A new approach to second-order nonlinear optical (NLO) materials is reported, in which chirality and supramolecular organization play key roles. Langmuir-Blodgett films of a chiral helicene are composed of supramolecular arrays of the molecules. The chiral supramolecular organization makes the second-order NLO susceptibility about 30 times larger for the nonracemic material than for the racemic material with the same chemical structure. The susceptibility of the nonracemic films is a respectable 50 picometers per volt, even though the helicene structure lacks features commonly associated with high nonlinearity. Susceptibility components that are allowed only by chirality dominate the second-order NLO response.

In search of a proper passivation for high-k Ge metal-oxide-semiconductor devices, the authors have deposited high-k dielectric layers on GeO2, grown at 350–450°C in O2. ZrO2, HfO2, and Al2O3 were deposited by atomic layer deposition (ALD). GeO2 and ZrO2 or HfO2 intermix during ALD, together with partial reduction of Ge4+. Almost no intermixing or reduction occurs during Al2O3 ALD. Capacitors show well-behaved capacitance-voltage characteristics on both n- and p-Ge, indicating efficient passivation of the Ge∕GeOx interface. The density of interface states is typically in the low to mid-1011cm−2eV−1 range, approaching state-of-the-art Si∕HfO2∕matal gate devices.

The incorporation of Gd into HfO2 thin films is shown to induce ferroelectricity. A significant influence of electric field cycling on both polarization as well as small-signal capacitance-voltage measurements can be observed. X-ray diffraction measurements are supported by infrared absorption analysis and give further evidence of the previously proposed non-centrosymmetric transition phase of space group Pbc21.

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Molecules in which the cores of copper and nickel octaazaphthalocyanines are fused to four nonracemic [7]helicenes are constructed. CD and UV−vis absorption spectroscopy show that these compounds aggregate when dissolved in 75% EtOH−25% CHCl3, but not in 60% EtOH−40% CHCl3. The UV−vis absorption spectra of films of the nickel phthalocyanine are similar to those of solutions of the aggregated molecules, suggesting that the structures of the aggregates in the neat samples and in solution are similar. A calculation based on molecular mechanics shows that the energy is minimized when the molecules stack in a chiral superstructure with a core-to-core distance of ca. 3.4 Å. Atomic Force Microscopic images are in accord with this structure if on the surface of mica the stacks are isolated and perpendicular to the surface. In Langmuir films, the molecules stack in the opposite way, with the stacking axis parallel to the water. Although the molecules are remarkably symmetrical, their Langmuir−Blodgett films give very large second-order nonlinear optical responses, dominated by the ca. 21 pm/V components of the susceptibility tensors that are allowed only because the materials are chiral.

We report on the thin film resistivity of several platinum-group metals (Ru, Pd, Ir, Pt). Platinumgroup thin films show comparable or lower resistivities than Cu for film thicknesses below about 5 nm due to a weaker thickness dependence of the resistivity. Based on experimentally determined mean linear distances between grain boundaries as well as ab initio calculations of the electron mean free path, the data for Ru, Ir, and Cu were modeled within the semiclassical Mayadas-Shatzkes model [Phys. Rev. B 1, 1382(1970] to assess the combined contributions of surface and grain boundary scattering to the resistivity. For Ru, the modeling results indicated that surface scattering was strongly dependent on the surrounding material with nearly specular scattering at interfaces with SiO 2 or air but with diffuse scattering at interfaces with TaN. The dependence of the thin film resistivity on the mean free path is also discussed within the Mayadas-Shatzkes model in consideration of the experimental findings.

Nonracemic helicene 1 forms high-quality Langmuir−Blodgett (LB) films, in which the molecules are organized in parallel columns with their edges exposed to the surface. Evidence for the edge-on exposure is the molecular area of a monolayer on water and, as determined by X-ray diffraction, the similarity of the interlayer spacings of multilayers to the diameters of the molecular columns that constitute nonracemic 1 in bulk. Evidence of the organization into parallel columns includes the linear dichroism of the films and the 180° periodicity with which rotating the films varies the amounts by which plane polarized light is rotated, the intensities of the second harmonics generated, and the films' degree of anisotropy. The circular dichroisms of a 10-layer LB film could be resolved from the effects of linear dichroism and linear birefringence. The CD and UV−vis absorption spectra of the films are similar to those of solutions in which the molecules are aggregated, not isolated. The measurement of a CD spectrum for a monolayer, carried out easily for nonracemic 1, is unprecedented.

Two-dimensional (2D) transition metal dichalcogenides are potential low dissipative semiconductor materials for nanoelectronic devices. Such applications require the deposition of these materials in their crystalline form and with controlled number of monolayers on large area substrates, preferably using growth temperatures compatible with temperature sensitive structures. This paper presents a low temperature Plasma Enhanced Atomic Layer Deposition (PEALD) process for 2D WS2 based on a ternary reaction cycle consisting of consecutive WF6, H2 plasma and H2S reactions. Strongly textured nanocrystalline WS2 is grown at 300 °C. The composition and crystallinity of these layers depends on the PEALD process conditions, as understood by a model for the redox chemistry of this process. The H2 plasma is essential for the deposition of WS2 as it enables the reduction of-W 6+ Fx surface species. Nevertheless, the impact of sub-surface reduction reactions needs to be minimized to obtain WS2 with well-controlled composition (S/W ratio of two).