The main technical and scientific task in HANDSOME is the development of the EduCrys setup. Although a desktop experiment for Czochralski growth of tin crystals at 232 °C (Demo-CZ) already existed, that setup was not suited for external users outside our lab. Hence, the central goal of HARDWARE development was a robust and compact setup, based on commonly available components at low-cost. An important decision was to employ a simple cooking plate as heat source. Although the overall size of the setup was increased roughly by a factor of 2, expensive custom-made parts and time-consuming implementation of safety features were avoided. The main body of EduCrys was made of standard aluminum profiles and plates containing both the hotplate and electronics. Significant efforts were needed to design the electronic control of the heating, motors and various sensors. Again, common components and ready-to-use development boards were employed as much as possible, so that the printed circuit board was the only custom-made part. A significant scientific value was achieved by a large number of sensors for the evaluation of temperature, heat transfer and energy consumption. At the end, a hardware setup with a cost of about 1200 Eur (excluding manufacturing and assembly) was achieved, which can be manufactured by workshops usually available at research and education institutions.
The hardware of EduCrys is controlled by a Raspberry Pi microcomputer, which provides also a convenient graphical interface (Linux operating system) for data evaluation and documentation. The control SOFTWARE has been implemented in Python, which is a widely known scripting language and is taught already at school level. An intuitive user interface with a single graphical window contains an overview of all sensor inputs including a time plot and camera images. Beyond the basic control of the hotplate and motors, the interface also supports programmable recipes for the experiments. The developed software was significantly simpler and much more user friendly compared to the command-line interface with an Arduino microcontroller in the former Demo-CZ setup. A future update may also include a more flexible, modular script design and remote control, e.g. using a smartphone app.
Two different series of EXPERIMENTS have been implemented for the EduCrys setup so far. The first topic addresses the basics of heat transfer by heat conduction, convection and radiation. These phenomena are not only relevant for crystal growth applications, but general physical courses, and demonstrate the wide potential of EduCrys applications. In a series of experiments, water in a glass beaker or metal pot is heated and boiled under various conditions (with/without lid, enclosed in metallic foil etc.), carefully monitoring both the temperature and the energy consumption. The second series of experiments is focused on the growth of tin crystals from melt in an aluminum crucible, similar to the Demo-CZ setup. Initially, basic effects of crystal growth are observed by pulling thin seed crystals and changing various process parameters such as pull speed, melt temperature and cooling fan speed. Then, a recipe to grow a crystal with a specified shape is developed and tested, which allows for a scientific discussion of many practical aspects of the Czochralski process in the industry and research. A lab manual suitable for courses at schools and universities has been prepared for both series of experiments.
