Sculptured thin films (STFs) are

nanostructure A nanostructure is a structure of intermediate size between microscopic and molecular structures. Nanostructural detail is microstructure at nanoscale. In describing nanostructures, it is necessary to differentiate between the number of dimen ...

d materials with unidirectionally varying properties that can be designed and realized in a controllable manner using variants of

physical vapor deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...

. The ability to virtually instantaneously change the growth direction of their columnar morphology, through simple variations in the direction of the incident

vapor In physics, a vapor (American English) or vapour (Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critical temperature,R ...

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...

, leads to a wide spectrum of columnar forms.

Forms

These forms can be: # two-dimensional, ranging from the simple slanted columns and chevrons to the more complex C- and S-shaped morphologies # three-dimensional, including simple

helix A helix (; ) is a shape like a cylindrical coil spring or the thread of a machine screw. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is for ...

es and

superhelix A superhelix is a molecular structure in which a helix is itself coiled into a helix. This is significant to both proteins and genetic material, such as overwound circular DNA. The earliest significant reference in molecular biology is from 1971, ...

es # combinations of two- and three-dimensional forms.

Properties

The column diameter and the column separation normal to the thickness direction of any STF are nominally constant. The column diameter can range from about 10 to 300 nm, while the density may lie between its theoretical maximum value to less than 20% thereof. The

crystallinity Crystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a large influence on hardness, density, transparency and diffusi ...

must be at a scale smaller than the column diameter. The chemical composition is essentially unlimited, ranging from

insulators Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work ...

semiconductors A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping levels ...

metals A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against no ...

. Most recently,

polymeric A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, bot ...

STFs have been deposited by combining physical and

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...

processes; and deposition on micropatterned substrates has also been carried out.

Uses

To date, the chief applications of STFs are in

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...

filters, Bragg filters, and spectral hole filters. At visible and

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

wavelengths, a single-section STF is a unidirectionally nonhomogeneous continuum with direction-dependent properties. Several sections can be grown consecutively into a multisection STF, which can be conceived of as an optical circuit that can be integrated with electronic circuitry on a

chip Chip may refer to: Food * Chip (snack), thinly sliced and deep-fried gastro item ** Potato chips (US) or crisp (UK) * Chips (fried potato strips) (UK) or french fries (US) (common as a takeout side) * Game chips, thin chip/French fries * Choco ...

. Being porous, an STF can act as a

sensor A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

of fluids and can be impregnated with

liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal can flow like a liquid, but its molecules may be oriented in a common direction as i ...

s for switching applications too. Applications as low-

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter (epsilon), is a measure of the electric polarizability of a dielectric material. A material with high permittivity polarizes more ...

barrier layers in electronic chips as well as

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

s have also been suggested.

Biomedical Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine)

applications such as

tissue scaffold Tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biolog ...

s, drug-delivery platforms,

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

traps, and labs-on-a-chip are also in different stages of development.

References

* {{cite book, author=Akhlesh Lakhtakia & Russell Messier, title=Sculptured Thin Films: Nanoengineered Morphology and Optics, year=2005, publisher=SPIE Press, Bellingham, WA, USA, isbn=0-8194-5606-3
Nanomaterials