Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity

Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implication in device applications. Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. The ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena, and engineering multifunctional oxide devices.Comment: 35 pages, Main text and the supplementary information combine

Experimental Study on the Acellular Demal Matrix Graft for the Root Coverage in Dog

Mucogingival surgery is a plastic surgical procedure designed to correct defects in the morphology, position, and dimensions of the gingiva surrounding the teeth. Many surgical techniques have been reported in mucogingival surgery. Since these procedures also include the soft tissue esthetic approach, the term periodontal plastic surgery has been proposed to be more appropriate.1 Root coverage is a procedure that falls with this definition, and it has attracted more interest than others

취성 박막에서의 주기적 균열 형성

학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2015. 8. 박윤.Crack, failure of materials, is recognized as separation pattern of materials. Throughout human history we have struggled to avoid and prevent this phenomenon because crack occurrence inherently means that objects already lost its original integrity and functionality. Moreover microscopic flaws placed in the materials body will easily alter its growth characteristic. So by their catastrophic growth nature, crack patterns are usually chaotic and unpredictable. But Mother Nature always has some exceptions. These periodic or ordered crack patterns are quite distinctive because not only for their rarity but also for unexplained mechanism in most of cases. Here simple but noble generation of ordered crack from thin film system is demonstrated by using conventional semiconductor fabrication techniques and its governing conditions of periodic pattern are discussed. Strong confinement of thin film crack and arbitrary steering of its propagation are realized by inserting thin metallic layer, thin polymeric layer and even atomically thin graphene layer in between substrate and brittle thin film. This thin interlayer-mediated controllability comes from local debonding of brittle medium or effective analogues of debonding due to relatively weak adhesion or elastic softness of interlayer. Following experiments and numerical calculation using Extended Finite Element Method (XFEM) from our study reveal that this wavy crack is intrinsically analogous to so called brittle adhesive crack. Previous studies of periodic cracks such as metallic insertion layer, self debonding sol-gel film, and even drying colloidal film, could be explained by similar mechanism. This finding could provide simple analogy on various ordered periodic crack systems existing in nature. And also this simple but noble method to control crack path could lead to the development of new concept of nano fabrication techniques.1 Introduction 1 1.1 Overview 1 1.1.1 Motivation 1 1.1.2 Overview of text 2 1.2 Brittle and ductile behaviors 3 1.3 Fracture dynamics 5 1.3.1 Griffiths energy balance approach 5 1.3.2 Fracture modes 6 1.3.3 Stress intensity factor 7 1.3.4 Fracture toughness 8 1.3.5 Linear fracture dynamics 9 1.4 Crack path prediction in mixed mode 10 1.5 Extended finite element method (XFEM) 10 1.6 Periodic crack in nature: literature review 11 1.6.1 Quenched glass case 11 1.6.2 Thin film periodic crack 13 2 Periodic crack generation by metal insertion layer 15 2.1 Motivation 15 2.2 Sample fabrication process 18 2.2.1 Cleaning and preparation of wafer 18 2.2.2 Lithography for deposition and lift off 19 2.2.3 Deposition of metal and SiO2 20 2.2.4 Spin on glass 21 2.2.5 Annealing process 21 2.3 Crack initiation: flaw, defect 22 2.3.1 FIB (Focused Ion Beam) milled notch 22 2.3.2 Metal pattern 23 2.3.3 Scratch 24 2.4 Crack path steering in curved way 26 2.5 Line density 28 2.6 Minimum width of crack track 30 2.7 Termination 31 2.8 Cross section inspection 33 2.9 Track width dependence of period 34 2.10 Discussion 35 3 Various insertion layers 36 3.1 Overview 36 3.2 Claim from previous study and thermal expansion stress scenario 36 3.3 Cavity sample 38 3.4 Polymer sample 40 3.5 Graphene sample 41 3.6 Crack steering with additional third (top) layer: stiffness rules 42 3.7 Discussion 44 4 Numerical approach for crack path prediction 47 4.1 Overview 47 4.2 Brittle adhesive crack case: similarity and implication 48 4.3 Numerical approach for cavity sample 49 4.4 Periodic mechanism 54 5 Controlled periodic crack system as application 55 5.1 Overview 55 5.2 Controlled nano channel: THz transmission 56 5.3 Nanowire generation template 58 5.4 Controlled cracking as material toughening tool 60 5.5 Discussion 62 6 Conclusion 63 6.1 Summary 63 6.2 Periodic thin film crack 64 6.3 Implication to other systems 65 6.4 Future work 67Docto

Flexibilization through Metropolis: The Case of Postfordist Seoul, Korea

Predicated upon a regulationist reformulation of postfordism, this paper attempts to explore the political economy of Korea's recent industrial restructuring which has led to a postfordist-like regime of accumulation. To do this, this study takes the Seoul metropolis as a case study. The underlying assumption is that the postfordism of Korea obtains its specificity through the metropolis of Seoul where a host of enabling conditions for postfordist regulation are concentrated. By looking into the process of Seoul becoming the locale of Korean postfordism, a more serious concern is to draw in the consequences which the metropolitanization of postfordism creates for urban society. It is assumed that in the course of postfordist urbanization Seoul's social and political life has been to a great extent enriched, but at the same time is deeply 'schizophrenic' due to its being exposed to two contrasting ultra (or post) modern and premodern socio-economic dynamics simultaneously. This urban schizophrenia (or bipolarity, in more common terms) derives from the processes in which Korea's postfordism operates within the context of 'semi-peripheral capitalist economy'. Copyright Joint Editors and Blackwell Publishers Ltd 1997.

Mitochondrial-Targeted Two-Photon Fluorescent Probes for Zinc Ions, H2O2, and Thiols in Living Tissues

Mitochondria provide the energy of the cells and are the primary site of oxygen consumption and the major source of reactive oxygen species. In mitochondria, metal ions and glutathione play vital roles in maintaining their structure and the redox environment. To understand their roles in mitochondria, it is crucial to monitor each of these chemical species in the mitochondria at the cell, tissue, and organism levels. An ideal tool for such purpose is the use of two-photon microscopy (TPM). Until recently, however, there has been no report on the two-photon (TP) probes suitable for such applications. In this paper, we summarize the mitochondria-targeted TP probes for Zn2+, H2O2, and thiols, as well as their bioimaging applications