Добірка наукової літератури з теми "Germanium Nanowire (GeNW)"

As a promising electronic material, Ge nanowire (GeNW) has attracted much attention for its low band gaps, high mobilities, and unprecedented dimensions. This article reviews recent research and advancement on this topic and summarizes many aspects of GeNWs, including preparation, surface chemistry, physical properties, functional devices, and controlled assembly. It is shown that GeNWs can be readily synthesized by chemical methods and their electronic properties are comparable or superior to that of the bulk counterparts. Studies of surface chemistry have revealed dominant roles of surfaces on nanowires, and this result led to successful passivations toward air-stable, high-performance functional devices. Finally, controlled assembly to organize chemically synthesized nanowires into functional structures is discussed. Doors are opened up to widely utilize this novel material as excellent electronic building blocks.

The fabrication of individual nanowire-based devices and their comprehensive electrical characterization remains a major challenge. Here, we present a symmetric Hall bar configuration for highly p-type germanium nanowires (GeNWs), fabricated by a top-down approach using electron beam lithography and inductively coupled plasma reactive ion etching. The configuration allows two equivalent measurement sets to check the homogeneity of GeNWs in terms of resistivity and the Hall coefficient. The highest Hall mobility and carrier concentration of GeNWs at 5 K were in the order of 100 cm2/(Vs) and 4×1019cm−3, respectively. With a decreasing nanowire width, the resistivity increases and the carrier concentration decreases, which is attributed to carrier scattering in the region near the surface. By comparing the measured data with simulations, one can conclude the existence of a depletion region, which decreases the effective cross-section of GeNWs. Moreover, the resistivity of thin GeNWs is strongly influenced by the cross-sectional shape.

In this work, germanium nanowires (GeNWs) were fabricated by galvanostatic electrodeposition using In nanoparticles from water solutions at different temperatures. It was found that in the temperature range from 10°C to 60°C there was no significant change in the structure of GeNWs, and the average diameter was about 40 nm. The growth time of GeNWs increases linearly with increasing temperature of the electrolyte solution. However, the structure of GeNW obtained at a solution temperature of 90°C has changed. It was shown that these GeNWs have a core-shell structure: the core is a crystalline Ge phase containing In atoms, and the shell is Ge oxides (hydroxides).

In this study, germanium nanowires (GeNWs) were grown directly on gold-evaporated germanium substrates by a solid-liquid-solid (SLS) mechanism in the temperature range 550°C- 650°C. The growth of GeNWs is very sensitive to the growth temperature and only in a limited temperature range (575°C-625°C) can GeNWs having excellent morphology and high surface density be successfully grown. These long, thin, and straight GeNWs have a high aspect ratio and are surrounded by an oxide layer. The composition of corresponding oxide layers is GeOx (x<2). As the thickness of Au film is decreased from 9 nm to 1 nm, the average diameter of GeNWs decreases from 119.3 nm to 38.5 nm. Our experimental results demonstrate that the diameter of germanium nano¬wires can be controlled by the thickness of Au metal film.

Germanium nanowire (GeNW) electrodes have shown great promise as high-power, fast-charging alternatives to silicon-based electrodes, owing to their vastly improved Li ion diffusion, electron mobility and ionic conductivity. Formation of...

Surface Enhanced Raman Spectroscopy (SERS) has become a powerful method for detection of diverse analytes ranging from solution of picomolar concentration to single molecule and single cell analysis. The distinctive nature of SERS technique comes from the resonance of surface plasmons of metal nanostructure due to oscillating electric field of the incident laser. Surface plasmon resonance results in enhanced electric field or hotspots in the vicinity of metal structure which results in amplified Raman signal. Optimum hotspots on SERS substrate are achieved by fabricating appropriate metal nanostructures. Efficacy of the nanostructures depends on efficient excitation of plasmon resonance and interaction of the plasmons with its adjacent environment. Hence, substrate with favorable optical property would aid in pushing the limits of detection. Recent development in biosensors for qualitative and quantitative detection using SERS technique involves precise engineering in fabrication of SERS substrates. The requirement of a fixed SERS platform, instead of conventional metal nanoparticle colloid, is preferred in a Lab-on-a-chip (LOC) system. This thesis focuses on exploring substrate effects on surface plasmon resonance of metal nanostructure. In the process, large area SERS substrates have been fabricated for detection of various analytes. One of such substrates has been integrated with centrifugal microfluidic (CMF) system. In this work, plasmon-substrate interaction has been studied elaborately using analytical models and computational tools. Silver nanoparticles have been fabricated on Si substrate by sputtering. Optical properties of the substrate have been modified by depositing SiO2, HfO2 and Si3N4 films of varying thickness. Non-radiative and radiative interactions have been observed prominently in SERS spectra which correlate with the optical property of the substrate. The most effective interaction has been the energy transfer between the plasmons and the polarization charges of the base Si substrate. These serve as guidelines to fabricate, modify and improve large area SERS substrates. Anodized Aluminum Oxide Template (AAOT) and Germanium Nanowire (GeNW) have been fabricated and subsequently coated with thin silver film for application in SERS as large area substrate. Anodization of Al thin film has been studied with varying fabrication parameters. Resulting nanopores have been coated with Ag and the evolution of silver film on the template has been observed. Optimized Ag structures show enhanced performance depending on the location of the hotspots on these substrates. Extensive experiments have been carried out to understand vapour-liquid-solid (VLS) growth of Si and Ge nanowires using plasma enhanced chemical vapour deposition (PECVD) technique with precise control over the length of the NWs. GeNWs with dielectric shell were coated with Ag film and AgNPs. Subsequently, the efficacy of the SERS substrates was compared. Aforementioned plasmon-substrate interactions have been observed in the characterization results of the large area substrates. However, tuning of these substrates for a specific wavelength is extremely complex. This brings the requirement of an ideal substrate possessing the following properties: i. Scalable fabrication process ii. Ease of tunability for any wavelength iii. High shelf life Hence, silver nano-buds have been fabricated to address the issues. Silver structures are fabricated on the tip of GeNWs through galvanic displacement reaction. An optimization technique has been developed to tune the substrate to any wavelength in real time. The analytical enhancement factors remain close to 105 for a wide range of wavelengths which is comparable to some of substrates fabricated by e-beam lithography. GeNW substrates do not require any specific packaging and silver can be formed easily on the substrates on demand. This substrate also addresses the most important issue of shelf life. Ag nano-bud substrate has been subsequently used in an integrated SERS microfluidic system for analysis of blood components. Centrifugal microfluidic (CMF) devices have been developed for plasma and cell separation from whole blood. A valving mechanism was developed to manipulate fluid flow on the same CMF disc which enables integration of multiple microfluidic networks. Later, soft lithography process has been modified to incorporate silver nano-bud SERS substrate in the CMF disc. Thus, a complete integrated CMF-SERS device has been fabricated. This does not require fabrication of SERS active site either on PDMS or on glass. Prefabricated SERS substrate has been used to accomplish this which has drastically reduced the process steps and complexity as compared to other methods reported in literature. As a proof-of-concept, SERS substrate has been integrated with plasma separation device and SERS spectrum has been obtained for plasma.

In this work, we compare the localized synthesis of germanium nanowires (GeNWs) to germanium nanowires synthesized under a globally high temperature environment. The localized synthesis of germanium nanowires is presented for the first time using the resistive heating of MEMS microbridges. The results of the localized synthesis process are then compared with the results of well-established high temperature synthesis processes for germanium nanowires. The effect of heat source and local temperature gradients on the resulting nanowires is assessed. The results suggest that optimal nanowire synthesis conditions in a high temperature furnace environment are no longer optimal in localized heating based synthesis. More specifically, there is a significant reduction in growth rates with the localized process. Differences in nanowire quality are observed as kinking and bending of the nanowires are a common result of the localized process yet rare in germanium nanowires synthesized in a global heating environment. Nanowires grown in a global heating environment exhibit larger average wire diameters, approximately 80 nm larger, compared to those synthesized using the localized heating process. Finally, nanowire tapering which is evident in the global heating process is not prevalent in the localized process.