Planned nanostructures of colloidal gold via self-assembly on hierarchically assembled organic bilayer template patterns with in-situ generated terminal amino functionality

Nano Letters

Volumn 4, Issue 5, 2004, Pages 845-851

  Liu, Shantang ^a   Maoz, Rivka ^a   Sagiv, Jacob ^a  

^a WEIZMANN INSTITUTE OF SCIENCE   (Israel)

Author keywords

[No Author keywords available]

Indexed keywords

AMINE; AMINO ACID; COLLOIDAL GOLD;

ACCURACY; ARTICLE; METHODOLOGY; MOLECULAR INTERACTION; NANOPARTICLE; NANOTECHNOLOGY; ORGANIC CHEMISTRY; RELIABILITY; REPRODUCIBILITY; STRUCTURE ANALYSIS; SURFACE PROPERTY;

EID: 2642561781     PISSN: 15306984     EISSN: None     Source Type: Journal    
DOI: 10.1021/nl049755k     Document Type: Article

References (53)

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41. Unpatterned NTS monolayers on large silicon and fused silica surfaces were first used to investigate the quantitative in-situ conversion of NTS into a corresponding amino-terminated C20 silane that preserves the molecular organization of its vinyl-terminated precursor (Maoz, R.; Liu, S.; Sagiv, J., to be submitted for publication), as well as the subsequent self-assembly of [Au-citrate] particles on amino-terminated monolayer templates obtained in this manner (Baptiste, A., Ph.D. Thesis, Université du Maine, France, June, 2003. Baptiste, A.; Maoz, R.; Liu, S.; Gibaud, A.; Sagiv, J., to be submitted for publication). In these studies it was thus possible to apply, besides SFM, a series of powerful macroscopic methods of chemical and structural surface analysis, such as FTIR and UV-vis spectroscopies, XPS, X-ray reflectivity, and grazing incidence small-angle X-ray scattering (GISAXS).
42. Unpatterned NTS monolayers on large silicon and fused silica surfaces were first used to investigate the quantitative in-situ conversion of NTS into a corresponding amino-terminated C20 silane that preserves the molecular organization of its vinyl-terminated precursor (Maoz, R.; Liu, S.; Sagiv, J., to be submitted for publication), as well as the subsequent self-assembly of [Au-citrate] particles on amino-terminated monolayer templates obtained in this manner (Baptiste, A., Ph.D. Thesis, Université du Maine, France, June, 2003. Baptiste, A.; Maoz, R.; Liu, S.; Gibaud, A.; Sagiv, J., to be submitted for publication). In these studies it was thus possible to apply, besides SFM, a series of powerful macroscopic methods of chemical and structural surface analysis, such as FTIR and UV-vis spectroscopies, XPS, X-ray reflectivity, and grazing incidence small-angle X-ray scattering (GISAXS).
43. 2OH, and their back oxidation to -COOH, with good preservation of the overall molecular organization of the multilayer (Maoz, R.; Sagiv, J., unpublished results. Wen, K., Ph.D. Thesis, Weizmann Institute, Israel, April 1999. Wen, K.; Maoz, R.; Cohen, H.; Sagiv, J.; Gibaud, A.; Desert, A.; Ocko, B. M., to be submitted for publication).
44. 2OH, and their back oxidation to -COOH, with good preservation of the overall molecular organization of the multilayer (Maoz, R.; Sagiv, J., unpublished results. Wen, K., Ph.D. Thesis, Weizmann Institute, Israel, April 1999. Wen, K.; Maoz, R.; Cohen, H.; Sagiv, J.; Gibaud, A.; Desert, A.; Ocko, B. M., to be submitted for publication).
45. We found that prolonged exposures of OTS/Si base monolayers to high humidity conditions, as may frequently happen during repeated inscriptions of patterns on a particular specimen held in a controlled humidity atmosphere, induce their partial lateral reorganization into somewhat denser and better ordered molecular structures, which leaves a corresponding small uncovered fraction (∼3%) of the total surface area. The monolayer-uncovered sites are tiny pinhole defects that cannot be detected by regular SFM imaging, however, if filled up with NTS, their presence is revealed following the amination step and the exposure to the colloidal [Au-citrate] solution, as a result of their decoration by adsorbed gold particles. Thus, gold particles would detrimentally adhere to such defect sites dispersed within unpatterned regions of the OTS base monolayer. Improved OTS base monolayers, free of this undesirable effect, could be assembled by filling the pinhole defects with OTS, followed by adequate stabilization of the densified OTS structure obtained in this manner. Details of the assembly of such improved base monolayers will be given in a forthcoming publication (Maoz, R.; Liu, S.; Sagiv, J.). Briefly, the procedure applied in the present work consists of the following steps: (i) OTS monolayers were assembled on double-side-polished p-type silicon wafer substrates (Semiconductor Processing Co., 0.5 mm thick, oriention 〈100〉, resistivity 8-11 Ωcm), by twice immersing the freshly cleaned hydrophilic substrate for ca. 30 s in a solution of OTS (5 mM) in pure bicyclohexyl (BCH), followed by sonication for ca. 2 min in analytical-grade toluene; (ii) densification and stabilization, by exposure of the OTS-coated specimen for 12 h to a 100% relative-humidity atmosphere (40°C), followed by additional immersion in the OTS solution for ca. 30 s, sonication in toluene, and final annealing for 10 min in a preheated oven at 115 °C. This sequence of operations is repeated three times, ending with the thermal annealing at 115°C. Such densified OTS/Si monolayers contain ∼3% more material than those produced without densification (as determined by quantitative infrared measurements) and display hysteresis-free static contact angles (equal advancing and receding values) of 116°-117° for water, 57° for bicyclohexyl, and 53° for n-hexadecane. These contact angle values are slightly but consistently higher (by 1°-2°) than those measured on same OTS/Si monolayers prior to their densification and stabilization. The assembly of NTS on the tip-inscribed monolayer patterns was done using the same procedure as in the assembly of the base OTS monolayer (without the densification/stabilization steps), by complete immersion of the patterned specimen in the NTS solution and final sonication in toluene.
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50. Because of various possible artifacts of the SFM imaging, the SFM-measured heights of nanoobjects such as the present self-assembled organic bilayer features are not necessarily identical to their real heights. For example, complete and incomplete NTS top layers are expected to behave differently under the compressive forces exerted by the tip, less rigid incomplete overlayer features suffering larger deformations that translate into lower apparent heights. To minimize the role of artifactal effects originating in different imaging conditions, a comparative evaluation of the SFM-measured heights of different features should be done on a relative basis, from images taken with the same tip and under identical image recording conditions. Ideally, all compared features are located within the scan range of a single image. This condition is fulfilled in the case of the array of dots discussed here, which allows a valid comparison of the relative heights of 81 individual dot features, and thus a direct evaluation of the reproducibility of the patterning and subsequent overlayer assembly processes.
51. For complete OTS/Si monolayers, the roughness of the OTS-coated surface is slightly lower than that of the uncoated silicon wafer substrate.
52. Maoz, R.; Sagiv, J., unpublished results.
53. Hoeppener, S.; Maoz, R.; Sagiv, J., to be submitted for publication.