26 Aug 2019

Integratable 3D Microtubular Asymmetric Supercapacitors

An integratable 3D microtubular asymmetric supercapacitor with ultrahigh energy density, long-term cycling stability and excellent mechanical performance is fabricated by modern on-chip microfabrication technologies and self-assembly procedures.

14 Aug 2019

Real-time tracking of microrobots in 3D in deep tissue

Opto-acoustic imaging is used to track microtubular robots in three dimensions, in real-time, in deep phantom and ex-vivo tissue.

Nano Lett. 19, 6612 (2019)

8 Jul 2019

Magnetic origami for microelectronics

Ancient art of paper-folding inspires new technology to create high performance microdevices.

5 Jul 2019

Rolled-up integrated tubular micro-supercapacitors

Tubular micro-supercapacitors with greatly reduced footprint area, improved electrochemical performance and self-protective function are created by self-assembling 2D films into “swiss roll” architectures.

19 Jun 2019

Microscale organic field-effect transistors (Micro-OFETs)

V. K. Bandari, Y. Gu, S. Shi, Y. Nan, K. He, Y. Li, N. Bandari, S. Moradi, H. Tian, F. Zhu, Y. Geng, D. Yan, O. G. Schmidt

Adv. Funct. Mater. 29, 1903738 (2019)

9 Nov 2018

Rolled‐up self‐assembly of compact inductors and transformers

D. D. Karnaushenko, D. Karnaushenko, H.‐J. Grafe, V. Kataev, B. Büchner, O. G. Schmidt

Adv. Electron. Mater. 4, 1800298 (2018)

31 Jul 2018

Brightest source of entangled photons

New broadband optical antenna for highly efficient extraction of entangled photons with a yield of 37% per pulse.

Nature Commun. 9, 2994 (2018)

9 Apr 2018

Manipulating photon−plasmon coupling in microtube cavities

In situ generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes is demonstrated by spatially resolved laser dewetting on microtube surfaces.

15 Jan 2018

Spermbot video now among Top 5 ever

The Spermbot video has now become the 5th most viewed video of the American Chemical Society. Click on the following link to watch it.

20 Dez 2017

American Chemical Society highlights our work as Top News

Original work:

ACS Nano 12, 327 (2018)

4 Dec 2017

Chemotherapeutic micromotor for targeted drug delivery

A sperm-driven micromotor acts as a targeted drug delivery system to potentially treat diseases in the female reproductive tract. 

3 Aug 2017

Thermal conductivity in radial and planar Si/SiOx hybrid superlattices

Thermal conductivities through radial and planar Si/SiO_x hybrid superlattices are substantially reduced -- putting forth a novel efficient way of managing phonon transport in Si-based devices.

26 May 2017

A material that collectively emits entangled photons on demand

Epitaxial GaAs quantum dots are optimized to such a degree that all of them emit entangled photons on demand upon illumination with light.
A property that may prove relevant for quantum communication technologies.

24 May 2017

Opportunities and challenges of medical microbots

In this extended comment we call on microrobotics researchers, materials scientists, bioimaging and medical specialists to work together to tackle the challenges on the way to in-vivo applications.

21 Mar 2017

Spermatozoa as robotic microswimmers

V. Magdanz, M. Medina-Sánchez, L. Schwarz, H. Xu, J. Elgeti, O. G. Schmidt

Adv. Mater. 29, 1606301 (2017)

24 Jan 2017

Monolithically integrated microtube cavities for optofluidic sensing

Monolithically integrated vertical ring resonators pave the way for optofluidics in three-dimensions on photonic chips.

30 Aug 2016

Piezo-controlled silicon integrated quantum dot photonics

The single photon emission from a single III-V quantum dot (QD) is tuned into resonance with that of another QD by a fully Si-integrated MEMS platform .

23 Jun 2016

Plasmon-photon coupling in tubular microcavities

Selective coupling of localized surface plasmons and resonant optical modes is achieved in cleverly patterned microtubular optical cavities. 

6 Jun 2016

High-performance DNA biosensor

Microtubular sensor reaches attomolar level detection of Avian Influenza Virus H1N1 DNA without any labelling or amplification. 

6 Jun 2016

Human cancer cell mitosis in transparent microtubes

Tumor cell devision is mimicked inside blood capillaries by investigating single-cell mitosis of living human cancer cells trapped inside rolled-up microtubes. 

18 Mar 2016

Spin-orbit coupling of light in asymmetric microcavities

We enable spin-orbit coupling of light confined to a closed path within an asymmetric optical microcavity and demonstrate a non-cyclic Berry phase acquired in a non-Abelian evolution.

18 Feb 2016

Organic nanocrystal diode for room temperature NO2 sensing

Organic diodes consisting of molecular nano-pyramid structures demonstrate high average sensitivity (151% ppm−1) and fast recovery time (12 min) for NO₂ detection.

27 Jan 2016

Scalable entangled photon sources for the long haul

With a silicon MEMS device we shift the entangled photon emission from a quantum dot by more than 3000 times of its radiative linewidth without spoiling the entanglement.

13 Jan 2016

American Chemical Society highlights our work as Top News

Original work:

Nano Lett. 16, 555 (2016)

21 Dec 2015

Micromotorized sperms for artificial fertilization

Magnetically activated microhelices serve as motors for transporting sperm cells with motion deficiencies to help them carry out their natural function. 

30 Nov 2015

Biogenic microdaggers for single-cell surgery and drug release

S. K. Srivastava, M. Medina-Sánchez, B. Koch, O. G. Schmidt

Adv. Mater. 28, 832 (2016)

Efficient wastewater cleaning by self-propelled micromotors

We present efficient wastewater-mediated activation of catalytic micromotors for the degradation of nitroaromatic pollutants in water.

The fastest entangled photon source

We demonstrate strain-tunable entangled-light-emitting-diodes operating at frequencies up to 400 MHz and entanglement fidelities as high as 0.83.

Biomimetic microelectronics for regenerative neuronal cuff implants

D. Karnaushenko, N. Münzenrieder, D. D. Karnaushenko, B. Koch, A. K. Meyer, S. Baunack, L. Petti, G. Tröster, D. Makarov, O. G. Schmidt

 Adv. Mater. 27, 6797 (2015)

High performance tubular GMI sensors

Arrays of rolled-up on-chip-integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils are demonstrated.

All-electric access to the magnetic-field-invariant magnetization of antiferromagnets

We provide new insights into the physics of the fundamentally-appealing magnetoelectric Cr₂O₃ and application-relevant IrMn antiferromagnets.

Neural stem cell migration under spatial confinement

We exploit the well-defined geometry and optical transparency of glass microtubes to investigate how scaffold dimensionality and cell confinement influence the spontaneous migration of neural stem cells.

Monolithic integration of vertical optical ring resonators

We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step towards 3D photonic integration.

Ultra-compact helical antennas for smart system implants

Ultra-compact helical antennas with a total length five times smaller compared to their conventional dipole counterparts are demonstrated to operate in the Industry-Scientific-Medical radio band. 

Magnetism in Möbius rings

 We demonstrate that the magnetic Möbius ring is a unique object because it unites two classes of geometrical effects, namely, topologically induced magnetization patterning and curvature induced chirality symmetry breaking.

Magnetic sense for everybody

We have developed an electronic skin with a magneto-sensory system that equips the recipient with a “sixth sense” able to perceive the presence of static or dynamic magnetic fields.

Transfer printed stretchable magnetoelectronics

M. Melzer, D. Karnaushenko, G. Lin, S. Baunack, D. Makarov, O. G. Schmidt

Adv. Mater. 27, 1333 (2015)

Rolled-up functionalized nanomembranes as three-dimensional cavities for single cell studies

We use micropatterning and strain engineering to encapsulate single living mammalian cells into transparent tubular architectures consisting of 3D rolled-up nanomembranes.

Nano Lett., 14, 4197 (2014)

Thermal conductivity of mechanically joined nanomembrane superlattices

Hybrid superlattices consisting of a large number of nanomembranes mechanically stacked on top of each other are fabricated by a roll-up and press-back technique. 

Large-area rolled-up nanomembrane capacitor arrays

R. Sharma, C. C. Bof Bufon, D. Grimm, R. Sommer, A. Wollatz, J. Schadewald, D. J. Thurmer, P. F. Siles, M. Bauer, O. G. Schmidt

Adv. Energy Mater. 4, 1301631 (2014)

Impedemetric sensing of ionic fluids and single cells in a single microtube

Ultracompact three-dimensional tubular structures integrating Au-based electrodes serve as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. 

Flexible thermoresponsive microjets

Flexible self-propelled microjets are formed by temperature-induced folding of thin polymer films into microtubes that contain an inner platinum layer for catalytic bubble propulsion in hydrogen peroxide.

Domain patterns of magnetic rolled-up microtubes

Rolled-up magnetic microtubes display spiral-like, longitudinally or azimuthally magnetized domain patterns. 

Stretching quantum dots till they become light

We demonstrate the creation of a light-hole exciton ground state by applying elastic stress to an initially unstrained quantum dot. 

A sperm driven micro-bio-robot

V. Magdanz, S. Sanchez, O. G. Schmidt

Adv. Mater. 25, 6581 (2013)

A wavelength-tunable single-photon emitting diode

The first all-electrically operated wavelength-tunable single-photon source is demonstrated.

Multichannel anodes for lithium-ion batteries

We employed rolled-up nanotechnology to fabricate sandwich-stacked SnO₂/Cu hybrid nanosheets as multichannel anodes for lithium-ion batteries with the use of carbon black as inter-sheet spacer.

Vertical add-drop filter made from a rolled-up ring resonator

A significant step towards integrated vertically rolled-up microcavities is demonstrated by interfacing SiO2 microtube optical ring resonators with tapered fibers. 

Chemotactic behaviour of artificial engines

Dr. L. Baraban, Dr. S. M. Harazim, Dr. S. Sanchez, Prof. Dr. O. G. Schmidt

Angew. Chem. Int. Edit. 52, 5552 (2013)

Diamond lattice photonic crystals from rolled-up membranes

A novel method for the fabrication of diamond lattice photonic crystals with full band gap by rolling strained pre-patterned titania membranes is proposed.

Dynamic molecular processes detected by nanomembrane based microtube cavities

Dynamic molecular processes of water and ethanol are detected on the surface of rolled-up opto-chemical microtube resonators.

Rolled-up trilayer nanomembranes improve durability and lifetime of batteries

We report about a new type of tubular configuration for excellent battery electrode performance made from naturally rolled-up C/Si/C trilayer nanomembranes.

Rolled-up field effect transistors

We fabricate inorganic thin film transistors with bending radii of less than 5μm maintaining their high electronic performance with on-off ratios of more than 100.000 and subthreshold swings of 160mV/dec.

Rolling their own for energy storage devices

C. Yan, W. Xi, W. Si, J. Deng, O. G. Schmidt

Adv. Mater. 25, 539 (2013)

Making quantum dots electronically symmetric

We demonstrate experimentally and theoretically that it is always possible to restore the excitonic degeneracy in quantum dots by the simultaneous application of large strain and electric fields.

Self - Elongating Nanowires

We report the self-assembled growth of Ge nanowires with a height of only 3 unit cells and a length of up to 2 micrometers by means of molecular beam epitaxy.

Stretchable magnetoelectronics

Stretchable magnetoelectronic devices are demonstrated for the first time.

Adv. Mater. 24, 6468 (2012)

Magnetically capped rolled-up nanomembranes

In this work, we address curvature-driven modifications of magnetic properties in confined cylindrically curved magnetic nanomembranes.

Printable magnetoelectronics

D. Karnaushenko, D. Makarov, C. Yan, R. Streubel, O. G. Schmidt

Adv. Mater. 24, 4518 (2012)

Elastic magnetic sensor with isotropic sensitivity for in-flow detection of magnetic objects

We present a conceptually new approach for the detection of magnetic objects flowing through a fluidic channel.

Self-propelled nanotools drilling into cells

We design nanoscale tools in the form of autonomous and remotely guided catalytically self-propelled rolled-up tubes.

Fabrication and applications of large arrays of multifunctional rolled-up SiO/SiO2 microtubes

S. M. Harazim, W. Xi, C. K. Schmidt, S. Sanchez, O. G. Schmidt

J. Mater. Chem. 22, 2878 (2012)

Tunable generation of correlated vortices in open superconductor tubes

We theoretically apply transport currents and magnetic fields to open superconducting tubes.

Engineering the properties of quantum-light-emitting diodes by strain

We present the first nanomembrane quantum-light-emitting diodes (QLEDs) integrated onto piezoelectric actuators. 

On-chip integration of rolled-up ring resonators as label-free optofluidic sensors

The advances we have made in engineering of tubular optical sensors and their on-chip integration allows us to fabricate rolled-up optofluidic ring resonators based on glass material with high quality factors fully integrated on-chip. 

Lab-in-a-tube

A lab-in-a-tube device comprises numerous ultracompact components in a single tube which can be developed using rolled-up technology.

Lab-in-a-tube for single cell optofluidic detection

E. J. Smith, S. Schulze, S. Kiravittaya, Y. Mei, S. Sanchez, O. G. Schmidt

Nano Lett. 11, 4037 (2011)

Magnetic microhelix coil structures

We design and investigate three-dimensional microhelix coil structures that are radial-, corkscrew-, and hollow-bar-magnetized. 

Rolled-up magnetic sensor for in-flow detection of magnetic objects

Rolled-up nanotech is used to fabricate magnetic sensor devices, which are directly integrated into fluidic architectures.

"Starting" and "stopping" microjet engines

We report the tuning of the propulsion power of catalytic microjets through illumination of a solution by a white-light source.

Superfast motion of catalytic microjet engines at physiological temperature

We fabricate microjet engines that acquire superfast speeds of 10 mm sec-1.

Towards remotely controlled intelligent microrobots

In this tutorial review we describe recent progress on catalytic microtubular engines fabricated by rolled-up nanotech.

Chem. Soc. Rev. 40, 2109 (2011)

Guinness World Record® for "Smallest Man-Made Jet Engine"

"The smallest man-made jet engine measures just 600nm across and weighs 1 picogram.

Microbots swimming in the flowing streams of microfluidic channels

The motion of artificial catalytic nanomachines is commonly studied in free bulk solution, which differs significantly from the stream-like channel networks existing in the human body. 

Transport of animal cell material by catalytic microbots

Animal cells can be transported within a fluid in a controllable manner by using artificial microbots.

Spin selective tunneling through SiGe quantum dots

We observe that spin-selective tunnel rates through individual quantum dots can be achieved with normal metallic contacts. 

Hybrid organic/inorganic molecular heterojunctions

We combine self-assembly and top-down methods to create hybrid junctions consisting of single organic molecular monolayers sandwiched between metal and/or single-crystalline semiconductor nanomembrane based electrodes.

Cardboard rolls on the nanoscale

We have exploited the card-board effect on the nanoscale to define the roll-up direction of ultra-thin membranes on a substrate surface.

Slowing down single photons from quantum dots

By guiding the emitted light of quantum dots through atom vapor the speed of the photons is reduced to less than 4% of the speed of light in vacuum.

Tubular optofluidic sensors for enhanced refractive index sensing

Optofluidic microcavities from rolled-up ring resonators with subwavelength wall thicknesses are fabricated with excellent sensing function.

Rolled-up nanotech for lithium energy storage devices

H.‐X. Ji, X.‐L. Wu, L.‐Z. Fan, C. Krien, I. Fiering, Y.‐G. Guo, Y. Mei, O. G. Schmidt

Adv. Mater. 22, 4591 (2010)

Self-wound ultra-compact energy storage elements

We demonstrate the self-assembly of ultra-compact energy storage devices based on self-wound three-dimensional hybrid organic/inorganic nanomembranes. 

First Swiss roll micro-supercapacitor

We demonstrate a redox Swiss roll micro-supercapacitor consisting of a self-rolled multilayered nanomembrane with an electrochemical active layer at either the outer or inner surface for different proton diffusion paths.

Neuron cells cultured in rolled-up microtubes

Primary mouse motor neurons and immortalised CAD cells, a cell line derived from the central nervous system, can be well cultured on arrays of rolled-up microtubes.

How nanostructures healthily cope with stress...

 Quantum dots are able to cope with increasing stress by cyclically incorporating large amounts of material from the substrate and corresponding changes of their shape.

Lateral Si quantum dot molecules

J. Dong, T. Zhang, Y. Zhang, L. Yang, R. Lu

Collective behaviour of artifcial autonomous systems

Artificial autonomous systems act as catalytic water striders at the air–liquid interface of hydrogen peroxide solution.

Highly efficient locomotion of hybrid biocatalytic microengines

We have designed a novel hybrid biocatalytic microengine.

Magnetic control of tubular catalytic microbots

A. A. Solovev, S. Sanchez, M. Pumera, Y. F. Mei, O. G. Schmidt

Adv. Funct. Mater. 20, 2430 (2010)

The DotFET becomes reality

On May 18, 2001 a patent to speed up Si transistors was filed by Schmidt and Eberl (US 6,498,359), which relies on a SiGe dot positioned below the channel of a Si transistor. This idea was now realized.

Rolled-up mesoscopic Josephson junctions

Mesoscopic Josephson junctions are developed simply relying on natural metallic film roughnesses, self-assembly and standard optical lithography.

Photovoltaic effect in ultrathin Si nanomembranes

Under local illumination, ultrathin silicon nanomembranes on insulator reveal a gate-controlled photovoltaic effect and negative transconductance in Schottky transistors applying both homo- and hetero-contacts.

Quantum transport through SiGe quantum dots

We have realized single-hole transistors based on self-assembled SiGe quantum dots. 

Stretch graphene, get more details...

We are continuously expanding the knowledge of how controllable external stresses, as a basic physical technique, modify the properties and unveil interesting physics of nanomaterials. 

Direct laser writing of nanoscale light-emitting diodes

We have fabricated sub-micrometer light emitting diodes in a mesoscopic semiconductor structure by means of a focused laser beam.

Electromechanical tuning of quantum dot emission energies

Elastic mechanical strain is a powerful control tool for engineering the electronic states in quantum dots.

Metamaterial fiber optics

E. J. Smith, Z. Liu, Y. Mei, O. G. Schmidt

Nano Lett. 10, 1, 1-5 (2010)

When Silicon becomes a better thermal insulator than glass…

Introducing Ge nanostructures into single-crystalline Si leads to thermal conductivities which are lower than any other SiGe alloy, amorphous Si  and even glass.

Rolled-up hyperlens

An investigation of the material makeup and surrounding medium of an optical rolled-up hyperlens is presented.

Applied Physics Letters 95, 083104 (2009)

Cell culturing in single tubes integrated on a Si Chip

Detailed investigations of individual yeast cells in a single transparent microtube reveal the mechanical interaction between the tube and the 2D confined cells causing different cellular assemblies. 

Advanced quantum dot configurations

We have presented an overview on approaches currently employed to fabricate advanced quantum dot configurations by epitaxial growth.

Microtubular jet engines

A. A. Solovev, Y. Mei, E. B. Ureña, G. Huang, O. G. Schmidt

Small 5, 1688 (2009)

Ferngesteuerte Mikroraketen

Wir haben winzige Mikroraketen hergestellt, die sich durch ein Magnetfeld fernsteuern lassen.

Spektrum der Wissenschaft, S.16, Juli 2009

Giant persistent photoconductivity in Si nanomembranes

We observe giant persistent photoconductivity from rough Si nanomembranes.

Epitaxial quantum dots in stretchable optical microcavities

Arrays of GaAs microring optical resonators with embedded quantum dots are placed on top of piezoelectric actuators, which allow the microcavities to be reversibly “stretched” or “squeezed” by applying relatively large biaxial stresses at low temperatures. 

Tuneable electronic shell structure of GaAs quantum dots

We have studied quantum dots for which the wetting layer thickness can be arbitrarily controlled.

Ultrathin AlN/GaN nanomembranes

Y. Mei, D. J. Thurmer, C. Deneke, S. Kiravittaya, Y.-F. Chen, A. Dadgar, F. Bertram, B. Bastek, A. Krost, J. Christen, T. Reindl, M. Stoffel, E. Coric†, O. G. Schmidt

ACS Nano 3, 1663 (2009)

Self-assembled quantum dot molecules

L. Wang, A. Rastelli, S. Kiravittaya, M. Benyoucef, O. G. Schmidt

Adv. Mater. 21, 2601 (2009)

From wrinkling to rolling

We have explored the change-over from wrinkling to rolling for compressively strained thin solid films.

New planar hybrid heterostructures and superlattices

We have invented an entirely new approach to create hybrid material layer stacks, which cannot be produced by any other technology. 

Spectral tunability of microtube resonators on glass

The tunability of optical resonant modes of spiral microtube cavities, rolled-up from square patterned SiO/SiO2 thin nanomembranes on glass substrates, is demonstrated experimentally by coating the tube walls by atomic layer deposition. 

Microtubular optical cavities

G. S. Huang, S. Kiravittaya, V. A. Bolaños Quiñones, F. Ding, M. Benyoucef, A. Rastelli1, Y. F. Mei, O. G. Schmidt

Appl. Phys. Lett. 94, 141901 (2009)

Towards tunable indistinguishable photons from distant quantum dots

In this work, we present steps towards the realization of quantum interference between two photons emitted from two independent QDs.

First single photon source on silicon substrate

we demonstrate triggered single-photon emission from a single quantum dot grown on Si substrate  for the first time.

First magnetic rolled-up microtubes demonstrated

Magnetic rolled-up microtubes are fabricated for the first time, and their hysteresis curves are measured.

Nanotechnology 20, 045703 (2009)

Towards flexible magnetoelectronics

Strongly enhanced GMR on flexible substrates is reported for Co/Cu multilayers deposited on plastics by introducing a photoresist buffer layer.

Strain engineered micro-/nanotubes on polymers

Y. Mei, G. Huang, A. A. Solovev, E. Bermúdez Ureña, I. Mönch, F. Ding, T. Reindl, R. K. Y. Fu, P. K. Chu, O. G. Schmidt

Adv. Mater. 20, 4085 (2008)

Quantum dot crystal defects

In analogy to a conventional crystal we have introduced the terminology and formation of vacancy and interstitial defects in artificial crystals.

Nanogrooves attract quantum dots

We demonstrate that gentle grooves on a Si substrate "attract" self-assembled SiGe quantum dots  and provide a way to control their position on the substrate.

Absolute positioning of quantum dots for large scale integration

We  control the nucleation sites of quantum dots by small pit patterns on the substrate surface.

Three-dimensional composition profiles of quantum dots

We have developed a simple “nanotomography” approach based on scanning probe microscopy and selective wet chemical etching. 

Integrated microtube resistors

Integrated ohmic devices are fabricated from Si-based microtubes, and linear I-V curves are measured for rolled-up tubes suspended between two electrodes.

Self-organisation into nanochannel networks

A. Malachias, Y. Mei, R. K. Annabattula, C. Deneke, P. R. Onck, O. G. Schmidt

ACS Nano 2: 1715 (2008)

Glucose detection on the femtoliter scale

We use Si/SiO microtubes as optofluidic components to sense glucose concentrations in water. 

Strongly coupled semiconductor microcavities

A focused laser beam is used both as optical excitation and local heat source to obtain strong coupling in photonic molecules. 

Lateral alignment of epitaxial quantum dots

Quantum dots constitute a natural template to construct refined artificial matter, such as artificial atoms, molecules and possibly artificial crystals with entirely new electronic and optical properties.

From dots to rods

Periodic metal patterns on a silicon surface provide unprecedented control over the morphology of highly ordered Ge islands.

Nanochannel arrays by deterministic layer wrinkling

We have developed a method that exploits the deterministic wrinkling and a subsequent bond-back of a semiconductor layer to create well-defined and versatile nanochannel networks.

Semiconductor/metal radial superlattices

Strained rolled-up heterostructures allow for the creation of radial superlattices incorporating crystalline and non-crystalline material.

Quantum wells illuminate the strain state of nanomembranes

The strain state of a wrinkled nanomembrane has been accurately analyzed by incorporating a quantum well into the layer and subsequently using micro-photoluminescence  to investigate the shift of the transition energy.

Perfectly resonant quantum dots

Laser processing is used as a post-growth method to tune, within a broad spectral range and with resolution-limited accuracy, the confined energy states of single quantum dots.

Si/SiO microtube optical ring resonators

Rolled-up Si/SiO tubes show optically resonant emission in the visible spectral range at room temperature.

Entangled photons from single quantum dots

We have succeeded in the fabrication of high quality InAs/GaAs quantum dots with degenerate exciton recombination and shown that quantum correlated photon pairs can be produced at temperatures as high as 30 K.