Submicron-thick Sn whiskers were electrically characterized. The whiskers were grown from a 500 nm thick Sn layer on a Cu substrate, which was kept in a thermal vacuum chamber (50 degrees C and 8.3 x 10-6mbar for 1000 h) to simulate the space circumstances. First, the electrical parameters were measured in ambient conditions by welding the whisker to a sample holder. Next, a real circumstance was simulated when whiskers touched a conductive surface using a probing method in a vacuum. The average breakdown voltage was 10-12 V. Two types of I-V characteristics of the whisker were observed: an abrupt breakdown in the case of needle-type whiskers and a slower breakdown in the case of nodule-type whiskers. Nodule-type whiskers had a relatively larger current capacity than needle-type whiskers. TEM investigations showed that both whisker types were mono-crystalline, but the nodule-type whiskers were more oxidized and contained more Cu/Cu6Sn5 inclusions than the needle-type whiskers, which explains the electrical differences. In ambient conditions, a whisker can conduct more than three times larger current (over 100 mA) than in vacuum due to the thermal management effect of the ambient air. The space industry can use the obtained electrical parameters for risk analyses and the development of short-circuit protection systems.

The dynamics of coherent acoustic phonons in the Bi2Se3 layered crystal system are investigated. The findings reveal that the frequency evolution of breathing modes with the number of the material quintuple layers and the dispersion relation both can be explained by a modified chain model with a nonuniform coupling force.

This work reports on the investigation of homogeneity of the inside of indium micro -bumps/ columns placed on Ti/Pt/Au under bump metallisation. This is very important for connection resistivity, long-time durability, and subsequent hybridisation process (e.g., die -bonding). Gold reacts with indium to form intermetallic alloys with different chemo-physical parameters than pure indium. The geometrical and structural parameters of intermetallic alloys were analysed based on transmission electron microscope images. Distribution of elements in the investigated samples was determined using the transmission electron microscope with energy dispersive spectroscopy method. A thickness of intermetallic alloy was 1.02 mu m and 1.67 mu m in non -annealed (A) and annealed (B) indium columns, respectively. The layered and column -like interior structure of alloys was observed for both samples, respectively, with twice bigger grains in sample B. The graded chemical composition of Au -In intermetallic alloy was detected for the non -annealed In columns in contrast to the constant composition of 40% of Au and 60% of In for the annealed sample B. The atomic distribution has a minor impact on the In column mechanical stability. A yield above 99% of an In column with a 25 mu m diameter and a 11 mu m height is possible for a uniform columnar structure of intermetallic alloy with a thickness of 1.67 mu m.

We demonstrate the generation of THz transients from FeCo/graphene heterostructure triggered by circular polarized femtosecond pulsed laser emission originated from the circular photgalvanic effect.

In this work we investigate an example of combining the thermal insulation properties of porous oxide material with the exceptional thermal conductivity properties of graphene flakes. Blocks were prepared using the original sol-gel method, with fumed silica and water glass as the main components, to form a porous glass foam matrix by heat treatment at 450 degrees C. The microstructure of the samples was determined by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The thermal and mechanical properties of the samples were also analysed and discussed with respect to their potential applications as novel thermo-smart composite materials.

The generation of THz transients in a FeCo/graphene nanobilayer, excited by femtosecond optical laser pulses is demonstrated. We assign the mechanism of the THz radiation to the inverse Rashba-Edelstein effect in graphene with λ REE on the order of 0.001 nm.

The focused ion beam (FIB) technique was used to fabricate a nanothermocouple (with a 90 nm wide nanojunction) based on a metal–semiconductor (Pt–Si) structure, which showed a sensitivity up to 10 times larger (with Seebeck coefficient up to 140 µV/K) than typical metal–metal nanothermocouples. In contrast to the fabrication of nanothermocouples which requires a high-tech semiconductor manufacturing line with sophisticated fabrication techniques, environment, and advanced equipment, FIB systems are available in many research laboratories without the need for a high-tech environment, and the described processing is performed relatively quickly by a single operator. The linear response of the manufactured nanothermocouple enabled sensitive measurements even with small changes of temperature when heated with a stream of hot air. A nonlinear response of the nanothermocouple (up to 83.85 mV) was observed during the exposition to an argon-laser beam with a high optical power density (up to 17.4 Wcm−2), which was also used for the laser annealing of metal–semiconductor interfaces. The analysis of the results implies the application of such nanothermocouples, especially for the characterization of laser beams with nanometer spatial resolution. Improvements of the FIB processing should lead to an even higher Seebeck coefficient of the nanothermocouples; e.g., in case of the availability of other suitable metal sources (e.g., Cr).

This paper presents the results of beam investigations on semiconductor IR lasers using novel detectors based on thermocouples. The work covers the design, the fabrication of detectors, and the experimental validation of their sensitivity to IR radiation. The principle of operation of the manufactured detectors is based on the Seebeck effect (the temperature difference between hot and cold junctions induced voltage appearance). The devices were composed of several thermocouples arranged in a linear array. The nano- and microscale thermocouples (the hot junctions) were fabricated using a typical Si-compatible MEMS process enhanced with focused ion beam (FIB) milling. The performance of the hot junctions was tested, focusing on their sensitivity to IR radiation covering the near-infrared (NIR) radiation (λ = 976 nm). The output voltage was measured as a function of the detector position in the XY plane. The measurement results allowed for reconstructing the Gaussian-like intensity distribution of the incident light beam.

Energy Harvesting is mainly associated with transformation of different sources of energy commonly found in the environment, which are undesirable and usually suppressed, (e.g. noise, mechanical vibrations, heat etc.), or widely available (e.g. sunlight, wave energy, biochemical processes) to useful electric energy [1]. One type of such transformation base on immediate demagnetization of the magnet by a stroke following an explosion or other strong impulse of force. During this demagnetization magnet loses its magnetic properties and generates huge magnetic field impulse around it, which allows to charge high voltage capacitors with large capacity. From the past few years this issue is of great interest in military applications [2]. The paper presents the results obtained using the rapid demagnetization method in the case of a NdFeB magnet and new hybrid core. The developed core consisted of three basic elements: a NdFeB magnet, Terfenol-D and a developed metallic alloy prepared with a suction casting method. The main goal of proposing a new type of core in the event of rapid demagnetization is to partially replace the permanent magnet with another material in order to reduce the rare-earth material, while keeping the amount of generated electricity at a level that allows powering low-power electrical devices. To "capture" rapid change of magnetic flux a small number of coils around the core was made. However, a very low voltage level at a very high current required the use of specialized electronic transducers capable of delivering the appropriate voltage level to power the microprocessor system. To overcome this problem the circuit designed by authors which enabled voltage processing from low impedance magnetic circuits was used. The obtained results demonstrated the usefulness of the system to resonant frequencies up to 1MHz. It should be noted that the estimated efficiency of transforming the impact energy and demagnetization of the core to electric current was only 0.01%. Therefore, the key challenge is to improve the energy transformation, which might be done by changes of core arrangement or harvester construction. References: [1] P.D. Mitcheson et al., Proceedings of the IEEE, 96, (2008) [2] J. Kaleta, R. Mech and P. Wiewiórski, Actuators, IntechOpen ISBN: 978-1-78923-429-9, (2018), doi:10.5772/intechopen.71518

We demonstrate generation of time-resolved THz transients in a FeCo/graphene nanobilayer, excited by femtosecond optical laser pulses. The signal sign dependency on the experimental geometry and the external magnetic field allows assigning the mechanism of the THz radiation to the inverse spin Hall effect with a spin-to-charge current conversation parameter of the order of 0.001 nm.

The present study is focused on the influence of Ti and Gd doping at the Ga site on the microstructure, magnetic and mechanical properties of the polycrystalline Ni50Mn25Ga20-(x)Z(x) (x = 0 or 5, Z = Gd, Ti) magnetic shape memory alloys. Microstructure investigations show that reference Ni50Mn25Ga25 and Ti-doped alloys, both in the as-cast and annealed state, are single phase materials, whereas Gd-doped sample reveals dendritic dual-phase structure with substantial distinction between Gd-rich and Gd-poor regions. Thermomagnetic measurements expose reversible martensitic transition in the Ni50Mn25Ga25 and Ni50Mn25Ga20Ti5 alloys, where Ti addition to NiMnGa composition leads to the decrease of phase transformation temperature from T-M = 193 K for reference sample to T-M = 172.5 K for Ti-doped material. Furthermore, the Ni50Mn25Ga20Gd5 alloy does not experience fully martensitic transition. Temperatures of magnetic transformation also varies with chemical composition and equals to 379 K, 318 K and 370 K for the annealed Ni50Mn25Ga25, Ni50Mn25Ga20Ti5 and Ni50Mn25Ga20Gd5 alloy, respectively. Mechanical properties investigation based on the nanoindentation measurements shows beneficial influence of doping elements on material hardness. In addition, planar distributions of hardness allow to deconvolute mechanical properties of each individual phase of the Ni50Mn25Ga20Gd5 alloy.

In recent years, amorphous and nanocrystalline Fe-based alloys, due to their unique soft magnetic properties, have emerged as one of the most promising group of modern materials for various electric applications. This work presents microstructure and AC/DC magnetic properties of the NANOPERM-type material. The as-quenched amorphous Fe76Mo8Cu1B15 alloy was prepared by rapid quenching method in a form of 10 mm wide and 0.025 mm thick ribbon. Partial nanocrystallization was obtained by subsequent annealing of amorphous precursor at 783 K for 30 min. Microstructure investigation of annealed sample confirmed precipitation of alpha-Fe nanograins dispersed in amorphous matrix. In order to assess soft magnetic properties of fabricated material the dependences of core losses versus frequency (50 Hz-20 kHz) at room temperature were established, together with eddy currents, hysteresis, and anomalous losses coefficients separation. The frequency dependent correlation between real and imaginary part of permeability was also presented. Moreover, DC hysteresis loops of both as-quenched and annealed alloy were recorded in temperature range from 200 K to 400 K.

The terahertz time-domain spectroscopy (THz-TDS) technique has been used to obtain transmission THz-radiation spectra of polymer nanocomposites containing a controlled amount of exfoliated graphene. Graphene nanocomposites (1 wt%) that were used in this work were based on poly(ethylene terephthalate-ethylene dilinoleate) (PET-DLA) matrix and were prepared via a kilo-scale (suitable for research and development, and prototyping) in-situ polymerization. This was followed by compression molding into 0.3-mm-thick and 0.9-mm-thick foils. Transmission electron microscopy (TEM) and Raman studies were used to confirm that the graphene nanoflakes dispersed in a polymer matrix consisted of a few-layer graphene. The THz-radiation transients were generated and detected using a low-temperature–grown GaAs photoconductive emitter and detector, both excited by 100-fs-wide, 800-nm-wavelength optical pulses, generated at a 76-MHz repetition rate by a Ti:Sapphire laser. Time-domain signals transmitted through the nitrogen, neat polymer reference, and 1-wt% graphene-polymer nanocomposite samples were recorded and subsequently converted into the spectral domain by means of a fast Fourier transformation. The spectral range of our spectrometer was up to 4 THz, and measurements were taken at room temperature in a dry nitrogen environment. We collected a family of spectra and, based on Fresnel equations, performed a numerical analysis, that allowed us to extract the THz-frequency-range refractive index and absorption coefficient and their dependences on the sample composition and graphene content. Using the Clausius-Mossotti relation, we also managed to estimate the graphene effective dielectric constant to be equal to ~7 ± 2. Finally, we extracted from our experimental data complex conductivity spectra of graphene nanocomposites and successfully fitted them to the Drude-Smith model, demonstrating that our graphene nanoflakes were isolated in their polymer matrix and exhibited highly localized electron backscattering with a femtosecond relaxation time. Our results shed new light on how the incorporation of exfoliated graphene nanoflakes modifies polymer electrical properties in the THz-frequency range. Importantly, they demonstrate that the complex conductivity analysis is a very efficient, macroscopic and non-destructive (contrary to TEM) tool for the characterization of the dispersion of a graphene nanofiller within a copolyester matrix.

The microstructure, magnetic and mechanical properties of the annealed at 1430 K Ni50Mn25Ga20Gd5 (at.%) magnetic shape memory alloy were studied. The Ni50Mn25Ga20Gd5 ingot was prepared in a bulk form by arc-melting method. Scanning electron microscopy supported by atomic force microscopy investigations confirmed a dual-phase microstructure of the studied alloy characterized by Gd-poor and Gd-rich phases. Temperature dependence of magnetic magnetization M(T) measured at high (mu H-0 = 2 T) and low (mu H-0 = 0:25 T) value of external magnetic fields revealed that the fabricated material undergoes reversible martensitic transition close to the room temperature. The Curie temperature for the investigated material calculated from the M(T) curve measured in zero-field cooled mode is 377 K. Mechanical properties of the Ni50Mn25Ga20Gd5 alloy investigated by the means of a series of nanoindentation tests allowed to separate hardness for the Gd-poor (435 HV) and Gd-rich (562 HV) phase.

The relationship between topography, thermomagnetic and mechanical properties in the as-cast Gd75Ge15Si5Pr5 alloy was studied. Atomic force microscopy investigations accompanied by micrograph analysis confirm dual phase nature (observed as dark and bright phase) of the investigated material. The mechanical properties studies performed with respect to the Oliver-Pharr procedure show that the average instrumental hardness, Young's modulus and elastic deformation energy to total energy ratio equal 905 HV and 596 HV, 131 and 91 GPa, 40% and 45% for the dark and bright phase, respectively. The Curie point defined as inflection point on the magnetization versus temperature curve M(T) recorded in zero-field cooled mode equals 283 K. From the law of approach to magnetic saturation the temperature dependence of effective anisotropy constant K-eff was calculated in ferromagnetic region. It is also stated that the minimum observed on thermomagnetic M(T) characteristic at 100 K is associated with K-eff(T) dependence. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Polycrystalline Ni50Mn25Ga20Gd5 (at%) magnetic shape memory alloy was investigated in the as-prepared state and after annealing at 1430 K for 3 h. Microstructural analysis reveals dual-phase nature of the material with substantial distinction between Gd-rich and Gd-poor phases. Magnetic measurements performed in wide range of temperatures confirm reversible martensitic transformation in the annealed sample undergoing close to the room temperature. When it comes to the magnetic transition, the Curie temperature of the investigated alloy remains approximately unchanged at 370 K. Topography investigations conducted on the atomic force microscope in contact mode allow to measure 8 mm difference between minimum and maximum point of the martensite profile. The results from a series of nanoindentation tests show that hardness of the Gd-rich phase is 23%-35% higher than hardness of the Gd-poor phase, depending on the annealing state. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Summary form only given. NANOPERM-type metallic glasses [1, 2] are still attractive candidates for variety of practical applications, because of their unique magnetic [3, 4] as well as mechanical properties [5]. Their annealing above crystallization temperature induces partial crystallization that is characterized by formation of α-Fe grains with typical sizes of up to tens of nanometers. Soft magnetic properties and mechanical properties of such nanocrystalline materials can be tailored not only with the aid of their chemical composition, but also by controlling the size the nanocrystalline grains created by heat treatment of amorphous precursor, their morphology, and structural composition. In order to understand magnetic and mechanical properties of NANOPERM-type alloys it is necessary to understand their microstructure and physical consequences of transformation from amorphous to nanocrystaline state. It is well known that structural changes demonstrate themselves also via macroscopic magnetic and mechanical parameters such as temperature dependence of magnetization, Curie temperature, AC and DC hysteresis loops as well as microhardness. We have studied a NANOPERM-type Fe76Mo8Cu1B15 alloy in form of ribbon 0.025 mm thick and 10 mm wide, produced by a rapid quenching method, with emphasis upon its magnetic and mechanical properties. All measurements were performed for the sample in the as-quenched state and after annealing at 837 K for 30 min. (above the primary crystalization temperature i.e. 723 K). Microstructure of the samples was studied by X-ray diffraction and AFM/LFM investigations. Temperature evolution of DC magnetization measured under zero-field cooling conditions using amorphous and nanocrystalline samples with different amounts of nanocrystalline grains was performed in temperature range from 50 K up to 400 K. In addition, DC hysteresis loops were also taken with the help of a VersaLab system (Quantum Design). Room tempertaure AC soft magnetic properties versus frequency and maximum induction were studied for toroidal samples by a hysteresisgraph (AMH-50K-S, Laboratorio ElletroFisico Engineering) at frequency up to 20 kHz. The Steinmetz coefficients for the amorphous and nanocrystaline alloys were calculated in the frequency range 50 Hz - 20 kHz. Mechanical characterization of investigated materials was performed by nanoindentation tests with respect to Oliver-Pharr method for maximum load of 250 mN. Sample of the Fe76Mo8Cu1B15 alloy in the as-quenched state was fully amorphous, which was confirmed by a broad halo in X-ray diffraction pattern and absence of visible precipitates on AFM/LFM images recorded in contact mode. The peaks present in X-ray diffraction pattern confirm two-phase behaviour of annealed material. It was also seen in measurements of microhardnesas for different regions in samples. The average values of hardness obtained for the amorphous matrix and nanocrystalline bcc grains are equal to 1221 HV and 1600 HV, respectively. The magnetic behavior described by DC hysteresis loops for the Fe76Mo8Cu1B15 alloy in the as-quenched state and after annealing at 837 K for 30 min. measured in the temperature range 200-400 K presented in Fig. 1 show a completely different behavior. The Curie temperature of the amorphous alloy equals 313 K, whereas for the annealed sample the higher value of the Curie point due to the nanocrystalline α-Fe phase was observed. For designing process and simulation of inductive elements (e.g. transformers, chokes) the AC magnetic characteristics are very important. Fig. 2 shows core losses as a function of maximum induction for the Fe76Mo8Cu1B15 alloy. It is seen that nanocrystalline material with low core losses in wide range of frequency and Curie point above 400 K (Fig. 1) is excellent candidate for high temperature and frequency soft magnetic material. Moreover, the Steinmetz coefficients K and α [6] calculated for the nanocrystalline Fe76Mo8Cu1B15 alloy increase from 0.0381 to 0.5840 and from 1.71 to 2.42, respectively for with frequency range 500 Hz - 20 kHz.

This paper presents impact of front and back laser mirror ion cleaning on quantum cascade laser characteristics. Cleaning of the front mirror makes the beam more symmetric and increases external differential quantum efficiency, while cleaning of the back mirror reduces the electrical resistance, increases the threshold current and slightly affects the optical polarization of the beam.

A new type of interconnections in power devices could be based on copper due to higher electrical and thermal conductivity, and significantly lower material price than for Au. This work presents fabrication technology of Cu-based interconnections for high power transistors and results of interconnections reliability. Magnetron co-sputtering deposition method was applied to create Cu alloys with Ru, Hf, Nb, NbN additives, as well as adhesion layers of Ti, NbN or NbTiN. Interconnection reliability was evaluated on test structures, where Cu lines were protected by thin metallic or dielectric cap against oxidation in air. Crystal structure of the Cu film is stabilized by small amount of Nb or NbN additive. Formed interconnections ensure resistivity below 5 μΩcm. Resistance of the Cu interconnection is stable after ageing in air at 250°C and at current stress of 5 MA/cm 2 for few hundred hours, while an insignificant increase in resistance is observed after 200 h ageing at 300 ° C and current stress of 2 MA/cm 2 .

High refractive index contrast gratings (HCGs) with their extraordinary optical properties are very interesting candidates to substitute Distributed Bragg Reflectors as mirrors in optoelectronic semiconductor devices. In this work we present results of optical examination of a large scale HCG structure fabricated by focused-ion beam etching technique. The measured reflectance spectra exhibit a strong dependence on polarization of incident light, which confirms theoretical predictions. We also studied optical properties of a cavity formed by the HCG stacked on a wafer containing a VECSEL-like epitaxial structure.