◽  
High Vacuum ◽  
Adsorbed Layer ◽  
Catalytic Reactions ◽  
Ultra High Vacuum ◽  
Defect Sites ◽  
Extreme Sensitivity ◽  
Photoemission Electron

Defects on surfaces are known to greatly enhance the rate of many catalytic reactions. In some cases, the active sites in catalysis may reside only at defect sites. Surface defects are best characterized by microscopic techniques. It was demonstrated earlier that catalytic reactions can be followed using an ultra high vacuum version of a classical photoemission electron microscope. This technique can image submonolayer coverages because of the extreme sensitivity of photoemission to local work function.We report here studies on the catalytic oxidation of adsorbed CO on Pt which was followed in situ and in real time. For temperatures below 500 K and for partial pressure ratios of oxygen to CO of less than ∽ 10:1, an adsorbed layer of CO forms which effectively blocks the co-adsorption of oxygen.

In situ studies of heterogeneous reactions using surface electron microscopies LEEM, MEM, and PEEM

1993 ◽  
Vol 51 ◽  
pp. 998-999
Author(s):  
W. Engel ◽  
B. Rausenberger ◽  
W. Swiech ◽  
C. S. Rastomjee ◽  
A. M. Bradshaw ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Surface Defects ◽  
Imaging Techniques ◽  
High Vacuum ◽  
Reaction Diffusion ◽  
Heterogeneous Reactions ◽  
Ultra High Vacuum ◽  
Electron Microscopies ◽  
Adsorption Sites ◽  
Physical And Chemical

The preferred imaging techniques for the observation of physical and chemical processes at solid surfaces with high temporal and spatial resolution are low-energy electron microscopy (LEEM), mirror electron microscopy (MEM) and photoemission electron microscopy (PEEM). In these techniques the energy transfer to the surface during the imaging process itself is small so that surface processes such as adsorption, diffusion, chemical reactions etc. remain largely undisturbed.LEEM, MEM and PEEM, which all can be performed in an ultra-high-vacuum surface microscope of the Bauer/Telieps type, have been applied to the study of CO/O reaction-diffusion fronts on a Pt(100) surface saturated with CO. These fronts develop after admission of oxygen to the surface (10-6 mbar) at surface defects which provide adsorption sites for oxygen and thus initiate the autocatalytic oxidation process. The formed CO2 is instantaneously desorbed, freeing adsorption sites which are then occupied by oxygen from the gas phase. The front propagates over the whole surface, leaving behind an oxygen-covered region.

Selective Oxidation of Ammonia on Ruthenium to Form p(2 x 2) Nitrogen Layer

2013 ◽  
Vol 6 (1) ◽  
Author(s):  
S. Balgooyen ◽  
I. Waluyo
Keyword(s):  
Low Temperature ◽  
High Vacuum ◽  
Hydrogenation Reaction ◽  
Ultra High Vacuum ◽  
Surface Chemical ◽  
Low Energy Electron Diffraction ◽  
Chemical Studies ◽  
Low Energy Electron ◽  
Temperature Programmed ◽  
Oxidation Of Ammonia

Oxidation of ammonia was used to prepare a p(2 x 2) nitrogen layer on the Ru(0001) surface as verified by temperature-programmed desorption (TPD) and low energy electron diffraction (LEED). The process takes place in an ultra-high vacuum (UHV) chamber. The surface is precovered with oxygen and then exposed to ammonia at low temperature. Upon heating, the ammonia is oxidized to form water, which desorbs at low temperature to leave a nitrogencovered surface. The resulting layer can be used in a variety of surface chemical studies, including a hydrogenation reaction, which is an important part in the study of the Haber-Bosch process, in which ruthenium is used as a catalyst.

Nanotribology of Diamond Films Studied by Atomic Force Microscopy

1990 ◽  
Vol 188 ◽  
Author(s):  
Gabi Neubauer ◽  
Sidney R. Cohen ◽  
Gary M. Mcclelland ◽  
Hajime Seki
Keyword(s):  
High Vacuum ◽  
Diamond Films ◽  
Ultra High Vacuum ◽  
Nanometer Scale ◽  
Kinetic Friction ◽  
Experimental Conditions ◽  
Stick Slip ◽  
Force Microscopy ◽  
Atomic Force ◽  
The Difference

ABSTRACTAn atomic force microscope, operated in ultra-high vacuum has been employed to study the tribological properties of diamond films under small loads (< 10−6 N) on a nanometer scale. The incidence of intermittent motion, “stick-slip”, while sliding a diamond tip across the diamond film, is detected under certain experimental conditions and is discussed with respect to the difference between static and kinetic friction, sample topography and a varying sample condition.

Growth and Structure of Al/MgO Interfaces

1994 ◽  
Vol 357 ◽  
Author(s):  
T. Wagner ◽  
M. Ruhle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Structural Defects ◽  
Cross Sectional ◽  
Aluminum Films ◽  
Transmission Electron

AbstractThe A1/MgO system has been used as a model system to study growth processes and structure at metal/ceramic interfaces. Aluminum films were grown on air-cleaved MgO (100) substrates in ultra high vacuum (UHV) by molecular beam epitaxy (MBE). The substrates and films were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), conventional transmission electron microscopy (CTEM), and high resolution transmission electron microscopy (HREM). XRD measurements exhibited a pronounced {100} texture. Employing electron diffraction in the TEM on cross sectional samples, we observed the following orientation relationship between Al and MgO: (100)A1 II (100)MgO; [010]A1 II [010]MgO. The atomistic structure of the interface was investigated by HREM. Regions of structural defects can be identified clearly at the interface.

Sign in / Sign up

Export Citation Format

Share Document