Electron Beam Imaging Research Articles

Biomineralisation in the Palaeozoic oceans: Evidence for simultaneous crystallisation of high and low magnesium calcite by phacopine trilobites

The chemical composition and microstructure of the calcite cuticles of eleven species of phacopine trilobites have been investigated by electron beam imaging, diffraction, and microanalysis, and results reveal that the lenses of their schizochroal eyes differed significantly in chemical composition from the rest of the cuticle in vivo. Apart from the eye lenses, most cuticles are inferred to have escaped extensive recrystallisation because their constituent crystals are sub-micrometre in size and have a preferred orientation that is consistent between species. Their current compositions of ~1.4 to 2.4mol% MgCO3 are likely to be close to original values, although as they commonly luminesce and contain detectable manganese and iron, some diagenetic alteration has taken place. The associated lenses have a microstructure that is suitable for focusing light, yet are optically turbid owing to the presence within calcite of micropores and crystals of microdolomite, apatite, celestite and pyrite. The microdolomite indicates that lenses recrystallised from an original high-Mg calcite composition and this is supported by the presence of nanometre-scale modulated microstructures in both the calcite and dolomite. These lenses currently contain ~1 to 6mol% MgCO3, and by comparison with the proportion of magnesium lost from echinoderm stereom in the same thin sections, may have contained ~7.5mol% MgCO3in vivo. In some samples, more extensive diagenetic alteration is evidenced by recrystallisation of the cuticle including lenses to coarse equant calcite or enrichment of the cuticle, but not necessarily the lenses, in magnesium accompanying replacement by a Mg–Fe phyllosilicate. The phacopine trilobites had to modify partition coefficients for magnesium considerably in order to grow lenses with contrasting compositions to the rest of their cuticles, and such a strong vital effect on biomineralisation suggests that incorporation of magnesium was essential for functioning of their calcite optical systems.

Transfer-printing of single DNA molecule arrays on graphene for high-resolution electron imaging and analysis.

Graphene represents the ultimate substrate for high-resolution transmission electron microscopy, but the deposition of biological samples on this highly hydrophobic material has until now been a challenge. We present a reliable method for depositing ordered arrays of individual elongated DNA molecules on single-layer graphene substrates for high-resolution electron beam imaging and electron energy loss spectroscopy analysis. This method is a necessary step toward the observation of single elongated DNA molecules with single base spatial resolution to directly read genetic and epigenetic information.

Combined electron beam imaging and ab initio modeling of T1 precipitates in Al–Li–Cu alloys

Among the many considerable challenges faced in developing a rational basis for advanced alloy design, establishing accurate atomistic models is one of the most fundamental. Here we demonstrate how advanced imaging techniques in a double-aberration-corrected transmission electron microscope, combined with ab initio modeling, have been used to determine the atomic structure of embedded 1 nm thick T1 precipitates in precipitation-hardened Al–Li–Cu aerospace alloys. The results provide an accurate determination of the controversial T1 structure, and demonstrate how next-generation techniques permit the characterization of embedded nanostructures in alloys and other nanostructured materials.

A new technique to derive particle size distributions and aerosol number concentrations directly from thermophoretic data

The manufacture of many high value-added powders takes place by the decomposition of gaseous precursors in aerosol tube reactors. Historically, process improvements were achieved by making changes on the outside of the reactor and observing what comes out at the end of the pipe. The development of increasingly accurate aerosol dynamics models based on engineering first principles has been limited because models were typically validated on integral properties of ex situ product, instead of particle properties measured at multiple positions inside the reactor. In this study, a model reactor was equipped to capture samples thermophoretically from 15 internal positions. Additional in-line measurements were achieved with a multi-stage inertial impactor and by traditional analysis of ex situ product. Calculations were performed to verify that thermophoresis was the dominant mechanism of particle capture. The thermophoretic samples were analyzed by electron beam microscopy and image analysis to develop particle size distributions at each of the internal positions inside the reactor. An approximation of Talbot's Equation for thermophoretic velocity allowed experimental measurements to be combined with thermophoretic sample data to give predictions of particle number concentration corresponding to the precise sampling locations. The combinations of particle size distributions and number concentrations provide powerful insights on particle nucleation and growth dynamics.

Ultrafast electron beam imaging of femtosecond laser-induced plasma dynamics

Plasma dynamics in the early stage of laser ablation of a copper target are investigated in real time by making ultrafast electron shadow images and electron deflectometry measurements. These complementary techniques provide both a global view and a local perspective of the associated transient electric field and charge expansion dynamics. The results reveal that the charge cloud above the target surface is composed predominantly of thermally ejected electrons and that it is self-expanding, with a fast front-layer speed exceeding 107 m/s. The average electric field strength of the charge cloud induced by a pump fluence of 2.2 J/cm2 is estimated to be ∼2.4×105 V/m.

Alteration and associated impurity element enrichment in detrital ilmenites from the Murray Basin, southeast Australia: a product of multistage alteration

Alteration and associated impurity element enrichment in detrital ilmenites from the Murray Basin in southeastern Australia was examined using electron-beam imaging and analysis techniques. A database of over 15 000 analyses from 22 deposits (16 coarse grained, six fine grained) showed a broad spectrum of alteration products from primary ilmenite through to pseudorutile, hydroxylian pseudorutile and minor leucoxene. Impurity element levels were strongly affected by the degree of alteration. Ilmenites from fine-grained deposits were less altered than their coarse-grained equivalents. Regional analysis of the data showed an increase in the degree of alteration towards the northern margins of the basin. Two types of ilmenite alteration were observed: a continuous process in which ilmenite alters to pseudorutile and then leucoxene (Type I) plus a second type of alteration which converts ilmenite directly to hydroxylian pseudorutile (Type II). Type I alteration was present throughout all deposits and occurred prior to final emplacement under acidic oxygenated conditions. Type II alteration was restricted to deposits in the more northern sectors of the basin. Conditions for the formation of Type II alteration are unknown but textural evidence indicates alteration was in situ. The Murray Basin ilmenites represent the final products of multi-stage alteration processes.

Start-to-end simulation of a Thomson source for mammography

Thomson scattering X-ray sources have many features which are of relevance for several applications: the main one is the capability to produce intense, quasi-monochromatic, tunable X-ray beams, after collimation, still with a reasonably small size apparatus. Applications to medical physics are straightforward, in particular in mammography where dose control in screening programs is the main relevant issue. An optimal choice of the X-ray energy to image the breast will result in a best image quality and hence will lead to a dose reduction. A Thomson scattering source is presently under development at the Frascati National Laboratories (LNF) of INFN (Istituto Nazionale di Fisica Nucleare). A complete simulation of the source including electron beam, laser beam, Thomson interaction and X-ray imaging is presented. The X-rays are generated in the energy range suitable for mammography and used to generate images of a mammographic phantom. Image quality is evaluated in terms of dose efficiency and compared to those obtained by monochromatic beams and conventional X-ray tubes.

A study of electrical characteristic changes in MOSFET by electron beam irradiation

Mechanisms for electrical characteristic changes in MOSFET caused by electron beam irradiation were studied using a SEM-based nano-probing system. A shift in V th occurs when a hole is trapped in a defect (oxygen vacancy) in the gate dielectric layer. Holes are generated when the plasmon is excited by electron beam irradiation. Further, an electric field is created by the positive charge-up resulting from electron beam irradiation of the ILD, causing an increase in leakage between gate and drain leading to an increase in I off. This study shows that advanced devices can be measured using a SEM-based nano-probing system without inducing electrical characteristic changes by optimizing the measurement conditions such as acceleration voltage, electron beam current, image magnification, ILD thickness, and electron beam irradiation time.

Optical fiber-based single-shot picosecond transient absorption spectroscopy

A new type of single-shot transient absorption apparatus is described based on a bundle of optical fibers. The bundle contains 100 fibers of different lengths, each successively giving approximately 15 ps longer optical delay. Data are collected by imaging light from the exit of the bundle into a sample where it is overlapped with an electron pulse or laser excitation pulse, followed by imaging onto a charge coupled device (CCD) detector where the intensity of light from each fiber is measured simultaneously. Application to both ultrafast pump-probe spectroscopy and pulse radiolysis is demonstrated. For pulse radiolysis, the prototype bundle provides the ability to collect data with a time resolution limited only by the electron pulse width of 7-10 ps, over a total single-shot time window of approximately 1.5 ns. Tunable probe light is obtained from a titanium-sapphire laser and an optical parametric amplifier. Corrections are made to remove the fiber-to-fiber variations in signal magnitude due to the spatial overlap of the electron beam and probe image. High quality data can be collected over most of the sensitivity range of the CCD camera detectors. The single-shot instrument is valuable for measurement of samples that are only available in very limited quantities, are too viscous to flow, or are rigid. It is therefore excellent in applications, such as picosecond pulse radiolysis, where the thousands of pulses per kinetic trace typical in classical pump-probe experiments can damage the sample before useful results could be obtained.

Hierarchical and Nanosized Pattern Formation Using Dual Beam Focused Ion Beam Microscope

Direct and controlled nanopatterning is a promising new area to study in nanofabrication. Dual ion and electron beam microscopy offers such nanofabrication potentials with simultaneous high resolution electron beam imaging and ion beam patterning. This work investigates the unexplored potentials of ion and electron dual beam microscope to create different feature shape and hierarchical sized nanopatterns. Nanotrack and nanopore patterns with 100 nm distance were created with focused ion beam on high purity aluminum substrate. The track width is less than 32 nm and the pore size is less than 50 nm. Different size nanopores have been precisely aligned to form hierarchical pore patterns. Also, the nanopatterns have been selectively modified to change the local nanofeature dimensions by sweeping low dose ions across a defined area. This work shows that dual beam focused ion beam technique is capable of overcoming some basic limitations of current nanofabrication processes and creating innovative nanopatterns for different applications.

Implications for Ultrafast Reflection Electron Diffraction from Temporal and Spatial Evolution of Transient Electric Fields

AbstractUnderstanding interaction of ultrafast pulsed laser with matter is critical for probing ultrafast processes in materials science, understanding the physics of laser ablation and the laser induced non-equilibrium carrier dynamics in metals and semiconductors, including plasmonics. When an intense laser pulse of femtoseconds (fs) in duration hits the surface of a targeted matter, it excites a hot electron gas. Part of the hot electrons is emitted from the surface in a way similar to thermionic emission. Electrons can also be emitted through multiphoton photoemission (MPPE) or thermally assisted MPPE. The emitted electrons travel at speeds that create transient electric fields (TEFs). To detect TEFs and study the dynamics of emitted electrons, we have developed a time resolved electron beam imaging technique that allows us to measure TEFs above a sample surface at picoseconds time resolution. We have also developed a model of the TEFs based on the propagation of emitted electrons and the percentage of electrons escaping from the surface. We examine the significance of TEFs for ultrafast reflection electron diffraction by examining anomalous effects in ultrafast reflection high energy electron diffraction (RHEED) of silicon surfaces.

Electron beam confinement and image contrast enhancement in near field emission scanning electron microscopy

In conventional scanning electron microscopy (SEM), the lateral resolution is limited by the electron beam diameter impinging on the specimen surface. Near field emission scanning electron microscopy (NFESEM) provides a simple means of overcoming this limit; however, the most suitable field emitter remains to be determined. NFESEM has been used in this work to investigate the W (1 1 0) surface with single-crystal tungsten tips of (3 1 0), (1 1 1), and (1 0 0)-orientations. The topographic images generated from both the electron intensity variations and the field emission current indicate higher resolution capabilities with decreasing tip work function than with polycrystalline tungsten tips. The confinement of the electron beam transcends the resolution limitations of the geometrical models, which are determined by the minimum beam width.

Tunable Nanostructures and Crystal Structures in Titanium Oxide Films

Controllable nanostructures in spin coated titanium oxide (TiO2) films have been achieved by a very simple means, through change of post deposition annealing temperature. Electron beam imaging and reciprocal space analysis revealed as-deposited TiO2films to be characterized by a dominant anatase phase which converts to the rutile form at 600 °C and reverts to the anatase modification at 1,200 °C. The phase changes are also accompanied by changes in the film microstructure: from regular nanoparticles (as-deposited) to nanowires (600 °C) and finally to dendrite like shapes at 1,200 °C. Photoluminescence studies, Raman spectral results, and X-ray diffraction data also furnish evidence in support of the observed solid state phase transformations in TiO2.

Transmission Electron Microscope-Induced Structural Evolution in Amorphous Fe, Co, and Ni Oxide Nanoparticles

The high-energy electron beams in transmission electron microscopes (TEM) are known to cause structural changes and damage in some materials. In this paper, we describe unique and reproducible TEM-induced changes to the morphology of amorphous metal oxide (Fe, Co, and Ni) nanoparticles. The studied particles were synthesized via literature methods and fully characterized by X-ray powder diffraction and time-resolved, low-dose TEM. As a result of electron beam irradiation, we observe these particles to transform from initially solid spheres to core/void/shell structures and eventually to hollow nanoparticles. The rate of these transformations depends on the size and composition of the particles but is not unique to the Fe oxide we previously reported. These data suggest that structural analysis of nanoparticles by TEM must consider the impact of the high-energy electron beam and use low-dose imaging.

Inhibiting spontaneous etching of nanoscale electron beam induced etching features: Solutions for nanoscale repair of extreme ultraviolet lithography masks

Electron beam induced etching (EBIE) is an important technique for repairing nanoscale defects on extreme ultraviolet (EUV) lithography masks as it provides excellent spatial resolution and etch selectivity while minimizing collateral damage to the mask. While EBIE itself is a complex process, a current problem with EBIE of the TaN EUV mask absorber layer using XeF2 is the spontaneous etching of repaired features during subsequent edits of the mask. This work explores three passivation techniques for controlling the spontaneous etching after an EBIE repair is made. An oxygen plasma was used to attempt to oxidize the TaN sidewalls, but it was not successful at stopping the spontaneous etching. An active electron beam induced passivation using water was successful at stopping the spontaneous etching. Also, simple adsorption of water molecules on the TaN sidewalls was successful at inhibiting spontaneous etching. The successful passivation strategies are affected by subsequent scanning electron beam imaging. It was determined that the electron beam activated passivation can be damaged by electron beam imaging in the presence of residual XeF2 on the surface. Also, the adsorbed water passivation strategy is susceptible to electron induced desorption of the water.

Focused Ion Beam in Thermal Science and Engineering

Laboratory of Thermodynamics, ETH Zurich CH-8092 Switzerland In this paper, utilizing a focused ion beam source for applications in thermal science is demonstrated. Focused-ion-beam (FIB) nanolithography has been used to make electrical contacts on nanometer-sized materials. However, a foreseeable damage occurring in these materials by highly energetic ion bombardment during metal deposition restrains its use. The appearance of the dual beam (conventional FIB with a scanning electron microscope) has facilitated the use of dual-beam FIB nanolithography owing to the possibility of acquiring electron beam images in situ and dissociating metalorganic compounds, giving rise to electron-beam-induced metal deposition [1]. Because interaction between electrons and the sample is less destructive than using ions, performing an electron-assisted deposition on the nanostructure can minimize undesired surface damage and structure modification of the nanostructure. The thermal properties of individual multi-walled carbon nanotubes was measured by utilizing the 4-point-probe 3-ω method, based on the fact that the third harmonic amplitude and phase as a response to applied alternate current at fundamental frequency, ω, can be expressed in terms of thermal conductivity and diffusivity. To this end, a microfabricated device composed of four metal electrodes was modified to manufacture nanometer-sized wires by using a focused ion beam source as shown in Fig. 1a. A carbon nanotube could then be suspended over a deep trench milled by the focused ion beam, preventing heat loss to the substrate (Fig. 1b). To deposit individual carbon nanotubes, we utilized the principle of dielectrophoresis (DEP). The dielectrophoresis has been considered as an excellent method for CNT manipulation. Herein, we applied a high-frequency (5 MHz) ac field combined with dc offset between the pads, 1 and 4. When a CNT touches the electrodes, it will stick to them and stays there by Van der Waals force [2]. Finally, to minimize the electrical contact resistance between carbon nanotubes and the metal electrodes, electron beam “soldering” was performed. The pads 1 and 4 have round shapes on the tip, which aids carbon nanotube deposition. Fig. 2 shows three different measurements of 3-ω signals for carbon nanotubes submerged in vacuum, air and deionized water. To this end, the 4-wire configuration (Fig. 1c) was utilized for measuring the 3

Quasianamorphic optical imaging system with tomographic reconstruction for electron beam imaging

We have developed a quasianamorphic optical tomography system coupled to a streak camera to provide continuous recording of the electron beam profile of an intense, long-pulse induction accelerator. A tomographic reconstruction method based on a maximum-entropy algorithm is used to reconstruct the images. The system has simplified the calculation of beam moments, eliminated ambiguity due to beam motion, and contributed to accelerator tuning.

Radiation damage to protein specimens from electron beam imaging and diffraction: a mini-review of anti-damage approaches, with special reference to synchrotron X-ray crystallography

Recent research progress using X-ray cryo-crystallography with the photon beams from third-generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X-ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300-400 kV accelerating voltage, low-dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 A (0.6 nm) for single particle specimens, and of 1.9 A for two-dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three-dimensional protein crystals during synchrotron X-ray diffraction.

Study and development of an innovative electron beam imaging system for dosimetry in IORT (Intra Operative Radiation Therapy)

Intra Operative Radiation Therapy (IORT) is a technique based on delivery of a high dose of ionising radiation to the cancer tissue, after tumour ablation, during surgery, while reducing the exposure of normal surrounding tissue. The Novac7 is a new linear accelerator expressly conceived to perform in the operating theatre. This accelerator supplies electron beams with high dose rate (up to 20 cGy/min). Because of these peculiar characteristics, classical dosimetric techniques are not able to give at once a real-time response and an extensive measure of the absorbed dose. In the framework of a research contract between ENEA (Italian National Agency for Environment and Alternative Energy Research) and the Physics Department of the University of Bologna, Italy, a new system has been developed to study and visualise the Novac7 electron beam. The system is conceived as a grid that consists of two bundles of scintillating optical fibers (SOF) over-crossing each other, optically coupled with two arrays of photodiodes as read-out system. The instrument samples the delivered beam at 100 Hz. A dedicated software collects the signals from the photodiodes and reconstructs the bi-dimensional image. Moreover it provides a series of dosimetric parameters. We studied an appropriate reconstruction algorithm searching for the best compromise between computational complexity and high precision. An accelerator ranging from 3 to 12 MeV has been used for the experimental tests. The various phases of design, development and characterisation of the instrument will be illustrated, as well as some experimental tests performed with the prototype. The system is able to give a real time response (within 30 s), while the resolution is of 1 mm. The response is linear versus dose and the measures are not affected by the high dose rate. The conclusions confirm the capability of the instrument to overcome problems encountered with classic dosimetry, showing that the results obtained strongly encourage the continuation of this research.

Novel methods to characterize bulk RE-BCO superconductors

We report on new techniques for the investigation of the radial and the axial homogeneity of top seeded melt-textured RE–Ba–Cu–O (REBCO) monoliths. Whereas the traditional Hall probe scanning technique of trapped fields at the surface of the superconductor provides only global information on the patterns of supercurrent flow, a modified scanning technique employing sequentially increasing activation fields leads to more detailed information on the flux penetration process and, therefore, on possible radial inhomogeneities of the defect structure for flux pinning. Particularly valuable information on this subject can be deduced from a new technique, the magnetoscan, that allows the flow of the local supercurrent in large bulk monoliths on the scale of less than 1 mm to be investigated. Combination of the magnetoscan with optical or electron beam imaging of the sample surface results in full characterization of the bulk microstructure, developed during the growth process, and its effective flux pinning capability. We show that these techniques can also be used to investigate axial inhomogeneities, i.e. those developing along the c-axis (growth direction), by removing layers of the monolith step by step and by observing the microstructure and the local supercurrent flow in sequential layers. It turns out that the c-growth sector is always characterized by a lower current carrying capability and that characteristic features of the growth morphology appear at the a-growth sector boundaries. Finally, initial results on the current flow in multi-seeded bulks will be presented.