Browsing by Author "Ervasti, M. M."

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Electronic components embedded in a single graphene nanoribbon
(2017-12-01) Jacobse, Peter H.; Kimouche, A.; Gebraad, T.; Ervasti, M. M.; Thijssen, J. M.; Liljeroth, P.; Swart, I.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The use of graphene in electronic devices requires a band gap, which can be achieved by creating nanostructures such as graphene nanoribbons. A wide variety of atomically precise graphene nanoribbons can be prepared through on-surface synthesis, bringing the concept of graphene nanoribbon electronics closer to reality. For future applications it is beneficial to integrate contacts and more functionality directly into single ribbons by using heterostructures. Here, we use the on-surface synthesis approach to fabricate a metal-semiconductor junction and a tunnel barrier in a single graphene nanoribbon consisting of 5- and 7-atom wide segments. We characterize the atomic scale geometry and electronic structure by combined atomic force microscopy, scanning tunneling microscopy, and conductance measurements complemented by density functional theory and transport calculations. These junctions are relevant for developing contacts in all-graphene nanoribbon devices and creating diodes and transistors, and act as a first step toward complete electronic devices built into a single graphene nanoribbon.
Modeling positronium beyond the single particle approximation
(2016-02-29) Zubiaga, A.; Ervasti, M. M.; Makkonen, I.; Harju, A.; Tuomisto, F.; Puska, M. J.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Understanding the properties of the positronium atom in matter is of interest for the interpretation of positron annihilation experiments. This technique has a unique capability for the investigation of nanometer sized voids and pores in soft molecular materials (polymers, liquids or biostructures) and porous materials. However, detailed interpretations of the experimental data rely on modeling of the annihilation properties of positronium in the host material. New applications of the technique are being developed but the computational models still are based on single particle approaches and there is no way to address the influence of the electronic properties of the host material. In this work we discuss new directions of research.