2D-materials

Johan Biscaras, Abhay Shukla

Wenyi Wu, Ali Fakih, Edoardo Sterpetti

Zhesheng Chen, Emilio Velez, Mohammed Boukhicha, Adrian Balan

Superconductivity, insulator-metal transition, charge density waves. These phenomena are directly related to the density of electronic levels at the Fermi level, the strength of electron-phonon coupling in a given material and to dimensionality. Our strategy is to control the density of states through the space charge doping method we have developed, as shown by a recent study on MoS₂ in which we induce superconductivity. The promise of this line of research is confirmed by ongoing work on various materials like hi-Tc superconductors, semiconductors and transition metal oxides. Our future work will concentrate on provoking and controlling phase transitions with space charge doping.
Kosterlitz-Thouless transitions and Topological order. Since space charge doping is active in a layer of the order of a nanometer, the doped area in our samples is always two dimensional. In two dimensions phase transitions are predicted to be of infinite order (Kosterlitz and Thouless), with a disordered high temperature phase and a quasi-ordered low-temperature phase. Space charge doping provides a new way of looking at the insulator-superconductor transition in a single 2D sample by varying carrier density and magnetic field and examining theoretical predictions.

Transparent Conducting Electrodes (TCE). We propose a new technique of producing TCE’s through space charge doping of large area thin films. The vast majority of TCE’s are deposited on glass substrates. We use the specifity of space charge doping to induce ultra-high carrier density and conductivity in thin films deposited on glass substrates. We have demonstrated this possibility in both layered materials (graphene) and oxides (ZnO).
Improving optoelectronic device efficiency. 2D materials are poised to introduce major gains in the field of optoelectronics as seen through the example of the simple photoconductor device. Combining layers of different materials with complementary properties can lead to a hybrid sandwich structure with new properties. Associating graphene (charge transport) with a layered semiconductor (light to charge conversion) can lead to a very efficient photoconductor. Instead of the lateral geometry for current transport in standard devices, a vertical geometry in ultra-thin devices can further maximize effective device volume and minimize losses in transport.

Anodic bonding: a method to make few layer 2D films of layered materials (WO 2009 074755)
Space Charge doping: A method to electrostatically dope 2D thin films (FR 1557308)

Sample fabrication and characterization: Anodic bonding, physical vapour deposition (sputtering, evaporation); micro-Raman, AFM
Clean room device fabrication
Low temperature magneto transport
In-situ space charge doping
Low temperature Raman spectroscopy
Low temperature infra-red spectroscopy