Deposition: Molecular Beam Epitaxy #1
- Deposition of epitaxial oxides from solid sources in activated oxygen (O or O3) at deposition rates from <0.005 to >0.5 Å/s
- In situ monitoring of substrate temperature, surface structure and morphology, and metal fluxes for precise control
- XPS energy resolution: 5 meV full width at half maximum (FWHM) on the Xe 5p3/2 peak from Xe gas excited with He-I light and 0.50 eV FWHM on the Ag 3d5/2 peak from polycrystalline Ag excited with monochromatic Al Kα X-rays
- XPD angular resolution: Full angles of acceptance of ±7°, ±4°, and ±1°; absolute angular accuracy of ±0.25°
- UPS energy resolution as low as 0.055 eV at 0.2-mm slit width
EMSL's molecular beam epitaxy (MBE) deposition system is used for the synthesis and characterization of novel oxide, ceramic, and mineral materials as crystalline films. These materials are of significant interest in a variety of scientific and technological fields, including electronics, magnetics, magneto-optics, photonics, thermal and photo- catalysis, and geochemistry. EMSL's MBE deposition system consists of a PNNL-designed, customized MBE chamber with:
- An electron cyclotron resonance plasma gas source for O2 and/or N2
- An ozone (O3) collection and delivery unit
- Four electron-beam evaporation solid sources
- Three effusion cell solid sources
- Substrate heater capable of annealing to 1000°C in oxygen; substrate temperature monitored by a two-color pyrometer and/or thermocouple
- In situ optical (atomic absorption) and reflection high-energy electron diffraction (RHEED) 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, outfitted with state-of-the-art X-ray and ultraviolet photoemission spectroscopy (XPS/UPS) and X-ray photoelectron diffraction (XPD) capabilities, allows researchers to measure detailed compositional and electronic/geometric structural properties of epitaxial films, surfaces, and interfaces.
- One, designed for in-situ photochemistry studies, is equipped with a gas doser, mass spectrometer, and arc light source.
The three ultrahigh vacuum chambers are connected by a 21-foot-long transfer system that allows samples to be moved from one system to another without atmospheric exposure.
All work using the MBE and in the associated laboratory areas 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, some of which are 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
- Possibility to accommodate other samples of similar size.
Platens are loaded onto a sample trolley capable of housing 12 platens. The trolley then can be moved along the transfer tube to load any individual platen into any of the three ultrahigh vacuum chambers.
Once in the growth chamber, samples can be cleaned by either sputter/anneal cycles or by exposure to the oxygen plasma or ozone. Oxygen partial pressures during cleaning or deposition are typically∼2 x 10-8 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. The system�s single quartz crystal oscillator (QCO) can be used for calibrating the AA detectors or for directly monitoring the metal flux during deposition. The AA is useful if accurate knowledge of the fluxes is needed when depositing more than one metal simultaneously. The effusion cells are controlled by temperature feedback and can be monitored by either the AA or the QCO, depending upon the material and rate. 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.
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