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Structural and optical properties of nanoparticles formed by laser ablation of porous silicon in liquids: Perspectives in biophotonics
摘要： The paper discusses the possibility of manufacturing silicon nanoparticles, which are suitable for contrasting biological tissues imaged by optical coherence tomography, by femtosecond laser ablation of porous silicon in various liquids. The manufactured nanoparticles are characterised by average sizes of 87, 112, and 102 nm for cases of ablation in water, ethanol, and liquid nitrogen, respectively, as well as a relatively narrow size distribution, which provides additional advantages for subsequent delivery into biological tissues. Electro chemical etching, which results in the formation of layers of porous silicon, allows the yield of ablation products to be increased several-fold by lowering the ablation threshold, thereby increasing the light scattering efficiency of the prepared suspensions compared with the case of using crystalline silicon as targets. The possibility of obtaining high-contrast images of a biotissue phantom based on an agar gel with embedded nanoparticles is shown. The magnitude of the contrast depends on the liquid used for ablation and correlates with the values of the reduced scattering coefficient of the studied suspensions.
关键词： silicon nanoparticles,laser ablation in liquids,atomic force microscopy,light scattering,optical coherence tomography,spectrophotometry
更新于2025-09-19 17:13:59
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Ink-Jet Printing of Polyaniline Layers for Perovskite Solar Cells
摘要： Polyaniline-based water-soluble ink has been developed to form hole-transport layers for perovskite solar cells by the ink-jet printing method. A study of the optical properties and surface morphology of layers composed of a complex of polyaniline and polysulfonic acid resulted in criteria determining the optimal conditions of their printing being suggested. The printed layers were found to be promising hole-transport layers for perovskite solar cells.
关键词： perovskites,atomic-force microscopy,polyaniline,solar cells
更新于2025-09-16 10:30:52
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Pressure effect on optical and structural properties of ZnMnO thin films grown by pulsed laser deposition
摘要： Zn0.95Mn0.05O thin films were deposited on Si substrate by pulsed laser ablation technique under different oxygen pressure. The structural and optical properties of the films were analyzed as a function of the oxygen gas pressure. The Mn concentration and the substrate temperature of the thin films were kept constant at 5 wt% and 200°C respectively. X-ray diffraction technique (XRD), atomic force spectroscopy (AFM), raman spectroscopy and UV-Vis were employed to characterize the optical properties and the crystalline structure of the films. The diffraction patterns revealed that the Mn0.05Zn0.95O thin films were polycrystalline with the wurtzite hexagonal structure of ZnO and highly oriented in c-axis direction, without any secondary phases. The average energy band gap of the films was evaluated around 3.23-3.56 eV. Raman spectrum showed E2 (low) mode of ZnO structure shifted to red and increased its FWHM.
关键词： Laser Ablation,X-ray Diffraction,UV-Vis Spectroscopy,Atomic Force Microscopy,Raman Spectroscopy
更新于2025-09-16 10:30:52
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Carrier Multiplication in PbS Quantum Dots Anchored on a Au Tip using Conductive Atomic Force Microscopy
摘要： Carrier multiplication (CM) is the amplification of the excited carrier density by two times or more when the incident photon energy is larger than twice the bandgap of semiconductors. A practical approach to demonstrate the CM involves the direct measurement of photocurrent in the device. Specifically, photocurrent measurement in quantum dots (QDs) is typically limited by high contact resistance and long carrier-transfer length, which yields a low CM conversion efficiency and high CM threshold energy. Here, the local photocurrent is measured to evaluate the CM quantum efficiency from a QD-attached Au tip of a conductive atomic force microscope (CAFM) system. The photocurrent is efficiently measured between the PbS QDs anchored on a Au tip and a graphene layer on a SiO2/Si substrate as a counter electrode, yielding an extremely short channel length that reduces the contact resistance. The quantum efficiency extracted from the local photocurrent data with an incident photon energy exhibits a step-like behavior. More importantly, the CM threshold energy is as low as twice the bandgap, which is the lowest threshold energy of optically observed QDs to date. This enables the CAFM-based photocurrent technique to directly evaluate the CM conversion efficiency in low-dimensional materials.
关键词： lead sulfide quantum dots,conductive atomic force microscopy,carrier multiplication,photocurrent measurement
更新于2025-09-16 10:30:52
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Self-powered perovskite/CdS heterostructure photodetectors
摘要： Methylammonium lead halide perovskites have gained a lot of attention because of their remarkable physical properties and potential for numerous (opto)electronic applications. Here, high-performance photodetectors based on CH3NH3PbI3 (MAPbI3)/CdS heterostructures, are demonstrated. The resulting self-powered MAPbI3/CdS photodetectors show excellent operating characteristics including a maximum detectivity of 2.3×1011 Jones with responsivity of 0.43 A/W measured at 730 nm. A temporal response time of less than 14 ms was achieved. The mechanisms of charge separation and transport at the interface of the MAPbI3/CdS junction were investigated via conductive atomic force microscopy (C-AFM) and photoconductive atomic force microscopy (PC-AFM). Obtained results show that grain boundaries exhibit higher photocurrent than flat regions of the top perovskite layer, which indicates that excitons preferentially separate at the grain boundaries of the perovskite thin film, i.e. at the edges of the MAPbI3 crystals. The study of the photoelectric mechanism at the nanoscale suggests the device performance could potentially be fine-tuned through grain boundary engineering, which provides essential insights for the fabrication of high-performance photodetector. The demonstrated self-powered photodetector is promising for numerous applications in low-energy consumption optoelectronic devices.
关键词： perovskite,photodetector,heterojunction,photovoltaic,self-powered photodetectors,photoconductive atomic force microscopy
更新于2025-09-16 10:30:52
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Omnidirectional light harvesting enhancement of dye-sensitized solar cells decorated with two-dimensional ZnO nanoflowers
摘要： Surface hydrophilicity has a crucial effect on adhesion forces in air. However, the influence demands clarification. A spherical tip was used to measure adhesion forces on silicon samples with different treatment methods on an atomic force microscope at high relative humidity. The treatment methods were plasma treatment with storage for a time and ultrasonic cleaning in alcohol and water. Both abnormally large and small adhesion forces were observed, and the adhesion force behavior is closely related to surface hydrophilicity. With plasma treatment, the maximum force can be as large as ~4.8 μN, which was attributed to the formation of siloxane bonds (Si-O-Si) between opposing surfaces and the capillary force due to a water bridge. However, the abnormally large adhesion force can only last for a few hours, and then either decreases gradually or decreases suddenly to an abnormally small value. The decrease was attributed to the displacement of hydroxyl groups by organic molecules and the adsorption of some other airborne contaminants on the surface. The possible reasons for abnormally small forces were also presented. However, the abnormal values were not observed on samples with ultrasonic cleaning. These results may help facilitate the anti-adhesion design for silicon-based small-scale systems.
关键词： pull-off force,water bridge,contact angles,Atomic force microscopy,adhesion by chemical bonding
更新于2025-09-12 10:27:22
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Mobility of charge carriers in self-assembled monolayers
摘要： We present a new approach to study charge transport within 2D layers of organic semi-conductors (OSCs) using atomic force microscopy (AFM)-based lithography applied to self-assembled monolayers (SAMs), fabricated from appropriate organothiols. The extent of lateral charge transport was investigated by insulating pre-defined patches within OSC-based SAMs with regions of insulating SAM made from large band gap alkanethiolates. The new method is demonstrated using a phenyl-linked anthracenethiolate (PAT), 4-(anthracene-2-ylethynyl)benzyl thiolate. I–V characteristics of differently shaped PAT-islands were measured using the AFM tip as a top electrode. We were able to determine a relationship between island size and electrical conductivity, and from this dependence, we could obtain information on the lateral charge transport and charge carrier mobility within the thin OSC layers. Our study demonstrates that AFM nanografting of appropriately functionalized OSC molecules provides a suitable method to determine intrinsic mobilities of charge carriers in OSC thin films. In particular, this method is rather insensitive with regard to influence of grain boundaries and other defects, which hamper the application of conventional methods for the determination of mobilities in macroscopic samples.
关键词： organic semiconductor,self-assembled monolayer,lateral charge transport,nanografting,conducting atomic force microscopy
更新于2025-09-12 10:27:22
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Supramolecular structures of terbium( <scp>iii</scp> ) porphyrin double-decker complexes on a single-walled carbon nanotube surface
摘要： This work mainly reports the observation of novel supramolecular structures of TbIII-5,15-bisdodecylporphyrin (BDP, C12P) double-decker complexes on the surfaces of single-walled carbon nanotubes (SWNTs) performed by scanning tunneling microscopy under an ultra-high vacuum and low temperature, atomic force microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and ultraviolet-visible spectroscopy. The molecules formed a well-ordered self-assembled helix-shaped array with regular periodicity on the tube surface. Additionally, some magnetic properties of the BDP-molecule as well as the resulting BDP-SWNT composites were investigated by superconducting quantum interference measurements. The molecule exhibits single-molecule magnetic (SMM) properties and the composite's magnetization increases almost linearly with decreasing temperature which is possibly due to the coupling between porphyrin molecules and SWNTs. Consequently, this may enable the development of more advanced spintronic devices based on porphyrin-nanocarbon composites.
关键词： Scanning tunneling microscopy,Magnetic properties,Supramolecular structures,Single-walled carbon nanotube,Atomic force microscopy,Terbium(III) porphyrin
更新于2025-09-11 14:15:04
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Topological and electrical properties of capped and annealed (0001) hydride vapor phase epitaxy GaN films on sapphire
摘要： In light of the necessity to anneal GaN to activate implanted dopants, the effects of the annealing temperature and time, the quality of the hydride vapor phase epitaxy grown GaN film, the quality of the annealing cap, and the effects of the stresses generated by the difference in the coefficients of thermal expansion of the film and the substrate are examined topographically using atomic force microscopy, and electrical measurements are made on Schottky diodes fabricated on the annealed samples. The results show that thermal decomposition begins at threading edge dislocations that form polygonized small angle grain boundaries during the annealing process; donor defects, probably nitrogen vacancies, are formed near the surface; and the donors are created more quickly when the annealing temperature is higher, the annealing time is longer, and the thermal stresses on the annealing cap are greater. The results suggest that the maximum annealing temperature is ～1300 °C, and at that annealing temperature, the annealing time should not exceed 4 min.
关键词： thermal decomposition,nitrogen vacancies,Schottky diodes,atomic force microscopy,GaN,annealing
更新于2025-09-11 14:15:04
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Formation and characterization of charge coupled structure of polyoxometalate particles and a GaAs-based nanowire for readout of molecular charge states
摘要： To investigate the molecular charge dynamics of polyoxometalate (POM) molecules, we formed and characterized a charge coupled structure with POM molecular particles and a GaAs-based nanowire. In our system, the charge sensitivity was locally increased by capacitive coupling between a metal tip and the POM particle. Surface dispersion of POM particles on the GaAs nanowire was carried out in a controlled manner by choosing an appropriate solvent and POM concentration. We found that, after POM surface dispersion, the current in the GaAs nanowire remarkably increased by charging the POM particles using a conductive atomic force microscopy tip. The current change strongly depended on humidity of the measurement environment. The nanowire current under capacitive coupling between the conductive tip and the POM particle on the nanowire surface showed steps with a height of approximately 70 nA, suggesting that multiple hole charging and discharging occurred in the particle in a synchronized manner.
关键词： conductive atomic force microscopy,GaAs-based nanowire,molecular charge states,charge coupled structure,polyoxometalate
更新于2025-09-11 14:15:04