Towards Oxide Electronics:a Roadmap

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics

Positronium as a probe of small free volumes in crystals, polymers and porous media

Positronium (a hydrogen-like bound state of an electron and a positron) is a convenient probe to determine the sizes of subnanometric free volumes (voids) in condensed matter. A review of experimental methods used in positron spectroscopy and examples of their application to the free volume studies are presented

Positron lifetime spectroscopy applied to the study of defects in metals and semiconductors

Studies have been made of fast timing techniques in various types of positron lifetime spectrometer and of the analysis procedures used for extracting positron lifetime and intensity values. Evaluation is made in terms of their usefulness and reproducibility in high resolution studies of lattice defects and their formation. The optimisation of a Fast-Slow 4-Way Routing Positron Lifetime Spectrometer has been attempted and the results are discussed in terms of changes in important spectrum parameters which have possibly been overlooked on comparative systems. Its viability as a non-destructive testing technique is considered. A Fast-Slow and a Fast-Fast Positron Lifetime Spectrometer have been constructed and studied. The Fast-Fast system has been developed such that it utilises the detector dynode pulses for timing, rather than the conventional anode pulse. By further optimisation of the time-pickoff method, a substantial improvement in the resolution has resulted. The system has been applied to studies of materials in which the defect types, their concentration and their specific trapping rates for positrons, are in question. A study has been made of the uncertainties arising from different approaches to the computer-aided analysis of multi-component decay spectra. Three analysis programs, all in common use, have been investigated and compared. Results are presented that clearly indicate the underlying reason for discrepancies in published positron lifetime data. A temperature study has been made of thermal vacancy creation in polycrystalline indium from 290 to 425 K by observing the variation in the positron trapping rate. Results are discussed in terms of a simple 2-state trapping model although attention has been paid to the question of pre-thermalisation trapping of positrons as the melting point is approached. Values of the monovacancy formation energy, E, are estimated using several types of analysis method for spectra from three sets of similar temperature measurements using the same sample, each made at differing stages of anneal. Differences in trapping rate variation with temperature (and thus in E) is interpreted as a sign of inadequate annealing and this is used to explain the discrepancies between previously published results. The nature of the defects in various types of gallium arsenide single crystal have been investigated by studying the effect of different dopants and their concentrations upon the rate and intensity of positron trapping at room temperature. Positron lifetimes and intensities in e and n&deg;-irradiated samples have been similarly measured. To determine further the characteristics of the defects, an isochronal anneal study was performed using n&deg;-irradiated gallium arsenide over the temperature range 290 to 725 K. This study was combined with infra-red spectroscopy measurements at each anneal stage in an attempt to correlate the variation of specific lifetime component intensities with those of a selection of infra-red spectral peaks whose origin is in question. The high defect concentrations created by the irradiation are shown to give rise to pre-thermalisation trapping of positrons.<p

Annual Report 2015 - Institute of Ion Beam Physics and Materials Research

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