Stable Scaffolds for Reacting Si Nanowires with Further Organic Functionalities while Preserving Si−C Passivation of Surface Sites

Abstract

Silicon nanowires (Si NWs) represent an attractive class of building blocks for nanoelectronics and sensors. However, for many applications, the presence of oxide on the Si NW surface is undesirable, because a defective oxide layer (e.g., native SiO 2 ) induces uncontrolled interface states in the band gap of the Si.Freshly prepared H-terminated Si NWs have low surface recombination velocities but are not stable in air for more than a few hours, because disordered oxide layers form.1 Recently, we have reported on Si NWs that were chemically modified by CH 3 functionalities through a covalent Si-C bond.2 The resulting CH 3 -Si NWs allowed formation of air-stable Si NW Field Effect Transistors (FETs) having on-off ratios in excess of 10 5 over a relatively small gate voltage swing ((2 V).2 Though CH 3 termination gives full coverage of the Si atop sites, 3 subsequent functionalization is not possible. The ability to attach a controlled functionality to a stable, fully passivated Si NW is highly desirable for a wide range of applications, especially for biosensors and systematic control over the electrical properties of Si NWs.Here, we report on Si NWs modified by covalent CH 3 s CHdCHs scaffolds, via SisC bonds, that give nearly full coverage of the Si atop sites and, at the same time, provide a route for subsequent functionalization. The obtained CH 3 sCHdCHsSi NWs exhibit superior oxidation resistance over Si NWs that are modified with CH 3 s or CH 3 sCtCs functionalities, which give nearly full coverage of the Si atop site too.The Si NWs investigated here were composed of 50 ( 10 nm diameter Si cores coated with 3-4 nm native SiO 2 skins (see Supporting Information, Figure 1S) and contained pronounced low index facets, such as (111), (100), and (112). 4 These Si NWs were terminated with methyl (CH 3 s), propenyl (CH 3 sCHdCHs), and propynyl (CH 3 sCtCs) functionalities using a chlorination/ alkylation route, 5 as described in section 2 of the Supporting Information. The obtained samples were characterized by high resolution X-ray photo electron spectroscopy (XPS); see Supporting Information, section 3.1. The measurements were done three times for each sample, and averages have been taken. Figure 2S of the Supporting Information shows an XPS scan of Si2p and C1s regions of propenyl-terminated Si NWs. The Si2p spectrum shows Si2p 3/2 and Si2p 1/2 in the expected 2:1 area ratio. No oxidized Si between 101.0 and 103.5 eV was observed (see Supporting Information, Figure 2SA). Three peaks were observed in the C1s region (see Supporting Information, Figure 2SB): (i) a peak at 284.0 eV for carbon atoms covalently bonded to silicon (C-Si); 5 (ii) a peak at 285.0 eV for carbons bonded to either hydrogen or another carbon atoms; and (iii) a peak at 286.6 eV for adventitious carbons bonded to oxygen from the wet chemical processing with THF and/or methanol rinse after functionalization. All the C1s and Si2p peaks mentioned were also observed for methyl-and propynyl-terminated Si NWs. The peak area ratio of the C-Si to the ...

Covalent Attachment of Alkyl Functionality to 50 nm Silicon Nanowires through a Chlorination/Alkylation Process

“…25 To this end, the H-terminated Si surfaces of both single-crystal and porous Si substrates have been alkylated using alkylmagnesium reagents, 5,[26][27][28] and halogenated surfaces have been alkylated using alkylmagnesium or alkyllithium reagents. 29 Alkylation has also been accomplished through free-radical initiation methods such as irradiating with ultraviolet light, 30,31 chemical free-radical activation, 32,33 thermal activation, 34,35 Lewis acid catalyzed hydrosilylation, 36,37 or visible-light-initiated modification of H-Si at room temperature.…”

Electrical Transport Features of SiNWs Random Network on Si Support after Covalent Attachment of New Organic Functionalities

“…Fig. 7 shows the JvsV characteristics across the RNpropenyl-SiNWs/n-Si after a subsequent covalent attachment at propenyl-SiNWs of TDBA for two different illumination time of a 365 nm broadband UV lamp [15,16]. It can be observed that the carrier transport across the propenyl-SiNWs/nSi junction is strongly affected by TDBA covalent attachment and is represented by a large increase of forward current level and rectification.…”

“…After immersion for 2 h, the samples were cleaned by rinsing with DMF and CH2Cl2, and dried by N2(g) flushing. [15,16] Figure 1(a-b) displays a typical top view (1a) and cross sectional scanning electron micrograph (1b) of a SiNWs random network fabricated on the n-Si substrate. The average SiNWs length, roughly corresponding to the thickness of the SiNWs random network, was estimated around 2 m, while the single SiNW had an estimated average diameter of 50 nm.…”

“…Specifically, it has been shown that propenyl scaffold lead to both full coverage of the Si sites and are capable of further functionalization. [15,16] This work aims to enlighten on the electrical transport properties of junctions built with a random network of the above mentioned functionalized SiNWs (RN-SiNWs) self assembled on a silicon support. Evidence of the further carrier transport modification across a similar junction including random network of subsequently functionalized propenyl -SiNWs is also presented.…”

Facile Method for Modification of the Silicon Nanowires and Its Application in Fabrication of pH-Sensitive Chips

“…14−16 However, such modification approach would bring about the inhomogeneity and variability in the number of Si−O−Si and Si−OH linkages, which could affect the consistency of the SiNWs-based devices. 8 In order to improve the controllability of the SiNWs-based devices, two-step amine-promoted reaction procedure has been used to passivate most of the SiO 2 /SiNW surface trap states by appropriate monolayers. 9 An alternative way is to remove the native oxide layer by hydrofluoric acid (HF) and the resultant Si−H bonds dominating the surface of the SiNWs could be utilized to functionalize the SiNWs.…”