A 30 μm Coaxial Nanowire Photoconductor Enabling Orthogonal Carrier Collection

Abstract

We describe the preparation and properties of a coaxial, three-layer, gold-CdSe-gold nanowire 30 μm in length that functions as a monolithic photodetector. The gold (Au) electrode core of this sandwich structure is prepared using the lithographically patterned nanowire electrodeposition (LPNE) method on a glass surface. A CdSe shell of defined thickness, d CdSe , from 200 to 280 nm is then electrodeposited on this Au nanowire. Finally, a conformal gold layer is electrodeposited on top of the CdSe shell. The two concentric gold electrodes within this architecture measure the photoconductivity of the ultrathin CdSe absorbing layer in the direction orthogonal to the nanowire axis. This architecture enables accelerated response/recovery of the nanowire to light while simultaneously maximizing the photoconductive gain without relinquishing any of the photoresponsive area of a "bare" nanowire. Characterization by scanning electron microscopy (SEM) of focused ion beam (FIB) cross sections together with electron dispersive X-ray spectroscopy (EDS) reveal the distinct core−multishell nanostructure, layer thicknesses, and layer compositions. The positiondependent photoresponse along the axis of the nanowire, probed using a laser spot, shows that the Au nanoshell significantly enhances the photocurrent. The performance of Au−CdSe−Au core−multishell nanowire photodetectors depend sensitively on the thickness of CdSe nanoshell over the range of from 200 nm < d CdSe < 280 nm. The highest performance was obtained for the d CdSe = 250 nm this device, which showed a photoconductive gain of 2172, a responsivity of 209 A·W −1 , a response time of 17 μs, and a recovery time of 96 μs.

Rapid, Wet Chemical Fabrication of Radial Junction Electroluminescent Wires

“…The CdSe shell, 350−1150 nm in radius, is electrodeposited from an aqueous plating solution according to the reaction: Cd 2+ + H 2 SeO 3 + 4H + + 6e − → CdSe(s) + 3H 2 O from a solution containing 0.30 M CdSO 4 , 0.70 mM SeO 2 , and 0.25 M H 2 SO 4 at pH 1−2. 20,21 As previously demonstrated, 20,21 a stoichiometric CdSe layer is obtained by activation-controlled electrodeposition at a constant potential of −0.60 V versus SCE (Figure 2d). Using an unstirred, room temperature plating solution, the duration of the CdSe growth is 50−250 s, depending on the shell thickness.…”

“…The CdSe shell, 350–1150 nm in radius, is electrodeposited from an aqueous plating solution according to the reaction: Cd 2+ + H 2 SeO 3 + 4H + + 6e – → CdSe(s) + 3H 2 O from a solution containing 0.30 M CdSO 4 , 0.70 mM SeO 2 , and 0.25 M H 2 SO 4 at pH 1–2. , As previously demonstrated, , a stoichiometric CdSe layer is obtained by activation-controlled electrodeposition at a constant potential of −0.60 V versus SCE (Figure d). Using an unstirred, room temperature plating solution, the duration of the CdSe growth is 50–250 s, depending on the shell thickness. , The deposition current increases during this deposition process in approximate proportion to the increasing area of the hemicylindrical CdSe surface (Figure e). Finally, the PEDOT:PSS layer with a thickness of 100–200 nm is deposited by spin-coating (2500 rpm, 80 s) onto the glass slide twice, with air drying of the layer between these two depositions.…”

“…The most critical steps of the EESC process are the two electrodeposition steps: gold in Step 5 and CdSe in Step 8. Gold electrodeposition occurs on a lithographically patterned nickel edge , under conditions of activation control at −0.90 V versus SCE, located at the foot of the gold plating wave (Figure b), in a commercial gold plating solution (Clean Earth Inc.). , Approximately 40 min is required to produce a gold nanowire that is ≈850 nm in width within a horizontal trench with a 60 nm height. During this 40 min, the gold plating current increases by a factor of approximately two (Figure c) as the solution-wetted gold surface roughens, as clearly seen in the SEM image of Figure e, for the gold nanowire (left edge).…”

Electrochemical Deposition of Conformal and Functional Layers on High Aspect Ratio Silicon Micro/Nanowires

“…Advances in nanoscience benefit from the development of methods for the synthesis of complex structures. − Fundamental light-matter interactions may be manipulated with the synthesis of well-defined one-dimensional (1D) nanostructures, which display novel sensing and light harvesting applications, − and the development of energy conversion devices − have been enabled by surface and architectural engineering of the chemical and physical properties of 1D materials. ,− In the field of medicine, nanoelectronic devices based on 1D Si nanowires have exhibited remarkable performance in bioelectronic and drug delivery applications. − Further applications of 1D materials could be broadened by synthetically elaborating these structures with distinct types of materials to yield complex compositions and architectures with enhanced or new functional properties.…”

Single Crossed Heterojunction Assembled with Quantum-Dot-Embedded Polyaniline Nanowires

“…Interestingly, one-dimensional organic nanostructures have been widely used to enhance the external quantum efficiency and to shorten the response time of photodetectors. In particular, some researchers have dedicated their studies to single NW-based photodetectors. − This efficient strategy takes advantage of the large surface-to-volume ratio and low dimensionality of one-dimensional nanostructures. Recently, p–n heterojunctions composed of NWs have attracted particular attention because of their excellent photoemission, photoconduction, photovoltaic, and rectification behaviors. − The excellent properties of these NW heterojunctions are attributed to not only the simple superposition of the individual contributions from both components but also the unique processes that occur at the interfaces formed between the components.…”