Synthesis and characterization of Cr doped CdS nanoparticles stabilized with polyvinylpyrrolidone

Undoped and Cr (2 and 4 at.%) doped CdS nanoparticles were synthesized in aqueous solution by simple chemical co-precipitation method using polyvinylpyrrolidone (PVP) as stabilizer. The prepared nanoparticles were examined using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). XRD pattern of the nanoparticles showed cubic zincblende phase with the particle size of the order of 3-4 nm, which was in good agreement with the results obtained from TEM studies. The EDAX analysis confirmed that Cd, Cr and S elements were present in the samples and the variations between the target and actual compositions were microscopic. UV-vis DRS spectra of the samples exhibited decrease in the band gap which further attests the incorporation of Cr into CdS nanoparticles. FTIR studies revealed that the undoped as well as Cr doped CdS nanoparticles were capped by polyvinylpyrrolidone.     

Structural and morphological properties of thin ZnO films grown by pulsed laser deposition

The pulsed laser deposition technique was used to produce zinc oxide thin films onto silicon and Corning glass substrates. Homogeneous surfaces exhibiting quite small Root Mean Square (RMS) roughness, consisting of shaped grains were obtained, their grain diameters being 40-90 nm at room temperature and at 650 °C growth respectively. Films were polycrystalline, even for growth at room temperature, with preferential crystallite orientation the (0 0 2) basal plane of wurtzite ZnO. Temperature increase caused evolution from grain to grain agglomeration structures, improving crystallinity. Compressive to tensile stresses transition with temperature was found while the lattice constant decreased.     

Structural characterization of Ga-doped Mg0.1Zn0.9O layers grown on ZnO/α-Al2O3 templates by P-MBE

In this study, structural properties of epitaxial Ga-doped Mg_0.1Zn_0.9O layers grown on ZnO/α-Al₂O₃ templates by plasma-assisted molecular beam epitaxy have been investigated by high-resolution transmission electron microscopy (HRTEM), and high resolution X-ray diffraction (HRXRD). From analysis of the diffraction pattern, the monocrystallinity of the Mg_0.1Zn_0.9O layer with hexagonal structure is confirmed. The orientation relationship between Mg_0.1Zn_0.9O and the template is determined as (0 0 0 1)_Mg0.1Zn0.9O(0 0 0 1)_ZnO(0 0 0 1)_Al2O3 and [ [ ]_ZnO[ . The density of dislocations near the top surface layers measured by plan-view TEM is about 3.610¹⁰ cm⁻², one order of magnitude higher than the value obtained for ZnO layers on α-Al₂O₃ with a MgO buffer. Cross-sectional observation revealed that the majority of threading dislocations are in the [0 0 0 1] line direction, i.e. they lie along the surface normal and consist of edge, screw, and mixed dislocations. Cross- sectional TEM and X-ray rocking curve experiments reveal that most of dislocations are edge dislocations. The interface of Mg_0.1Zn_0.9O and ZnO layers and the effect of excess Ga-doping in these layers have been also studied.     

Graphene oxide monolayers as supporting films for high resolution transmission electron microscopy

A novel kind of TEM support composed of graphene oxide monolayers was fabricated by a facile solution-cast method. Compared to the conventional carbon supporting films, such graphene oxide film (GO-film) performed better stability under high-energy electron beams and better dispersion effect for water-soluble nanoparticles. Quantitative improvement in TEM imaging resolution for nanomaterials on such GO-films compared to the commercial ultrathin carbon films was demonstrated.     

Electron energy loss spectroscopy analysis of the interaction of Cr and V with MWCNTs

The presented scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) results show the strong reaction of Cr and V with the graphitic walls of MWCNTs. For Vanadium, an interfacial VC layer could be observed at the interface between VN and MWCNTs, when the samples were heated in situ to 750 °C. Knowledge about this interfacial VC layer is important for the formation of VN-MWCNT hybrid materials, used in supercapacitor electrodes, often synthesized at high temperatures. Chromium reacts at 500 °C with the MWCNTs to form Cr₃C₂ and in some cases, dissolved the MWCNT completely. Together with the previously published results about the interaction of MWCNTs with Cu (no interaction) and Ni (a slight rehybridisation trend for the outermost MWCNT-wall observed with EELS) (Ilari et al., 2015) the influence of the valence d-orbital occupancy of 3d transition metals on the interaction strength with CNTs is shown experimentally. For a transition metal to form chemical bonds towards CNT-walls, unoccupied states in its valence d-orbitals are needed. While Ni (2 unoccupied states) interacts only slightly, Cr (5 unoccupied states) and V (7 unoccupied states) react much stronger and can dissolve the MWCNTs, at least partially.     

Chemical and structural analysis of low-temperature excimer-laser annealing in indium-tin oxide sol-gel films

We investigated the influence of excimer-laser annealing (ELA) on the electrical, chemical, and structural properties of indium–tin oxide (ITO) films prepared by a solution process. The ITO film was prepared by the sol-gel method and annealed by excimer-laser pulses with an energy density up to 240?mJ/cm². Hall measurements showed that the ELA substantially enhanced the electrical properties of the ITO films, including their resistivity, carrier density, and mobility, as increasing the laser energy density. In-depth x-ray photoelectron spectroscopy analysis of the chemical states in the film surface showed that the ELA reduced carbon species and promoted both an oxidation and crystallization. These changes were consistent with results of x-ray diffraction and transmission electron microscopy measurements, where expansions in the microcrystal growth were observed for higher laser energy density. We comprehensively understand that the chemical rearrangement and concomitant crystallization are the main factors for achieving the electrical properties during the ELA. These results suggest the potential of the ELA-treated sol-gel films for providing high-quality ITO films at low temperatures toward the flexible device applications.     

Effect of swift heavy ion irradiation on photoluminescence properties of ZnO/PMMA nanocomposite films

We report a study on the SHI induced modifications on structural and optical properties of ZnO/PMMA nanocomposite films. The ZnO nanoparticles were synthesized by the chemical route using 2-mercaptoethanol as a capping agent. The structure of ZnO nanoparticles was confirmed by XRD, SEM and TEM. These ZnO nanoparticles were dispersed in the PMMA matrix to form ZnO/PMMA nanocomposite films by the solution cast method. These ZnO/PMMA nanocomposite films were then irradiated by swift heavy ion irradiation (Ni⁸⁺ ion beam, 100 MeV) at a fluence of 1×10¹¹ ions/cm². The nanocomposite films were then characterized by XRD, UV-vis absorption spectroscopy and photoluminescence spectroscopy. As revealed from the absorption spectra, absorption edge is not changed by the irradiation but the optical absorption is increased. Enhanced green luminescence at about 527 nm and a less intense blue emission peak around 460 nm were observed after irradiation with respect to the pristine ZnO/PMMA nanocomposite film.     

Spermatozoon of the freshwater rotifer Brachionus calyciflorus (Rotifera,Monogononta): Advances in morphological and ultrastructural studies

The morphological and ultrastructural features of the spermatozoon in Brachionus calyciflorus are described using light, fluorescence and transmission electron microscopy (TEM). The mature spermatozoon, which appears to be thread-like, is composed of a slightly expanded anterior of cell body region and a flagellum region without acrosome. The cell body region and flagellum region are respectively 16–27 μm and 20–33 μm in length (n = 60). The spermatozoon is characterized by a mass of dense tubular materials, which occupy most of the cell. Some mitochondria are distributed around the nuclear region in the anterior of the cell body region, while in the posterior portion of cell body, the chromatin often contains a single lobated nucleus arranged at the center of cell. The flagellum contains the classic axoneme (9 × 2 + 2) and possesses lateral undulating membrane. Mature B. calyciflorus males have no germ cell stages earlier than the spermatids in the testis. TEM examination reveals rigid rods as well as predominant typical spermatozoon in the testis. Observations, based on successive photographs and videos, enabled a first-time recording of the unique inverted movement of the spermatozoon, which indicated that the movement of the spermatozoon is driven by the flagellum. Our study also provides further supplementary insights into the phylogenetic systematics of the Rotifera.     

Growth and characterization of β-SiC films obtained by fs laser ablation

We achieved the growth of cubic silicon carbide (SiC) films on (1 0 0)Si substrates by pulsed laser deposition (PLD) at moderate temperatures such as 750 °C, from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The morphology of deposited films is dominated by columns nucleated from a thin nanostructured beta silicon carbide (β-SiC) interface layer. The combined effects of columnar growth, tilted facets of the emerging columns and the presence of particulates on the film surface, lead to a rather rough surface of the films.     

Ultrastructure of antennal sensilla of an autoparasitoid Encarsia sophia (Hymenoptera: Aphelinidae)

Encarsia sophia (Hymenoptera: Aphelinidae) is a parasitoid utilized for biological control of Bemisia tabaci, with selection of prey aided by chemoreceptor organs. The morphology and distribution of the antennal sensilla (chemoreceptors) of E. sophia were examined using Transmission electron micrographs. The total antennal length for E. sophia was 429.28 ± 0.95 μm for females and 437.19 ± 8.21 for males, and each antennae was found to consist of seven sensilla of different types. Both sexes possessed sensilla chaetica, sensilla trichodea, basiconic capitate peg sensilla, multiporous grooved-surface placoid sensilla (MG-PS), uniporous rod-like sensilla, nonporous finger-like sensilla, and sensilla coeloconica. Transmission electron micrographs of longitudinal sections of female antennae showed that they were composed of fat body, cuticle, mesoscutello-metanotal muscles, neurons, and glandular tissue, and cross-sections of the basal MG-PS showed sensillar lymph cavities and dendrites. The MG-PSs were imbedded in an electron-dense mass with cuticular invaginations which acted as pores that connected to a central lumen. The possible function of each type of sensilla is discussed.     

Thermal stability of ultrathin amorphous carbon films synthesized by plasma-enhanced chemical vapor deposition and filtered cathodic vacuum arc

Abstract

Ultrathin hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and hydrogen-free amorphous carbon (a-C) films of similar thickness deposited by filtered cathodic vacuum arc (FCVA) were subjected to rapid thermal annealing (RTA). Cross-sectional transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were used to study the structural stability of the films. While RTA increased the thickness of the intermixing layer and decreased the sp³ content of the a-C:H films, it did not affect the thickness or the sp³ content of the a-C films. The superior structural stability of the FCVA a-C films compared with PECVD a-C:H films, demonstrated by the TEM and EELS results of this study, illustrates the high potential of these films as protective overcoats in applications where rapid heating is critical to the device functionality and performance, such as heat-assisted magnetic recording.     

Correlative microscopy of a carbide-free bainitic steel

In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite–austenite (M–A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M–A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation.     

Directional crystallization and self-assembling initiated by mechanical shock or electron beam in nanocrystalline Co-C and Fe-C films

We investigated iron and cobalt films with 20% carbon concentration with nanocrystalline structure. One of the aims of this work is to analyze the physical nature of high-speed structural self-assembling as often happens in explosive crystallization processes in these films.     

Preparation and characterization of Fe3O4 magnetic composite microspheres covered by a P(MAH-co-MAA) copolymer

A magnetic core–shell-layered polymer microsphere (MPS) was successfully synthesized by a dispersion polymerization route, where the modified Fe₃O₄ nanoparticles (MFN) were used as a core, while poly(maleic anhydride-co-methacrylic acid) P(MAH-co-MAA) as a shell was covered on the surface of the Fe₃O₄ nanoparticles. Environmental scanning electron microscope (ESME) and transmission electron microscope (TEM) measurements indicate that the magnetic P(MAH-co-MAA)/Fe₃O₄ composite microspheres assume sphericity and have a novel core–shell-layered structure. The crystal particle sizes of the unimproved Fe₃O₄ and the MFN samples vary from 8 to 16 nm in diameter, and the average size is about 10.6 nm in diameter. The core–shell magnetic composite microspheres can be adjusted by changing the stirring speed. Since multiple Fe₃O₄ cores were coated with a proper percentage of P(MAH-co-MAA) copolymers, and therefore lower density was acquired for the MPS, which improved sedimentation and dispersion behavior. The saturated magnetization of pure Fe₃O₄ nanoparticles reaches 48.1 emu g⁻¹ and the value for composite nanoparticles was as high as 173.5 emu g⁻¹. The nanoparticles show strong superparamagnetic characteristics and can be expected to be used as a candidate for magnetism-controlled drug release.     

Integrity of functional self-assembled monolayers on hydrogen-terminated silicon-on-insulator wafers

Silicon-on-insulator (SOI) wafers are commonly used to design microelectronics, energy conversion, and sensing devices. Thin solid films on the surfaces of SOI wafers have been a subject of numerous studies. However, SOI wafers modified by self-assembled monolayers (SAMs) that can also be used as functional device platforms have been investigated to a much lesser extent. In the present work, tert-butoxycarbonyl (t-boc, (CH₃)₃-C-O-C(O)-)-protected 1-amino-10-undecene monolayers were covalently attached to a H-terminated SOI (1 0 0) surface. The modified wafers were characterized by X-ray photoelectron spectroscopy to confirm the stability of the SAM/Si interface and the integrity of the secondary amine in the SAM. The transmission electron microscopy investigation suggested that this t-boc-protected 1-amino-10-undecene SAM produces atomically flat interface with the 2 μm single crystalline silicon of the SOI wafer, that the SiO_x and both available Si/SiO_x interfaces are preserved, and that the organic monolayers are stable, with apparent thickness of 1.7 nm, which is consistent with the result of the density functional theory modeling of the molecular features within a SAM.     

Magnetic properties and characterization of CoCrM/TiCr/Si films produced by pulsed laser deposition

A series of nanogranular CoCrM/TiCr thin films have been fabricated by pulsed-laser deposition on Si(1 1 1) substrates at 450–500 °C. The crystal structure and magnetic properties of these films were investigated. The transmission electron microscope images with selected area diffraction and X-ray diffraction showed that the structure of as-prepared films is dependent on laser energy and deposition temperature. It was found that the microstructure of CoCrM/TiCr films consisted of fine dispersive crystal grains, while the preferential c-axis orientation of films deteriorated when the thickness of CoCr-alloy layer increased along with metal doping into the CoCr films. The magnetic properties of CoCrM/TiCr films formed on Si are strongly dependent on the thickness of magnetic layer, grain structure, and grain shape. Enhancement of coercivity and squareness of the laser-deposited film is probably due to the improvement in the magnetocrystalline anisotropy energy and the reduction in the thickness of magnetic layer.     

Size dependence of lattice parameter for SixGe1−x nanoparticles

The phenomenon of the influence of the size of a material on its properties has been predicted theoretically and was confirmed for many materials experimentally by many researchers. It is a purpose of this paper to increase understanding of the influence of size on properties for silicon, germanium and alloy silicon-germanium nanoparticles. The relationships between lattice parameter and inverse particle radius had been investigated. The data obtained from the experiments show an unpredicted result that the lattice parameter of the Si_xGe_1−x nanoparticle expands by up to 1.5% when the size of the particle decreases to 7 nm. A calibration technique for a higher precision measurement of the lattice parameter is presented. The particles under investigation were deposited on an amorphous carbon substrate in order to prevent the influence of the misfit between deposit and crystalline substrate on the particle’s behavior.     

UHV-HREM and diffraction of surfaces

Characterization of the structure of surfaces is very important in order to develop a fundamental understanding of the electronic, mechanical and chemical properties of a material. While transmission electron microscopy imaging (TEM) and diffraction (TED) techniques are capable of providing surface structural information at the atomic level, such data would be suspect if obtained under conventional vacuum conditions (10^-6–10^-8 Torr). Ultrahigh vacuum (UHV) conditions are imperative during both preparation and observation of clean surfaces/interfaces. Conventional TEM techniques are very powerful for UHV-TEM investigations; however, the marriage of surface science and conventional TEM to yield an UHV-TEM is a complex task. These complexities and some of the results obtained using UHV-TEM and UHV-TED techniques for surfaces i.e. solid-vacuum interfaces will be illustrated.     

Raman characterization of the structural evolution in amorphous and partially nanocrystalline hydrogenated silicon thin films prepared by PECVD

Hydrogenated silicon (Si:H) thin films were obtained by plasma‐enhanced chemical vapor deposition (PECVD). Raman spectroscopy was used to investigate the structural evolution in phosphor‐doped n‐type amorphous hydrogenated silicon thin films, which were prepared under different substrate temperatures and gas pressures. Meanwhile, the effect of nitrogen doping on the structure of P‐doped thin films was also investigated by Raman spectroscopy. Moreover, the transition from the amorphous state to the nanocrystalline state of undoped Si:H films deposited through low argon dilution was studied by Raman spectroscopy, X‐ray diffraction, and transmission electron microscopy. The results show that Raman spectroscopy can sensitively detect the structural evolution in hydrogenated silicon thin films deposited under different conditions in a PECVD system. Copyright © 2010 John Wiley & Sons, Ltd.     

Grain boundary potential and charge density at grain boundaries of chemically prepared thin silver sulfide films

The grain boundary potential and interface state charge density at the grain boundaries of silver sulfide (Ag₂S) thin films prepared by chemical conversion of cadmium sulfide (CdS) films have been determined from the dc resistance of the material and are found to be sensitive to annealing. A reduction in the grain boundary potential and the grain boundary charge density of the film has been noticed when the source CdS film is annealed at different temperatures prior to chemical conversion. The variation in the grain boundary charge density of the grown Ag₂S film with source annealing temperature has been found to be similar to that of thin cadmium sulfide film, reported earlier. An additional low temperature heat treatment of the sample results in an enhancement in the charge density at the grain boundaries. The change in the silver vacancy and/or oxygen and sulfur content of the films as revealed from the energy dispersive spectra of the films suggests possible role of film composition on the grain boundary charge density.