Table of contents

High performance AlGaN/GaN high electron mobility transistors grown by plasma-assisted molecular beam epitaxy were fabricated. An integrated slant field-plate was used to suppress the DC-RF dispersion and enhance the breakdown. A recessed-gate structure was adopted to increase the cutoff frequency from 17.5 to 22 GHz. And a CF₄-plasma treatment prior to gate metallization was found effective in reducing the gate leakage by one order of magnitude and improving the stability of the RF power operation. Treatment in a mixture of HF and HNO₃ acid was essential to ensure the effectiveness of the CF₄-plasma treatment. Combination of these technologies yielded state-of-the-art MBE grown AlGaN/GaN HEMTs with stable high-power and high-efficiency operation. At 4-GHz frequency and 48-V bias, a CW power of 12 W/mm with 64% associated efficiency was achieved.

The room-temperature (RT) growth of ultraviolet-emitting hexagonal gallium nitride (h-GaN) on a sapphire substrate using photochemical vapor deposition (PCVD) has been demonstrated. A high photoluminescence (PL) peak at 3.47 eV was observed at 5 K, indicating a high-quality crystalline structure for h-GaN. A RT PL energy peak of 3.40 eV indicated the reduction of thermal residual stresses in GaN. In addition, the RT growth resulted in the formation of dendrite-like GaN, which originated from the low kinetic energy of the precursors for migration. A high PL peak at 3.55 eV observed at 5 K in the dendrite-like GaN indicated the quantum size effect.

We report improvements in the growth characteristics of AlGaN/GaN heterostructures on 4H-SiC substrates using plasma-assisted molecular beam epitaxy. Employing recently established N-rich growth conditions at temperatures in the thermal decomposition regime of homoepitaxial (0001) GaN, this method proved successful for the reduction of threading dislocations in heteroepitaxial growth on SiC by simultaneously preserving good surface morphology free of excess Ga. This self-recovery of surface morphology at high growth temperatures overcomes the restrictions of using two-step GaN buffers as common under Ga-rich conditions. Initial results from unoptimized high electron mobility transistor structures grown under this approach exhibit decent mobilities, output powers and associated power added efficiencies larger than 1330 cm²/(V s), 7 W/mm, and 50% at 48-V drain bias, respectively.

GaN has been grown on Si(110) substrates by metalorganic vapor phase epitaxy using a low-temperature AlN nucleation layer. The atomic arrangement at the AlN/substrate interface has been investigated by high-resolution transmission electron microscopy. Lattice images of the AlN/Si interface taken along the <1120>_AlN∥<110>_Si and <1100>_AlN∥<001>_Si projections show an abrupt crystalline interface. A highly coherent epitaxial relationship between (1100)_AlN and (001)_Si planes is observed. The atomic bonding configuration at the AlN/Si interface is analyzed taking into consideration the chemical coordination, lattice mismatch, and net charge balance. A structure model of the bonding at the interface is presented.

This article reports the deposition of ZnO thin films in supercritical CO₂ solutions likely for the first time. Zincacetylacetonate was dissolved in supercritical CO₂, together with oxygen, and was processed at 8–13 MPa and 230–380 °C. Continuous crystalline films were obtained on Si and sapphire at temperatures higher than 280 °C. The-band-edge emission at 370 nm was confirmed in photoluminescence spectra.

We have studied a self-assembled growth technique to form ultra-low density InAs quantum dots on GaAs by molecular beam epitaxy. After growing a GaAs layer under a particular condition, we have deposited an InAs layer of far less than the critical thickness and performed an annealing process. By optimizing these process steps, the density of dots is successfully controlled over a wide range from 10⁴ to 10⁸ cm^-2, at which the average interdot distance gets as long as 100 µm. Photoluminescence spectra of low dot density samples have shown discrete single-dot features even under a macroscopic optical excitation. These dots are found to be formed preferentially on GaAs mounds especially when the dot density is around 2.5×10⁵ cm^-2.

We show that the rotation of a magnetic domain wall (DW) can be induced by the injection of a dc current into a magnetic wire with a DW. A novel three-terminal device that produces microwaves by utilizing the current-induced DW rotation is proposed. The frequency of the microwaves can be tuned by adjusting the current density through the wire, and the amplitude of the microwaves can be regulated through a dc bias applied to the magnetic tunnel junction.

Magnetic domain wall (DW) dynamics in submicron ferromagnetic wires has been investigated in real-time regime by using tunneling magnetoresistance effect. The DW velocity as a function of magnetic field increases at low field range and takes a local maximum. After stagnation, the velocity starts to increase again. This is a typical signature of the Walker breakdown. Above the Walker field, the real-time traces of individual events show complex behaviors, which suggest the stochastic nature of the DW motion.

Real-time measurements of spin-transfer induced magnetization switching were performed at room temperature on elliptical CoFeB/MgO/CoFeB magnetic tunnel junctions (60×170 nm²) using a storage oscilloscope. Free layer thickness and thermal stability factor (K_uV/k_BT) were 2 nm and 17, respectively. Under small dc current with short rise time (200 ps), the switching processes essentially comprised long waiting time and short transition time (less than 400 ps). We found, for the first time, that switching probability density was considerably lower for few ns after the rise of the current, and became constant later. Existence of this "non-reactive time" could be a critical issue for fast writing applications.

Interfacial electronic states of 4H-SiC/SiO₂ on (0001), (0001), and (1120) are studied by means of ab initio calculations. We find that the calculated densities of localized inversion traps are in the increasing order from (1120), (0001), to (0001).

The electrical properties of leaky ferroelectric BiFeO₃ thin films were evaluated by using a high-speed positive-up-negative-down (PUND) measurement technique. The leakage current density was estimated from the gradient of the pulse response when a constant electric field was applied. The relative permittivity was estimated from an abrupt decrement when the applied field was removed. The twofold remanent polarization without the influence of the leakage current was estimated by subtracting the contribution of a paraelectric component from the abrupt increment in the pulse response when a positive pulse was applied.

Lead-free piezoelectric Mn-doped Na_0.5K_0.5NbO₃ (NKN) single crystals have been fabricated by self flux method using KF–NaF eutectic composition. The color of the obtained crystals was different depending on the doped Mn-chemicals. The large-sized single crystals with crystal face of orthorhombic (110) were obtained by optimized heat-treatment condition of the holding time at 1050 and 950 °C of 5 h and the cooling rate of 0.25 °C/min, and their piezoelectric properties were successfully measured by a resonance-antiresonance method. The piezoelectric strain constant (d₃₃) of 0.5 mol % Mn-doped NKN single crystal was 161 pC/N, and the longitudinal electro-mechanical coupling factor (k₃₃) showed 0.64.

Tunnel junction devices employing epitaxial, (001)-oriented SrTiO₃ barriers with thicknesses between 4 and 5 nm were fabricated by sputtering on (001) Pt/MgO substrates. The quality of the Pt/SrTiO₃ interface was characterized by transmission electron microscopy and the current transport studied as a function of temperature and bias field. At low voltages the junctions showed excellent insulting properties and temperature dependent, non-linear current–voltage characteristics. If junctions were biased to high fields (>1.25 MV/cm) current hysteresis was observed. The hysteresis is shown to be due to time-dependent tunnel barrier properties at high fields.

The influence of the dipole of an insulator surface on temporal changes in the source–drain current was investigated by using organic field-effect transistors with a surface-modified SiO₂ insulator. The source–drain current decreased drastically with respect to time when the dipoles of the insulator surface displaced slightly. In order to obtain highly stable organic transistors, it is thus necessary to remove the mobile dipoles from the insulator surface.

Highly oriented thin-films of poly(3-hexylthiophene) (P3HT) have been successfully fabricated by slide-coating method, in which the chloroform solution is sandwiched between a Si wafer and a slide glass, and followed by slow drawing of the Si wafer with respect to the slide glass. The performance of this organic field-effect transistor (OFET) based on the P3HT film exhibit high-performance of up to 0.056 cm² V^-1 s^-1 in FET mobility. This simple solution process is an effective method to fabricate the well-ordered structure of the P3HT film and its OFETs.

At room temperature, we demonstrate an unambiguous detection of the ground- and excited-state transitions of mid-infrared GaInSb/AlGaInSb type I quantum well (QW) lasers grown on GaAs using a new technique based on Fourier transform infrared surface photovoltage spectroscopy. It is found that none of the currently established spectroscopic techniques is able to detect even the ground state transition of these mid-infrared QW lasers at room temperature. The spectroscopic results are in reasonable agreement with the laser emission spectra at low temperatures.

A linearly-polarized, single-lobed beam has been demonstrated in a surface-emitting photonic-crystal laser under single-mode operation by employing fine-tuned elliptical lattice points and π-phase shift. A crystal structure, including the elliptical lattice points with a short/long axis ratio of 0.95, has been successfully fabricated. The resulting beam was strongly polarized in one direction, although the shape of the lattice points was nearly circular. It was found that two-dimensional optical coupling was compatible with strong linear polarization.

In this paper, we present an experimental observation of the optical nonlinear characteristics of a CdS-coated Ag particle at room temperature. By using sub-picosecond pulses generated by a tunable optical parametric amplification system, we confirm that the light intensity scattered by the particle considerably decreases with an increase in the incident light intensity at a photon energy higher than the energy corresponding to the interband absorption edge of CdS. The nonlinear phenomena presented in this paper are observed in an event in which localized surface plasmons enhance the two-photon absorption in CdS and cause the valence electrons to be excited into the conduction band of CdS and to further move to a higher energy band of Ag without additional energy supply.

Optical near-fields have a hierarchical nature, meaning that they exhibit different behavior at different scales of observation. This is one notable feature in nanometer-scale light-matter interactions, besides the ability to break through the diffraction limit of light. We studied such hierarchy in optical near-fields by engineering the shape of metal nanostructures. We numerically and experimentally demonstrated a hierarchical optical response from triangular-shaped metal nanostructures. Strong localized electric fields were excited on a smaller scale, whereas two different states were excited on a larger scale. Combined with localized energy-dissipation on the smaller-scale, this hierarchy should enable novel functionality, such as traceability of optical memories.

A diode-pumped microchip green light source which was based upon a diffusion-bonded Nd:YVO₄/KTiOPO₄ composite crystal and had a built-in thermoelectric element was developed. The source had the small volume of 0.7 cm³ and showed the average green power of up to 25 mW and the average electrical power consumed in the thermoelectric element of 15 mW at the interior temperature of 51 °C, under the driving condition of the duty ratio of 50%, the average electrical power consumed in pump diode of about 304 mW, and the ambient temperature of 20 °C, which resulted in the electrical-to-optical conversion efficiency of up to 7.8%. The power of the source was so stable with the fluctuation of less than 0.2%. Our source is the smallest green laser with the built-in temperature-controlling unit to our knowledge and thought to be useful in many applications including the portable laser display system.

We present a new cladding design for the photonic crystal fibers in order to achieve simultaneously high nonlinearity, dispersion-flattened characteristic, low confinement loss, and polarization maintaining properties. The finite difference method with anisotropic perfectly matched boundary layer is used as the numerical design tool. A nonlinear coefficient of the order 35 W^-1 km^-1 is obtained with a high birefringence of the order 1.5×10^-4 at a 1550 nm wavelength. Ultra-flattened dispersion of 0±0.31 ps nm^-1 km^-1 is also obtained in a 1440 to 1600 nm wavelength range with low confinement losses less than 0.05 dB/m in the entire dispersion-flat band.

In a reflective self-organized lightwave network (R-SOLNET), an optical waveguide and optical devices with reflective materials on their core facets are placed in a photo-refractive material, whose refractive index increases with write beam exposure. By introducing write beams from the waveguide, self-aligned waveguides are formed between them by the "pulling water" effect induced by the reflected write beams from the reflective materials. R-SOLNET was formed between an optical fiber and an Al micro-mirror with an angular misalignment of 3°, or an offset of 30 µm. Finite difference time domain calculations revealed that Y-branch R-SOLNET is formed by placing two reflective materials.

We derive continuous spectral representation of the non-equilibrium Green's function in an open system. Based on this result, we construct a theory of quantum transport and formulate a practical coarse-grain method for device simulations. As an illustration, we apply the method to quantum ballistic electron transport in model three-dimensional metal–oxide–semiconductor field-effect transistors.

An analytical device model for a graphene nanoribbon phototransistor (GNR-PT) is presented. GNR-PT is based on an array of graphene nanoribbons with the side source and drain contacts, which is sandwiched between the highly conducting substrate and the top gate. Using the developed model, we derive the explicit analytical relationships for the source–drain current as a function of the intensity and frequency of the incident radiation and find the detector responsivity. It is shown that GNR-PTs can be rather effective photodetectors in infrared and terahertz ranges of spectrum.

To elucidate forces providing high mechanical strength during formation of carbon nanotube (CNT) yarns and sheets, internanotube static friction force was investigated using a transmission electron microscope with a nanomanipulation system. Results show that the static friction force depends strongly on the CNT surface state. That force between two as-grown CNTs grown by chemical vapor deposition is much larger than that for highly crystalline CNTs. The as-grown CNT surfaces generally have amorphous carbon and defects. For CNT yarns and sheets, the frictional force attributable to surface roughness, rather than the van der Waals force, affects interactions among CNTs.

A thin amorphous TiO₂ layer was prepared using anodic oxidation of Ti. Resistance switching of amorphous TiO₂ was investigated by sweeping in a continuous voltage scan and pulse bias voltage. The bipolar switching was observed without the need of a forming process. Switching of the Ti/amorphous-TiO₂/Pt based structure showed good endurance. The switching mechanism and current–voltage characteristics were investigated from combinatorial analysis of the conducting filaments' evolution and the space-charge limited current conduction. The oxygen-vacancies migration involved redox processes, which is responsible for the recovery and rupture of sub-TiO_x based conducting filaments inside the amorphous TiO₂ layer.

We report the core-multishell GaP/GaAs/GaP nanowires grown in a metalorganic vapor phase epitaxy system by a combination of the vapor–liquid–solid growth mode and conventional vapor phase epitaxy method. By growing GaAs sacrificial segments on the core GaP nanowires followed by selective chemical etching, Au particles were removed and top faceted core-shell nanowires were formed after the shell growth. Analysis by transmission electron microscopy indicated that the shell layers were epitaxially grown on the sides of core GaP nanowires.

By using non-collinear density-functional calculations, we clarified the magnetic states of zigzag-edged graphene nanoribbons (ZGNRs). In the novel non-collinear states that were found, the angle θ between the magnetic moments at the two edges were canted, i.e., 0 <θ< 180°, which was in contrast with the case of antiferromagnetic (AFM; θ=180°) and ferromagnetic (FM; θ=0°) states. As θ increased from 0 to 180°, the band gap increased and the total energy decreased. As a result, the AFM state was the ground state and had the maximum band gap, whereas the FM state had the highest energy and no band gap. As a result of the development of nanotechnology, the magnetic fields with canted directions between the two edges can be applied. Therefore, we expect that the spin canting angle θ can be varied by the introduction of magnetic fields, so the band gap of ZGNRs can be controlled. It is thus suggested that ZGNRs are potential candidates for spintronics applications.

Multi-walled carbon nanotubes (MWNTs) of various diameters have been analyzed by Raman spectroscopy to clarify the influence of the diameter of MWNTs on their Raman spectra. The G-band frequency of MWNTs determined by curve fitting decreases with increasing tube diameter for diameters less than around 20 nm, beyond which it is almost constant. We believe that the G-band frequency of MWNTs with diameters less than 20 nm is affected by the interlayer spacing of MWNTs, and the behavior of the G-band frequency of MWNTs with diameters exceeding 20 nm can be explained on the basis of the optical penetration depth in graphite.

The alignments of nematic liquid crystalline molecules on self-organized microwrinkles are demonstrated and shown to be directly related to the orientation of the microwrinkles. The microwrinkle-based twisted-nematic liquid crystal cell shows a common electro-optical response.

Using designed nanopatterns, we fabricate pairs of quasi-one-dimensional arrays of self-organized microwrinkles with bistable orientation states to investigate the effect of the interaction between arrays on the hysteresis of the microwrinkle orientations subjected to a rotating uniaxial compressive strain field. The distorted hysteresis loops for the short separation between arrays indicate that the non-parallel configurations of microwrinkle orientations between arrays observed during the transitions are stabilized. Simulations using the corresponding Ising model suggest that the microwrinkle orientations between arrays are coupled via anti-ferromagnetic-like interactions.

An excellent barrier effect against Cu ion drift is demonstrated using self-assembled monolayer (SAM) barrier dielectrics in which phosphorous (P) atom is contained. Three kinds of SAMs, such as P-, carbon (C-), and nitrogen (N-) containing SAMs with the identical molecular structure, were wet-chemically formed on a thermal SiO₂. The X-ray reflectance and infrared absorption spectroscopy revealed that nearly 1-nm-thick monolayers were successfully formed. The barrier effects of SAMs were investigated by the time-dependent dielectric breakdown measurements of Cu/SAM/SiO₂/Si metal–insulator–semiconductor structures under applying a bias-temperature stress. The time-to-breakdown t_BD of P-SAM was approximately 10-fold compared to SiO₂ without SAM formation. The t_BD of C-SAM and N-SAM were, on the other hand, well agreed with that of SiO₂, indicating that the barrier effects of C- and N-SAMs are much weaker than that of P-SAM. From these results, we concluded that the existence of P atom in the SAM molecule to form Cu-P complex is the key for the barrier mechanism of the SAM studied in this report.

In the sub-100-nm mass production of semiconductor devices, thin-film resists dispersing acid generator molecules, referred to as chemically amplified resists, have been used. Feature sizes in lithography are approaching the molecular scale with the rapid progress in miniaturization. With reductions in lateral dimensions, a decrease in resist thickness is inevitable and the effects of interfaces become significant. A requirement for ultrafine fabrication is the uniformity of resist components. In this work, the depth profile of the acid generator distribution was investigated by X-ray reflectivity measurement at SPring-8. The depth profile in thin resist films was clarified. It was found that the depth profile varies with acid generator concentration.

A high-quality electron beam with a central energy of 0.56 GeV, an energy spread of 1.2% rms, and a divergence of 0.59 mrad rms was produced by means of a 4 cm ablative-capillary-discharge plasma channel driven by a 3.8 J 27 fs laser pulse. This is the first demonstration of electron acceleration with an ablative capillary discharge wherein the capillary is stably operated in vacuum with a simple system triggered by a laser pulse. This result of the generation of a high-quality beam provides the prospects to realize a practical accelerator based on laser-plasma acceleration.

Electron beams with a current of 2–200 pA and energies less than 6 eV were injected into a magnetic mirror trap and accumulated inside it by applying the electron cyclotron resonance heating. Introducing electrostatic potentials, a long term accumulation was made possible. This technique will be applicable for accumulating low energy positrons in a high vacuum without introducing a buffer gas.

The complex wave number in lossy photonic crystals composed of microplasmas was verified experimentally by measuring the refractive index and the transmittance in a microwave range. These experimental results coincide with the dispersion relation obtained by a modified plane-wave expansion method. In particular, an extraordinary reduction of attenuation was observed in a certain frequency band, which is attributed to a loss term in the dielectric function and periodicity in the structure. These results indicate that a method of dynamic control for electromagnetic waves can be realized using of the dispersion relation in complex space.

The behavior of N₂⁺ ions in a low-frequency driven atmospheric pressure He plasma jet effused into ambient air was analyzed from laser induced fluorescence (LIF) spectroscopy measurements. The gas temperature derived from the rotational distribution was kept near room temperature and the drift velocity of N₂⁺ ions estimated from the line shape was almost zero as compared to the apparent speed of the plasma bunch given by the spatiotemporal intensity profile. This shows that the mechanism of moving plasma bunches can be attributed to the ionization wave propagation similar to the streamer in positive corona discharge.

Photoresists containing adamantane derivatives have been widely used in ArF lithography. However, their performance upon exposure to next-generation exposure sources such as extreme ultraviolet (EUV) radiation and an electron beam (EB) has not been sufficiently studied. In this study, we synthesized acrylic terpolymers containing adamantylmethacrylates as a model photopolymer and exposed then to an ArF excimer laser, EUV and EB. The relationship between the sensitivities to these exposure sources was clarified. Although the sensitivities to EB and EUV showed the same trend, those to EUV and the ArF excimer laser depended on the molecular structure of the resist.

Organic spin-on-glass (O-SOG) has been newly proposed as a replication material used in room-temperature (RT)-nanoimprinting. O-SOG is very suitable for optical applications thanks to its good optical properties, including a high refractive index of 1.56 and a transparency that exceeds 98%. O-SOG microlens arrays were successfully replicated by using RT-nanoimprinting. UV pre-irradiation offered O-SOG-nanoimprinted patterns the property of maintaining their initial profiles after 300 °C annealing, while the patterns without any treatment completely disappeared after 300 °C annealing due to the polymer reflow.

Si microwell arrays containing Pt–Pd thin film were fabricated by the chemical etching of a Si substrate through a polystyrene honeycomb mask using a patterned metal catalyst. The honeycomb mask, which was formed by the utilization of binary colloidal crystals composed of large silica spheres and small polystyrene spheres, acted as a mask for metal deposition. After immersing a locally Pt–Pd-coated Si substrate into a solution containing hydrofluoric acid and hydrogen peroxide, an ordered Si microwell array with a hexagonal arrangement could be obtained by site-selective metal-assisted chemical etching. Moreover, the notable feature of this process is that an isolated circular Pt–Pd film used as a catalyst remained at the bottom of each well after chemical etching.

Antireflection (AR) structures of polymer composed of an ordered array of holes with a tapered shape were formed by imprinting using a metal mold prepared from an anodic porous alumina. The metal molds (Ni) were prepared using an anodic porous alumina as a template and were used for the photoimprinting of polymers. The obtained AR structure exhibited a low reflectance of less than 1% for a single surface.

A laboratory-scale laser plasma soft X-ray microscope using Wolter mirror optics was applied to three-dimensional (3D) imaging using imaging tomography. To obtain a high-resolution tomogram, a relayed tandem configuration was used. The image contrast when the focal position of a test pattern was changed was measured to evaluate the effective depth of focus of an imaging area along the optical axis of the system. Some naturally dried biological cells were observed and their 3D volume images were obtained with a spatial resolution better than 300 nm.

To investigate the production of carbon clusters by the impact reaction occurring when an asteroid collides with a satellite, a model experiment using a 2-stage light-gas gun is carried out. A small metal ball of 3 km/s velocity is injected into a thin isopropyl-alcohol layer with a metal back plate in nitrogen gas. After the impact reaction, the carbon soot produced is collected and analyzed, and the production of fullerenes is confirmed.

All-solid-state switchable mirror based on magnesium–titanium (Mg–Ti) thin film which has a near colorless transparent state was improved by using aluminum buffer layer. The device with buffer layer showed fast and steady switching from the reflective to the transparent states due to the effect of a better conductive aluminum buffer layer. In the durability test, it also showed steady durability over one thousand cycles of switching. This technique of an inserting buffer layer has good generality for switchable mirror application. Furthermore, the results will offer good information in the research field of the relationship between aluminum and hydrogen or proton.

To measure the moisture content of soil, we developed a method that measures the magnetic field generated when the primary magnetic field is exposed. Soil contains two different types of materials: water as a diamagnetic material and iron sand as a ferromagnetic material. Water shows a constant phase shift from the primary magnetic field as well as a frequency dependence of the magnetic field strength, and iron sand showed the opposite characteristics. Using these magnetic properties, a moisture content signal was extracted, even with interference of the iron sand.

We present an experimental study of plasma enhanced chemical vapor deposition (PECVD) of SiO₂ films from tetraethoxysilane (TEOS) using a plasma jet based on capillary dielectric barrier discharge (CDBD) at atmospheric pressure. We tried three different configurations: (a) coaxial type, (b) a crossed type with a vertical plasma jet and a tilted TEOS supply, and (c) another crossed type with the reversed arrangement. The deposition rate of SiO₂ films increased with the driving frequency of the plasma jet in all configurations, and as the best record it reached up to 280 nm/s at a frequency of 15 kHz in the configuration (c) with the aid of O₃ supply, which was three times as fast as that measured in the configuration (a) without O₃ supply.

Laser-induced molecular micro-jets of perylene molecules have been successfully generated in water and diiodomethane layers. The perylene molecules were ejected from a thin film of perylene molecules used as a source by photoexcitation using 4-ns laser pulses onto a borosilicate glass substrate used as a target. The gap between the source and the target was filled with water or diiodomethane. After the ejection, the perylene molecules passed through the liquid layer and were implanted into the target. The focusing of the molecular micro-jet and consequently the shape of the implanted molecular dots depends on the molecular species and type of liquid. This novel technique can be used for the fabrication of a pattern of functional molecular dots on a designated region of hard materials and can be used to manufacture molecular devices, molecular sensors, and optoelectronic devices.

The absolute frequency of the 4 ²S_1/2–3 ²D_5/2 optical clock transition of ⁴⁰Ca⁺ ions has been measured for the first time with respect to the Système International (SI) second. A single ⁴⁰Ca⁺ ion is laser-cooled in a small ion trap and the transition frequency is measured as the average of two symmetrical Zeeman components. The frequency is determined to be 411 042 129 776 385 (±18) Hz from 48 measurements.

The strong photoabsorption of typical backbone polymers such as poly(4-hydroxystyrene) (PHS) has been a concern in extreme ultraviolet (EUV) lithography. The development of highly sensitive chemically amplified resists by polymer absorption enhancement seems an unacceptable strategy for overcoming this problem because the side wall angle is basically determined by the gradient of energy absorption, namely the absorption coefficient of the polymer. In this study, the feasibility of a high-absorption resist process was investigated by a simulation based on EUV sensitization mechanisms. Compared with PHS-based resists, the fourfold enhancement of polymer absorption is feasible without side wall degradation partly due to the long migration range of secondary electrons, although it is necessary to reduce the resist thickness to 20 nm.