Dr. Polychronis Tsipas

Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

A. Sotiropoulos

E. K. Evangelou

The Schottky barrier height in metal/Ge contacts shows weak dependence on the metal work function indicating strong Fermi-level pinning close to the Bardeen limit. The pinning factor

S

is about 0.05 and the charge neutrality level (CNL) is only about

0.09 eV

above the top of the valence band. Because of this, the Fermi level in Ge lies higher than CNL in most cases of interest so that unpassivated acceptorlike gap states at the interface are easily filled, building up a net negative fixed charge. This could prevent efficient inversion of a

p

-type Ge surface in a metal-oxide-semiconductor structure.

16 December 2013 in Applied Physics Letters

Journal Article

Spyros Kassavetis

D. Tsoutsou

E. Golias

High-quality, large-area MoSe₂ and MoSe₂/Bi₂Se₃ heterostructures on AlN(0001)/Si(111) substrates by molecular beam epitaxy

Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

24 March 2015 in Nanoscale

Journal Article

K. E. Aretouli

D. Tsoutsou

S. A. Giamini

Two-dimensional semiconductor HfSe2 and MoSe2/HfSe2 van der Waals heterostructures by molecular beam epitaxy

Atomically thin MoSe₂ films grown epitaxially on AlN by MBE have high crystallinity, smooth surface and interface morphology, and sizable semiconductor band gap for use in nanoelectronics.

6 April 2015 in Applied Physics Letters

Journal Article

K. E. Aretouli

D. Tsoutsou

J. Marquez-Velasco

Evidence for hybrid surface metallic band in (4 × 4) silicene on Ag(111)

Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe₂ and MoSe₂/HfSe₂ van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe₂ are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe₂ compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe₂ and MoSe₂ layers resulting in a small valence band offset of only 0.13 eV at the MoSe₂/HfSe₂ heterointerface and a weak type II band alignment.

2 December 2013 in Applied Physics Letters

Journal Article

D. Tsoutsou

E. Golias

Epitaxial 2D SnSe₂/ 2D WSe₂ van der Waals Heterostructures

The electronic band structure of monolayer (4 × 4) silicene on Ag(111) is imaged by angle resolved photoelectron spectroscopy. A dominant hybrid surface metallic band is observed to be located near the bulk Ag sp-band which is also faintly visible. The two-dimensional character of the hybrid band has been distinguished against the bulk character of the Ag(111) sp-band by means of photon energy dependence experiments. The surface band exhibits a steep linear dispersion around the

{\bar{K}}_{Ag}

point and has a saddle point near the

{\bar{M}}_{Ag}

point of Ag(111) resembling the π-band dispersion in graphene.

25 August 2016 in ACS Applied Materials & Interfaces

Journal Article

Kleopatra Emmanouil Aretouli

Dimitra Tsoutsou