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Content: Preface Selected publications Statistics (Publications and patents, Concluded scientific degrees; Appointments and honors; Invited conference contributions, colloquia, lectures and talks; Conferences, workshops, colloquia and seminars; Exchange of researchers; Projects) Doctoral training programme Experimental equipment User facilities and services Organization chart and personnel

After the successful evaluation in 2015 we started research and further development of our largescale facilities, in particular the Ion Beam Center (IBC), in the framework of Helmholtz’s Programmeoriented Funding scheme (POF) which coordinates scientific cooperation on a national and international scale. Most of our activities are assigned to the Helmholtz program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a minor part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”. A few highlights which have been published in 2015 are reprinted in this annual report in order to show the variety of the research being performed at the Institute, ranging from self-organized pattern formation during ion erosion or DNA origami patterning, over ferromagnetism in SiC and TiO2 to plasmonics and THz-spectroscopy of III-V semiconductors. A technological highlight published recently is the demonstration of nanometer scale elemental analysis in a Helium ion microscope, making use of a time-of-flight detector that has been developed at the IBC. In addition to these inhouse research highlights, also users of the IBC, in particular of the accelerator mass spectrometry (AMS), succeeded in publishing their research on geomorphology in Nepal in the high-impact journal Science (W. Schwanghart et al., Science 351, 147 (2015)), which demonstrates impressively the added value of transdisciplinary research at the IBC. In order to further develop the IBC, we have started in 2015 the design and construction of our new low energy ion nanoengineering platform which was highly recommended by the POF evaluators. It will consist of two-dimensional materials synthesis and modification, high-resolution ion beam analysis and high-resolution electron beam analysis and will come into full operation in 2019.

Independent of the type of doping, it is challenging to achieve in semiconductors an effective carrier concentration much above 10^20 /cm3. On the other hand, the successful realization of defect free n-type and p-type ultra-doped Ge layers will enable a range of devices from sensors to quantum computers. In the case of conventional doping techniques (using equilibrium processing) the maximum carrier concentration is limited by the out-diffusion of dopants, a relatively low solid solubility limit, clustering and self-compensation processes. To overcome such limitations we have utilised strong nonequilibrium process consisting of an ion beam implantation to introduce dopants into Ge and rear-side millisecond range flash lamp annealing (FLA) for recrystallization of implanted layer and dopant activation. In contrast to conventional annealing procedures, rear-side FLA leads to full recrystallization of Ge and dopant activation independent of the pre-treatment. The maximum carrier concentration is well above 10^20 /cm3 for n-type and above 10^21 /cm3 for p-type dopants. The so-fabricated n-type Ge can be used in the field of mid-infrared plasmonics which has not been accessible by group-IV semiconductors. Single crystalline n-type Ge with carrier concentrations as high as 2.2×10^20 /cm3 displays a room-temperature plasma frequency above 1850 /cm1 (?=5.4 ?m), which is the highest value ever reported for n-type Ge. In the case of Ga implanted Ge the maximum effective carrier concentration measured at 3K is 1.1×10^21 /cm3 which is two times higher than the solid solubility limit of Ga in Ge. Our p-type Ge is defect and cluster free and shows the superconductivity at Tc = 0.95 K. These results base on the successful combination of ion beam implantation followed by the novel approach consisting of millisecond range rear-FLA. This work has been partially supported by the EU 7th Framework Programme "EAgLE" (REGPOT-CT-2013-316014).

This past year 2014 was the year when we finally completely arrived as a “full member” in the Helmholtz Association. This is related to the successfully passed research evaluation in the framework of the Program Oriented Funding (POF), which will give us a stable and predictable funding for the next five years (2015 – 2019). This is particularly true for our large-scale user facilities, like the Ion Beam Center (IBC) and the electron accelerator ELBE with the free-electron laser. Most of our activities are assigned to the program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”. Our research and facilities were well appreciated by the evaluation committee, who made the following judgement about the Ion Beam Center: “The Ion Beam Centre (IBC) of HZDR is an internationally leading ion-beam facility (with ion energies ranging from several eV to several tens of MeV). At both the national and international level it is one of the key players and is unique in its kind. The synergy between forefront research and user service has been leading to a very good publication output for both in-house research and user research. … The very broad range of beam energies, the versatility of techniques and applications – both for ion beam modification of materials and for ion-beam analysis – makes the IBC unique in its kind. … The strength of IBC is that its activities are based on a combination of forefront research and user service, which mutually interact in synergy and strengthen one another. In turn, this synergy has been leading to a very good publication output for both in-house research and user research.” In order to make our Annual Report a bit more compact, we have decided to include only four full journal papers this year. This was also triggered by the fact that our publication activities have turned out be become more diverse, in more diverse journals than in the past, and often through longer papers, which would be too long to reprint them here. However, apart from the constantly quantitatively high publication output, we succeeded to publish in excellent journals such as Nature Physics, Nano Letters and Physical Review Letters, in fields as diverse as ion beam physics, magnetism and terahertz spectroscopy. Two of our scientists, Dr. Artur Erbe and Dr. Alexej Pashkin obtained their Habilitation in 2014, both at University of Konstanz. For the first time, we are hosting an Emmy Noether Young Investigator Group funded by the Deutsche Forschungsgemeinschaft (DFG); the group works on the hot topic of magnonics and is headed by Dr. Helmut Schultheiß. Finally we would like to cordially thank all partners, friends, and organizations who supported our progress in 2014. Special thanks are due to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Minister of Education and Research of the Federal Government of Germany. Numerous partners from universities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank again all IIM staff for their efforts and excellent contributions in 2014.

The year 2013 was the third year of HZDR as a member of the Helmholtz Association (HGF), and we have made progress of integrating ourselves into this research environment of national Research centers. In particular, we were preparing for the evaluation in the framework of the so-called program oriented funding (POF), which will hopefully provide us with a stable funding for the next five years (2015 – 2019). In particular, last fall we have submitted a large proposal in collaboration with several other research centers. The actual evaluation will take place this spring. Most of our activities are assigned to the program “From Matter to Materials and Life” (within the research area “Matter”). A large fraction of this program is related to the operation of large-scale research infrastructures (or user facilities), one of which is our Ion Beam Center (IBC). The second large part of our research is labelled “in-house research”, reflecting the work driven through our researchers without external users, but still mostly utilizing our large-scale facilities such as the IBC, and, to a lesser extent, the free-electron laser. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a small part of our activities in the program “Nuclear Waste Management and Safety” (within the research area “Energy”).

Ga-rich (~ 10 at.%) Si and Ge films were fabricated by high-fluence Ga+ ion implantation through a SiO2 capping layer. The structure and the electrical transport properties of these films have been studied after flash-lamp [1-3] and rapid thermal annealing [4, 5]. Amorphous, Ga-rich nanoprecipitates are embedded in a heavily p-type doped semiconductor matrix [3, 4]. These nanoprecipitates become superconducting below critical temperatures up to 7 K. They can interact due to the proximity effect in the degenerately doped semiconductor matrix and form a random network of Josephson junctions. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. In particular, Ga-rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance [6, 7] . The possibility to prepare and modify Ga-rich Si and Ge films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [1] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, et al., Phys. Rev. Lett.,2009, 102, 217003. [2] R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, et. al., Low Temp. Phys., 2011, 37, 1098. [3] V. Heera, J. Fiedler, M. Naumann, R. Skrotzki, et al., Supercond. Sci. Technol., 2014, 27, 055025. [4] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2011, 83, 214504. [5] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2012, 85, 134530. [6] V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, et al., Appl. Phys. Lett., 2012, 100, 262602 [7] V. Heera, J. Fiedler, R. Hübner, B. Schmidt, et al., New. J. Phys., 2013, 15, 083022

Ge films with a mean Ga content of about 8 at.% and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change of the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters up to 10,000 atoms. Since no percolating Ga cluster exists, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.

es hat kein Abstract vorgelegen

In 2012 the HZDR, and in consequence also the Institute of Ion Beam Physics and Materials Research (IIM) including its Ion Beam Center (IBC), has undergone a scientific evaluation. The evaluation committee composed of the Scientific Advisory Board and numerous external experts in our field of research concluded that “the overall quality of the scientific work is excellent”, that “there are an impressive number of young scientists working enthusiastically on a variety of high-level projects” and that “the choice of these projects represents a clear underlying strategy and vision”. We feel honored and are proud that the external view on our scientific achievements is that extraordinary. In view of this outstanding result we would like to express our gratitude to all our staff members for their commitment and efforts! In the past year, we continued our integration into the Helmholtz Association of German Research Centers (HGF) with our Institute mostly active in the research area “Matter”, but also involved in a number of activities in the research area “Energy”. In this respect, many consultations were held with the Helmholtz centers contributing to common research areas to precisely define the role we will play in the newly established HGF program “From Matter to Materials and Life” (see schematic below). Our IBC has been recognized as a large-scale user facility for ion beam analysis and modification of materials, i.e., specializing on materials science. In particular, the IBC plays a prominent role in the recently approved Helmholtz Energy Materials Characterization Platform (HEMCP), which mainly concentrates on the development of dedicated analytical tools for the characterization of materials required for future energy technologies. The successes achieved by the IBC allows us to invest 7200 k€ to further improve and strengthen the ion beam capabilities at the Institute. In addition to this infrastructure-related grant, we were also successful in our funding application for the establishment of the International Helmholtz Research School for Nanoelectronic Networks (IHRS NANONET), aiming at promoting the next generation of leading scientists in the field of nanoelectronics. The IHRS NANONET is coordinated by our Institute and offers a well-structured PhD program to outstanding students of all nationalities with emphasis on interdisciplinary research and comprehensive training in technical and professional skills.

Si films sputter deposited on SiO2 substrates are enriched with Ga by ion implantation through a capping SiO2 layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga rich nanograins are embedded in a nanocrystalline Si matrix. The nanograins are metallic in the normal state and superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current controlled sheet resistance. The possibility to fabricate and tailor films of Ga rich Si with microelectronics compatible technology make it a promising material for the integration of superconducting circuits into Si devices.

Superconducting Ga-rich layers in Ge are fabricated by Ga implantation through a thin SiO2 cover layer. After annealing in a certain temperature window, Ga accumulation at the SiO2/Ge interface is observed. However, no Ga containing crystalline phases are identified. Thus it is suggested that the volatile Ga is stabilized in an amorphous mixture of all elements available at the interface. Electrical transport measurements reveal p-type metallic conductivity and superconducting transition. The superconducting properties of the samples with high Ga concentration at the interface change dramatically with etching the amorphous surface layer. A critical temperature of 6 K is measured before, whereas after etching it drops below 1 K. Therefore, one can conclude that the superconducting transport is based on two different layers: a Ga-rich amorphous phase at the interface and a heavily Ga-doped Ge layer. Finally, the comparison of the transport properties of Ga-rich Ge with those of Si demonstrates distinct differences between the interface layers and even the deeper lying doped regions.

We report on two unconventional routes of embedding superconducting nanolayers in a semiconducting environment. Ion implantation and subsequent annealing have been used for preparation of superconducting thin-films of Ga-doped germanium (Ge:Ga) [1] as well as 10 nm thin amorphous Ga-rich layers in silicon (Si:Ga) [2]. Structural investigations by means of XTEM, EDX, RBS/C, and SIMS have been performed in addition to low-temperature electrical transport and magnetization measurements. Regarding Ge:Ga, we unravel the evolution of Tc with charge-charrier concentration while for Si:Ga recently implemented microstructuring renders critical-current densities or more than 50 kA/cm2. Combined with a superconducting onset at around 10 K, this calls for onchip application in novel heterostructured devices.

The first year of membership of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in the Helmholtz Association of German Research Centers (HGF) was a year of many changes also for the Institute of Ion Beam Physics and Materials Research (IIM). The transition period, however, is not yet over, since the full integration of the Center into the HGF will only be completed in the next period of the so-called program-oriented funding (POF). This funding scheme addresses the six core research fields identified by the Helmholtz Association (Energy; Earth and Environment; Health; Key Technologies; Structure of Matter; Aeronautics, Space and Transport) to deal with the grand challenges faced by society, science and industry. Since the Institute has strong contributions to both core fields “Key Technologies” and “Structure of Matter”, intense discussions were held amongst the leading scientists of the Institute, across the Institutes of the HZDR, and finally with leading scientists of other Helmholtz centers, to determine the most appropriate classification of the Institute’s research. At the end we decided to establish ourselves in Structure of Matter, the core field in which most of the large-scale photon, neutron and ion facilities in Germany are located. As a consequence, the Ion Beam Center (IBC) of the Institute submitted an application to become a HGF recognized large-scale facility, providing more than 50% of its available beam time to external users. This application perfectly reflects the development of the IBC over more than a decade as a European Union funded infrastructure in the framework of the projects “Center for Application of Ion Beams in Materials Research (AIM)” (1998-2000, 2000-2003, 2006-2010) and subsequently as the coordinator of the integrated infrastructure initiative (I3) “Support of Public and Industrial Research using Ion Beam Technology (SPIRIT)” (2009-2013). Another part of the Institute’s activities is dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. This facility is also open to external users and funded by the European Union.

Superconductivity in elemental group-IV semiconductors is of great interest because of both, the high potential for new microelectronic applications and its underlying physics. To observe superconductivity at ambient pressure conditions high doping levels are needed. Sufficient doping concentrations of few at.% were achieved first for boron doped diamond [1]. Suprisingly also silicon, the basic material of todays microelectronic indurstry becomes superconducting below 0.6 K when heavily doped with boron [2]. In our previous work we used ion implantation and short-term annealing to fabricate superconducting Ga doped Ge layers with critical temperatures below 1 K [3]. The solid solubility is exceeded by far and therefore the presence of Ga clusters has to be excluded [4]. However the question arises, how superconducting precipitates influence the low- temperature transport properties. We demonstrate the possibility of embedding extrinsic superconducting nanolayers in commercial microelectronic Si wafers. Ga implantation (4x1016cm-2) through a 30 nm SiO2 cover layer is used because Ga itself is a superconducting element. Sturctural investigations by means of RBS/C and TEM reveal the stabilization of a Ga-rich layer at the SiO2/Si interfae after rapid thermal annealing (RTA). At defined RTA temperatures of 600 – 700°C this interface layer becomes superconducting [5,6]. Amorphous Ga has a critical temperature of 7 K which is comparable to the value of our Ga-rich interface layers. High critical magnetic fields up to 14 T and critical current densities as high as 50 kA/cm2 make the Si:Ga layers interesting for applications. These results in combination with investigations on similar prepared Ga-rich layers at SiO2/Ge interfaces imply that superconductivity driven by Ga clusters occurs at temperatures of 6 – 7K [7]. If in Ge the onset of superconductivity is below 1 K, it can clearly be attributed to a doping effect. Financial support by DFG (HE 2604/7-1) is gratefully acknowledged. [1] E. A. Ekimov et al., Nature 2004;428:542. [2] E. Bustarret et al., Nature 2006;444:465. [3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 2009;102:217003. [4] V. Heera et al., J. Appl. Phys. 2010;107:053508. [5] R. Skrotzki et al., Appl. Phys. Lett. 2010;97:192505. [6] J. Fiedler et al., Phys. Rev. B 2011;83:214504. [7] J. Fiedler et al., Phys. Rev. B 2012;85:134530.

Superconductivity is a fascinating ground state of matter and has been discovered one century ago. A new debate about the fundamental physical background and technological potential of superconducting group-IV semiconductors occurred, since superconductivity at ambient pressure conditions was shown for boron doped diamond [1] and silicon [2]. These unusual superconductors open the way towards new microelectronic devices and applications. In our previous work, we used Ga-ion implantation and subsequent short-time annealing for creating highly Ga doped layers in Ge. [3] These layers show an intrinsic superconducting transition at temperatures below 1 K because of the high doping level. [4] In a next step we could show the feasibility to stabilize Ga-rich layers at SiO2/Si [5,6] and SiO2/Ge [7] interfaces by using a 30 nm SiO2 cover layer during implantation and annealing. The presented structural investigations by means of Rutherford Backscattering Spectrometry (RBS) and cross-sectional Transmission Electron Microscopy (XTEM) reveal the presence of a 10 nm thin, superconducting layer at the interfaces containing Ga-rich precipitates. In both cases the critical temperature increases to 7 K which is comparable to amorphous Ga and therefore enables the detailed investigation of the influence of superconducting precipitates on the superconducting properties of doped semiconductor layers. However, the previous investigations were done on 1 x 1 cm2 size samples. The possibility of fabricating superconducting microstructures in Si with standard microelectronic lithography will be shown. Theses microstructures still undergo a superconducting transition below 7 K. High critical magnetic fields in the range of 10 T and high critical current densities of 50 kA/cm2 were achieved. For applications in superconducting microelectronics a Josephson-Junction has to be implemented. [8] We plan to use a Focused Ion Beam (FIB) for this task. Details about the sample processing, layer microstructure and processing of superconducting microstructures will be presented. [1] E. A. Ekimov et al., Nature (London) 428 (2004) 542. [2] E. Bustarret et al., Nature 444 (2006) 465. [3] V. Heera et al., J. Appl. Phys. 107 (2010) 053508. [4] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003. [5] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505. [6] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504. [7] J. Fiedler et al., Phys. Rev. B 85 (2012) 134530. [8] J. Q. You et al., Nature 474 (2011) 589.

Beginning in 2004, the interest in superconductivity of elemental group-IV semiconductors has been renewed because Ekimov et al. [1] showed that boron doped diamond could become superconducting at ambient pressure conditions. Besides fundamental physical background of driving a semiconductor into a superconducting state, the high potential for applications in new microelectronic devices is in the main focus. High doping levels are needed to observe superconductivity at ambient pressure conditions in elemental group-IV semiconductors. Gas immersion laser doping is used to fabricate superconducting boron doped silicon [2]. The possibility to use Ga-ion implantation and short-time annealing for creating superconducting Ga-doped Ge layers was shown in our previous work [3, 4]. These highly doped Ge-layers show an onset of superconductivity below 1 K. All doping techniques mentioned above exceed the equilibrium solid solubility limit by far and the question arises, whether the observed superconductivity is a doping effect or related to dopant clusters [5]. Especially if the doping element itself is a superconductor, like Ga in Ge, it was not clear how superconducting precipitates influence the low-temperature transport properties. To investigate these effects, we stabilized superconducting Ga-rich layers at SiO2/Si interfaces [6, 7]. Again, we have used ion implantation through a 30 nm thick SiO2 cover layer and rapid thermal annealing. The critical temperature of 7 K is comparable to the values obtained for amorphous Ga. Furthermore, high critical magnetic fields of 14 T and critical current densities of 50 kA/cm2 were achieved. With the results of the investigations discussed above, we could go one step further and fabricate similar Ga-rich layers at SiO2/Ge interfaces. Now it is possible to investigate selectively the influence of superconducting Ga-rich areas on the normal- and superconducting properties of Ga-doped Ge. It will be shown that the critical temperature changes dramatically while the critical magnetic field stays rather constant. The results of detailed microstructural investigations by means of XTEM and time-of-flight SIMS will be correlated with electrical properties. Finally, the presented results indicate that superconductivity with critical temperatures around 1 K can clearly be attributed to a doping effect. [1] E. A. Ekimov et al., Nature (London) 428 (2004) 542. [2] E. Bustarret et al., Nature 444 (2006) 465. [3] T. Herrmannsdörfer et al., Phys, Rev. Lett. 102 (2009) 217003. [4] V. Heera et al., J. Appl. Phys. 107 (2010) 053508. [5] N. Dubrovinskaia et al., PNAS 105 (2008) 11619. [6] R. Skrotzki et al., Appl. Phys. Lett. 97 (2010) 192505. [7] J. Fiedler et al., Phys. Rev. B 83 (2011) 214504.

TEM investigation contributing to the comprehension of superconductivity in Ga-doped Si

Ga-rich layers in Si were fabricated by 80 keV Ga implantation through a 30 nm SiO2 cover layer and subsequent rapid thermal annealing for 60 s in a temperature range between 500°C and 1000°C. Fluences of 2x1016cm-2 and 4x1016cm-2, leading to Ga peak concentrations of 8 at.% and 16 at.%, are chosen. Residual damage in the implanted layers and the Ga distribution were investigated by Rutherford-backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent Hall-effect measurements were carried out in order to determine the electrical properties of the implanted layers. It is shown that annealing at temperatures up to 800°C leads to the formation of poly-crystalline layers containing random distributed amorphous clusters. At the Si/SiO2 interface a dense and narrow band of Ga-rich clusters is observed. For 4x1016cm-2 the amount of mobile Ga is higher than for 2x1016cm-2 and an increase of the cluster density at the Si/SiO2 interface was found. Due to the higher cluster density for 4x1016cm-2 this interface layer can become superconducting below 7 K with critical fields exceeding 9 T at optimized annealing conditions. Critical currents are above 1 kA/cm2 and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900°C and above, the implanted layers are single crystalline and no amorphous precipitates were found.