Osaka University

About: Osaka University is a education organization based out in Osaka, Japan. It is known for research contribution in the topics: Laser & Population. The organization has 83778 authors who have published 185669 publications receiving 5158122 citations. The organization is also known as: Ōsaka daigaku.

Chemical identification of individual surface atoms by atomic force microscopy

Abstract: Dynamic force microscopy, which works by detecting the interaction force between the oscillating tip of an atomic force microscope (AFM) and a surface, has been refined to the extent that it can achieve true atomic resolution of insulator, semiconductor and metal surfaces. In a landmark publication in this issue this technique has been used to perform the chemical identification of individual atoms in a multi-element system. The method involves precise quantification of short-range chemical forces between the probed atoms and the AFM tip, and provides a robust and general recognition tool suitable for both cryogenic and room temperature environments. The cover shows a topographic image of a surface alloy made up of silicon (red), tin (blue), and lead atoms (green) in equal proportions on a silicon (111) substrate. This atomic identification method is relevant to a wide range of research areas such as catalysis, materials science and semiconductor technology. Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with atomic resolution1,2. At cryogenic temperatures, scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed molecules3,4,5 and of the electronic properties of magnetic impurity atoms6,7, thereby allowing chemical identification. But in many instances, and particularly for insulating systems, determining the exact chemical composition of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true atomic resolution8,9,10, by detecting and precisely measuring11,12,13 the short-range forces that arise with the onset of chemical bonding between the tip and surface atoms14,15 and that depend sensitively on the chemical identity of the atoms involved. Here we report precise measurements of such short-range chemical forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows us to use the chemical force measurements as the basis for atomic recognition, even at room temperature. We illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the three constituent atomic species silicon, tin and lead, even though these exhibit very similar chemical properties and identical surface position preferences that render any discrimination attempt based on topographic measurements impossible.

Analysis of Cytokinin Mutants and Regulation of Cytokinin Metabolic Genes Reveals Important Regulatory Roles of Cytokinins in Drought, Salt and Abscisic Acid Responses, and Abscisic Acid Biosynthesis

Abstract: Cytokinins (CKs) regulate plant growth and development via a complex network of CK signaling. Here, we perform functional analyses with CK-deficient plants to provide direct evidence that CKs negatively regulate salt and drought stress signaling. All CK-deficient plants with reduced levels of various CKs exhibited a strong stress-tolerant phenotype that was associated with increased cell membrane integrity and abscisic acid (ABA) hypersensitivity rather than stomatal density and ABA-mediated stomatal closure. Expression of the Arabidopsis thaliana ISOPENTENYL-TRANSFERASE genes involved in the biosynthesis of bioactive CKs and the majority of the Arabidopsis CYTOKININ OXIDASES/DEHYDROGENASES genes was repressed by stress and ABA treatments, leading to a decrease in biologically active CK contents. These results demonstrate a novel mechanism for survival under abiotic stress conditions via the homeostatic regulation of steady state CK levels. Additionally, under normal conditions, although CK deficiency increased the sensitivity of plants to exogenous ABA, it caused a downregulation of key ABA biosynthetic genes, leading to a significant reduction in endogenous ABA levels in CK-deficient plants relative to the wild type. Taken together, this study provides direct evidence that mutual regulation mechanisms exist between the CK and ABA metabolism and signals underlying different processes regulating plant adaptation to stressors as well as plant growth and development.