silicon and pentacene

Ultrashort pulse length lasers operating in the near-infrared region show promise for submicrometer lateral resolution by laser desorption-based mass spectrometry (MS) imaging. However, these experiments must balance lateral resolution and molecular fragmentation since abundant atomic ions are observed at the high laser irradiances that can be generated by tightly focused ultrashort pulse laser beams. It is shown here that combining ultrashort pulse laser desorption with laser postionization (fs-LDPI) allows for a considerable increase of molecular ion signal while operating with lower laser irradiances, yielding the added benefit of reduced molecular fragmentation. This Letter presents several experimental results in support of the fs-LDPI approach for MS imaging. First, the lateral resolution for MS imaging of molecular species desorbed by ∼75 fs, 800 nm laser pulses was determined to be <2 μm for a simulated organic electronic device under vacuum. Next, the dependence of precursor ion survival on both desorption laser fluence and delay between desorption and photoionization laser pulses was observed for a small molecule desorbed from an organic multilayer that was originally devised as a model of a bacterial biofilm. When considered in light of recent results in the literature (Milasinovic et al. J. Phys. Chem. C 2014, DOI: 10.1021/jp504062u), these experiments demonstrate the potential for submicrometer spatial resolution MS imaging by fs-LDPI.

Topics: Chlorobenzoates; Ions; Lasers; Molecular Imaging; Naphthacenes; Silicon; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Vacuum

The injection of charge carriers into a pentacene thin film formed on a Si substrate was investigated by scanning tunneling microscopy (STM). Tip height versus bias voltage (z-V) spectroscopy reveals the characteristic charge transport properties of the molecular film, i.e., the conductivity and the threshold energy of charge injection. The abrupt descent of the tip into the film owing to the transition of film conductance, which depends on the degree of charge carrier injection, was observed for crystallized pentacene thin films. The lower film conductance at around zero bias voltage is still higher than that of a vacuum. This indicates that the carrier injection barrier between the pentacene and the semiconducting substrate is extremely low. The convergence of the carrier injection endpoints into a narrow range of electric-field intensity implies that the main factor contributing to barrier formation and collapse is not the bias voltage but the electric field.

Topics: Electric Conductivity; Macromolecular Substances; Materials Testing; Membranes, Artificial; Molecular Conformation; Nanostructures; Naphthacenes; Particle Size; Silicon; Static Electricity; Surface Properties

Organic thin-film transistors (OTFTs) offer unprecedented opportunities for implementation in a broad range of technological applications spanning from large-volume microelectronics and optical displays to chemical and biological sensors. In this Progress Report, we review the application of organic transistors in the fields of flexible optical displays and microelectronics. The advantages associated with the use of OTFT technology are discussed with primary emphasis on the latest developments in the area of active-matrix electrophoretic and organic light-emitting diode displays based on OTFT backplanes and on the application of organic transistors in microelectronics including digital and analog circuits.

Topics: Color; Computer Terminals; Naphthacenes; Organic Chemicals; Plastics; Semiconductors; Silicon; Transistors, Electronic

The growth of pentacene films on different metal (Ga, Pb, Bi, Ag) induced Si(111)-(square root(3) x square root(3))R30 degrees surfaces is investigated by scanning tunneling microscopy. On surfaces with high atomic surface roughness, such as GaSi-square root(3), beta-PbSi-square root(3), and alpha-BiSi-square root(3), pentacene forms an initial disordered wetting layer followed by the growth of crystalline thin films. The growth behavior is independent of the metallicity of the substrate surface in this regime. On the other hand, on surfaces with low adatom surface roughness, pentacene molecules form self-organized structures without forming a wetting layer. Moreover, the molecular orientation is critically dependent on the surface metallicity. This work reveals that the growth mode of pentacene on solid surfaces is determined by the combined effects of structural and electronic properties of the substrate.

Topics: Electrons; Metals; Naphthacenes; Silicon; Surface Properties