Gwo-Ching Wang, Ultrathin Film Physics & Nanostructure Science Lab, Rensselaer Polytechnic Institute

Ferromagnetic Resonance Spectroscopy (FMR)

In FMR the microwave frequency is used. The FMR signal is measured by monitoring the microwave losses in the studied film as a function of applied dc field H. In our lab we setup a UHV FMR with a cylindrical cavity. For details, please see paper by M. Li et. al. 1996. In the same UHV system one can also perform MOKE (magneto-optic Kerr effect) measurement. The FMR has been applied to measure magnetization, anisotropy constant, anisotropy field of magnetic thin films, and exchange couplings of trilayers. The line width of the resonance peak is related to magnetic inhomogeneity. For reviews please see Prof. B. Heinrich' papers.

High Resolution Low Energy Electron Diffraction (HRLEED)

There are about 50 Henzler types of HRLEED system (U. Scheithauer, G. Meyer, and M. Henzler, Surface Science 178, 441, (1986)) in the world. We believe our group is one of the most productive users of HRLEED besides Henzler's group in Hannover, Germany. The HRLEED system not only can resolve domain size from a few angstroms to 2000 angstroms but also has millisecond temporal resolution. Numerous novel surface, overlayer, and thin film phenomena have been observed using this system. HRLEED is particularly ideal for real-time monitoring of 2D island growth (or shrinking) of overlayer and multilayer structure on surfaces quantitatively. HRLEED is complementary to the grazing incidence X-ray diffraction technique for surface ordering studies. The latter uses an intense synchrotron radiation source and can achieve very high spatial resolution. For the study of the dynamics of growth, HRLEED has the advantage of high temporal resolution. Because of the strong interactions between the electrons and surface atoms, the number of counts per seconds is very high for each data point for electron diffraction. One can obtain an angular profile within a very short period of time (e.g. milliseconds). We have built an atomic resloution STM in house and have used it for the study of rough surfaces. The STM is powerful for real space imaging of surfaces and submonolayer or monolayer films. However, when it is used for multilayer thicker film study the maximum depth that the tip can probe is limited to less than ten layers high unless the tip is very sharp. That is the valley of rough surfaces or rough films can not be reached by the tip. We believe for dynamic study of rough surfaces and multilayer thick films the diffraction technique has certain advantages and is statistically quantitative.

Partially Ionized Beam (PIB) Deposition System

Ion-based or ion-assisted thin film deposition techniques such as ion beam deposition, sputtering, ion plating, plasma-enhanced chemical vapor deposition, and ionized cluster beam (ICB) deposition have attracted increasing attention in the semiconductor community in recent years. The ICB deposition technique which is more preferred to be called "partially ionized beam" (PIB) deposition has several advantages over the conventional evaporation-deposition or sputtered deposition techniques:

It can grow epitaxial film at lower temperature.
It has small charge-to-mass ratio in the beam so that there is no space charge problem.
The ions can enhance surface chemical reaction.
The ions can enhance surface adatoms migration and diffusion.
It has a self-cleaning effect during deposition.

Why use Partially Ionized Beam (PIB)?

Using the energy of the self ions that are accelerated to the sample changes can occur in surface structure without annealing the sample.
Changes in grain orientation have been observed using the PIB deposition.

How does PIB work?

By partially ionizing deposition material and providing an accelerating voltage the ions are attracted towards the sample. The additional energy within the self ions allows for different types of growth not normally seen using the traditional thermal deposition.