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We demonstrate the fabrication of sub-20 nm gate-all-around silicon (Si) nanowire field effect transistor structures using self-assembly. To create nanopatterned Si feature arrays, a block-copolymer-assisted hard mask approach was utilized using a topographically patterned substrate with well-defined Si3N4 features for graphoepitaxially alignment of the self-assembled patterns. Microphase-separated long-range ordered polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block-copolymer-derived dot and line nanopatterns were achieved by a thermo-solvent approach within the substrate topographically defined channels of various widths and lengths. Solvent annealing parameters (temperature, annealing time, etc.) were varied to achieve the desired patterns. The BCP structures were modified by anhydrous ethanol to facilitate insertion of iron oxide features within the graphoepitaxial trenches that maintained the parent BCP arrangements. Vertical and horizontal ordered Si nanowire structures within trenches were fabricated using the iron oxide features as hard masks in an inductively coupled plasma (ICP) etch process. Cross-sectional micrographs depict wires of persistent width and flat sidewalls indicating the effectiveness of the mask. The aspect ratios could be varied by varying etch times. The sharp boundaries between the transistor components was also examined through the elemental mapping.

We present a highly scalable, room-temperature strategy for fabricating vertical silicon nanotube arrays derived from a toroidal micelle pattern via a water vapor-induced block copolymer (BCP) self-assembly mechanism. A polystyrene-b-poly(ethylene oxide) (PS-b-PEO) BCP system can be self-assembled into toroidal micelle structures (diameter: 400-600 nm) on a PS-OH-modified substrate in a facile manner contrasting with other complex processes described in the literature. It was found that a minimum PS-b-PEO thickness of ∼86 nm is required for the toroidal self-assembly. Furthermore, a water vapor annealing treatment at room conditions (∼25 °C, 60 min) is shown to vastly enhance the ordering of micellar structures. A liquid-phase infiltration process was used to generate arrays of iron and nickel oxide nanorings. These oxide structures were used as templates for pattern transfer into the underlying silicon substrate via plasma etching, resulting in large-area 3D silicon nanotube arrays. The overall simplicity of this technique, as well as the wide potential versatility of the resulting metal structures, proves that such room-temperature synthesis routes are a viable pathway for complex nanostructure fabrication, with potential applicability in fields such as optics or catalysis.

The activity of silver nanomaterials as an antimicrobial is well-known with authors noting strong size and shape effects. This paper explores if the antimicrobial activity relates to unique size-related properties of the nanodimensioned materials or a more physical effect. Staphylococcus aureus and Pseudomonas aeruginosa were explored as test bacteria. They can cause serious human infections and are becoming resistant to pharmaceutical antimicrobials. Silver nanopatterns on a substrate surface were used as the antimicrobial agent. We demonstrate a cost-effective facile route to fabricate a well-ordered, periodic, and dimension-controlled silver lines and dots pattern on a substrate surface. This allowed precise definition of the silver materials to explore size and shape effects. Polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) microphase separated thin films were used as structural templates. Well-ordered PS-b-PEO thin film with vertical and parallel oriented PEO cylinders was achieved by a solvent vapor annealing approach through careful optimization of experimental parameters. A selective inclusion method (into one block of the BCP) of silver nitrate was used to generate the silver nanopatterns. Spin coating precursor-ethanol solution and subsequent UV/ozone treatment produce silver nanopattern arrays. They exhibited a significant growth-inhibitory effect on Staphylococcus aureus and Pseudomonas aeruginosa biofilms. However, data suggest this is associated with high surface area rather than a unique nanodimension related property change dictated by size or shape.

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.

Nanopatterns can readily be formed by annealing block copolymers (BCPs) in organic solvents at moderate or high temperatures. However, this approach can be challenging from an environmental and industrial point of view. Herein, we describe a simple and environmentally friendly alternative to achieve periodically ordered nanoscale phase separated BCP structures. Asymmetric polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin film patterns of different molecular weight were achieved by annealing in supercritical carbon dioxide (sc-CO2). Microphase separation of PS-b-PEO (16,000–5000) film patterns were achieved by annealing in scCO2 at a relatively low temperature was previously reported by our group. The effects of annealing temperature, time and depressurisation rates for the polymer system were also discussed. In this article, we have expanded this study to create new knowledge on the structural and dimensional evolution of nanohole and line/space surface periodicity of four other different molecular weights PS-b-PEO systems. Periodic, well defined, hexagonally ordered films of line and hole patterns were obtained at low CO2 temperatures (35–40 °C) and pressures (1200–1300 psi). Further, the changes in morphology, ordering and feature sizes for a new PS-b-PEO system (42,000–11,500) are discussed in detail upon changing the scCO2 annealing parameters (temperature, film thickness, depressurization rates, etc.). In relation to our previous reports, the broad annealing temperature and depressurisation rate were explored together for different film thicknesses. In addition, the effects of SCF annealing for three other BCP systems (PEO-b-PS, PS-b-PDMS, PS-b-PLA) is also investigated with similar processing conditions. The patterns were also generated on a graphoepitaxial substrate for device application., Data from publication: Nanomater. 2021, 11 (3), 669(1-15)

We present a highly scalable, room-temperature strategy for fabricating vertical silicon nanotube arrays derived from a toroidal micelle pattern via a water vapor-induced block copolymer (BCP) self-assembly mechanism. A polystyrene-b-poly(ethylene oxide) (PS-b-PEO) BCP system can be self-assembled into toroidal micelle structures (diameter: 400–600 nm) on a PS-OH-modified substrate in a facile manner contrasting with other complex processes described in the literature. It was found that a minimum PS-b-PEO thickness of ∼86 nm is required for the toroidal self-assembly. Furthermore, a water vapor annealing treatment at room conditions (∼25 °C, 60 min) is shown to vastly enhance the ordering of micellar structures. A liquid-phase infiltration process was used to generate arrays of iron and nickel oxide nanorings. These oxide structures were used as templates for pattern transfer into the underlying silicon substrate via plasma etching, resulting in large-area 3D silicon nanotube arrays. The overall simplicity of this technique, as well as the wide potential versatility of the resulting metal structures, proves that such room-temperature synthesis routes are a viable pathway for complex nanostructure fabrication, with potential applicability in fields such as optics or catalysis.

International audience; Area-selective deposition is a promising technique for positional self-alignment of materials at a prepatterned surface. Critical to this is the development of molecular systems that have selective surface binding and can act as templates to material growth. This paper reports how end functionalized polymers can be used to create oxide films through a grafting method. Here, we detail a facile approach for rapid grafting (in seconds) of polymer brush films with complete coverage over large areas with high uniformity (pinhole free). Subsequent conversion to an oxide (∼3–4 nm thickness) is performed via liquid-phase metal ion infiltration. Exposing the covalently grafted polymer brush (P2VP-OH) to a metal salt-solvent solution (using the Al3+ ion as a model species) swells the polymer, facilitating ion inclusion. Early results suggest that a solvent-mediated approach to polymer film infiltration can be used to develop inorganic films in a facile process. While data shows inclusion into both large-area and patterned films, the mechanism and understanding of these have been limited. In particular, the solution-mediated process described here shows the precise tailoring of nanometer-thin polymer films that are pinhole-free and that can be activated to create semiconductor-compatible oxide films that are parallel in quality to ALD- or CVD-derived processes. A surface deactivation strategy is also realized using a hydroxyl-terminated polystyrene (PS-OH) brush that prevents the deposition of ions. We consider this strategy as a means to prevent electromigration of ions as well as the possibility of coating ALD layers.

Block Copolymer (BCP) self-assembly has shown promise as a next generation nanolithography technology as their phase separation at a nanometre scale can overcome the limitations of conventional lithography. Here, we report on using an alternative method to conventional thermal and solvent annealing by exposing as-cast micellar polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin film to a mild argon plasma. Resulting films show controllable perpendicular and parallel (to the surface plane) orientations of a hexagonal phase forming PEO, depending on the morphology of the initial micelle shape. The ability to define orientation is a critical advantage because complex solvent or substrate control is usually needed. This method is a fast process, that could help to reduce thermo-solvent annealing time (hours) to few seconds, while allowing phase separation on large and industrial substrates. Further, etching is also realized during the plasma exposure. We discuss the balance between the energy input of the argon plasma leading to large-scale surface reorganisation, and the possible damage of the surface due to cross-linking and/or etching.

Hexagonally arranged dense monodispersed iron oxide, cobalt oxide and cobalt iron oxide nanoparticle arrays are generated using block copolymer (BCP) inclusion methodology on substrate. Polystyrene-b-poly(ethylene oxide) (PS-b-PEO) BCP nanopatterns forming perpendicularly oriented PEO cylinders is used as a structural template. The PEO microdomains are modified by ethanol which selectively incorporate metal ions through chemical coordination. The formation of oxides and composites and removal of polymers is performed by UV/Ozone treatment. The precursor-solution concentrations and aging time are tuned to create uniform diameter, ordered monodispersed nanoparticles. The stability of the oxides is investigated by high temperature calcination. XPS reveals the phases of as-prepared oxides and after annealing. The cation distribution is determined for the nanocomposite, from curve fitted Co 2p and Fe 2p spectra, (Co0.4Fe0.6)[Co0.6Fe1.4]O4 corresponds to cobalt ferrite, CoFe2O4 represent cations in tetrahedral and octahedral sites respectively. The diameter, height, defectivity of nanoparticle arrays for all the oxides are examined.

The use of a low-χ, symmetric block copolymer as an alternative to the high-χ systems currently being translated towards industrial silicon chip manufacture has been demonstrated. Here, the methodology for generating on-chip, etch resistant masks and subsequent pattern transfer to the substrate using ultra-small dimension, lamellar, microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) is described. Well-controlled films of a perpendicularly oriented lamellar pattern with a domain size of ∼8 nm were achieved through amplification of an effective interaction parameter (χeff) of the BCP system. The self-assembled films were used as ‘templates’ for the generation of inorganic oxides nanowire arrays through selective metal ion inclusion and subsequent processing. Inclusion is a significant challenge because the lamellar systems have less chemical and mechanical robustness than the cylinder forming materials. The oxide nanowires of uniform diameter (∼8 nm) were isolated and their structure mimics the original BCP nanopatterns. We demonstrate that these lamellar phase iron oxide nanowire arrays could be used as a resist mask to fabricate densely packed, identical ordered, good fidelity silicon nanowire arrays on the substrate. Possible applications of the materials prepared are discussed, in particular, in the area of photonics and photoluminescence where the properties are found to be similar to those of surface-oxidized silicon nanocrystals and porous silicon.

One-dimensional nanostructures with controllable morphologies and defects are appealing for use in nanowire devices. This paper details the influence of colloidal magnetite iron oxide nanoparticle seeds to regulate the radial dimension and twin boundary formation in Ge nanowires grown through a liquid-injection chemical vapor deposition process. Control over the mean nanowire diameter, even in the sub-10 nm regime, was achieved due to the minimal expansion and aggregation of iron oxide nanoparticles during the growth process. The uncommon occurrence of heterogeneously distributed multiple layer {111} twins, directed perpendicular to the nanowire growth axis, were also observed in 〈111〉-directed Ge nanowires, especially those synthesized from patterned hemispherical Fe3O4 nanodot catalysts. Consecutive twin planes along 〈111〉-oriented nanowires resulted in a local phase transformation from 3C diamond cubic to hexagonal 4H allotrope. Localized polytypic crystal phase heretostructures were formed along 〈111〉-oriented Ge nanowire using magnetite nanodot catalysts.

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 orientations compared to Si due to difference in surface properties without any prior surface treatments. This methodology allows to create Ge nanopatterns for device fabrication since native oxides on Ge often induce patterning challenges. Subsequently, a selective metal inclusion method was used to form hardmask nanoarrays to pattern transfer into those substrates through dry etching. The hardmask allows to create good fidelity, low line edge roughness (LER) materials nanopatterns.

A simple method to fabricate well-defined silver nanodots of different sizes using self-assembled polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer was developed. The most well-defined nanodot patterns were observed using optimal concentrations of silver precursor (0.4, 0.6, and 1.2%) with average sizes of 10, 18, and 28 nm by different molecular weights of PS-b-PEO. Silver nanodot patterns were not observed at higher Ag precursor concentrations. In addition, after repeated depositions, the antimicrobial activity (AA) towards bacteria increased compared to well-defined nanodot arrangements. The AA of the silver nanodots was significantly affected by the concentration used independent of the particle size of the silver nanodots. Potentially, silver nanodots can be used as antimicrobial packaging application to preserve the quality of food products due to the data generated here demonstrated that these materials significantly delayed the growth of Pseudomonas fluorescens and Staphylococcus aureus. Industrial relevance Food wastage is a significant cost to industry and society as a whole and impacts all stages of the food distribution cycle from transport and storage to shelf life and end-consumer use. Antimicrobial packaging could significantly decrease product decomposition and add value for producers by preserving product shelf life. Metal-based nanoparticles (NPs) (especially Ag) have previously been identified as potential antimicrobials but their performance is dependent on factors such as size and shape, concentration, morphology, composition and crystallinity. Their use in packaging has been limited partly by issues such as size control, powder handling, surface attachment and application to polymer films which can be challenging. We developed a novel method for generating antimicrobial surfaces based around the self-assembly of a polystyrene-b-polyethylene (PS-b-PEO) block copolymer that is a simple, effective and efficient method for generating highly uniform size and shape defined NPs (as nanodots) on a surface in a well-defined arrangement without the need of expensive lithographic techniques. The developed silver nanodot surfaces exhibited good antimicrobial activity against Gram-positive and Gram-negative bacteria and potentially can be used in antimicrobial packaging applications.

Thin films of block copolymers (BCPs) are widely accepted as potentially important materials in a host of technological applications including nanolithography. In order to induce domain separation and form well-defined structural arrangements, many of these are solvent-annealed (i.e. solvent swollen) at moderate temperatures. The use of solvents can be challenging in industry from an environmental point of view as well as having practical/cost issues. However, a simple and environmentally friendly alternative to solvo-thermal annealing for the periodically ordered nanoscale phase separated structures is described herein. Various asymmetric polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin films were annealed in a compressible fluid, supercritical carbon dioxide (scCO2), to control nanodomain orientation and surface morphologies. For the first time, periodic well defined, hexagonally ordered films with sub-25 nm pitch size were demonstrated using a supercritical fluid (SCF) process at low temperatures and pressures. Predominant swelling of PEO domains in scCO2 induces nanophase separation. scCO2 serves as green alternative to the conventional organic solvents for the phase segregation of BCPs with complete elimination of any residual solvent in the patterned film. The depressurization rate of scCO2 following annealing was found to affect the morphology of the films. The supercritical annealing conditions could be used to define nanoporous analogues of the microphase separated films without additional processing, providing a one-step route to membrane like structures without affecting the ordered surface phase segregated structure. An understanding of the BCP self-assembly mechanism can be realized in terms of the deviation in glass transition temperature, melting point, viscosity, interaction parameter and volume fraction of the constituent blocks in the scCO2 environment.

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 luminescent due to the substitution of Ce4+ ions in the cubic symmetric lattice by the dopant ions. The thermal stability of the fluorescence properties was also investigated.

A simple technique is demonstrated to fabricate horizontal, uniform, and hexagonally arranged Sinanowire arrays with controlled orientation and density at spatially well defined locations on a substrate based on an in situ hard-mask pattern-formation approach by microphase-separated block-copolymer thin films. The technique may have significant application in the manufacture of transistor circuitry.

This Article presents a simple methodology for the fabrication of two-dimensional arrays of lead zirconate titanate (PZT) nanodots on n-doped Si substrates via the directed self-assembly of PS-b-PEO block copolymer templates. The approach produces highly ordered PZT nanodot patterns, with lateral widths and heights as small as 20 and 10 nm, respectively, and a coverage density as high as ∼68 × 109 nanodots cm–2. The existence of a perovskite phase in the nanodots was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The piezo-amplitude and ferroelectric domain response obtained from the nanodots, through piezoresponse force microscopy, confirmed the presence of ferroelectricity in the PZT arrays. Notably, PZT nanodots with a thickness ∼10 nm, which is close to the critical size limit of PZT, showed ferroelectric behavior. The presence of a multi-a/c domain structure in the nanodots was attributed to their polycrystalline nature.

Fluorescent silica nanoparticles (NPs) have potential in biomedical applications as diagnostics and traceable drug delivery agents. In this study, we have synthesized fluorescent dye grafted silica NPs in two step process. First, a stable method to synthesize various sizes of silica NPs ranging from 20 to 52, 95, 210 and 410 nm have been successfully demonstrated. Secondly, as-synthesized silica NPs are readily grafted with some fluorescent dyes like IR-820 and fluorescein isothiocyanate (FITC) dyes by simple impregnation method. IR-820 and FITC dyes are ‘activated’ by (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)triethoxysilane (APTS) respectively prior to the grafting on silica NPs. UV–vis spectroscopy is used to test the stability of dye grafted silica NPs. The fluorescent dye grafted silica NPs are quite stable in aqueous solution. Also, a new type of dual dye-doped hybrid silica nanoparticles has been developed. The combination of microscopic and spectroscopic techniques shows that the synthesis parameters have significant effects on the particle shape and size and is tuneable from a few nanometers to a few hundred nanometers. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging.

Our goal is to develop a facile process to create patterns of inorganic oxides and metals on a substrate that can act as hard masks. These materials should have high etch contrast (compared to silicon) and so allow high-aspect-ratio, high-fidelity pattern transfer whilst being readily integrable in modern semiconductor fabrication (FAB friendly). Here, we show that ultra-small-dimension hard masks can be used to develop large areas of densely packed vertically and horizontally orientated Si nanowire arrays. The inorganic and metal hard masks (Ni, NiO, and ZnO) of different morphologies and dimensions were formed using microphase-separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films by varying the BCP molecular weight, annealing temperature, and annealing solvent(s). The self-assembled polymer patterns were solvent-processed, and metal ions were included into chosen domains via a selective inclusion method. Inorganic oxide nanopatterns were subsequently developed using standard techniques. High-resolution transmission electron microscopy studies show that high-aspect-ratio pattern transfer could be affected by standard plasma etch techniques. The masking ability of the different materials was compared in order to create the highest quality uniform and smooth sidewall profiles of the Si nanowire arrays. Notably good performance of the metal mask was seen, and this could impact the use of these materials at small dimensions where conventional methods are severely limited.

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 copolymers formed under solvent vapour annealing was monitored using atomic force microscopy (AFM) so as to understand the morphological changes of the films upon 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.) has 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 the structural variation of the phase separated nanostructured films through the exposure to ethanol are also described.

Nanoparticles of the cubic phase of zirconia (ZrO2) of size range 4.5–8.7 nm have been synthesized by alkaline hydrolysis of a zirconium salt followed by solvothermal reaction. Subsequently, the room-temperature stability of cubic ZrO2nanoparticles has been explored with the goal of understanding how crystal structure tends to transform into a structure of higher symmetry with decreasing crystallite size. The room-temperature-stable cubic phase in nanosized ZrO2has been observed to transform into the monoclinic phase at 873 K. The crystalline phases of ZrO2nanocrystals have been determined quantitatively by Rietveld refinement. Lattice constant and internal strain increase with decreasing particle size. Growth kinetics studies have established that cubic nanocrystals are more stable at smaller crystallite sizes. UV–visible absorption spectra show an absorption peak at 275 nm which indicates a lowering of the band gap energy. Photoluminescence spectra of zirconia nanoparticles show an emission peak at 305 nm at room temperature. The modification of the optical properties is explained on the basis of oxygen vacancies present within the samples.

Cadmium hydroxide (Cd(OH)2) and cadmium oxide (CdO) nano and micro crystals were synthesized in ethanol–water medium using cadmium foil both as a source and substrate under solvothermal condition. Different concentrations of ammonium hydroxide, hydrazine hydrate, sodium hydroxide and potassium hydroxide were added to study the structural and morphological variations in the products. Synthesis was carried out at different temperatures to study the growth stages of the nano/microstructures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The as-prepared Cd(OH)2 products were transformed to CdO by thermal treatment in air. The possible growth mechanism for the formation of different morphologies at different basic medium has been proposed. The optical absorption measurement was carried out to determine the values of the band gap of CdO.

Microcages and nanowires of InN were synthesized by ammonification of an indium precursor in the temperature range 650―700 °C. The phases of the ammonified products were identified through X-ray diffraction (XRD). Morphology and crystal structure of the samples were determined through field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) analysis. The thermal behavior of the precursor and synthesized InN powder was investigated using thermogravimetric analysis (TGA). The growth mechanism for the formation of different morphologies at various experimental conditions is explained on the basis of diffusion and vapor-solid process following least action principle. Large blue shift (1―1.5 eV) in the apparent band gap was observed with the increase of reaction time. The contributions of refractive index and the existence of three simultaneous direct transitions at 0.8, 1, 1.4 eV were identified from the optical absorption spectra. Electrical measurements were carried out to obtain a band gap of 1.25 eV in the sample.

Bipyramidal-shaped single crystalline nanocones of ZnO, doped with Mn2+ ions up to different concentrations, were synthesized through a solvothermal route and characterized by X-ray diffraction and transmission electron microscopy. The compositional analysis was also carried out by energy-dispersive analysis of X-rays (EDAX). Positron annihilation studies were carried out to extract information on the vacancy-type defect clusters and their evolution under doping, which may have a major influence on the physical properties of the material. In the undoped ZnO, trivacancy-type defects of the type VZn+O+Zn are present. Doping by Mn2+ ions reduced them to divacancies (VZn+O) as a result of the ion-vacancy complex formation. These were indicated by the measured positron lifetimes and coincidence Doppler broadening measurements. An interesting observation is the reduction in base diameters of the nanocones at high (>1 atom %) dopant concentrations, an effect of increased strain due to occupancy of Zn2+ vacancy s...

Cadmium oxide (CdO) micro-octahedrons and nanowires were synthesized by a simple solvothermal process using ethanol as a solvent. The amount of NaOH and the synthesis temperature were the key parameters to control the phase and morphology of the as-synthesized products. The phase purity of the samples was determined through X-ray diffraction (XRD). Lower concentration of NaOH and higher-synthesis temperature favored the formation of CdO micro/nanostructures. Morphologies of the products were identified through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At higher temperature and low NaOH concentrations, nanowires were protruded from the octahedron facets. HRTEM images and SAED patterns reveal the single-crystalline nature of the octahedrons and polycrystalline nature of the nanowires. Cd(OH)2 samples, obtained at low synthesis temperature, were annealed at different temperatures to test the feasibility of the products to transform to CdO. Positron annihilation measuremen...

Metal/semiconductor core/shell radial heterostructured coaxial nanowires are reported for the first time. The radial coaxial nanowires consisted of a crystalline metallic Ag core and semiconducting amorphous Si shell. The Ag core nanowire growth was guided by the gold-catalyst-assisted vapor−liquid−solid process, whereas the amorphous Si shell formation could be attributed to the surface diffusion of the Si species through the liquid Au droplets to the nanowire surface.

Ellipsoidal and prism shaped ZnO nanocrystals with hexagonal cross-sections have been synthesized by a simple solvothermal process. The ellipsoidal ZnO nanocrystals possessed a unique hexagonal cross-section having two sharp pointed ends and a flattened central part. The well faceted prism like particles resembled hexagonal cones in their shape. Dimensions of the nanocrystals increased systematically with the increase in the synthesis temperature. The synthesized nanocrystals exhibited near band edge UV emission centered at ∼400 nm. An additional defect related green emission band at ∼500 nm was observed from the samples synthesized at higher temperatures.

Nanowire arrays of cubic zinc sulfide are synthesized on zinc foil by a simple thermal evaporation route at relatively low temperature (

Uniform as well as flower like patterns of SnS2 nanoflakes were produced by a thermal evaporation process. Interpenetrating phenomenon was observed between the individual nanoflakes during the course of their lateral growth. The interpenetrating growth and controlled vapor concentration as well as the substrate temperature leads to the formation of flower like assemblies of SnS2 nanoflakes. Morphology and growth mechanism of the nanostructures were studied by scanning electron microscopic observations at different stages of the nanoflake growth. The produced nanoflakes were characterized by X-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopic measurements. SnS2 nanoflakes were perfectly single crystalline and growth direction of the nanoflakes was along the {101}-lattice plane.

Cd(OH) 2 and CdO nano/micro crystals were synthesized in ethanol–water medium using cadmium foil as a source under solvothermal condition. The experimental parameters such as ratio of ethanol to water, concentration of NaOH and synthesis temperature all play important role in determining the size, shape and crystalline phase of the products. The products were characterized by X-ray diffraction and scanning electron microscopy. Nano/micro crystals of CdO were also achieved by thermal treatment of Cd(OH) 2 crystals in air at different temperatures.

Wurtzite GaN nanowires and nanoribbons were produced directly from Ga metal by an Au catalyst assisted thermal evaporation process in a flowing ammonia atmosphere. We have investigated the effect of different experimental parameters on the morphology of the nanoforms. The diameters of the nanowires were varied between 20 and 40 nm while the widths of the nanoribbons were within 100–250 nm. Microstructural studies by TEM reveals the role of vapor–liquid–solid process in the nucleation of GaN nanoforms. The evolution of the ribbon like morphology was attributed to the vapor–solid process. Photoluminescence study showed UV–blue emission from the GaN nanostructures. Field emission studies indicated the possibility of these materials to be used as the cathode materials in field emission based devices.

We report a noninvasive optical technique based on micro-Raman spectroscopy to study the temperature-dependent phonon behavior of normal (nondefective) and twinned germanium nanowires (Ge-NWs). We studied thermophysical properties of Ge-NWs from Raman spectra, measured by varying excitation laser power at ambient condition. We derived the laser-induced temperature rise during Raman measurements by analyzing the Raman peak position for both the NWs, and for a comparative study we performed the same for bulk Ge. The frequency of the Ge-Ge phonon mode softens for all the samples with the increase in temperature, and the first-order temperature coefficient (χT) for defected NWs is found to be higher than normal NWs and bulk. We demonstrated that apart from the size, the lamellar twinning and polytype phase drastically affect the heat transport properties of NWs.

Block copolymer (BCP) self-assembly is a low-cost means to nanopattern surfaces. Here, we use these nanopatterns to directly print arrays of nanodots onto a conducting substrate (Indium Tin Oxide (ITO) coated glass) for application as an electrochemical sensor for ethanol (EtOH) and hydrogen peroxide (H2O2) detection. The work demonstrates that BCP systems can be used as a highly efficient, flexible methodology for creating functional surfaces of materials. Highly dense iron oxide nanodots arrays that mimicked the original BCP pattern were prepared by an ‘insitu’ BCP inclusion methodology using poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO). The electrochemical behaviour of these densely packed arrays of iron oxide nanodots fabricated by two different molecular weight PS-b-PEO systems was studied. The dual detection of EtOH and H2O2 was clearly observed. The as-prepared nanodots have good long term thermal and chemical stability at the substrate and demonstrate promising electrocatalytic performance.

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 sputtering methods, atomic layer deposition, sequential infiltration synthesis, metal-salt inclusion and aqueous metal reduction methodologies forming isolated nanofeatures are highlighted in di-BCP systems. Functionalities and newly reported uses for electronic and non-electronic technologies based on the inherent properties of incorporated inorganic nanostructures using di-BCP templates are highlighted. We outline the potential for extension of incorporation methods to triblock copolymer features for more diverse applications. Challenges and emerging areas of interest for inorganic infiltration of BCPs are also discussed.

Ultra-small feature size (∼8 nm domain width) nanopatterns have been achieved using a symmetric polystyrene-b-polyethylene oxide (PS-b-PEO) block copolymer (BCP) of low molecular weight (PS and PEO blocks of 5.5 and 5.3 kg mol−1 respectively). The work represents the smallest feature size attained and the first observation of a well-controlled film of a perpendicularly oriented lamellar pattern in thin film form for this system. The polymer synthesized and described herein has a value χN (=7.7), below the expected BCP phase segregation limit of 10.5. These patterns were achieved by amplification of the effective interaction parameter (χeff) of the BCP system by the addition of lithium chloride (LiCl) salt. A model where the Li+ ions strongly coordinate with the PEO block without affecting the PS chain is proposed to explain the ordered self-assembly. The morphological and structural evolution for these PS-b-PEO/LiCl thin films was investigated by variation of the experimental parameters such as temperature, annealing time, salt concentrations, solution aging time, annealing solvent etc. All the experimental parameters have significant effects on the morphology, domain spacing, defectivity or surface roughness of these symmetric BCP thin films as evident from different microscopic and spectroscopic techniques. Possible hard mask applications in the area of lithography are demonstrated.

ZnO doughnutlike cluster particles were prepared by a simple solvothermal route using an ethylene glycol (EG)−water solvent system. It was observed that ZnO doughnuts were obtained when an equal or higher volume fraction of EG was used in the solvent. Microstructural studies revealed that these doughnut-shaped particles were clusters of small hexagonal plates arranged in a regular fashion. Because of the capping property of EG, these constituent hexagonal plates arranged in an angular oriented attachment scheme with a view to minimize their surface energies. The resulting assemblies were concave from one side and convex from the reverse side. With the increasing percentage of EG, the concentration of the capping element increased, resulting in the reduction of the size of the constituent plates, which in turn helps the formation of more and more densely packed ZnO doughnuts. Increases in temperature and pressure also favor the formation of densely packed ZnO doughnuts. These ZnO samples exhibited a strong...

Hexagonal cones and columns of ZnO were synthesized by solvothermal process with their diameters ranging from the nanometer to micrometer scale. All the nano/micro structures were perfectly single crystalline. Morphological control over the products was achieved by varying the composition of the ethanol–water system used as the solvent as well as its pH level. The ZnO nano/micro crystals were found to have wurtzite crystal structure. The optical absorbance and photoluminescence spectra of all the samples showed excitonic character at room temperature indicating excellent crystal quality of the products.

Metallic Zn and Cd nanowires were produced by a simple thermal evaporation process using their respective sulfide powders as the precursors. Metallic nanowires were found to be of pure phase without the presence of any sulfide or oxide phases. These nanowires were single crystalline. Diameters of both the Zn and Cd nanowires varied within 100–150 nm and their lengths were approximately a few micrometers. Crystal structure, phase and chemical purity of the nanowires were characterized by XRD and EDAX. The morphology and crystallinity of the products were revealed by SEM and TEM studies.

Helium ion microscopy (HIM) has been used to study nanopatterns formed in block copolymer (BCP) thin films. Owing to its’ small spot size, minimal forward scattering of the incident ion and reduced velocity compared to electrons of comparable energy, HIM has considerable advantages and provides pattern information and resolution not attainable with other commercial microscopic techniques. In order to realize the full potential of BCP nanolithography in producing high density ultra-small features, the dimensions and geometry of these BCP materials will need to be accurately characterized through pattern formation, development and pattern transfer processes. The preferred BCP pattern inspection techniques (to date) are principally atomic force microscopy (AFM) and secondary electron microscopy (SEM) but suffer disadvantages in poor lateral resolution (AFM) and the ability to discriminate individual polymer domains (SEM). SEM suffers from reduced resolution when a more surface sensitive low accelerating voltage is used and low surface signal when a high accelerating voltage is used. In addition to these drawbacks, SEM can require the use of a conductive coating on these insulating materials and this reduces surface detail as well as increasing the dimensions of coated features. AFM is limited by the dimensions of the probe tip and a skewing of lateral dimension results. This can be eliminated through basic geometry for large sparse features, but when dense small features need to be characterized AFM lacks reliability. With this in mind, BCP inspection by HIM can offer greater insight into block ordering, critical dimensions and, critically, line edge roughness (LER) a critical parameter whose measurement is well suited to HIM because of its’ enhanced edge contrast. In this work we demonstrate the resolution capabilities of HIM using various BCP systems (lamellar and cylinder structures). Imaging of BCP patterns of low molecular weight (MW)/low feature size which challenges the resolution of HIM technique. Further, studies of BCP patterns with domains of similar chemistry will be presented demonstrating the superior chemical contrast compared to SEM. From the data, HIM excels as a BCP inspection tool in four distinct areas. Firstly, HIM offers higher resolution at standard imaging conditions than SEM. Secondly, the signal generated from He+ is more surface sensitive and enables visualization of features that cannot be resolved using SEM. Thirdly; superior chemical contrast enables the imaging of un etched samples with almost identical chemical composition. Finally, dimensional measurement accuracy is high and consistent with requirements for advanced lithographic masks.

Cylindrical phase polystyrene-b-polyethylene oxide (PS-b-PEO) block copolymer (BCP) was combined with lower molecular weight poly/ethylene glycols at different concentrations and their effect on the microphase separation of BCP thin films were studied. Well-ordered microphase separated, periodic nanostructures were realized using a solvent annealing approach for solution cast thin films. By optimizing solvent exposure time, the nature and concentration of the additives etc. the morphology and orientation of the films can be controlled. The addition of the glycols to PS-b-PEO enables a simple method by which the microdomain spacing of the phase separated BCP can be controlled at dimensions below 50 nm. Most interestingly, the additives results in an expected increase in domain spacing (i.e. pitch size) but in some conditions an unexpected reduction in domain spacing. The pitch size achieved by modification is in the range of 16-31 nm compared to an unmodified BCP system which exhibits a pitch size of 25 nm. The pitch size modification achieved can be explained in terms of chemical structure, solubility parameters, crystallinity and glass transition temperature of the PEO because the additives act as PEO 'stress cracking agents' whereas the PS matrix remains chemically unaffected.

This paper outlines alternative uses of block copolymer (BCP) patterning compared to their well-researched exploitation in defining silicon circuitry and interconnects. The challenge in these alternative applications is usually to define ‘active’ patterns of materials other than silicon and instead of using the self-assembled block copolymer pattern as a means to form an on-chip etch mask, to use it as a template for deposition of functional components. In this paper we briefly discuss progress in the field of block copolymer patterning and some potential applications. The paper will then outline two examples in the area of sensing and antimicrobial surfaces. Here, polystyrene-b-polyethylene oxide (PS-b-PEO) is used as a suitable template as it forms well-ordered arrangements on several substrate types. The PEO block can then be used as a host block towards precursor inclusion from solution because of its’ selective chemistry. Onward processing then creates a pattern of included materials that mimics the original BCP arrangement. To demonstrate the potential of these methods we illustrate examples as sensors and antimicrobial surfaces which both take advantage of the small feature size, high surface area and coverage that can be attained by these techniques.

Nanocrystalline samples of nickel oxide were synthesized through solvothermal and sol-gel routes, and the grain sizes were determined through x-ray diffraction and transmission electron microscopy. Fourier transform infrared, optical absorption and positron annihilation spectroscopy studies were done to characterize them further and study the defects at nanoscale. The onset of quantum confinement effects is indicated by characteristic blue-shift in optical absorption spectra and widening of the band gap. Positron annihilation parameters changed as a result and the causes are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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 Ce(4+) ions by Eu(3+) 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 Ce(4+) to Ce(3+) 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 before annihilation. Coincidence Doppler broadening measurements indicated the annihilation of positrons with electrons of different species of atoms and the characteristic S-W plot showed a kink-like feature at the particle sizes where quantum confinement effects began.

A novel, simple and in situ hard mask technology that can be used to develop high aspect ratio silicon nanopillar and nanowire features on a substrate surface is demonstrated. The technique combines a block copolymer inclusion method that generates nanodot arrays on substrate and an inductively coupled plasma (ICP) etch processing step to fabricate Si nanopillar and nanowire arrays. Iron oxide was found to be an excellent resistant mask over silicon under the selected etching conditions. Features of a very high aspect ratio can be created by this method. The nanopillars have uniform diameter and smooth sidewalls throughout their entire length. The diameter (15-27 nm) and length of the nanopillars can be tuned easily. Different spectroscopic and microscopic techniques were used to examine the morphology and size, surface composition and crystallinity of the resultant patterns. The methodology developed may have important technological applications and provide an inexpensive manufacturing route to nanodimensioned topographical patterns. The high aspect ratio of the features may have importance in the area of photonics and the photoluminescence properties are found to be similar to those of surface-oxidized silicon nanocrystals and porous silicon.