Band alignment of MAPb(I1 –xBrx)3 thin films by vacuum deposition
In this work, the mixed bromide iodideleadperovskites CH3NH3Pb(I1 –xBrx)3 (0 ≤ x ≤ 0.67) thin films were prepared by co-evaporation of CH3NH3I, PbI2, and PbBr2. The electronic properties of CH3NH3Pb(I1 –xBrx)3 thin films were investigated byX-ray and ultraviolet photoelectron spectroscopyin-situ. The results of core level bindingenergy show that there is nochemical shift of the C1s, N1s, Br3d5, and I3d5 when the Br composition changes, while there is an approximately linearchemical shift of Pb4f7 to higher bindingenergy as the Br composition increases. The density functional theory calculation reveals that...
Source: Applied Physics Letters - December 8, 2016 Category: Physics Authors: Xianzhong Zhou, Wang Ye, Xiaoli Li, Wei Zheng, Richeng Lin, Feng Huang and Dingyong Zhong Source Type: research
Gain spectroscopy of a type-II VECSEL chip
Using optical pump –white light probespectroscopy, the gaindynamics is investigated for a vertical-external-cavity surface-emitting laser chip, which is based on a type-IIheterostructure. The active region of the chip consists of a GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs multiple quantum well. For this structure, a fully microscopic theory predicts a modal room temperature gain at a wavelength of 1170 nm, which is confirmed by the experimentalspectra. The results show a gain buildup on the type-II chip that is delayed relative to that of a type-I chip. This slower gaindynamics is attributed to a diminished cooling rate a...
Source: Applied Physics Letters - December 8, 2016 Category: Physics Authors: C. Lammers, M. Stein, C. Berger, C. M öller, C. Fuchs, A. Ruiz Perez, A. Rahimi-Iman, J. Hader, J. V. Moloney, W. Stolz, S. W. Koch and M. Koch Source Type: research
Universality in freezing of an asymmetric drop
We present the evidence of universality in conical tipformation during the freezing of arbitrary-shaped sessile droplets. The focus is to demonstrate the relationship between this universality and theliquid drop shape. We observe that, in the case of asymmetric drops, this universal shape is achieved when the tip reconfigures by changing its location, which subsequently alters the frozen drop shape. The proposed “two-triangle” model quantifies the change in the tip configuration as a function of the asymmetry of the drop that shows a good agreement with the experimental evidence. Finally, based on the experimental and ...
Source: Applied Physics Letters - December 8, 2016 Category: Physics Authors: Md Farhad Ismail and Prashant R. Waghmare Source Type: research
Combined optical sizing and acoustical characterization of single freely-floating microbubbles
In this study we present a combined optical sizing and acoustical characterization technique for the study of thedynamics of single freely-floatingultrasound contrast agent microbubbles exposed to long burstultrasound excitations up to the milliseconds range. A co-axial flow device was used to position individual microbubbles on a streamline within the confocal region of threeultrasound transducers and a high-resolution microscope objective. Bright-fieldimages of microbubbles passing through the confocal region were captured using a high-speedcamera synchronized to the acoustical data acquisition to assess the microbubble ...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Ying Luan, Guillaume Renaud, Jason L. Raymond, Tim Segers, Guillaume Lajoinie, Robert Beurskens, Frits Mastik, Tom J. A. Kokhuis, Antonius F. W. van der Steen, Michel Versluis and Nico de Jong Source Type: research
Decreasing luminescence lifetime of evaporating phosphorescent droplets
Laser-inducedphosphorescence has been used extensively to study spray dynamics. It is important to understand the influence of dropletevaporation in the interpretation of such measurements, as it increases luminescence quenching. By suspending a single evaporating n-heptane droplet in an acoustic levitator, the properties of lanthanide-complex europium-thenoyltrifluoroacetone-trioctylphosphine oxide (Eu-TTA-TOPO)phosphorescence are determined through high-speed imaging. A decrease was found in the measuredphosphorescence decay coefficient (780 → 200 μs) with decreasing droplet volumes (10−9 → 10–11 m3) ...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: D. D. van der Voort, N. J. Dam, A. M. Sweep, R. P. J. Kunnen, G. J. F. van Heijst, H. J. H. Clercx and W. van de Water Source Type: research
Mechanisms for light induced degradation in MAPbI3 perovskite thin films and solar cells
Organometal halideperovskites are highly promising materials for photovoltaic applications, yet their rapid degradation remains a significant challenge. Here, the light-inducedstructural degradation mechanism of methylammoniumlead iodide (MAPbI3)perovskitefilms anddevices is studied in low humidity environment usingX-Ray Diffraction, Ultraviolet-Visible (UV-Vis) absorption spectroscopy,Extended X-ray Absorption Fine Structure spectroscopy, Fourier Transform Infrared spectroscopy, anddevice measurements. Under dry conditions, theperovskitefilm degrades only in the presence of both light and oxygen, which together induce the...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Ghada Abdelmageed, Leila Jewell, Kaitlin Hellier, Lydia Seymour, Binbin Luo, Frank Bridges, Jin Z. Zhang and Sue Carter Source Type: research
Interface magnetization transition via minority spin injection
The interfacemagnetization of n-type BaTiO3/La0.7Sr0.3MnO3heterojunction is selectively probed by magnetic second-harmonic generation at 80 K. The injection of minority spins at the interface causes a sudden, reversibletransition of the spin alignment of interfacial Mn ions fromferromagnetic toantiferromagnetic exchange coupled, while the bulkmagnetization remains unchanged. We attribute the emergent interfacialantiferromagnetic interactions to weakening of the double-exchange mechanism caused by the strong Hund's rule coupling between injected minority spins and local magnetic moments. Theeffect is robust and may serve...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: F. Fang, H. Zhai, X. Ma, Y. W. Yin, Qi Li and G. L üpke Source Type: research
Tunnel electroresistance in BiFeO3 junctions: size does matter
Inferroelectrictunnel junctions, the tunnelresistance depends on thepolarization orientation of theferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications, device scalability is essential, which requires a clear understanding of the relationship betweenpolarization reversal andresistance change as the junction size shrinks. Here we show a robust tunnel electroresistance in BiFeO3-based junctions with diameters ranging from 1200 to 180 nm. We demonstrate that the tun...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: S. Boyn, A. M. Douglas, C. Blouzon, P. Turner, A. Barth élémy, M. Bibes, S. Fusil, J. M. Gregg and V. Garcia Source Type: research
Accessing Rashba states in electrostatically gated topological insulator devices
We study the low temperature electrical transport in gated BiSbTe1.25Se1.75/hexagonal-Boron Nitride van der Waals heterostructure devices. Our experiments indicate the presence of Rashba spin-split states confined to the sample surface. While such states have been observed previously in photo-emission spectroscopy and STM experiments, it has not been possible to unambiguously detect them by electrical means and their transport properties remain mostly unknown. We show that these states support highmobility conduction with Hall effectmobilities∼2000 to 3000 cm2/V-s that are paradoxically much larger than themobilities o...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Abhishek Banerjee, Ananthesh Sundaresh, Kunjalata Majhi, R. Ganesan and P. S. Anil Kumar Source Type: research
Reconfigurable heat-induced spin wave lenses
We study the control and manipulation of propagatingspin waves in yttrium irongarnetfilms using a local laser-inducedheating. We show that, due to the refraction ofspin waves in the thermal gradients, the heated region acts as a defocusing lens for Damon-Eshbachspin waves and as a focusing lens for backward volumewaves enablingcollimation of spin-wave beams in the latter case. In addition to the focusing/defocusing functionality, the localheating allows one to manipulate the propagation direction of the spin-wave beams and to efficiently suppress their diffraction spreading by utilizing causticeffects. (Source: Applied Physics Letters)
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: O. Dzyapko, I. V. Borisenko, V. E. Demidov, W. Pernice and S. O. Demokritov Source Type: research
Tailoring capping layers to reduce stress gradients in copper metallization
Capping layers for back-end-of-linemetallization, which primarily serve as diffusion barriers to prevent contamination, also play a role in mitigating electromigration in the underlying conductive material. Stress gradients can be generated incoppermetallization due to the conditions associated with the capping process. To study the effects ofdeposition and subsequent annealing on the mechanical response ofcopperfilms with various capping schemes, we employed a combination of conventional and glancing incidenceX-ray diffraction techniques to quantify the stress gradient maxima. TheCufilms withdielectric caps, such as silic...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Conal E. Murray, Deepika Priyadarshini, Son Nguyen and E. Todd Ryan Source Type: research
Tunable whispering gallery modes lasing in dye-doped cholesteric liquid crystal microdroplets
This paper reports the observation of optically pumpedwhispering gallery mode(WGM) lasing emission from dye-doped emulsionmicrodroplets of cholestericliquid crystals (CLCs) suspended in an immiscible aqueous environment. The higher index contrast between the immersion liquid and CLCmicrodroplet contributes to the generation ofWGM resonance so that lasing emission can be realized in the CLCmicrodroplet viatotal internal reflection. TheWGM lasing nature is verified by numerical simulations as well as experiment of size-dependent lasing action. The lasing wavelength depends on therefractive index of the CLCmicrodroplet and ca...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Yan Wang, Hanyang Li, Liyuan Zhao, Yongjun Liu, Shuangqiang Liu and Jun Yang Source Type: research
Terahertz master-oscillator power-amplifier quantum cascade lasers
We report on the realization of a monolithically integrated master-oscillator power-amplifier architecture in a terahertzquantum cascade laser (THz-QCL) with a metal-metal waveguide. The master-oscillator section is a first-order distributed feedback(DFB) laser. Instead of using a thick anti-reflection coating, we exploit adiffraction grating together with an absorbing boundary in the power-amplifier section to efficiently extract the laser radiation and suppress the self-lasing in it. The devices demonstrate a stable generation and power amplification of single-mode emission. The amplification factor is about 5, and the o...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Huan Zhu, Fangfang Wang, Quan Yan, Chenren Yu, Jianxin Chen, Gangyi Xu, Li He, Lianhe Li, Li Chen, A. Giles Davies, Edmund H. Linfield, Jiaming Hao, Pierre-Baptiste Vigneron and Raffaele Colombelli Source Type: research
Incorporation of gold into silicon by thin film deposition and pulsed laser melting
We report on the incorporation ofgold intosilicon at a peak concentration of 1.9 × 1020 at./cm3, four orders of magnitude above the equilibrium solubility limit, usingpulsed laser melting of athin filmdeposited on thesilicon surface. We vary thefilm thickness and laser process parameters (fluence, number of shots) to quantify the range of concentrations that can be achieved. Our approach achievesgold concentrations comparable to those achieved withion implantation followed bypulsed laser melting, in a layer with high crystalline quality. This approach offers an attractive alternative toion implantation for forming ...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Jeffrey M. Warrender, Quentin Hudspeth, Girish Malladi, Harry Efstathiadis and Jay Mathews Source Type: research
Temperature invariant energy value in LED spectra
Relativeemission spectra oflight-emitting diodes (LEDs) depend on thejunction temperature. The high-energy region of theemission spectrum can be modelled with Maxwell-Boltzmann distribution as a function ofenergy andjunction temperature. We show that according to the model and our experiments, the normalizedemission spectra at differentjunction temperatures intersect at a uniqueenergy value. The invariant intersectionenergy exists for many types of LEDs and can be used to determine the alloy composition of thematerial. Furthermore, the wavelength determined by the intersectionenergy can be used as a temperature invariant w...
Source: Applied Physics Letters - December 7, 2016 Category: Physics Authors: Hans Baumgartner, Anna Vaskuri, Petri K ärhä and Erkki Ikonen Source Type: research
