Multifunctional Diamond Sensor for Deep Ocean Deployment

Sequestration of CO2 in the planets oceans is one approach under consideration as humankind flights to tackle climate change. In this process CO2 would be pumped to depth greater than 3km where it liquefies and, as it is heavier than water would form permanent lakes on the ocean floor. The potential for CO2 storage this way is enormous. However, our oceans naturally contain CO2 at shallow depths and this has the effect of mild acidification of the marine environment - if the acidification is allowed to increase, severe adverse effects on marine life will result. Thus, there is a real need to monitor the pH of oceans over large areas and at many depths should CO2 sequestration technology become a reality. At present this involves the temporary deployment of large expensive equipment in limited regions of our seas. With the emergence of the internet-of-things (IoT) the concept of a permanently deployed more intelligent far-reaching network of ocean sensors has emerged - should such devices be sufficiently small and robust they could stay in position for years, occasionally rising to the surface to relay data bursts. Diamond is an ideal material for sensor fabrication that must survive in harsh environments and diamond pH sensors have been demonstrated by a number of groups. However, the real value for such devices lies in a multifunctional sensors within a robust housing with encased control electronics for remote operation. Moreover, most sensors demonstrated with diamond technology to date rely upon metal contacts on the sensor face that would readily corrode in the marine environment.<br/> <br/>In this paper we show the design and realisation of a diamond sensor with housing suitable for high pressure deployment, where the ocean only sees a diamond face for the sensor. Real-time measurement of pH, dissolved oxygen, water resistivity and temperature are achieved. At the heart of this sensor technology lies conductive patterns of graphitic-like material within the diamond created by a laser direct write-process. The prospects for these devices will be discussed.