In this experiment, the vapor pressure of a sample processed in TEMPUS is measured. As the sample is heated up, the vapor builds up and a molecular beam is emitted through small orifice in the cell. Subsequently, the atoms of analyzed sample deposit on the surface of a piezoelectric resonator operated in microbalance mode. Here, small shifts of resonance frequency, which are caused by the increase of the mass due to the deposition, are measured and evaluated.
Experimental setup consists of two parts: cup with corresponding holder installed in TEMPUS and control electronics in the rack. The Ag (flight day 1) or Ag60Cu40 (flight day 3) sample is heated in the cup, and the vapor pressure of Ag/AgCu increases with the temperature. The molecular beam of atoms is leaving the cup through small orifice and is directed towards the cup holder where a shutter, microbalance and temperature sensor are installed. The beam is deposited on the surface of piezoelectric resonator causing a shift of resonance frequency. The shutter, driven by two miniature electromagnets, allows the PI to open/close the path for molecular beam. The temperature sensor installed in the vicinity of the microbalance is used to assist further temperature compensation of the data.
The equipment installed on rack includes a network analyzer, digital multimeter, shutter control, accelerometer, three additional piezoelectric resonators and notebook. The network analyzer sweeps frequency in the vicinity of resonators fundamental mode (approximately 5MHz) and 3rd overtone (approximately 15MHz) and measures response of the microbalance. The signals used here are low power (typically around 1mW) and low voltage (less than 1V). The multimeter is used to periodically measure the temperature sensor (Pt100). Shutter control allows experimenter to open the shutter for selected time period (selectable 1 up to 15 seconds). The shutter is operated at low voltages (less than 5V) and low current (100mA). The accelerometer connected to the notebook (5V 0,1A) provides g-data in the same time domain. Three additional resonators perpendicular to axes X, Y and Z provide resonance frequency data for reference. Notebook controls aforementioned measurement instruments and stores all acquired data.