Deposition: Molecular Beam Epitaxy #1

Research using EMSL's molecular beam epitaxy (MBE) deposition system centers around the synthesis and characterization of novel oxide, ceramic, and mineral materials as crystalline films. Such materials are of significant interest in a variety of scientific and technological fields, including electronic, magnetics, magneto-optics, photonics, thermal and photocatalysis, and geochemistry.

EMSL's MBE deposition system consists of a PNNL-designed, custom MBE chamber with:

• An electron cyclotron resonance plasma gas source
• Four electron-beam evaporation solid sources
• Three effusion cell solid sources
• In situ optical (atomic absorption) and high-energy electron diffraction probes for real-time monitoring of the metal fluxes and surface structure and morphology, respectively.

In addition, the MBE deposition system is equipped with two additional chambers:

• One is outfitted with state-of-the-art X-ray and ultraviolet photoemission spectorscpoy (XPS/UPS) as well as X-ray photoelectron diffraction (XPD) capabilities. These techniques allow researchers to measure detailed compositional and electronic/geometric structural properties of epitaxial films, surfaces, and interfaces.
• One is designed for in situ photochemistry studies. This chamber is equipped with a gas doser, Auger electron spectrometer, mass spectrometer, and visible light source.

These three ultrahigh vacuum chambers are connected by a 21-foot-long transfer system that allows samples to be moved from one system to another using ultrahigh vacuum capabilities.

All work with the MBE and in the associated laboratory must be performed in compliance with EMSL practices and permits.

System Configuration and Operational Overview

Substrates are loaded into the MBE deposition system on transferable sample platens equipped with transferable thermocouples. The allowable sample shapes and sizes are

• 1.0-mm thick, 9.35±0.05-mm diameter disks
• 1.0-mm thick, 1.00±0.05-cm² squares.

Two types of platens are available—one designed for a maximum temperature of 1200°C and one designed for up to 2000°C. Platens are loaded onto a sample trolley that is capable of housing 12 platens. The trolley then moves along the transfer tube and loads the platens in any of the three ultrahigh vacuum chambers.

Once in the chamber, samples can be cleaned by either sputter/anneal cycles or by annealing in the oxygen plasma. Chamber pressures during operation of the plasma, whether during cleaning or deposition, are typically ~2  x 10^-6 Torr to ~3 x 10^-5 Torr. The electron beam evaporators can be controlled either manually or via closed-loop feedback control using the atomic absorption (AA) signal. There is a single quartz crystal oscillator (QCO) in the system for calibrating the AA detectors that can be used instead of the AA system to monitor metal flux. The AA is required when depositing more than one metal simultaneously if accurate knowledge of the fluxes is needed. The effusion cells are controlled by temperature feedback and can be monitored by either the AA or the QCO. The deposition process can be controlled by computer to a large extent, or manually if preferred. All seven solid sources and the sample manipulator have pneumatically actuated shutters.

The same heating capability that is present in the MBE chamber is also present on the XPS/UPS/XPD manipulator. Note that the two emission angles (polar and azimuth) cannot be changed when the sample is being heated.

Individuals can use this instrument independently for their research.

All Related Publications Related Publications

1. Bioreduction of hematite nanoparticles by the dissimilatory iron reducing bacterium Shewanella oneidensis MR-1.
2. Nanotechnology-Based Electrochemical Sensors for Biomonitoring Chemical Exposures .
3. Imaging Consecutive Steps of O2 Reaction with Hydroxylated TiO₂(110): Identification of HO₂ and Terminal OH Intermediates.
4. Cation dopant distributions in nanostructures of transition-metal doped ZnO:Monte Carlo simulations.
5. Antibody recognition force microscopy shows that outer membrane cytochromes OmcA and MtrC are expressed on the exterior surface of Shewanella oneidensis MR-1.