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The fastest and the wettest logical cell
The fastest and the wettest logical cell

German scientists from Ruhr University have managed to construct the fastest (tentatively) and wettest (most definitely) logical cell out of fine jets of water. The article is published in the international journal APL Photonics.

in the international journal APL Photonics. Currently existing electronics are based upon semiconductor resistors. The resulting speed of computational systems is limited by the size of semiconductors and their switching speed. For decades engineers and scientists have been managing to improve the transistor density in microelectronics (Moore’s law), hence us being able to enjoy all the modern blessings of an electronic age, for example, watching videos of kittens on a pocketable supercomputer (smartphone). However, if we were to come up with new ways to squander our time, using only transistors might no longer be enough. Their sizes (4-5 nm) are edging dangerously close to sizes of individual atoms (0.1-0.2 nm). A few years of progress and any further progress becomes unfeasible.

That is where the German scientific team enters the stage. They were able to develop a superfast switch, a basic logical cell, based on water. The main benefit of such approach is the speed at which the switch works: used pseudo stable states of water exist only for tens of femtoseconds, therefore the theoretical frequency of such logical cell can amount to Terahertz, thousands of times faster that the current champions of semiconductor transistors (5000-6000 Megahertz under normal conditions). This way, Moore’s law can be conquered not by shrinking the logical elements, but by speeding them up.

To transform water into a switch scientists used its unusual properties. Water has a plethora of different structured states, some of which can be observed under normal conditions, some – only under very specific conditions. It is those that are discussed in the paper. Under high pressures and temperatures akin to those existing within gas giants, water can transform into a metallic state, distributing shared electrons within the whole volume of liquid. The same state can be achieved without the aforementioned extreme conditions. After sequential irradiation of one molecule of water by a group of photons (high intensity beam is needed, for example, laser) one electron from a molecule can become delocalized, simply put, it becomes so fast that it gets distributed to neighboring molecules.

To increase concentration of free electrons the clean water is not enough. High concentration of iodide ions and electromagnetic beam focused on a very small volume of water are also needed. The first does not present any problems ‒ one can just add appropriate salts. The second, however, is not trivial. Scientists had to manufacture unique ultrathin nozzles, which made the water form fine but stable jet/layer of water (14-43 micrometers, stable within 1% for more than hundred hours, see picture). Narrow photon beam “optically pumps” this small jet of water with energy, this in turn leads to some electrons transferring to higher energy states, until some of them become energetic enough to leave the orbits of atoms.

The fastest and the wettest logical cell
Source: Ruhr Universität Bochum, Press Release.

After electron delocalization water abruptly starts to conduct electricity (becomes metallic). This changes a whole list of its properties. The most useful for fast detection is the changes in its absorption spectra.

It is preferable to observe spectral changes in water not in visible range, but in Terahertz (THz) range , energetically situated between microwave and infrared radiation. Electromagnetic waves in this range are strongly absorbed by water. More importantly, these waves have fundamental connections with water structures. Obtaining a fine beam of THz radiation for this project was a complicated technological process in itself, as further discussed in the paper. Depending on how water structures absorbed this THz radiation researchers were able to distinguish its different states.

Even at current stage both steps in logical cell work take extremely little time: pumping electrons with energy takes less than 50 femtoseconds, while the subsequent spectrum acquisition takes 25 femtoseconds. Thereby scientists were able to achieve response frequency of such a cell approximating 1 THz. One should not confuse the frequency of detecting beam measured in the same THz and the frequency of a logical cell. However, the coincidence is not accidental, as anyone can easily grasp the fact that if water structures respond in Terahertz range, it is impossible to measure those changes any faster.

Current development of new logical cell based on water is only in an infancy stage of solving the technological hurdles. However, quite soon these or other similar technologies based on unique water properties could serve as a basis for new technological leap.