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8 nm feature size nanopatterns have been fabricated from a symmetric polystyrene-b-polyethylene oxide BCP of low molecular weight using lithium ion addition.
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Molecular self-assembling block copolymers (BCPs) have shown promise as a next generation bottom-up lithography technology. However, a critical step in advancing this approach is the elimination of polymer dewetting due to bulk solvent... more
Molecular self-assembling block copolymers (BCPs) have shown promise as a next generation bottom-up lithography technology. However, a critical step in advancing this approach is the elimination of polymer dewetting due to bulk solvent nucleation and thermodynamically driven film rupture that can occur during the solvent vapor annealing process. We report on the pattern formation via phase segregation of spin coated diblock copolymer films through the investigation of annealing parameters in the limit of high solvent vapor saturation conditions that results in wafer-scale patterning without observing polymer dewetting defects. Specifically, the work addresses polymer dewetting in diblock copolymer nanodot templates through the use of a "neutral" functionalization layer and the development of a custom-built solvent vapor annealing chamber to precisely control saturation conditions. Furthermore, the long anneal times (4 h) using a standard static solvent vapor annealing proc...
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Pure phase and europium doped ceria nanocrystals have been synthesized by a single step simple solvothermal process. Different spectroscopic, diffractive and microscopic techniques were used to determine the morphology, size, crystal... more
Pure phase and europium doped ceria nanocrystals have been synthesized by a single step simple solvothermal process. Different spectroscopic, diffractive and microscopic techniques were used to determine the morphology, size, crystal structure and phase of all the samples. Electron energy loss spectroscopy (EELS) for elemental mapping confirmed that good solid solutions were formed and that the particles had a homogeneous distribution of europium. The defect chemistry was more complex than might be expected with the incorporation of each Eu3+ ion resulting in the production of an anion vacancy since the doping results in charge compensating (i.e. for Eu3+) anion vacancies as well as vacancies due to oxygen removal from the crystallite surface. Variations in nanoparticles dimension and lattice parameters were measured as a function of dopant concentrations and their variations explained. The band gap of the samples could be tailored by the doping. The doped samples were found to be l...
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Tailored pore size mesoporous silica, incorporating different concentrations of transition metal-based catalysts, has been used as platforms for the growth of carbon nanotubes by the chemical vapor deposition method. Thermogravimetric... more
Tailored pore size mesoporous silica, incorporating different concentrations of transition metal-based catalysts, has been used as platforms for the growth of carbon nanotubes by the chemical vapor deposition method. Thermogravimetric analysis alongside EDX/SEM was employed to characterize the samples prior to CNT growth. The CNTs produced were characterized using Raman Spectroscopy and HI RES SEM. Raman spectroscopy showed good quality highly graphitic CNTs whose diameters matched the corresponding pores of the matrices. The density of the CNTs was found to be high for higher metal concentrations for the same pore diameters. Fe and Co were found to be better catalysts for growth of CNTs than Ni.
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Materials: Ethylene oxide (all materials Sigma Aldrich unless stated) was dried over CaH 2 , purified through n-BuLi twice for 30 min at-10 0 C and was then distilled into an appropriately calibrated Pyrex ampule for use. Phosphazene base... more
Materials: Ethylene oxide (all materials Sigma Aldrich unless stated) was dried over CaH 2 , purified through n-BuLi twice for 30 min at-10 0 C and was then distilled into an appropriately calibrated Pyrex ampule for use. Phosphazene base (P 4-t-Bu) (1M solution in hexane), sec-BuLi (1.4 M solution in cyclohexane) and acetic acid (Panreac) were used without further purification. Benzene (Chem Lab, 99.7%) was freshly distilled from CaH 2 and polystyryl lithium (PS (+) Li (and and kept for further use. Styrene and dibutylmagnesium were purified through CaH 2 distillation and added to calibrated Pyrex ampules. Various other solvents/salts were used as detailed toluene, Tetrahydrofuran (THF), anhydrous alcohol (ETH), Dimethylformamide (DMF) and Lithium chloride. Single crystal (100) boron doped (P type) silicon wafers with a native silica layer were used as general substrates. Different hard mask substrates such as Si-ARC (anti-reflective coating), alumina and carbon hard mask (CHM) etc...
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Microphase separation is readily achieved in both PS-b-PEO diblock copolymer thin films and in PS homopolymer/PS-b-PEO polymer blends via solvent annealing. In situ synthesis of PS homopolymer with a symmetric PS-b-PEO diblock copolymer... more
Microphase separation is readily achieved in both PS-b-PEO diblock copolymer thin films and in PS homopolymer/PS-b-PEO polymer blends via solvent annealing. In situ synthesis of PS homopolymer with a symmetric PS-b-PEO diblock copolymer results in a cylindrical structure rather than a predicted lamellar morphology for the diblock due to the increased amount of PS present. Solvent annealing in toluene results in ordered structures of PEO cylinders orientated parallel to the substrate in the PS matrix. Solvent annealing in a mixed toluene/water environment creates an essentially ‘neutral’ solvent environment resulting in a perpendicular orientation. PS-b-PEO/PS thin films with cylinders orientated parallel have a smaller cylinder centre-to-cylinder centre spacing than films with cylinders orientated perpendicular due to the location to the PS homopolymer. If the molecular weight of the diblock is sufficiently low for a given Flory-Huggins parameter microphase separation will not occur...
This article describes for the first time the controlled monolayer doping (MLD) of bulk and nanostructured crystalline silicon with As at concentrations approaching 2x10^20 atoms cm-3. Characterization of doped structures after the MLD... more
This article describes for the first time the controlled monolayer doping (MLD) of bulk and nanostructured crystalline silicon with As at concentrations approaching 2x10^20 atoms cm-3. Characterization of doped structures after the MLD process confirmed that they remained defect and damage free, with no indication of increased roughness or a change in morphology. Electrical characterization of the doped substrates and nanowire test structures allowed determination of resistivity, sheet resistance and active doping levels. Extremely high As-doped Si substrates and nanowire devices could be obtained and controlled using specific capping and annealing steps. Significantly, the As-doped nanowires exhibited resistances several orders of magnitude lower than the pre-doped materials.
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Research Interests: Engineering, Materials Science, Electron Beam Lithography, Silicon, Nanomaterials, and 14 moreNanotechnology, Polymers, Medicine, Polymerization, Block Copolymer, Lithography, CHEMICAL SCIENCES, Electroplating, Aluminum oxide, Organosilicon Compounds, Block Copolymers, Commensurability, Solvents, and Volatilization
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... more
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 polystyren...
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Extending the resolution and spatial proximity of lithographic patterning below critical dimensions of 20 nm remains a key challenge with very-large-scale integration, especially if the persistent scaling of silicon electronic devices is... more
Extending the resolution and spatial proximity of lithographic patterning below critical dimensions of 20 nm remains a key challenge with very-large-scale integration, especially if the persistent scaling of silicon electronic devices is sustained. One approach, which relies upon the directed self-assembly of block copolymers by chemical-epitaxy, is capable of achieving high density 1 : 1 patterning with critical dimensions approaching 5 nm. Herein, we outline an integration-favourable strategy for fabricating high areal density arrays of aligned silicon nanowires by directed self-assembly of a PS-b-PMMA block copolymer nanopatterns with a L(0) (pitch) of 42 nm, on chemically pre-patterned surfaces. Parallel arrays (5 × 10(6) wires per cm) of uni-directional and isolated silicon nanowires on insulator substrates with critical dimension ranging from 15 to 19 nm were fabricated by using precision plasma etch processes; with each stage monitored by electron microscopy. This step-by-ste...
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Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate... more
Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce4+ ions by Eu3+ ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1–1 atom% due to the reduction of Ce4+ to Ce3+ and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7–8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons b...
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Films of self assembled diblock copolymers (BCPs) have attracted significant attention for generating semiconductor nanoarrays of sizes below 100 nm through a simple low cost approach for device fabrication. A challenging abstract is... more
Films of self assembled diblock copolymers (BCPs) have attracted significant attention for generating semiconductor nanoarrays of sizes below 100 nm through a simple low cost approach for device fabrication. A challenging abstract is controlling microdomain orientation and ordering dictated by complex interplay of surface energies, polymer-solvent interactions and domain spacing. In context, microphase separated poly (styrene-b-ethylene oxide) (PS-b-PEO) thin films is illustrated to fabricate nanopatterns on silicon and germanium materials trenches. The trenched templates was produced by simple electron beam lithography using hydrogen silsesquioxane (HSQ) resist. The orientation of PEO, minority cylinder forming block, was controlled by controlling trench width and varying solvent annealing parameters viz. temperature, time etc. A noticeable difference in microdomain orientation was observed for Si and Ge trenches processed under same conditions. The Ge trenches promoted horizontal ...
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A new enzyme-free sensor based on iron oxide (Fe3O4) nanodots fabricated on an indium tin oxide (ITO) substrate via a block copolymer template was developed for highly sensitive and selective detection of hydrogen peroxide (H2O2). The... more
A new enzyme-free sensor based on iron oxide (Fe3O4) nanodots fabricated on an indium tin oxide (ITO) substrate via a block copolymer template was developed for highly sensitive and selective detection of hydrogen peroxide (H2O2). The self-assembly-based process described here for Fe3O4 formation is a simple, cost-effective, and reproducible process. The H2O2 response of the fabricated electrodes was linear from 2.5 × 10-3 to 6.5 mM with a sensitivity of 191.6 μA mM-1cm-2 and a detection limit of 1.1 × 10-3 mM. The electrocatalytic activity of Fe3O4 nanodots toward the electroreduction of H2O2 was described by cyclic voltammetric and amperometric techniques. The sensor described here has a strong anti-interference ability to a variety of common biological and inorganic substances.
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Polymer brush films with chemical functionality to attach to site specific substrate areas are introduced for area selective deposition (ASD) application. It is demonstrated that polymer brushes with chemically defined end sites can be... more
Polymer brush films with chemical functionality to attach to site specific substrate areas are introduced for area selective deposition (ASD) application. It is demonstrated that polymer brushes with chemically defined end sites can be selectively bound to copper-specific regions of patterned copper/silica (Cu/SiO2 ) substrates. The process described overcomes various limitations of currently used technology including cost, complexity, and throughput, with potential implications for future electronic devices and nanomanufacturing. A comparative study of amine-terminated polystyrene and amine-terminated poly-2-vinyl pyridine polymer brushes (i.e., PS-NH2 and P2VP-NH2 ) with similar molecular weights display contrasting behavior on patterned Cu/SiO2 line features. Further, a thiol terminated poly-2-vinyl pyridine polymer brush (i.e., P2VP-SH) is investigated as a direct spin-on process to fabricate a metal oxide layer atop Cu areas only. The results presented here detail a novel metho...
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Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such... more
Nanostructured surfaces are common in nature and exhibit properties such as antireflectivity (moth eyes), self-cleaning (lotus leaf), iridescent colors (butterfly wings), and water harvesting (desert beetles). We now understand such properties and can mimic some of these natural structures in the laboratory. However, these synthetic structures are limited since they are not easily mass produced over large areas due to the limited scalability of current technologies such as UV-lithography, the high cost of infrastructure, and the difficulty in nonplanar surfaces. Here, we report a solution process based on block copolymer (BCP) self-assembly to fabricate subwavelength structures on large areas of optical and curved surfaces with feature sizes and spacings designed to efficiently scatter visible light. Si nanopillars (SiNPs) with diameters of ∼115 ± 19 nm, periodicity of 180 ± 18 nm, and aspect ratio of 2-15 show a reduction in reflectivity by a factor of 100, <0.16% between 400 an...
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The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the... more
The development of non-equilibrium group IV nanoscale alloys is critical to achieving new functionalities, such as the formation of a direct bandgap in a conventional indirect bandgap elemental semiconductor. Here, we describe the fabrication of uniform diameter, direct bandgap Ge1-xSnx alloy nanowires, with a Sn incorporation up to 9.2 at.%, far in excess of the equilibrium solubility of Sn in bulk Ge, through a conventional catalytic bottom-up growth paradigm using noble metal and metal alloy catalysts. Metal alloy catalysts permitted a greater inclusion of Sn in Ge nanowires compared with conventional Au catalysts, when used during vapour-liquid-solid growth. The addition of an annealing step close to the Ge-Sn eutectic temperature (230 °C) during cool-down, further facilitated the excessive dissolution of Sn in the nanowires. Sn was distributed throughout the Ge nanowire lattice with no metallic Sn segregation or precipitation at the surface or within the bulk of the nanowires. ...
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Solvo-thermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(D,L-lactide)... more
Solvo-thermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(D,L-lactide) (PS-b-PLA) BCP films using topographically patterned silicon nitride was demonstrated with alignment over macroscopic areas. Interestingly, we observed lamellar patterns aligned parallel as well as perpendicular (perpendicular microdomains to substrate in both cases) to the topography of the graphoepitaxial guiding patterns. PS-b-PLA BCP microphase separated with high a degree of order in an atmosphere of tetrahydrofuran (THF) at an elevated vapor pressure (at ca. 40-60°C). Grazing incidence small angle X-ray scattering (GISAXS) measurements of PS-b-PLA films reveals the through-film uniformity of perpendicular microdomains after STVA. Perpendicular lamellar orientation was observed on both hydrophilic and relatively hydrophobic surfaces with a dom...
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Block copolymers (BCPs) and their directed self-assembly (DSA) has emerged as a realizable complementary tool to aid optical patterning of device elements for future integrated circuit advancements. Methods to enhance BCP etch contrast... more
Block copolymers (BCPs) and their directed self-assembly (DSA) has emerged as a realizable complementary tool to aid optical patterning of device elements for future integrated circuit advancements. Methods to enhance BCP etch contrast for DSA application and further potential applications of inorganic nanomaterial features (e.g., semiconductor, dielectric, metal and metal oxide) are examined. Strategies to modify, infiltrate and controllably deposit inorganic materials by utilizing neat self-assembled BCP thin films open a rich design space to fabricate functional features in the nanoscale regime. An understanding and overview on innovative ways for the selective inclusion/infiltration or deposition of inorganic moieties in microphase separated BCP nanopatterns is provided. Early initial inclusion methods in the field and exciting contemporary reports to further augment etch contrast in BCPs for pattern transfer application are described. Specifically, the use of evaporation and sp...
Research Interests: Engineering, Microelectronics And Semiconductor Engineering, Inorganic Chemistry, Polymer Chemistry, Semiconductor Physics, and 9 moreSemiconductor Devices, Nanotechnology, Advanced Materials, Block Copolymer, Nanoscience, Physical sciences, polymer science and Engineering, CHEMICAL SCIENCES, and Patterning
Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow... more
Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow thin films to be rapidly deposited over a large range of surfaces including curved, flexible or plastic substrates without extensive processing of comparative vapour or physical deposition methods. To increase the effectiveness and versatility of dip-coated thin films, alterations to commonly used precursors can be made that facilitate controlled thin film deposition. The effects of polymer assisted deposition and changes in solvent-alkoxide dilution on the morphology, structure, optoelectronic properties and crystallinity of vanadium pentoxide thin films was studied using a dip-coating method using a substrate withdrawal speed within the fast-rate draining regime. The formation of sub-100 nm thin films could be achieved rapidly from dilute alkoxide b...
In this work we report how single crystal nanowires can be assembled into regular arrays using mesoporous thin films to define the architecture. Mesoporous thin films were prepared by a sol–gel method. These provide films of very regular... more
In this work we report how single crystal nanowires can be assembled into regular arrays using mesoporous thin films to define the architecture. Mesoporous thin films were prepared by a sol–gel method. These provide films of very regular structure and dimensions. The films produced in this way have almost single crystal like structures and can also exhibit strong epitaxy to the underlying silicon substrate. The films are subjected to a supercritical fluid (SCF) environment in which a precursor is decomposed to yield nanowires of metals, ...
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Research Interests: Materials Engineering, Biomedical Engineering, Biotechnology, Silicon, Nanotechnology, and 13 moreBlock Copolymer, Nanowires, Cell line, Humans, Neuroprosthetics, Nanoscience, Microelectrodes, Neurons, Materials Testing, Equipment Design, Cell Survival, Equipment Failure Analysis, and Electric Conductivity
In this work, we are reporting a very simple and efficient method to form lamellar structures of symmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer thin films with vertically (to the surface plane) orientated lamellae... more
In this work, we are reporting a very simple and efficient method to form lamellar structures of
symmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer thin films with
vertically (to the surface plane) orientated lamellae using a solvent annealing approach. The
methodology does not require any brush chemistry to engineer a neutral surface and it is the
block neutral nature of the film-solvent vapour interface that defines the orientation of the
lamellae. The microphase separated structure of two different molecular weight lamellar forming
PS-block-P4VP copolymer formed under solvent vapour annealing was monitored using atomic
force microscopy (AFM) so as to understand morphological changes of the films under different
solvent exposure. In particular, the morphology changes from micellar structures to well-defined
microphase separated arrangements. The choice of solvent/s (single and dual solvent exposure)
and the solvent annealing conditions (temperature, time etc.) had important effects on structural
transitions of the films and it was found that a block neutral solvent was required to realize
vertically aligned P4VP lamellae. The results of structural variation of the phase separated
nanostructured films through the exposure to ethanol are also described.
symmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymer thin films with
vertically (to the surface plane) orientated lamellae using a solvent annealing approach. The
methodology does not require any brush chemistry to engineer a neutral surface and it is the
block neutral nature of the film-solvent vapour interface that defines the orientation of the
lamellae. The microphase separated structure of two different molecular weight lamellar forming
PS-block-P4VP copolymer formed under solvent vapour annealing was monitored using atomic
force microscopy (AFM) so as to understand morphological changes of the films under different
solvent exposure. In particular, the morphology changes from micellar structures to well-defined
microphase separated arrangements. The choice of solvent/s (single and dual solvent exposure)
and the solvent annealing conditions (temperature, time etc.) had important effects on structural
transitions of the films and it was found that a block neutral solvent was required to realize
vertically aligned P4VP lamellae. The results of structural variation of the phase separated
nanostructured films through the exposure to ethanol are also described.