Atomic and Molecular Layer Deposition of Chiral Thin Films Showing up to 99% Spin Selective Transport

Spin electronics is delivering a much desired combination of properties such as high speed, low power, and high device densities for the next generation of memory devices. Utilizing chiral-induced spin selectivity (CISS) effect is a promising path toward efficient and simple spintronic devices. To be compatible with state-of-the-art integrated circuits manufacturing methodologies, vapor phase methodologies for deposition of spin filtering layers are needed. Here, we present vapor phase deposition of hybrid organic-inorganic thin films with embedded chirality. The deposition scheme relies on a combination of atomic and molecular layer deposition (A/MLD) utilizing enantiomeric pure alaninol molecular precursors combined with trimethyl aluminum (TMA) and water. The A/MLD deposition method deliver highly conformal thin films allowing the fabrication of several types of nanometric scale spintronic devices. The devices showed high spin polarization (close to 100%) for 5 nm thick spin filter layer deposited by A/MLD. The procedure is compatible with common device processing methodologies.

Chirality Nanosensor with Direct Electric Readout by Coupling of Nanofloret Localized Plasmons with Electronic Transport

The detection of enantiopurity for small sample quantities is crucial, particularly in the pharmaceutical industry; however, existing methodologies rely on specific chiral recognition elements, or complex optical systems, limiting its utility. A nanoscale chirality sensor, for continuously monitoring molecular chirality using an electric circuit readout, is presented. This device design represents an alternative real-time scalable approach for chiral recognition of small quantity samples (less than 10³ adsorbed molecules). The active device component relies on a gold nanofloret hybrid structure, i.e., a high aspect ratio semiconductor-metal hybrid nanosystem in which a SiGe nanowire tip is selectively decorated with a gold metallic cap. The tip mechanically touches a counter electrode to generate a nanojunction, and upon exposure to molecules, a metal-molecule-metal junction is formed. Adsorption of chiral molecules at the gold tip induces chirality in the localized plasmonic resonance at the electrode-tip junction and manifests in an enantiospecific current response.

Recent advances in techniques for fabrication and characterization of nanogap biosensors: A review

Nanogap biosensors have fascinated researchers due to their excellent electrical properties. Nanogap biosensors comprise three arrays of electrodes that form nanometer-size gaps. The sensing gaps have become the major building blocks of several sensing applications, including bio- and chemosensors. One of the advantages of nanogap biosensors is that they can be fabricated in nanoscale size for various downstream applications. Several studies have been conducted on nanogap biosensors, and nanogap biosensors exhibit potential material properties. The possibilities of combining these unique properties with a nanoscale-gapped device and electrical detection systems allow excellent and potential prospects in biomolecular detection. However, their fabrication is challenging as the gap is becoming smaller. It includes high-cost, low-yield, and surface phenomena to move a step closer to the routine fabrications. This review summarizes different feasible techniques in the fabrication of nanogap electrodes, such as preparation by self-assembly with both conventional and nonconventional approaches. This review also presents a comprehensive analysis of the fabrication, potential applications, history, and the current status of nanogap biosensors with a special focus on nanogap-mediated bio- and chemical sonsors.

Broad-band high-gain room temperature photodetectors using semiconductor-metal nanofloret hybrids with wide plasmonic response

Semiconducting nanowires are widely studied as building blocks for electro-optical devices; however, their limited cross-section and hence photo-response hinder the utilization of their full potential. Herein, we present an opto-electronic device for broad spectral detection ranging from the visible (VIS) to the short wavelength infra-red (SWIR) regime, using SiGe nanowires coupled to a broadband plasmonic antenna. The plasmonic amplification is obtained by deposition of a metallic nanotip at the edge of a nanowire utilizing a bottom-up synthesis technique. The metallic nanotip is positioned such that both optical plasmonic modes and electrical detection paths are coupled, resulting in a specific detectivity improvement of ∼1000 compared to conventional SiGe NWs. Detectivity and high gain are also measured in the SWIR regime owing to the special plasmonic response. Furthermore, the temporal response is improved by ∼1000. The fabrication process is simple and scalable, and it relies on low-resolution and facile fabrication steps with minimal requirements for top-down techniques.

Diversification of Device Platforms by Molecular Layers: Hybrid Sensing Platforms, Monolayer Doping, and Modeling

Inorganic materials such as semiconductors, oxides, and metals are ubiquitous in a wide range of device technologies owing to the outstanding robustness and mature processing technologies available for such materials. However, while the important contribution of inorganic materials to the advancement of device technologies has been well established for decades, organic-inorganic hybrid device systems, which merge molecular functionalities with inorganic platforms, represent a newer domain that is rapidly evolving at an increasing pace. Such devices benefit from the great versatility and flexibility of the organic building blocks merged with the robustness of the inorganic platforms. Given the overwhelming wealth of literature covering various approaches for modifying and using inorganic devices, this feature article selectively highlights some of the advances made in the context of the diversification of devices by surface chemistry. Particular attention is given to oxide-semiconductor systems and metallic surfaces modified with organic monolayers. The inorganic device components, such as semiconductors, metals, and oxides, are modified by organic monolayers, which may serve as either active, static, or sacrificial components. We portray research directions within the broader field of organic-inorganic hybrid device systems that can be viewed as specific examples of the potential of such hybrid device systems given their comprehensive capabilities of design and diversification. Monolayer doping techniques where sacrificial organic monolayers are introduced into semiconducting elements are reviewed as a specific case, together with associated requirements for nanosystems, devices, and sensors for controlling doping levels and doping profiles on the nanometric scale. Another series of examples of the flexibility provided by the marriage of organic functional monolayers and inorganic device components are represented by a new class of biosensors, where the organic layer functionality is exploited in a functioning device for sensing. Considerations for relying on oxide-terminated semiconductors rather than the pristine semiconductor material as a platform both for processing and sensing are discussed. Finally, we cover aspects related to the use of various theoretical and computational approaches to model organic-inorganic systems. The main objectives of the topics covered here are (i) to present the advances made in each respective domain and (ii) to provide a comprehensive view of the potential uses of organic monolayers and self-assembly processes in the rapidly evolving field of molecular-inorganic hybrid device platforms and processing methodologies. The directions highlighted here provide a perspective on a future, not yet fully realized, integrated approach where organic monolayers are combined with inorganic platforms in order to obtain versatile, robust, and flexible systems with enhanced capabilities.