DFF Sapere Aude Topforsker project

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In June 2014, Philip Hofmann was awarded a Sapere Aude Topforkser grant from the Danish Council for Independent Research (DFF). This page reports on the progress of the project.



The project


The experimental isolation of graphene, a single layer of carbon atoms, has shown that truly two-dimensional (2D) materials can exist, contrary to previous predictions. Meanwhile, it has been shown that small flakes of 2D MoS2 or TaS2 can also be isolated from their three-dimensional (3D) parent materials and that the materials' 2D and 3D versions behave very differently. In this project we will use an alternative approach to grow 2D materials directly on a surface in ultra-high vacuum. This will give rise to higher quality, larger areas and the freedom to design entirely new materials.  This type of synthesis will also allow studies by powerful and complementary techniques such as angle-resolved photoemission spectroscopy, scanning tunnelling microscopy and nano-scale transport. We will determine in what way and why the 2D solids are different from their 3D counterparts and how we can influence their properties.


Senior people associated with the project


Philip Hofmann

Jeppe Vang Lauritsen

Alexander Ako Khajetoorians


Publications


Growth and electronic structure of epitaxial single-layer WS2 on Au(111), Maciej Dendzik, Matteo Michiardi, Charlotte Sanders, Marco Bianchi, Jill A. Miwa, Signe Grønborg, Jeppe Vang Lauritsen and Philip Hofmann, arxiv1509.05133

Physical Review B 92, 245442 (2015).


Observation of Ultrafast Free Carrier Dynamics in Single Layer MoS2, Antonija Grubisic Cabo, Jill Miwa, Signe Grønborg, Jonathon Riley, Jens Johannsen,  Cephise Cacho, Oliver Alexander, Richard Chapmann, Emma Springate, Marco Grioni, Jeppe Lauritsen, Philip King, Philip Hofmann, and Søren Ulstrup,

Nano Letters 15, 5883 (2015).


159. Synthesis of Epitaxial Single-Layer MoS2 on Au(111), Signe Grønborg, Søren Ulstrup, Marco Bianchi, Maciej Dendzik, Charlotte Sanders, Jeppe Lauritsen, Philip Hofmann, and Jill Miwa, Langmuir 35 9700 (2015).


Tunable Hot Carrier Multiplication and Cooling in Graphene, Jens Christian Johannsen, Søren Ulstrup, Alberto Crepaldi, Federico Cilento, Michele Zacchigna, Jill Miwa, Cephise Cacho, Richard Chapman, Emma Springate, Felix Fromm, Christian Raidel, Thomas Seyller, Philip King, Fulvio Parmigiani, Marco Grioni and Philip Hofmann,

Nano Letters 15, 326 (2015).


Electronic Structure of Epitaxial Single-Layer MoS2, Jill A. Miwa, Søren Ulstrup, Signe G. Sørensen, Maciej Dendzik, Antonija Grubišić Čabo, Marco Bianchi, Jeppe Vang Lauritsen, Philip Hofmann, arxiv1410.0615,

Physical Review Letters, 114, 046802 (2015).


Scientific Highlights


Electronic structure of single-layer MoS2


As in the case of graphene, many layered materials change their properties in subtle but important ways when thinned down to a single unit layer. Important examples of this are the transition metal dichalcogenites such as MoS2. While bulk MoS2 is a semiconductor with an indirect band gap, a single layer has a direct band gap. Moreover, the top of the valence band has been predicted to be split by the spin-orbit interaction. By growing high-quality epitaxial MoS2 layers on the (111) surface of gold and then inspecting these with angle-resolved photoemission spectroscopy on ASTRID2, we have been able to directly measure the band structure of single-layer MoS2 in unprecedented detail. In fact, the sample quality and resolution is so good that even the predicted spin-orbit splitting can be observed.
















Jill A. Miwa, Søren Ulstrup, Signe G. Sørensen, Maciej Dendzik, Antonija Grubišić Čabo, Marco Bianchi, Jeppe Vang Lauritsen, Philip Hofmann, arxiv1410.0615,  Physical Review Letters 114, 046802 (2015).