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.

Study of the kinetics and mechanism of rapid self-assembly in block copolymer thin films during solvo-microwave annealing

Microwave annealing is an emerging technique for achieving ordered patterns of block copolymer films on substrates. Little is understood about the mechanisms of microphase separation during the microwave annealing process and how it promotes the microphase separation of the blocks. Here, we use controlled power microwave irradiation in the presence of tetrahydrofuran (THF) solvent, to achieve lateral microphase separation in high- lamellar-forming poly(styrene-b-lactic acid) PS-b-PLA. A highly ordered line pattern was formed within seconds on silicon, germanium and silicon on insulator (SOI) substrates. In-situ temperature measurement of the silicon substrate coupled to condition changes during "solvo-microwave" annealing allowed understanding of the processes to be attained. Our results suggest that the substrate has little effect on the ordering process and is essentially microwave transparent but rather, it is direct heating of the polar THF molecules that causes microphase separation. It is postulated that the rapid interaction of THF with microwaves and the resultant temperature increase to 55 degrees C within seconds causes an increase of the vapor pressure of the solvent from 19.8 to 70 kPa. This enriched vapor environment increases the plasticity of both PS and PLA chains and leads to the fast self-assembly kinetics. Comparing the patterns formed on silicon, germanium and silicon on insulator (SOI) and also an in situ temperature measurement of silicon in the oven confirms the significance of the solvent over the role of substrate heating during "solvo-microwave" annealing. Besides the short annealing time which has technological importance, the coherence length is on a micron scale and dewetting is not observed after annealing. The etched pattern (PLA was removed by an Ar/O-2 reactive ion etch) was transferred to the underlying silicon substrate fabricating sub-20 nm silicon nanowires over large areas demonstrating that the morphology is consistent both across and through the film.

The morphology of ordered block copolymer patterns as probed by high resolution imaging

The microphase separation of block copolymer (BCP) thin films can afford a simple and cost-effective means to studying nanopattern surfaces, and especially the fabrication of nanocircuitry. However, because of complex interface effects and other complications, their 3D morphology, which is often critical for application, can be more complex than first thought. Here, we describe how emerging microscopic methods may be used to study complex BCP patterns and reveal their rich detail. These methods include helium ion microscopy (HIM) and high resolution x-section transmission electron microscopy (XTEM), and complement conventional secondary electron and atomic force microscopies (SEM and TEM). These techniques reveal that these structures are quite different to what might be expected. We illustrate the advances in the understanding of BCP thin film morphology in several systems, which result from this characterization. The systems described include symmetric, lamellar forming polystyrene-b-polymethylmethacrylate (PS-b-PMMA), cylinder forming polystyrene-b-polydimethylsiloxane (PS-b-PDMS), as well as lamellar and cylinder forming patterns of polystyrene-b-polyethylene oxide (PS-b-PEO) and polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP). Each of these systems exhibits more complex arrangements than might be first thought. Finding and developing techniques whereby complex morphologies, particularly at very small dimensions, can be determined is critical to the practical use of these materials in many applications. The importance of quantifying these complex morphologies has implications for their use in integrated circuit manufacture, where they are being explored as alternative pattern forming methods to conventional UV lithography.

Formation of sub-7 nm feature size PS-b-P4VP block copolymer structures by solvent vapour process

The nanometer range structure produced by thin films of diblock copolymers makes them a great of interest as templates for the microelectronics industry. We investigated the effect of annealing solvents and/or mixture of the solvents in case of symmetric Poly (styrene-block-4vinylpyridine) (PS-b-P4VP) diblock copolymer to get the desired line patterns. In this paper, we used different molecular weights PS-b-P4VP to demonstrate the scalability of such high χ BCP system which requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Bare Silicon Substrates were also modified with polystyrene brush and ethylene glycol self-assembled monolayer in a simple quick reproducible way. Also, a novel and simple in situ hard mask technique was used to generate sub-7nm Iron oxide nanowires with a high aspect ratio on Silicon substrate, which can be used to develop silicon nanowires post pattern transfer.

Fabrication of sub-10 nm lamellar structures by solvent vapour annealing of block copolymers

Fabrication of nanoscale patterns through the bottom-up approach of self-assembly of phase-separated block copolymers (BCP) holds promise for nanoelectronics applications. For lithographic applications, it is useful to vary the morphology of BCPs by monitoring various parameters to make “from lab to fab” a reality. Here I report on the solvent annealing studies of lamellae forming polystyrene-blockpoly( 4-vinylpyridine) (PS-b-P4VP). The high Flory-Huggins parameter (χ = 0.34) of PS-b-P4VP makes it an ideal BCP system for self-assembly and template fabrication in comparison to other BCPs. Different molecular weights of symmetric PS-b-P4VP BCPs forming lamellae patterns were used to produce nanostructured thin films by spin-coating from mixture of toluene and tetrahydrofuran(THF). In particular, the morphology change from micellar structures to well-defined microphase separated arrangements is observed. Solvent annealing provides a better alternative to thermal treatment which often requires long annealing periods. The choice of solvent (single and dual solvent exposure) and the solvent annealing conditions have significant effects on the morphology of films and it was found that a block neutral solvent was required to realize vertically aligned PS and P4VP lamellae. Here, we have followed the formation of microdomain structures with time development at different temperatures by atomic force microscopy (AFM). The highly mobilized chains phase separate quickly due to high Flory-Huggins (χ) parameter. Ultra-small feature size (~10 nm pitch size) nanopatterns were fabricated by using low molecular weight PSb- P4VP (PS and P4VP blocks of 3.3 and 3.1 kg mol-1 respectively). However, due to the low etch contrast between the blocks, pattern transfer of the BCP mask is very challenging. To overcome the etch contrast problem, a novel and simple in-situ hard mask technology is used to fabricate the high aspect ratio silicon nanowires. The lamellar structures formed after self-assembly of phase separated PS-b-P4VP BCPs were used to fabricate iron oxide nanowires which acted as hard mask material to facilitate the pattern transfer into silicon and forming silicon nanostructures. The semiconductor and optical industries have shown significant interest in two dimensional (2D) molybdenum disulphide (MoS2) as a potential device material due to its low band gap and high mobility. However, current methods for its synthesis are not ‘fab’ friendly and require harsh environments and processes. Here, I also report a novel method to prepare MoS2 layered structures via self-assembly of a PS-b-P4VP block copolymer system. The formation of the layered MoS2 was confirmed by XPS, Raman spectroscopy and high resolution transmission electron microscopy.

Delivering enhanced efficiency in the synthesis of α-diazosulfoxides by exploiting the process control enabled in flow

Continuous-flow generation of α-diazosulfoxides results in a two- to three-fold increase in yields and decreased reaction times compared to standard batch synthesis methods. These high yielding reactions are enabled by flowing through a bed of polystyrene-supported base (PS-DBU or PS-NMe2) with highly controlled residence times. This engineered solution allows the α-diazosulfoxides to be rapidly synthesized while limiting exposure of the products to basic reaction conditions, which have been found to cause rapid decomposition. In addition to improved yields, this work has the added advantage of ease of processing, increased safety profile, and scale-up potential.

Greener methodology for the synthesis of alpha-diazocarbonyl compounds and a novel approach to dioxinone derivatives

This thesis outlines a more environmentally benign approach to diazo transfer, and the investigation of the reactivity of -diazocarbonyl compounds when subjected to transition metal and lanthanide catalysis. Extensive studies were carried out to find the optimum conditions for a greener diazo transfer methodology, and this was also applied to a continuous process for the synthesis of -diazo--ketoesters. The first chapter includes a literature review of the synthesis and subsequent reactivity of -diazocarbonyl compounds. An overview of the applications of flow chemistry for the synthesis of hazardous intermediates is also included. The applications of lanthanide catalysts in organic synthesis is also discussed. The second chapter outlines the extensive studies undertaken to determine the optimum conditions for a greener diazo transfer methodology, including base and solvent studies. Use of water as a viable solvent for diazo transfer was successfully investigated. Diazo transfer to a range of -diazo--ketoesters was achieved using 5 mol% triethylamine or DMAP in water with high conversions. Polystyrene-supported benzenesulfonyl azide as an alternative diazo transfer reagent was also explored, as well as investigations into cheaper generation of this safer reagent. This polymer-supported benzenesulfonyl azide was used with 25 mol% of base in water to achieve successful diazo transfer to a range of -diazo--ketoesters. The third chapter describes the application of the new methodology developed in Chapter 2 to a continuous processing approach. Various excellent conditions were identified for both batch and flow reactions. A series of -diazo--ketoesters were synthesised with excellent conversions using 25 mol% triethylamine in 90:10 acetone water using flow chemistry. Successful diazo transfer was also achieved using a polymer-supported benzenesulfonyl azide in water under flow conditions. The fourth chapter discusses the reactivity of -diazo--ketoesters under transition metal and lanthanide catalysis. This chapter describes the synthesis of a range of -ketoesters via transesterification, which were used to synthesise a range of novel -diazo--ketoesters that were used in subsequent decomposition reactions. A novel route to dioxinones via rhodium(II) catalysis is reported. Attempted OH and SH insertion reactions in the presence of various lanthanide(II) catalysts are outlined, leading to some unexpected and interesting rearrangement products. The experimental details, including spectroscopic and analytical data for all compounds prepared, are reported at the end of each chapter.