 The Institute monitoring of crystal growth using Mephisto experiment is a collaborative American and French investigation of the fundamentals of crystal growth. The French Space Agency, CNES, and the French Nuclear Energy Agency, CENG, designed and built Mephisto, the crystal growth hardware for this experiment. Project management and support functions of the experiments are provided by personnel of the NASA Lewis Research Center in Cleveland, Ohio. The experiment will fly as part of the second United States microgravity payload USMP-2 aboard the Space Shuttle Columbia. The United States principal investigator for this Mephisto flight is Professor Reza Apostien, chair of the Department of Materials Science and Engineering at the University of Florida. The data from this French American collaboration will be analyzed and the scientific information will be exchanged. The knowledge gained from these experiments will be of fundamental importance to the semiconductor industry. For the upcoming USMP-2 mission, Dr. Bastien and his research team have chosen bismuth with small amounts of tin to study solidification and crystal growth. Researchers have found that crystals grown from this alloy possess a well-behaved C-beck coefficient. This property of the bismuth tin crystal allows a non-intrusive, real-time measurement of the solid liquid interface temperature. The measurement of temperature and other local conditions at the solid liquid interface or boundary between solid and liquid material are important to scientists in understanding the structural and chemical composition of the crystals that are produced. To illustrate a solid liquid interface, consider the point at which the solid wax of a burning candle turns to liquid. The solid liquid interface continues to move downward as the candle continues to burn. The hardware is mounted on a bridge-like carrier in the space shuttle's cargo bay. The French-built Mephisto furnace is designed to grow crystals under well-controlled conditions of temperature and velocity. As the experiment begins, the sample rods are melted. The thermal condition is identical for all three samples. As illustrated here, the red components represent the furnaces, while the blue components represent the heat sinks or cooling sections. The furnace on the left is stationary, while the furnace on the right is mounted on a sliding mechanism. As the experiment continues, the melted sample rod is slowly solidified. The boundary between the liquid and solid material, or solid liquid interface, occurs between the red and blue components of the Mephisto apparatus. As the mobile furnace moves toward the fixed furnace, the solid liquid interface moves also. This causes the temperature of the liquid material to fall slightly below its freezing point before solidifying. This process, known as supercooling, provides a means of controlling the solidification of the crystal. This is a key variable in determining the structural composition of the crystal. Supercooling is used to describe the temperature of the interface when the interface is moving. If the interface is not moving, in other words, if we are not growing crystals, the interface temperature is exactly at the melting point. However, when the interface moves, its temperature is slightly below the melting point, and the difference between the actual interface temperature and the melting point of that interface is called supercooling. It is actually the driving force that causes the interface to move. Although Mephisto processes all three samples simultaneously, different measurements are taken of each sample. The C-beck technique is a non-intrusive way of measuring the temperature of the solid liquid interface. A voltage across the sample is created by a potential difference between the stationary solid and liquid interface and the moving solid and liquid interface. The level of supercooling at the interface in the moving furnace is determined from this voltage difference. Another measurement is Peltier marking. These markings are created by pulsing an electric current through the sample. This current pulse causes a momentary change in the local chemical composition that outlines the shape of the solid liquid interface. By examining the shape of this interface, scientists can determine the growth conditions necessary to reduce crystals with fewer imperfections and more uniform composition. At the conclusion of the experiment, the final two centimeters of one of the melted sample rods is gas quenched. The quenching instantaneously freezes the tin in the liquid. The quenched sample can then be analyzed to determine the at-temperature concentration of tin in the liquid. All this experiment information is transmitted to the payload operations control center in real time as it is happening. The principal investigator can issue commands to adjust or repeat any segment of the experiment, such as re-running some of the melting rates. From these experiments we hope to learn the fundamentals that are involved in solidification of crystals. We hope to understand what is happening at the solid liquid interface and use this understanding in improving our scientific and technological basis for crystal growth. So how is all this experimentation with crystal growth going to help us here on earth? Well, since the inception of the first crystal set, when people were amazed by the miracle of wireless communications, the development and ever-increasing use of crystals has generated the search for improvement in crystal quality. On earth, gravity makes the growing process more complex. Non-uniformity, defects and voids are common and result in adverse effects on the properties of the crystal. By growing crystals in space, these earthbound effects are eliminated. We'll have a better understanding of the growth process which will enable us to optimize techniques for growing crystals here on earth. This information translates into practical uses, such as the development of better semiconductors. Electrical circuits are built into the silicone crystals used in today's solid state devices. In industry, complex machining operations, robotic assembly and automated inspection are all controlled by crystal equipped mechanisms. In the medical field, new techniques in the operating rooms are the result of advances in crystal technology. Computers are increasingly faster and more efficient because of better quality crystals. And today's communications have come a long way from the first crystal set. This experiment will help to advance the fundamental knowledge of solidification and crystal growth. It is a collaborative international exercise in which the scientific data will be shared in exchange for the benefit of all of us.