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Preface and Acknowledgments
No full textThe 27th International Conference on Defects in
Semiconductors (ICDS-2013) was held in Bologna, Italy,
July 22–26, 2013. The conferences in this series, which dates
back to 1959, are held every 2 years and provide a valuable
forum where researchers studying the fundamentals of
defects in semiconductors can share their most recent findings
with colleagues and thereby advance understanding in
this technologically and scientifically important field. The
proceedings are published in part in the Journal of Applied
Physics (mostly by invited papers) and in part in the AIP
Proceedings (mostly contributed papers).
Following tradition, a tutorial day was held on July 2l to
help students and newcomers become familiar with important
experimental and theoretical techniques used to study
defects in semiconductors. The five speakers in the tutorial
were Professors Michael Stavola (Lehigh University, USA),
Michelle Moram (Imperial College London, UK), Michael
Reshchikov (Virginia Commonwealth University, USA),
John Morton (University College London, UK), and Audrius
Alkauskas (University of California, Santa Barbara, USA).
Nearly 50 junior scientists attended the tutorial day and
thoroughly enjoyed the lectures. The atmosphere was most
pleasant and the scientific level excellent. We thank the
speakers for helping to educate the next generation of
researchers. The Fraunhofer Institute for Solar Energy subsidized
this event.
The conference itself attracted 256 participants from 36
countries. There were 6 plenary, 25 invited, and 67 contributed
talks. Over 200 posters were distributed among two
poster sessions. A wide range of defect-related issues was
discussed in semiconductor materials ranging from the
traditional group IV, III-V, and II-VI materials to organic
semiconductors, and nanostructures. The defect issues
included localized impurities and native defects, dislocations,
interfaces and surfaces, magnetic impurities and spintronics,
radiation-induced defects, as well as numerous
defect-related issues in devices. Many attendees noted the
high scientific level in the various sessions.
An international Jury of five distinguished scientists was
assigned the difficult task of selecting the Corbett Award
winner. The Jury interviewed the six finalists during the
poster sessions. Following a difficult debate, one winner was
selected: Adurafimihan A. Abiona from the University of
New South Wales, Canberra, Australia. He received the
award at the conference banquet.
As is always the case in ICDS conferences, the registration
fees covered only part of the expenses. This conference
would not have been possible without the financial support
provided by the Fraunhofer Institute for Solar Energy (ISE,
Freiburg, Germany), the higher administration of the
University of Bologna, the Department of Physics and
Astronomy of the University of Bologna and the Enrico
Fermi Center. We thank these institutions for their help putting
this conference together. We also thank the Department
of Physics and Astronomy for providing personnel to work
at the conference site and the local organizing committee.
Finally, we thank the members of the program committee
who helped select presenters and the many referees who
reviewed manuscripts. We also thank the speakers and poster
participants who made the conference so interesting and
enjoyable for all. We hope to see a similarly enthusiastic
crowd of scientists in Finland, at ICDS-2015
Irradiation effects on the compensation of semi-insulating GaAs for particle detector application
No full textThe distribution of the electric field and its spatial extent are key predictors of the charge collection efficiency of particle detectors. The electric field is strictly related to the electrically active defects, which are significantly modified by irradiation. In this paper we analyze the native and radiation-induced defects and infer the mechanisms controlling the electrical properties of
semi-insulating GaAs Schottky diodes. The correlation between the electric-field distribution and deep levels confirms that the compensation mechanisms are mainly due to the donorlike centers and to their enhanced neutralization, which occurs for moderately high electric fields. Moreover, taking into account the charge balance among native and irradiation-induced defects, the active region extent is predicted
Fine-Tuning Design of GaAs Nanowire Arrays: from the Tweezing Effect of Electron Beam to the Adhesion-Induced Lateral Collapsing for the Realization of Sophisticated 3D Architectures
No full textThe superior chemical and physical properties of natural surfaces are frequently related to the multi-scale design of micro- and nano-structures on them. Following this bio-mimetic approach, the geometrical tailoring of semiconductor nanowire (NW) arrays allows rising a novel nanofabrication concept, where the semiconductor properties and the boosting effect of quantum properties merge into morphology-based functionalities. This contribution presents the results of Molecular Beam Epitaxy grown GaAs NW arrays locally patterned by the electron beam-mediated bending and by their adhesion-induced bundling. We explain the self-assembly of NWs into clusters in the frame of adhesion properties of natural contact surfaces (“gecko effect”), by generalizing the concept of “lateral collapse of fibrils”. We demonstrate how a careful choice of material properties and geometrical design of semiconductor NW arrays may turn the scanning electron microscope into a new patterning tool with nanoscale fine-tuning of the structure of NW-decorated surfaces. Additionally, the NW bending by the electron beam has further advantages in respect to the traditional elastocapillary method. In fact it allows to implement NW aggregation under vacuum ambient, so as to avoid the contamination of the delicate NW surface by external substances (liquids). The potential applications of tailored NW arrays range from energy conversion to nanoelectronics, chemical and biological sensing, and bioengineering
Impact of Processing Conditions on the Level Scheme of Silicon Nanowires Synthesized by Top-Down Techniques
No full textMassive and reliable synthesis of semiconductor NWs is an essential pre-requisite for the stepping out from the proof-of-concept stage towards real-world manufacturing of NW-based devices. In this respect it becomes of main concern to answer the question of how growth conditions could introduce point and/or extended defects into NW inner structures, mirroring themselves into the NW level schemes, and finally affecting NW-based device performances.
We report here on the investigation of electrically active defects of Si NWs fabricated by two different top-down techniques, Reactive Ion Etching (RIE) [1] (Fig. 1a) and Metal-Assisted wet Chemical Etching (MaCE) [2] (Fig1b), by means of Deep Level Transient Spectroscopy (DLTS). Our studies reveal the existence of intra-gap levels induced during the Si NWs growth in both cases. We discuss their origin in cross-reference with the different physical mechanisms underlying the samples’ processing features.
Differently from the case of MaCE Si NWs, the low density of RIE etched Si NWs has led us to develop a procedure in order to realize the Schottky barrier junction which is the conditio-sine-qua-non for performing DLTS characterization. Since the same procedure can be adopted for DLTS-probing of NW arrays under every density condition, this in turn opens the way to the systematic study of electrically active defects in semiconductor NWs by means of the sophisticated DLTS technique, of far-reaching consequence about defect characterization in semiconductor NWs.
[1] S. Leopold et al., J. Vac. Sci. Technol. B, 29, 011002 (2011).
[2] A. Irrera et al., Nanotechnology, 23, 075204 (2012)
Photo-Induced Nonlinearities in Fowler-Nordheim Plots for Field Emission of SiC Nanowires
No full textIn this contribution the field emission by tunneling of electrons of 3C-SiC nanowires on Si substrate, grown by CVD method via Ni catalyst, has been investigated. Scanning electron images have quantified the low density of the nanowires over the sample surface. In order to exclude any contribution to the Field Emission phenomenon from the Si substrate, the field emission measurements have been performed before and after removing the SiC nanowires. The Field Emission experiments have been carried out in dark conditions and by shining the sample surface. The extracted Fowler-Nordheim (F-N) plots show that the Field Emission from nanowires is highly sensitive to illumination parameters. When using lighting, a partition in three regions of the F-N plot has been observed. In the low field region, the F-N plot is linear or metallic-like, then it follows a saturation-current region and finally the high field region is characterized by a sharp increase.
Departure from the standard F-N theory, that is the influence of light and temperature on the Field Emission phenomenon, is well assessed for bulk semiconductor cathodes [1], but it has been rarely observed in single SiC nanowires [2]. To the authors’ knowledge, this contribution reports for the first time the strong deviation from F-N linear behavior for multiple SiC nanowires dispersed over planar substrate.
Field Emission data from quantum-confined structures are both useful for the study of their fundamental physics, but also because of promising technological applications, such as electron sources, high-resolution electron beam instruments, and Field Emission displays.
[1] G. N. Fursey, Field Emission in Vacuum Microelectronics (Kluwer Academic, New York, 2005)
[2] M. Choueib , A. Ayari, P. Vincent, M. Bechelany, D. Cornu, and S. T. Purcell, "Strong deviations from Fowler-Nordheim behavior for field emission from individual SiC nanowires due to restricted bulk carrier generation", Physical Review B 79, 075421 (2009
Electron Beam Patterning of GaAs Nanowires: Tailoring the Morphology of Semiconductor Nanowire Arrays for a Bio-mimetic Functionalization Approach
No full textThe superior chemical and physical properties of natural surfaces are frequently related to the multi-scale design of micro- and nano-structures on them. Following this bio-mimetic approach, the geometrical tailoring of semiconductor nanowire (NW) arrays allows rising a novel nanofabrication concept, where the semiconductor properties and the boosting effect of quantum properties merge into morphology-based functionalities. This contribution presents the results of Molecular Beam Epitaxy grown GaAs NW arrays locally patterned by the electron beam-mediated bending and by their adhesion-induced bundling. We explain the self-assembly of NWs into clusters in the frame of adhesion properties of natural contact surfaces (“gecko effect”), by generalizing the concept of “lateral collapse of fibrils”. We demonstrate how a careful choice of material properties and geometrical design of semiconductor NW arrays may turn the scanning electron microscope into a new patterning tool with nanoscale fine-tuning of the structure of NW-decorated surfaces. Additionally, the NW bending by the electron beam has further advantages in respect to the traditional elastocapillary method. In fact it allows to implement NW aggregation under vacuum ambient, so as to avoid the contamination of the delicate NW surface by external substances (liquids). The potential applications of tailored NW arrays range from energy conversion to nanoelectronics, chemical and biological sensing, and bioengineering
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
sj-doc-1-eso-10.1177_23969873241247436 – Supplemental material for Predictors of severe intracerebral hemorrhage expansion
No full textSupplemental material, sj-doc-1-eso-10.1177_23969873241247436 for Predictors of severe intracerebral hemorrhage expansion by Andrea Morotti, Qi Li, Jawed Nawabi, Giorgio Busto, Federico Mazzacane, Anna Cavallini, Ashkan Shoamanesh, Mauro Morassi, Frieder Schlunk, Laura Piccolo, Giacomo Urbinati, Debora Pezzini, Maurizio Paciaroni, Enrico Fainardi, Ilaria Casetta, Alessandro Padovani and Andrea Zini in European Stroke Journal</p
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