Synthetic Metals 86 (1997) 2297-2298
Self-assembled fullerene derivatives layers on gold and silicon surfaces Haiwon Lee’ and Il Cheol Jeonb “Department of Chemistry, Hanynag University, Seoul 133-791, South Korea bDepartment of Chemistry, Jeonbuk National University, Jeonbuk 56X-7S6, South Korea Abstract Self-assembled mono- and multilayer of fhllerene-diaminododecane on aminopropyldimethyhnethoxysilane-modified quartz plate and self-assembled monolayer of 3-acetylthio-2-(acetylthioacetyl)- 1axapropanefnlleroid~ on gold surface were prepared. They are aimed to get ideally covered mono- and multilayer films on various surfaces. Adsorption kinetics using quartz crystal microbalance, UV and contact angle measurements were performed to confirm complete coverage of self-assembled molecular films compared to the calculated theoretical coverage of monolayer. Kqwor&
: Self-assembly using surface chemistry, fillerenes and den’vatives, W- ETS absorption
1. Introduction The self-assembly of molecules is one of the key processes of imminent technological interest in the adsorption and selforganization of organic molecules on various solid surfaces into an ordered structure[ 11. Physically adsorbed multilayer rirllerene films via LB technique has been reported , but only few papers focused on self-assembled molecular films were repoxted[f-51. Mirkin and his colleagues reported the first self-assembled monolayer of C& onto (aminopropyl)silanized IT0 glass and onto cysteamine modified gold surfaces. We have tried to confirm the formation of unformed self-assembled &I monolayer on systemic in-situ modified gold surfaces by quartz crystal microbalance(QCM) measurement, but failed to control the complete coverage of fhllerene monolayer on systemic modified QCM electrode. In this report, we demonstrate the formation of mono- and multilayer of fitllerene molecule bound to APS modified quartz plate as shown in scheme I and the formation of dithioacetate containing llleroid monolayer on gold by means of QCM, UV STM measurements. Recent results of forming Nlerene layer by a single step self-assembling method and by a two-step self-assembly give the relative easiness of preparation methods.
Scheme I. Synthetic scheme for the formation of bilayer of cd0 onto modified quartz plate. by QCM and contact angle data. QCM data were collected with 10 MHz, AT-cut crystals in the fundamental mode.
2. Experiment Fullerene, diamninododecane, ethanol, cyclohexane and dichlomethane was purchased from Aldrich and 3aminopropyldimethylmethoxysilane was purchased from United Chemical Technologies. All chemicals were used without further purification. Fulleroid containing dithioacetate, 3-acethylthio-2(acethylthioacetyl)-1,3-propanediol(AAAF) as shown in Scheme II. Fullerene’diauminododecane multilayer was prepared as mported in the previous paperrS] and and their characterization of multilayer was carried out by UV and ellipsomeric measurements. The adsorption of AAAF was perfbrmed in 1m.M dithiochloromethane solution of AAAF for 5 min, then confirmed 0379-6779/'97/$17.0001997EkevierScienceS.A AlIrig.htsreserved PII So3794779(%)04S444
scheme Il. synthetic scheme of AAAF
H. Lee, I.C. Jeon /Synthetic Metals 86 (1997) 2297-2298
3. Results and Discussion
Figure 1 shows the UV spectra of (a)one monolayer of GO on APS modified quartz plate, (b)dried CSO reacted with diaminododecane(DAD) on quartz, (c)dried Cao film on quartz and (d) GO in n-hexane solution. As reported in reference 5, W absorption maxima of COOprepared in various methods are similar each other, except the major difference in the peak at 328 mn. Intensity of absorption peaks at 260 and 328 mn decreases linearly as the concentration of C& in hexane solution. Once Cao molecule is adsorbed as a self-assembled molecular layer, the blue shift of absorption peaks with the continuous growth of peak intensity at 194 nm and 214 mn region are observed. However the peak at 328 mn is completely disappeared at the both self-assembled COO molecular tihn and dried GO film coated on quartz plate. This is probably due to the effect of both adduct formation of fullerene with guest molecules and the decrease of intermolecular interaction between fullerene molecules.
Figure 2 shows the resonant frequency changes for 10 MHz quartz crystal to the adsorption of 0.1 mM of AAAF on gold surface. GO surface coverage on gold surface was estimated by QCM measurements as 1.5 x lur” mol/cm’ and matches well to the monolayer coverage previously published 1.4 x lo”’ mol/cm2, based on Cao crystal structure. Tpe agreement between the previous measurement and our data makes us quite confident with the surface coverage data. Significantly, one-step adsorption of AAAF could be better and reliable for well-covered monolayer formation compared to the two-step fhllerene adsorption on prelayer fbrmed Born a solution.
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Fig. 2. Resonant frequency changes for a 10 MHz, AT-cut quartz crystal in the fundamental mode before and after the addition of AAAF to dichloromethaue solution.
4. Conclusions 190
W8WlUlathIltlll Fig. 1. W spectra of (a)self-assembled GO monolayer on APSmodified quartz plate, (b)dried cbo -DAD film coated on quartz plate, (c)dried Cao coated on quartz plate, and (d) GO in hexane solution. In a typical in-situ QCM measurement with self-assemble monomolecular fhlllerene on cysteamine modified gold electrode, cysteamine modified electrode was soaked in a 1 mM hexane solution of GUI for 1 day at room temperature in order to measure mass changes with a function of time. However we have failed to obtain a reproducible resonant frequency decrease for the ideal monolayer coverage of fnllerene monolayer. The experimental monolayer coverage was much larger compared to the predicted value for a monolayer of GO. This is most probably due to the formation of GO cluster, On the basis of our recent QCM results, we found that it is extremely difficult to remove physisorbed fhllerene molecules from the self-assembled firllerene monomolecular layer. However, it could be possible to remove residual physisorbed &I by rinsing and self-assembled monolayer films. Chrr STM and QCM results suggested that the physisorbed fhllerene is not easy to be removed by simple rinse.
Self-assembled fi&rene and dithioacete containing fblleroid molecular films were prepared and their umfbrmity and coverage awere characterized by QCM, W and STM methods Single-step self-assembly technique for adsorption of fhllerene derivatives on substrates can make a better monolayer with a 111 coverage compared to the two-step self-assembly method. Acknowledgment This work was supported by KOSEF(93-0500-07-l-3). References [l] A. Uhnan, Ultrathin organic Films, Academic Press, 1991  K. Chen, W. Caldwell and C. Mirkin, J. Am. Chem. Sot. 115, 1193 (1993)  V. Tsuknrk, L. Lander and W. Brittain, Langmuir, 10, 996 (1994)  W. Caldwell, K. Chen, C. Mirkin and S. Babinec, Langmuir, 9, 1945 (1993) [S] J. Bae, E. Kim and H. Lee, Mol. Cryst. Liq. Cryst. 267, 139 (1995)