Penetration Depth Of Electrons Research Articles

Cathodoluminescence of ZnO Nanostructure Arrays Hydrothermally Grown on the Patterned Seed Layers Using a Polystyrene-Sphere-Based Lithographic Method

Periodically distributed ZnO nanostructure arrays were hydrothermally grown on silicon substrates. For the preferential, site-selective growth of the ZnO nanostructures, a seed layer was patterned using self-assembled monolayers of polystyrene spheres (PSs) lithography technique. The size of the seed layer was controlled by the size of PSs, which was determined by oxygen plasma etching time. Due to the existence of numerous nucleation sites, flower-like (FL) ZnO nanostructures grew on the large seed layer over 800 nm in diameter. By reducing the size of the seed layer, we could make a couple of ZnO nanowires grow on a single seed layer island. We examined the cathodoluminescence (CL) spectra of FL ZnO nanostructure arrays and coupled (CO) ZnO nanowire arrays. Since the dimension of the nanostructures is smaller than or comparable to the penetration depth of the incident electron, CL signal would be generated in the whole body of the nanostructures. So, the CL intensity might be proportional to the surface area through which the photons could escape. As a result, it is natural that the CL intensity from the FL ZnO nanostructure arrays should be stronger than that from the CO ZnO nanowire arrays. However, in spite of the smaller surface area, the CL intensity was strikingly enhanced in the CO ZnO nanowire arrays compared with the closely-packed ZnO nanowire arrays. It could be attributed to the suppression of the near-band-edge ultraviolet emission in the [0001] direction, which was observed in the monochromatic CL measurement.

Plasma Damage Mechanism of Electron Beam Curing Process for Spin on Dielectrics

This letter presents the plasma damage mechanism of electron beam curing process for spin on dielectrics. Device damage is studied using the antenna gate metal-oxide-semiconductor field-effect transistor (MOSFET) in terms of the threshold voltage variation as a function of electron beam conditions such as ambient and cathode voltage. Threshold voltages of nMOSFET are decreased by an electron beam curing process without antenna ratio dependency. The electron energy and interlayer dielectric thickness between active devices and metal layers largely affect the variation of threshold voltage. From the experimental results, it is concluded that device damage induced by an electron beam curing process is characterized as radiation damage rather than electron charging damage. For the damage free electron beam curing process, it is essential to control the penetration depth of high-energy electrons by adjusting the cathode voltage while considering the dielectric thickness over active devices.

Controllable Shrinking and Shaping of Glass Nanocapillaries under Electron Irradiation

The ability to reshape nanopores and observe their shrinkage under an electron microscope is a powerful and novel technique. It increases the sensitivity of the resistive pulse sensing and enables to detect very short and small molecules. However, this has not yet been shown for glass nanocapillaries. In contrast to their solid-state nanopore counterparts, nanocapillaries are cheap, easily fabricated and in the production do not necessitate clean room facilities. We show for the first time that quartz nanocapillaries can be shrunken under a scanning electron microscope beam. Since the shrinking is caused by the thermal heating of the electrons, increasing the beam current increases the shrink rate. Higher acceleration voltage on the contrary increases the electron penetration depth and reduces the electron density causing slower shrinkage. This allows us to fine control the shrink rate and to stop the shrinking process at any desired diameter. We show that a shrunken nanocapillary detects DNA translocation with six times higher signal amplitudes than an unmodified nanocapillary. This will open a new path to detect small and short molecules such as proteins or RNA with nanocapillaries.

Y2O3–Lu2O3 co-doped molybdenum secondary emission material

A new kind of RE2O3–Mo cathodes co-doped with Y2O3 and Lu2O3 were prepared by a solid–liquid method combined with the spark plasma sintering technique. The secondary electron emission property and secondary emission mechanism of the cathode have been studied. The results show that Y2O3–Lu2O3 co-doped Mo cathode exhibits better secondary emission property than single Y2O3 doped molybdenum cathode, and the maximum secondary emission yield (δmax) can reach 4.616 after being activated at 900°Cb. The Y2O3–Lu2O3 co-doped Mo cathode has high penetration depth of primary electrons and moderate escape depth of secondary electrons. Furthermore, the work function of Y2O3–Lu2O3–Mo cathode (2.41eV) is lower than that of Y2O3–Mo cathode (3.59eV). These phenomena are responsible for its excellent secondary emission property.

Hard x-ray phase contrast imaging using a tabletop Talbot–Lau interferometer with multiline embedded x-ray targets

We demonstrate hard x-ray phase contrast imaging (XPCI) using a tabletop Talbot-Lau interferometer in which the x-ray source and source grating are replaced with an x-ray source with multiline metal targets embedded in a diamond substrate. This source realizes an array of linear x-ray sources of a few micrometers width without fabrication difficulty because of the shallow penetration depth of electrons irradiated to the metal targets. This enhances the coherence of x rays from each linear source and allows XPCI within 45 cm source-detector distance under 1.2 W input power for 8 keV x rays.

Selective Ablation of Thin Films by Ultrashort Laser Pulses

Laser ablation of bulk solid could obtain superior machining accuracy by utilizing ultrashort pulses due to the smaller laser-induced thermal diffusion length, which minimizes the heat affected zone. In selective laser ablation of thin films, the precise control of the heat affected zone in the vertical direction becomes critical in order to avoid the damage of the substrate. For this application an effective thermal penetration depth can be defined determined by not only the optical penetration depth, but also the lattice thermal diffusion length in short pulse ablation or the hot- electron penetration depth in case of ultrashort laser ablation. The ablation characteristics, such as the threshold fluence and the multi-pulse incubation effect, are strongly dependent on the film thickness when it is in the range of the effective thermal penetration depth.

Modification of Particle Filled Polymers with High Energy Electrons Under In‐Stationary Conditions of Melt Mixing

AbstractSummary: Polymer modification with high energy electrons is well‐established in polymer industry and used for degradation, cross‐linking, grafting, curing, and polymerization. These applications use local and temporal precise input of energy in order to generate excited atoms or molecules and ions for subsequent molecule changes via radical induced chemical reactions. In the present study, high energy electrons have been used to modify polyolefine (polyethylene and polypropylene) systems in presence of a grafting agent under stationary and in‐stationary conditions. Polymer modification with high energy electrons under stationary conditions characterizes a process where required absorbed dose is applied to polymers in solid state and at room temperature. Polymer modification with high energy electrons under in‐stationary conditions is a novel process where required absorbed dose is applied in molten state during melt mixing process. In this novel process, the penetration depth of electrons is limited to a part of mixing volume. The total mixing volume is modified due to the change of polymer mass within the penetration depth of electrons during mixing process. A 1.5 MeV electron accelerator has been directly coupled to a banbury mixing chamber in order to study this novel process. In comparison to the stationary process, the main differences are working at higher temperature, absence of any crystallinity, intensive macromolecular mobility as well as intensive mixing during dose application. The influence of both processes on mechanical properties and flame resistance of polymer composites is discussed.

E-beam invasiveness on 65 nm complementary metal-oxide semiconductor circuitry

Postsilicon debug techniques may require e-beam imaging and nanomachining in the vicinity of live metal-oxide semiconductor (MOS) devices. In that context the authors have investigated the invasiveness of e-beam irradiation on MOS devices to 65 nm integrated circuits, tracked as percent change in ring-oscillator frequencies. Device preparation consisted of backside thinning by mechanical polish, local laser chemical etching to 10 μm Si, and finally, focused ion beam gas-assisted etching, leaving 200–2000 nm remaining Si. This was followed by e-beam exposure at various acceleration energies and doses, from a marginally detectable device degradation dose of 10−4 nC/μm2, and beyond a dose causing total transistor failure around 1.25 nC/μm2, at 30 keV. The authors find that relative frequency degradation depends on irradiation dose as a power law which may be applied to limit unwarranted device degradation. E-beam nanomachining is typically performed at low acceleration energies, conveniently reducing the electron penetration depth, and hence a negligible dose makes it to the devices. This was verified experimentally on 65 nm devices. The results herein put upper bounds on damage-free e-beam-based circuit edit and failure analysis in post-Si debug.

From 2D slices to 3D volumes: Image based reconstruction and morphological characterization of hippocampal cells on charged and uncharged surfaces using FIB/SEM serial sectioning

3D imaging at a subcellular resolution is a powerful tool in the life sciences to investigate cells and their interactions with native tissues or artificial objects. While a tomographic experimental setup achieving a sufficient structural resolution can be established with either X-rays or electrons, the use of electrons is usually limited to very thin samples in transmission electron microscopy due to the poor penetration depths of electrons. The combination of a serial sectioning approach and scanning electron microscopy in state of the art dual beam experimental setups therefore offers a means to image highly resolved spatial details using a focused ion beam for slicing and an electron beam for imaging. The advantage of this technique over X-ray μCT or X-ray microscopy attributes to the fact that absorption is not a limiting factor in imaging and therefore even strong absorbing structures can be spatially reconstructed with a much higher possible resolution. This approach was used in this study to elucidate the effect of an electric potential on the morphology of cells from a hippocampal cell line (HT22) deposited on gold microelectrodes. While cells cultivated on two different controls (gold and polymer substrates) did show the expected stretched morphology, cells on both the anode and the cathode differed significantly. Cells deposited on the anode part of the electrode exhibited the most extreme deviation, being almost spherical and showed signs of chromatin condensation possibly indicating cell death. Furthermore, EDX was used as supplemental methodology for combined chemical and structural analyses.

Evolution and control of dislocations in GaN grown on cone-patterned sapphire substrate by Metal Organic Vapor PhaseEpitaxy

In this paper, three GaN epilayers grown on commercially available cone-patterned sapphire substrates (PSS) by Metal Organic Vapor Phase Epitaxy (MOVPE) were investigated. Voltage dependence of monochromatic cathodoluminescence (CL) was applied to investigate the threading dislocation (TD) behaviors. Fewer TDs were observed in CL images when the penetration depth of electron was made shorter by altering the acceleration voltage from 30 to 5 kV. It was shown that many TDs were generated on the peaks of the cones, in-between cones, and in the coalescence regions, while there was almost no TD above the slopes of the cones. When the growth pressure was changed from 200 to 100 Torr during the final stage, fewer TDs were observed in CL images, and the full widths at half maximum (FWHMs) for the (0 0 2) and (1 0 2) reflections’ X-ray diffraction (XRD) rocking curves decreased. Furthermore, when the growth temperature was decreased from 1040 to 1000 °C during the middle stage, a clear hexagonal distribution of TDs was observed and the FWHMs for the (0 0 2) and (1 0 2) reflections’ XRD rocking curves further decreased. Atomic force microscopy (AFM) was used to investigate the surface morphology of the samples. In situ optical reflectivity spectra were measured to monitor the growth mode during the different growth stages. Based on the CL and reflectivity spectra results, the process of TDs’ evolution and distribution was deduced and sketched.

Study of Semiconductor Multilayer Structures by Cathodoluminescence and Electron Probe Microanalysis

Complementary nondestructive electron probe methods were used for characterization of semiconductor multilayer structures. We used cathodoluminescence and electron probe microanalysis for studying laser heterostructures based on GaAs/AlGaAs/InGaAs/GaAs and InGaN/GaN. Our latest investigation showed the possibility of measuring the composition of buried layers and determining the composition of thin nanoscale layers by electron probe microanalysis. Simultaneous use of local cathodoluminescence is very useful for defect study in bulk semiconductors, epilayers, and multilayer heterostructures. This method allows characterization of charge-carrier transport properties and diffusion length in multilayer structures, using the variation of the electron beam energy and calculation of the electron penetration depth.

Emission property of Y 2O 3-doped Mo secondary emitter

Y 2O 3-doped Mo secondary emitters were prepared by liquid-liquid doping and solid-solid doping, respectively. The back-scattered scanning observation result indicates that the emitter prepared by liquid-liquid doping has fine microstructure whereas that prepared by solid-solid doping has large grain size. Y 2O 3-doped Mo emitter with small grain size prepared by liquid-liquid doping exhibits high emission property, i.e., the secondary electron yield can get to 5.24, about 1.7 times that prepared by solid-solid doping. Moreover, Y 2O 3-doped Mo emitter exhibits the best emission performance among La 2O 3-doped Mo, Y 2O 3-doped Mo, Gd 2O 3-doped Mo and Ce 2O 3-doped Mo emitters due to the largest penetration depth of primary electrons and escape depth of secondary electrons in this emitter. The secondary emission of the emitter with small grain size can be explained by reflection emission model and transmission emission model, whereas only transmission emission exists in the emitter with large grain size.

Morphological and topological analysis of coarsened nanoporous gold by x-ray nanotomography

Nanoporous gold has numerous potential applications 1 in optical-active materials, catalysts, sensors, mechanical actuators, fuel cell and microbalance electrodes, and as a coating for medical devices. Nanoporous gold is fabricated by dealloying silver-gold solid solutions. This results in fully openporosity bicontinuous nanoporous structures, following the rearrangement of the gold atoms into interconnected ligaments as the silver atoms are selectively removed. 2 Optimization of the optical, chemical, and mechanical properties of nanoporous gold depends on its pore size, which is tunable by structural coarsening during annealing. 3 Various electronbased techniques have been employed to determine the morphology of nanoporous gold films after dealloying, but none are suited to three-dimensional 3D study of thick specimens of coarsened nanoporous gold. Tomographic transmission electron microscopy provides very high spatial resolution but is limited to examining thin films, and cannot image coarsened structures once the gold ligament size is close to the electron penetration depth. 4,5 Focused ion beam FIB-scanning electron microscopy serial sectioning 6 combines high resolution with depth penetration, however, being a destructive method, it cannot be used to observe dynamic processes and structural evolution in 3D. X-ray microcomputed tomography is a powerful nondestructive tomographic tool whose resolution is however typically limited to the micron scale. 7 Transmission x-ray microscopy TXM using synchrotron x-ray sources offers 30 nm resolution, fast image acquisition, and the ability to nondestructively image samples tens of microns thick. Combining TXM with tomographic methods allows complex nanostructures to be imaged in 3D. 8 Here, we perform x-ray nanotomography on a dealloyed and coarsened nanoporous gold wire. We quantitatively analyze the morphological and topological properties of nanoporous gold from the reconstructed images using methods developed in earlier work. 9

Study on the correlation between plasma electron temperature and penetration depth in laser welding processes

The plasma electron temperature has been estimated starting from the spectroscopic analysis of the optical emission of the laser-generated plasma plume during quite diverse stainless steel welding procedures (c.w. CO2 and pulsed Nd:YAG). Although the optical emissions present different spectral features, a discrete contribution of several iron lines can be highlighted in both types of welding. We have found that the electron temperature decreases as the laser power is enhanced, in static as well as dynamic conditions. Such a result could be useful to develop a closed loop control system of the weld penetration depth.

Charge regulation mechanism of grounded-coated insulators

We have performed the measurement of the trapped charge density on the gold-coated glass substrates under electron-irradiation in scanning electron microscope (SEM), using the so-called electrostatic influence method. We show that the generated internal electric field shortens the penetration depth of incident electrons, leading to spurious effects for microanalysis such as the migration of mobile ions.

Absorption effect on the cathodoluminescence spectrum ofn-GaN

The cathodoluminescence spectrum of n -GaN crystal has been studied with emphasis placed on its self-absorption behavior. An improved analysis of cathodoluminescence spectral shift with electron penetration depth is shown, according to the following approach: (i) a main band and a sub-band, both of Gaussian nature, are used for spectral convolution; (ii) the observed absorption edge is still described in terms of the Urbach rule, but the Urbach tail is experimentally retrieved by directly using the absorption spectrum (at low energies) obtained from standard cathodoluminescence spectra; (iii) an experimental approach is used to retrieve the actual morphology of the cathodoluminescence probe.

Resolving power of lens‐less low energy electron point source microscopy

Simulations show the resolving power of lens-less low energy electron point source microscopy to be approximately 15 A for electron energies of between 14 and 105 eV. This resolution can be improved to 10 A by employing a composite hologram method. However, these values fall short of predictions of at least 3 A resolution for electron energies in this range because the limited divergence angle of the electron beam had not previously been taken into account. Also shown is that electron coherence from field emitting tips that terminate in a single atom will not limit the resolving power as much as the beam divergence angle. The penetration depth of electrons with energies of between 50 and 100 eV, into biological molecules, was estimated from the inelastic mean free path length to be 25 A . This places an upper limit on the size of biological molecules for which internal structural information can be obtained using low energy electrons.

Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy

We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100 eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250 eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.

Superhydrophobic polytetrafluoroethylene thin films with hierarchical roughness deposited using a single step vapor phase technique

Superhydrophobic polytetrafluoroethylene films with hierarchical surface roughness were deposited using pulse electron deposition technique. We were able to modulate roughness of the deposited films by controlling the beam energy and hence the electron penetration depth. The films deposited at higher beam energy showed contact angle as high as 166°. The scanning electron and atomic force microscope studies revealed clustered growth and two level sub-micron asperities on films deposited at higher energies. Such dual-scale hierarchical roughness and heterogeneities at the water–surface interface was attributed to the observed contact angle and thus its superhydrophobic nature.

Stopping and scattering of relativistic electron beams in dense plasmas and requirements for fast ignition

The interaction of a relativistic electron with a dense plasma is studied in the context of inertial fusion fast ignition. Expressions for the electron stopping power and deflection are given and implemented in a three-dimensional (3D) Monte Carlo code. Electron range and penetration depth are computed as functions of the electron energy and plasma parameters; approximate expressions are also proposed. Conditions for fast ignition are studied by including the 3D Monte Carlo code in a 2D hydrodynamic code. The required beam energy is determined as a function of mean electron energy for monoenergetic and exponential energy distributions and a uniform initial deuterium–tritium plasma with a density of 300 g cm−3. A simple model is shown to agree with the code.