The Tousimis 815B Series C CPD is a critical point dryer, used to dehydrate or dry physically sensitive biological and MEMS samples, to preserve delicate nano- and micro-scale structures and features which might otherwise be distorted or destroyed in the process of air drying or vacuum-baking. In the Tousimis Critical Point Dryer, water in the sample is first dissolved and displaced by soaking the sample in pure isopropanol or acetone. Then, under high pressure, the solvent is itself displaced by liquid CO2. At this high pressure, the CO2 is above its critical point, which means the density of the liquid and gas phase of CO2 are equivalent, and the evaporation of the CO2 can occur without volumetric changes to the sample, and without the effects of liquid surface tension that would collapse the sample at normal atmospheric temperatures and pressures.
The Automegasamdri-915B Critical Point Drying (CPD) tool is used for carbon dioxide (CO2) drying after release of bulk or surface micromachined devices. Critical point drying is an efficient method of drying delicate samples without damaging it’s structure by surface tension that occurs when changing from the liquid to the gaseous phase. The release is usually performed by immersion of the device in hydrofluoric acid followed by subsequent immersions in several beakers of DI water. The CPD requires that the device be completely free of acid or water before introducing it to the chamber. To avoid this, the device should be placed in isopropyl alcohol for at least one hour.