New, energy-saving, efficient and cost-effective processing technologies such as 2D and 3D inkjet printing (IJP) for the production and integration of intelligent components will be opening up very interesting possibilities for industrial applications of molecular materials in the near future. Beyond the use of home and office based printers, "inkjet printing technology" allows for the additive structured deposition of photonic and electronic materials on a wide variety of substrates such as textiles, plastics, wood, stone, tiles or cardboard. Great interest also exists in applying IJP in industrial manufacturing such as the manufacturing of PCBs, of solar cells, printed organic electronics and medical products. In all these cases inkjet printing is a flexible (digital), additive, selective and cost-efficient material deposition method. Due to these advantages, there is the prospect that currently used standard patterning processes can be replaced through this innovative material deposition technique. A main issue in this research area is the formulation of novel functional inks or the adaptation of commercially available inks for specific industrial applications and/or processes.
In this contribution we report on the design, realization and characterization of novel active and passive inkjet printed electronic devices including circuitry and sensors based on metal nanoparticle ink formulations and the heterogeneous integration into 2/3D printed demonstrators. The main emphasis of this paper will be on how to convert scientific inkjet knowledge into industrially relevant processes and applications.
Photonic membranes are widely used kind of 2D photonic crystals in signal processing. We develop the
approach uniting both in-plane and out-of-plane geometries as well as resonator properties of membrane-like
photonic crystals (MPC). The resonator standing modes are excited by an external source through the special
inputs and may be controlled due to nonlinear coating. We study typical 1D and 2D photonic membrane
resonators of rectangular form with nonlinear inclusions as an important element of logical devices. The drastic
change of the reflectivity due to so-called nonlinear band shift effect is investigated and two main signal
processing schemes are analyzed for Si/SiO2 MPC covered with nonlinear doped glasses. General design of alloptical
logic gates and adder design are discussed. Novel calculation method based on the analytical basis of
resonator's eigenstates is used to obtain dependencies for reflectivity, modal spectrum and field distribution for
chosen working frequencies.
The photonic crystal (PhCr) sample of a proper shape can exhibit good resonator properties with extremely high
Q-factor. The resonator standing modes may be excited by an external source through the special inputs and be
controlled due to nonlinear coating. We study typical 1D and 2D photonic resonators of rectangular form with
nonlinear inclusions as an important element of logical devices. Depending on the beam intensity and chosen
working point near the photonic band edge, the reflectivity may drastically change thus performing the logic
operations. The seeming nonlinear band shift effect arises in linear PhCr's total internal reflection area due to
nonlinear covering layer. Two main signal processing schemes exist in logic devices made on the base of
photonic resonators. We analyze theoretically the resonator parameters for CdS/CdSe and CdS/SiO2 photonic
crystals covered with nonlinear doped glasses and preferring processing scheme for IR wavelengths. General
design of logic gates and adder design are discussed. Novel calculation method based on 1D resonator's
eigenstates analytical basis is used to obtain 2D spectrum.
The perturbation theory (PT) for electromagnetic eigenwaves in finite-finite 2D metamaterials is developed. A
simple procedure to find the essential part of full solution for electromagnetic field 2D photonic crystals (PhCr)
is proposed. The existance of PT small parameter for electromagnetic modes in finite 2D PhCr is proven if sizes
are sufficiently big. The spectrum and amplitude distribution for several types of 2D states: band, waveguide,
surface and pure local states are considered for PhCr binary samples counting several hudred elementary cells in
both directions. Ways of controlled field redistribution inside the structure are analyzed for glass, silicon and
silicon-glass 2D PhCr.
In our work, we considered theoretically 1D and 2D photonic bandgap (PBG) systems containing nonlinear
covers with short response time in femtosecond area. The short signal passing through the PBG system the
angular total reflection area was calculated by FDTD, transfer matrix and perturbation theory methods. The
photonic structure vs intensity behaviour was investigated for a few systems consisting of periodically layered
structures covered with an optically nonlinear material. Theoretical estimations of the logical gate parameters
were made for linear 2D Si-SiO2 , Si-air and Ge-Se photonic crystals covered with the nonlinear doped glass. It
was shown that the beam angular-frequency diagrams contain extremely sensitive areas inside the total reflection
range, where the weak nonlinearity leads to dramatic change in light reflection and transmission. Two principal
schemes of all-optical logical devices were analyzed and possible applications in all-optical adders and logical
gates were discussed.
Polaritonic resonancies are investigated in 2D silicon photonic crystals. Theoretically unpredicted
reduction in the transmittance of electromagnetic radiation and the step formation are observed for
wavelengths less than optical period of structures due to directed and decay optical modes formed by
macroporous silicon as a short waveguide structure. Prevalence of absorption over reflection of light
testify to the polaritonic type band formation. Surface polaritons are formed on decay modes in a silicon
matrix or macropore at formation of directed optical modes relatively on macropore or silicon matrix.
Absorption, photoconductivity and Raman scattering maxima are determined by a corresponding
maximum of a longitudinal component of electromagnetic waves in macroporous silicon structure as
short waveguide with a specific surface. Longitudinal component of electromagnetic waves in
investigated structure interacts effectively with surface oscillators, and polaritonic resonances in 2D
silicon photonic crystals are observed.
In this paper we analyze theoretically how introduction of the third component into the two-dimensional photonic crystal influences on the photonic band structure and the density of states of the system. We consider the periodic array of cylindrical air rods in a dielectric and the third medium is introduced as an intermediate layer of the thickness d and the dielectric constant εi between the air pores and the dielectric background. Various combinations of the parameters R (pores radius), d, and εi which allow the band gap to appear were considered. Using the plane wave method we have obtained the band structures and density of states for the triangular lattice 2D photonic crystals. The dependencies of the band gaps width and gaps edges position on the interlayer dielectric constant and interlayer thickness were analyzed. In the framework of this approach we have estimated the influence of the surface oxide layer on the band structure of macroporous silicon. We observed the shift of the gap edges to the higher or lower frequencies depending on the interlayer thickness and dielectric constant. We have shown that the existence of a native oxide surface layer should be taken into consideration to understand the optical properties of 2D photonic crystals, particularly in macroporous silicon structures.
Out-of-plane optical transmission spectra of 2D photonic macroporous silicon structures are investigated. By the plane wave expansion method all possible 2D lattice symmetries are considered and analyzed both in general case and for p-, s-polarizations. Sharp increase of absorption and formation of photonic band gaps is measured for wavelengths between one and two optical periods of macroporous silicon structure. Thus, for periodic structures one photonic band gap is formed, and some narrow peaks of density of states are formed for structure with the arbitrary macropore distribution. Theoretically unpredicted reduction in the transmittance of electromagnetic radiation and the step formation are observed for wavelengths less than optical period of macropores. Transmission spectra of macroporous silicon as well as steps were explained by a model of directed and decay optical modes formed by macroporous silicon as a short wave-guide structure. Prevalence of absorption over reflection of light, dependence of photoconductivity on incidence angle of the electromagnetic radiation testify to formation of the polaritonic type band formation.
Effects of increase in absorption of electromagnetic radiation, enhancement of photoconductivity and surface wave formation in 2D photonic macroporous silicon were investigated. Dependence of photoconductivity on a corner of the falling of the electromagnetic radiation, prevalence of absorption over reflection of light, as well as enhancement of the photoconductivity in comparison with the monocrystalline silicon testify to formation of surface waves (surface polaritons) in illuminated macroporous silicon structures. For wavelengths less than optical period of macropores there is an essential reduction in transmittance of electromagnetic radiation to (2-3)•10-2 (in comparison with the homogeneous material) and the polaritonic band formation. Conformity of spectra of photoconductivity of macroporous silicon to spectra of intrinsic photoconductivity of monocrystal silicon testifies the enrichment of a macropore surface by photocarriers and formation of a surface electromagnetic wave of plasmon type. Elecrtroreflectance spectroscopy of macroporous silicon surface showed an intrinsic electric field near 106 V/cm due to positive charge built in oxide layer on the walls of the macropores. Thus, electronic gas is quantified in a surface layer of the macroporous silicon structure. Polariton frequencies in long-wave part of the macroporous silicon optical transmittance are commensurable with experimental values of the surface plasmon frequency in the two dimensional electronic gas on Si-SiO2 boundary.
The use of semiconductor nanocrystals as a passive Q-switch in an eye-safe laser system is demonstrated. These lasers recently became popular in laser radar, three-dimensional scanning, targeting, and communication applications. Such applications require the laser to operate under Q-switching, generating a laser pulse with duration on the order of tens of nanoseconds, and a peak power on the order of a megawatt. Semiconductor nanocrystals exhibit unique physical properties, associated with the quantum size effect. The PbS and PbSe nanocrystals show a size-tunable absorption resonance in the near IR spectral region (1000-3000 nm), saturable absorbing properties, suitable as a functional Q-switch in eye-safe lasers. The quantum confinement effect and the saturable absorption can be manifested only in high quality nanocrystals with a narrow size distribution and passivated surfaces. Thus, a special synthetic procedures have been used for the preparation of PbSe core, PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystals. Then, a passively Q-switched Er:glass laser has been assembled, while the laser output energy, Q-switch threshold energies, and pulse width have been measured.
Laser, operating in the range of 1-2 μm (NIR), is currently an attractive candidate for various applications include ranging, 3D scanning laser radar, communication and other areas where human contact with the laser radiation is possible. The present work is focused on application of PbSe or PbSe/PbS semiconductor nanometer-sized crystals (NCs) for passive Q-switching of NIR laser. Owing to narrow band gap and large exciton Bohr radius of the bulk materials, the NCs of PbSe and PbS acquire unique properties: The quantization effects are strongly pronounced in PbSe and PbS NCs, the strong quantum confinement is thus easily obtained, and the ground-state absorption edge can be tuned over a wide wavelength range (from the visible to infrared). The NCs gain properties of saturable absorber, which allow using them as optical switches. We propose a colloidal synthesis procedure for the preparation of size-selected NCs, suitable for Q-switching of NIR laser. Colloidal synthesis allows simple control over the size of the crystals, and therefore, provides a possibility to produce the samples with desired absorption band position. This method is also very effective for stabilization of NCs and a passivation of their surface with the help of organic ligands.