scholarly journals A NEW SETUP FOR THE STUDY OF ADSORPTION/DESORPTION PROCESSES AND NANOPARTICLES FORMATION IN POROUS ALUMINA

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
C. Marinelli ◽  
E. Mariotti ◽  
N. Papi ◽  
F. Sarri ◽  
A. Ziccardi ◽  
...  
Keyword(s):  
Coming Out ◽  
Porous Alumina ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Rubidium Atoms ◽  
Rb Vapor ◽  
Alkali Atoms ◽  
Confinement Region ◽  
Promising Application ◽  
Adsorption Desorption

We present a setup devoted to the study of adsorption and desorption processes of alkali atoms after deposition on a 300 nm thick porous alumina substrate in an Ultra High Vacuum chamber. Rubidium atoms, delivered by a dispenser source, enter the 20-30 nm diameter pores, diffuse in and stick to their walls. A 1 W power laser is used in order to induce detachment and take the atoms back in the vapor phase in a very tight confinement region. The desorbed atoms coming out the sample can be monitored via both a resonant optical detection and an electronic amplifier after ionization. The desorbing laser is also able to promote the formation of Rubidium nanoparticles, as the high Rb vapor density in the pores favors aggregation around nucleation point defects. In this way, the apparatus allows for the study of the fundamental processes related to atom – surface interactions in presence of light as well as of several promising application to nanomaterials.

scholarly journals On-surface trapping of alkali atoms by crown ethers in ultra high vacuum

2019 ◽  
Vol 1 (5) ◽  
pp. 1721-1725 ◽  
Author(s):  
Matus Stredansky ◽  
Elia Turco ◽  
Zhijing Feng ◽  
Roberto Costantini ◽  
Giovanni Comelli ◽  
...  
Keyword(s):  
Crown Ethers ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Alkali Atoms ◽  
Organic Architecture ◽  
Trapping Sites

Crown ethers of a hetero-organic architecture in ultra-high vacuum are the preferential trapping sites for Na atoms.

The adsorption, desorption, and exchange reactions of oxygen, hydrogen, and water on platinum surfaces. III. Water adsorption and exchange with oxygen and hydrogen

1977 ◽  
Vol 55 (10) ◽  
pp. 1658-1666 ◽  
Author(s):  
Y. K. Peng ◽  
P. T. Dawson
Keyword(s):  
Exchange Reaction ◽  
Hydrogen Adsorption ◽  
High Vacuum ◽  
Adsorbed Water ◽  
Ultra High Vacuum ◽  
Exchange Reactions ◽  
Adsorption Of Water ◽  
Apparent Activation Energies ◽  
Distribution Studies ◽  
Adsorption Desorption

Ultra-high vacuum thermal desorption experiments have been carried out on the adsorption of water, and the D2O/H and D216O/18O exchange reactions on platinum previously characterized by oxygen and hydrogen adsorption studies. Water is weakly adsorbed and only at T < 150 K, an observation confirmed by using H2 adsorption as a chemical probe for the presence of adsorbed water. The thickness of the adsorbed D2O layers was determined by a novel method involving monitoring the power output of the temperature programmer. Exchange occurs between adsorbed H and a D2O overlayer and the extent of exchange increases with the thickness of the overlayer. Isotope distribution studies show that the surface is heterogeneous and the exchange reaction does not occur at uniform rate. Exchange occurs between adsorbed 18O and a D216O overlayer. The extent of exchange is constant up to T ∼ 300 K showing that D2O is more strongly bound on O-covered Pt presumably as a result of H bonding. Heterogeneity also is apparent in the O-exchange reaction. The apparent activation energies for exchange are 1.8 and 2.9 kcal mol−1 for the half- and fully-covered surfaces, respectively.

Ultra-high vacuum system for adsorption–desorption studies of hydrogen storage on/in carbon nanotubes

2006 ◽  
Vol 200 (10) ◽  
pp. 3203-3205 ◽  
Author(s):  
Leszek Stobinski ◽  
Der-Chi Tien ◽  
Chih-Yu Liao ◽  
Hong-Ming Lin ◽  
Wen-Shiow Kao
Keyword(s):  
Carbon Nanotubes ◽  
Hydrogen Storage ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Vacuum System ◽  
Adsorption Desorption

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

1971 ◽  
Vol 29 ◽  
pp. 226-227 ◽  
Author(s):  
George H. N. Riddle ◽  
Benjamin M. Siegel
Keyword(s):  
Vacuum Chamber ◽  
Pyrolytic Graphite ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Graphite Substrate ◽  
Nickel Substrate ◽  
Routine Procedure ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

A High Voltage Electron Microscopy Study of Sub-Oxide Formation in Vanadium

1971 ◽  
Vol 29 ◽  
pp. 212-213
Author(s):  
R. H. Geiss ◽  
R. L. Ladd ◽  
K. R. Lawless
Keyword(s):  
High Vacuum ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Ultra High Vacuum ◽  
Pure Oxygen ◽  
Pressure Oxidation ◽  
High Voltage Electron Microscopy ◽  
Oxidation Study ◽  
Voltage Electron ◽  
Good Agreement

Detailed electron microscope and diffraction studies of the sub-oxides of vanadium have been reported by Cambini and co-workers, and an oxidation study, possibly complicated by carbon and/or nitrogen, has been published by Edington and Smallman. The results reported by these different authors are not in good agreement. For this study, high purity polycrystalline vanadium samples were electrochemically thinned in a dual jet polisher using a solution of 20% H2SO4, 80% CH3OH, and then oxidized in an ion-pumped ultra-high vacuum reactor system using spectroscopically pure oxygen. Samples were oxidized at 350°C and 100μ oxygen pressure for periods of 30,60,90 and 160 minutes. Since our primary interest is in the mechanism of the low pressure oxidation process, the oxidized samples were cooled rapidly and not homogenized. The specimens were then examined in the HVEM at voltages up to 500 kV, the higher voltages being necessary to examine thick sections for which the oxidation behavior was more characteristic of the bulk.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

A Field Emission System For Transmission Electron Microscopy

1973 ◽  
Vol 31 ◽  
pp. 298-299
Author(s):  
Michel Troyonal ◽  
Huei Pei Kuoal ◽  
Benjamin M. Siegelal
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
Optical System ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Objective Lens ◽  
Electron Optical System ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Emission System

A field emission system for our experimental ultra high vacuum electron microscope has been designed, constructed and tested. The electron optical system is based on the prototype whose performance has already been reported. A cross-sectional schematic illustrating the field emission source, preaccelerator lens and accelerator is given in Fig. 1. This field emission system is designed to be used with an electron microscope operated at 100-150kV in the conventional transmission mode. The electron optical system used to control the imaging of the field emission beam on the specimen consists of a weak condenser lens and the pre-field of a strong objective lens. The pre-accelerator lens is an einzel lens and is operated together with the accelerator in the constant angular magnification mode (CAM).

Hetero-Epitaxy of Group Va Metals on Sapphire

1972 ◽  
Vol 30 ◽  
pp. 492-493
Author(s):  
J. E. O'Neal ◽  
J. J. Bellina ◽  
B. B. Rath
Keyword(s):  
Thermal Contact ◽  
High Vacuum ◽  
Electron Beam Evaporation ◽  
Ultra High Vacuum ◽  
Backing Plate ◽  
Sapphire Substrates ◽  
Deposition Parameters ◽  
Polishing Damage ◽  
Reflection Electron Diffraction

Thin films of the bcc metals vanadium, niobium and tantalum were epitaxially grown on (0001) and sapphire substrates. Prior to deposition, the mechanical polishing damage on the substrates was removed by an in-situ etch. The metal films were deposited by electron-beam evaporation in ultra-high vacuum. The substrates were heated by thermal contact with an electron-bombarded backing plate. The deposition parameters are summarized in Table 1.The films were replicated and examined by electron microscopy and their crystallographic orientation and texture were determined by reflection electron diffraction. Verneuil-grown and Czochralskigrown sapphire substrates of both orientations were employed for each evaporation. The orientation of the metal deposit was not affected by either increasing the density of sub-grain boundaries by about a factor of ten or decreasing the deposition rate by a factor of two. The results on growth epitaxy are summarized in Tables 2 and 3.

Sign in / Sign up

Export Citation Format

Share Document