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A bimetallic nanocrystal is a crystalline particle containing two metallic chemical elements, with important dimensions on the nanoscale. Its atoms may form an alloy, chemically ordered regions, a core surrounded by a shell or spatially separated domains. Composition alone does not determine which arrangement is present.

For example, a gold–silver particle can expose a surface composition different from its bulk average. That affects surface chemistry and interaction with light. Establishing its structure requires complementary evidence: electron microscopy can reveal morphology, elemental mapping can locate the elements, and diffraction can constrain the crystal structure. These measurements answer different questions rather than providing interchangeable particle descriptions.

A nanohybrid material combines distinguishable material components with at least one component or important structural feature on the nanoscale. Examples include inorganic nanoparticles dispersed in an organic polymer, or nanoparticles carrying a functional molecular coating. The term alone does not specify a unique composition or structure.

The interface is often central: particles may provide an optical or catalytic response, while the surrounding material supplies mechanical support or processability. Performance depends on particle dispersion, interfacial bonding and the properties of each component. A mixed chemical composition is insufficient evidence for a designed hybrid structure; measurements must establish which components exist and how they are arranged. Electron microscopy, spectroscopy and bulk-property measurements can provide complementary evidence.

A nanomaterial has constituent particles or structural features on the nanoscale, conventionally around $1$–$100\mathrm{nm}$. A collection of nanoparticles is one example; a bulk piece containing nanoscale internal structure can also be relevant. The scientific interest lies in how dimensions and interfaces affect behavior, rather than in treating $100\mathrm{nm}$ as a universal physical threshold.^[ref]

A simple geometric calculation explains one important effect. Suppose a fixed volume $V$ of solid is divided into identical spherical nanoparticles of radius $r$. Ignoring contact between particles, their number $N$ and total surface area $A$ areReducing $r$ from $50\mathrm{nm}$ to $5\mathrm{nm}$ makes $1000$ times as many particles and ten times as much surface area, at the same total volume. More material is consequently close to an interface. Surface reactions and interactions with the surrounding medium can become much more influential; this geometric result alone does not guarantee a faster useful reaction or a more stable material.^[ref]

Size can also affect electronic behavior through quantum confinement. Which effect matters depends on the material, shape and environment. A useful comparison therefore holds composition fixed, measures particle dimensions with electron microscopy, and compares a chosen property across a size series. Such a comparison separates a size-dependent change from a change caused merely by using a different substance.^[ref]

A nanoparticle is a particle whose external dimensions lie on the nanoscale. Its behaviour can depend strongly on its size, shape and surface chemistry, even when its overall chemical chemical composition is fixed.

For a sphere of radius $r$, the ratio of surface area to volume isHalving $r$ therefore doubles the surface area exposed per unit volume. At fixed total volume, making many smaller particles exposes more material to the surrounding medium. This helps explain why surface reactions and attached molecules can have a large effect on nanoparticles.^[ref]

The size of an individual nanoparticle also differs from the size of an particle aggregate containing many particles. Reports of particle size consequently need to identify what was measured. Gold nanoparticles provide a visible example: their interaction with light can differ markedly from bulk gold.

The nanoscale is a range of dimensions conventionally around $1$–$100$ nanometres, where a nanometre is $10^{-9}$ metres. It describes a length scale, not a distinct substance. A film can have nanoscale thickness while extending over a macroscopic area.^[ref]

Properties change when a relevant dimension approaches a physical length controlling the behaviour, such as an electronic confinement length or a characteristic surface region. For a sphere, surface area divided by volume is $3/r$, so reducing its radius increases the relative importance of its surface. Nanoscale geometry can consequently influence chemical reactions and interaction with light even without changing the constituent chemical element.^[ref]

A nanostructure has structural features on the nanoscale. The relevant dimension may be the thickness of a thin film, the diameter of a nanowire, or the overall size of a nanoparticle. A material can therefore be macroscopically large while containing nanostructures internally.

The geometry matters because it changes the relative importance of surfaces, the distances over which charge carriers move, and sometimes the allowed quantum states. A thin film and a nanoparticle made from the same chemical material need not have the same properties: their quantum confinement dimensions and exposed surface areas differ. Characterizing a nanostructure requires specifying which dimensions are small, its shape and its chemical chemical composition, rather than reporting a single size alone.^[ref]

Nanotechnology studies and controls matter whose important dimensions are on the nanoscale, conventionally about $1$–$100$ nanometres. A nanometre is $10^{-9}$ metres. The scientific interest comes from changes in behaviour at these dimensions, including the increasing role of surfaces and, in suitable systems, quantum confinement.^[ref]

For example, subdividing a fixed volume into smaller nanoparticles increases the exposed surface area, changing how much material can participate in a surface reaction. Nanostructures can also alter electrical conductivity, interaction with light and mechanical properties by controlling geometry rather than changing only chemical chemical composition. Useful nanotechnology therefore combines fabrication with measurements of structure and properties, such as electron microscopy or atomic force microscopy.^[ref]