Nanoparticulate zinc oxide is regarded as one of the most promising inorganic materials for printable field-effect transistors (FETs), which work in the n-channel enhancement mode, due to the compatibility with solution, low-temperature, and high throughput processes. Since nanoparticulate films are composed of the nanoparticles and their agglomerates, the roughness of the interface to the insulating layer, where the channel of the FETs is formed, is a critical issue. Thus, the influence of the interface roughness on the field-effect mobility of the FETs is investigated in conjunction with film roughness and capacitance analyses. The field-effect mobility increases almost by a factor of 50, from 2.0×10−4 to 8.4×10−3 cm2 V−1 s−1, even if the reduction in the average roughness of the films is as small as 1.7 nm.

Field-effect mobilities are the most important figures of merit to evaluate the feasibility of semiconductors for thin-film transistors ͑TFTs͒. They are, however, sometimes extracted from TFTs with the active semiconductor area undefined and in small channel ratios without the effect of the fringing electric field at the ends of source/drain electrodes taken into account. In this letter, it is demonstrated that the field-effect mobilities extracted from undefined nanoparticulate zinc oxide ͑ZnO͒ TFTs at the channel ratio of 2.5 are overestimated by 418%, and the choice of large channel ratios gives the real value of field-effect mobilities.Thin-film transistors ͑TFTs͒ fabricated in lowtemperature and high throughput processes are in great demand for low-cost and large-area production. 1 Organic semiconductors, including small molecules 2 and conjugated polymers, 3,4 have intensively been studied and developed for TFTs, taking the advantage of compatibility with lightweight and flexible substrates. As an alternative route, inorganic semiconductors, including crystalline oxides 5-7 and amorphous oxides, 8,9 have been attracting significant interest in the past decade. 10 These inorganic TFTs generally work in the n-channel mode and benefit from transparency to visible lights, processibility with solutions, and compatibility with lightweight and flexible substrates as well. In order to evaluate the feasibility of any semiconducting material for TFTs, the most important figure of merit is the field-effect mobility . It is frequently extracted from the transfer characteristics of TFTs in the saturation regime, according to the equationwhere C i is the gate capacitance per unit area, W and L are the channel width and length, respectively, and I ds , V gs , and V th are the drain current, the gate voltage, and the threshold voltage, respectively. The channel ratio is commonly defined by W / L. In the case of polycrystalline zinc oxide ͑ZnO͒ TFTs, 11-14 early investigations have shown of 0.1-1.2 cm 2 V −1 s −1 for a channel ratio of 6-40. However, it has been reported that the fieldeffect mobility strongly depends on the channel ratio, ranging from 1.9 to 27 cm 2 V −1 s −1 for the channel ratio from 64 to 1.4. 15-17 Figure 1͑a͒ shows a top-view image of a typical TFT in the bottom gate configuration with the active semiconductor area undefined. It is expected that, particularly in the case of small channel ratios, the effective channel width W eff is not equivalent to the geometrical channel width W 0 but is extended somewhat because of the fringing electric field at the ends of the electrodes, which can lead to the overestimation of the field-effect mobility. Actually, the mobilities reported on the undefined TFTs 12,14-17 seem much higher than those reported on the defined TFTs, 11,13 if they are compared at the same channel ratio. In this letter, therefore, nanoparticulate ZnO TFTs in the bottom gate configuration are modeled with the channel width extensions ⌬W 1,2 included in the effective channel width W eff , as s...

The reaction of iPr3SiPLi2 with SnCl2 in the mol ratio 1:1 leads to the formation of [Sn7(PSiiPr3)7] (1). The cluster [Sn8(PSiiPr3)6Cl2] (3) is obtained, if the same reaction is carried out with a slight excess of the metal salt. Similar lithium chloride elimination reactions between SnCl2 and iPr3SiAsLi2 in the mol ratio 1:1 and 2:3, however, yield [Sn7(AsSiiPr3)7] (2) and [Sn4(AsSiiPr3)6Li4(Et2O)2] (4), respectively. The metal salt GeCl2(diox)2 (diox = 1,4‐dioxane) reacts with iPr3SiPLi2 to give [Ge6(PSiiPr3)6] (5). Compounds 1−5 were characterised by NMR and IR spectroscopic techniques as well as elemental analysis. The crystal structures were identified by X‐ray diffraction analysis, which confirmed that the heptameric skeletons of 1 and 2 are structurally analogous. The Sn/P cluster 3 contains subvalent tin atoms, while 4 forms a Sn4As6Li4 rhombododecahedron and 5 a slightly distorted hexagonal prism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The compound [BiP(SiPh2tBu)2]2 (1), featuring a Bi–Bi double bond and two Bi–P single bonds, has been obtained from thereaction of BiCl3 with the lithium phosphanide LiP(SitBuPh2)2.As a byproduct of this transmetallation/redox reaction the diphosphane P2(SitBuPh2)4 (2) has been isolated. This compound shows a remarkably short P–P bond due to π interactions of the phosphorus atoms. The reaction of the dilithium phosphandiide Li2PSitBuPh2 with BiCl3 yielded the bicyclic compound [Bi2(PSiPh2tBu)4] (3), exhibiting a Bi–Bi single bond. NMR studies of 3 show the availability of four different P atoms, as observed in the crystal structure. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Homogeneous, smooth and densely-packed nanoparticulate ZnO films for field-effect transistors (FETs) are formed by spin-coating suspensions of ZnO nanoparticles in an organic solvent, followed by baking at 150 C. The morphology of the films is strongly dependent on the type and amount of surfactant polymers that are employed to cap ZnO nanoparticles and stabilize the suspensions. Infrared spectroscopy, atomic force microscopy, electron microscopy and electrical characterization reveal that a certain amount of surfactant is needed to make the size of the agglomerates small enough to form such nanoparticulate films; however, an excess amount of surfactant results in an increase in the resistivity of the nanoparticulate films owing to the electrically semi-insulating nature of the surfactants. FETs composed of the nanoparticulate ZnO films in the bottom gate configuration operate in the n-channel enhancement mode with a clear saturation current at higher drain voltages. The field-effect mobility of the FETs varies by more than three orders of magnitude dependent on the type and amount of surfactants, exhibiting the highest value of 8 Â 10 À3 cm 2 V À1 s À1 . This clearly indicates that the appropriate development and synthesis of surfactants for inorganic nanocrystal suspensions are highly important for low-temperature and solution-processed FETs, compatible with plastic substrates, towards printable electronics.