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

Sensing spin systems with Pico-Radian sensitivity

Introduction The spin is a fundamental quantum property of matter. Spin states are coupled to the chemical environment and can be coherently manipulated using microwave radiation. Spectroscopic techniques such as electron spin resonance (ESR) and nuclear magnetic resonance have been used to obtain deep insights into spin systems [1,2]. However, conventional techniques typically sense the global response of spin systems and are therefore not suitable for obtaining local information about the specimen. Objectives This work aims to develop spin-sensitive techniques for transmission electron microscopy (TEM) to study spin systems on the nanoscale. Materials & methods The magnetic field B0 created at the pole piece of the TEM is utilized for polarizing the spins in the specimen. A custom-built TEM holder with an integrated microresonator allows for coherent manipulation of spin states by the supply of microwaves (excitation field B1), leading to a collective spin precession M in the specimen [3]. The electron probe, positioned in aloof-mode, interacts with the precessing spins, resulting in beam deflections. These deflections can be extracted by acquiring images in momentum space and subsequent image processing. The setup and the basic concept of the experiment is illustrated in Figure 1. Results Extracting deflections from the modulated electron beam allows for obtaining signals that are similar to absorption and dispersion spectra observed in conventional ESR spectroscopy. The signals vary with the position of the electron probe relative to the specimen, showing the potential of the developed technique for collecting local information about the sample. Moreover, frequency and magnetic field sweeps confirm the expected Zeeman splitting of spin states. The concept is further optimized by incorporating different electron microscopy modes to enhance both sensitivity and spatial resolution. Conclusion Our study proves the feasibility of performing ESR measurements within a TEM by analyzing spin induced modulations of the electron beam. The developed technique allows us to sense beam deflections with pico-radian sensitivity and can potentially lay the foundation for studying spin system with high sensitivity on the atomic scale. References [1] Bienfait, A.; et al. Nat. Nanotechnol. 2016, 11, 253. [2] Callaghan, P. T. Principles of Nuclear Magnetic Resonance Microscopy; Clarendon Press: Oxford, 1993. [3] Jaroš, A.; et al. Electron spin resonance spectroscopy in a transmission electron microscope. arXiv Preprint arXiv:2408.16492 (2024)

Ge quantum wire memristor

Abstract 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.</jats:p

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires

Metastable germanium-tin alloys are promising materials for optoelectronics and optics. Here we present the first electrical characterization of highly crystalline Ge0.81Sn0.19 nanowires grown in a solution-based process. The investigated Ge0.81Sn0.19 nanowires reveal ohmic behavior with resistivity of the nanowire material in the range of ∼1 × 10−4 Ω m. The temperature-dependent resistivity measurements demonstrate the semiconducting behavior. Moreover, failure of devices upon heating to moderate temperatures initiating material degradation has been investigated to illustrate that characterization and device operation of these highly metastable materials have to be carefully conducted

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