José Abad

Surface potential domains on lamellar P3OT structures

In this work the electrostatic properties of poly(3-octylthiophene) thin films have been studied on a nanometer scale by means of electrostatic force microscopy and Kelvin probe microscopy (KPM). The KPM images reveal that different surface contact potential domains coexist on the polymer surface. This result, together with additional capacitance measurements, indicates that the potential domains are related to the existence of dipoles due to different molecular arrangements. Finally, capacitance measurements as a function of the tip-sample bias voltage show that in all regions large band bending effects take place.

Synthesis and reactivity of 2-amino-5-nitrophenylpalladium(II) compounds

Abstract Reaction of [Pd(PPh 3 ) 4 ] with RBr (R = C 6 H 3 NH 2 -2, NO 2 -5) yields trans -[PdBr(R)(PPh 3 ) 2 ]. This reacts with AgNO 3 to give the nitrato-complex trans -[Pd(ONO 2 )(R)(PPh 3 ) 2 ], which in turn reacts with halide anions to give trans -[PdX(R)(PPh 3 ) 2 ] (X = Cl, I) and with neutral bidentate ligands to give cis -[Pd(R)(PPh 3 )(L-L)]NO 3 (L-L = 2,2′-bipyridine, 1,10-phenanthroline, 1,2-bis(diphenylphosphino)ethane). The complex trans -[PdBr(R)(PPh 3 ) 2 ] reacts with AgClO 4 to give species that react with pyridine to give trans -[Pd(R)(PPh 3 ) 2 (py)]ClO 4 .

Thermal frequency noise in dynamic scanning force microscopy

Thermal fluctuation of the cantilever position sets a fundamental limit for the precision of any scanning force microscope. In the present work we analyze how these fluctuations limit the determination of the resonance frequency of the tip-sample system. The basic principles of frequency detection in dynamic scanning force microscopy are revised and the precise response of a typical frequency detection unit to thermal fluctuation of the cantilever is analyzed in detail. A general relation for thermal frequency noise is found as a function of measurement bandwidth and cantilever oscillation. For large oscillation amplitude and low bandwidth, this relation converges to the result known from the literature, while for low oscillation amplitude and large bandwidth, we find that the thermal frequency noise is equal to the width of the resonance curve and, therefore, stays finite, contrary to what is predicted by the relation known so far. The results presented in this work fundamentally determine the ultimate l...

Step-induced tip polarity reversal investigated by dynamic force microscopy on KBr(001)

We present atomic resolution images of monatomic step edges on the KBr(001) surface imaged by dynamic force microscopy operated in the non-contact mode. Under certain experimental conditions, we observe a systematic and reversible change of the atomic contrast when the tip crosses the step. This change is attributed to the reversal of the polarity of the ionic tip under the influence of the tip-substrate interaction in the immediate vicinity of the step edge. This polarity reversal is attributed to a change in the atomic structure of the tip and is described by a transition between the two potential wells of a two-level system localized near the tip apex. The case of two monatomic steps imaged in succession is also investigated in detail. The results indicate that the two-level system associated with the reversal of the tip polarity involves the movement of a very limited number of ions on the tip.

Note: Submicrometer-precision sample holder for accurate re-positioning of samples in scanning force microscopy

In this work we describe two simple and compact submicrometer-precision sample holders that are easily integrated into a Scanning Force Microscopy (SFM) system. The designs are based on a traditional kinematic mounting or on self-adjustment of the sample holder and the upper piece of the piezoelectric scanner. With these sample holders the sample position is automatically recovered to within about 100 nm. The setup allows ex situ manipulation of the sample and SFM imaging of the same region without the aid of an optical microscope, positioning marks, and tedious re-allocation.

Synthesis, reactivity, and X-ray crystal structure of [Rh{C6H4N(O)O-2}(η-C5Me5)Cl]

Reaction of [{Rh(η-C5Me5)Cl2}2] with [Hg(C6H4NO2-2)2](1/1) or [Hg(C6H4NO2-2)Cl](1/2) in the presence of an excess of [NMe4]Cl gives [[graphic omitted]-2}(η-C5Me5)Cl]. This compound reacts with AgClO4 giving solutions from which, after addition of the corresponding ligands, the cationic complexes [[graphic omitted]-2}(η-C5Me5)(PPh3)]ClO4, [[graphic omitted]-2}(η-C5Me5)(py)]ClO4(py = pyridine), [Rh(C6H4NO2-2)(η-C5Me5)(bipy)]ClO4(bipy = 2,2′-bipyridyl) can be obtained. The crystal structure of [[graphic omitted]-2}(η-C5Me5)Cl] has been determined by an X-ray diffraction study. Crystals are orthorhombic, space group Pbca, with a= 14.574 2(5), b= 14.917 8(6), c= 14.678 2(6)A, and Z= 8. The molecule exhibits a pseudo-octahedral geometry around the rhodium atom with the C6H4(O)O-2 group acting as a chelating ligand, bonded to the metal through a carbon atom of the phenyl ring [Rh–C(1) 2.023(3)A] and an oxygen atom of the nitro group [Rh–O(1) 2.142(3)A]. The co-ordination of the nitro group causes a lengthening of the N–O(Rh) bond distance [N–O(1) 1.260(4)A] compared with the unco-ordinated N–O bond length [1.224(4)A]. Infrared data indicate that the aryl ligand co-ordinates in the same way in the complexes [[graphic omitted]-2}(η-C5Me5)(PPh3)]ClO4 and [[graphic omitted]-2}(η-C5Me5)(py)]ClO4 but it is unidentate in the compound [Rh(C6H4NO2-2)(η-C5Me5)(bipy)]ClO4.