Preparation, structural and photoluminescent properties of CdS/silicon nanoporous pillar array

Abstract

A silicon nanoporous pillar array (Si-NPA) is a silicon hierarchical structure with regularly patterned surface morphology. Through a heterogeneous reaction process, nanocrystallites of cadmium sulfide (nc-CdS) were grown onto Si-NPA and a uniquely patterned nanocomposite structure (CdS/Si-NPA) was obtained. The nc-CdS, whose average size was evaluated to be ∼25 nm, mainly grew at two typical sites of the Si-NPA. One was the top sites of the porous pillars where nc-CdS clusters were formed, and the other was the valley sites surrounding the porous pillars where nc-CdS rings were formed. The nc-CdS was proved to be separated from the Si-NPA substrate by a thin layer of SiO 2 with a thickness of ∼1.3 nm. In addition to the two red photoluminescence (PL) bands observed in the Si-NPA, a green PL band peaked at ∼495 nm was observed in CdS/Si-NPA when it was excited by 370 nm wavelength ultraviolet light. Based on these experimental results, the green and red PL bands of CdS/Si-NPA were attributed to the radiative recombination of the excitons occurring in nc-CdS and Si-NPA separately.

Capacitive humidity sensing properties of carbon nanotubes grown on silicon nanoporous pillar array

“…The mechanism might be as follows. As has been proved previously [8] , Si-NPA possessed a nanoporous surface structure similar to that of traditional porous silicon (PS). The surface of PS has been proved to be hydrophobic [16][17][18] , which would lead to the surface being difficult for vapor adsorption but easy for vapor desorption.…”

“…Although the sensitivity was greatly improved for capacitive sensors, the problem of slow response/recovery speed remains unsolved [6] . In the papers published previously [7][8][9] , we reported the study on the capacitive humidity sensing properties of a silicon hierarchical structure, silicon nanoporous pillar array (Si-NPA), through which a very fast response/recovery speed was achieved. The excellent response/recovery behavior of Si-NPA-based sensors was attributed to the formation of a regular pillar array, which was believed to have brought an effective pathway for vapor transportation.…”

“…The preparation of Si-NPA substrate has been described in detail elsewhere [7,8] . Si-NPA samples with an area of 20 mm×20 mm were dipped in a ferrocene/alcohol solution for 5 min, and then placed in a quartz tube furnace for growing CNTs by thermal CVD.…”

Characterization of silicon nanoporous pillar array as room-temperature capacitive ethanol gas sensor

“…Si-NPA used here was prepared by hydrothermally etching the (1 1 1) oriented, boron doped (ρ = 0.015 cm) single crystal silicon wafers in the solution of hydrofluoric acid containing ferric nitrate [17,18]. The microstructure and surface morphology of Si-NPA were investigated by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM).…”

“…Li). [17,18], which was a triple hierarchical structure constructed on single crystal silicon wafers, and excellent humidity sensing properties including high sensitivity and fast response rate were achieved in the Si-NPA-based sensors [19,20]. In this paper, the room-temperature capacitive ethanol gas sensing properties of Si-NPA were studied and the underlying mechanisms were analyzed based on its unique surface structure, morphology, and physical properties.…”