Engineering of structures, materials and devices with important nanoscale dimensions.
Fabrication of small structures from deposited, patterned surface films. A structural layer can be built on a sacrificial layer and released by selective removal of that support while retaining anchors. Film thickness sets a vertical dimension; residual stress, access to the sacrificial material and release-induced stiction require separate control.
A temporary material supporting another structure during fabrication, then removed selectively. In an oxide-supported polysilicon beam, selective oxide removal makes an air gap while protected substrate contacts retain anchors. Removal must reach beneath the structure without destroying it; a purely vertical etch may not release a lateral overhang.
Selective removal of a sacrificial layer using gaseous reactants rather than a bulk liquid bath. A compatible vapor-phase oxide etch can avoid the liquid drying step responsible for one form of stiction. Selectivity, byproducts, humidity and access to the undercut region still matter.
Replication of a patterned master into a deformable or curable material to define nanoscale features. A subsequent filling, etching or transfer step can turn the replicated geometry into a functional structure. Master defects, residual layers, shrinkage and release damage must be controlled in repeated large-area fabrication.
Organization of interacting building blocks into a structure through their own dynamics under specified environmental conditions. A useful description states the components, interactions, environment and reversible transport/rearrangement mechanisms. A favourable thermodynamic equilibrium structure can still fail to form if aggregation or glassy arrest prevents defect correction.
A molecular layer formed through adsorption and lateral organization at a substrate. Anchoring groups, chain packing and exposed terminal chemistry jointly determine its properties. Hydroxyl-terminated alkanethiol films on gold provide a nonbiological example with controllable water wetting.
A structure whose relevant features have nanometre-scale dimensions.
A particle with dimensions on the nanometre scale.
Deposition of clusters produced in a gas-phase aggregation source. Source conditions control the size distribution, and optional mass selection narrows it. Landing energy and substrate interactions can change the structure delivered to a surface.
A nanoparticle formed from several crystallographic domains joined by twin boundaries. Low-energy external facets can compensate the internal boundary and elastic-strain cost; fivefold motifs cannot extend as an unstrained periodic bulk crystal.
A multiply twinned particle containing twenty approximately tetrahedral domains around a common centre. Its idealized exterior has twenty triangular facets; surface-energy reduction competes with strain and twin-boundary costs.
A fivefold-twinned particle with five approximately tetrahedral domains sharing an axis. Five ideal fcc tetrahedral wedge angles leave an angular deficit of about , accommodated by strain and defects.
Formation of particles or films by delivering precursor droplets into a heated environment where solvent evaporation and precursor decomposition occur. Drying and reaction within droplets can produce dense or porous particles.
A nanoscale particle containing two metallic elements. Spatial arrangements include disordered alloys, chemically ordered alloys, core-shell structures and segregated domains; composition alone does not specify the arrangement.
A processable dispersion of nanoparticles with a solvent and any stabilizers or binders. For a metallic printed conductor, drying, ligand removal and consolidation must turn the deposited particles into a connected low-resistance structure without damaging the substrate.
Directional plasma etching used for deep, high-aspect-ratio features. Alternating fluorine-based silicon etching and sidewall passivation is one implementation; transport, mask erosion, charging, scallops and aspect-ratio-dependent etch rate constrain the achievable structure.
An elongated structure with nanoscale transverse dimensions. Crystal structure, growth direction, sidewall facets and surface chemistry determine its properties and morphology.
A solution route in which a polyol serves as solvent and reducing medium for metal nucleation and growth. For silver wires, controlled seed structure and capping chemistry can favour axial growth. Temperature, reduction rate, seed population, halides, oxygen and ligand coverage act together; the method is not defined by a single universal recipe.
A high-aspect-ratio silver structure with nanoscale cross section. Low intrinsic metal resistivity and sparse network connectivity make such wires useful for flexible transparent conductors, but nanowire junction resistance, insulating ligands, tarnish and mechanical connectivity can dominate device performance.
A silver wire composed of five twinned fcc domains around its axis, commonly with a pentagonal cross section. Sidewall passivation and atom addition at ends can favour one-dimensional growth from a multiply twinned seed. Cross-sectional microscopy and diffraction are stronger evidence for this structure than the outer wire outline alone.[ref]
Polyol Synthesis of Uniform Silver Nanowires: A Plausible Growth Mechanism and the Supporting Evidence by Yugang Sun and others. Microtomed cross sections and fivefold-twin evidence
Growth by direct incorporation of vapour-derived species into a solid, without the defining liquid reservoir of vapor–liquid–solid growth. It can thicken a nanowire sidewall during tip growth.
Growth in which vapour supplies a liquid catalyst or reservoir and solid material precipitates at its interface. A cooled solid catalyst residue need not reproduce the liquid growth state.
A crystalline particle with nanoscale dimensions. Its shape and growth kinetics depend on exposed interfaces, defects and material supply, not just its bulk crystal structure.
Addition or rearrangement of material in a nanocrystal. Solute addition, Ostwald ripening and oriented attachment are distinct mechanisms that can coexist.
Preferential adsorption of charged species onto particular crystal faces, reducing their normal incorporation rates. Both solution speciation and actual surface charge matter; crystallographic polarity alone does not fix adsorption selectivity.
Selection of unequal growth along otherwise equivalent directions, through defects, selective adsorption, kinetics or external asymmetry. A lower-symmetry shape need not imply a different bulk lattice.
Joining of crystallites after compatible crystallographic alignment. Elimination of exposed interface drives the process; incomplete rotation and healing can leave defects.
Growth by incorporation of dissolved individual atoms, ions or molecular units into a crystal, driven by supersaturation and limited by transport or attachment kinetics.
Removal of material with a focused ion beam, for example to prepare a thin transmission electron microscopy specimen. Implantation, amorphization and redeposition can require a low-energy finishing step.
Stripe-like thickness variations caused by nonuniform milling through regions with different sputtering response.
A nanoscale, approximately spherical carbon structure. Surface oxidation and grafting can change dispersion without requiring any biological processing.
A nanoscale gold particle whose optical, surface and colloidal behavior depends on size, shape and surface chemistry.
Surface-bound molecules surrounding a nanoparticle. Solvation and interactions between outer groups influence dispersibility and aggregation.
Deposition through physical release and transport of material, including evaporation and sputtering.
Thickness deposited on a feature sidewall or bottom relative to a reference planar surface. Geometry, arrival directions, sticking and surface mobility all influence it.
Exclusion of arriving material from a region by an intervening feature. A broad incident angular distribution can reduce shadowing but does not guarantee conformality.
Deposition from a heated or electron-beam-evaporated source. High-vacuum transport is strongly directional and can give poor recessed-feature coverage.
Film deposition through chemical reactions of gas-phase precursors at a surface. Surface kinetics and delivery through a boundary layer can separately limit growth.
A chemical vapor deposition route in which catalyst particles form or travel in the gas stream rather than remaining on a macroscopic support. For carbon nanotubes, particle nucleation, tube growth and aggregation can occur in one flowing reactor. Product withdrawal becomes possible when the growing network is sufficiently connected.
Continuous withdrawal and consolidation of a connected carbon nanotube aerogel from a synthesis reactor. It differs from later spinning of a prepared liquid dispersion and from drawing a pre-grown substrate-supported forest.[ref]
Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis by Ya-Li Li and others. 2004, furnace synthesis and continuous withdrawal
Cyclic film deposition using separated, ideally self-limiting surface reactions. Precursor saturation and purge steps help control conformality and thickness.
Deposition in which a plasma activates gaseous precursors, permitting film growth at reduced substrate temperature. Plasma damage, composition and surface chemistry still need control.
Growth limited principally by surface reaction kinetics. Uniform substrate temperature and controlled reactant concentrations help obtain uniform thickness.
Growth limited principally by transport of reactants to a surface, rather than their surface reaction rate.
Controlled removal of a material by a chemical, plasma or physical process. etch selectivity compares removal rates for different materials; directionality compares removal rates along different geometric directions. High selectivity does not imply a vertical profile, and high directionality does not guarantee an undamaged surface.
A durable patterned layer used to protect underlying material during an etch. Its thickness and etch selectivity must survive the intended depth; erosion and lateral bias can change final feature dimensions even when the starting pattern is correct.
Chemical stripping of organic material, commonly photoresist, by reactive species produced in a plasma. oxygen radicals convert suitable organic material into volatile oxidation products. A remote source reduces direct energetic ion bombardment, but exposed materials can still oxidize and inorganic residue can remain.
An etch that removes a material in different directions without a strongly preferred geometrical direction. It can undercut an overhang and release a sacrificial layer, but can also widen a patterned opening. Access and transport can make the realized undercut nonuniform even with locally isotropic chemistry.
Creating a dense final pattern through several less-dense exposures or through additional pattern-transfer and pitch-division steps. Overlay and etch control replace part of the burden that would otherwise fall on single-exposure optical resolution.
Mask-based optical pattern transfer across a small noncontact gap. Fresnel diffraction across the gap blurs edges; a common resolution estimate is for wavelength , gap and process factor .
Splitting a final pattern between separate lithographic steps to reduce the feature density that each exposure must resolve. The steps need a suitable intervening fixation, transfer or spacer process. Minimum single-feature width, pattern decomposition and overlay remain limitations.
A sequence that exposes and transfers one sparse pattern, then applies fresh resist and transfers a second aligned pattern. Their union defines a denser final mask or etched layer. Pattern transfer between exposures prevents simple addition of optical dose from replacing two independently resolved exposures.
Pattern-dependent modification of mask edges or assist features to compensate the finite imaging and pattern-transfer process. It is assessed by the resulting printed dimensions, not by similarity of the mask to the desired layout.
Illumination using noncentral pupil directions to place useful mask diffraction orders inside a projection lens. Grating orientation, coherence and process window affect the benefit.
A lithographic mask that controls optical phase as well as transmission to improve useful interference contrast. Benefits and phase conflicts depend on the pattern.
Pattern projection using extreme-ultraviolet radiation, multilayer reflective optics and a reflective mask.
Unintended exposure near a written feature caused by electron scattering in the resist and substrate. The deposited-energy distribution is broader than the incident probe, requiring dose or geometry correction for dense and isolated patterns.
Nonlocal dose deposition that changes developed features through scattering and neighboring exposures.
Adjustment of exposure dose or shape to compensate for energy deposited outside the intended write location.
Projection lithography using a liquid between the final lens and wafer to increase numerical aperture through its refractive index, with stringent optical and chemical compatibility requirements.
The ratio of etch rates of a target and a protected or underlying material. Endpoint control and surface damage matter as well as this ratio.
Patterning a deposited film by dissolving an underlying patterned sacrificial resist. Film in exposed openings remains while film on the resist is removed.
The axial image-side range over which a specified image criterion remains satisfied. Lithographic scaling is often written ; specify whether a quoted range is full width or one-sided.
A radiation-sensitive patterning film. Positive resist becomes more soluble after suitable exposure; processing sets its dose response.
A photoresist whose exposed regions dissolve faster in the developer than unexposed regions.
A photoresist whose exposed regions become less soluble in developer over the relevant process window, so adequately exposed regions remain after development.
Radiant energy per exposed area. For steady intensity and exposure duration , ; the developed photoresist profile also depends on chemical processing.
The inverse logarithmic dose range between retention and clearing, . Larger contrast permits a smaller aerial-image intensity ratio.
The smallest aerial-image modulation that permits full clearing in bright regions while preserving the initial thickness in dark regions.
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Nanotechnology is the science and engineering of manipulating matter at the nanoscale, typically defined as involving structures ranging from 1 to 100 nanometers (nm) in size. To put this in perspective, a nanometer is one-billionth of a meter, which is about 100,000 times smaller than the diameter of a human hair. Nanotechnology involves the study, design, and application of materials and devices at this incredibly small scale, where unique physical and chemical properties often emerge.
