A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...

Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials

Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

Liquid crystals are nowadays widely used in all types of display applications. However their unique electro-optic properties also make them a suitable material for nondisplay applications. We will focus on the use of liquid crystals in different photonic components: optical filters and switches, beam-steering devices, spatial light modulators, integrated devices based on optical waveguiding, lasers, and optical nonlinear components. Both the basic operating principles as well as the recent state-of-the art are discussed.

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Liquid-crystal photonic applications

Silicon nitride (SiN) is emerging as a competitive platform for CMOS-compatible integrated photonics. However, active devices such as modulators are scarce and still lack in performance. Ideally, such a modulator should have a high bandwidth, good modulation efficiency, low loss, and cover a wide wavelength range. Here, we demonstrate the first electro-optic modulators based on ferroelectric lead zirconate titanate (PZT) films on SiN, in both the O- and the C-band. Bias-free operation, bandwidths beyond 33 GHz and data rates of 40 Gbps are shown, as well as low propagation losses ($\alpha\approx 1$ dB/cm). A $V_\pi L\approx$ 3.2 Vcm is measured. Simulations indicate that values below 2 Vcm are achievable. This approach offers a much-anticipated route towards high-performance phase modulators on SiN.

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Nanophotonic Pockels modulators on a silicon nitride platform

Silicon nitride (SiN) is emerging as a competitive platform for CMOS-compatible integrated photonics. However, active devices such as modulators are scarce and still lack in performance. Ideally, such a modulator should have a high bandwidth, good modulation efficiency, low loss, and cover a wide wavelength range. Here, we demonstrate the first electro-optic modulators based on ferroelectric lead zirconate titanate (PZT) films on SiN, in both the O-band and C-band. Bias-free operation, bandwidths beyond 33 GHz and data rates of 40 Gbps are shown, as well as low propagation losses (α ≈ 1 dB cm−1). A half-wave voltage-length product of 3.2 V cm is measured. Simulations indicate that further improvement is possible. This approach offers a much-anticipated route towards high-performance phase modulators on SiN. Active devices such as modulators made of silicon nitride still lack performance. Here, the authors demonstrate electro-optic modulators based on ferroelectric lead zirconate titanate films on silicon nitride, in both the O- and the C-band with a modulation bandwidth beyond 33 GHz and with data rates of 40 Gbps.

https://biblio.ugent.be/publication/8574558/file/8574563.pdf

The Poisson-Nernst-Planck equations describe the dynamics of charge transport in an electric field. Although they are relevant in many applications, a general solution is not known and several aspects are not well understood. In many situations nonlinear effects arise for which no analytical description is available. In this work, we investigate charge transport in a planar device on application of a voltage step. We derive analytical expressions for the dynamical behavior in four extreme cases. In the ``geometry limited'' regime, applicable at high voltages and low charge contents, we neglect diffusion and the electric field induced by the charges. This leads to a uniform movement of all charges until the bulk is completely depleted. In the ``space charge limited'' regime, for high voltages and high charge contents, diffusion is still neglected but the electric field is almost completely screened over transient space charge layers. Eventually, however, the bulk becomes depleted of charges and the field becomes homogeneous again. This regime is solved under the assumption of a homogeneous current density, and is characterized by a typical ${t}^{\ensuremath{-}3/4}$ behavior. In the ``diffusion limited'' regime, valid for low voltages and low charge contents, diffusion is the dominant transport mechanism and prevents the charges from separating. This results in only very small deviations from a homogeneous charge distribution throughout the device. In the ``double layer limited'' regime, for low voltages and high charge contents, the combination of dominant diffusion and screening of the electric field results in large variations occurring only in thin double layers near the electrodes. Numerical simulations confirm the validity of the derived analytical expressions for each of the four regimes, and allow us to investigate the parameter values for which they are applicable. We present transient current measurements on a nonpolar liquid with surfactant and compare them with the external current predicted by the theoretical description. The agreement of the analytical expressions with the experiments allows us to obtain values for a number of properties of the charges in the liquid, which are consistent with results in other works. The confirmation by simulations and measurements of the derived theoretical expressions gives confidence about their usefulness to understand various aspects of the Poisson-Nernst-Planck equations and the effects they represent in the dynamics of charge transport.

Dynamics of charge transport in planar devices.

Owing to the nonlinear effect of optical field-induced director reorientation, self-focusing of an optical beam can occur in nematic liquid crystals and an almost diffraction-compensated propagation can be observed with milliwatts of light power and propagation lengths of several millimeters. This opens the way for applications in all-optical signal handling and reconfigurable optical interconnections. Self-focusing of an optical beam in nematic liquid-crystal cells has been studied experimentally and by means of numerical simulation. The relationships between bias voltage, cell thickness and required optical power have been examined, thus allowing the determination of the most favorable conditions for soliton-like beam propagation.

Jeroen Beeckman

Papers

Liquid-crystal photonic applications

Nanophotonic Pockels modulators on a silicon nitride platform

Nanophotonic Pockels modulators on a silicon nitride platform

Dynamics of charge transport in planar devices.

Simulations and experiments on self-focusing conditions in nematic liquid-crystal planar cells.