a. Overall Plan On the Construction

     We are in the process of constructing a versatile ultrahigh vacuum (UHV) system that enables the investigation of soft-contact formation and the development of novel contact strategies for technologically important material systems. This instrument, as schematically shown in Fig. 5, has several stations that accept samples: (1) metal deposition/surface-analysis station, (2) stamping/electrical-characterization station (3) sample load-lock station, (4) sample flipping station, (5) organic material deposition station, (6) glove box, and (7) scanning tunneling microscopy (STM) station. Several of these stations are described in detail below. Samples, of nominal size 3.5 cm x 2.1 cm, are carried in a “sample transporter” and transferred between various stations by a wobble stick, which is also used to perform simple mechanical maneuvers in UHV. A major part of the system, not shown in the top view of Fig. 5, is an evaporation facility, which sits underneath the metal deposition station. Additionally, there are several surface analysis capabilities on the proposed instrument, including a double-pass cylindrical mirror analyzer (CMA), a reverse-view low energy electron diffraction (LEED), and an oscillating Kelvin probe. Several pieces of the overall system are existing equipment and involve no construction, acquisition, and expenses. Designs of several new pieces of the instrument are also finished or near completion. These will be described in detail below. The complete system has a rather modest footprint (~8’ x 6’) and will be housed, along with three racks of electronics, in one of several available lab spaces, owned by the physics department, in the Ingersoll Building of the Brooklyn College campus. Standard service utilities, including power, chilled water, compressed gas, and vacuum, are available in these lab spaces. Various parts for the instrument will be made in the machine shop by two skilled machinists, provided for by the university.

     The instrument is to be constructed in two stages. In Phase 1, we plan to design and construct stations (1) through (4), as outlined above. An existing Si-based molecular beam epitaxy chamber will be connected to these stations at this stage, and will provide the metal deposition capability needed for the initial assessment of the instrument. By the completion of Phase 1, the system will be fully operational to conduct the kind of in-situ stamping and characterization experiments as shown in Fig. 3. It will also have full surface analysis capability by then. Note that station (7) STM is included in Phase 1, as it is existing equipment. At this stage, we plan to make good use of our website, and also through other means of communication, to announce the concept of the new instrument, to attract potential users, and to provide updates on the status of this instrument. In Phase 2, which covers the next 9 months of the project, we plan to have students design and construct a dedicated metal-evaporation chamber and also stations (5) and (6), as outlined above. Additions in Phase 2 enhance our ability to study more materials and interfaces, and they add the capabilities to deposit organic material in situ and to attach self-assembled monolayer (SAM) molecules on the surface of the sample. Phase 2 is also used to test, modify, and calibrate the operational parts of the instrument, and to train interested users of the instrument. New developments/results will be announced on the website. Finally, in the remaining 3 months of the project, performance of the added parts of the instrument will be evaluated. The final three months is also used to document the operation procedures/instructions on the website and to establish a web-based sign-up program for the instrument. It is also time to publish the design and the principles behind the operation of this instrument in a scientific journal.

b. The Metal Deposition/Surface Analysis Station

     The basic housing for the sample manipulator, shown in Fig. 6, is assembled from an 8” x-y stage, a differentially pumped 4.5” rotatable flange, a 4.5” welded-bellows linear translator, a 2.75” linear translator, a rotary feedthrough, a hollow rotary feedthrough, and other vacuum hardware. The temperature of the sample can be controlled in the range 100-1300 K, by resistive heating and by contact to a LN2 reservoir. From its normal, downward position, the sample can receive deposition, through shadow mask, from sources in the evaporation chamber below. In-house designed and machined parts are used to construct a compact sample holder, attached through three 1/4” rods to a double-sided 2.75” conflat flange, and a liquid nitrogen reservoir, attached through thermal isolation and three 1/4” rods to the larger 4.5” conflat flange. As shown in Fig. 7, the design of the sample holder is near completion. The inner rotation feedthrough provides, through a bevel gear set, sample tilt of up to ~90o, and the outer rotation from the hollow rotary feedthrough is used to unlock/lock the sample through loaded springs. A receptacle for the sample transporter is constructed on the LN2 reservoir. The relative motion between the sample holder and the LN2 fixture, provided by the 2.75” linear translator, allows the height of the sample transporter to be adjusted to the loading or unloading configuration. The same motion, with the sample properly secured on the sample holder (and with the sample transporter detached), could provide cooling to the sample if desired. Samples are held on both ends by flexible tantalum clamps (~0.010” thick), which do not put excess stress on the sample while pressed against the milled and tantalum-coated bottom of the LN2 reservoir. The two sides of the sample holder are electrically isolated and can supply resistive heating to semiconducting and conducting samples and substrates. Sample temperature can be measured by a thermocouple bead spot-welded to the tantalum clamp and also by hand-held pyrometer through a nearby quartz viewport. With the sample holder tilted 90o, a rotation of the 4.5” flange can bring the sample to face low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and an oscillating Kelvin probe. The x-y movement on the 8” flange provides fine adjustment of the sample position for surface analyses. Sample tilting is facilitated by counter-weight (not shown) to minimize stress on the mechanical linkage. Copper bushings are used on stainless steel axle to minimize galling, with “catchers” to prevent the metal powder from entering the sample area. In addition, linear recirculating ball-bearings are used to guide the motion and maintain the rigidity between the sample holder and the liquid nitrogen assembly. Deposition can be performed through an aperture, with or without shadow masks. A sliding adjustment on the shadow mask holder allows two different patterns to be accessed. Combined with sample rotation, a variety of patterns can be deposited on the sample through masking.

c. The Stamping/Electrical-Characterization Station

     This station is made up of an upper sample manipulator and a lower stamping/characterization mechanism. The upper manipulator, with rotational and x-y-z translational movements, controls the precision placement of sample for the stamping experiment. It also provides sample heating and holds the weights used in the stamping experiments. Samples can be placed in two positions on the manipulator: one with clamping and heating capabilities; the other, with the sample freestanding, is used to drop the sample onto the lower jig. The rotational motion from the rotary feedthrough is used to adjust the height of the “sample transporter” to either the loading or the unloading position. The main features of the lower clamping station are a small platform with temperature control, from LN2 to elevated temperature, and an electrical probe with x-y-z adjustment. A port is available to add a second probe, if the need arises. A mirror wedged on the chamber ceiling provides a top-down view of the probe position with respect to the pattern on the sample. Weights, as opposed to mechanical drives, have been chosen as a simple means to provide the stamping pressure, without precise alignment. They are hung from a support rod with small separations between them, as shown in the left hand of Fig. 8. As the weight assembly is continuously lowered, the weights of the individual blocks are applied to the sample, one-by-one from the bottom up. The under side of the bottom block is gold coated, connected electrically, and can be used as an electrode for the electrical measurement. For weights ranging from 50 g to 1.00 kg, the nominal pressure exerted on the sample is 1.2 - 24 kPa, which should be adequate for contact stamping. The actual pressure will depend on the pattern used.

d. Evaporation Chamber

     There is a Si-based molecular beam epitaxy (Si-MBE) system in the PI’s laboratory, which is presently employed for NSF-sponsored research on nano-particle assembly in liquid thin films. This is the chamber that will provide the evaporation of metal during Phase 1 of the development of our instrument. As shown in the red shaded area of Fig. 9, the present Si-MBE chamber has LN2 shrouding and partitioning to separate a 40 c.c. e-gun and a dual (Temescal-GEMINI) 16 c.c. e-gun in two compartments. In addition, two ionized Knudsen cells, originally designed for impurity doping of Si, are available for depositions. There are two INFICON electron impact emission spectroscopy (EIES) sensors to optically detect the flux intensities and two independently controlled shutters. The Si-MBE chamber is pumped by a large cryo-pump. The Si-MBE chamber has large volume e-guns and was designed for sustained use and co-evaporations. It is adequate for initial evaluation and testing of the UHV stamping mechanism, but is cumbersome (and costly) to use for the exploring of new materials. Therefore in Phase 2, a less elaborate deposition chamber will be constructed, as shown in the green-shaded area of Fig. 9, to take over the responsibility of metal evaporation. Material evaporation can be provided by a small “button” e-gun, capable of handling four different materials, and a series of evaporation boats. Each boat is individually powered and shielded from the other boats. A linear translator allows a particular boat to be centered for the deposition. In addition, ports are set aside for inclusion of Knudsen cells in the new evaporation chamber. Deposition is monitored by both quartz crystal monitor and EIES sensor. LN2 shrouding and shuttering serve to minimize the contamination of the main chamber.

e. Organic Deposition Chamber

     To minimize cross contamination, the organic evaporation chamber is pumped by an ion pump and normally valved off from the main chamber. It has an extendable arm to receive sample from the main chamber and retract to a fixed sample stage inside the organic evaporation chamber. Evaporation boats are used to evaporate organic molecules through a shielding. A crystal oscillator is used to monitor the thickness of the deposition.

f. Scanning Tunneling Microscope

     An existing Omicron UHV-STM1 is attached to the main chamber. Special cassettes are made to receive samples for STM scan and transfer to the evaporation station via the usual “sample transporter” assembly. Cassettes are also used to replace scanning tips used in the STM.

g. Vacuum Vessel and Pumps

     The main stainless steel chamber, which houses the metal evaporation and stamping stations has already been bought and received. Selected drawings of the chamber are shown in Fig. 10. An ion getter pump will provide pumping for the main chamber.

h. Miscellaneous

     The sample transporter is constructed from stainless steel and tantalum sheet metal to minimize its weight. An Omicron style platen allows it to be picked up by the wobble stick. The wobble stick is also used to slide an arm on the sample transporter to move the sample. The sample flipper receives and rotates the sample without touching the center portion of the sample. The glove box is a standard commercial product with nitrogen capability.