Deposition, Portable System/UHV Transfer
EMSL's portable deposition and electrochemical systems/ultrahigh vacuum (UHV) sample transfer system–located in the Interfacial and Nanoscale Science Facility–offer UHV transport of samples that might become tainted by atmospheric exposure among equipment systems and even geographic locations.
Deposition Station
EMSL's deposition station is a portable UHV system equipped with a Knudsen evaporator and an Omicron electron beam evaporator for thin film deposition, and a thickness monitor. The system is capable of cooling and heating samples from -150°C to 1100°C–accomplished via electron beam heating and liquid nitrogen cooling. Sample temperature is measured using a Type K thermocouple and an optical pyrometer. Samples up to a maximum of 12 mm × 12 mm in area and 3 mm in thickness can be accommodated by this station and are mounted on EMSL sample platens. Samples are introduced to the system either from air, or without exposure to air from a vacuum suitcase or from other transfer systems.
Electrochemical Station
EMSL's electrochemical station is designed to transport samples between a UHV environment and an electrochemical or solution cell with exposure only to electrolyte vapor and a nitrogen cover gas. This multilevel vacuum system accepts samples mounted on EMSL platens from another element of the EMSL transfer system, a vacuum suitcase, or air. The upper level of the electrochemical station's chamber is pumped by a cryopump and generally remains in UHV conditions. The middle level is pumped by a turbo pump, which can be used to initially pump from controlled environment conditions present during liquid exposure. By design, this system presents one surface of a sample to solution for exposure or electrochemical testing.
The electrochemical cell (a "cup" maintained in a controlled environment) is designed to have a small reference electrode, a counter electrode, while the sample serves as the working electrode. Solution is added to the cell through tubing outside of the controlled atmosphere, and solution and a gas line are available to rinse and blow liquid from the sample as needed. The cell design is flexible and can be altered for specific purposes. For example, if a dissolution experiment were to be conducted, fresh solution could be added to the cell and "exposed" solution withdrawn for other types of analysis. The electrochemical cells are designed to be connected to standard electrochemical controllers (e.g., a Princeton Applied Research Model 273), of which there are many around the laboratory.
In a "typical" mode of operation, a sample could be cleaned or otherwise prepared (clean, with defects or a contaminant deposited); exposed to solution for an electrochemical test; and returned to an analysis chamber to determine the consequences of the electrochemical exposure. By interconnecting this system with other portable experimental stations and/or analysis chambers, a variety of special experiments can be created.
UHV Sample Transfer System
Developed jointly by PNNL and Thermionics Northwest, a common or standard sample mount has been implemented in approximately 16 stations within EMSL. This overall capability allows samples to be moved among the 16 different experimental or analysis stations without being exposed to the atmosphere. In addition, the general platen design enables compatibility with many systems at locations around the world. Five portable experimental stations that use the transfer capability can be interconnected to different analysis and deposition systems, and allow for design of many unique experiments. Elements of the UHV Sample Transfer System include the following:
- Common Sample Holder Design. The bases of the sample interchange capability are EMSL sample platens that can be moved into and out of any of the EMSL platen-compatible systems. Depending on platen and manipulator design, samples can be heated and cooled in different ways to different temperatures. The platens have three different designs (stainless-steel ambient, high temperature, and surface chemistry); however, all designs are compatible for mounting at each station.
- Portable Experimental Stations. Two portable experimental stations provide capabilities for film deposition and electrochemistry and solution exposure.
- Vacuum Suitcases. Four "vacuum suitcases" enable samples to be transported throughout EMSL and to different locations. These suitcases can be ambient atmosphere or actively pumped with a battery pack.
- Compatible Systems. In addition to the two portable experimental stations, some of EMSL's synthesis and analysis capabilities are directly compatible with the UHV Sample Transfer System:
The following information briefly describes the EMSL platens, basic transfer system elements, and portable experimental stations to facilitate user planning.
EMSL Platens and Basic Transfer System Elements
EMSL's UHV Sample Transfer System offers UHV transport among equipment systems and even geographic locations. The common platen shape enables several types of platens, with different purposes, to be moved into and out of a wide range of UHV instrumentation. In addition to the platens, several basic elements are key to the transfer system design: receiver docks, manipulators, manipulator receivers, specimen introduction systems, and vacuum suitcases, as well as the portable experimental stations. Many of these basic elements (including platens, docks, and transfer forks) are now part of the Thermionics Northwest product line. Users seeking to make their systems compatible with this design can contact Thermionics Northwest for additional information.
Platens
At EMSL, three types of sample platens are available. All are designed to isolate samples, fit all receivers, fit 34-mm interior diameter tubes, and tolerate minimum pressure spikes.
- Stainless-Steel Ambient Platen. This Type I stainless-steel ambient platen is designed for simplicity and mechanical stability in ambient conditions (without any built-in temperature measurement capabilities). Although this platen can be heated or cooled when it is attached to receivers with heating and cooling facilities, no temperature measurements can be made because there is no thermocouple connected to the platen.
- High-Temperature Platen. The heating and cooling facility includes two pairs of thermocouple contacts incorporated into the platen. The design enable researchers to heat specimens to at least 1250 K and to cool the same sample to 150 K.
- Surface Chemistry Platen. This is a solid mount that provides isolation from the other surfaces. The heating (resistive) and cooling facility is incorporated in this platen as well as one pair of contacts for thermocouple and one pair of contacts for power. The design enables researchers to pass 20 amps of electrical current through the sample and cool the sample to 150 K. The sample also can be heated by an electron beam or radiant heater.
Receiver Docks
The receiver dock is equipped with four locking fingers, allowing the sample platen to be mated to the dock by orienting it so that the ramps can receive the dock's fingers. Rotating the fork releases the platen, while the fingers on the dock grip and lock the platen to the manipulator. When used as power leads, the contacts are bilayer and include a copper inner layer for electrical conduction and a steel outer layer to provide strength.
Manipulator
The receiver dock manipulator can be connected to different manipulator configurations and can receive all types of platens. Based on experimental need, the manipulator can include (in combination or singly) liquid nitrogen cooling; one of three types of internal heaters (electron beam, nude filament, or ceramic-coated radiant); and 20 amps of current routed directly through the platen. Epitaxy beam heating up to 2000 K can also be achieved.
Manipulator Receiver
The manipulator receiver is equipped with four clips to hold the sample platen and a pan-type filament for heating.
Vacuum Suitcases
Vacuum suitcases are small portable systems that hold one to three sample platens. These small chambers can be pumped with small ions and are sealed by a gate valve that bolts onto the introduction system of many instruments.
