The missing link: Ferrocene and porphyrin monolayers are tethered on silicon surfaces with short (see picture, left) or long (right) linkers. Electron transfer to the silicon substrate is faster for monolayers with a short linker.Ferrocene and porphyrin derivatives are anchored on Si(100) surfaces through either a short two-carbon or a long 11-carbon linker. The two tether lengths are obtained by using two different grafting procedures: a single-step hydrosilylation is used for the short linker, whereas for the long linker a multistep process involving a 1,3-dipolar cycloaddition is conducted, which affords ferrocene-triazole-(CH(2))(11)-Si or Zn(porphyrin)-triazole-(CH(2))(11)-Si links to the surface. The modified surfaces are characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Cyclic voltammetry experiments show that the redox activity of the tethered ferrocene or porphyrin is maintained for both linker types. Microelectrode capacitor devices incorporating these modified Si(100) surfaces are designed, and their capacitance-voltage (C-V) and conductance-voltage (G-V) profiles are investigated. Capacitance and conductance peaks are observed, which indicates efficient charge transfer between the redox-active monolayers and the electrode surface. Slower electron transfer between the ferrocene or porphyrin monolayer and the electrode surface is observed for the longer linker, which suggests that by adjusting the linker length, the electrical properties of the device, such as charging and discharging kinetics and retention time, could be tuned.

Organosilyl/-germyl polyoxotungstate hybrids [PW(9)O(34)(tBuSiO)(3)Ge(CH(2))(2)CO(2)H](3-) (1a), [PW(9)O(34)(tBuSiO)(3)Ge(CH(2))(2)CONHCH(2)C[triple bond]CH](3-) (2 a), [PW(11)O(39)Ge(CH(2))(2)CO(2)H](4-) (3a), and [PW(11)O(39)Ge(CH(2))(2)CONHCH(2)C[triple bond]CH](4-) (4a) have been prepared as tetrabutylammonium salts and characterized in solution by multinuclear NMR spectroscopy. The crystal structure of (NBu(4))(3)1a.H(2)O has been determined and the electrochemical behavior of 1a and 2a has been investigated by cyclic voltammetry. Covalent grafting of 2a onto an n-type silicon wafer has been achieved and the electrochemical behavior of the grafted clusters has been investigated. This represents the first example of covalent grafting of Keggin-type clusters onto a Si surface and a step towards the realization of POM-based multilevel memory devices.