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Construction and Application of a Novel Combination Glove Box Deposition System to the Study of Air-Sensitive Materials by Tunneling Spectroscopy

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Construction and Application of a Novel Combination Glove Box Deposition System to the Study of Air-Sensitive Materials by Tunneling Spectroscopy Construction and application of a novel combination glove box deposition system to the study of air-sensitive materials by tunneling spectroscopy Cite as: Review of Scientific Instruments 55, 1120 (1984); https://doi.org/10.1063/1.1137895 Submitted: 27 February 1984 . Accepted: 20 March 1984 . Published Online: 04 June 1998 K. W. Hipps, and Ursula Mazur ARTICLES YOU MAY BE INTERESTED IN A Versatile, Inert Atmosphere Vacuum Glove Box Review of Scientific Instruments 40, 414 (1969); https://doi.org/10.1063/1.1683961 Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips The Journal of Chemical Physics 121, 11965 (2004); https://doi.org/10.1063/1.1814076 Review of Scientific Instruments 55, 1120 (1984); https://doi.org/10.1063/1.1137895 55, 1120 © 1984 American Institute of Physics. Construction and application of a novel combination glove box deposition system to the study of air-sensitive materials by tunneling spectroscopy K. W. Hipps and Ursula Mazur Department of Chemistry and Chemical Physics Program, Washington State University, Pullman, Washington 99164-4630 (Received 27 February 1984; accepted for publication 20 March 1984) The construction and application of a high-vacuum deposition system housed in a recirculating, catalytically scrubbed, inert-atmosphere glove box is reported. This system is specifically applied to the fabrication of tunnel diodes used in a surface vibrational spectroscopy called inelastic electron tunneling spectroscopy or lETS. Through the use of this inert-atmosphere adsorption/ fabrication system, tunneling spectra have been obtained from a variety of air-sensitive compounds adsorbed on aluminum oxide. Up to now, spectra of some of the species reported here have been unattainable by the adsorption techniques used in lETS. The test molecules employed in this study included TCNE (tetracyancethylene), TCNQ (tetracyanoquinodimethane), and CO2(CO)s' TCNE adsorbed reactively on thin-film alumina under nitrogen to form a species with a vibrational spectrum similar to that of the TCNE-- 2 ion, while TCNQ appears to form the monoanion under the same adsorption conditions. INTRODUCTION I. EXPERIMENTAL SETUP Inelastic electron tunneling spectroscopy (lETS), or tunnel­ A. Glove box deposition system ing spectroscopy, is a successful surface technique used to measure the molecular vibrations, 1-3 and in some cases elec­ The glove box unit (model HE-453-2 Dri-Lab) was pur­ tronic transitions,4 of a wide range of organic,5-s inorgan­ chased from Vacuum Atmospheres Co. The approximate ic, 9-11 and biological compounds 12.13 absorbed on an insulat­ dimensions of the box are 115 X 33 X 33 in. (the length of the ing substrate forming the barrier of a metal-insulator-metal air lock is included in the lIS-in. total length measurement). tunnel junction. Although the junction fabrication requires a This unit has three work stations with viewing panels and high-vacuum system, the adsorption step itself is often per­ glove ports. The fourth station (at the air-lock end) is covered formed outside the vacuum chamber. Here, the molecule of with an aluminum panel. Ten lIS-Vat 20-A, one 208-V at interest is applied as a neat liquid or from solution onto a 30-A, and two 20-V at 4OO-A power input receptacles were substrate and the excess is spun off. Alternatively, volatile provided by the manufacturer. Also provided were two iso­ and sublimable absorbents can be introduced directly into lated ground BNC connectors, a 50-pin feedthrough which the vacuum system. Whereas the first adsorption method is presently used for the quadrupole control lines, and two allows one to study only those molecules which are stable in fluid inlet ports. The atmosphere in the box is constantly air, the second method permits working with air-sensitive recirculated at the rate of 40 cfm through a catalyst bed materials provided they can be vaporized. Thus, air-sensitive (model MO-40-IV Dri-Lab) located in a separate unit sta­ materials which are not stable in the gas phase could not be tioned outside the glove box. The catalyst removes oxygen to studied by lETS. - 1 ppm and water vapor to S 10 ppm. Only ultrapure-qual­ Until now tunneling spectroscopists have been limited ity gases are used in the box. A deposition system of our own to studying those molecules which can be adsorbed under design and fabricated in the University machine shop is the conditions described above. In this paper we report on housed in the work station opposite the air lock (see Fig. 1). the construction and the application of a high-vacuum depo­ The deposition system is composed of a stainless-steel sition system housed in a recirculating, catalytically tooled collar base (l2X 6 in. high) and a glass bell jar (12X 10 scrubbed, controlled-atmosphere glove box. We have suc­ in.). The system is pumped by a 4-in. oil-diffusion pump with cessfully utilized this novel setup for preparing tunnel junc­ an integral liquid-nitrogen trap. A pressure of 2 X 10- H Torr tions from which tunneling spectra of air- and water-sensi­ can be obtained in 1 h. The stainless-steel collar base has tive compounds, adsorbed on alumina from solution, can be seven side ports fitted with three high-current feedthroughs, obtained. The molecules studied via our controlled atmo­ a thermocouple gauge, the head of a quadrupole residual gas sphere system include TCNE, TCNE - 1,14 TCNE - 2,14 analyzer (model SX-200 from VG. Co.), and a precision leak TCNQ, and CO2(CO)8' The results of part of these studies, valve. Rotary motion, glow discharge, octal electrical, and and a comparison with results obtained with conventional gas inlet feedthroughs are mounted on the bottom of the tunneling techniques, are reported here. tooled collar base. The interior of the collar base is fitted with 1120 Rev. Sci. Instrum. 55 (7), July 1984 0034-6748/84/071120-05$01.30 © 1984 American Institute of Physics 1120 ether and acetone can be handled successfully in this man­ ner. Typically, one keeps the doping chamber under a slight vacuum when injecting the solution containing the adsor­ bate through the septum. This prevents any solvent conta­ mination of the atmosphere in the glove box, and holds the bell jar in place during the doping procedure. Once the sub­ strate is exposed to the desired compound, the excess solu­ tion is spun off and the vacuum chamber IS evacuated to about 300 mTorr. The doping chamber is then partially e back-filled with nitrogen. The evacuationlback-fill proce­ dure is repeated three or more times in order to remove the residual solvent vapor in the chamber. At this point the dop­ ing chamber is opened and the substrate is returned to the vacuum system for top-metal deposition. FIG. I. Schematic representation of the glove box deposition system: (a) de­ Solution preparation, handling, and storage are essen­ position chamber, (b) doping chamber, (c) spinner, (d) air lock, (e) to high tial features to realizing the potential of this fabrication sys­ vacuum, (t) to roughing pump. tem and to prevent contamination of the system. We are presently using the Kontes Scientific line of microflex vials and valves as preparation/storage vessels. These valves are removable metal shields which prevent evaporated materials all Teflon in construction and are also equipped with re­ from coating the walls of the deposition system. The configu­ placeable silicon rubber septa. Aldrich Chemical offers a ration of the deposition sources and the shields allow for easy similar line which we are planning to try. Sample prepara­ handling and removal. Thus, they can be cleaned without tion is as follows: The solute is added to the vial (under inert compromising the integrity of the glovebox atmosphere. conditions if necessary) and a valve with a fresh septum is The quadrupole mass spectrometer serves multiple used to seal the vial. A 22-gauge needle is used to puncture duty in this system. It can be used to monitor the residual the septum and provide entry to the vial. The needle is con­ gases in the vacuum chamber, or it can be used to follow the nected to a manifold having high-purity N2 gas and vacuum desorption of adsorbed species. Further, by utilizing the con­ available. The vial is alternately evacuated and back-filled trolled leak valve mounted on the collar base, the entire de­ with N2 gas. The freshly distilled deairated (and if necessary, position system becomes a mass spectrometer for character­ dried) solvent is transferred by syringe to the vial and further izing the content and quality of the atmosphere in the glove pump/back-fill cycles are performed. The Teflon valve is box. In this latter context, it is principally used to check for closed and the sample is transported through the air lock of contamination by organic molecules and water. The atmo­ the glove box/deposition system. sphere leak integrity of the glove box is determined external­ We found that junction fabrication can be performed in ly by a Leybold Utratest M2 "sniffer-type" helium leak de­ this glove box deposition system with relative ease and that tector. This leak-test procedure is repeated at monthly the atmosphere in the glove box is sufficiently hydrocarbon intervals to ensure the integrity of the gloves. A 60-W tung­ free. Blank alumina substrates can be exposed to the glove sten filament bulb having a large opening in its envelope is box atmosphere for periods of 1/2 h or longer and their tun­ allowed to bum in the glove box at all times. It serves as a neling spectra show no signs of hydrocarbon contamination. catastrophe indicator and the mean time to failure for one of these bulbs is about 3 weeks.
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