Fabrication of high-quality-factor photonic crystal microcavities in InAsP/InGaAsP membranes

Optical fiber taper waveguides are used to improve the efficiency of room temperature photoluminescence measurements of AlGaAs microdisk resonant cavities with embedded self-assembled InAs quantum dots. As a near-field collection optic, the fiber taper improves the collection efficiency from microdisk lasers by a factor of ∼15–100 times in comparison to conventional normal incidence free-space collection techniques. In addition, the fiber taper can serve as an efficient means for pumping these devices, and initial measurements employing fiber pumping and collection are presented. Implications of this work towards chip-based cavity quantum electrodynamics experiments are discussed

Fabrication of Two-Dimensional Photonic Crystals in AlGaInP/GaInP Membranes by Inductively Coupled Plasma Etching

The fabrication process of two-dimensional photonic crystals in an AlGaInP/GaInP multi-quantum-well membrane structure is developed. The process includes high resolution electron-beam lithography, pattern transfer into SiO₂ etch mask by reactive ion etching, pattern transfer through AlGaInP/GaInP layer by inductively coupled plasma (ICP) etching and a selective undercut wet etch to create the freestanding membrane. The chlorine-based ICP etching conditions are optimized to achieve a vertical sidewall. The photonic crystal structures with periods of a=160-480nm are produced.Singapore-MIT Alliance (SMA

Suspension and Measurement of Graphene and Bi2Se3 Atomic Membranes

Coupling high quality, suspended atomic membranes to specialized electrodes enables investigation of many novel phenomena, such as spin or Cooper pair transport in these two dimensional systems. However, many electrode materials are not stable in acids that are used to dissolve underlying substrates. Here we present a versatile and powerful multi-level lithographical technique to suspend atomic membranes, which can be applied to the vast majority of substrate, membrane and electrode materials. Using this technique, we fabricated suspended graphene devices with Al electrodes and mobility of 5500 cm^2/Vs. We also demonstrate, for the first time, fabrication and measurement of a free-standing thin Bi2Se3 membrane, which has low contact resistance to electrodes and a mobility of >~500 cm^2/Vs

Nanostressors and the nanomechanical response of a thin silicon film on an insulator

Journal ArticlePseudomorphic three-dimensional Ge nanocrystals (quantum dots) grown on thin silicon-on-insulator substrates can induce significant bending of the silicon template layer that is local on the nanometer scale. We use molecular dynamics simulations and analytical models to confirm the local bending of the Si template and to show that its magnitude approaches the maximum value for a freestanding membrane. The requisite greatly enhanced viscous flow of SiO2 underneath the Si layer is consistent with the dependence of the viscosity of SiO2 on shear stress

Quantitative Determination of the Mechanical Properties of Nanomembrane Resonators by Vibrometry In Continuous Light

We present an experimental study of the bending waves of freestanding \ce{Si3N4} nanomembranes using optical profilometry in varying environments such as pressure and temperature. We introduce a method, named Vibrometry in Continuous Light (VICL) that enables us to disentangle the response of the membrane from the one of the excitation system, thereby giving access to the eigenfrequency and the quality ($Q$) factor of the membrane by fitting a model of a damped driven harmonic oscillator to the experimental data. The validity of particular assumptions or aspects of the model such as damping mechanisms, can be tested by imposing additional constraints on the fitting procedure. We verify the performance of the method by studying two modes of a $478~\textrm{nm}$ thick \ce{Si3N4} freestanding membrane and find $Q$ factors of $2 \times 10^4$ for both modes at room temperature. Finally, we observe a linear increase of the resonance frequency of the ground mode with temperature which amounts to $550~\textrm{Hz}/^{\circ}\mathrm{C}$ for a ground mode frequency of $0.447~\textrm{MHz}$. This makes the nanomembrane resonators suitable as high-sensitive temperature sensors

Freestanding Ultrathin Nanoparticle Membranes Assembled at Transient Liquid-Liquid Interfaces

We present a synthetic route for the realization of ultrathin freestanding nanoparticle membranes that are built of gold nanoparticles protected with trimethoxysilane-bearing ligands. The mechanism relies on interfacial assembly in an oil-water mixture. Upon shaking, nanoparticles are transported to the liquid-liquid interface of the oil droplets and form a network through the formation of Si-O-Si bridges. Reticulation of the nanoparticles during the dynamic process of droplet coalescence allows the formation of ultrathin membranes of only a few NP-layers in thickness and square centimeters in dimension. The membranes can be manipulated, such as locally perforated, without causing their collapse. Furthermore they cqn be transferred onto solid or holey substrates. The synthetic route is compatible with a co-assembly of dopants. As an example, membranes were doped with single walled carbon nanotubes, which resulted in a sizable increase of their electric conductivity

Focused Ion Beam Induced Deflections of Freestanding Thin Films

Prominent deflections are shown to occur in freestanding silicon nitride thin membranes when exposed to a 50 keV gallium focused ion beam for ion doses between 1014 and 1017 ions/cm2. Atomic force microscope topographs were used to quantify elevations on the irradiated side and corresponding depressions of comparable magnitude on the back side, thus indicating that what at first appeared to be protrusions are actually the result of membrane deflections. The shape in high-stress silicon nitride is remarkably flat-topped and differs from that in low-stress silicon nitride. Ion beam induced biaxial compressive stress generation, which is a known deformation mechanism for other amorphous materials at higher ion energies, is hypothesized to be the origin of the deflection. A continuum mechanical model based on this assumption convincingly reproduces the profiles for both low-stress and high-stress membranes and provides a family of unusual shapes that can be created by deflection of freestanding thin films under beam irradiation.Engineering and Applied SciencesMolecular and Cellular Biolog