Sculptured thin film
Encyclopedia
Sculptured thin films are nanostructure
d materials with unidirectionally varying properties that can be designed and realized in a controllable manner using variants of physical vapor deposition
. The ability to virtually instantaneously change the growth direction of their columnar morphology, through simple variations in the direction of the incident vapor
flux
, leads to a wide spectrum of columnar forms.
, while the density may lie between its theoretical maximum value to less than 20% thereof. The crystallinity
must be at a scale smaller than the column diameter. The chemical composition is essentially unlimited, ranging from insulators to semiconductors to metals. Most recently, polymeric STFs have been deposited by combining physical and chemical vapor deposition
processes; and deposition on micropatterned substrates
has also been carried out.
as polarization filters, Bragg filters
, and spectral hole filters. At visible
and infrared
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
. Being porous, an STF can act as a sensor
of fluids and can be impregnated with liquid crystals for switching applications too. Applications as low-permittivity
barrier layers in electronic chips as well as solar cells have also been suggested. Biomedical applications such as tissue scaffolds, drug-delivery platforms, virus
traps, and labs-on-a-chip
are also in different stages of development.
Nanostructure
A nanostructure is an object of intermediate size between molecular and microscopic structures.In describing nanostructures it is necessary to differentiate between the number of dimensions on the nanoscale. Nanotextured surfaces have one dimension on the nanoscale, i.e., only the thickness of the...
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
Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...
. The ability to virtually instantaneously change the growth direction of their columnar morphology, through simple variations in the direction of the incident vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
, 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 helixHelixA helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
es and superhelixSuperhelixA 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....
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 nm1 E-9 m
To help compare different orders of magnitudes this page lists lengths between 10−9 metres and 10−8 metres .Distances shorter than 1 nanometre*1 nm = 1 nanometre = 1000 picometres = 10 angstroms...
, while the density may lie between its theoretical maximum value to less than 20% thereof. The crystallinity
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 big influence on hardness, density, transparency and diffusion. In a gas, the relative positions of the atoms or...
must be at a scale smaller than the column diameter. The chemical composition is essentially unlimited, ranging from insulators to semiconductors to metals. Most recently, polymeric STFs have been deposited by combining physical and chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
processes; and deposition on micropatterned substrates
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
has also been carried out.
Uses
To date, the chief applications of STFs are in opticsOptics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
as polarization filters, Bragg filters
Fiber Bragg grating
A fiber Bragg grating is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by adding a periodic variation to the refractive index of the fiber core, which generates a...
, and spectral hole filters. At visible
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
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
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
. Being porous, an STF can act as a sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
of fluids and can be impregnated with liquid crystals for switching applications too. Applications as low-permittivity
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
barrier layers in electronic chips as well as solar cells have also been suggested. Biomedical applications such as tissue scaffolds, drug-delivery platforms, virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
traps, and labs-on-a-chip
Lab-on-a-chip
A lab-on-a-chip is a device that integrates one or several laboratory functions on a single chip of only millimeters to a few square centimeters in size. LOCs deal with the handling of extremely small fluid volumes down to less than pico liters. Lab-on-a-chip devices are a subset of MEMS devices...
are also in different stages of development.