Yarmoff Research

Facilities We have four major ultra high-vacuum (UHV) chambers. All of the UHV chambers include complete facilities for sample preparation and characterization.   They all contain sputter guns for sample cleaning, Low Energy Electron Diffraction (LEED) for characterization of sample ordering, and Auger Electron Spectroscopy (AES) for determining sample cleanliness. For use with all of the chambers, we have an array of evaporators, getters and electrochemical cells that are used to deposit various adsorbates, films and nanostructures. Chamber 1: The chamber is a 14" diameter stainless steel bell jar pumped with a 500 l/s ion pump and a titanium sublimation pump.  It is the primary instrument for performing alkali ion scattering from metal and semiconductor single crystal surfaces and from thin films grown on single crystals. The sample manipulator (VG) has two rotational degrees of freedom adjusted via computer-controlled stepping motors, and has liquid nitrogen cooling and electron beam heating. This chamber contains a Perkin-Elmer CMA for AES and a Princeton rear-view LEED optics. We have also recently completed construction of a He resonance lamp for UPS that can be mounted in this chamber. An Kimball Physics alkali ion gun, which produces up to a 5 keV beam of Na+, K+, Cs+ or Li+ ions with a spot size of <1 mm2, is mounted on a turntable that is adjustable via a computer-controlled stepping motor to enable scattering angles up to 168 degrees. There is an electron gun, which can be used for work function and other measurements, mounted on the turntable next to the alkali ion gun. A pulsed alkali ion beam is produced by sweeping the beam past an aperture with deflection plates. With this source, we have achieved pulse widths of ~40 ns, which corresponds to an energy resolution of about 0.5% for 2 keV ions. Scattered ions and neutrals are measured with time-of-flight (TOF). The TOF leg contains a set of deflection plates used to separate the scattered ions from the scattered neutrals.   Scattered positive ions, negative ions and emitted electrons are also measured at high-resolution with a Comstock electrostatic energy analyzer (ESA) that is mounted inside this chamber. The ESA is operated in the constant pass-energy mode to maintain a fixed resolution throughout a spectrum. Chamber 2: In addition to the standard items, this UHV chamber contains facilities for x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and ESD.   It is a 12" diameter stainless-steel bell-jar pumped with a 400 l/s ion pump and titanium sublimation pump, with an attached load-lock "baby" chamber that is pumped by a 60 l/s turbomolecular pump.   This system is used for growing nanostructures, with the STM as a diagnostic. It is also used for looking at chemically synthesized nanostructures and self-assembled monolayer samples, because of the load lock.   We are in the process of adding a cryogenic manipulator for doing temperature dependent measurements and to use deposition at low temperature as a unique method for nanomaterial fabrication. Alkali ions for scattering, recoil and electron emission experiments are produced by a second Kimball Physics alkali ion gun, which is mounted on a fixed 2-3/4" conflat flange.  This chamber contains a second Comstock ESA for measuring scattered ions and emitted electrons, and a Comstock electron gun that can be used to assist with work function measurements and for ESD.   Chamber 3:   This instrument is the primary tool for the metal/semiconductor ion scattering experiments.  It consists of a 12" diameter stainless steel bell jar pumped by ion and titanium sublimation pumps, which is attached to an external ion accelerator. The UHV chamber contains LEED and AES as analytical tools, and has a sample manipulator (Thermionics/VG) with two rotational degrees of freedom. Metal and semiconductor ions with kinetic energies up to 20 keV are produced by a diffusion-pumped Colutron ion source. The source can be operated with either solid or gaseous materials.   For example, Si+ ions are produced from gaseous SiCl4 (a high vapor pressure liquid).   There are vertical and horizontal deflection plates incorporated into the ion source, which are used for producing a pulsed beam for TOF by sweeping the beam past an aperture.   The ion source is attached to the chamber via a differentially pumped beam line.   There is a velocity filter in this beam line for mass selection of the primary ion beam, and an Einzel lens for focusing the beam onto the sample.   The Einzel lens/deflection plate sections are pumped with a 240 l/s and a 330 l/s turbomolecular pump. Scattered ions and neutrals are measured with TOF.   There are two positions that the TOF leg can be placed - one arranged for backscattering and the other for forward scattering.   This arrangement is ideal for the proposed research, as the backscattering leg will be used for asymmetric scattering, while the forward scattering leg will be needed for symmetric scattering.   The TOF leg contains deflection plates that can separate scattered ions from neutrals in order to make charge state distribution measurements.   Scattered and recoiled ions and emitted electrons are measured with a third Comstock ESA, which is mounted on a rotatable turntable inside the chamber. Chamber 4:   This instrument is the primary tool for the surface transport studies. It is a 12" stainless steel bell jar pumped with an ion pump and titanium sublimation pump, and routinely attains pressures in the 10-11 torr range.  There are facilities for sample preparation and surface characterization, including a double-pass cylindrical mirror analyzer (CMA) for determining sample composition and purity by Auger Electron Spectroscopy (AES). We also have an x-ray source that could be incorporated into the chamber along with the CMA for x-ray photoelectron spectroscopy (XPS) should there be a need for chemical information about the surfaces. Currently, this chamber has a Heliatran cryostat mounted on an x-y-z manipulator.  A custom sample holder containing a sample heater is attached to the manipulator. The sample holder is designed so that an electrode structure for contactless measurements could be attached to the sample in situ following surface preparation. This will involve mounting the electrode structure onto a linear motion feedthrough that can reach the sample.