The covalent functionalization of GaN and AlN surfaces with organosilanes is demonstrated. Both octadecyltrimethoxysilane and aminopropyltriethoxysilane form self-assembled monolayers on hydroxylated GaN and AlN surfaces, confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The monolayer thickness on GaN was determined to 2.5± 0.2 nm by x-ray reflectivity. Temperature-programmed desorption measurements reveal a desorption enthalpy of 240 kJ/ mol. The application of these devices for electronic detection of specific biomolecular processes is a promising approach for novel biosensors based on molecular recognition, such as specific antibody detection or label-free detection of deoxyribonucleic acid ͑DNA͒ hybridization. For this purpose, the covalent attachment of specific molecules with controlled structural order and composition on group III-nitride devices is a basic requirement.Covalent coupling of biomolecules to oxidized and hydrogen-terminated silicon surfaces has been investigated in numerous works during recent decades. 3,4 Covalent grafting of self-assembled monolayers ͑SAMs͒ of organosilanes on oxidized silicon surfaces 5-7 is widely used as the first step of surface functionalization with biomolecules for electronic detection of enzyme activity and DNA hybridization with Si-based field effect transistors. 8,9 In contrast, the surface chemistry on AlGaN alloys has not yet been studied in great detail. Pioneering work has been carried out by Bermudez, 10,11 who has analyzed the adsorption of different organic molecules, such as anilines or octanethiols on GaN surfaces, from the gas phase. In a recent publication Kang et al. 12 have reported the electrical detection of immobilized proteins on AlGaN / GaN transistors, modified with aminopropyltriethoxysilane ͑APTES͒ molecules in a liquid phase reaction. However, the covalent immobilization of molecules was not proven.In this letter, we report the covalent attachment of SAMs of octadecyltrimethoxysilane ͑ODTMS͒ and APTES on hydroxylated GaN and AlN surfaces. Complementary analysis by x-ray photoelectron spectroscopy ͑XPS͒, atomic force microscopy ͑AFM͒, and temperature-programmed desorption mass spectrometry proves covalent coupling of the SAMs to the surface. Immobilization of single-stranded 20-mer oligonucleotides on APTES-modified nitride surfaces and hybridization is demonstrated by fluorescence microscopy.GaN and AlN layers with a thickness of 2 m were grown by metalorganic chemical vapor deposition ͑MOCVD͒ on c-plane sapphire substrates. AFM over a scan area of 4 m 2 revealed a root-mean-square surface roughness of 0.2 nm for GaN and 0.3 nm for AlN, respectively.The presence of hydroxyl groups on the hydrophilic surface is an essential requirement for the silanization process. 5-7 Therefore, the substrates were immersed in H 2 SO 4 :H 2 O 2 ͑3:1͒ solution for 20 min, rinsed with deionized water ͑18 M⍀ cm, Millipore͒ and dried under nitrogen flux prior to silanization. In addition to the activation of surface hydroxyl groups, this...

The AM1 method was used to carry out a theoretical study of different isomers of [16]annulene and of the reversible transformation between them preserving the molecular periphery. Transition states were located on the corresponding potential energy hypersurface.

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