Nanoscale aluminum plasmonic waveguide with monolithically integrated germanium detector

Surface plasmon polaritons have rapidly established themselves as a promising concept for molecular sensing, near-field nanoimaging, and transmission lines for emerging integrated ultracompact photonic circuits. In this letter, we demonstrate a highly compact surface plasmon polariton detector based on an axial metal-semiconductor-metal nanowire heterostructure device. Here, an in-coupled surface plasmon polariton propagates along an aluminum nanowire waveguide joined to a high index germanium segment, which effectively acts as a photoconductor at low bias. Based on this system, we experimentally verify surface plasmon propagation along monocrystalline Al nanowires as thin as 40 nm in diameters. Furthermore, the monolithic integration of plasmon generation, guiding, and detection enables us to examine the bending losses of kinked waveguides. These systematic investigations of ultrathin monocrystalline Al nanowires represent a general platform for the evaluation of nanoscale metal based waveguides for transmission lines of next generation high-speed ultracompact on-chip photonic circuits

A novel planar optical sensor for simultaneous monitoring of oxygen, carbon dioxide, pH and temperature

The first quadruple luminescent sensor is presented which enables simultaneous detection of three chemical parameters and temperature. A multi-layer material is realized and combines two spectrally independent dually sensing systems. The first layer employs ethylcellulose containing the carbon dioxide sensing chemistry (fluorescent pH indicator 8-hydroxy-pyrene-1,3,6-trisulfonate (HPTS) and a lipophilic tetraalkylammonium base). The cross-linked polymeric beads stained with a phosphorescent iridium(III) complex are also dispersed in ethylcellulose and serve both for oxygen sensing and as a reference for HPTS. The second (pH/temperature) dually sensing system relies on the use of a pH-sensitive lipophilic seminaphthorhodafluor derivative and luminescent chromium(III)-activated yttrium aluminum borate particles (simultaneously acting as a temperature probe and as a reference for the pH indicator) which are embedded in polyurethane hydrogel layer. A silicone layer is used to spatially separate both dually sensing systems and to insure permeation selectivity for the CO2/O2 layer. The CO2/O2 and the pH/temperature layers are excitable with a blue and a red LED, respectively, and the emissions are isolated with help of optical filters. The measurements are performed at two modulation frequencies for each sensing system and the modified Dual Lifetime Referencing method is used to access the analytical information. The feasibility of the simultaneous four-parameter sensing is demonstrated. However, the practical applicability of the material may be compromised by its high complexity and by the performance of individual indicators

Ge quantum wire memristor

Despite being known of for decades, the actual realization of memory devices based on the memristive effect is progressing slowly, due to processing requirements and the need for exotic materials which are not compatible with today's complementary-metal-oxide-semiconductor (CMOS) technology. Here, we report an experimental study on a Ge quantum wire device featuring distinct signatures of memristive behavior favorable for integration in CMOS platform technology. Embedding the quasi-1D Ge quantum wire into an electrostatically modulated back-gated field-effect transistor, we demonstrate that individual current transport channels can be addressed directly by controlling the surface trap assisted electrostatic gating. The resulting quantization of the current represents the ultimate limit of memristors with practically zero off-state current and low footprint. In addition, the proposed device has the advantage of non-destructive successive reading cycles capability. Importantly, our findings provide a framework towards fully CMOS compatible ultra-scaled Ge based memristors

Electrical and Structural Properties of Si1−xGex Nanowires Prepared from a Single-Source Precursor

Si1−xGex nanowires (NWs) were prepared by gold-supported chemical vapor deposition (CVD) using a single-source precursor with preformed Si–Ge bonds. Besides the tamed reactivity of the precursor, the approach reduces the process parameters associated with the control of decomposition characteristics and the dosing of individual precursors. The group IV alloy NWs are single crystalline with a constant diameter along their axis. During the wire growth by low pressure CVD, an Au-containing surface layer on the NWs forms by surface diffusion from the substrate, which can be removed by a combination of oxidation and etching. The electrical properties of the Si1−xGex/Au core-shell NWs are compared to the Si1−xGex NWs after Au removal. Core–shell NWs show signatures of metal-like behavior, while the purely semiconducting NWs reveal typical signatures of intrinsic Si1−xGex. The synthesized materials should be of high interest for applications in nano- and quantum-electronics

Insights into the Synthesis Mechanisms of Ag-Cu3P-GaP Multicomponent Nanoparticles

Metal-semiconductor nanoparticle heterostructures are exciting materials for photocatalytic applications. Phase and facet engineering are critical for designing highly efficient catalysts. Therefore, understanding processes occurring during the nanostructure synthesis is crucial to gain control over properties such as the surface and interface facets’ orientations, morphology, and crystal structure. However, the characterization of nanostructures after the synthesis makes clarifying their formation mechanisms nontrivial and sometimes even impossible. In this study, we used an environmental transmission electron microscope with an integrated metal-organic chemical vapor deposition system to enlighten fundamental dynamic processes during the Ag-Cu3P-GaP nanoparticle synthesis using Ag-Cu3P seed particles. Our results reveal that the GaP phase nucleated at the Cu3P surface, and growth proceeded via a topotactic reaction involving counter-diffusion of Cu+ and Ga3+ cations. After the initial GaP growth steps, the Ag and Cu3P phases formed specific interfaces with the GaP growth front. GaP growth proceeded by a similar mechanism observed for the nucleation involving the diffusion of Cu atoms through/along the Ag phase toward other regions, followed by the redeposition of Cu3P at a specific Cu3P crystal facet, not in contact with the GaP phase. The Ag phase was essential for this process by acting as a medium enabling the efficient transport of Cu atoms away from and, simultaneously, Ga atoms toward the GaP-Cu3P interface. This study shows that enlightening fundamental processes is critical for progress in synthesizing phase- and facet-engineered multicomponent nanoparticles with tailored properties for specific applications, including catalysis

Electrical and Structural Properties of Si_1−<i>x</i>Ge<i>_x</i> Nanowires Prepared from a Single-Source Precursor

Si1−xGex nanowires (NWs) were prepared by gold-supported chemical vapor deposition (CVD) using a single-source precursor with preformed Si–Ge bonds. Besides the tamed reactivity of the precursor, the approach reduces the process parameters associated with the control of decomposition characteristics and the dosing of individual precursors. The group IV alloy NWs are single crystalline with a constant diameter along their axis. During the wire growth by low pressure CVD, an Au-containing surface layer on the NWs forms by surface diffusion from the substrate, which can be removed by a combination of oxidation and etching. The electrical properties of the Si1−xGex/Au core-shell NWs are compared to the Si1−xGex NWs after Au removal. Core–shell NWs show signatures of metal-like behavior, while the purely semiconducting NWs reveal typical signatures of intrinsic Si1−xGex. The synthesized materials should be of high interest for applications in nano- and quantum-electronics

Interface Dynamics in Ag–Cu3P Nanoparticle Heterostructures

Earth-abundant transition metal phosphides are promising materials for energy-related applications. Specifically, copper(I) phosphide is such a material and shows excellent photocatalytic activity. Currently, there are substantial research efforts to synthesize well-defined metal–semiconductor nanoparticle heterostructures to enhance the photocatalytic performance by an efficient separation of charge carriers. The involved crystal facets and heterointerfaces have a major impact on the efficiency of a heterostructured photocatalyst, which points out the importance of synthesizing potential photocatalysts in a controlled manner and characterizing their structural and morphological properties in detail. In this study, we investigated the interface dynamics occurring around the synthesis of Ag–Cu3P nanoparticle heterostructures by a chemical reaction between Ag–Cu nanoparticle heterostructures and phosphine in an environmental transmission electron microscope. The major product of the Cu–Cu3P phase transformation using Ag–Cu nanoparticle heterostructures with a defined interface as a template preserved the initially present Ag{111} facet of the heterointerface. After the complete transformation, corner truncation of the faceted Cu3P phase led to a physical transformation of the nanoparticle heterostructure. In some cases, the structural rearrangement toward an energetically more favorable heterointerface has been observed and analyzed in detail at the atomic level. The herein-reported results will help better understand dynamic processes in Ag–Cu3P nanoparticle heterostructures and enable facet-engineered surface and heterointerface design to tailor their physical properties

Direct Observation of Liquid–Solid Two‐Phase Seed Particle‐Assisted Kinking in GaP Nanowire Growth

In the last decades, the metal‐assisted growth approach of semiconductor nanowires (NWs) has shown its potential in controlling crystal properties, such as crystal structure, composition, and morphology. Recently, literature reports have shown successful semiconductor NW growth with multiphase seed particles under growth conditions. Exploring alternative metal seeds and the mechanisms for growing semiconductor NWs is an exciting research field aiming to improve the control over the crystal growth process. Herein, the gallium phosphide (GaP) NW growth using Cu as seed particles inside an environmental transmission electron microscope is studied. In particular, the transformations of the Cu‐rich seed particles during the nucleation and growth of GaP NWs are observed. The supply of a relatively high amount of Ga atoms by the precursor mixture led to a solid Cu‐rich seed particle core covered by a liquid phase. Different growth dynamics within the two‐phase seed particle resulted in local competition in NW growth. As a result, the GaP NW kinked into another growth direction by forming a new interface at the NW growth front. The generated results enable insights into fundamental processes occurring in the seed particle during growth, creating leverage points for controlling the NW morphology