Maxime Vallet

Antiphase domain tailoring for combination of modal and 4¯ -quasi-phase matching in gallium phosphide microdisks

We propose a novel phase-matching scheme in GaP whispering-gallery-mode microdisks grown on Si substrate combining modal and 4¯ -quasi-phase-matching for second-harmonic-generation. The technique consists in unlocking parity-forbidden processes by tailoring the antiphase domain distribution in the GaP layer. Our proposal can be used to overcome the limitations of form birefringence phase-matching and 4¯ -quasi-phase-matching using high order whispering-gallery-modes. The high frequency conversion efficiency of this new scheme demonstrates the competitiveness of nonlinear photonic devices monolithically integrated on silicon.

Highly strained AlAs-type interfaces in InAs/AlSb heterostructures

Spontaneously formed Al-As type interfaces of the InAs/AlSb system grown by molecular beam epitaxy for quantum cascade lasers were investigated by atomic resolution scanning transmission electron microscopy. Experimental strain profiles were compared to those coming from a model structure. High negative out-of-plane strains with the same order of magnitude as perfect Al-As interfaces were observed. The effects of the geometrical phase analysis used for strain determination were evidenced and discussed in the case of abrupt and huge variations of both atomic composition and bond length as observed in these interfaces. Intensity profiles performed on the same images confirmed that changes of chemical composition are the source of high strain fields at interfaces. The results show that spontaneously assembled interfaces are not perfect but extend over 2 or 3 monolayers.

Performance Enhancement via Incorporation of ZnO Nanolayers in Energetic Al/CuO Multilayers

Al/CuO energetic structure are attractive materials due to their high thermal output and propensity to produce gas. They are widely used to bond components or as next generation of MEMS igniters. In such systems, the reaction process is largely dominated by the outward migration of oxygen atoms from the CuO matrix toward the aluminum layers, and many recent studies have already demonstrated that the interfacial nanolayer between the two reactive layers plays a major role in the material properties. Here we demonstrate that the ALD deposition of a thin ZnO layer on the CuO prior to Al deposition (by sputtering) leads to a substantial increase in the efficiency of the overall reaction. The CuO/ZnO/Al foils generate 98% of their theoretical enthalpy within a single reaction at 900 °C, whereas conventional ZnO-free CuO/Al foils produce only 78% of their theoretical enthalpy, distributed over two distinct reaction steps at 550 °C and 850 °C. Combining high-resolution transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry, we characterized the successive formation of a thin zinc aluminate (ZnAl2O4) and zinc oxide interfacial layers, which act as an effective barrier layer against oxygen diffusion at low temperature.

Elastic properties of AlAs-like and InSb-like strained interfaces in [InAs/AlSb] heterostructures

Elastic properties of [InAs/AlSb] heterostructures coherently grown on a (001) InAs substrate are investigated by the density functional theory and compared to the prediction of the linear elasticity theory. The stress-strain curves of the four involved binaries (InAs, AlAs, AlSb, and InSb) are first studied: a significant deviation to the linear elasticity theory is observed for strain above 2.5% (in absolute value). Nevertheless, the relationship between the out-of-plane and in-plane strains is in a good agreement with the prediction of the linear elasticity theory. In the heterostructures, highly strained perfect AlAs-like and InSb-like interfaces are examined. The interfacial strains calculated using the density functional theory are in a surprisingly good agreement with the prediction of the linear elasticity theory. The reduction of the layer thickness to the thinnest possible InAs or AlSb layers while keeping perfect interfaces does not change these conclusions.