Doping methodologies using monolayers offer controlled, ex situ doping of nanowires (NWs), and 3D device architectures using molecular monolayers as dopant sources with uniform, self‐limiting characteristics. Comparing doping levels and uniformity for boron‐containing monolayers using different methodologies demonstrates the effects of oxide capping on doping performances following rapid thermal anneal (RTA). Strikingly, for noncovalent monolayers of phenylboronic acid (PBA), highest doping levels are obtained with minimal thermal budget without applying oxide capping. Monolayer damage and entrapment of molecular fragments in the oxide capping layer account for the lower performance caused by thermal damage to the PBA monolayer, which results in transformation of the monolayer source to a thin solid source layer. The impact of the oxide capping procedure is demonstrated by a series of experiments. Details of monolayer fragmentation processes and its impact on doping uniformity at the nanoscale are addressed for two types of surface chemistries by applying Kelvin probe force microscopy (KPFM). These results point at the importance of molecular decomposition processes for monolayer‐based doping methodologies, both during preanneal capping step and during rapid thermal processing step. These are important guidelines to be considered for future developments of appropriate surface chemistry used in monolayer doping applications.
Fabrication of self-forming nanojunction devices is demonstrated using positioning of nanofloret-like building blocks that serve as self-assembled electrodes. A main feature of the device is a self-formed nanogap bridging between the nanofloret (NF) hybrid nanostructures (HNS) and a macroscopic counterelectrode. When nanostructures are introduced to the device they provide facile bridging across the nanostructure. This strategy is used to demonstrate electronic measurements across molecules and nanoparticles. Connecting the NF nanojunction to the micro-, and macro-scales is achieved by applying standard, robust, optical lithography. In addition, the devices are operable at ambient conditions and in solvent environments, where introducing molecules to the device results in a prominent change in the conductance characteristics. Furthermore, introduction of quantum dots results in the mapping of their band structure at ambient conditions. Our results provide a proof-of-concept of large scale self-forming nanogap device platform realized using simple fabrication tools. Such a technology can be used for molecular detectors, as a potential building block for molecular electronics, or as a platform for fundamental research.
We present an optoelectronic device for broad spectral detection using SiGe nanowires coupled to a plasmonic antenna.
operating mechanisms designed for utilizing physical effects such as surface plasmon resonance (SPR), [9] nanoparticle enhanced SPR, [10] electric impedance, [11] field effect transistor (FET), bio sensors (BioFET), [12-15] and more. Attaining high specificity in many of the currently available detection schemes is typically achieved by introducing antibodies or other recognition elements at the device surface. For example, the principle of detection in BioFET relies on the change in source-drain current caused by the binding event of a specific target molecule to the acceptor/antibody molecules attached on the conductive channel using surface chemistry modification. [16] Therefore, although the method is considered "label-free," in fact, it is required to functionalize the device with specific molecular components designed to provide the selectivity toward a priori known analyte molecules. A more fundamental limitation of such approaches is the nonselective adsorption of other molecules that result in similar, or even indistinguishable, signal from the intended analyte, leading to false positive detection signal. Therefore, nonselective adsorption, which is often encountered in real-life applications is a fundamental challenge that is tightly linked with the need to introduce antibodies or other chemical selective groups at the device interface. Semiconducting nanowires have received considerable attention in the context of FET sensing devices owing to their superior response sensitivity owing to their large surface to volume ratio. [17-19] However, the specificity and selectivity challenge remain since the signal change in these detectors relies on the same principles discussed above. This is common to many of the detection schemes for which the operation principle provides limited information regarding the identity of the molecule causing the detection signal in effect. Therefore, it is highly desirable to develop detection schemes with wider spectrum of data. By doing so, quantitative and specific information can be retrieved instead of a sparse information channel. Such single channel magnitude is translated to concentration of the assumed analyte, at best. Currently, information-rich methods are available in the form of analytical methods such as mass spectrometry, optical spectroscopy, magnetic and electronic resonance, scanning tunneling microscopy (STM) and more. These methods, however, Real-time and label-free recognition of molecules is highly desired in numerous fields; however, most existing detection schemes require specific functionalization of the device suited for the molecule to be detected and is often complicated by nonselective adsorption. Current detection methodologies that deliver detailed molecular-level information typically require elaborate analytical instrumentation to overcome these limitations, rendering those costly, not scalable, and nonportable techniques. Herein, a detection scheme is presented that rely on measurement of the tunneling currents through molecules under ambient co...
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