Interfacial Synthesis of Layer-Oriented 2D Conjugated Metal-Organic Framework Films toward Directional Charge Transport.

The development of layer-oriented two-dimensional conjugated metal-organic frameworks (2D c-MOFs) enables access to direct charge transport, dial-in lateral/vertical electronic devices, and the unveiling of transport mechanisms but remains a significant synthetic challenge. Here we report the novel synthesis of metal-phthalocyanine-based p-type semiconducting 2D c-MOF films (Cu2[PcM-O8], M = Cu or Fe) with an unprecedented edge-on layer orientation at the air/water interface. The edge-on structure formation is guided by the preorganization of metal-phthalocyanine ligands, whose basal plane is perpendicular to the water surface due to their π-π interaction and hydrophobicity. Benefiting from the unique layer orientation, we are able to investigate the lateral and vertical conductivities by DC methods and thus demonstrate an anisotropic charge transport in the resulting Cu2[PcCu-O8] film. The directional conductivity studies combined with theoretical calculation identify that the intrinsic conductivity is dominated by charge transfer along the interlayer pathway. Moreover, a macroscopic (cm2 size) Hall-effect measurement reveals a Hall mobility of ∼4.4 cm2 V-1 s-1 for the obtained Cu2[PcCu-O8] film. The orientation control in semiconducting 2D c-MOFs will enable the development of various optoelectronic applications and the exploration of unique transport properties.

High-Performance Vertical Organic Transistors of Sub-5 nm Channel Length.

Miniaturization of electronic circuits increases their overall performance. So far, electronics based on organic semiconductors has not played an important role in the miniaturization race. Here, we show the fabrication of liquid electrolyte gated vertical organic field effect transistors with channel lengths down to 2.4 nm. These ultrashort channel lengths are enabled by using insulating hexagonal boron nitride with atomically precise thickness and flatness as a spacer separating the vertically aligned source and drain electrodes. The transistors reveal promising electrical characteristics with output current densities of up to 2.95 MA cm-2 at -0.4 V bias, on-off ratios of up to 106, a steep subthreshold swing of down to 65 mV dec-1 and a transconductance of up to 714 S m-1. Realizing channel lengths in the sub-5 nm regime and operation voltages down to 100 µV proves the potential of organic semiconductors for future highly integrated or low power electronics.

Contact and edge effects in graphene devices.

Electrical transport studies on graphene have been focused mainly on the linear dispersion region around the Fermi level and, in particular, on the effects associated with the quasiparticles in graphene behaving as relativistic particles known as Dirac fermions. However, some theoretical work has suggested that several features of electron transport in graphene are better described by conventional semiconductor physics. Here we use scanning photocurrent microscopy to explore the impact of electrical contacts and sheet edges on charge transport through graphene devices. The photocurrent distribution reveals the presence of potential steps that act as transport barriers at the metal contacts. Modulations in the electrical potential within the graphene sheets are also observed. Moreover, we find that the transition from the p- to n-type regime induced by electrostatic gating does not occur homogeneously within the sheets. Instead, at low carrier densities we observe the formation of p-type conducting edges surrounding a central n-type channel.

High-performance carbon nanotube field effect transistors with a thin gate dielectric based on a self-assembled monolayer.

Individual single-walled carbon nanotube (SWCNT) field effect transistors (FETs) with a 2 nm thick silane-based organic self-assembled monolayer (SAM) gate dielectric have been manufactured. The FETs exhibit a unique combination of excellent device performance parameters. In particular, they operate with a gate-source voltage of only -1 V and exhibit good saturation, large transconductance, and small hysteresis (

New charge-transfer salts for reversible resistive memory switching.

We found novel organic charge-transfer salts that exhibit reversible resistive memory switching phenomena. Homogeneous layers of these complexes can be easily fabricated using solution processing. The copper-2,3-dichloro-5,6-dicyano-p-benzoquinone complex was investigated in more detail. Devices made of this complex can be reversibly switched between a high and a low resistance state by applying voltage pulses as short as 1 micros. The memory states remain stable for more than 15 h without an electricity source.