Microwave Diffraction Techniques from Macroscopic Crystal Models

This project concerns itself with the diffraction of microwave radiation from the three dimensional planes of a macroscopic crystal model. A study of earlier activities indicates that microwave diffraction studies on ordered matrices have been done on model systems that do not represent crystals but only accurately spaced reflecting surfaces. In order to demonstrate diffraction techniques from macroscopic crystal structures, it was assumed that: (1) the reflecting surfaces of a working model could be embedded within a styrofoam ball model that represented the supposed shape of the atom or ion, and (2) microwave energy reflected from a surface is proportional to the surface area of that surface as is the x-ray energy reflected proportional to the atomic number of the atom or ion for small angles of incidence. The analysis of x-ray diffraction data concerns itself with Bragg angle measurements and the intensity of the Bragg reflections. Intensity results from macroscopic models have previously not been reported. In addition to the quantitative results obtained for the Bragg angles, qualitative results for intensity measurements could not be expected from a macroscopic model since: (1) The lack of collimators and filters for the microwave source permitted other than parallel monochromatic wavefronts; and (2) only a limited number of unit cells are possible if a reasonable sized model is to be preserved. The laboratory investigations, prepared to utilize the equipment developed in the classroom, serve also to introduce the computer as a teaching and problem-solving aid. The study indicates that crystal models can be built with structural alterations and doping that can be detected with microwave techniques. Additional laboratory investigations and the existing computer programs can be utilized to study the properties of imperfect crystals in the classroom.