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Structural characterization of bulk and nanoparticle lead halide perovskite thin films by (S)TEM techniques
摘要： Lead halide (APbX3) perovskites, in polycrystalline thin films but also perovskite nanoparticles (NPs) have demonstrated excellent performances to implement a new generation of photovoltaic and photonic devices. The structural characterization of APbX3 thin films using (scanning) transmission electron microscopy ((S)TEM) techniques can provide valuable information that can be used to understand and model their optoelectronic performance and device properties. However, since APbX3 perovskites are soft materials, their characterization using (S)TEM is challenging. Here, we study and compare the structural properties of two different metal halide APbX3 perovskite thin films: bulk CH3NH3PbI3 prepared by spin-coating of the precursors in solution and CsPbBr3 colloidal NPs synthetized and deposited by doctor blading. Both specimen preparation methods and working conditions for analysis by (S)TEM are properly optimized. We show that CH3NH3PbI3 thin films grown by a one-step method results in the formation of tetragonal perovskite thin films with good adherence to an underlying TiO2 layer, which is characterized by a photoluminescence (PL) emission band centered at 775 nm. The perovskite thin films based on CsPbBr3 colloidal NPs, which are used as the building blocks of the film, they are preserved by the deposition process, even if small gaps are observed between adjacent NPs. The crystal structure of CsPbBr3 NPs is cubic, which is beneficial for optical properties due to its optimal band gap. The absorption and PL spectra measured in both the thin film and the colloidal solution of CsPbBr3 NPs are very similar, indicating a good homogeneity of the thin films and the absence of aggregation of NPs. However, a particular care was required to avoid long electron irradiation times during our structural studies, even at a low voltage of 80 kV, as the material was observed to decompose through Pb segregation.
关键词： structural characterization,TEM,thin films,optoelectronics,STEM,nanoparticles,perovskite
更新于2025-09-23 15:23:52
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Surface chemical states of gold nanoparticles prepared using the solution-plasma method in a CsCl aqueous solution
摘要： In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution‐plasma method are characterized via transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy with synchrotron radiation (SR‐XPS). The particle diameter is measured over the process time via TEM. During the solution‐plasma process, small particles of 2.1 to 2.2‐nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR‐XPS. The SR‐XPS measurements obtained using incident X‐ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X‐ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR‐XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface.
关键词： solution‐plasma method,TEM,gold nanoparticles,XPS,surface chemical states
更新于2025-09-23 15:23:52
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Synthesis, characterization and photo-response of p-type cupric oxide thin films prepared by sol-gel technique
摘要： Cupric oxide (CuO) has been deposited onto glass and n-Si (1 0 0) substrate by sol-gel technique. pH of the sol and annealing temperature during film growth were found to be the key parameters for depositing the above film. Microstructural, optical and bonding environmental studies were performed on the above films. The grain sizes in these polycrystalline films varied between ～50 and 100 nm. Films were preferentially oriented in (?1 1 1) direction. Electrical and galvanomagnetic measurements indicated films to be predominantly p-type with carrier concentration value ～3.47 × 10^15/cm^3 and mobility values ～4.475 cm^2/Vs. A typical p-CuO/n-Si hetero-junction structure has been successfully fabricated with open circuit voltage (VOC) ～359 mV and short-circuit current density (JSC) ～4.65 mA/cm^2, fill factor (FF) ～0.38 and efficiency (η) ～1.05%.
关键词： CuO,Raman,TEM,XRD,XPS,PV
更新于2025-09-23 15:23:52
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Sensing of iron(III)-biomolecules by surfactant-free fluorescent copper nanoclusters
摘要： Surfactant-free copper nanoclusters (sf-CuNCs) synthesized in the absence of external stabilizer, could be promising fluorescence biosensors because of the presence of relatively exposed surfaces that may ease coupling with biomolecules. This article shows that sf-CuNCs are effective fluorescence sensor of iron(III)-biomolecules: hemin, cytochrome C (cyt C), and ferritin. Although, sf-CuNCs are found to be weaker sensor of aqueous Fe3+ (Stern-Volmer constant (KSV) 3.0 × 103 M?1 and limit of detection (LOD) up to 2 μM) compared to other capped CuNCs, however, the sensing ability markedly increases in the presence of Fe(III)-biomolecules. KSV (LOD) are 5.3 × 104 M?1 (0.8 μM), 9.0 × 105 M?1 (68 nM), 1.6 × 106 M?1 (16.50 nM), respectively for cyt C, hemin and ferritin. We carried out detailed mechanistic investigations of the quenching process using time-resolved fluorescence, zeta potential and transmission electron microscopy (TEM) measurements. We found that fluorescence quenching is associated with complexation of Fe3+ with CuNCs which changes zeta potential of the sf-CuNCs and leads to aggregation of CuNCs. Moreover, fluorescence quenching, zeta potential and aggregation of CuNC can be reversed by addition of vitamin C which is a very strong chelator and reducing agent of Fe(III). Vitamin C reduces Fe(III) to Fe(II) and promotes disassembly of CuNCs-aggregates to regenerate fluorescence intensity. Since, the sensing is primarily governed by complex formation with Fe3+, absence of ligands on the surface of sf-CuNCs may be detrimental to quenching to aqueous Fe3+ but favors binding with the biomolecules.
关键词： Iron sensing,Copper nanocluster,Proteins,TEM,Fluorescence
更新于2025-09-23 15:23:52
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Operando XAS and NAP-XPS investigation of CO oxidation on meso- and nanoscale CoO catalysts
摘要： In contrast to Co3O4, CoO has been much less studied for CO oxidation. Herein, the phase changes of commercial mesoscopic CoO (particle size ?1 μm) and nanosized CoO (20–50 nm particle size), the latter prepared by vacuum reduction of commercial Co3O4, were examined by operando X-ray absorption (XAS) and near-ambient pressure X-ray photoemission (NAP-XPS) spectroscopy during CO oxidation, as well as ex situ by transmission electron microscopy and di?raction (TEM/SAED). Commercial mesoscopic CoO exhibited CO oxidation activity at ?200 °C, but even up to 530 °C in pure O2 no substantial (bulk) oxidation was observed by operando XAS, likely due to the large grains and bulk nature of CoO. After pre-oxidation at 400 C, electron di?raction detected thin surface layers of Co3O4. This increased activity but the activity of nanosized Co3O4 of equal surface area was still not reached. For nanosized CoO (surface layers on vacuum-reduced Co3O4), operando NAP-XPS/XAS, acquired during CO oxidation, revealed oxidation of CoO to Co3O4 above 150 °C, yielding the activity of nanosized Co3O4. Evidently, the nanoscale CoO shell on a Co3O4 core with small grains more easily and more completely transformed to Co3O4 than mesoscopic (bulk) CoO with large grains. Our study demonstrates how ?exible and dynamic surfaces of cobalt oxide materials adjust to various reaction environments, which also depends on grain size and morphology (bulk vs. thin layers), illustrating the importance of operando techniques to determine active catalyst phases under reaction conditions.
关键词： CO oxidation,CoO,Co3O4,NAP-XPS,XAS,TEM,Operando
更新于2025-09-23 15:23:52
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(S)TEM methods contributions to improve the fabrication of InGaN thin films on Si, and InN nanostructures on flat Si and rough InGaN
摘要： The main results of a complete study by Transmission and Scanning-Transmission Electron Microscopies ((S)TEM) are described for (i) InGaN/Si (111) heterostructures in the whole compositional range of the alloys, and (ii) InN quantum dots (InN QDs) directly grown on Si wafers or on relatively rough InGaN/Si (111) templates. The combination of many (S)TEM-based techniques allowed to evaluate different characteristics of the systems under study: (InN QD/) InGaN/Si and InN QD/Si interfaces and crystal qualities, structural and chemical imperfections and other important features. InxGa1-xN thin films are often identified as single-crystalline, very homogeneous in composition, and mostly wurtzite-type, remarkably at any value of x. Also, (S)TEM techniques revealed that the InN nanostructures were hexagonal single crystals, mostly epitaxial to the supporting lattice. The InN crystals also exhibited partially cubic arrangements when allocated onto In-rich InxGa1-xN (i.e. x > 0.7).
关键词： Semiconductors,TEM,Heterojunctions,Crystal structure.,Nitride materials,Crystal growth,Transmission Electron Microscopy
更新于2025-09-23 15:23:52
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Structural study of MgO and Mg-doped ZnO thin films grown by atomic layer deposition
摘要： Pure MgO, 1 and 10 at% Mg-doped ZnO layers were grown by atomic layer deposition technique onto (001)-oriented α-Al2O3 and GaN substrates. The structure and the microstructure of the deposited layers were studied by TEM in detail. The pure MgO layer starts to grow with epitaxy with (100)-type defects that transforms to random orientation. In the 10 at% Mg-doped samples epitaxial cubic MgO buffer layer forms at the interface. This buffer layer helps the ZnO to grow epitaxially in the case of α-Al2O3 substrate forming a ZnO/MgO/c-plane α-Al2O3 hetero-structure showing higher mobility with lower carrier concentration, while in the case on GaN substrate the ZnO is strongly textured. Consequently for higher concentration Mg doping (with the formation of MgO buffer layer) α-Al2O3 is better choice to grow epitaxial ZnO layer. The 1 at% Mg-doping of the epitaxial ZnO layer grown onto GaN substrate was successfully implemented, while in the case of α-Al2O3 substrate a thin cubic MgO buffer layer forms. This shows that the success of low concentration Mg doping in ZnO largely depends on the choice of substrate material as well.
关键词： Mg-doped ZnO,ALD,MgO,TEM
更新于2025-09-23 15:23:52
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Silver Nanostructures on Graphene Oxide as the Substrate for Surface-Enhanced Raman Scattering (SERS)
摘要： Nanosized surface-enhanced Raman scattering (SERS) substrates fabricated by the controlled growth of metal nanostructures on water-dispersed two-dimensional nanomaterials can open a new avenue for SERS analysis of liquid samples in biological fields. In this work, regular and uniform Ag nanostructures were grown on the surface of graphene oxide (GO) through a microwave-assisted hydrothermal method. Polyamidoamine (PAMAM) dendrimers were assembled on the surface of GO to form GO/PAMAM templates for growing Ag nanostructures, which are primarily comprised of Ag dimers and trimers. The prepared Ag/GO nanocomposites are highly dispersed and stable in aqueous solution and may be used as substrates for enhanced Raman detection of rhodamine 6 G (R6G) in aqueous solution. This special substrate provides high-performance SERS and suppresses R6G fluorescence in aqueous solution and is promising as a nanosized material for the enhanced Raman detection of liquid samples in biological diagnostics.
关键词： graphene oxide (GO),Surface-enhanced Raman scattering (SERS),polyamidoamine (PAMAM) dendrimers,transmission electron microscopy (TEM),Fourier transform infrared (FTIR) spectroscopy,rhodamine 6G (R6G)
更新于2025-09-23 15:23:52
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Inverse size-dependence of piezoelectricity in single BaTiO3 nanoparticles
摘要： The piezoelectric charge coefficients d33 of single BaTiO3 (BT) nanoparticles (NPs) were characterized using a transmission electron microscope (TEM) that is equipped with a precise charge meter and an in-situ TEM indentation holder that enables controlled compression experiments. An exceptionally high d33 of 1775 pC/N was obtained in NPs that are smaller than the critical diameter (D; typically known as < 100 nm) that has been regarded as the lower limit to permit for ferroelectricity in BT. The mechanical conversion efficiency of piezoelectric BT nanogenerators enhanced as D of BT NPs was decreased; this result corresponds with the single-NP compression measurements of d33. This quantification of the effect of D in ferroelectric materials may guide development of efficient and high-powered nanostructured piezoelectric energy devices such as piezoelectric nanogenerators.
关键词： in-situ TEM,size effect,STEM,Ferroelectric,piezoelectric,nanogenerator
更新于2025-09-23 15:23:52
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Quality of extracellular vesicle images by transmission electron microscopy is operator and protocol dependent
摘要： Transmission electron microscopy (TEM) has nanometre resolution and can be used to distinguish single extracellular vesicles (EVs) from non-EV particles. TEM images of EVs are a result of operator image selection. To which extent operator image selection reflects the overall sample quality, and to which extent the images are comparable and reproducible, is unclear. In a first attempt to improve the comparability and reproducibility of TEM to visualise EVs, we compared operator image selection to images taken at predefined locations from the same grids, using four EV TEM preparation protocols, a single EV-containing sample and a single TEM instrument. Operator image selection leads to high-quality images that are more similar between the protocols. In contrast, images taken at predefined locations reveal differences between the protocols, for example in number of EVs per image and background quality. From the evaluated protocols, for only one protocol the operator image selection is comparable to the TEM images taken at predefined locations. Taken together, operator image selection can be used to demonstrate the presence of EVs in a sample, but seem less suitable to demonstrate the quality of a sample. Because images taken at predefined locations reflect the overall quality of the EV-containing sample rather than the presence of EVs alone, this is a first step to improve the comparability and reproducibility of TEM for monitoring the quality of EV-containing samples.
关键词： urine,negative staining,transmission electron microscopy (TEM),Exosomes,extracellular vesicles (EVs),microvesicles
更新于2025-09-23 15:23:52