Transmission Electron Microscopy Electron Beam Research Articles

Connecting Theory with Experiment to Understand the Sintering Processes of Ag Nanoparticles

A complementary combination of long-time atomistic molecular dynamics simulations and real-time transmission electron microscopy (TEM) images has been utilized for unraveling, at an atomic resolution, the nature of the sintering process of Ag nanoparticles (NPs) induced on the surface of an α-Ag2WO4 crystal for the first time, under the exposure of a TEM electron beam (EB). Temporal evolution of calculated and experimental results highlights the role of the lattice plane matching and the stacking faults along the disorder-to-order transitions of the oriented attachment process. This phenomenon is considered as an example of surface plasmon resonances (SPRs), in which the EB has two effects: first, it provokes the formation of the Ag NPs that, due to the electron irradiation, become SPR electric dipoles, and, second, these Ag NPs undergo sintering processes that are controlled by dipole–dipole interactions forming larger clusters. The predictive power of the simulation model was verified experimentally, pa...

Novel bismuth tri-iodide nanostructures obtained by the hydrothermal method and electron beam irradiation

Bismuth tri-iodide is a layered compound semiconductor which has suitable properties as material for ionizing radiation detection devices. Monocrystals and polycrystalline thin films have been studied for this application, but only recently, the development of nanostructures of this compound has emerged as an interesting alternative for using such nanostructures in new types of radiation detectors or for including them in other applications. Considering this, we present in this work BiI3 nanoparticles successfully synthesized by the hydrothermal method, using a Teflon-lined stainless steel autoclave, at a temperature of 180°C during 8–20h, with BiCl3 and NaI as source materials. We characterized the nanoparticles by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron dispersive spectroscopy (EDS). We obtained small rounded or hexagonal particles (10–20nm in size) and larger structures. The maximum orientation of the nanostructures is along the (0 0 l) family planes and occurs after 16h of synthesis, which arises as the best condition for obtaining BiI3 oriented nanostructures. When a 100kV TEM electron beam was converged on the larger structures, we obtained highly oriented BiI3 hexagonal and rod shaped nanostructures. We found that particles’ shape does not depend on the synthesis time. In addition, results were compared with the ones obtained for nanoparticles synthesized from solution. The present work is an advance in the synthesis of BiI3 nanostructures by the hydrothermal method, and is also the first step on seeking the amenable control of morphology and size of such structures using electron beam irradiation. This last process may be particularly appropriate for producing nanostructures for future applications in new devices.

In Situ Transmission Electron Microscopy Modulation of Transport in Graphene Nanoribbons.

In situ transmission electron microscopy (TEM) electronic transport measurements in nanoscale systems have been previously confined to two-electrode configurations. Here, we use the focused electron beam of a TEM to fabricate a three-electrode geometry from a continuous 2D material where the third electrode operates as side gate in a field-effect transistor configuration. Specifically, we demonstrate TEM nanosculpting of freestanding graphene sheets into graphene nanoribbons (GNRs) with proximal graphene side gates, together with in situ TEM transport measurements of the resulting GNRs, whose conductance is modulated by the side-gate potential. The TEM electron beam displaces carbon atoms from the graphene sheet, and its position is controlled with nanometer precision, allowing the fabrication of GNRs of desired width immediately prior to each transport measurement. We also model the corresponding electric field profile in this three-terminal geometry. The implementation of an in situ TEM three-terminal platform shown here further extends the use of a TEM for device characterization. This approach can be easily generalized for the investigation of other nanoscale systems (2D materials, nanowires, and single molecules) requiring the correlation of transport and atomic structure.

B11-P-03Interactions of TEM electron beam with liquid and nanoparticles in the liquid

Sensitivity of compositional analysis with energy dispersive X-ray spectrometer (EDS) has been improved, since a large solid angle Si drift detector (SDD) and a system with multiple detectors were realized [1,2]. Up to now, transmission electron microscopy (TEM)-EDS has been mostly untouched in the analysis of semiconductor dopants, because of their low concentration. There has been a strong desire to see “limit of detection (LOD)”, using a multiple SDD analysis system. In this study, we explore a concentration at LOD for a dopant in Si device using an FETEM (JEM-2800, JEOL) with two SDDs, whose sensing area is 100 mm each. We examined an As-doped Si wafer as a sample. The concentration profile along z direction has been verified by secondary ion mass spectrometry (SIMS). We made a cross sectional sample for TEM observation. We define an dopant concentration (Cdopant ) at LOD as

In situ experimental mechanics of nanomaterials at the atomic scale

Sub-micron and nanostructured materials exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. These properties are important for their applications as building blocks for the fabrication of nano- and micro-devices as well as for their use as components for composite materials, high-strength structural and novel functional materials. These nano-related deformation and mechanical behaviors, which are derived from possible size and dimensional effects and the low density of defects, are considerably different from their conventional bulk counterparts. The atomic-scale understanding of the microstructural evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials, novel structures and applications. This review presents the recent developments in the methods, techniques, instrumentation and scientific progress for atomic-scale in situ deformation dynamics on nanomaterials, including nanowires, nanotubes, nanocrystals, nanofilms and polycrystalline nanomaterials. The unusual dislocation initiation, partial-full dislocation transition, crystalline–amorphous transitions and fracture phenomena related to the experimental mechanics of the nanomaterials are reviewed. Current limitations and future aspects using in situ high-resolution transmission electron microscopy of nanomaterials are also discussed. A new research field of in situ experimental mechanics at the atomic scale is thus expected. The properties of a material depend not only on its composition but also on the exact arrangement of its atoms. In particular, nanostructured materials such as nanotubes, nanocrystals or polycrystalline materials are much stronger and more elastic than their bulk counterparts and exhibit different plastic deformations, making them suitable for a variety of applications. Lihua Wang and co-workers review how recent developments in transmission electron microscopy (TEM) techniques enable materials scientists to characterize, at the atomic scale, both the chemical composition of a nanomaterial and its deformation dynamics under stress and strain, in situ, and in real time. Some possible pitfalls and challenges remain — for example, over-irradiation with the TEM electron beam may damage the sample studied, and observations must typically be carried out under vacuum — but such detailed characterization provides a good understanding of the mechanisms at play. It therefore holds promise for the control of the mechanical, but also chemical and physical, properties of nanostructured materials through the application of stress or strain. Nanostructured materials always exhibit high strength, ultra-large elasticity and unusual plastic deformation behaviors. The atomic-scale understanding of the microstructure evolution process of nanomaterials when they are subjected to external stress is crucial for understanding these ‘unusual’ phenomena and is important for designing new materials and applications. In situ transmission electron microscopy (TEM) experiments provide the possibility for direct observation of the deformation mechanisms at the atomic scale. This review presents the recent developments of techniques and scientific progress for the atomic-scale in situ TEM deformation dynamics on nanomaterials. Current limitations and future aspects are also discussed.

Investigating the role of microbes in mineral weathering: Nanometre-scale characterisation of the cell–mineral interface using FIB and TEM

Focused ion beam (FIB) sample preparation in combination with subsequent transmission electron microscopy (TEM) analysis are powerful tools for nanometre-scale examination of the cell–mineral interface in bio-geological samples. In this study, we used FIB-TEM to investigate the interaction between a cyanobacterium (Hassallia byssoidea) and a common sheet silicate mineral (biotite) following a laboratory-based bioweathering, incubation experiment. We discuss the FIB preparation of cross-sections of the cell mineral interface for TEM investigation. We also establish an electron fluence threshold (at 200keV) in biotite for the transition from scanning (S)TEM electron beam induced contamination build up on the surface of biotite thin sections to mass loss, or hole-drilling within the sections. Working below this threshold fluence nanometre-scale structural and elemental information has been obtained from biotite directly underneath cyanobacterial cells incubated on the biotite for 3 months. No physical alteration of the biotite was detected by TEM imaging and diffraction with little or no elemental alteration detected by STEM–energy dispersive X-ray (EDX) elemental line-scanning or by energy filtered TEM (EF-TEM) jump ratio elemental mapping. As such we present evidence that the cyanobacterial strain of H. byssoidea did not cause any measurable alteration of biotite, within the resolution limits of the analysis techniques used, after 3 months of incubation on its surface.

Synthesis and Characterization of Hydrocarbon Coating Prepared by in Situ Electron Beam Deposition on ZnSe Nanowire

Hydrocarbon coating has been performed on a single ZnSe nanowire to construct a core/shell nanostructure using transmission electron microscopy (TEM) via in situ electron beam induced deposition. Hydrocarbon contamination resulting from the pump oil vapor of the vacuum system of the TEM column chamber was used as source precursor for the coating. The thickness of the coating layer strongly depends on vacuum level of TEM column chamber, deposition time, and electron beam intensity and, thus, is controllable under TEM inspection. Microstructures of the hydrocarbon coating characterized by TEM demonstrated the amorphous characteristics. Electrical characteristics of such a core/shell ZnSe/hydrocarbon nanostructure were examined and compared with the naked ZnSe nanowire. The significant reduction in the threshold voltage suggests the amorphous hydrocarbon shell has a semiconducting nature but relatively lower Schottky barrier height.

CVD‐Fabricated Aluminum Oxide Coatings from Aluminum tri‐iso‐propoxide: Correlation Between Processing Conditions and Composition

AbstractThis paper presents results on aluminum oxide thin films processed using metal–organic (MO) CVD from aluminum tri‐iso‐propoxide (ATI) without any additional oxygen source, in the temperature range 623–973 K. The films do not diffract X‐rays, except when grown at 973 K or annealed at 1073 K. Their composition was investigated using several techniques; electron probe micro analysis (EPMA), energy dispersive X‐ray spectroscopy (EDX), elastic recoil detection analysis (ERDA), and Rutherford back‐scattering spectroscopy (RBS). It corresponds to the formula AlO(OH) for those grown at 623 K. The composition of films prepared above 688 K corresponds to the formula Al2O3. Between 623 K and 688 K, partly hydroxylated films are obtained. This is confirmed by Fourier transform infrared (FTIR) transmission spectroscopy (no OH absorption band in the 3500 cm–1 region for films prepared above 688 K), and by thermogravimetric analysis (TGA, DTG) (no significant mass loss for films prepared above 688 K). Observations using the transmission electron microscopy (TEM) showed that films prepared at 623 K are amorphous, while those prepared at 973 K are nanocrystalline. In both cases, γ‐Al2O3 crystals are formed and progressively grow on exposure to the TEM electron beam. Knowing the correlation between processing conditions and the composition of such films should help optimize the process with regards to any aimed property of use.

PVP-capped twinned gold plates from nanometer to micrometer

PVP (poly(vinyl pyrrolidone))-capped micrometer-sized twinned gold (Au) plates with the shape of hexagon or triangle have been successfully synthesized in a large quantity by reducing hydrogen tetrachloroauric acid (HAuCl4·3H2O) using ethylene glycol in the presence of (PVP) molecules at 200°C under the extra condition of autogenous pressure. Clear twin boundaries in thus-obtained Au plates have been observed by scanning electron microscope (SEM). To further elucidate the mechanism of formation of the twinned Au plates, transmission electron microscopy (TEM) has been employed to characterize smaller Au nanoplates obtained simultaneously with the Au microplates, the occurrence of 1/3{422} forbidden reflections in selected area electron diffraction (SAED) can be believed to result from the presence of twinning boundary within the Au (111) plane normal to TEM electron beam. In addition, X-ray photoelectron spectroscopy (XPS) experiment has confirmed that PVP molecules exist on the surface of the Au cores, which may play a very important role in the formation and evolution of the twinned Au plates. A possible growth mechanism has been suggested to explain the Au plate evolution from nanometer to micrometer.

Carbon nanotube electrostatic biprism: principle of operation and proof of concept.

During in situ transmission electron microscopy (TEM) field emission experiments, carbon nanotubes are observed to strongly diffract the imaging TEM electron beam. We demonstrate that this effect is identical to that of a standard electrostatic biprism. We also demonstrate that the nanotube biprism can be used to capture electron-holographic information.

Evidence of electron-stimulated self-diffusion in GaN crystals

In situ transmission electron microscopy (TEM) experiments revealed that dimples formed in hexagonal GaN thin crystals by irradiation of a focused TEM electron beam recovers to flatten the surface under a subsequent electron irradiation with a moderately defocused beam. The electron-stimulated recovery can be attributed neither to knock-on damage nor beam heating effects but to electronically enhanced self-diffusion in the GaN crystals.

Mechanisms of void formation in Ge implanted SiO 2 films

The present paper reports on annealing of Ge implanted SiO 2 films and emphasize the observation of voids and the mechanism behind their formation which is considered new. Samples were prepared by ion implanting fluences of 3 × 10 16 and 1 × 10 17 cm −2 respectively of 100 keV Ge into amorphous SiO 2 films which were subsequently annealed up to 1000 °C in a N 2 atmosphere. The structure of the films was studied by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). The most striking of the observations is that spherical voids with diameters up to tens of nanometers are observed in the films after annealing at 1000 °C for 1 h. The volume fraction of voids increases with the Ge fluence. The mechanism behind the void formation is indicated by the evolution of the sample structure after increasing annealing time or temperature; Ge first segregates into nanocrystals which then increase in size by diffusion and Oswald ripening. Ge is quite mobile in SiO 2, and as oxygen or moisture from the annealing atmosphere diffuse in from the surface, the Ge will be bonded in an oxide closer to the surface than the precipitate. There is thus a net flux of Ge out of the nanoprecipitate into an oxide closer to the surface. The volume occupied by the Ge precipitate becomes a void. This model is discussed and it is concluded that it fits the observations. We also report on the filling of the voids by beam induced migration under TEM electron beam exposure.

Electronically induced dislocation glide motion in hexagonal GaN single crystals

Dislocations in crystalline powder of hexagonal GaN intentionally deformed by crushing were examined by transmission electron microscopy (TEM) in order to see if the recombination enhanced dislocation glide (REDG) effect is present in this solid. It was found that dislocations with a Burgers vector of a-type (a/3〈112̄0〉) on the (0001) basal plane and a {11̄0n} pyramidal plane exhibit glide motion at room temperature under the influence of the electron beam used for TEM observations. From a quantitative comparison with the thermal mobility of basal dislocations empirically predicted for h-GaN, the authors concluded that the dislocation glides arose from the REDG effect induced by electronic excitation due to the TEM electron beam irradiation. Some implications of the results were discussed.

The Effect of a Thin Sample on the Extended Defect Evolution in Si+ Implanted Si

ABSTRACTThe annealing kinetics of implant damage in Si+ implanted Si has been investigated using in-situ and ex-situ annealing of transmission electron microscopy (TEM) samples prepared prior to annealing. The defect evolution at 800°C was studied for a Si wafer implanted with Si+ at 100keV to a dose of 2×1014 cm-2. This implant was above the sub-threshold loop formation threshold allowing one to study simultaneously the {311} defect dissolution and dislocation loop nucleation and growth. In order to study the effect on the defect evolution of using a thin sample for an in-situ annealing experiment, a pair of samples, one thick and one thinned into a TEM sample, were annealed in a furnace simultaneously. It was found that the presence of a second surface 2000Å below the implant damage did not affect the extended defect evolution. For the in-situ annealing study it was found that the {311} dissolution process and sub-threshold dislocation loop formation process was not affected by the TEM electron beam at 160kV as long as an 800°C furnace pre-anneal was done prior to in-situ annealing. The dissolution rate of the {311} defects was used to confirm the TEM holder furnace temperature. The results of both the in-situ the {311} defects is released during the 311 dissolution process and 30% comes to reside in dislocation loops. Thus, the loops appear to contain a significant fraction of the total interstitial concentration introduced by the implant.