Advances in Science and Technology Vol. 82

Abstract: A gas cluster is an aggregate of a few to several thousands of gaseous atoms or molecules, and it can be accelerated to a desired energy after ionization. Since the kinetic energy of an atom in a cluster is equal to the total energy divided by the cluster size, a quite-low-energy ion beam can be realized. Although it is difficult to obtain low-energy monomer ion beams due to the space charge effect, equivalently low-energy ion beams can be realized by using cluster ion beams at relatively high acceleration voltages. Not only the low-energy feature but also the dense energy depositions at a local area are important characteristics of the irradiation by gas cluster ions. All of the impinging energy of a gas cluster ion is deposited at the surface region, and this dense energy deposition is the origin of enhanced sputtering yields, crater formation, shockwave generation, and other non-linear effects. GCIBs are being used for industrial applications where a nano-fabrication process is required. Surface smoothing, shallow doping, low-damage etching, trimming, and thin-film formations are promising applications of GCIBs. In this paper, fundamental irradiation effects of GCIB are discussed from the viewpoint of low-energy irradiation, sputtering, and dense energy depositions. Also, various applications of GCIB for nano-fabrications are explained.

Abstract: Dense photonic integration requires miniaturization of materials, devices and subsystems, including passive components (e.g., engineered composite metamaterials, filters, etc.) and active components (e.g., lasers, modulators, detectors). This paper discusses passive and active devices that recently have been demonstrated in our laboratory, including monolithically integrated short pulse compressor utilized with silicon on insulator material platform and design, fabrication and testing of nanolasers constructed using metal-dielectric-semiconductor resonators confined in all three dimensions.

Abstract: Aluminium and hafnium oxide films doped with CeCl₃/TbCl₃/MnCl₂ were deposited at 300 °C by ultrasonic spray pyrolysis. The films analysed by X-Ray diffraction exhibit a very broad band typical of amorphous materials. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ is observed upon UV excitation at 280 nm (peak emission wavelength of AlGaN-based LEDs). Such energy transfer gives place to a simultaneous emission of the donor and acceptor ions in the blue, green, yellow and red regions, resulting in cold white light emission, with chromaticity coordinates and colour temperatures: (0.30,0.32) and 7300 K (AOCTM film), and (0.32,0.37) and 6400 K (HOCTM film). Thus, this type of thin films might contribute to the development of efficient AlGaN-based LEDs pumped phosphors for cold white light generation.

Abstract: Mesostructured SiO2 films functionalized with the azo-chromophore Disperse Red 1 were synthesized by sol-gel method. The mesostructured long-range order in the films was determined by X-Ray Diffraction. The azo-chromophores in the films work as nano-impellers through their photo-induced trans-cis reversible isomerization. When the films are doped, they are able to control the release of the dopant by all-optical processes. We used the dye laser Rhodamine 6G as dopant, its very distinctive luminescence around 550 nm allows to follow the release. Polarized green and infrared laser light were used as pump sources to direct the movement of the nano-impellers. 299 nm light was used as a probe to induce the Rhodamine 6G luminescence, which was measured as function of the pumping time with a photomultiplier coupled to a monochromator. The results corresponding to the green and to the infrared pumping sources are compared in order to determine the feasibility to photo-control the nano-impellers movement through a two-photon absorption process.

Abstract: In the present work the influence of neodymium concentration (0-1at-%) and sintering conditions on 8/65/35 PLZT:Nd³⁺ ceramics were studied. All ceramic powders were synthesized by MOM technique from high purity raw materials (>99,9%), and subsequently sintered by free sintering and hot uniaxial pressing method. To analyze the powders and ceramics more the XRD, EDS SEM, and ferroelectric measurements were performed. Optical spectra were examined for all prepared samples, and their optical properties were analyzed using reflectance, excitation and luminescence measurements. The study gives a detailed account of the relationships between doping and preparing conditions on the basic physical and dielectric and optical properties of obtained ceramic materials.

Abstract: Development of the fundamental materials for field-controlled spectrally active optics is essential for new concept of optics, such as: membrane optics, filters for LIDARs, windows for sensors and probes, telescopes, spectroscopes, cameras, light valves, light switches, flat-panel displays, etc. The dopants of rare earth elements create a number of absorption and emission band structures and can easily be incorporated into many high quality crystalline and amorphous hosts. In wide band-gap semiconductors, like ScN and AlN with rare earth dopants, the existing deep levels can capture or emit the mobile charges, and can be ionized with the loss or capture of the carriers. This is a fundamental basis for smart optic materials. ScN and AlN doped with rare earth elements (Er, Ho) were tested under an applied electric field to characterize spectral and refractive index shifts by the Stark Effect. Decrease in refractive index under an applied electric field was observed as a shift in absorption coefficient using a variable angle spectroscopic ellipsometer. Under an electric field, mobile carriers are redistributed within the space charge region (SCR) to reveal this electro-refractive effect. The main research goal is to facilitate concept demonstration and testing of field-controlled spectrally smart active optics for optical multi-functional capabilities in a selected spectral range.

Abstract: Providing realistic impressions about a virtual ambient for interaction with human’s auditory, visual, and tactile perception is one of the core challenges of modern imaging systems. However, particularly tactile displays with high spatial resolution implemented as a large-scale integrated microelectromechanical system are not yet realized. Here, we report on a multimodal display with thousands of actuator pixels, which generates both visual and tactile impressions of a virtual surface. The fully polymeric, monolithically integrated device consists of an actuator array made from poly(N-isopropylacrylamide). This material is a stimuli-responsive, particularly temperature-sensitive hydrogel. Controlling the actuator temperature via an optoelectrothermic interface between an upper and lower temperature the actuator can be switched from the swollen to the shrunken state (volume change up to 90%) in several hundred milliseconds. To benefit from this highly dynamic behaviour it is necessary to use a control unit which provides the required temperature changes also in the range of milliseconds. For characterizing the time behaviour of our optoelectrothermic control unit we use the change in transparency of PNIPAAm caused by the phase transition. In this paper we preferably discuss the time behaviour of the display devices.

Abstract: To confirm whether chiral organic radical compound 1, which showed the generation of a sort of spin glass-like inhomogeneous ferromagnetic interactions (the average spin-spin interaction constant J > 0) in the bulk liquid crystalline state under weak magnetic fields, has a spin easy axis or exhibits anisotropic magnetic interactions in the SmC* or SmC phase, we have measured the temperature dependence of g-value and relative paramagnetic susceptibility (χ_rel) for the ferroelectric SmC* phase of (2S,5S)-1 confined in a thin sandwich cell by EPR spectroscopy.

Abstract: In the field of sensing, WGM microresonators are receiving a growing interest as optical structures suitable for the realization of miniature sensors with high sensitivity. When properly excited, WGM microresonators are able to strongly confine light, by means of total internal reflection,along the equatorial plane near their spherical surface. The corresponding supported resonances show low losses and a high quality factor Q (107-109). These high values of the Q factor make possible the detection of any minute event that occurs on the surface of the spherical microcavity. In fact, any minimum change in the surface of the sphere or in the physical and optical properties of the surrounding environment reduces the Q factor value and modifies the position of the resonancesinside the dielectric microcavity. From a direct measurement of this resonance shift, one can infer the amount of analyte that produces this variation.