Simple, robust molecular self-assembly on germanium

Abstract

We report the facile fabrication of high-quality, robust alkanethiolate self-assembled monolayers (SAMs) on germanium substrates. Our approach to produce SAMs on technologically important substrates takes advantage of the many strategies previously developed for gold-thiol self-assembly. Direct self-assembly of alkanethiols on germanium is impeded by the presence of the native germanium oxide. Using a mixture of water and ethanol, we create an environment where both adsorbate and oxide are sufficiently soluble to enable SAM deposition in a single step. By manipulating reaction conditions, monolayers form spontaneously on untreated germanium, which opens new avenues for the exploitation of self-assembly on semiconductor surfaces. While our analyses initially focused on 1-dodecanethiol on Ge(100), this method is robust and we have extended its use to include a range of adsorbates on Ge(100) as well as to the Ge(111) and Ge(110) substrates.

1-Dodecanethiol based highly stable self-assembled monolayers for germanium passivation

“…The intensity of C 1s (mixture solvent, 60 • C) > C 1s (mixture solvent, 25 • C) > C 1s (pure ethanol, 25 • C) > C 1s (pure ethanol, 60 • C) > C 1s (blank Ge). Based on the comparison of water contact angles and XPS spectra, it can be concluded that the mixture solvent system can suppress the degeneration/re-oxidation of NDM-passivated Ge and improve the coverage of NDM SAMs on Ge surface, and the moderate heating condition (60 • C) in mixture solvent system can improve the assembled coverage of NDM SAMs further [31]. The detailed temperature influence on NDM SAMs formation would be discussed in the following section.…”

“…2 inset (b)), and the WCA was quickly increased to ∼101 • . In comparison to NDM quick assembly on Au (1 1 1) in seconds or minutes [34], the NDM SAMs formation process on Ge (1 1 1) was slower [29,31]. Following, the adsorbates were assembled in order with a slow reorganization process and the final WCA (Â Ge NDM ) reached a limit value ∼108 • (stable state, marked "c", Fig.…”

“…The detailed description was as following: The experimental group was SAMs obtained in NDM/water-ethanol (v/v = 1:1) mixture solvent at room temperature for 24 h. To investigate the function of water, the control group I was SAMs obtained in NDM/pure ethanol solvent in same conditions, similar to the conventional methods [14,24]. In addition, as moderate heating could improve the SAMs formation efficiency [16,22,31], two other control groups II and III were carried out in NDM/pure ethanol solvent and NDM/water-ethanol (v/v = 1:1) mixture solvent at 60 • C for 24 h, respectively. The WCA and XPS results were collected in Fig.…”

“…Considering the water solubility of GeO 2 , and the presence of water vapor gives rise to the formation of higher Ge oxidation states, a mixture solvent contained water and ethanol was utilized to dissolve NDM [31]. As NDM and Ge oxide were soluble in ethanol and water respectively, through mixing these two solvents in an appropriate ratio, a suitable condition might be realized in which both Ge oxide and NDM are sufficiently soluble, and high quality NDM SAMs can be obtained, simultaneously.…”

“…The monolayer formation process was as following: Firstly, a 10 mM NDM solution in mixture solvent (water/ethanol, v/v = 1:1) was prepared [31], and the experimental solution for monolayer formation should be degassed to remove the negative dissolved oxygen (O 2 ) with pure N 2 for 30 min. Then the obtained Cl-terminated Ge samples were immersed in the prepared NDM/water-ethanol solution at room temperature (∼25 • C) for 24 h to obtain high quality monolayer film.…”