Kikuchi lines, known since 1928 [S. Kikuchi, Jpn. J. Phys. 5, 83 (1928)], are generated by irradiating a crystal with high-energy e-beam in SEM or TEM and observing backscattered electrons diffraction on crystalline planes. The Kikuchi line effect gave rise to several useful tools in electron microscopy of crystalline and nanocrystalline materials [K. Saruwatari, et al., J. Mineral. Petrol. Sci. 103, 16 (2007)]. We have discovered a similar diffraction effect but of the crystal’ own thermally emitted electrons.

Representing field emission data on a Fowler–Nordheim plot is both very common and strongly not recommended. It leads to a spurious estimation of the emitter parameters despite a very good data fit. There is a lack of a reliable method of analysis and a proper estimation of the uncertainty in the extracted parameters. In this article, we show that the uncertainty in the estimation of the field enhancement factor or the emission area can be as high as ±50% even for a tungsten single emitter in good ultrahigh vacuum conditions analyzed by the Murphy–Good model. Moreover, the choice of the exact Murphy–Good method can have a noticeable impact. We found that advanced analysis methods, based on the measurement of the differential conductance of the emitter, are so demanding in terms of emitter stability that up to now its requirements are probably out of reach in any field emission laboratory.

Graphene has attracted special attention due to its mechanical and electrical properties. In this work, we describe the effects of sub-10 keV electron beam irradiation on the electrical conductivity of few-layer graphene films deposited on a glass substrate. The irradiation process was performed in vacuum at 10–6 Torr for 30 min per sample. The superficial chemical structure and optical properties of the samples were evaluated before and after electron irradiation using spectroscopic techniques (UV-Vis, Raman, and XPS), and the Van der Pauw method was used to determine the sheet resistance. It was found that the sheet resistance and the defect density decrease as the energy of incident electrons increases. For instance, the sheet resistance has been reduced by 17.3% after the sample was irradiated with a 10 keV electron beam. This could be explained by the reduction of defect density on the irradiated samples caused by the removal of oxygen content on graphene flakes, estimated by Raman and XPS, respectively. Hence, electron beam irradiation could be used to modify the electrical conductivity of graphene films based on defect engineering.

We have investigated the laser micromachining of microsieves with 3D micropore geometries. We hypothesize that mechanical cues resulting from the positioning and machining of ablated holes inside a pyramidal microcavity can influence the direction of neuronal outgrowth and instruct stem cell-derived neural networks in their differentiation processes. We narrowed the number of variations in device fabrication by developing a numerical model to estimate the stress distribution in a cell interacting with the laser-tailored unique 3D geometry of a microsieve’s pore. Our model is composed of two components: a continuous component (consisting of the membrane, cytoplasm, and nucleus) and a tensegrity structural component (consisting of the cytoskeleton, nucleoskeleton, and intermediate filaments). The final values of the mechanical properties of the components are selected after evaluating the shape of the continuous cell model when a gravity load is applied and are compared to the shape of a cell on a glass substrate after 3 h. In addition, a physical criterion implying that the cell should not slip through a hole with a bottom aperture of 3.5 μm is also set as a constraint. Among all the possible one- or multi-hole configurations, six cases appeared promising in influencing the polarization process of the cell. These configurations were selected, fabricated, and characterized using scanning electron microscopy. Fabricated microsieves consist of a 20 μm thick Norland Optical Adhesive 81 (NOA81) foil with an array of inverted pyramidal microcavities, which are opened by means of KrF 248 nm laser ablation. By changing the position of the laser beam spot on the cavities (center, slope, or corner) as well as the direction of laser beam with respect to the NOA81 microcavity foil (top side or back side), different ablation configurations yielded a variety of geometries of the 3D micropores. In the one-hole configurations when the shot is from the top side, to make the desired diameter of 3.5 μm (or less) of an opening, 1500 laser pulses are sufficient for the center and slope openings. This requirement is around 2000 laser pulses when the aperture is positioned in the corner. In back side ablation processes, the required number of pulses for through-holes at the center, slope, and corner positions are 1200, 1800, and 1800 pulses, respectively. In conclusion, we developed a microsieve platform that allows us to tailor the 3D topography of individual micropores according to the selection of cases guided by our numerical stress distribution models.

Amorphous mixed-anion semiconductors (AMASs) such as amorphous zinc oxynitride and amorphous zinc oxysulfide (a-ZnOS) have attracted attention as rare-metal-free amorphous semiconductors that exhibit electron mobility comparable to or greater than the electron mobilities of typical amorphous oxide semiconductors (AOSs), including amorphous In–Ga–Zn–O (a-IGZO). A characteristic feature of AMASs is that their conduction-band minimum (CBM) mainly consists of s-orbitals of the single cation, in contrast to conventional AOSs, whose CBM is composed of s-orbitals of multiple cations. This unique band structure suggests that the potential of carrier electrons in AMASs exhibits less spatial fluctuation than that of carrier electrons in AOSs. In this study, we analyzed the temperature dependence of the electron transport properties of a-ZnOS thin films using the random barrier model to evaluate the potential barrier height and its spatial variation. The analyses revealed that the barrier height of a-ZnOS is comparable to that of a-IGZO. This result was attributed to the large covalent nature of Zn–S bonds strongly influencing the potential at the CBM through the antibonding interaction.

We fabricated a cold cathode-driven x-ray source with vertically aligned carbon nanotubes (VACNTs). Dose and spatial resolution characteristics are compared to commercially available portable x-ray sources, and our system outperformed its counterparts. At the same 1.0 mAs condition, our x-ray source represented a dose rate of 0.37 mGy/s, which is 7.8 and 2.4 times greater than that of the thermionic emitter and paste carbon nanotubes based commercial x-ray sources, respectively. In addition, our x-ray source represented better image resolution by achieving a nominal focal spot size of 0.35 mm. We believe that high quality x-ray properties were attained, thanks to the narrow electron beam divergence and high reduced brightness of the electrons from VACNTs, and that this will open up advanced x-ray applications.

Radiation damage in electronic devices is known to be influenced by physics, design, and materials system. Here, we report the effects of biasing state (such as ON and OFF) and pre-existing damage in GaN high electron mobility transistors exposed to γ radiation. Controlled and accelerated DC biasing was used to prestress the devices, which showed significant degradation in device characteristics compared to pristine devices under ON and OFF states after γ irradiation. The experiment is performed in situ for the ON-state to investigate transient effects during irradiation until the total dose reaches 10 Mrad. It shows that threshold voltage, maximum transconductance, and leakage current initially decrease with dosage but slowly converge to a steady value at higher doses. After 10 Mrad irradiation, the OFF-state device demonstrates larger RON and one order of magnitude increased leakage current compared to the ON-state irradiated device. The micro-Raman study also confirms that the ON-state operation shows more radiation hardness than OFF and prestressed devices. Prestressed devices generate the highest threshold voltage shift from −2.85 to −2.49 V and two orders of magnitude higher leakage current with decreased saturation current after irradiation. These findings indicate that high electric fields during stressing can generate defects by modifying strain distribution, and higher defect density can not only create more charges during irradiation but also accelerate the diffusion process from the ionizing track to the nearest collector and consequently degrade device performances.

High aspect ratio (HAR) structures have many promising applications such as biomedical detection, optical spectroscopy, and material characterization. Bottom-up self-assembly is a low-cost method to fabricate HAR structures, but it remains challenging to control the structure dimension, shape, density, and location. In this paper, an optimized top-down method using a combination of pseudo-Bosch etching and wet isotropic thinning/sharpening is presented to fabricate HAR silicon (Si) nanopillar and nanocone arrays. To achieve these structure profiles, electron beam lithography and reactive ion etching were carried out to fabricate silicon pillars having a nearly vertical sidewall, followed by thinning or sharpening by wet etching with a mixture of hydrofluoric (HF) acid and nitric acid (HNO3). For the dry etching step using the pseudo-Bosch process, the sidewall angle is largely dependent on the SF6/C4F8 gas flow ratio, and it was found that a vertical profile can be attained with a ratio of 22/38. For the wet etching process, a very large HNO3/HF volume ratio is shown to give smooth etching with a slow and controllable etching rate. The final structure profile also depends on the pattern density/array periodicity. When the array period is large, silicon nanopillar is thinned down, and its aspect ratio can reach 1:135 with a sub-100 nm apex. When the pillar array becomes very dense (periodicity much smaller than height), a very sharp nanocone structure is obtained after wet etching with an apex diameter under 20 nm.

The mechanical properties characterization of silicon nanowires is generally performed by tensile nanomechanical loading tests with in situ strain quantification. While the strain is characterized by electron beam (e-beam) microscopy techniques, the understanding of the sample-electron interaction is essential to guarantee artifact-free measurements. In this work, we investigated suspended strained silicon nanowires under electron beam exposure in a scanning electron microscope (SEM). The fabricated nanowires had their initial stress profile characterized by Raman spectroscopy and finite element method simulations. Then, the sample was exposed to an e-beam where we observed a gradual electrical charging of the sample, verified by the image drift, and down deflection of the suspended nanowire caused by electrostatic forces. These additional stresses induced the mechanical fracture of the nanowires in the corner region due to accumulated stress. These results ascribe electrostatic mechanical loading concerns that may generate undesirable additional stresses in nanomechanical tests performed in SEM, demonstrating the importance of proper sample preparation to avoid electrostatic charging effects. Here, we propose a simple and effective method for imposing the structures under an impinging electron beam at an equipotential, which mitigates the charging effects acting on the nanowire.

Two- or three-dimensionally patterned subwavelength structures, also known as metamaterials, have the advantage of arbitrarily engineerable optical properties. In thermophotovoltaic (TPV) applications, metamaterials are commonly used to optimize the emitter’s radiation spectrum for various source temperatures. The output power of a TPV device is proportional to the photon flux, which is proportional to the emitter size. However, using 2D or 3D metamaterials imposes challenges to realizing large emitters since fabricating their subwavelength features typically involves complicated fabrication processes and is highly time-consuming. In this work, we demonstrate a large-area (78 cm2) thermal emitter. This emitter is simply fabricated with one-dimensional layers of silicon (Si) and chromium (Cr), and therefore, it can be easily scaled up to even larger sizes. The emissivity spectrum of the emitter is measured at 802 K, targeting an emission peak in the mid-infrared. The emissivity peak is ∼0.84 at the wavelength of 3.75 μm with a 1.2 μm bandwidth. Moreover, the emission spectrum of our emitter can be tailored for various source temperatures by changing the Si thickness. Therefore, the results of this work can lead to enabling TPV applications with higher output power and lower fabrication cost.

The fabrication of carbon nanohorns (CNHs) from a methane precursor with argon in an inductively coupled plasma was recently demonstrated with a high production rate of ∼20 g/h by Casteignau et al. [Plasma Chem. Plasma Process. 42, 465 (2022)]. The presence of a promotor gas such as hydrogen was found to be important for the growth of CNHs, but the mechanisms at play remain unclear. Here, we study the impact of different promotor gases by replacing hydrogen with nitrogen and helium at different promotor:precursor (Pm:Pr) ratios, X:CH4 = 0.3–0.7 (X = H2 or N2, Ar, and He), and global flow rates FX+FCH4=1.7 and 3.4 slpm. The nature of the promotor gas is shown to directly influence the morphology and the relative occurrence of CNHs, graphitic nanocapsules (GNCs), and graphene nanoflakes. Using quantitative transmission electron microscopy, we show that CNHs are favored by an X:CH4 = 0.5, preferably with X = He or N2. With a lower total flow rate (1.7 slpm) of N2, even larger production rates and higher selectivity toward CNHs are achieved. Optical emission spectroscopy was used to probe the plasma and to demonstrate that the nature promotor gas strongly modulates the C2 density and temperature profile of the plasma torch. It is shown that CNHs nucleation is favored by high C2 density at temperatures exceeding 3500 K localized at the exit-end of the nozzle, creating a reaction zone with extended isotherms. H2 favors CH4 dissociation and creates a high C2 density but cools the nucleation zone, which leads to structures with a strong graphitic character such as GNCs.

In this work, hafnium zirconium oxide (HZO)-based 100 × 100 nm2 ferroelectric tunnel junction (FTJ) devices were implemented on a 300 mm wafer platform, using a baseline 65 nm CMOS process technology. FTJs consisting of TiN/HZO/TiN were integrated in between metal 1 (M1) and via 1 (V1) layers. Cross-sectional transmission electron microscopy and energy dispersive x-ray spectroscopy analysis confirmed the targeted thickness and composition of the FTJ film stack, while grazing incidence, in-plane x-ray diffraction analysis demonstrated the presence of orthorhombic phase Pca21 responsible for ferroelectric polarization observed in HZO films. Current measurement, as a function of voltage for both up- and down-polarization states, yielded a tunneling electroresistance (TER) ratio of 2.28. The device TER ratio and endurance behavior were further optimized by insertion of thin Al2O3 tunnel barrier layer between the bottom electrode (TiN) and ferroelectric switching layer (HZO) by tuning the band offset between HZO and TiN, facilitating on-state tunneling conduction and creating an additional barrier layer in off-state current conduction path. Investigation of current transport mechanism showed that the current in these FTJ devices is dominated by direct tunneling at low electric field (E 0.4 MV/cm). The modified FTJ device stack (TiN/Al2O3/HZO/TiN) demonstrated an enhanced TER ratio of ∼5 (2.2× improvement) and endurance up to 106 switching cycles. Write voltage and pulse width dependent trade-off characteristics between TER ratio and maximum endurance cycles (Nc) were established that enabled optimal balance of FTJ switching metrics. The FTJ memory cells also showed multi-level-cell characteristics, i.e., 2 bits/cell storage capability. Based on full 300 mm wafer statistics, a switching yield of >80% was achieved for fabricated FTJ devices demonstrating robustness of fabrication and programming approach used for FTJ performance optimization. The realization of CMOS-compatible nanoscale FTJ devices on 300 mm wafer platform demonstrates the promising potential of high-volume large-scale industrial implementation of FTJ devices for various nonvolatile memory applications.

Flexible electrodes are prepared by deposition on polyethylene naphthalate substrates, which melt at elevated temperatures, and are, therefore, generally unsuitable for deposition at high temperatures. However, only limited improvement in the conductivity can be achieved for Al-doped ZnO (AZO) films formed at low temperatures. Multilayer transparent conductive films (AZO/Ag/AZO), in which a conductive metal such as Ag is sandwiched between AZO, exhibit superior resistivity and electrical stability against bending compared to AZO films and have attracted considerable attention. In this study, AZO transparent conducting films were investigated as alternatives to indium tin oxide. The electrical characteristics of AZO/Ag/AZO films are not optimal at low temperatures owing to oxidation of Ag and its diffusion into the AZO layer. We, therefore, developed transparent conductive films with an AZO/Ag/Cu/AZO structure in which an intermediate Cu layer suppresses the oxidation of Ag and inhibits its diffusion into the substrate-side AZO layer, changing the deposition conditions of Cu. The optimal characteristics were obtained at a Cu deposition rate of 0.08 nm/s. A further increase in Cu layer thickness suppresses the oxidation of the Ag layer and its diffusion into the substrate-side AZO layer, thereby improving resistivity. Notably, a 5 nm thick Cu layer exhibited exclusive Cu regions, which further prevented the oxidation of Ag and its diffusion into the substrate side of the AZO layer, with a resistivity of 5.12 × 10−5 Ω cm. This resistivity is comparable to that of existing transparent conducting films used in practical applications; however, the transmittance of the AZO/Ag/Cu/AZO film was reduced owing to the low transparency of Cu.

This article discusses the development of a cold cathode electron beam (C-beam) based on vertically aligned carbon nanotubes (VACNTs) and the optimization of field emission (FE) from C-beam architecture design. The characteristics of the electron beam are typically required to match the applications of interest. To study the FE, five distinct multi-array emitter island designs, viz., 65 × 65, 75 × 75, 90 × 90, 100 × 100, and 240 × 240 μm2, were fabricated. The island 240 × 240 μm2 (single island) was divided into a group of four subislands each with dimensions 65 × 65, 75 × 75, 90 × 90, and 100 × 100 μm2. We explored the field-screening effect of these different island designs using experiments and modeling, and we discovered that the size of the island had a significant impact on the FE properties. Moreover, we found that the island’s size significantly affected its I–V properties, with a 75 × 75 μm2 island offering 0.7 mA anode current the best emission current among other islands. Additionally, tungsten cross wire (EN 12543-5), a typical resolution testing object, had its focal spot size (FSS) measured using x-ray imaging, and the lowest FSS of 0.45 and 0.49 mm in both vertical and horizontal directions was obtained. This innovative method has a great deal of promise for developing the next generation of VACNT-based electron sources.

The paper deals with numerical modeling of electrothermal phenomena in 3D GaN core-shell light-emitting diode (LED) structures that were developed in the frame of GECCO project.1 The simulations investigate the influence of pillar dimensions on the LED work conditions. The inherent feature of such a design is the discrepancy between the internal contact footprint current density JFP and the current density on the junction active area JAA, which, at the same contact current, decreases when the pillar is taller. The simulations indicate that the decrease of JAA results in significant changes in the LED parameters. At the same diode current, i.e., constant light emission, it leads to the voltage decrease leading to the reduction of power delivered to the diode and, consequently, to the increase of its efficiency.

A pneumatic controlled nanosieve device is demonstrated for the efficient capture and release of 15 nm quantum dots. This device consists of a 200 nm deep glass channel and a polydimethylsiloxane-based pneumatic pressure layer to enhance target capture. The fluid motion inside the nanosieve is studied by computational fluidic dynamics (CFD) and microfluidic experiments, enabling efficient target capture with a flow rate as high as 100 μl/min. In addition, microgrooves are fabricated inside the nanosieve to create low flow rate regions, which further improves the target capture efficiency. A velocity contour plot is constructed with CFD, revealing that the flow rate is the lowest at the top and bottom of the microgrooves. This phenomenon is supported by the observed nanoparticle clusters surrounding the microgrooves. By changing the morphology and pneumatic pressure, this device will also facilitate rapid capture and release of various biomolecules.

Analysis of interdigitated transducers often relies on phenomenological models to approximate device electrical performance. While these approaches prove essential for signal processing applications, phenomenological models provide limited information on the device’s mechanical response and physical characteristics of the generated acoustic field. Finite element method modeling, in comparison, offers a robust platform to study the effects of the full device geometry on critical performance parameters of interdigitated transducer devices. In this study, we fabricate a surface acoustic wave resonator on semi-insulating GaAs (100), which consists of an interdigitated transducer and acoustic mirror assembly. The device is subsequently modeled using fem software. A vector network analyzer is used to measure the experimental device scattering response, which compares well with the simulated results. The wave characteristics of the experimental device are measured by contact-mode atomic force microscopy, which validates the simulation’s mechanical response predictions. We further show that a computational parametric analysis can be used to optimize device designs for series resonance frequency, effective coupling coefficient, quality factor, and maximum acoustic surface displacement.

Oral squamous cell carcinoma (OSCC) is one of the most common lip and oral cavity cancer types. It requires early detection via various medical technologies to improve the survival rate. While most detection techniques for OSCC require testing in a centralized lab to confirm cancer type, a point of care detection technique is preferred for on-site use and quick result readout. The modular biological sensor utilizing transistor-based technology has been leveraged for testing CIP2A, and optimal transistor gate voltage and load resistance for sensing setup was investigated. Sensitivities of 1 × 10−15 g/ml have been obtained for both detections of pure CIP2A protein and HeLa cell lysate using identical test conditions via serial dilution. The superior time-saving and high accuracy testing provides opportunities for rapid clinical diagnosis in the medical space.

Surface coatings have been widely used to improve phosphor characteristics for the purpose of increasing luminescence intensity and protecting against degradation. In this study, an uncoated La2O2S:Eu3+ thin film is compared to films coated by graphene oxide, as prepared or annealed in an inert or reducing atmosphere. The characteristic red emission of Eu3+ ions was observed for all samples and attributed to 5D0-7F2 transitions, while no luminescence associated with graphene oxide was observed. The luminescence intensity from the as-coated sample and the one annealed in an inert Ar atmosphere was less, compared to the uncoated film, whereas the coated sample annealed in a reducing atmosphere (Ar/H2) had emission, which was of similar intensity to the uncoated sample. Its degradation, and that of the uncoated sample, were studied by recording Auger electron spectroscopy and cathodoluminescence measurements, simultaneously. During electron irradiation, the surface of the uncoated sample was converted to a much more luminescent layer as C and S were gradually removed from the surface. Auger electron spectroscopy measurements of the coated sample showed that even initially, it had almost no S on the surface. The loss of S was attributed to annealing in Ar/H2, where H2S gas may be produced as the phosphor was converted into La2O3. This La2O3 subsequently formed La(OH)3 due to its hydroscopic nature. Unlike the uncoated sample, from which C due to unintentional contamination was fairly easily removed from the surface, C on the surface of the coated sample became less but was resistant to removal, which was associated with the formation of CHLaO3 at the surface as suggested by x-ray diffraction. Although coating with graphene oxide did not result in chemically stable La2O2S:Eu3+ thin films, the cathodoluminescence intensity of both the uncoated and graphene oxide coated samples annealed in reducing atmosphere increased during electron beam exposure (with no change in the form of the emission spectra) so that such films may have potential cathodoluminescence applications.

Silicon gated field emitter arrays have been used as a vacuum transistor to demonstrate a 152 kHz Colpitts oscillator. The transfer and output characteristics of the 1000 × 1000 silicon arrays were measured using a collector placed ≈ 1 mm away with a gate voltage up to 40 V and a collector voltage up to 200 V. The data were used to establish an LTspice transistor model based on a field emission tip model and a collector current model that fit the characteristics. Then, the LTspice model was used to design a low frequency Colpitts oscillator. Furthermore, experiments were carried out to successfully demonstrate the oscillation. Oscillation frequency was 152 kHz with a peak to peak voltage of 25 V for a tip to ground series resistance value of 10 kΩ at 50 V on the gate and 210 V on the collector. Further, the oscillator was also tested at 50, 100, 200, 300, and 400 °C. It was observed that frequency shifts for each temperature which is due to the change in the overall capacitance of the test setup. This type of device could be used as a temperature sensor in harsh environments.