The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.
An ion beam source using electrospray ionization is presented for nondestructive vacuum deposition of mass‐selected large organic molecules and inorganic clusters. Electrospray ionization is used to create an ion beam from a solution containing the nanoparticles or molecules to be deposited. To form and guide the ion beam, radio frequency and electrostatic ion optics are utilized. The kinetic energy distribution of the particles is measured to control the beam formation and the landing process. The particle mass‐to‐charge ratio is analyzed by in situ time‐of‐flight mass spectrometry. To demonstrate the performance of the setup, deposition experiments with gold nanoclusters and bovine serum albumin proteins on graphite surfaces were performed and analyzed by ex situ atomic force microscopy. The small gold clusters are found to form three‐dimensional agglomerations at the surface, preferentially decorating the step edges. In contrast, bovine serum albumin creates two‐dimensional fractal nanostructures on the substrate terraces due to strong intermolecular interactions.
Metal-organic coordination interactions are prime candidates for the formation of self-assembled, nanometer-scale periodic networks with room-temperature structural stability. We present X-ray photoelectron spectroscopy measurements of such networks at the Cu(100) surface which provide clear evidence for genuine metal-organic coordination. This is evident as binding energy shifts in the O 1s and Fe 3p photoelectron peaks, corresponding to O and Fe atoms involved in the coordination. Our results provide the first clear evidence for charge-transfer coordination in metal-organic networks at surfaces and demonstrate a well-defined oxidation state for the coordinated Fe ions.
Novel
p-type semiconducting polymers that can facilitate ion penetration,
and operate in accumulation mode are much desired in bioelectronics.
Glycol side chains have proven to be an efficient method to increase
bulk electrochemical doping and optimize aqueous swelling. One early
polymer which exemplifies these design approaches was p(g2T-TT), employing
a bithiophene-co-thienothiophene backbone with glycol
side chains in the 3,3′ positions of the bithiophene repeat
unit. In this paper, the analogous regioisomeric polymer, namely pgBTTT,
was synthesized by relocating the glycol side chains position on the
bithiophene unit of p(g2T-TT) from the 3,3′ to the 4,4′
positions and compared with the original p(g2T-TT). By changing the
regio-positioning of the side chains, the planarizing effects of the
S–O interactions were redistributed along the backbone, and
the influence on the polymer’s microstructure organization
was investigated using grazing-incidence wide-angle X-ray scattering
(GIWAXS) measurements. The newly designed pgBTTT exhibited lower backbone
disorder, closer π-stacking, and higher scattering intensity
in both the in-plane and out-of-plane GIWAXS measurements. The effect
of the improved planarity of pgBTTT manifested as higher hole mobility
(μ) of 3.44 ± 0.13 cm2 V–1 s–1. Scanning tunneling microscopy (STM) was in
agreement with the GIWAXS measurements and demonstrated, for the first
time, that glycol side chains can also facilitate intermolecular interdigitation
analogous to that of pBTTT. Electrochemical quartz crystal microbalance
with dissipation of energy (eQCM-D) measurements revealed that pgBTTT
maintains a more rigid structure than p(g2T-TT) during doping, minimizing
molecular packing disruption and maintaining higher hole mobility
in operation mode.
The ion beam deposition (IBD) of rhodamine dye molecules on solid surfaces in high vacuum is explored in order to characterize the possibility of fabricating molecular coatings or nanostructures from nonvolatile molecules. Molecular ion beams with a well-defined composition are deposited on silicon oxide surfaces with a controlled kinetic energy. Photoluminescence spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are employed in order to characterize the sample with respect to coverage, homogeneity, and the fraction of intact landed ions (soft-landing ratio). We find that homogeneous rhodamine films of defined composition can be produced at energies of 2؊100 eV. The coverage is found to be proportional to the ion dose. Soft-landing is observed for energies up to 35 eV.
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