@misc{SmithRichterRies1998, author = {Smith, Roger and Richter, Asta and Ries, Ronald}, title = {Foundations of a Virtual Laboratory}, series = {Wissenschaftliche Beitr{\"a}ge 2/1998}, volume = {4}, journal = {Wissenschaftliche Beitr{\"a}ge 2/1998}, number = {2}, issn = {0949-8214}, doi = {10.15771/0949-8214_1998_2_24}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-7689}, pages = {120 -- 124}, year = {1998}, abstract = {A project was funded by the European Union to build foundations for a virtual laboratory where experimental and theoretical results could be combined into an audio-visual interactive presentation through the use of modern computers. The process of thin film growth and modification by energetic ion beams was chosen as the first topic for this new educational tool. Different models for thin film growth are developed and compared to experimental results in the presentation. Particular examples include spiral formation, modelled using cellular automata, island growth using Monte-Carlo methods and the first few layers of growth using classical molecular dynamics. Most of the examples are related to the growth of C60 films for which a number of experimental results had been obtained and previously reported in this journal [1]. The principle property under investigation was the structure and morphology of the films. Nine separate computer movies of the dynamics of these processes were developed on a fast PC under Windows95 and incorporated into a computer presentation made using the Authorware package. Experimental images obtained from a scanning force microscope were also included and compared to the computer models along with music and verbal explanation. In addition to the interactive version of the multi-media presentation, a non-interactive version was also made which is suitable for lectures or conference presentation. This version lasts approximately 25 minutes. Approximately 100 CD's of this work were made and are being distributed to various laboratories. A copy of the CD is available on request.}, language = {en} } @misc{RichterRiesVollstaedtetal.2000, author = {Richter, Asta and Ries, Ronald and Vollst{\"a}dt, Heiner and Recht, Heidrun}, title = {Konventionelle und neue Kohlenstofformen in ihrer modernen Anwendung}, series = {Wissenschaftliche Beitr{\"a}ge 1/2000}, volume = {5}, journal = {Wissenschaftliche Beitr{\"a}ge 1/2000}, number = {1}, issn = {0949-8214}, doi = {10.15771/0949-8214_2000_1_5}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-7270}, pages = {39 -- 44}, year = {2000}, abstract = {Diamanten kommen in der Natur vor und werden technisch {\"u}ber die Hochdruck-Hochtemperatur-Synthese erzeugt oder als polykristalline Schicht durch chemische Gasphasenabscheidung aus einem Kohlenwasserstoffplasma abgeschieden. Mit der Verarbeitung von Diamantk{\"o}rnern in Verbundwerkstoffen werden neue leistungsf{\"a}hige Schneid- und Polierwerkzeuge entwiCkelt. Diamantbeschichtungen oder Diamantkeramiken erm{\"o}glichen die Herstellung von d{\"u}nnen Schneidwerkzeugen und Anwendungen in Elektronik und Optik mit extremer Belastbarkeit. Fullerene, Nanor{\"o}hrchen und Zwiebelstrukturen aus Kohlenstoff haben sich seit ihrer Entdeckung im Jahre 1985 zu einem eigenst{\"a}ndigen Forschungsgebiet entwickelt und besitzen außergew{\"o}hnliche mechanische, optische und elektronische Eigenschaften, die sie f{\"u}r unterschiedlichste Anwendungen pr{\"a}destinieren.}, language = {de} } @misc{RichterBrzezinka1995, author = {Richter, Asta and Brzezinka, Klaus-Werner}, title = {Thin Film Deposition and Modification of Fullerenes by Laser Radiation}, series = {Wissenschaftliche Beitr{\"a}ge 1/1995}, volume = {1}, journal = {Wissenschaftliche Beitr{\"a}ge 1/1995}, number = {1}, issn = {0949-8214}, doi = {10.15771/0949-8214_1995_17}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-8118}, pages = {100 -- 103}, year = {1995}, abstract = {Laser ablation from solid fullerene pellet and textured graphite targets has been probed for deposition of thin fullerite and diamond-like carbon (DLC) films by means of a pulsed C02 laser. Ablation of fullerene material does not yield fullerite films, but results in amorphous pregraphitic carbon structures. At very low laser flux structural transformations are observed with increasing exposure time. These thermal effects cannot completely decompose the fullerenes without increase of the laser power density. Thermal evaporation is a suitable method to deposite fullerite fllms of high quality, thus epitaxial fullerite films are grown on mica. Sandwich C60/DLC structures are produced by laser deposition which show a sharp interface as can be deduced from the superposition of the characteristic Raman spectra of the fullerite and the DLC.}, language = {en} } @misc{Richter1998, author = {Richter, Asta}, title = {"Computersimulation \& Computergraphik" : Sommerschule vom 22.-26. September 1997 an der TFH Wildau}, series = {Wissenschaftliche Beitr{\"a}ge 2/1998}, volume = {4}, journal = {Wissenschaftliche Beitr{\"a}ge 2/1998}, number = {2}, issn = {0949-8214}, doi = {10.15771/0949-8214_1998_2_18}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-7626}, pages = {95 -- 97}, year = {1998}, abstract = {Ziel der Sommerschule "Computersimulation \& Computergraphik" war es, in einem Piloprojekt Kontakte, Wissensaustausch und Vernetzung zwischen verschiedenen Fachdisziplinen {\"u}ber gemeinsam genutzte moderne Medien und Computertechniken zu erreichen. Gleichzeitig wurden praktische Fertigkeiten f{\"u}r die Computersimulation und Computergraphik vermittelt und interessante Anwendungen in Technik und Wirtschaft demonstriert. Es wurde w{\"a}hrend dieser Woche auf anschauliche und praktische Weise anhand verschiedener Softwarepakete eine Einf{\"u}hrung in die komplexe Thematik gegeben und gezeigt, wie Visualisierung auf PCs und im Internet realisiert werden kann.}, language = {de} } @misc{RichterChenKoegleretal.2011, author = {Richter, Asta and Chen, Chun-Liang and K{\"o}gler, Reinhard and Talut, Georg}, title = {Irradiation effects in nanostructured FeCrAl oxide dispersion strengthened steel}, series = {Wissenschaftliche Beitr{\"a}ge 2011}, volume = {15}, journal = {Wissenschaftliche Beitr{\"a}ge 2011}, issn = {0949-8214}, doi = {10.15771/0949-8214_2011_1_10}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus-1112}, pages = {73 -- 79}, year = {2011}, abstract = {Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y-Al-O nanoparticles, high dislocation densities and fine grains. The material contains nanoparticles with an average diameter of 21 nm. Irradiation of these alloys was performed with a dual beam irradiation of 2.5 MeV Fe+/31 dpa and 350 keV He+/18 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. Additionally to structural changes, the effect of the irradiation generated defects on the mechanical properties of the ODS is investigated by nanoindentation. A clear hardness increase in the irradiated area is observed, which reaches a maximum at a close surface region. This feature is attributed to synergistic effects between the displacement damage and He implantation resulting in He filled vacancies}, language = {en} } @misc{WolfRiesNowickietal.2002, author = {Wolf, Bodo and Ries, Ronald and Nowicki, Marek and Richter, Asta}, title = {Tiefenregistrierende Nanoh{\"a}rtemessung - Verfahren, Beispiele und Anwendungsm{\"o}glichkeiten}, series = {Wissenschaftliche Beitr{\"a}ge 2002}, volume = {7}, journal = {Wissenschaftliche Beitr{\"a}ge 2002}, issn = {0949-8214}, doi = {10.15771/0949-8214_2002_17}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-6977}, pages = {96 -- 104}, year = {2002}, abstract = {Die tiefenregistrierende Nanoh{\"a}rtemessung hat sich in den letzten 10 Jahren zu einer Standardmethode der nanomechanischen Pr{\"u}fung entwickelt. Einerseits erschließt sie Strukturgr{\"o}ßen von 10 nm bis 1 μm Abmessung, andererseits liefert sie aber auch deutlich mehr Informationen als die klassische H{\"a}rtepr{\"u}fung. In der Arbeit wird die Methode der tiefenregistrierenden H{\"a}rtepr{\"u}fung aus der Sicht der technischen Realisierung, der Auswertung der Kraft-Tiefen-Kurven sowie der Interpretation der Ergebnisse dargestellt. Am Beispiel der Photoplastizit{\"a}t wird eine in situ-Modifizierung der mechanischen Eigenschaften vorgestellt, d. h. die H{\"a}rte ver{\"a}ndert sich reversibel durch Lichteinwirkung w{\"a}hrend der Messung. Ionenimplantation und UV-Exposition sind irreversible Methoden der Variation mechanischer Eigenschaften. Hier liefert der Vergleich von Kraft-Tiefe-Kurven vor und nach der Behandlung wertvolle Informationen {\"u}ber das Materialverhalten.}, language = {de} } @misc{RichterSmith1996, author = {Richter, Asta and Smith, Roger}, title = {Surface Growth Modes analysed with Modern Microscopic and Computing Techniques}, series = {Wissenschaftliche Beitr{\"a}ge 1/1996}, volume = {2}, journal = {Wissenschaftliche Beitr{\"a}ge 1/1996}, number = {1}, issn = {0949-8214}, doi = {10.15771/0949-8214_1996_15}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-8258}, pages = {72 -- 78}, year = {1996}, abstract = {It is demonstrated how new microscopes with atomic resolution in combination with modern fast computers and computational techniques can be used in a complementary way in the analysis and explanation of crystal growth on surfaces. Examples are given of spiral formation, fractal growth, fullerene formation and the growth of C60 films.}, language = {en} } @misc{RichterErinski2001, author = {Richter, Asta and Erinski, Dobri}, title = {Qualit{\"a}tsanforderungen bei der Laserbearbeitung metallischer Pr{\"a}zisionsfolien}, series = {Wissenschaftliche Beitr{\"a}ge 2001}, volume = {6}, journal = {Wissenschaftliche Beitr{\"a}ge 2001}, issn = {0949-8214}, doi = {10.15771/0949-8214_2001_28}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9103}, pages = {173 -- 181}, year = {2001}, abstract = {Metallpr{\"a}zisionsfolien finden eine immer breitere Anwendung in vielen Bereichen der modernen Fertigung. Materialst{\"a}rken von 5μm bis 300μm sind f{\"u}r ein breites Spektrum von Anwendungen interessant. Dabei werden hohe Qualit{\"a}tsanforderungen gestellt: Maßtoleranzen im Bereich von wenigen Mikrometern, gratarme Konturen und beeintr{\"a}chtigungsfreie Funktionsoberfl{\"a}chen. Die mehrlagige Bearbeitung flacher Werkst{\"u}cke bringt beachtliche Vorteile, u. a. gratarme Schnittkanten h{\"o}chster Qualit{\"a}t. In diesem Fall werden mehrlagige Folienpakete gleichzeitig aufgespannt und gelasert. Die gezielte Anwendung von Haltefolien stabilisiert das Folienpaket im Gasstrom und erh{\"o}ht somit die Fertigungsqualit{\"a}t. Um die Trennung der Folienlagen zu erm{\"o}glichen und um die angestrebte hohe Oberfl{\"a}chenqualit{\"a}t zu erreichen, sind geeignete Trennmittel zu verwenden.}, language = {de} } @misc{RichterWildenauerRies1997, author = {Richter, Asta and Wildenauer, Franz-Xaver and Ries, Ronald}, title = {Untersuchung von Biofilmen mit dem Rasterkraftmikroskop}, series = {Wissenschaftliche Beitr{\"a}ge 1/1997}, volume = {3}, journal = {Wissenschaftliche Beitr{\"a}ge 1/1997}, number = {1}, issn = {0949-8214}, doi = {10.15771/0949-8214_1997_12}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9125}, pages = {63 -- 68}, year = {1997}, abstract = {Technische Prozesse k{\"o}nnen erheblich durch Biofilme beeinflußt werden und spielen in weiten Bereichen der Technik und Biotechnologie eine große Rolle. Ein zentrales Problem beim Einsatz von Werkstoffen in biologischen Systemen ist die Ansiedlung von Zellen und deren Stoffwechselprodukten auf Festk{\"o}rperoberfl{\"a}chen. Erst hiervon gehen alle nachfolgenden Reaktionen aus, wie Kontamination von Implantaten und medizinischen Ger{\"a}ten, Biokorrosion und die Bildung von Biofilmen in technischen Ger{\"a}ten. Die in der Biotechnologie eingesetzten Werkstoffe m{\"u}ssen bestimmten technischen und biologischen Forderungen gen{\"u}gen. Die Kl{\"a}rung der Adh{\"a}sionsmechanismen der Bakterien auf unterschiedlichen Werkstoffoberfl{\"a}chen und des sich aus einem ersten Zellhaufen entwickelnden Biofilms sowie die Reaktionen und die Transportmechanismen an und in ihm sind die Voraussetzung zur Interpretation der Werkstoffsch{\"a}digung und des Zellverhaltens. Neben der konventionellen Licht- und Rasterelektronenmikroskopie steht mit der Raster-Kraft- Mikroskopie (SFM) ein neues Verfahren zur Abbildung von Oberfl{\"a}chen biologischer Systeme mit hoher Aufl{\"o}sung zur Verf{\"u}gung. Ziel der Arbeiten ist es, mit dem SFM Untersuchungen von Biofilmen auf verschiedenen Werkstoffoberfl{\"a}chen durchzuf{\"u}hren. Hierzu ist es notwendig, die Raster-Kraft-Mikroskopie an die Besonderheiten biologischer Strukturen anzupassen. Aufgrund dieser Oberfl{\"a}chenuntersuchungen lassen sich dann geeignete Werkstoffe und Beschichtungen f{\"u}r den Einsatz in biologischen Systemen ausw{\"a}hlen.}, language = {de} } @misc{MueckSoshnikovWolfetal.2003, author = {M{\"u}ck, Marcel and Soshnikov, Alexander and Wolf, Bodo and Richter, Asta}, title = {Vom Indent zum Scratch - Nanomechanische Tests}, series = {Wissenschaftliche Beitr{\"a}ge 2003}, volume = {8}, journal = {Wissenschaftliche Beitr{\"a}ge 2003}, issn = {0949-8214}, doi = {10.15771/0949-8214_2003_1_11}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-3869}, pages = {59 -- 64}, year = {2003}, abstract = {Da Bauteile immer kleiner und Beschichtungen immer d{\"u}nner werden, erlangt die direkte und genaue Bestimmung mechanischer Eigenschaften im Nanobereich immer gr{\"o}ßere Bedeutung. Versteht man die Effekte im Nanobereich, wird es einfacher, auch Effekte im Makrobereich vorherzusagen. Damit bekommen die entsprechenden Messmethoden eine entscheidende Bedeutung bei der Entwicklung der Materialien und Herstellungsmethoden im Hinblick auf optimierte Produkteigenschaften. Aus diesem Grund entwickelte sich jenseits der klassischen mechanischen Pr{\"u}fverfahren, welche in der Makrodimension angesiedelt sind, in den letzten f{\"u}nf Jahren ein neuer Zweig der Werkstoffpr{\"u}fung, der sich mit den Materialeigenschaften im Nanobereich besch{\"a}ftigt. Dies ist von grundlegender Bedeutung f{\"u}r die Nanotechnologie. In diesem Bericht sollen zwei Ger{\"a}te in Bezug zueinander gesetzt werden, die die Messung verschiedener nanomechanischer Eigenschaften erlauben. Dabei handelt es sich um das TriboScope (Hysitron Inc.) als Aufsatz f{\"u}r ein Rasterkraftmikroskop (SFM) und das Nanoscan (Technological Institute for Superhard and Novel Carbon Materials; Troitsk/Russland), dargestellt in den Abbildungen 1 und 2. Diese erm{\"o}glichen die Messung von H{\"a}rte und E-Modul einer Oberfl{\"a}che.}, language = {de} } @misc{GrunerMueckRichter2004, author = {Gruner, Michael and M{\"u}ck, Marcel and Richter, Asta}, title = {Neuartige Diamant-Metall-Verbundfolien zum Feinschleifen von Saphir}, series = {Wissenschaftliche Beitr{\"a}ge 2004}, volume = {9}, journal = {Wissenschaftliche Beitr{\"a}ge 2004}, issn = {0949-8214}, doi = {10.15771/0949-8214_2004_1_4}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-3987}, pages = {20 -- 25}, year = {2004}, abstract = {Das ProInno-Projekt „Feinschleifen von Saphir" (www.tfhwildau.de/mmueck) besch{\"a}ftigt sich mit der Weiterentwicklung eines Verbundwerkstoffes f{\"u}r den Feinschleifprozess. Bei diesem Verbundwerkstoff handelt es sich um Diamantk{\"o}rner, die in einer Kupfer-Zinn-Matrix eingebettet sind. In dem Projekt werden die Wirkungsmechanismen des neuartigen Verbundmaterials genauer untersucht. Mit diesen Erkenntnissen erfolgt eine Optimierung der einzelnen Komponenten und des Mischungsverh{\"a}ltnisses auf praxisbezogene Eigenschaften des Werkstoffes. Es ist geplant, hieraus ein marktf{\"a}higes Produkt zur Oberfl {\"a}chenbearbeitung harter Materialien zu entwickeln.}, language = {de} } @article{DubrovinskaiaDubrovinskyCrichtonetal.2005, author = {Dubrovinskaia, Natalia and Dubrovinsky, Leonid and Crichton, Wilson and Langenhorst, Falko and Richter, Asta}, title = {Aggregated diamond nanorods, the densest and least compressible form of carbon}, series = {Applied Physics Letters}, volume = {87}, journal = {Applied Physics Letters}, number = {8}, issn = {0003-6951}, doi = {10.1063/1.2034101}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-5646}, year = {2005}, abstract = {We report the synthesis of aggregated diamondnanorods (ADNRs) from fullerene C60C60 at 20(1) GPa and 2200  °C using a multianvil apparatus. Individual diamond nanoroads are of 5-20 nm in diameter and longer than 1μm1μm. The x-ray and measured density of ADNRs is ∼0.2\%-0.4\%∼0.2\%-0.4\% higher than that of usual diamond. The extremely high isothermal bulk modulusKT=491(3)GPaKT=491(3)GPa [compare to KT=442(4)GPaKT=442(4)GPa of diamond] was obtained by in situx-ray diffraction study. Thus, ADNRs is the densest among all carbonmaterials and it has the lowest so far experimentally determined compressibility.}, language = {en} } @article{WolfRichter2003, author = {Wolf, Bodo and Richter, Asta}, title = {The concept of differential hardness in depth sensing indentation}, series = {New Journal of Physics}, volume = {5}, journal = {New Journal of Physics}, number = {15}, issn = {1367-2630}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-5657}, pages = {15.1 -- 15.17}, year = {2003}, abstract = {Since in-depth sensing indentation load-depth data of the entire loading-unloading cycle are available, more information than a single hardness value and an elastic modulus can be extracted from the experimental data. The conventional hardness H (h) = F (h)/Ac(h) and the differential hardness Hd(h)=dF/dAc are calculated as continuous functions of depth h and compared to each other in this paper (F: load, Ac: contact area). It turns out that Hd describes the momentary material resistance to deformation, whereas H integrates over deformation states from first tip-sample contact to current penetration h. This difference is particularly important for materials not homogeneous in depth (e.g. layer systems), and for situations where time-dependent external factors influence the momentary deformation resistance. Photoplasticity is considered as an example for the latter.}, language = {en} } @article{OuAnwandKoegleretal.2014, author = {Ou, Xin and Anwand, Wolfgang and K{\"o}gler, Reinhard and Zhou, Hong-Bo and Richter, Asta}, title = {The role of helium implantation induced vacancy defect on hardening of tungsten}, series = {Journal of Applied Physics}, volume = {115}, journal = {Journal of Applied Physics}, number = {12}, issn = {1089-7550}, doi = {10.1063/1.4870234}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-5623}, year = {2014}, abstract = {Vacancy-type defects created by helium implantation in tungsten and their impact on the nano-hardness characteristics were investigated by correlating the results from the positron annihilation spectroscopy and the nano-indentation technique. Helium implantation was performed at room temperature (RT) and at an elevated temperate of 600 °C. Also, the effect of post-annealing of the RT implanted sample was studied. The S parameter characterizing the open volume in the material was found to increase after helium irradiation and is significantly enhanced for the samples thermally treated at 600 °C either by irradiation at high temperature or by post-annealing. Two types of helium-vacancy defects were detected after helium irradiation; small defects with high helium-to-vacancy ratio (low S parameter) for RT irradiation and large defects with low helium-to-vacancy ratio (high S parameter) for thermally treated tungsten. The hardness of the heat treated tungsten coincides with the S parameter, and hence is controlled by the large helium-vacancy defects. The hardness of tungsten irradiated at RT without thermal treatment is dominated by manufacturing related defects such as dislocation loops and impurity clusters and additionally by trapped He atoms from irradiation effects, which enhance hardness. He-stabilized dislocation loops mainly cause the very high hardness values in RT irradiated samples without post-annealing.}, language = {en} } @article{MaierClausiusRichteretal.2021, author = {Maier, Petra and Clausius, Benjamin and Richter, Asta and Bittner, Benjamin and Hort, Norbert and Menze, Roman}, title = {Crack Propagation in As-Extruded and Heat-Treated Mg-Dy-Nd-Zn-Zr Alloy Explained by the Effect of LPSO Structures and Their Micro- and Nanohardness}, series = {Materials}, volume = {14}, journal = {Materials}, number = {13}, publisher = {MDPI}, issn = {1996-1944}, doi = {10.3390/ma14133686}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14194}, year = {2021}, abstract = {The investigation of the crack propagation in as-extruded and heat-treated Mg-Dy-Nd-Zn-Zr alloy with a focus on the interaction of long-period stacking-ordered (LPSO) structures is the aim of this study. Solution heat treatment on a hot extruded Mg-Dy-Nd-Zn-Zr (RESOLOY®) was done to change the initial fine-grained microstructure, consisting of grain boundary blocky LPSO and lamellar LPSO structures within the matrix, into coarser grains of less lamellar and blocky LPSO phases. C-ring compression tests in Ringer solution were used to cause a fracture. Crack initiation and propagation is influenced by twin boundaries and LPSO lamellae. The blocky LPSO phases also clearly hinder crack growth, by increasing the energy to pass either through the phase or along its interface. The microstructural features were characterized by micro- and nanohardness as well as the amount and location of LPSO phases in dependence on the heat treatment condition. By applying nanoindentation, blocky LPSO phases show a higher hardness than the grains with or without lamellar LPSO phases and their hardness decreases with heat treatment time. On the other hand, the matrix increases in hardness by solid solution strengthening. The microstructure consisting of a good balance of grain size, matrix and blocky LPSO phases and twins shows the highest fracture energy.}, language = {en} } @article{SmithChristopherKennyetal.2003, author = {Smith, Roger and Christopher, D. and Kenny, S. D. and Richter, Asta and Wolf, Bodo}, title = {Defect generation and pileup of atoms during nanoindentation of Fe single crystals}, series = {Physical Review B}, volume = {67}, journal = {Physical Review B}, number = {24}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14855}, year = {2003}, abstract = {Complementary large scale molecular-dynamics simulations and experiments have been carried out to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe {110}, {100}, and {111}. The defect formation and motion causes the complex mechanisms of plastic and elastic deformation which is reflected in the pileup patterns. The experimental results show distinct patterns of pileup material which are dependent on the individual crystal faces and the superposition of the stress field of the indenter. The highest pileup around the indenter hole occurs on the {100} surface and the shallowest on {111}. The least symmetric surface is {110} which produces an experimental pileup pattern displaying only twofold symmetry with the axially symmetric indenter. The pyramidal indenter produces an asymmetric pattern which changes as the crystal is rotated with respect to the tip but repeats with threefold rotational symmetry. Material displacement occurs primarily in planes of the {110} family. Pileup is formed by cross slip between planes of the same family which intersect in ⟨111⟩ directions. For the {110} surface, dislocation loops propagate in the four in-plane ⟨111⟩ directions and the two inclined ⟨111⟩ directions. The loops that propagate in the in-plane directions are terminated by edge dislocations at the surface. These transport material away from the tip but cannot produce pileup. The loops that propagate in the inclined direction cross slip and cause the observed pileup. The {100} surface has fourfold rotational symmetry and all the ⟨111⟩ directions are inclined. The dislocation loops propagate in these directions and cross slip readily occurs, leading to a large pileup. The {111} face shows the least pileup which is more spread out over the surface. In this case the dislocation loops propagate in shallow slip planes and do not readily cross slip. Experimentally determined force-depth curves show distinct "pop-ins" which correspond to the formation of dislocations. The contact pressure (nanohardness) is not a constant and increases with decreasing indentation depth. It also changes with crystal face. Calculated force-depth curves match the experimental trend but give estimates of the nanohardness and Young's modulus higher than those values experimentally determined.}, language = {en} } @article{RymarczykCzerwoszRichter2011, author = {Rymarczyk, Joanna and Czerwosz, Elzbieta and Richter, Asta}, title = {Topography and nanomechanical properties of Pd-C films}, series = {Central European Journal of Physics}, volume = {9}, journal = {Central European Journal of Physics}, number = {2}, issn = {2391-5471}, doi = {10.2478/s11534-010-0134-5}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-9649}, pages = {300 -- 306}, year = {2011}, abstract = {Atomic force microscopy (AFM) topographical studies and results of nanoindentation experiment for several palladium-carbon films (Pd-C film) deposited on various substrates and with varying palladium content are presented. Pd-C films were prepared by a physical vapor decomposition (PVD) process and next were modified by a chemical vapor decomposition (CVD) method to obtain carbonaceous porous structure with dispersed palladium nanograins and a variation in roughness. The dependence of film topography on the kind of substrate such as Al2O3, Mo polycrystalline foil and fused silica was studied by AFM. Nanomechanical properties such as hardness and the reduced indentation modulus were determined by nanoindentation. A comparison of these values for films with different Pd content deposited on various substrates is presented.}, language = {en} } @unpublished{RichterAnwandChenetal.2017, author = {Richter, Asta and Anwand, Wolfgang and Chen, Chun-Liang and B{\"o}ttger, Roman}, title = {Evaluation of defect formation in helium irradiated Y2O3 doped W-Ti alloys by positron annihilation and nanoindentation}, series = {Journal of Nuclear Materials}, journal = {Journal of Nuclear Materials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-10048}, year = {2017}, abstract = {Helium implanted tungsten-titanium ODS alloys are investigated using positron annihilation spectroscopy and nanoindentation. Titanium reduces the brittleness of the tungsten alloy, which is manufactured by mechanical alloying. The addition of Y2O3 nanoparticles increases the mechanical properties at elevated temperature and enhances irradiation resistance. Helium ion implantation was applied to simulate irradiation effects on these materials. The irradiation was performed using a 500 kV He ion implanter at fluences around 5 × 1015 cm-2 for a series of samples both at room temperature and at 600 °C. The microstructure and mechanical properties of the pristine and irradiated W-Ti-ODS alloy are compared with respect to the titanium and Y2O3 content. Radiation damage is studied by positron annihilation spectroscopy analyzing the lifetime and the Doppler broadening. Three types of helium-vacancy defects were detected after helium irradiation in the W-Ti-ODS alloy: small defects with high helium-to-vacancy ratio (low S parameter) for room temperature irradiation, larger open volume defects with low helium-to-vacancy ratio (high S parameter) at the surface and He-vacancy complexes pinned at nanoparticles deeper in the material for implantation at 600 °C. Defect induced hardness was studied by nanoindentation. A drastic hardness increase is observed after He ion irradiation both for room temperature and elevated irradiation temperature of 600 °C. The Ti alloyed tungsten-ODS is more affected by the hardness increase after irradiation compared to the pure W-ODS alloy.}, language = {en} } @inproceedings{RichterRies1999, author = {Richter, Asta and Ries, Ronald}, title = {Mechanical properties of fullerite and diamondlike carbon films using surface acoustic waves and nanoindentation}, series = {Proc. SPIE 3725, International Conference on Solid State Crystals '98: Epilayers and Heterostructures in Optoelectronics and Semiconductor Technology, (8 April 1999)}, booktitle = {Proc. SPIE 3725, International Conference on Solid State Crystals '98: Epilayers and Heterostructures in Optoelectronics and Semiconductor Technology, (8 April 1999)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14840}, pages = {94 -- 101}, year = {1999}, abstract = {C60 and amorphous diamond-like carbon (DLC) films have been grown by thermal evaporation and laser ablation techniques at different substrate temperatures and on various substrates. The elastic modulus and the hardness of the films have been investigated by surface acoustic waves and nanoindentation. Both methods are completely new and designed for investigations of very thin films. For homogeneous C60 films the Young's modulus was found to be 14 GPa and the Poisson's ratio of 0.2. The measured nanohardness of 167 MPa corresponds with the microhardness value of 130 MPa. There is a correlation between deposition techniques and hardness as well as Young's modulus for DLC films.}, language = {en} } @inproceedings{RymarczykCzerwoszRichter2009, author = {Rymarczyk, Joanna and Czerwosz, Elzbieta and Richter, Asta}, title = {FEM modelling of nanoindentation experiment for nanostructural Me-carbon film (Me = Pd, Ni)}, series = {Proc. SPIE 7502, Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2009}, booktitle = {Proc. SPIE 7502, Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2009}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-14837}, year = {2009}, abstract = {This work presents a comparison of numerical simulation and experimental data for nanoindentation studies of nanostructural Me-carbonaceous films (where Me = Pd or Ni). Films containing palladium or nickel nanograins embedded in a carbonaceous matrix were synthesized by a PVD process. The topography of films was characterized by AFM and the mechanical properties were analyzed by nanoindentation. Nanoindentation experiments were performed with a tip made of diamond with a shape of a 90° cube corner three-sided pyramid in a Hysitron Triboscope. The finite element method (FEM) was used to simulate the indentation experiment in such heterogeneous material on nanoscale.}, language = {en} }