Frank Volmer
RWTH Aachen University
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Publication
Featured researches published by Frank Volmer.
Nano Letters | 2011
Ahmet Avsar; Tsung-Yeh Yang; Sukang Bae; Jayakumar Balakrishnan; Frank Volmer; Manu Jaiswal; Zheng Yi; Syed Rizwan Ali; G. Güntherodt; Byung Hee Hong; Bernd Beschoten; Barbaros Özyilmaz
We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications.
Nano Letters | 2014
Marc Drögeler; Frank Volmer; Maik Wolter; Bernat Terrés; Kenji Watanabe; Takashi Taniguchi; G. Güntherodt; Christoph Stampfer; Bernd Beschoten
We present a new fabrication method of graphene spin-valve devices that yields enhanced spin and charge transport properties by improving both the electrode-to-graphene and graphene-to-substrate interface. First, we prepare Co/MgO spin injection electrodes onto Si(++)/SiO2. Thereafter, we mechanically transfer a graphene-hBN heterostructure onto the prepatterned electrodes. We show that room temperature spin transport in single-, bi-, and trilayer graphene devices exhibit nanosecond spin lifetimes with spin diffusion lengths reaching 10 μm combined with carrier mobilities exceeding 20,000 cm(2)/(V s).
Nano Letters | 2016
Marc Drögeler; Christopher Franzen; Frank Volmer; Tobias Pohlmann; Luca Banszerus; Maik Wolter; Kenji Watanabe; Takashi Taniguchi; Christoph Stampfer; Bernd Beschoten
We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5 μm in single layer graphene nonlocal spin transport devices at room temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a Si/SiO2 substrate and the subsequent dry transfer of a graphene-hBN-stack on top of this electrode structure where a large hBN flake is needed in order to diminish the ingress of solvents along the hBN-to-substrate interface. Interestingly, long spin lifetimes are observed despite the fact that both conductive scanning force microscopy and contact resistance measurements reveal the existence of conducting pinholes throughout the MgO spin injection/detection barriers. Compared to previous devices, we observe an enhancement of the spin lifetime in single layer graphene by a factor of 6. We demonstrate that the spin lifetime does not depend on the contact resistance area products when comparing all bottom-up devices indicating that spin absorption at the contacts is not the predominant source for spin dephasing.
Physical Review B | 2013
Frank Volmer; Marc Drögeler; Eva Maynicke; N. von den Driesch; M. L. Boschen; G. Güntherodt; Bernd Beschoten
We investigate spin and charge transport in both single and bilayer graphene non-local spin-valve devices. Similar to previous studies on bilayer graphene, we observe an inverse dependence of the spin lifetime on the carrier mobility in our single layer devices. This general trend is only observed in devices with large contact resistances. Furthermore, we observe a second Dirac peak in devices with long spin lifetimes. This results from charge transport underneath the contacts. In contrast, all devices with low ohmic contact resistances only exhibit a single Dirac peak. Additionally, the spin lifetime is significantly reduced indicating that an additional spin dephasing occurs underneath the electrodes.
Physical Review B | 2014
Frank Volmer; Marc Drögeler; Eva Maynicke; N. von den Driesch; M. L. Boschen; G. Güntherodt; Christoph Stampfer; Bernd Beschoten
By successive oxygen treatments of graphene nonlocal spin-valve devices we achieve a gradual increase of the contact-resistance\char21{}area products
arXiv: Mesoscale and Nanoscale Physics | 2015
Frank Volmer; Marc Drögeler; Tobias Pohlmann; G. Güntherodt; Christoph Stampfer; Bernd Beschoten
({R}_{c}A)
Physical Review B | 2017
Frank Volmer; Bernd Beschoten; Christoph Stampfer; S. Pissinger; Sebastian Kuhlen; M. Ersfeld
of Co/MgO spin injection and detection electrodes and a transition from linear to nonlinear characteristics in the respective differential
Applied Physics Letters | 2017
Marc Drögeler; Luca Banszerus; Frank Volmer; Takashi Taniguchi; Kenji Watanabe; Bernd Beschoten; Christoph Stampfer
dV\text{\ensuremath{-}}dI
Physica Status Solidi B-basic Solid State Physics | 2017
Marc Drögeler; Frank Volmer; Christoph Stampfer; Bernd Beschoten
curves. With this manipulation of the contacts, both spin lifetime and the amplitude of the spin signal can significantly be increased by a factor of seven in the same device. This demonstrates that contact-induced spin dephasing is the bottleneck for spin transport in graphene devices with small
Physical Review Letters | 2011
Tsung-Yeh Yang; Jayakumar Balakrishnan; Frank Volmer; Ahmet Avsar; Manu Jaiswal; Samm J; Ali; Alexandre Pachoud; Minggang Zeng; Popinciuc M; G. Güntherodt; Bernd Beschoten; Barbaros Özyilmaz
{R}_{c}A