As attention continues to be drawn on the superior properties exhibited by graphene, the ultrathin wonder material, researchers from around the world continue to work towards emulating this thin and intrinsic design with other potentially useful materials.
In their own quest to develop thin and electrically conductive sheets for future electronic device applications, a group of researchers led by Raymond McQuaid, Amit Kumar and Marty Gregg from Queen’s University have developed “domain walls” that exist within crystalline materials.
The quest towards developing more compact and thinner electronic devices that simultaneously offers consumers an improved functional speed, greater memory storage and other necessary components has led researchers to focus on the circuits present within these devices. To create smaller electronic devices, they must be equipped with smaller circuits, however, the demand for the numerous advanced components to be present within these devices often causes an increase in the size of the final product.
Domain walls have previously been determined to maintain a consistent conductivity when present in thin-film BiFeIO3 circuits, however, the ability to maintain stability in such charged-wall configurations has been difficult to achieve. More specifically, there is a significant lack in techniques that are capable of controlling the charge states of domain walls, despite their developed use in proper ferroelectric applications.
In their effort to develop a method that allows for the ability to control the conductivity of charged domain walls, the Queens University researchers utilized proper-ferroelastic improper-ferroelectric Cu3B7O13Cl single crystals, more formally referred to as a Cu-Cl boracite single crystal plate. Topological confirmation measurements were taken by use of atomic force microscopy (AFM), as well as nanoscale spatially resolved current mapping to measure the domain wall conductivity.
The Cu-Cl boracite crystal exhibited head-to-head 90° domain walls, as well as tail-to-tail 90° walls and uncharged 180° domain walls. The writing technique employed in this study is unique to domain walls, as the researchers applied a fine-tipped metal probe onto the surface of the crystal at a pressure order of 1GPa.
When this pressure was applied to the surface of the crystal, the domain wall mobility was found to increase, thereby initiating the growth of conductive domain wall patterns that are capable of stretching to the full length of the domain wall.
The unique conductive nature of the domain walls is especially impressive when the length and thickness of the crystal structure is considered. When artificially synthesized, the Cu-Cl boracite crystals can measure at several hundreds of microns in length, while maintaining an extremely thin structure measuring at only a few nanometers thickness.
While the intensity of the applied pressure affected the development of the microcircuits along the domain wall, it also changed the specific nature of the circuit itself. The applied probe initiates the creation of these domains a that surround the point of contact between the metal probe and the surface of the crystal, thereby creating a unique pattern of conductive walls.
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In addition to this ease of manipulation by added stress to the crystal, the applied electric fields within these walls can change the location in which the microcircuit arises, which has the potential to be a useful tool in the future applications of domain walls in voltage-operated devices.
As the development of reconfigurable electronic devices continues to be a point of interest for its specific industries, the work developed in this study has the potential to change the development and behavior of these microcircuits in useful products.
While their results are promising, the Queens University researchers urge future work to be conducted on further understanding how temperature and pressure variations can affect the stability and inert conductive nature of these domain walls.
- “Injection and controlled motion of conduting domain walls in improper ferroelectric Cu-Cl boracite” R. McQuaid, M. Campbell, et al. Nature Communications. (2017). DOI: 10.1038/ncomms15105.
- Image: Shutterstock.com/tcareob72