2D Materials: Electronic structure, Devices and Applications

Permanent Personnel

Johan Biscaras, Abhay Shukla

Current PhD Students:

Wenyi Wu, Ali Fakih, Edoardo Sterpetti

Past PhD students

Zhesheng Chen, Emilio Velez, Mohammed Boukhicha, Adrian Balan

Research areas:

Phase transitions in 2D driven by space charge doping and dimensionality

- 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.

Onset of two-dimensional superconductivity in space charge doped few-layer Molybdenum Disulphide

http://www.nature.com/articles/ncomms9826

Space charge induced electrostatic doping of two-dimensional materials: Graphene as a case study

http://aip.scitation.org/doi/abs/10.1063/1.4932572?journalCode=apl

Anharmonic phonons in few-layer MoS2: Raman spectroscopy of ultralow energy compression and shear modes

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.87.195316

Devices and Applications

- 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.

A high performance graphene/few-layer InSe photo-detector

http://pubs.rsc.org/en/Content/ArticleLanding/2015/NR/C5NR00400D#!divAbstract

Anodic bonded 2D semiconductors: from synthesis to device fabrication

https://hal.archives-ouvertes.fr/hal-01053499/

Single step fabrication of N-doped graphene/Si3N4/SiC heterostructures

http://link.springer.com/article/10.1007%2Fs12274-014-0444-9

Patents

- 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)

Graphene made easy: High quality, large-area samples

http://www.sciencedirect.com/science/article/pii/S0038109809000829

Space charge induced electrostatic doping of two-dimensional materials: Graphene as a case study

http://aip.scitation.org/doi/abs/10.1063/1.4932572?journalCode=apl

Techniques:

- 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

Relevant publications

Self-organized metal-semiconductor epitaxial graphene layer on off-axis 4H-SiC(0001)

http://link.springer.com/article/10.1007%2Fs12274-014-0584-y

Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

http://aip.scitation.org/doi/10.1063/1.4867348

Edge state in epitaxial nanographene on 3C-SiC(100)/Si(100) substrate

http://aip.scitation.org/doi/10.1063/1.4818547

Control of the degree of surface graphitization on 3C-SiC(100)/Si(100)

http://www.sciencedirect.com/science/article/pii/S0039602811003906

Epitaxial Graphene on 4H-SiC(0001) Grown under Nitrogen Flux: Evidence of Low Nitrogen Doping and High Charge Transfer

http://pubs.acs.org/doi/abs/10.1021/nn304315z

Epitaxial graphene on single domain 3C-SiC(100) thin films grown on off-axis Si(100)

http://aip.scitation.org/doi/10.1063/1.4734396

High quality 2D crystals made by anodic bonding: a general technique for layered materials

https://hal.archives-ouvertes.fr/hal-01053374/

Sharp interface in epitaxial graphene layers on 3C-SiC(100)/Si(100) wafers

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.83.205429

Anodic bonded graphene

https://hal.archives-ouvertes.fr/hal-00569705

Epitaxial graphene on cubic SiC(111)/Si(111) substrate

http://aip.scitation.org/doi/abs/10.1063/1.3427406?journalCode=apl