an array of rolled up nanomembranes

IIN seminars 2022

Thursday, October 27, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Caspar Hopfmann

Thursday, September 29, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Volker Neu

"Towards Magnetic Domain Wall Racetrack Memory"

Recent achievements in the manipulation of magnetization in nano-structures by spin-polarized current give promises for a new branch of nonvolatile memories - Spin Transfer based memory. Among them, the domain-wall memory (DWM) or racetrack memory shows a unique possibility for 3D integration. The operation of racetrack memory is based on the motion of domain walls in atomically thin, perpendicularly magnetized nanowires, which are interfaced with adjacent metal layers with high spin-orbit coupling. This wire could be shaped into various forms, like a meander or closed ellipse. With the polymer platform, developed at the IIN, I am aiming to give it a new degree of freedom, by fabricating a 3D spiral racetrack memory.

In my talk, I will present a versatile technique for the fast and accurate characterization of the material stacks for the domain wall memory, both in a planar and rolled state. The developed technique tremendously increases the speed of stack optimization in the search for the best configuration. The polymer rolled-down micro-tubes with a diameter of about 25 µm that are perfectly suitable for the true 3D integration of the racetrack memory, will be shown. Finally, preliminary results of the domain wall motion on a flat polymer platform will be presented, by direct imagining with a Kerr microscope.

Thursday, September 15, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Volker Neu

Switching magnetic elements by Oersted fields from current carrying planar coils

Thursday, June 23, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Prof. Rudolf Schäfer

"Spins, Bits, and Flips: Essentials for High-Density Magnetic Random-Access Memory"

IEEE Magnetics Society Distinguished Lecturer 2022

In this talk, I will describe the seminal discoveries that enabled magnetic tunnel junctions (MTJ) for pervasive use in hard disk drives, MRAM, and magnetic sensors, such as the discovery of tunnel magnetoresistance (TMR) at room temperature, the invention of spin-transfer torque as the means to flip magnetization without a magnetic field, and the prediction and realization of high TMR using MgO tunnel barriers. As the demand for faster and higher density memory persists, still more breakthroughs are needed for MTJs contained in device pillars (or bits) just tens of nanometers in diameter. These advances require tuning of material properties at the atomic scale as well as across arrays of millions of bits in a memory chip. I will describe the magnetic properties of MTJs that are essential for high-performance MRAM, including perpendicular magnetic anisotropy, damping parameter, exchange constant, thermal stability factor, and TMR, and how to engineer these properties to deliver high spin-transfer torque efficiency and high data retention in spin-transfer torque MRAM devices.

Thursday, June 02, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Mariana Medina Sanchez

"Developing a 3D oviduct-mimicking system for the study of embryo development and microrobotic transport"

Infertility is a disease that affects 72.4 million people worldwide, affecting equally males and females. Regarding the female factor, oviduct dysfunction is one of the major causes of infertility (1). The oviduct plays a vital role in selecting the best gametes, guiding them to the site of fertilization, and supporting the development of the resulting zygote by providing a physiological environment. Furthermore, it is responsible for the embryo transport through the oviduct to the uterus in perfect synchronization with the endometrium preparation.
Therefore, significant efforts have been made to improve embryo culture conditions to resemble the fluid secreted by the oviduct epithelial cells (OEC). The development of co-culture systems of gametes or embryos with OEC has increased implantation and pregnancy rates due to the interaction with molecules secreted by the tubal tissue (2). Different microfluidic approaches were used to mimic the anatomy of the oviduct and resulted in an improved embryo production (3). However, most reported systems are based on well plate inserts, or 2D/2.5D cell culture platforms, which differ from the in vivo oviduct anatomy. Moreover, these platforms are manually assembled and not suitable for mass production.
My thesis aims at developing a modular oviduct-uterus on a chip that allows emulation of the bovine estrous cycle in vitro. This platform will serve to study embryo transport and development from the ampulla to the uterus by providing a physiological microenvironment. Additionally, it will allow the investigation of magnetic microcarrier behavior in realistic conditions and their interactions with the surrounding OEC for future implementation in assisted reproductive techniques. In the first part of this work, bovine OEC culture and their differentiation in commercial cell culture inserts were established.
In parallel, different scaffolds were developed, ranging from a 2D microfluidic chamber to a 2.5D porous scaffolds and a 3D porous microtube that mimics the oviducts anatomy and serves as a support for cell growth and differentiation.  Furthermore, cell characterization by histological analysis and biocompatibility of scaffold materials are presented.

1. Honoré et al. Fertil. Steril, 71 (1999), pp. 785-795
2. Kattal et al. Fertil. Steril, 90 (2008), pp. 1069-1076
3. Ferraz et al. Lab Chip, 17 (2017), pp. 905-916

Tuesday, May 31, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Prof. Rudolf Schäfer

"Exploring the Potentials of Spin-Orbitronics"

IEEE Magnetics Society Distinguished Lecturer 2022

This lecture will provide a theoretical perspective of the advancement of the fascinating field of spin-orbitronics, focusing on two emblematic mechanisms: the spin-orbit torque and the Dzyaloshinskii-Moriya interaction. I will examine what theory and materials modeling can tell us about these two effects, and what future research directions they open. I will first introduce key concepts in spintronics, such as spin currents and spin-transfer torque, and show how spin-orbit coupling enables new physical effects of high interest for potential applications. I will present standard phenomenological descriptions of these two effects, spin-orbit torque and Dzyaloshinskii-Moriya interaction, determine the symmetry rules that govern them, and give a broad overview of the current state-of-the-art of the field from experimental and theoretical standpoints. Finally, I will explore how spin-orbitronics takes a completely new form in materials possessing low crystalline symmetries, such as Fe3GeTe2, CuPt/CoPt bilayers, and noncollinear antiferromagnets (e.g., Mn3Sn).
I hope this seminar will not only encourage electrical engineers to engage in this beguiling field of research and explore the device implications of this new technology but also reach out to scientists working in adjacent fields (terahertz science, for instance) who could bring inspiring new ideas to spintronics.

Thursday, May 12, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Prof. Rudolf Schäfer

"Topological transitions in 3D superconductor curved nanoarchitectures"

Extending nanostructures into the third dimension has become a vibrant research avenue in condensed-matter physics, because of geometry- and topology-induced phenomena. Modern advances of high-tech fabrication techniques, in particular, self-rolling and direct writing, have allowed for generating geometrically and topologically nontrivial manifolds at the nanoscale, which determine novel electronic, magnetic, optical and transport properties of such objects [1]. Prospect directions and current challenges in the domain of superconductivity and vortex matter in curved 3D nanoarchitectures and their great potential for magnetic field sensing, bolometry, and information technology have been demonstrated [2]. A topological transition between the vortices and phase slips under a strong transport current is found in open superconductor nanotubes with a submicron-scale inhomogeneity of the normal-to-the-surface component of the applied magnetic field [3]. When the magnetic field is orthogonal to the axis of the nanotube, the induced voltage shows a peak as a function of the magnetic field due to a nontrivial topology of superconducting screening currents. Topological transitions in open superconductor nanotubes are investigated under gradual and abrupt switch-on of the transport current and magnetic field [4]. Most of peaks in the induced-voltage--magnetic-field characteristics occur in the presence of abrupt switch-on of the current or the field. An abrupt switch-on triggers the transition from the vortex patterns to the phase-slip regime. The dependence of the superconducting regimes on the switch-on speed and the stability of such regimes implies a barrier between them. As a result, there exists a novel hysteresis effect in the current-voltage characteristic of open nanotubes. Dynamic topological transitions in open superconductor nanotubes occur under a combined dc+ac transport current [5]. The key effect is a transition between two regimes of superconducting dynamics. The first regime is characterized by a pronounced first harmonic in the FFT spectrum of the induced voltage at the ac frequency. The second regime is represented by a rich FFT spectrum of the induced voltage with pronounced low-frequency components because of an interplay between the internal dynamics of vortices or phase slips and the dynamics driven by the ac.

[1] V. M. Fomin, Self-rolled Micro- and Nanoarchitectures: Topological and Geometrical Effects. De Gruyter, Berlin-Boston, 148 pp. (2021).
[2] V. M. Fomin, O. V. Dobrovolskiy, Appl. Phys. Lett. 120, 090501 (2022).
[3] R. O. Rezaev, E. I. Smirnova, O. G. Schmidt, V. M. Fomin, Communications Physics 3, 144 (2020).
[4] I. Bogush, V. M. Fomin, Phys. Rev. B 105, 094511 (2022).
[5] V. M. Fomin, R. O. Rezaev, O. V. Dobrovolskiy, (2021).

Thursday, April 21, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Mariana Medina Sanchez

"Microrobotic transport of zygotes and gametes towards in vivo assisted fertilization"

Micromotors have great potential in biomedical applications as they can be used for drug delivery, cell transport, and microsurgery, among others [1]. In the area of assisted reproduction, micromotors that transport zygotes and gametes within the female reproductive system will allow less harsh procedures, reducing the risk of ectopic and multiple pregnancies, and increasing pregnancy rates [2]. However, this will require a lot of improvements of the current state of this technology. The main challenges are to improve microrobots’ biocompatibility, biodegradability, motion control, real-time bio-imaging, stimuli responsivity, payload transport, and target specificity [3,4]. In this work, two ideas to address these challenges are presented. The first consists of soft hydrogel-based microrobots fabricated by droplet microfluidics with varying sizes (from 20 to 120 µm). This technique allows the embedding of materials within the micromotors, such as contrast agents or drugs. The micromotors are externally actuated by rotating magnetic fields and driven with feedback-loop control. It is shown that the contrast agents loaded into the micromotors enable their visualization by ultrasound and photoacoustics in a hybrid fashion. It is also demonstrated how these micromotors can biodegrade and deliver drugs in a controlled manner [5]. Second, an idea to develop a new type of micromotor with a design that will allow for more efficient movement and increased functionality is presented. This micromotor can transform and adapt its shape to trap and release large payloads. It continues with the previously developed solutions, being built with biocompatible and biodegradable materials, capable of transporting drugs and contrast agents that allow real-time tracking, and cell cargo-delivery, towards their in vivo application.


  1. J. Mujtaba, et al, Advanced Materials 33(22), 2007465, 2021.
  2. M Medina-Sánchez, L Schwarz, AK Meyer, F Hebenstreit, OG Schmidt. Nano Letters 16 (1), 555-561, 2016. 355, 2016.
  3. M. Medina-Sánchez and O. G. Schmidt, Nature, 545(7655), 406–408, 2017.
  4. L. Sonntag, et al, Molecules, 24(18), 1–34, 2019.
  5. D. Castellanos-Robles et al (2022) (Under preparation)

Thursday, April 7, 2022, 10 a.m.
A1E.10 (lecture hall)

invited by Dr. Libo Ma

"3D optical coupling in self-assembled microtubular cavities"

Optically coupled whispering-gallery-mode (WGM) microcavities are widely studied to tune the resonant eigenfrequency and the spatial distribution of the resonant modes, indicating a variety of nontrivial physical phenomena and practical applications ranging from mode-selective lasing to non-Hermitian photonics. In general, the WGM microcavities support 2D confined resonant modes where the corresponding optical coupling is fixed at a 2D plane. The efficient 3D confined optical coupling of resonant light has not been reported, in which the wavevector can exist in more than one direction (i.e., azimuthal and axial directions) for both fundamental and applied studies. Since microtubular cavities providing 3D confinement of light, it is of high interest to design and regulate resonant trajectories of 3D confined light supported by microtubular cavities for the investigation of 3D optical coupling of resonant modes. In the first coupling system, the interlayer nanogap in the tube wall enables a single resonant trajectory partially splitting into two or three ones while sharing the same axial confinement resulting in multiple sets of 3D confined resonant modes in a single microtubular cavity. The largely overlapping optical field in the split trajectories enables strong optical coupling of 3D confined resonant modes. The anticrossing feature and the modes changing-over were demonstrated as direct evidence of strong coupling. In the second coupling configuration, parallelly neighboring double-microtube system is fabricated and characterized to examine the 3D optical coupling which is confirmed by the anticrossing feature and the modes changing-over. Our work offers a compact and robust design for realizing 3D optical coupling based on microtubular cavities, which is of high interest for promising applications in sensing and lasing.

Thursday, April 7, 2022, 9:00 a.m.
A 1E.10 (lecture hall)

invited by Dr. Libo Ma

"Optoelectronics and Photonics studies on 2D materials based microdevices"

Over the past years, 2D materials having unique and superior electronic and optical properties are considered as intriguing building blocks for future generation smaller, more flexible and more efficient opto-electronic nanodevices [1, 2]. Meanwhile, organic small molecules offer wide material selection and excellent mechanical flexibility, by which the energy gap of organic semiconductor (OSCs) can cover the entire spectral range from ultraviolet to near-infrared. However, the short exciton diffusion length and low mobility in organic materials are significant challenges for obtaining high efficiency and fast response time [3, 4]. To solve this problem, heterojunction phototransistors have been designed by the combination of 2D and OSCs materials, showing significantly improved dynamic response performance. Moreover, having the extraordinary properties, 2D materials with planar geometries are assembled into three-dimensional (3D) architectures to exploit practical applications. Recently rolled-up nanotechnique has been implemented for 2D materials to create threedimensional (3D) architectures to improve the hydrogen storage, heat transfer and prominent raman enhancement for ultrasensitive molecular sensing properties of the graphene [5, 6]. Here we utilize the rolled-up nanotechnique to assemble monolayer graphene into 3D tubular structure for the investigation of optical coupling and interaction between whispering gallery modes and curved graphene.

In this seminar, firstly I will demonstrate a fast phototransistor based on bulk MoS2/VOPc heterojunction. The charge transfer interface formed by the MoS2/VOPc interface is found to suppress the persistent photoconductance (PPC) phenomenon in MoS2 by separating photo-generated holes from the VOPc molecules. The MoS2/VOPc phototransistor shows fast photo-response <15ms decay and rise time from pristine MoS2 (5s). In the second part, I will report the self-rolling of monolayer graphene into 3D microtubular cavities to study the tuning of optical coupling based on microtubular cavities. Monolayer graphene was rolled up into microtubes accompanying with pre-patterned strain layers. Raman spectra were characterized before and after rolling graphene into microtubes. Due to the free-standing graphene enwrapped in the tubular structure, high quality factor of resonant modes and enhanced photoluminance are expected.

[1] Novoselov, K. S, et al. Science. 306, (2004), 666−669. 
[2] Lee, G. H, et al. Science. 340, (2013), 1073−1076. 
[3] M. Mahdi et al. Mater. Lett, 200, (2017), 10−13.
[4] S. Das et al. Annu. Rev. Mater. Res, 45, (2015), 1−27.
[5] Varshney, V, et al. ACS Nano. 4, (2010),1153.
[6] Zhe, Ma, et al. ACS Appl. Mater. Interfaces. 13, (2021), 49146−49152


Thursday, 24.03.2022, 10 a.m.
A 1E.10 (lecture hall)

invited by Prof. Rudolf Schäfer

"X-ray imaging of three-dimensional spin textures"

Claire Donnelly
Max Planck Institute for Chemical Physics of Solids, Noethnitzer Str 40, 01187 Dresden, Germany


Three dimensional magnetic systems promise significant opportunities for applications, for example providing higher density devices and new functionalities associated with complex topology and greater degrees of freedom [1,2]. With recent advances in both characterization and nanofabrication techniques, the experimental investigation of these complex systems is now possible, opening the door to the elucidation of new physical properties, and representing the first steps towards higher dimensional magnetic devices.

In this seminar I will speak about our work on the characterization of 3D nanomagnetic systems with X-ray magnetic tomographic techniques [3,4,5].  In this way, both the static configuration [3,5], and dynamical behaviour [4,6], of topological structures within the bulk of a system [3,4,7], as well as in nanoscale structures [5,6,8] have been revealed. Within these complex configurations, recent advances in analytical techniques [7] have provided new capabilities to locate and identify 3D magnetic solitons, leading to the first observation of nanoscale magnetic vortex rings [7,9].

As well as existing within bulk and thin film systems, 3D spin textures can be introduced via the patterning of complex 3D magnetic nanostructures [10], leading to the realisation of highly coupled curvilinear systems [8]. These new experimental capabilities for 3D magnetic systems open the door to complex three-dimensional magnetic structures, and their dynamic behaviour.

  1. Fernández-Pacheco et al., Nature Communications 8, 15756 (2017).
  2. C. Donnelly and V. Scagnoli, J. Phys. D: Cond. Matt. 32, 213001 (2020).
  3. C. Donnelly et al., Nature 547, 328 (2017).
  4. C. Donnelly et al., Nature Nanotechnology 15, 356 (2020).
  5. K. Witte, et al., Nano Letters 20, 1305 (2020). 
  6. S. Finizio et al., Nano Letters (2022)
  7. C. Donnelly et al., Nat. Phys. 17, 316 (2020)
  8. C. Donnelly et al., Nature Nanotechnology 17, 136 (2022)
  9. N. Cooper, PRL. 82, 1554 (1999).
  10. L. Skoric et al., Nano Letters 20, 184 (2020). 

IIN seminar
Thursday, 17.02. 2022, 1 p.m.
A 1E.10 (lecture hall)

invited by Dr. Caspar Hopfmann

"Towards highly efficient entangled photon pair sources based on GaAs quantum dots using positioned circular Bragg grating cavities"

Ghata Satish Bhayani (IFW Dresden)


In order to enable upcoming quantum communication networks, bright, integrable and reproducible on-demand entangled photon pair sources are needed [1].
So far GaAs quantum dot membrane devices are combined with GaP solid immersion lenses in order to fabricate bright sources of entangled photon pairs [2].
The achievable brightness and device integration using this method are however limited, therefore planar circular Bragg grating cavities are desirable alternatives [3].
Quantum dots in the center of Bragg cavities feature enhanced light-matter interaction (Purcell effect), which is driven by the cavity Q-factor and mode volume, compared to bulk quantum dots.
Based on these premises, the goal is to develop free-standing circular Bragg grating cavities [4] with deterministically positioned single droplet etched GaAs quantum dots. One of the challenges to obtain an efficient and highly entangled photon pair source is to position the quantum dot accurately in the center of the cavity. In order to meet this challenge, it is planned to perform AFM lithography around single quantum dots in order to mark the position of circular Bragg cavities fabricated using electron beam lithography.


Lectures summer term 2022

Lecturer: Dr. Caspar Hopfmann and others

Summer term 2022
Time: Mondays, 11:10-12:40 (3. DS)
Place: TU Dresden, REC/B214


  • April 4 (week 14)
    Overview: Introduction quantum network principles, concepts and potential applications
  • April 11 (week 15)
    Theory basics: Refresher basic quantum mechanical principles and quantum network theory
  • April 25 (week 17):
    Flying qubits and detection systems: Principles of flying quits - system overview, encoding, limitations; In-depth view on single particle (photon) quantum
  • May 2 (week 18):
    Quantum entanglement and teleportation: Theoretical description, practical consequences, limitations
  • May 9 (week 19):
    Quantum light sources In-depth view on quantum light sources, concepts, limitations, applications
  • May 16 (week 20):
    Quantum memories Concepts, principles, practical approaches
  • May 23 (week 21):
    Quantum key distribution Principles and photonic implementations of Quantum Key Distribution
  • May 30 (week 22):
    Optical qubit processing and manipulation Principles, practical approaches
  • June 13 (week 24):
    Long distance entanglement dirstibution Quantum repeaters, fiber networks, satellites
  • June 20 (week 25):
    Multipartite entanglement distribution Principles, Limitations, solutions - Graph states
  • June 27 (week 26):
    Quantum network synchronization Concepts, principles, applications
  • July 4 (week 27):
    Berry phase entanglement Basics (theory), concepts, applications
  • July 11 (week 28):