Suchergebnisse

We theoretically study helicity-dependent photocurrent in a three-dimensional topological insulator Bi2Te3 under elastic scattering of different symmetries. By exploring spin-selective optical transitions and symmetry-breaking scattering, we are able to address the out-of-plane spin texture of the topological helical surface states and to generate directional, spin-polarization tunable photocurrent that is otherwise forbidden for the original C-3v symmetry of the surface. This can be achieved regardless of the Fermi level, even under the condition when the topological states are inaccessible in dark. This work paves the way to robustly explore the out-of-plane spin texture for harvesting opto-spintronic functionalities of topological insulators. ; Funding Agencies|Linkoping University; Swedish Research CouncilSwedish Research Council [2016-05091]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

Laser heating of rhenium in a diamond anvil cell to 3000 +/- 300 K at about 200 GPa results in formation of two previously unknown rhenium carbides, hexagonal WC-type structured ReC and orthorhombic TiSi2-type structured ReC2. The shortest C-C distances [1.758(3) angstrom at 219(5) GPa and 1.850(4) angstrom at 180(7) GPa] found in honeycomb-like carbon nets in the structure of ReC2 are quite unusual. The Re-C solid solution formed at multimegabar pressure has the carbon content of approximate to 20 at%. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [5K16WC1, 05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

We propose native oxide AlGaO(x)outer protective layer for GaAs/AlGaAs core-multishell nanowires to provide yearly stable stronger optical and electrical confinement within the nanowire core. We prepared core-multishell NWs consisting of GaAs core, Al0.2Ga0.8As multi-layered barrier layer, and amorphous Al(0.9)Ga(0.1)O(x)outer shell, which was obtained simply by growing Al-rich AlGaAs and exposing the NWs to the ambient air. Photoluminescence from the NWs reveals that the Al(0.9)Ga(0.1)O(x)outer shell provides efficient optical confinement and creates a compressive strain in the interior of the NW that enhances and blueshifts the photoluminescence of the GaAs core. ; Funding Agencies|KAKENHI from Japan Society of Promotion of Science [19H00855, 16H05970]; Canon foundationCanon Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

In this work, we design and fabricate a wireless system with the main operating device based on zinc oxide (ZnO) nanowires. The main operating device is based on piezoelectric nanogenerator (NG) achieved using ZnO nanowires grown hydrothermally on paper substrate. The fabricated NG is capable of harvesting ambient mechanical energy from various kinds of human motion, e.g., footsteps. The harvested electric output has been used to serve as a self-powered pressure sensor. Without any storage device, the signal from a single footstep has successfully triggered a wireless sensor node circuit. This study demonstrates the feasibility of using ZnO nanowire piezoelectric NG as a low-frequency self-powered sensor, with potential applications in wireless sensor networks. ; Funding Agencies|CeNano grant; Swedish Government strategic research area in material science on functional materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

The potential of flexible retirement will not be realised until the fear of substantial income loss is allayed. At present, for people looking at flexible retirement options, the occupational pension is not the vehicle to use, as the SFO (Superannuation Funds Office) does not look favourably on those planning in advance to wind down their career gradually insisting, as it does, that a fixed retirement age constitutes part of the scheme. Norman Fowler's consultative document on Personal Pensions (1984) aims to encourage more take‐up of occupational schemes through the individual being given freedom to choose the type of benefits suiting individual needs; in effect, this will allow people to contract out of the State earnings‐related scheme. Greater attention needs to be given to training trade union representatives in pension matters — many, at the moment, being expected to discuss very complex issues with little or no training.

CaMnO3 is a perovskite with attractive magnetic and thermoelectric properties. CaMnO3 films are usually grown by pulsed laser deposition or radio frequency magnetron sputtering from ceramic targets. Herein, epitaxial growth of CaMnO3-y (002) films on a (112 over bar 0)-oriented LaAlO3 substrate using pulsed direct current reactive magnetron sputtering is demonstrated, which is more suitable for industrial scale depositions. The CaMnO3-y shows growth with a small in-plane tilt of Funding Agencies|Swedish Research Council (VR)Swedish Research Council [2016-03365]; Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows program [KAW 2020.0196]; Electron Microscopy Laboratory at Linkoping University; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Swedish Energy AgencySwedish Energy AgencyMaterials & Energy Research Center (MERC) [46519-1]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [RIF 14-0074]

Reflective structural colors are of interest for many applications as alternatives to dyes and pigments and many different solutions have been proposed. The ideal systems should provide high reflectance efficiency while keeping good chromaticity and offering tunability throughout the visible spectral range. It is challenging to achieve such combined features with a simple single structure. Here we address this challenge using a concept that combines the Fabry-Perot effect with a broadband absorbing layer. Our easy-to-fabricate structures form highly reflective optical nanocavities with improved chromaticity throughout the visible compared with the two separate concepts. The addition of an additional cavity layer and a transparent top coating further improves the chromaticity and allows the formation of black surfaces. ; Funding Agencies|Swedish Foundation for Strategic ResearchSwedish Foundation for Strategic Research; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

The influence of the aluminium content (x) on crater wear mechanisms of Ti1-xAlxN coated WC-Co inserts in highspeed turning of 316L stainless steel was investigated. Electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the wear behaviour. Ti1-xAlxN coatings with x <= 0.53 showed, after 1/3 of the tool life, a thick adhered layer composed of oxides and metallic species from the steel, and no diffusion of workpiece material into the coating. These coatings presented the best wear resistance and least abrasive wear. The high aluminium content Ti0.38Al0.62N coating showed the worst crater wear resistance. This is assigned to interdiffusion of workpiece elements and oxygen into the coating as a consequence of spinodal decomposition of the cubic TiAlN-phase, resulting in more severe abrasive wear. ; Funding Agencies|VINNOVAVinnova [2016-05156]; Swedish government strategic research area grant AFM -SFO MatLiU [2009-00971]

Nanowires (NWs) based on ternary GaAsP and quaternary GaNAsP alloys are considered as very promising materials for optoelectronic applications, including in multi-junction and intermediate band solar cells. The efficiency of such devices is expected to be largely controlled by grown-in defects. In this work we use the optically detected magnetic resonance (ODMR) technique combined with photoluminescence measurements to investigate the origin of point defects in Ga(N)AsP NWs grown by molecular beam epitaxy on Si substrates. We identify gallium vacancies, which act as non-radiative recombination centers, as common defects in ternary and quaternary Ga(N)AsP NWs. Furthermore, we show that the presence of N is not strictly necessary for, but promotes, the formation of gallium vacancies in these NWs. ; Funding: Linkoping University; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2019-04312]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Kinetic modeling has been used to study the decomposition chemistry of ammonia at a wide range of temperatures, pressures, concentrations, and carrier gases mimicking the conditions in chemical vapor deposition (CVD) of metal nitrides. The modeling shows that only a small fraction of the ammonia molecules will decompose at most conditions studied. This suggests that the fact that the high NH3 to metal ratios often employed in CVD is due to the very low amount of reactive decomposition products being formed rather than due to rapid decomposition of ammonia into stable dinitrogen and dihydrogen as suggested by purely thermodynamic equilibrium models. ; Funding Agencies|Swedish foundation for Strategic Research through the project "Time-resolved low temperature CVD for III-nitrides" [SSF-RMA 15-0018]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at the Linkoping University (Faculty Grant SFO Mat LiU) [2009 00971]; Swedish Research Council (VR)Swedish Research Council

Perovskite solar cells are promising candidates for next-generation photovoltaics. Fullerenes and their derivatives can act as efficient electron transport layers, interfacial modification layers, and trap state passivators in perovskite solar cells, all of which play an important role in increasing efficiency, reducing current hysteresis, and enhancing device stability. Herein, recent progress in the use of fullerenes and their derivatives in perovskite solar cells is reviewed, with a particular emphasis on fullerene chemical structures that affect device performance. Potential fullerene candidates that could further improve device performance and stability are also discussed. ; Funding Agencies|973 Project [2014CB845601]; National Science Foundation of China [U1205111, 21390390, 21721001, 51502252]; Swedish Research Council (VR) [330-2014-6433]; Swedish Research Council (FORMAS) [942-2015-1253]; European Commission Marie Sklodowska-Curie Actions [INCA 600398]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; China Scholarship Council [201706315013]

The cuticle of the scarab beetle Cotinis mutabilis reflects left-handed polarized light indicating the presence of a helicoidal structure. Different in-depth pitches in the cuticle are corroborated by optical microscopy images of the cuticle which originally is yellowish or reddish but becomes greenish after gently scratching its top side. Using the Mueller-matrix formalism the degree of polarization (total and circular) of reflected light is determined for unpolarized incident light. The effects of the finite thickness of the cuticle on the broadening and strength of the selective Bragg reflection are discussed on the basis of dispersion relations for optical modes in helicoidal structures and simulated spectra. (C) 2017 The Author(s). Published by Elsevier Ltd. ; Funding Agencies|Conacyt-Mexico; Knut and Alice Wallenberg foundation; Swedish Research Council; Carl Tryggers foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]

We report on a thin film synthesis technique which allows for unprecedented control over the crystalline phase formation in metastable transition metal nitride based layers. For the model material system of V0.26Al0.74N, a complete transition from hexagonal to supersaturated cubic structure is achieved by tuning the incident energy, hence subplantation depth, of Al+ metal ions during reactive hybrid high power impulse magnetron sputtering of Al target and direct current magnetron sputtering of V target in Ar/N-2 gas mixture. These findings enable the phase selective synthesis of novel metastable materials that combine excellent mechanical properties, thermal stability, and oxidation resistance. ; Funding Agencies|German Research Foundation (DFG) [SFB-TR 87]; VINN Excellence Center Functional Nanoscale Materials (FunMat-2) Grant [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkping University [SFO-Mat-LiU 2009-00971]; Knut and Alice Wallenberg Foundation [2011.0143]; Aforsk Foundation [16-359]

The influence of B4C incorporation during magnetron sputter deposition of Cr/Sc multilayers intended for soft X-ray reflective optics is investigated. Chemical analysis suggests formation of metal: boride and carbide bonds which stabilize an amorphous layer structure, resulting in smoother interfaces and an increased reflectivity. A near-normal incidence reflectivity of 11.7%, corresponding to a 67% increase, is achieved at λ = 3.11 nm upon adding 23 at.% (B + C). The advantage is significant for the multilayer periods larger than 1.8 nm, where amorphization results in smaller interface widths, for example, giving 36% reflectance and 99.89% degree of polarization near Brewster angle for a multilayer polarizer. The modulated ion-energy-assistance during the growth is considered vital to avoid intermixing during the interface formation even when B + C are added. ; Funding agencies: Swedish Science Council; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

The first Fe-based MAX phase is realized by solid-state substitution reaction of an Fe/Au/Mo2GaC thin-film diffusion couple, as determined by X-ray diffraction and scanning transmission electron microscopy. Chemical analysis together with elemental mapping reveals that as much as 50 at.% Fe on the A site can be obtained by thermally induced Au and Fe substitution for Ga atomic layers in Mo2GaC. One-sixth of the original Ga is also replaced by Au atoms. When annealing Mo2GaC thin films covered with Fe only, the Mo2GaC phase remains intact, that is, Au acts as a catalyst for the substitution reaction. [GRAPHICS] . ; Funding Agencies|Swedish Foundation for Strategic Research (Stiftelsen for Strategisk Forskning, SSF) through the Synergy Grant FUNCASE; Knut and Alice Wallenberg (KAW) Foundation [KAW 2015.0043]; Swedish Research Council (Vetenskapsradet, VR) [621-2012-4425, 642-2013-8020, 2013-4018]; Swedish Government Strategic Research Area (SFO) [2009-00971]