[en] In the presented scientific research project, the radiation protection of soil surfaces impacted by former industrial utilization or mining was investigated. This radiation protection of the contaminated soil surfaces was carried out by bioremediation techniques. The soil surfaces include larger agricultural or forestry areas useful for the production of sustainable plant-based raw materials and renewable energies. The contaminated areas show a positive climatic water balance with a subsequent impact of SM/R contaminants onto the adjacent ground water. During this scientific research project, the introduction of sustainable, biosphere conserving methods for a long-term remediation of slightly to moderately HM/R- contaminated areas was investigated; these areas are characterized by a radiotoxic amplifying potential due to a continued occurrence of radionuclides and heavy metals/ metalloids. The insights into transfer processes from the soil substrate over the mediating soil water phase and by microbes into the plant roots, into the shoots and the leaves of the plants represent necessary requirements for the control of SM/R transfer into the plants and its optimization. In this research project, considerable investigations were carried out for the understanding of binding of HM/R in the different plant compartments, also depending on different soil additives. The obtained first scientific results and their practical applicability were transformed onto experimental soil areas under natural field conditions. The transfer processes could be optimized and finally bioremediation efficiency could be enhanced due to the accompanying modifications (different soil additives of the field experiments). This new remediation method, further developed to a field application, represents a new tool for the stabilization / and extraction of HM/R on the field site and improves the efficiency of bioremediation processes. A pacification of the large areas with slightly to medium contaminated geosubstrates now can be carried out within the radiation protection regulations. Hence, the project provides a substantial contribution to the radiation protection of HM/R contaminated soils. Within the research project, ways for the utilization of HM/R- contaminated plant residuals were highlighted; this gives a substantial contribution for minimization of wastes, the winning of sustainable bioenergy and the recycling of materials. Here, different ways of solutions were investigated. The research project was carried out within the scientific funding program ''Closedown and decommissioning of nuclear facilities''. The results of the project will contribute to the development of a biologically benign, sustainable technique for the remediation of large contaminated areas that originate mostly from the legacy of the former U mining. As a general result of this comprehensive research project, a phytostabilization/ phytoextraction of such SM/R contaminated sites is feasible with a protection of ground water, and the plant crop from phytoremediation of the HM/R contaminated field site can be utilized for the winning of bioenergy (gaseous/ liquid products or thermal utilization). The beneficial combination of phytoremediation and subsequent utilization of the biomass can be further developed to an innovative and sustainable remediation technology with national and international application potential.

[en] Epitaxial silicon nanowires (NWs) of short heights (∼280 nm) on Si <111> substrate were grown and doped in situ with boron on a concentration range of 10¹⁵-10¹⁹ cm^-3 by coevaporation of atomic Si and B by molecular beam epitaxy. Transmission electron microscopy revealed a single-crystalline structure of the NWs. Electrical measurements of the individual NWs confirmed the doping. However, the low doped (10¹⁵ cm^-3) and medium doped (3x10¹⁶ and 1x10¹⁷ cm^-3) NWs were heavily depleted by the surface states while the high doped (10¹⁸ and 10¹⁹ cm^-3) ones showed volume conductivities expected for the corresponding intended doping levels

[en] Single undoped Si nanowires were electrically characterized. The nanowires were grown by molecular-beam epitaxy on n⁺ silicon substrates and were contacted by platinum/iridium tips. I-V curves were measured and electron beam induced current investigations were performed on single nanowires. It was found that the nanowires have an apparent resistivity of 0.85 Ω cm, which is much smaller than expected for undoped Si nanowires. The conductance is explained by hopping conductivity at the Si-SiO₂ interface of the nanowire surface

[en] Ion implantation is one of the key processing steps in fabricating planar silicon devices and circuits in the ultra large scale integration (ULSI) technology. With ion implanatation one can selectively dope specific areas on a planar silicon device defined by lithographic masks and confine the vertical penetration depth of the dopant atoms into the bulk of silicon at that region. However, this process has so far not been fully exploited in nanoelectronics, especially in doping silicon nanowires (Si NWs). Si NWs which are promising candidates for future nanoelectronics have mostly been doped in situ. We demonstrate that ion implantation can also effectively dope vertical Si NWs both n and p-type. We implanted boron as p-type dopant, and separately phosphorus and arsenic as n-type dopants on the Si NWs grown by molecular beam epitaxy. We demonstrate homogeneous doping along the length of the NWs, as well as formation of an axial p-n junction inside the NWs and performed detailed structural and electrical characterizations of individual NWs. For the p-n junction formation a combined approach of in situ p-doping and ex situ n-doping was used. Our results show significant differences between n and p-doping which conform to theory.

[en] We present growth studies of InSb nanowires grown directly on InSb_{(1-bar1-bar1-bar)B} and InAs_{(1-bar1-bar1-bar)B} substrates. The nanowires were synthesized in a chemical beam epitaxy (CBE) system and are of cubic zinc blende structure. To initiate nanowire nucleation we used lithographically positioned silver (Ag) seed particles. Up to 87% of the nanowires nucleate at the lithographically pre-defined positions. Transmission electron microscopy (TEM) investigations furthermore showed that, typically, a parasitic InSb thin film forms on the substrates. This thin film is more pronounced for InSb_{(1-bar1-bar1-bar)B} substrates than for InAs_{(1-bar1-bar1-bar)B} substrates, where it is completely absent at low growth temperatures. Thus, using InAs_{(1-bar1-bar1-bar)B} substrates and growth temperatures below 360 deg. C free-standing InSb nanowires can be synthesized.

[en] For the development of nano-optical devices nano wires (NW) are of emerging interest. One of the most important steps in the fabrication of Si devices is doping using ion beam implantation. However, this may lead to a distortion of the NW's crystalline structure or even to an amorphization. A subsequent annealing procedure is necessary to recover the crystalline structure. The advantage of implanted Si NW's is that the electrical conductivities are significantly higher than MBE-grown in-situ doped ones. NW's of about 100nm in diameter and 100.400 nm in length, nominally undoped, were MBE grown on Si(111) using Au as a growth-initiator. We followed the structural changes of the NW's caused by implantation and annealing. We used rapid thermal annealing up to a temperature of 1100 C of about 30 seconds to remove a possible damage induced by implantation. Diffraction experiments were carried out at the ID01 ESRF beamline using a microfocused X-ray beam in combination with a 2D detector to obtain 3D diffraction patterns. Our experiments have shown that defect structure and form of the investigated NW's change after implantation and annealing.

[en] Much progress has been achieved over the past 20 years in remediating sites contaminated by heavy metal. However, very large contaminated areas have presented major problems to this day because of remediation costs. Phytoremediation is a new, emerging, sustainable technique of remediating areas with low heavy-metal contamination. One advantage of phytoremediation is the comparatively low cost of the process, which may make it usable also on large areas with low levels of contamination. Besides extracting and immobilizing metals, respectively, phytoremediation among other things also contributes to improving soil quality in terms of physics, chemistry, and ecology. Consequently, phytoremediation offers a great potential for the future. Research into phytoremediation of an area contaminated by heavy metals and radionuclides is carried out on a site in a former uranium mining district in Eastern Thuringia jointly by the Friedrich Schiller University, Jena, and the Technical University of Dresden in a project funded by the German Federal Ministry for Education and Research. The project serves to promote the introduction of soft, biocompatible methods of long-term remediation and to develop conceptual solutions to the subsequent utilization of contaminated plant residues. Optimizing area management is in the focus of phytoremediation studies. (orig.)

[en] Full text: Deep level transient spectroscopy technique is used on a Ti Schottky diode on n-type silicon with embedded Sb-mediated Ge quantum dots (QDs). We discovered an electron trap and two hole traps within the Si band gap at the plane of Ge QDs. An electron trap has activation energy of 87±7 meV. One hole trap has activation energy of 304±32 meV, while the second hole trap is represented by the energy sub-band between 125 and 250 meV above the top of the Si valence band. The electron level (87±7 meV) and the hole energy sub-band (125-250 meV) are identified as energetic states of Ge QDs array. The deepest trap level for holes (304 meV) has not been identified yet. (author)

[en] Vertical epitaxial short (200-300 nm long) silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si(111) substrates were separately doped p- and n-type ex situ by implanting with B, P and As ions respectively at room temperature. Multi-energy implantations were used for each case, with fluences of the order of 10¹³-10¹⁴ cm^-2, and the NWs were subsequently annealed by rapid thermal annealing (RTA). Transmission electron microscopy showed no residual defect in the volume of the NWs. Electrical measurements of single NWs with a Pt/Ir tip inside a scanning electron microscope (SEM) showed significant increase of electrical conductivity of the implanted NWs compared to that of a nominally undoped NW. The p-type, i.e. B-implanted, NWs showed the conductivity expected from the intended doping level. However, the n-type NWs, i.e. P- and As-implanted ones, showed one to two orders of magnitude lower conductivity. We think that a stronger surface depletion is mainly responsible for this behavior of the n-type NWs.

[en] The Negative Differential Capacitance (NDC) effect on Ti Schottky diodes formed on n-type Silicon samples with embedded Germanium Quantum Dots (QDs) is observed and reported. The NDC-effect is detected using capacitance-voltage (CV) method at temperatures below 200 K. It is explained by the capture of electrons in Germanium QDs. Our measurements reveal that each Ge QD captures in average eight electrons