Pulsed Laser Deposition System

Since Fall of 2010, the Pulsed Laser Deposition (PLD) System is operational and part of the user program. Our PVD PLD/MBE-2000 machine is based on a Lambda Physik COMPex PRO 110 Laser with 248nm KrF emission capable of producing pulses of 400mJ pulse energy at 20ns pulse duration with a maximum repetition rate of 100 Hz.

The deposition chamber achieves a vacuum of 5·10-9 Torr when baked out and still reaches considerable 1·10-8 Torr in a fast procedure without bake out. A target changer allows loading of 6 ablation targets without breaking the vacuum in the deposition chamber. The laser raster, target rotation and target raster options enable optimized target use and deposition conditions in particular when utilized in concert with continuous substrate rotation. These means assure excellent thickness homogeneity. Discrete target rotation in turn enables us to grow structurally sophisticated combinatorial films. Substrates can be heated up to 950ºC in vacuum, inert gases such as Argon or reactive gases such as Oxygen atmosphere. The latter allows, e.g., for the growth of complex oxide thin films with proper stoichiometry. A corrosion resistant SiC heater assures consistent operation in those extreme sample environments. In-situ and real-time monitoring of the growth process is possible by measuring RHEED intensity oscillations whenever the films grow in a layer-by-layer mode. Installation of mu-metal shielding on the target stage is an additional effort we make to reduce the effect of magnetic stray-fields on the electron beam.

Armed with these state-of-the-art growth capabilities, the machine has been used to fabricate a variety of thin film multilayer structures. Although metallic thin film multilayers are in general more challenging for PLD methodology than oxide growth, we put our machine to the test and have demonstrated the fabrication of, e.g., very smooth Fe/Cr multilayers on single crystal MgO substrates (see figure of small angle X-ray diffraction pattern). Other projects utilize the unique PLD potential for growth in reactive gas atmosphere to fabricate epitaxial layers of oxides such as BaTiO3 and ZnO.

The operation of the PLD apparatus is fully automated with a user-friendly computer interface based on Labview programming. The safety during all steps of the experimental procedure is, in addition to extensive user training, implemented in the software through control of interlocks crosschecking the conditions for safe operation. The software offers single layer deposition by direct user control. In addition it allows utilizing the programmable complex layer recipe which provides convenient and consistent multilayer deposition. The user-machine interaction is largely confined to the computer control thus minimizing potential errors. For example, single or multistep heat treatment processes and the setting of key parameters such as total pressure and individual flow rates of gases can be fully controlled through the software.

 

PLD System Specialist: Dr. Shah Valloppilly
e-mail: svalloppilly2@unl.edu

Pulsed Laser Deposition System

 

X-ray diffraction pattern

Small angle X-ray diffraction pattern of metallic superlattice MgO(100)/Cr(7.25nm)/ [Fe(1.65nm)/Cr(0.86nm)]18/Cr(0.80nm) grown by Tathagata Mukherjee (Binek group) using PLD.