Aachen Graphene FLAGSHIP seminars

Tuesday, February 27, 2024, 12:00 to 13:00 pm

Speaker: Dr. Johannes Schwenk, Ecole Polytechnique Fédéral de Lausanne (EPFL)

Title: The quantum states in graphene measured by atomic force microscopyPlace: Physik-Hörsaal 28 D001 [4284]

Abstract:

The physics and transport properties of graphene devices are governed by their microscopic properties. Therefore, we combine in-situ transport and Atomic Force Microscopy (AFM) measurements at low temperatures and in a magnetic field to gain insight to the quantum hall edge states in a graphene Hall bar. In the presented study, carried out at NIST Gaithersburg, USA, we map the local chemical potential along the border of the hall bar and reveal the four-fold symmetry breaking of the electron energy levels in the zero energy Landau Level.

 

Wednesday, January 10, 2024, 14:30 to 15:30 pm

Speaker: Prof. Barbaros Oezyilmaz, National University of Singapore

Title: Disorder Engineering in 2D:  From ferromagnetic signature in Co doped NbSe2 below Tc  to achieving ultra-low k dielectrics in monolayer amorphous carbon (MAC)

Place: Physik-Hörsaal 28 D001 [4284]

Abstract:

Disordered systems in the atomic limit offer several existing possibilities in both basic science and applications difficult to realize with 2D crystals. Examples range from higher order topological insulators to perfect Li ion membranes/solid state electrolytes. In my talk I will discuss two examples.

First, I will discuss monolayer amorphous carbon (or amorphous graphene) to date the only realization of an atomically thin, free standing amorphous material [1]. Despite significant advancements in using 2D materials for integrated circuits, one crucial building block, namely a 2D ultralow-k (ULK) dielectric is missing. The challenge lies in achieving a dielectric constant (k) less than three as traditional low-k dielectrics are inherently unstable at the 2D limit. Specifically, low-k materials are necessary to minimise parasitic capacitances as the distance between conductive elements shrinks below 10 nm. Moreover, advanced architectures like gate-all-around field effect transistors (GAA FET) require even lower dielectric constants (k<2) at sub-3nm thickness. Layer-by-layer grown amorphous carbon (ML-AC), as thin as 0.8 nm, is a mechanically robust 2D ULK dielectric with k of 1.35 and dielectric strength of 28-31 MVcm-1. Moreover, ML-AC overcomes the vulnerability of existing dielectrics to ion diffusion degradation with a record metal ion diffusion time to failure (TTF) of 1010 s for even a single layer. Therefore, otherwise necessary additional layers occupying up to 3 nm can be eliminated, which is especially significant as metal line widths approach 10 nm. Combined with its low-temperature, direct and conformal growth even on a dielectric, these critical features enable substantial improvements in silicon-based semiconductor electronics and ensure compatibility with future 2D electronics [2].

Next, I will discuss niobium diselenide (NbSe2) with dilute cobalt (Co) intercalation and show that such systems spontaneously display ferromagnetism below the superconducting transition temperature (T_C). The tunnelling magnetoresistance shows a bistable state, suggesting a ferromagnetic order in superconducting Co-NbSe2 [3]. We propose a RKKY exchange coupling mechanism based on spin-triplet superconducting order parameter to mediate such ferromagnetism. Non-local lateral spin valve measurements with Hanle spin precession signals up to micrometres below T_C suggest an intrinsic spin-triplet state in superconducting NbSe2 as key ingredient.

[1] Toh, C.-T. et al., Synthesis and properties of free-standing monolayer amorphous carbon. Nature (2020).

[2] Toh, C.-T. et al., 2D Ultralow-k Amorphous Carbon, under review.

[2] Qu, Tingyu et al., [2306.06659] Ferromagnetic Superconductivity in Two-dimensional Niobium Diselenide (arxiv.org).

 

Wednesday, November 8, 2023, 12:00 to 13:00 pm

Speaker: Prof. David Goldhaber-Gordon, Stanford University

Title: Electrons in twisted layers: design, surprise, and a new set of eyes

Place: Physik-Hörsaal 28 D001 [4284]

Abstract:

When two atomically-thin layers of a material are stacked one atop each other, with a relative twist angle between them, properties can emerge that bear little resemblance to the behavior of the individual layers. Though much can be predicted and designed about such structures, I will share two vignettes about how my students aimed for a particular behavior but found something quite different. The first led to the discovery of the first experimentally-known "orbital magnet", a ferromagnet in which the tiny microscopic magnets that align with each other are not electron spins but tiny circulating current loops. The second surprise was observation of resistance that skyrocketed with the application of a magnetic field, along with other striking electronic properties -- this one took years to figure out, but we've recently explained it.

Each of these two surprises turned out to be caused by a structural feature of the layered stack which had not previously been considered important. Finally, I'll describe a refined approach to stacking and a newly-developed technique for mapping the structure of twisted layers, which together might help us get more repeatable control of structure and thus electronic properties in such twisted systems.

 

Wednesday, October 25, 2023, 12:00 to 13:00 pm

Speaker: Prof. Bart Macco,Eindhoven University of Technology

Title: Atomic-Scale Processing for Future Semiconductor Devices

Place: Physik-Hörsaal 28 D001 [4284]

Abstract:

Atomic-Scale Processing (ASP) is a toolbox to deposit or etch films at the atomic scale. It started mostly with atomic layer deposition (ALD), but insights have advanced this to new concepts, including atomic layer etching (ALE) and area-selective deposition (ASD). Together with extreme ultraviolet lithography (EUV), this toolbox has really enabled the last few chip nodes and is driving next generation nanoelectronics. But ASP is also gaining ground in solar, batteries, memory, … In our group in Eindhoven, we focus on mechanistic research of ASP: How the interaction of precursors, ions and photons with surfaces leads to film deposition and resulting film properties. This is often done using in-situ studies, while we mostly validate our films in devices through collaborations. My own research within the group is focused on ASP for future semiconductor devices, focusing on 2D TMDs, amorphous oxide semiconductors and fluorite ferroelectrics.

Aiming to complement my materials-based research, I am currently on a sabbatical at AMO in Aachen to learn more about the device processing side of semiconductor devices. In return, in this seminar I want to give a comprehensive introductory overview of what atomic-scale processing is. I will start “tutorial-like” at the basics of ALD, moving to the concept of ALE and ASD. I will cherry-pick a few of our recent in-situ studies and focus on the main practical insights we got from that. In the end, I will focus on my own research on ALD for 2D TMDs and amorphous oxide semiconductors.

 

Tuesday, July 4, 2023, 12:30 to 13:30pm

Magnetism in Van der Waals Heterostructures Copyright: © Prof. Chen

Speaker: Prof. Yong P. Chen, Purdue University, AIMR, and Aarhus University

Title: Van der Waals Magnets based Heterostructures: platforms to engineer and probe novel magnetism

Place: Physik-Hörsaal 28 D001 [4284]

Abstract:

In past few years, various 2D van der Waals (vdW) layered magnetic materials (including ferromagnets, antiferromagnets and even candidate spin liquids) have emerged – they have both challenged our fundamental understanding of magnetism while also brought exciting opportunities to realize novel physics and functionalities.  I will discuss our recent experimental work focusing on heterostructures based on such magnetic 2D materials as platforms to realize and probe novel magnetic states. I will describe how stacking two antiferromagnets (each possessing zero measured magnetization) on top of each other can result in a ferromagnet with significant magnetization and much more, such as “Moire magnetism” made by “twistronics”. I will also describe how by interfacing with a heavy metal with strong spin-orbit coupling, one can perform (spin sensitive) electrical transport measurement and probe the enigmatic spin states of an insulating “quantum spin liquid” material (which has been proposed as a platform to realize exotic quasiparticles such as Majorana fermions or even non-Abelian anyons).  

References:

[1] G. Cheng et al., "Emergence of electric-field-tunable interfacial ferromagnetism in 2D antiferromagnet heterostructures", Nature Communications 13, 7348 (2022)

[2] G. Cheng et al., "Electrically tunable moiré magnetism in twisted double bilayer antiferromagnets", Nature Electronics (2023) doi: 10.1038/s41928-023-00978-0

[3] H. Idzuchi et al., "Spin sensitive transport in a spin liquid material: revealing a robustness of spin anisotropy", arxiv:2204.03158

 

Monday, June 26, 2023, 11:15 to 12:00pm

Speaker: Dr. Iris Niehues, CIC nanoGUNE BRTA, Donostia – San Sebastián, Spain

Title: Manipulating the Optical Properties of 2D Semiconductors on the Nanoscale

Ort: Physik-Hörsaal 28 D001 [4284]

Abstract:

Transition metal dichalcogenides (TMDC) have gained a lot of attention due to their unique material properties. The optical response of these atomically thin semiconductors is dominated by excitons – bound electron hole pairs. Next to their outstanding optical properties 2D materials also possess exceptional mechanical properties. They are extremely flexible and can withstand mechanical strain of up to 10%. I will show how strain manipulates the exciton energies [1,2] as well as the exciton-phonon coupling in TMDCs [3,4]. In addition, local strain can be used to create single-photon emitters at low temperatures [5]. I will also discuss near-field techniques which allow to reach optical nanoscale resolution. We have used these methods to measure the local carrier density of molecule-intercalated MoS2 crystals (Fig. 1), which show superconductivity at low temperatures [6].

References:

[1] R. Schmidt, I. Niehues, R. Schneider et al, 2D Mater. 3, 021011 (2016)
[2] I. Niehues, A. Blob, T. Stiehm et al., Nanoscale 11, 12788-1292 (2019)
[3] I. Niehues, R. Schmidt, M. Drueppel et al., Nano Lett. 18, 1751-1757 (2018)
[4] I. Niehues, P. Marauhn, T. Deilmann et al., Nanoscale 12, 20786-20796 (2020)
[5] J. Kern, I. Niehues, P. Tonndorf et al., Adv. Mat. 28, 7101 (2016)
[6] J. Pereira, D. Tezze, I. Niehues et al., Adv. Funct. Mater. 2208761 (2022)

 

Tuesday, June 6, 2023, 12:30 to 14:30pm

Speaker: Prof. Subho Dasgupta, Department of Materials Engineering, Indian Institute of Science in Bangalore

Title: Printed 2D electronics with predominant intra flake transport

Venue: Physik-Hörsaal [4284]

Abstract:

Printed/solution-processed electronics are beginning to attract commercial success in different application domain including low-cost wearables, biosensors, biomedical tags, packaging etc. Among the available semiconductor technologies, exfoliated 2D semiconductors show a rare combination of physical properties, such as large-enough band gap to attain sufficient On-Off ratio, matched electron and hole mobility, and excellent mechanical reliability to suit flexible electronic applications. Moreover, the solvent-exfoliated TMD-nanosheets can be processed at low temperatures, and be compatible with inexpensive polymer substrates. However, the poor inter-flake transport in solution-processed 2D-TMD network transistors limits their device performance and application potential. In this seminar, a novel device geometry is proposed that can be particularly suitable for printing methods of device fabrication; here, an additional metal layer is printed on top of the nanoflake based semiconductor channel to reduce the channel dimentions to the thickness of the printed 2D-TMD nanosheet layer. In this process, not only the narrow-channel thin film transistors (TFTs) are obtained with large current density, but the devices demonstrate predominantly intra-flake transport. The high mobility MoS2 field-effect transistors (FETs) thus produced show simultaneous large current saturation (>310 μA μm−1) and high On-Off ratio (>106). In addition, a channel-capacitance-modulation induced subthermionic transport is also observed, which resulted in subthreshold slope ~7.5 mV dec−1. Next, unipolar depletion-load type all-NMOS inverters and logic electronics are demonstrated with switching frequency >1 kHz, which may certainly be sufficient to be used at biosensor interfaces. Furthermore, all-2D CMOS electronics are presented following an identical protocol and with tellurene flakes as the p-type semiconductor material. Lastly, a novel concept of a tunable diode would be demonstrated, where, an external voltage applied to a third terminal (gate electrode) can tune the barrier height of the printed heterojunction and alter the rectification ratio by more than two orders of magnitude from pure Ohmic to a diode-like behavior. This allows us to create a filter that may either allow an AC signal to pass or converts it to a DC output, when required.

 

Tuesday, May 16, 2021, 12:00 to 13:00pm

Speaker: Prof. Pawel Hawrylak, University of Ottawa

Title: Dirac Fermions in quantum dots in 2D materials

Abstract:

We describe here our recent theoretical work on Dirac and massive Dirac Fermions in  quantum dots in 2D crystals. The goal is to design nanostructures with the three functionalities of a quantum circuit: electronics, photonics and spintronics, in a single material and at the nanoscale[1,2]. The design tools include materials, size, shape, type of edge, sublattice symmetry, topology, gates, number of layers and carrier density in graphene, bilayer graphene and TMDC quantum dots. In particular, we discuss how size engineering leads to optical gaps in graphene from THz to UV [1,3,4] , edge engineering leads to gap oscillation [4], sublattice engineering allows design of magnetic moments,[1,2] layer and gate engineering allows generation of voltage tunable excitons in the THz range[5],  carrier density engineering allows for the realization of broken symmetry valley and spin polarized states in bilayer graphene and TMDCs gated quantum dots [6-8].

Selected References:

[1] A.D.Guclu, P. Potasz, M. Korkusinski and P. Hawrylak,”Graphene Quantum Dots”, Springer  2014; P. Hawrylak, F. Peeters, K. Ensslin, Editors,  Carbononics–integrating electronics, photonics and spintronics with graphene quantum dots, Focus issue, Physica status solidi (RRL)-Rapid Research Letters 10 (1), 11(2016).

[2] A.D.Guclu,P. Potasz, O.Voznyy, M. Korkusinski, P. Hawrylak, Phys.Rev.Lett.103, 246805 (2009).

[3] Cheng Sun, Florian Figge, I.Ozfidan, M. Korkusinski, Xin Yan, Liang-shi Li, Pawel Hawrylak and John A. McGuire, Biexciton binding in colloidal graphene quantum dots”, NanoLetters 15,5742(2015).

[4] Y. Saleem, L. Najera Baldo, A. Delgado Gran , L. Szulakowska and  P. Hawrylak,              ” Evolution of bandgap with size in armchair and zigzag graphene quantum dots”, Journal of Physics: Condensed Matter 31 (30), 305503 (2019).

[5]Y. Saleem, K. Sadecka, M. Korkusinski, D. Miravet, A. Dusko and P. Hawrylak, “Theory of Excitons in Gated Bilayer Graphene Quantum Dots”,  Nano Lett. 23, 2998 (2023).

[6] Abdulmenaf Altintas, Maciej Bieniek, Amintor Dusko, Marek Korkusinski, Jaroslaw Pawlowski, and Pawel Hawrylak, Spin-valley qubits in gated quantum dots in a single layer of transition metal dichalcogenides, Physical Review B 104 (19), 195412, 2021

[7]. L. Szulakowska, M. Bieniek, M. Cygorek, P.Hawrylak, “Valley and spin polarized broken symmetry states of interacting electrons in gated MoS2 quantum dots”, Phys.Rev. B102, 245410 (2020).

[8] Marek Korkusinski,Yasser Saleem, Amintor Dusko, Daniel Miravet, and Pawel Hawrylak, “Spontaneous spin and valley symmetry broken states of interacting massive Dirac Fermions in a bilayer graphene quantum dot”, submitted to Nature Physics 2023.

 

Tuesday, February 14, 2021, 12:00 to 13:00pm

Speaker: Ermin Malic, Philipps-University Marburg

Title: Exciton optics, dynamics, and transport in atomically thin materials

Abstract: Monolayer transition metal dichalcogenides (TMDs) and related van der Waals heterostructures exhibit a rich exciton physics including bright and a variety of dark states as well as spatially separated interlayer excitons. Solving 2D material Bloch equations for excitons, phonons and photons, we obtain a microscopic access to the interplay of optics, ultrafast dynamics and transport of excitons in these technologically promising materials.
In joint theory-experiment studies, we shed light on the importance of dark excitons on (i) low-temperature photoluminescence spectra of TMD monolayers and twisted homobilayers, (ii) temperature dependent exciton-exciton annihilation processes, (iii) ultrafast charge transfer dynamics in TMD heterostructures, (iv) exciton funneling in strained TMD monolayers as well as (v) anomalous exciton transport in TMD bilayers.
The gained microscopic insights into the spatiotemporal exciton dynamics are crucial for understanding and controlling many-particle phenomena governing exciton optics, dynamics and transport in technologically promising 2D materials and related heterostructures.

 

Tuesday, October 11, 2021, 12:00 to 13:00pm

Title: Enhancing Biosensor Response with Graphene “Lighting-Rods”

Abstract: Graphene field-effect transistor (GFET) sensors have emerged as a promising platform for
detection of clinical biomarkers, such as DNA, RNA, proteins, and antibodies [1]. As such,
graphene is interesting to create a new class of low-cost, point-of-need diagnostic systems. In
order to be competitive for these applications, GFET sensors must provide target specificity, have
high sensitivity, and achieve a result in a short period of time. While sensitivity and specificity can
readily be achieved using appropriate surface functionalization, rapid readout remains a
challenge.
In this talk, I will show how dielectrophoresis (DEP) can be used as an effective technique to
create graphene GFET sensors with ultra-fast response. DEP is a technique by which a neutral,
but polarizable particle can be attracted toward a location where a large electric field gradient
exists [2]. Due to its atomic-scale thickness, graphene can produce enormous electric field
gradients at its edges, effectively acting as a nanoscale “lightning rod” [3]. When an AC bias is
applied, this same effect can selectively attract polarizable neutral particles via the DEP effect.
Here, I will describe the theory of DEP trapping, and show how a variety of nanoparticles can be
trapped at extremely-low voltages at graphene edges [3]. I will also show recent results whereby
trapped particles at the graphene edges can be detected electrically, and also describe several
strategies to enhance the sensitivity of DEP GFET devices [4]. Finally, I will discuss future
challenges to realize fully-functional DEP-enhanced GFET biosensors.
As part of this presentation, I will also give an introduction to the University of Minnesota (UMN),
one of the largest universities in the United Sates by student population, the Minnesota Nano
Center, which is a primary driver of nanoscale fabrication innovation in the Upper Midwest of the
United States, and also other 2D-material research in the Koester NanoDevice Group at UMN.

[1] I. Prattis, E. Hui, P. Gubeljak, G. S. Kaminski Schierle, A. Lombardo, and L. G. Occhipinti, “Graphene for biosensing applications in point-of-care testing,” Trends in Biotechnology 39, 1065-1077 (2021).

[2] A. H. Pohl, Dielectrophoresis. Cambridge University, 1978.

[3] A. Barik, Y. Zhang, R. Grassi, B. P. Nadappuram, J. B. Edel, T. Low, S. J. Koester, and S.-H. Oh, “Graphene-edge dielectrophoretic tweezers for trapping of biomolecules,” Nat. Commun. 8, 1867 (2017).

[4] N. Izquierdo, R. Li, S.-H. Oh, and S. J. Koester, “Demanding more from graphene-based sensors: design and development of multi-functional GFET with dielectrophoresis enhanced sensing capabilities,” to be presented at the 2022 Fall MRS Meeting, Boston, MA, USA,  Nov. 27 – Dec. 2, 2022.

 

Tuesday, September 13, 2021, 12:30 to 13:30pm

Title: New perspectives on Layer Transfer and Artificial Crystalline Heterostructures

Abstract: Layer transfer introduces a paradigm shift in the way crystalline heterostructures could be
synthesized. In contrast to established growth methods of epitaxial heterostructures which
must oblige to matching conditions at the interface with respect to surface energies, lattice
parameter and crystal symmetry, layer transfer allows in principle for the combination of any
crystalline materials.
In particular, the potential to create novel artificial crystalline heterostructures has been
demonstrated with 2-dimensional van der Waals (2D vdW) materials. New functional
interfaces can be realized by novel combinations of different 2D vdW materials. More
astonishing, emerging physical properties can be produced by reassembling layers of the
same material in different ways for example by introducing a twist angle between the layers.
In this way so called Moiré materials can be created which for 2D vdW materials allow for
unique ways of band structure engineeringc, famously the formation of flat bands at magic
angle twisted bilayer graphene. It also has been realized that stacking of 2D materials creates
periodic strain patterns. Yet, because the interlayer interaction in 2D vdW materials is
intrinsically weak and intralayer bonds are always stronger, it is not possible to create defect
structures within the layer that is to produce artificial twist boundaries characterized by
screw dislocation networks. This is different with covalently or ionic bonded materials such as
oxides. For example, in oxidic perovskites the bonding character is almost ionic, making it
possible to produce nm thin films in (100)-orientation virtually without surface
reconstruction. Yet interaction to other polar surfaces remains strong and as demonstrated
in the past via wafer bonding of single crystals dislocation networks at the interface occur
after thermal annealing.
The potential of layer transfer for future crystal assembly has been recognized by Leibniz
Institut für Kristallzüchtung IKZ. After providing a brief general overview of the IKZ and the
research activities of the section "Semiconductor Nanostructures", I will discuss preliminary
results on growth, release and transfer of thin epitaxial perovskite films. As outlook, we
propose that artificial twist boundaries in nm thin perovskite films can serve as innovative
nanoengineering platform for epitaxial oxides. Advanced control of local strain gradients
offers manifold ways to influence internal degrees of freedom at the nanoscale beyond the
possibilities of classical strain engineering in heteroepitaxy and opening up new avenues to
investigate flexoelectric effects. In addition, I will present recent advances of in situ growth
of 2D vdW multilayers and heterostructures.

 

Tuesday, May 4, 2021, 12 to 1pm

Title: Tuning Nonlinearities and Modal Coupling in Two Dimensional Electromechanical Resonators

Abstract: The advent of two-dimensional materials such as graphene and transition metal dichalcogenides have generated immense interests in the area of nanoelectromechanical systems (NEMS). Their extraordinary properties such as low mass, atomically thin dimensions, high mechanical strength, and unique electrical and optical properties make them an excellent candidate for NEMS. These resonators are extremely sensitive to external stimuli. This is particularly important for research, from both application and fundamental point of view. Nonlinearities in these devices play a vital role in the dynamics as dimensions are reduced to atomic scale. A clear understanding of nonlinearities and the ability to control and manipulate them to enhance the performance are pivotal for applications of these devices.

In this talk, I will discuss the ability to tune and effectively nullify Duffing nonlinearity in molybdenum disulfide (MoS2) resonators. I will discuss the effect of in-built strain in the resonator on the cancellation voltage of Duffing nonlinearity. The simulations and observed results can serve as a simple guide to design and control nonlinearities and to effectively improve the linear dynamic range in these devices for next generation two dimensional resonant sensors.

 

Further, the multiple vibrational modes of a two-dimensional resonator are  inherently coupled through the strain in the membrane and can be manipulated through parametric techniques. Parametric manipulation enables us to control the coupling among mechanical modes of resonator. I will discuss our experimental observation of strong coupling between mechanical modes of  MoS2  resonator. Parametric pumping is utilized for cooling and heating of mechanical modes. This work holds promise for phonon manipulation studies in 2D membranes.

 

Thursday, January 16, 2020, 2 to 3pm

Tomás Palacios (MIT) on the topic: "From Transistors to Synthetic Cells"

The lecture will take place in the "Physikhörsaal" (28D001) in the physics centre of RWTH Aachen at Campus Melaten.

Abstract:
Two-dimensional materials enjoy a vast array of unique properties, from extreme thinness and mechanical
flexibility to amazing quantum physics. These properties will have a tremendous impact in future
electronics by enabling large area, high speed, ubiquitous sensing and processing. This talk will review
some of the recent progress on the use of graphene and other two-dimensional materials in these
applications. In particular, it will discuss state-of-the-art MoS and WSe transistors for ultra-low power 2 2
CMOS circuits [1-2], graphene-based chemical [3] and infrared sensors [4], large area devices for energy
harvesting [5], and a new generation of micro-systems that probe the limits of electronics.

[1] NanoLetters, 16 (2016) 7798-7806.; [2] NanoLetters, 15 (2015) 4928-4934; [3] Applied Materials
and Interfaces, 10 (2018) 16169-16176. [4] Heterogeneous Integration of 2D Materials and Devices on
a Si Platform, Chapter in Beyond CMOS Technologies for Next Generation Computer Design (2019),
Springer. [5] Nature (2019) https://doi.org/10.1038/s41586-019-0892-1

 

 

Tuesday, January 7, 2020, 12 to 1 pm

Prof. Barbaros Ozyilmaz from the National University of Singapore (NSU) gives a talk about "2D Amorphous Materials and other Research Efforts at the Centre for Advanced 2D Materials"

 

Tuesday, April 10, 2018, 12 to 1pm

Peter Bøggild of DTU Denmark gives a talk about "Graphene at the edge of perfection"

 

Friday, June 15, 2018, 1 to 2pm

Dr. Shu Nakaharai (NIMS & MANA) on the topic: "Polarity-Controllable Transistors on 2D Materials"

The lecture will take place in room S3 in building Otto-Blumenthal-Str. 2 (above the workshop) at Campus Melaten.

Abstract:
Two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) have been expected for future channel materials due to their atomically-thin and smooth surfaces, which can lead to reducing the short channel effects in the aggressively scaled CMOS technology. On the other hand, there remain some challenging issues of carrier doping, control of carrier type and transistor polarity. In this talk, at first, we will discuss how we can overcome the issue of carrier type control in TMDC semiconductors. Here, it will be reviewed that MoTe2, in contrast to MoS2, exhibits only weak Fermi level pinning at the Schottky junctions, and it can behave as both n- and p-type transistors depending on the work function of the contact metals. Finally, it will be discussed that MoTe2 can be expected to be the ideal ambipolar channel in a unique concept of polarity-controllable transistors in which the transistor polarity (n/p) can be changed by electrostatic gating.
 

 

 

Wednesday, June 5, 2018, 12 to 1pm

Dr. Shu Nakaharai (NIMS & MANA) on the topic: "Polarity-Controllable Transistors on 2D Materials"

Abstract:
Two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) have been expected for future channel materials due to their atomically-thin and smooth surfaces, which can lead to reducing the short channel effects in the aggressively scaled CMOS technology. On the other hand, there remain some challenging issues of carrier doping, control of carrier type and transistor polarity. In this talk, at first, we will discuss how we can overcome the issue of carrier type control in TMDC semiconductors. Here, it will be reviewed that MoTe2, in contrast to MoS2, exhibits only weak Fermi level pinning at the Schottky junctions, and it can behave as both n- and p-type transistors depending on the work function of the contact metals. Finally, it will be discussed that MoTe2 can be expected to be the ideal ambipolar channel in a unique concept of polarity-controllable transistors in which the transistor polarity (n/p) can be changed by electrostatic gating.