Aleksandr Oseev

Phoxonic crystals—a new platform for chemical and biochemical sensors

A new sensor platform is based on so-called phoxonic crystals. Phoxonic crystals are structures designed for simultaneous control of photon and phonon propagation and interaction. They are characterized by a periodic spatial modulation of the dielectric constant as well as elastic properties on a common wavelength scale. Multiple scattering of photons and phonons results in a band gap where propagation of both waves is prohibited. The existence of photonic and phononic band gaps opens up opportunities for novel devices and functional materials. The usage of defect modes is an advantageous concept for measurement. The defect also acts as point of measurement. We show theoretically that the properties of the defect mode can be tailored to provide very high sensitivity to optical and acoustic properties of matter confined within a defect cavity or surrounding the defect or being adsorbed at the cavity surface. In this paper, we introduce the sensor platform and analyze the key features of the sensor transduction scheme. Experimental investigations using a macroscopic device support the theoretical findings.

Towards a SAW based phononic crystal sensor platform

A Surface Acoustic Wave (SAW) sensor platform based on phononic crystals specifically designed for chemical and biosensing will be introduced. The unique feature of this sensor concept is the possibility to determine volumetric properties of analytes at volume as low as 1 nl. The sensor platform has the capability paving the way to study chemical reactions in microreactors or biomaterials directly in their physiological environment without any label.

Determining liquid properties by extraordinary acoustic transmission through phononic crystals

This contribution shows how a resonance-induced extraordinary acoustic transmission through a phononic crystal structure can be used as sensor for liquid properties. The phononic crystal consists of a metal plate with a periodic array of holes. Ultrasound propagates in a way that the incidence direction of sound is perpendicular to the plate. A characteristic transmission peak has been found to strongly depend on liquid sound velocity. The respective peak maximum frequency serves as measure for liquid composition. Numerical calculations based on FDTD and FEA reveal more insides to the propagation characteristics, in particular the presence of specific plate modes. Experimental investigations using a laser vibrometer and the Schlieren method support the theoretical findings.

Phononic crystal based liquid sensor governed by localized defect resonances

Phononic crystal sensors are promising for liquid sensor applications. We have already shown that the frequency of narrow transmission bands depends on properties of liquids confined within a 2D phononic crystal. In comparison to almost all liquid sensor platforms where sensors respond to effects close to the sensor surface, e.g. mass load due to absorption of molecules in a recognition layer, the objective of the liquid cavity resonators is the determination of volumetric (bulk) properties of the liquid. The quality factor is the most crucial parameter of sensor performance. Therefore, classical microacoustic resonance sensors must avoid radiation of acoustic energy into the liquid. The phononic crystal sensor concept tailors acoustic wave propagation in a way to excite a specific mode within the band gap of the phononic crystal. We apply surface acoustic wave (SAW) devices as reliable platform for the realization of phononic crystal sensor. It performs both excitation of a selected liquid cavity resonance and its detection. The liquid cavity microchannel is realized within an overlayer of the SAW device. The liquid in the microchannel becomes a part of vibrating overlayer and determines its acoustic properties. The sensor development contains three parts: development of the SAW platform including etching of periodic elements, design of the overlayer containing the microchannels, and optimization of acoustic coupling between the two elements. We present simulation results of the overlayer with the acoustic field penetrating the liquid. We further report on technology to realize phononic crystal structures with well-defined shape and depth of etched structures in SAW substrates which prove the correctness and feasibility of our approach.

SAW-Based Phononic Crystal Microfluidic Sensor—Microscale Realization of Velocimetry Approaches for Integrated Analytical Platform Applications

The current work demonstrates a novel surface acoustic wave (SAW) based phononic crystal sensor approach that allows the integration of a velocimetry-based sensor concept into single chip integrated solutions, such as Lab-on-a-Chip devices. The introduced sensor platform merges advantages of ultrasonic velocimetry analytic systems and a microacoustic sensor approach. It is based on the analysis of structural resonances in a periodic composite arrangement of microfluidic channels confined within a liquid analyte. Completed theoretical and experimental investigations show the ability to utilize periodic structure localized modes for the detection of volumetric properties of liquids and prove the efficacy of the proposed sensor concept.

Micro- and nanostructure of a titanium surface electric-spark-doped with tantalum and modified by high-frequency currents

We have studied the characteristics of the porous microstructure of tantalum coatings obtained by means of electric spark spraying on the surface of commercial grade titanium. It is established that, at an electric spark current within 0.8–2.2 A, a mechanically strong tantalum coating microstructure is formed with an average protrusion size of 5.1–5.4 µm and pore sizes from 3.5 to 9.2 µm. On the nanoscale, a structurally heterogeneous state of coatings has been achieved by subsequent thermal modification at 800–830°C with the aid of high-frequency currents. A metal oxide nanostructure with grain sizes from 40 to 120 nm is formed by short-time (~30 s) thermal modification. The coating hardness reaches 9.5–10.5 GPa at an elastic modulus of 400–550 GPa.

Structure of metal-oxide Ti-Ta-(Ti,Ta)xOy coatings during spark alloying and induction-thermal oxidation

The study focuses on combined spark alloying of titanium and titanium alloy surface and porous matrix structure oxidation. The metal-oxide coatings morphology is the result of melt drop transfer, heat treatment, and oxidation. The study establishes the influence of technological regimes of alloying and oxidation on morphological heterogeneity of metal- oxide system Ti-Ta-(Ti,Ta)xOy.

Hybrid structures based on gold nanoparticles and semiconductor quantum dots for biosensor applications

Background The luminescence amplification of semiconductor quantum dots (QD) in the presence of self-assembled gold nanoparticles (Au NPs) is one of way for creating biosensors with highly efficient transduction. Aims The objective of this study was to fabricate the hybrid structures based on semiconductor CdSe/ZnS QDs and Au NP arrays and to use them as biosensors of protein. Methods In this paper, the hybrid structures based on CdSe/ZnS QDs and Au NP arrays were fabricated using spin coating processes. Au NP arrays deposited on a glass wafer were investigated by optical microscopy and absorption spectroscopy depending on numbers of spin coating layers and their baking temperature. Bovine serum albumin (BSA) was used as the target protein analyte in a phosphate buffer. A confocal laser scanning microscope was used to study the luminescent properties of Au NP/QD hybrid structures and to test BSA. Results The dimensions of Au NP aggregates increased and the space between them decreased with increasing processing temperature. At the same time, a blue shift of the plasmon resonance peak in the absorption spectra of Au NP arrays was observed. The deposition of CdSe/ZnS QDs with a core diameter of 5 nm on the surface of the Au NP arrays caused an increase in absorption and a red shift of the plasmon peak in the spectra. The exciton–plasmon enhancement of the QDs’ photoluminescence intensity has been obtained at room temperature for hybrid structures with Au NPs array pretreated at temperatures of 100°C and 150°C. It has been found that an increase in the weight content of BSA increases the photoluminescence intensity of such hybrid structures. Conclusion The ability of the qualitative and quantitative determination of protein content in solution using the Au NP/QD structures as an optical biosensor has been shown experimentally.

Heat-Resistant Ferroelectric-Polymer Nanocomposite with High Dielectric Constant

The high dielectric constant ferroelectric-polymer nanocomposite was developed for producing the heat-resistant and chemical stable planar layers. According to the composite coatings formation conditions, the following value ranges of dielectric constant and loss factor were received: 30–400 for dielectric constant and 0.04–0.1 for loss tangent, accordingly. Unlike of composite components, the obtained composite material is characterized by thermo-stability of electrical parameters up to 250 °C. The dielectric frequency spectra of the composite exhibit two clearly visible peaks in contrast to the spectra of the polymer and ferroelectric ceramics. The developed composite material can be used as a built-in film capacitors material in microelectronic devices.

SAW based phononic crystal liquid sensor - Periodic microfluidic channels approach

We report on practical realization of novel liquid sensor upon a base of typical SAW device design. The sensor is implemented as a periodic microfluidic structure atop a piezoelectric substrate. Simultaneous employment of phononic crystal phenomenon and structural resonance inside the phononic crystal is the basic idea behind. The phononic crystal band gap prevents propagation of traveling waves through the structure and their conversion and scattering into the substrate. The structural resonance enables acoustic signal amplification at frequencies predetermined by materials composing the structure. The sensor operates at high frequencies and potentially is capable to measure sound velocity and bulk viscosity of liquids with a precision superior to established instruments. The periodic microfluidic structure is made of SU-8 layers atop of lithium niobate based SAW device and acts as a liquid analyte container. It applies MEMS technology with a specific attention to the multilayer fabrication and exceptional parameters control. Experimental results demonstrate the feasibility of this approach providing a distinct and predictable sensor response on speed of sound of analyte.