Weak Epitaxy Growth Research Articles

Weak Epitaxy Growth and Phase Behavior of Planar Phthalocyanines on p-Sexiphenyl Monolayer Film

We systematically investigated the weak epitaxy growth (WEG) behavior of a series of planar phthalocyanine compounds (MPc), i.e., metal-free phthalocyanine (H2Pc), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), iron phthalocyanine (FePc), cobalt phthalocyanine (CoPc), grown on a p-sexiphenyl ( p-6P) monolayer film by selected area electron diffraction (SAED) and atomic force microscopy (AFM). Two types of epitaxial relations, named as incommensurate epitaxy and commensurate epitaxy, were identified between phthalocyanine compounds and the substrate of the p-6P film. The tiny variation of the lattice constant of phthalocyanine compounds can result in different crystal orientations. The change rule of incommensurate and commensurate epitaxy was extracted. The tendency of commensurate epitaxy becomes weaker as the lattice constant b increases, while it gets stronger as the substrate temperature is elevated. Large size and continuous H2Pc films can be obtained by controlling the growth conditions. The WEG method is generally applicable in the whole family of planar phthalocyanine compounds and may be used to fabricate other high-quality organic films.

Weak Epitaxy Growth of Metal-Free Phthalocyanine on p-Sexiphenyl Monolayer and Double-Layer Films

Weak epitaxy growth (WEG) can afford high-mobility thin films of disk-like organic semiconductor of which mobility is up to the level of the corresponding single crystals. We investigated the WEG behavior and mechanism of planar phthalocyanine in the model system of metal-free phthalocyanine (H2Pc) grown on p-sexiphenyl (p-6P) ultrathin films (monolayers and double layers). Highly oriented H2Pc films with molecules standing up exhibited two kinds of different in-plane orientations, i.e., three sets of in-plane orientations and only one set of in-plane orientation, on p-6P monolayer and double-layer films, respectively. The surface geometrical channels of p-6P substrate dominated the oriented nucleation and growth of H2Pc film. Consequently, the H2Pc film showed incommensurate and commensurate epitaxy on p-6P ultrathin films.

Electrical properties in vanadyl-phthalocyanine-based metal-insulator-semiconductor devices

We investigated electrical properties of vanadyl phthalocyanine (VOPc) metal-insulator-semiconductor (MIS) devices by the measurement of capacitance and conductance, which were fabricated on ordered para-sexiphenyl (p-6P) layer by weak epitaxy growth method. The VOPc∕p-6P MIS diodes showed a negligible hysteresis effect at a gate voltage of ±20V and small hysteresis effect at a gate voltage of ±40V due to the low interface trap state density of about 1×1010eV−1cm−2. Furthermore, a high transition frequency of about 10kHz was also observed under their accumulation mode. The results indicated that VOPc was a promising material and was suitable to be applied in active matrix liquid crystal displays and organic logic circuits.

Switch-on transient behavior of vanadium phthalocyanine based organic transistors

The authors investigated the switch-on transient properties of p-type vanadium phthalocyanine (VOPc) transistors, which were fabricated by weak epitaxy growth on ordered para-sexiphenyl (p-6P) layer. The overshoot phenomenon of drain current had been observed in the VOPc∕p-6P transistors, which was explained by the filling of carriers in traps of organic films. The small overshoot value of about 35% and transient duration time of 2ms demonstrated the low trap concentration in organic films, which were comparable to the reported hydrogenated amorphous-silicon thin-film transistors. Therefore, the VOPc∕p-6P transistors can be applied in active matrix liquid crystal display as switch elements.

Weak Epitaxy Growth Affording High‐Mobility Thin Films of Disk‐Like Organic Semiconductors

Thin films of phthalocyanine compounds show weak epitaxial growth on a monodomain film of a rod-like molecule (see figure). The resulting organic electronic devices exhibit high charge carrier mobilities close to those of the single-crystal devices.

High mobility vanadyl-phthalocyanine polycrystalline films for organic field-effect transistors

The organic films of vanadyl-phthalocyanine (VOPc) compounds showed weak epitaxy growth (WEG) behavior on thin ordered para-sexiphenyl (p-6P) layer with high substrate temperature. The WEG of VOPc molecules standing up on the p-6P layer leaded to high in-plane orientation and their layer-by-layer growth behavior. In consequence, high quality VOPc films were obtained, which were consisted of lamellar crystals. Organic field-effect transistors with VOPc∕p-6P films as active layers realized high mobility of above 1cm2∕Vs. This result indicated that nonplanar compounds can obtain a device performance better than planar compounds, therefore, it may provide a rule to find disklike organic semiconductor materials.

Epitaxial electrodeposition of lead selenide films on indium phosphide single crystals

Epitaxial electrodeposition of PbSe films on (1 1 1)InP single crystals is demonstrated thanks to high energy electron diffraction. The presence of Cd(II) in the solution is mandatory in order to obtain an epitaxial growth which can be continued up to 0.2 μm. High resolution electron microscopy images show the structural organization of the PbSe/(1 1 1)InP and reveal the quasi absence of stacking faults and microtwins. On (1 0 0)InP single crystals a weak epitaxial growth is observed.