Search results for "Applied Physics"
showing 10 items of 1226 documents
Low-temperature growth of n ++-GaN by metalorganic chemical vapor deposition to achieve low-resistivity tunnel junctions on blue light emitting diodes
2018
We report on low-resistivity GaN tunnel junctions (TJ) on blue light-emitting diodes (LEDs). Si-doped n ++-GaN layers are grown by metalorganic chemical vapor deposition directly on LED epiwafers. Low growth temperature (<800 °C) was used to hinder Mg-passivation by hydrogen in the p ++-GaN top surface. This allows achieving low-resistivity TJs without the need for post-growth Mg activation. TJs are further improved by inserting a 5 nm thick In0.15Ga0.85N interlayer (IL) within the GaN TJ thanks to piezoelectric polarization induced band bending. Eventually, the impact of InGaN IL on the internal quantum efficiency of blue LEDs is discussed.
Amorphous hydrogenated carbon (a-C:H) depositions on polyoxymethylene: Substrate influence on the characteristics of the developing coatings
2016
Abstract After oxygen plasma treatment polyoxymethylene (POM) material was exposed to acetylene plasma to progressively deposit two different types of amorphous hydrogenated carbon (a-C:H) films. Radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) was used to generate both plasma processes. The surface morphology of the coated samples has been investigated by atomic force microscopy (AFM) and their chemical composition by Diffusive Reflectance Infrared Fourier Transform (DRIFT) and Raman spectroscopy. Results revealed the absence of a solid interlayer formation between the a-C:H films and POM. The in sequence exposure of oxygen and acetylene plasma on POM substrate prevents…
ALD thin ZnO layer as an active medium in a fiber-optic Fabry–Perot interferometer
2015
Abstract A novel optical fiber sensor of temperature using a thin ZnO layer fabricated by atomic layer deposition (ALD) is demonstrated for the first time. The thin ZnO layer was grown on the face of a standard optical telecommunication fiber SMF-28 and operates as a Fabry–Perot interferometer sensitive to temperature. The interferometer characterization was made in the temperature range extending from 50 to 300 °C with resolution equal to 1 °C. The output signal was analyzed by measurement of the shift of the maxima in spectral pattern. The sensitivity of temperature measurement is about 0.05 nm/°C. Furthermore, very good linearity of the sensor was achieved with correlation coefficient R2…
Evolution of the sp2 content and revealed multilayer growth of amorphous hydrogenated carbon (a-C:H) films on selected thermoplastic materials
2017
Amorphous hydrogenated carbon (a-C:H) films were gradually deposited on high-density polyethylene (HDPE), polyethylene terephthalate (PET) and polyoxymethylene (POM) via an indirect (f-type) and a direct (r-type) plasma-enhanced chemical vapor deposition (PECVD) process with acetylene plasma. The surface morphologies of the thicker r-depositions on the three different thermoplastics have been analyzed by atomic force microscopy (AFM) at varying micrometer scales. Absorbance spectroscopy has been used to characterize the optical properties of all coatings. Intrinsic stress release phenomena are revealed on thicker layers through the detection of characteristic surface corrugations. Based on …
Correlation between milling parameters and microstructure characteristics of nanocrystalline copper powder prepared via a high energy planetary ball …
2007
The microstructure evolution of Cu-nanostructured powders versus the ball milling conditions was investigated by whole peak profile powder pattern modeling method. This method allows defining in some approach the characteristics of as-milled Cu powder microstructure in terms of crystallite size, type and density of dislocations and twin faults density. It is shown that the change of microstructure characteristics of as-milled Cu powder versus the ball milling conditions (under constant time of the ball milling) depend on only some energy parameters of the milling, for example, average size of crystallite is uniquely defined by energy of the shock, whereas the portion of edge and screw compo…
Some aspects of the MOCVD growth of ZnO on sapphire using tert-butanol
2002
The growth of ZnO on (0001) sapphire substrates using metalorganic chemical vapor deposition is reported. Diethylzinc and tertiarybutanol were used, respectively, as zinc and oxygen sources. Growth conditions are detailed such as the substrate temperature and the precursors partial pressures. The influence of the cleanness state of the MOCVD silica reactor is emphasized, since it modifies both layer quality and crystalline orientation, and since it also affects growth process steps like sapphire thermal treatment and buffer layer deposition. ZnO epitaxial layers are characterised by scanning electron microscopy (SEM) to assess the surface orientation and morphology, X-ray diffraction (XRD) …
Partial Discharge Measurements under DC Voltages Containing Harmonics Produced by Power Electronic Devices
2018
Partial Discharge (PD) monitoring is one of the main diagnostic instrument to evaluate the reliability of modern electrical transmission and distribution systems. The widespread use of High voltage dc (HVDC) connections increase the demand of voltage source converters (VSCs) which, as a consequence, has brought about new challenges in the field of partial discharge measurements. In fact, the output voltage waveforms generated by AC/DC modular multilevel converters (MMCs) are affected by a significant harmonic content which influences the Partial Discharges (PDs) activity. For this reason, previous research mainly investigated the PD phenomenon on the AC side of the converter. The aim of the…
Giant Spin Seebeck Effect through an Interface Organic Semiconductor
2019
Interfacing an organic semiconductor C60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12: YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient spin current transport via the thermally driven spin Seebeck effect (SSE). Experiments and first principles calculations consistently show that the presence of C60 reduces significantly the conductivity mismatch between YIG and Pt and the s…
Microstructure Design for Fast Lifetime Measurements of Magnetic Tunneling Junctions
2019
The estimation of the reliability of magnetic field sensors against failure is a critical point concerning their application for industrial purposes. Due to the physical stochastic nature of the failure events, this can only be done by means of a statistical approach which is extremely time consuming and prevents a continuous observation of the production. Here, we present a novel microstructure design for a parallel measurement of the lifetime characteristics of a sensor population. By making use of two alternative designs and the Weibull statistical distribution function, we are able to measure the lifetime characteristics of a CoFeB/MgO/CoFeB tunneling junction population. The main param…
Modulating the polarization of broadband terahertz pulses from a spintronic emitter at rates up to 10 kHz
2021
Reliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction of the electric field of linearly polarized terahertz electromagnetic pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic terahertz emitter. Polarity modulation of the terahertz field with more than 99% contrast at a rate of 10 kHz is achieved using a harmonic magnetic field. By adding a static magnetic field, we modulate the direction of the terahertz field between angles of, for instance, −53° and 53° at kilohertz rates. We believe our approach makes spintronic terahertz emitters a promising source for low-noise modula…