Browsing by Subject "Silver nanowire"

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Open Access
Photocurrent generation in low dimensional nanomaterials
(2022-11) Razeghi, Mohammadali
This thesis focuses on crucial issue on the understanding the underlying mechanisms of photoresponse in low-dimensional nanomaterials. As the size goes down to the micro and nano level, fine features and induced inhomogeneities like strain, thickness variation, substrate, and junctions become influential in determining plausible effects that can explain and control the light-matter interactions in an optoelectronic device. To develop a better understanding of the fundamental physical characteristics of nanomaterials and optimize thermal and electrical transport in nanomaterial devices, microscopic investigation at a single crystal level is required. In this thesis, I investigated photocurrent generation in two extreme cases: metallic silver nanowire (Ag NW) and semiconducting multilayer molybdenum disulfide (MoS2) using scanning photocurrent microscopy (SPCM). SPCM provides spatial mapping of photoresponse along with corresponding reflected light intensity with a few hundred nanometer resolution. Two terminal devices of Ag and Ag network devices are made by drop-casting NW and placing indium as metal contacts. The SPCM maps show that the NW- NW junctions and NW-contacts interface locally enhance the plasmonic field and act as hot spots. The increased temperature at hot spots is enough to modulate the resistance and results in a photo-bolometric response under the bias voltage. To further enhance the photo-bolometric effect, we decorated the nanowires with plasmonic Ag nanoparticles. The nanoparticles increase the number of hot spots and strengthen light coupling into plasmons. We also attributed zero bias response to the photothermoelectric effect. The photocurrent is generated by the Seebeck coefficient difference caused by nanogaps and nonuniformities in the geometry along the Ag NW. The second part of this thesis describes photocurrent generation by substrate engineering of a few-layer MoS2. To partially suspend a crystal, a flake of MoS2 is exfoliated and then transferred on a substrate with rectangular or circular holes. We observed photocurrent generation from the junction of the supported and suspended parts. Substrate effects like induced doping play an essential role in determining the properties of two-dimensional materials. Our investigations show that the Seebeck coefficient of the suspended part is changed due to isolation from the substrate. The difference in the Seebeck coefficient of suspended and supported regions forms a thermoelectric junction. We also investigated the impact of carrier type and concentration on photocurrent generation by gating experiments.
Open Access
Use of optical methods for studying photocurrent generation mechanism in silver nanowires and defects in glass
(2021-06) Üstünçelik, Merve
The light-matter interaction covers a wide range of physical phenomena which can be used for the investigation of materials. This interaction can be used both spectroscopically and microscopically to investigate fundamental material properties such as structural, optical, and electrical properties. In this thesis, I used optical methods to characterize materials on macro and nanoscales based on diﬀerent light phenomena such as scattering, transmission, absorption, and re-ﬂection. First, I used Raman spectroscopy in a diﬀraction-limited setup to show that the trapped gas inside the bubble defects can be identiﬁed in a matter of seconds non-destructively. Also, I investigated near-ﬁeld methods to gain further understanding about chemical, optical and structural information in nanomate-rials by using an aperture-based transmission mode Near-ﬁeld Scanning Optical Microscopy (SNOM). Finally, I used scanning photocurrent microscopy to demon-strate photocurrent generation in silver nanowires and nanowire networks. This thesis demonstrates that light-matter interaction can provide useful information in the characterization of a vast class of materials. The advantages of the non-destructive Raman technique in defects analyses, the challenges of working in the near-ﬁeld region in nanomaterials characterization, and also the photocurrent generation in silver nanowires for the ﬁrst time have been demonstrated with experimental results.