The reduction of diazonium salts has recently been proposed as a robust covalent modification scheme for graphene surfaces. While preliminary studies have provided indirect evidence that this strategy decorates graphene with aryl moieties, the molecular ordering and conformation of the resulting adlayer have not been directly measured. In this Article, we report molecular-resolution characterization of the adlayer formed via the spontaneous reduction of 4-nitrophenyl diazonium (4-NPD) tetrafluoroborate on epitaxial graphene on SiC(0001) using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS). An atomically flat inhomogeneous layer of covalently bonded organic molecules is observed after annealing the chemically treated surface at ∼500 °C in UHV. STM and STS results indicate that the adlayer consists predominantly of aryl oligomers that sterically prevent uniform and complete covalent modification of the graphene surface. The adsorbed species can be selectively desorbed by the STM tip above a threshold sample bias of -5 V and tunneling current of 1 nA, thus enabling the fabrication of a diverse range of graphene nanopatterns at the sub-5 nm length scale.

The ultrahigh vacuum (UHV) scanning tunneling microscope (STM) enables patterning and characterization of the physical, chemical, and electronic properties of nanostructures on surfaces with atomic precision. On hydrogen-passivated Si(100) surfaces, selective nanopatterning with the STM probe allows the creation of atomic-scale templates of dangling bonds surrounded by a robust hydrogen resist. Feedback-controlled lithography, which can remove a single hydrogen atom from the Si(100):H surface, demonstrates high-resolution nanopatterning. The resulting patterns can be used as templates for a variety of materials to form hybrid silicon nanostructures while maintaining a pristine background resist. The versatility of this UHV-STM nanolithography approach has led to its use on a variety of other substrates, including alternative hydrogen-passivated semiconductor surfaces, molecular resists, and native oxide resists. This review discusses the mechanisms of STM-induced hydrogen desorption, the postpatterning deposition of molecules and materials, and the implications for nanoscale device fabrication.

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Infrared absorption spectra are reported for rare-gas-carbon dioxide van der Waals complexes in the region of the v3 fundamental vibrational transition of C 0 2 using a pulsed molecular beam and a diode laser. The observed linewidths of 90 MHz (f.w.h.m.) allowed the determination of rotational constants for the ground and first excited vibrational states along with the frequencies of the band origins and centrifugal distortion constants which were constrained to be equal in both vibrational states. Effective structures of the complexes have been determined.

Using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM), many olefins have been shown to self-assemble on the hydrogen-passivated Si(100)-2 x 1 surface into one-dimensional nanostructures. This paper demonstrates that similar one-dimensional nanostructures can also be realized using alkynes. In particular, UHV STM, sum frequency generation (SFG), and density functional theory (DFT) are employed to study the growth mechanism and binding configuration of phenylacetylene (PA) one-dimensional nanostructures on the Si(100)-2 x 1:H surface. Molecular-resolution UHV STM images reveal the binding position and spacing of PA with respect to the underlying silicon dimer rows. Furthermore, UHV STM characterization of heteromolecular one-dimensional nanostructures of styrene and PA shows distinct electronic contrast between the two molecules, which is confirmed using simulated STM images derived from DFT and provides insight into the nature of PA binding to silicon. Additional evidence from SFG measurements corroborates the conclusion that the terminal carbon atoms of PA retain pi-conjugation following reaction to the Si(100)-2 x 1:H surface.