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High-Resolution Label-Free Studies of Molecular Distribution and Orientation in Ultrathin, Multicomponent Model Membranes with Infrared Nano-Spectroscopy AFM-IR
摘要： Biological membranes are undoubtedly very interesting systems. Unfortunately, their analysis is very complicated and therefore simplified artificial models, like Langmuir monolayers, are frequently applied. In this work a novel method of label-free monomolecular films analysis based on infrared nano-spectroscopy (AFM-IR) is presented. In order to verify applicability of this approach well-defined referential system of sphingomyelin (SM), cholesterol (Chol) and cyclosporin A (CsA) is applied. AFM-IR method allows to directly and chemoselectively map the distribution of components in model lipid membranes. Additionally the orientation of Chol and SM molecules in the monolayer is determined by application of two perpendicular infrared laser polarizations. This paper is the first report of using AFM-IR to analyze LB films with extremely high sensitivity.
关键词： phase separation,lipid rafts,Langmuir-Blodgett films,Cyclosporin A,AFM-IR
更新于2025-09-19 17:15:36
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Deposition of p-type Al doped PbS thin films for heterostructure solar cell device using feasible nebulizer spray pyrolysis technique
摘要： Doping of metal atoms with PbS thin films can make significant influence on the structural and electron transport properties which makes it suitable for photovoltaic and other device applications. The objective of the present work is to study the structural, morphological, optical and electrical properties of PbS:Al thin films as a function of different Al doping percentage. PbS and Al doped PbS thin films were deposited using Nebulizer Spray Pyrolysis (NSP) on soda lime glass substrates by varying Al doping level from 0 wt% to 8 wt%. Polycrystalline nature with face centered cubic crystal structure was noticed for all the prepared films from XRD pattern. The orientation along (200) plane was observed for all the prepared films. From AFM analysis, the observed surface roughness values were considerably decreased on increasing the Al doping concentration. The calculated optical band gap values exhibits increasing trend and shifted from 1.54 eV to 1.66 eV on increasing Al doping concentration. The electrical resistivity value of the PbS:Al thin films were reduced from 3.08 ? 103 to 1.63 ? 103 Ωcm with raise in Al doping level. The solar cell efficiency for FTO/n-CdS/p-PbS:Al structure constructed from 6% of Al doped PbS film was about 0.44%.
关键词： SEM/AFM,Hall effect measurement,PbS:Al structure,UV visible,Solar cell,X-ray diffraction
更新于2025-09-19 17:13:59
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Interface analysis of Ag/na??type Si contacts in na??type PERT solar cells
摘要： To increase efficiencies of bifacial solar cells, emitter, back surface field (BSF), and metal patterns must be optimized. We study the influence of paste volume, through multiple prints, of two silver pastes on the contact formation at the rear side of n-type passivated emitter and rear totally diffused (n-PERT) solar cells with two BSF doping profiles. Differences in fingers' electrical properties were found between pastes. Contact resistivity shows a relative difference of 27.6%, partially explained by changes in the silver crystallites formation at the Ag/Si interface and in the crystallites' penetration depth. Variations in crystallites formation and penetration between pastes can reach 38.4% and 48.8%, respectively. Line resistance shows a difference between pastes, appearing as the main cause of an absolute efficiency difference of 2.9%. Fingers' structural and electrical properties are modified by increasing the paste volume. Microstructure analysis reveals that additional metallic printing does not only increase line cross sectional area but also increases the formation of silver crystallites, which can reach a relative increment of 23.9% between first and second prints. Further printing does not necessarily decrease contact resistivity, but reduces line resistance in up to 94.9%, which results in an absolute efficiency increase of 2.2%. In addition, the higher presence of silver oxide in the finger is related to a higher efficiency in the formation of silver crystallites. Finally, BSF doping has an influence in the open circuit voltage, short circuit current density, and contact resistivity, with differences that can reach 8.7 mV, 0.2 mA/cm2, and 6.1 mΩcm2, respectively, depending on paste and number of prints.
关键词： solar cells,FE-SEM,metallization,XPS,AFM
更新于2025-09-19 17:13:59
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All-optical InAsP/InP nanowire switches integrated in a Si photonic crystal
摘要： We report the successful demonstration of all-optical switching using a sub-wavelength InP/InAsP nanowire integrated in a silicon photonic crystal at telecommunication wavelengths. In this work, we employed two different hybrid nanowire cavities based on an air-trench in photonic crystals. These hybrid cavities have the advantages of both material functionality of III-V material and the low propagation loss of the silicon waveguide. The nanowire induced line-defect photonic crystal cavity shows a Q-factor of 25000, higher than the hybrid systems we previously demonstrated. The switching time is 150 ps, which is among the fastest nanowire switches reported. We found that the switching time was clearly dependent on the Q-factor. From measurements performed while changing pump power, we have estimated the switching energy to be a few hundred femtojoules. This value is lower than that of a reference silicon photonic crystal cavity without a nanowire and an air trench under the same pumping condition. This indicates that the InP/InAsP nanowire integrated in a silicon photonic crystal has potential to contribute to reducing the switching energy.
关键词： all-optical switch,AFM manipulation,nanophotonics,photonic crystal,nanowire,photonic integrated circuits
更新于2025-09-19 17:13:59
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Interplay between electronic and structural transitions in VO <sub/>2</sub> revealed by ellipsometry
摘要： Temperature-dependent spectroscopic ellipsometry measurements, combined with AFM investigations, have been performed to reveal the interplay between the structural and electronic phase transitions during the insulator-to-metal transition in VO2 thin films with different thicknesses. A comprehensive analysis of the macroscopic optical response in the framework of an anisotropic Bruggeman effective medium approximation yields the hysteretic shape evolution of the metallic inclusions and the changes in film roughness due to the structural transitions during a temperature cycle. The authors show that the structural modifications in the material across the transition affect the metallic cluster shape in the vicinity of the percolation threshold, leading to an altered absorption by the localized plasmon resonances. The structural changes are supported by AFM measurements and can be explained by the particular strain present in different films.
关键词： VO2,AFM,localized plasmon resonances,spectroscopic ellipsometry,Bruggeman effective medium approximation,insulator-to-metal transition
更新于2025-09-19 17:13:59
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Stereochemistry controlled supramolecular architectures of novel tetrahydroxy functionalized amphiphilic carbocyanine dye
摘要： The synthesis of novel amphiphilic 5,5',6,6'-tetrachlorobenzimidacarbocyanine (TBC) dye derivatives with amino-propanediol head groups differing in stereochemistry (chiral enantiomers, meso-form, and conformer) is reported. For the achiral meso-form, a new synthetic route towards asymmetric cyanine dyes was established. All compounds form J-aggregates in water whose optical properties were characterized by spectroscopic methods. The supramolecular structure of the aggregates was investigated by cryo-transmission electron microscopy (cryo-TEM), cryo-electron tomography (cryo-ET), and atomic force microscopy (AFM) revealing extended sheet-like aggregates for the chiral enantiomers and nanotubes for the mesomer, respectively, while the conformer forms predominately needle-like crystals. The experiments demonstrate that the aggregation behavior of compounds can be controlled solely by head group stereochemistry which in case of the enantiomers enables formation of extended hydrogen bond chains by the hydroxyl functionalities. In case of the achiral meso-form, however, such chains turned out to be sterically excluded.
关键词： Stereochemistry,cryo-TEM,supramolecular architectures,amphiphilic carbocyanine dye,cryo-ET,J-aggregates,AFM
更新于2025-09-19 17:13:59
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Ambient atmosphere laser-induced local ripening of MoS <sub/>2</sub> nanoparticles
摘要： Transition metal dichalcogenide (TMDC) ultrathin layers have attracted considerable interest in the recent years. Their peculiar functional properties can be exploited in electronics, spintronics, optoelectronics, photonics, energy production, harvesting and storage. The availability of cost-effective, green, and efficient growth processes is of paramount importance and significant effort has been made in the research on various production methodologies. Here we report on a simple laser-based process which allows the direct writing of thin TMDC layers. In detail, by direct exposure to laser irradiation of a dip-coated MoS2 precursor, we obtained a three-dimensional arrangement of MoS2 nanoparticles in the form of platelets with a lateral dimension of about 50 nm and thickness down to bilayers. The characterization was assessed by AFM and Raman spectroscopy. The platelets are formed only in the central region of the laser spot, confirming that the material out of the spot is indeed an unprocessed precursor. By tuning the precursor deposition, we demonstrate the fabrication of MoS2 patterns with designed layer numbers. The proposed approach is highly versatile and can be applied also for the controlled growth of other TMDCs, as proved by the successful generation of WS2 layers.
关键词： Transition metal dichalcogenide,MoS2,direct writing,laser-induced,Raman spectroscopy,AFM
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE Conference on Control Technology and Applications (CCTA) - Hong Kong, China (2019.8.19-2019.8.21)] 2019 IEEE Conference on Control Technology and Applications (CCTA) - Novel Micro Scanning with Integrated Atomic Force Microscope and Confocal Laser Scanning Microscope
摘要： Integrated atomic force microscope (AFM) and confocal laser scanning microscope (CLSM) can quickly obtain the three-dimensional (3-D) surface of the sample in large scanning range and recover the region of interesting (ROI) in nanoscale resolution. However, the traditional cooperative algorithm for integrated microscopes occupies too much scanning time. In this work, we develop a novel cooperative algorithm for the integrated microscopes to reduce scanning time of AFM and achieve higher scanning speed. First, the calibration of the microscopes will be implemented. Next, CLSM starts a large range scan first and then define the region of interesting (ROI) by edge detection. And then, the scan regions of the AFM are arranged based on the ROI and adaptive scanning region method is proposed to reduce the scanning time. Furthermore, variable speed scanning based on the height information obtained from CLSM image is applied to increase the AFM scanning speed. Finally, the scanning images obtained from AFM and CLSM are merged together. A series of experimental results show that proposed cooperative algorithm can save approximately 69.2% of scanning time compared with that obtained by traditional cooperative algorithm.
关键词： Atomic force microscope (AFM),adaptive scanning range,confocal laser scanning microscope (CLSM),regions of interest (ROI),variable speed scanning
更新于2025-09-16 10:30:52
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Improving carrier transport in strontium-doped cuprous oxide thin films prepared by Nebulizer spray pyrolysis for solar cell applications
摘要： Strontium-doped Cu2O thin ?lms of different doping concentrations (0, 3, 5 and 7%) are deposited successfully with the help of Nebulizer spray technique. All the samples were characterized by XRD, AFM, Raman, UV–Vis, photoluminescence and Hall effect, and solar cell ef?ciency is calculated. From the XRD studies, the cubic structural phase of Cu2O is con?rmed. The micrographs of AFM explain that the particles were uniformly distributed on the surface with homogeneous grains. The band gap value ranges from 2.17 to 1.95 eV as the doping concentration increases from 0 to 7%. The PL emission at * 630 nm also con?rms the cuprous oxide phase. The deposited ?lm exhibits p-type conductivity with low resistivity of 0.90 9 102 X cm and high carrier concentration of 22.7 9 1015 cm-3. A heterojunction solar cell of FTO/n-ZnO/p-Sr-doped Cu2O is fabricated, and the power conversion ef?ciency (g) is 0.75% for 7% Sr-doped ?lm.
关键词： Strontium-doped Cu2O,Resistivity and heterojunction solar cell,AFM,Optical studies,Raman
更新于2025-09-16 10:30:52
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Nanoscale chemical mapping of oxygen functional groups on graphene oxide using atomic force microscopy-coupled infrared spectroscopy
摘要： The unambiguous determination of the chemical functionality over graphene oxide (GO) is important to unleash its potential applications. However, the mapping of oxygen functionalities distribution remains to be unequivocally determined because of highly inhomogeneous non-stoichiometric structures and ultra-thin layers of GO. In this study, we report an experimental observation of the spatial distribution of oxygen functional groups on monolayer and multilayer GO using AFM-IR, atomic force microscopy coupled with infrared spectroscopy. Overcoming conventional IR diffraction limit for several micrometers, the novel AFM-IR reaches high spatial resolution (cid:1)20 nm and could detect IR absorption on (cid:1)1 nm thickness of monolayer GO. With nanoscale chemical mapping, the distribution of different oxygen functional groups is distinguished with AFM-IR over the GO surface. It allows us to observe that these oxygen functional groups prefer to sit on the fold areas, in discrete domains and on the edges of GO, which gave more insights into its chemical nature. The determination of the position of functional groups through precise imaging contributes to our understanding of GO structure-properties relations and paves the way for targeted tethering of polymers, biomaterials, and other nanostructures.
关键词： Chemical functionality,AFM-IR,Spatial distribution,Graphene
更新于2025-09-16 10:30:52