Temperature dependence of the optical gap of diamond-like carbon films investigated by a piezoelectric photothermal spectroscopy

Temperature dependences of the optical gap of diamond-like carbon （DLC） films were investigated by using a piezoelectric photothermal （PPT） spectroscopy, that detects the nonradiative transition of photoexcited electrons. Since the PPT signal intensity is expected to be proportional to its optical absorption coefficient, the optical gap was estimated by a Tauc plot. The temperature coefficient of the optical gap energy was found to be very small compared with that of other semiconductor such as Si. This result implies that the device performance is expected to be stable by temperature change and the DLC films are excellent as the next generation solar cells materials

Temperature dependence of the optical gap of diamond-like carbon films investigated by a piezoelectric photothermal spectroscopy

AbstractTemperature dependences of the optical gap of diamond-like carbon (DLC) films were investigated by using a piezoelectric photothermal (PPT) spectroscopy, that detects the nonradiative transition of photoexcited electrons. Since the PPT signal intensity is expected to be proportional to its optical absorption coefficient, the optical gap was estimated by a Tauc plot. The temperature coefficient of the optical gap energy was found to be very small compared with that of other semiconductor such as Si. This result implies that the device performance is expected to be stable by temperature change and the DLC films are excellent as the next generation solar cells materials

A Review on Mechanics and Mechanical Properties of 2D Materials - Graphene and Beyond

Since the first successful synthesis of graphene just over a decade ago, a variety of two-dimensional (2D) materials (e.g., transition metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered. Among the many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both experimentally and theoretically. The coupling between the mechanical and other physical properties (thermal, electronic, optical) is also of great interest in exploring novel applications, where mechanics has to be combined with condensed matter physics to establish a scalable theoretical framework. Moreover, mechanical interactions between 2D materials and various substrate materials are essential for integrated device applications of 2D materials, for which the mechanics of interfaces (adhesion and friction) has to be developed for the 2D materials. Here we review recent theoretical and experimental works related to mechanics and mechanical properties of 2D materials. While graphene is the most studied 2D material to date, we expect continual growth of interest in the mechanics of other 2D materials beyond graphene

Photothermal Deflection Spectroscopy of Amorphous, Nanostructured and Nanocomposite Thin Films

The energy needs of the modern world are growing day by day, while sources of non-renewable fossil fuels are limited, so there is a need to efficiently use the existing resources and explore renewable energy sources. In order to harvest, store and efficiently utilize renewable energy, we need to explore new materials and improve the performance of existing ones. Among others, hydrogenated amorphous silicon (a-Si:H) with high optical absorption in the visible range of electromagnetic spectrum, is a low cost material for solar cells. But the efficiency of such solar cells is comparatively low because of intrinsic defects associated with its material structure and its degradation under illumination. Also the optical transparency and electrical conductivity of the window electrode are important factors that affect solar cell performance. Transparent and conducting carbon-based films (TCCF) have great potential to be used as electrodes in optoelectronics due to their transparency and high electrical conductivity. TCCF are not yet as competitive with indium-tin oxide (ITO) as transparent electrical conductors. In order to improve the efficiency of such materials, one needs to understand and curtail the defects for better cell performance. This study is an experimental investigation of the optical and thermal properties of solar-grade materials and nanocomposites using photothermal deflection spectroscopy (PDS). PDS is a non-contact experimental technique based on the mirage effect. An automated PDS setup was assembled that is capable of measuring weak optical absorptions and thermal properties of thin film samples. A complementary setup, the 3-omega method, for thermal conductivity measurement was also built and used to compare the results obtained by the two methods. However, our primary focus was on the PDS setup as a non-contact, non-destructive and sensitive technique. Also the role of convection heat transfer in PDS in the presence of highly thermally conducting nanoparticles in photothermal fluid is investigated. The defects formation in a-Si:H thin films under light soaking was investigated and a model is proposed for self-repair of defects in thin films. Also optical, electrical and thermal properties of a set of graphene/graphene-like platelet thin films were investigated. A relationship between the electrical and thermal conductivities of these samples was established that could be applied to a large class of graphene-based thin films. The trade-off between electrical and thermal properties, along with transparency, will help the design of applications where electrical conductance, thermal management and transparency are required

Femtosecond laser techniques for fabrication of QTF and tailoring of its optical properties for gas sensing applications

This Ph.D. thesis reports on the development of femtosecond (fs) laser machining processes fabrication of QTF and tailoring of its optical properties for gas sensing applications . Pursuing such a strategy would allow for the exploitation of many advantages of fs-laser processing such high precision and quality of processing, low environmental impact and flexible production processes. The issue related to the transparency of quartz in the 1 to 5 μm range has been addressed by developing a blackening approach for quartz crystals. This strategy consists in the laser surface texturing of the target material, in order to enhance its optical absorption in a particular wavelength range. In particular, a femtosecond pulsed laser was used to create matrices-like patterns on the surfaces of quartz crystal wafers. These matrix patterns were designed to reduce and flatten the quartz transmittance across the wavelength range of interest. Finally, a proof of concept was demonstrated by implementing two laser-textured QTF as photodetector in a LITES setup for detection of two water vapor absorption features at 1.39 μm and 7.38 μm. An environmental-sustainable method for QTF prototype production was developed through direct laser cut of quartz wafers exploiting femtosecond laser ablation. This activity was performed in collaboration with the FOLAS Lab research group in their facilities at the Faculty of Mechanical Engineering at University of Ljubljana. This method exploited a milling channel approach to cut through the complete depth of the target wafers. This process was characterized as function of the femtosecond laser working parameters and was then employed for the cut of actual QTFs. The resonant properties of the laser-cut devices were evaluated experimentally by means of photoacoustic excitation and they were found to be comparable both to their simulated behavior and to the performances of standard QTFs, thus confirming the validity of this manufacturing technique

NIR-emissive Alkynylplatinum(II) Terpyridyl Complex as a turn-on selective probe for heparin quantification by induced helical self-assembly behaviour

The extent of self-assembly viametal–metal and π-π stacking interactions, induced by the polyanionic biopolymers, enables the class of alkynylplatinum(II) terpyridyl complexes to be applicable for the sensing of important biomacromolecules through the monitoring of spectral changes. Strong demand arises for the design of selective and practical detection techniques for the quantification of heparin, a highly negative-charged polysaccharidethat can function as anticoagulant, due to the prevention of hemorrhagic complications upon overdose usage.Aconvenient sensing protocol for the detection of UFH and LMWH, two common forms of heparins in clinical use, in buffer and biological medium has been demonstrated with the spectral changes associated with the induced self-assembly of a NIR-emissive platinum(II) complex. The detection range has been demonstrated to cover clinical dosage levels and the structurally similar analogues can be effectively differentiated based on their anionic charge density and the formation of supramolecular helical assembly of the platinum(II) complex with them ...postprin

Report / Institute für Physik

The 2014 Report of the Physics Institutes of the Universität Leipzig presents a hopefully interesting overview of our research activities in the past year. It is also testimony of our scientific interaction with colleagues and partners worldwide. We are grateful to our guests for enriching our academic year with their contributions in the colloquium and within the work groups. The open full professorship in the Institute for Experimental Physics I has been filled with an outstanding candidate. We could attract Prof. Ralf Seidel from the University of Münster. He is an expert in molecular biophysics that complements the existing strength in cellular biophysics. Prof. Hollands could fill all positions of his ERC Starting Grant, so that the work on the project \"Quantum Fields and Curvature – Novel Constructive Approach via Operator Product Expansion\" is now running at full pace. Within the Horizon 2020 project LOMID \"Large Cost-effective OLED Microdisplays and their Applications\" (2015-2017) with eight European partners including industry the semiconductor physics group contributes with transparent oxide devices. A joint laboratory for single ion implantation was established between the Leibniz-Institute for Surface Modification (IOM) and the university under the guidance of Profs. Rauschenbach and Meijer. The EU IRSES Network DIONICOS \"Dynamics of and in Complex Systems\", a consortium of 6 European and 12 non-European partners, including sites in England, France and Germany as well as in Russia, Ukraine, India, the United States and Venezuela, started in February 2014. In the next four years the Leipzig node headed by Prof. Janke will profit from the numerous international contacts this network provides. With a joint project, Prof. Kroy and Prof. Cichos participate in the newly established priority research programme SPP 1726 \"Microswimmers\", which started with a kick-off workshop in October 2014. In 2014 the International Graduate College \"Statistical Physics of Complex Systems\" run by the computational physics group has commenced its third 3-years granting period funded by Deutsch-Französische Hochschule (DFH-UFA). Besides the main partner Université de Lorraine in Nancy, France, now also Coventry University, UK, and the Institute for Condensed Matter Physis of the National Academy of Sciences of Ukraine in Lviv, Ukraine, participate as associated partners. During the last week of September the TCO2014 conference \"Transparent Conductive Oxides – Fundamentals and Applications\" took place in honor of the 100th anniversary of the death of Prof. Dr. KarlW. Bädeker. In 1907 Karl Bädeker had discovered transparent conductive materials and oxides in Leipzig. About a hundred participants joined for many invited talks from international experts, intense discussion and new cooperations. At the end of November the by now traditional 15th nternational Workshop on Recent Developments in Computational Physics \"CompPhys14\" organized by Prof. Janke took place in Leipzig. Around 60 scientists from over 10 different countries exchanged ideas and discussed recent progress in several fields of computational physics. Work has successfully continued in the Centers of Excellence (Sonderforschungsbereiche) SFB 762 \"Functionality ofOxide Interfaces\" and SFB TRR 102 \"Polymers under Multiple Constraints: Restricted and Controlled Molecular Order and Mobility\" (just renewed for 2015-2019). Our activities and success are only possible with the generous support fromvarious funding agencies for which we are very grateful and which is individually acknowledged in the brief reports