Nanostructured copper oxides and phosphates from a new solid-state route

Nanostructured copper containing materials of CuO, Cu3(PO4)3 and Cu2P2O7 have been prepared by solid-state pyrolysis of molecular CuCl2·NC5H4OH (I), CuCl2·CNCH2C6H4OH (II), oligomeric [Cu(PPh3)Cl]4 (III), N3P3[OC6H4CH2CN·CuCl]6[PF6] (IV), N3P3[OC6H5]5[OC5H4N·Cu][PF6] (V), polymeric chitosan·(CuCl2)n (VI) and polystyrene-co-4-vinylpyridine PS-b-4-PVP·(CuCl2) (VII) precursors. The products strongly depend on the precursor used. The pyrolytic products from phosphorus-containing precursors (III), (IV) and (V) are Cu phosphates or pyrophosphates, while non-phosphorous-containing precursors (VI) and (VII), result in mainly CuO. The use of chitosan as a solid-state template/stabilizer induces the formation of CuO and Cu2O nanoparticles. Copper pyrophosphate (Cu2P2O7) deposited on Si using (IV) as the precursor exhibits single-crystal dots of average diameter 100 nm and heights equivalent to twice the unit cell b-axis (1.5–1.7 nm) and an areal density of 5.1–7.7 Gigadots/in.2. Cu2P2O7 deposited from precursor (VI) exhibits unique labyrinthine high surface area deposits. The morphology of CuO deposited on Si from pyrolysis of (VI) depends on the polymer/Cu meta ratio. Magnetic measurements performed using SQUID on CuO nanoparticle networks suggest superparamagnetic behavior. The results give insights into compositional, shape and morphological control of the as-formed nanostructures through the structure of the precursors.

Synthesis and characterization of cyclotriphosphazenes containing silicon as single solid-state precursors for the formation of silicon/phosphorus nanostructured materials

The synthesis and characterization of new organosilicon derivatives of N3P3Cl6, N3P3[NH(CH2)3Si(OEt)3]6 (1), N3P3[NH(CH2)3Si(OEt)3]3[NCH3(CH2)3CN]3 (2), and N3P3[NH(CH2)3Si(OEt)3]3[HOC6H4(CH2)CN]3 (3) are reported. Pyrolysis of 1, 2, and 3 in air and at several temperatures results in nanostructured materials whose composition and morphology depend on the temperature of pyrolysis and the substituents of the phosphazenes ring. The products stem from the reaction of SiO2 with P2O5, leading to either crystalline Si5(PO4)6O, SiP2O7 or an amorphous phase as the glass Si5(PO4)6O/3SiO2·2P2O5, depending on the temperature and nature of the trimer precursors. From 1 at 800 °C, core−shell microspheres of SiO2 coated with Si5(PO4)6O are obtained, while in other cases, mesoporous or dense structures are observed. Atomic force microscopy examination after deposition of the materials on monocrystalline silicon wafers evidences morphology strongly dependent on the precursors. Isolated islands of size ∼9 nm are observed from 1, whereas dense nanostructures with a mean height of 13 nm are formed from 3. Brunauer−Emmett−Teller measurements show mesoporous materials with low surface areas. The proposed growth mechanism involves the formation of cross-linking structures and of vacancies by carbonization of the organic matter, where the silicon compounds nucleate. Thus, for the first time, unique silicon nanostructured materials are obtained from cyclic phosphazenes containing silicon.

The optical response of nanostructured surfaces and the composite diffracted evanescent wave model

Investigations of the optical response of subwavelength-structure arrays milled into thin metal films have revealed surprising phenomena, including reports of unexpectedly high transmission of light. Many studies have interpreted the optical coupling to the surface in terms of the resonant excitation of surface plasmon polaritons (SPPs), but other approaches involving composite diffraction of surface evanescent waves (CDEW) have also been proposed. Here we present a series of measurements on very simple one-dimensional subwavelength structures to test the key properties of the surface waves, and compare them to the CDEW and SPP models. We find that the optical response of the silver metal surface proceeds in two steps: a diffractive perturbation in the immediate vicinity (2–3 mu m) of the structure, followed by excitation of a persistent surface wave that propagates over tens of micrometres. The measured wavelength and phase of this persistent wave are significantly shifted from those expected for resonance excitation of a conventional SPP on a pure silver surface.

Writing self-assembled monolayers with Cs: Optimization of atomic nanolithography imaging using self-assembled monolayers on gold substrates

We report the results of a study into the factors controlling the quality of nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent postetch pattern definition, and minimum feature size all depend on the quality of the Au substrate used in material mask atomic nanolithographic experiments. We find that sputtered Au substrates yield much smoother surfaces and a higher density of {111}-oriented grains than evaporated Au surfaces. Phase imaging with an atomic force microscope shows that the quality and percentage coverage of SAM adsorption are much greater for sputtered Au surfaces. Exposure of the self-assembled monolayer to an optically cooled atomic Cs beam traversing a two-dimensional array of submicron material masks mounted a few microns above the self-assembled monolayer surface allowed determination of the minimum average Cs dose (2 Cs atoms per self-assembled monolayer molecule) to write the monolayer. Suitable wet etching, with etch rates of 2.2 nm min-1, results in optimized pattern definition. Utilizing these optimizations, material mask features as small as 230 nm in diameter with a fractional depth gradient of 0.820 nm were realized.

The nature of alkanethiol self-assembled monolayer adsorption on sputtered gold substrates

A detailed study of the self-assembly and coverage by 1-nonanethiol of sputtered Au surfaces using molecular resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au surface composed predominantly of {111} oriented grains. The domains of the alkanethiol monolayer are observed with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. STM imaging shows that the (4 × 2) superlattice structure is observed as a (3 × 2√3) structure when imaged under noncontact AFM conditions. The 1-nonanethiol molecules reside in the threefold hollow sites of the Au{111} lattice and aligned along its lattice vectors. The self-assembled monolayer (SAM) contains many nonuniformities such as pinholes, domain boundaries, and monatomic depressions which are present in the Au surface prior to SAM adsorption. The detailed observations demonstrate limitations to the application of 1-nonanethiol as a resist in atomic nanolithography experiments to feature sizes of ∼20 nm.