User:Dwtheturtle/sandbox/Laser-induced forward transfer

Laser-induced forward transfer (LIFT) is the printing process of using optical stimulation provided by laser pulses to move particles from a source surface to a target surface. The duration of the laser pulses depends on the material to be printed, but is typically in the range of nanoseconds, picoseconds, or femtoseconds (i.e. from 10-7 seconds to 10-15 seconds long). LIFT is a form of nanolithography and was first developed and used in 1986 at Johns Hopkins University as a replacement for inkjet printing. As of 2017, the process continues to be researched and further developed. The technique has many potential applications in nanotechnology by allowing the production of nanoscale structures such as nanoantennas.

History
LIFT was first used in 1986 by a group of scientists at Johns Hopkins University. It is a development of the photolithographic technique known as multiphoton lithography. Prior to the development of this technology, substances suitable for inkjet or laser printing techniques, such as pulsed laser deposition, were limited to substances such as aluminium due to physical and chemical properties. With the development of LIFT, more substances (e.g. copper) have the potential to be laser-printed, many of which are more desirable in characteristics such as conductivity. LIFT is also versatile compared to some prior nanoprinting techniques, as it requires only that the two substrates are sufficiently close and can be carried out at atmospheric conditions (i.e. room temperature and pressure).

Setup
During LIFT, particles must be transferred from the source substrate to the receiver substrate, where they will attach. The source substrate will be coated in the substance to be printed and must be transparent, so the laser pulse can pass through and stimulate this coating. The two substrates are then brought very close together (with less than 100 micrometers between them), parallel to each other, with the coated face of the source facing the target.

Process
LIFT can be divided into four stages: The method through which the particles are ejected from the source material is still being explored. The ejection is believed to be the result of either the thermal stress produced by the energy from the laser or due to the vaporization of some source material. The process has been investigated using the law of conservation of energy in relation to the system, giving a result that suggests that either of the above mechanisms are possible, or a combination of the two.
 * 1) The laser pulse is absorbed by the coating substance.
 * 2) A nanodroplet of molten substance is formed.
 * 3) The nanodroplet is ejected from the source material.
 * 4) The nanodroplet is deposited on the receiver substrate.

Applications
LIFT has potential in many fields on a nanoscopic scale due to its versatility and accuracy, evident through the fact that it can be used at room temperature and pressure, is fast, and can print a large variety of substances, both organic and inorganic. As a result, it can be used in electronics to print conductive materials, or in biotechnology and bioengineering to print organic molecules.

Electronics
Since LIFT provides the ability to print in conductive substances on a nanoscale, it allows for the development of nanotechnology. Using this process, many products made using other printing techniques, such as inkjet, can now be produced with greater accuracy. These include gas sensors which, when printed with this technique, have been shown to be much more receptive to the target stimulus. LIFT may also further the development of flexible OLED screens which could be used in commercial products such as mobile phones. Nanoantennas could also be built which could detect tiny particles such as atoms.

Biotechnology
With LIFT, organic materials such as DNA or polymers could be printed, potentially leading to the development of nanostructures. LIFT has proven to be able to print rat and human neural cells, and pig eye lens cells with little to no lasting damage, and continued to multiply even after the process. It has also printed DNA with very little damage. As a result, LIFT could potentially be used medically to repair and restore various parts of the body. LIFT could also have various applications in bioengineering such as the production of biosensors, structures which can detect certain substances within an organism.

Limitations
In some cases, the substance that is to be transferred may be unsuitable for LIFT, as they may be fragile. Another layer can be added in between the source substrate and the coating so that the laser does not directly affect the coating. This is called the dynamic release layer. In this process, the dynamic release layer is vaporized by the laser which propels the coating. However, this technique may cause the vaporized substance to form an impurity in the propelled droplet of coating.

Future Development
The process continues to be studied with regard to the mechanisms employed, and the accuracy of the output. As of November 2017, the method through which the particles are ejected from the source material is unknown and continues to be investigated. Possible mechanisms include the vaporization of or the build-up of thermal stress in the source material causing it to eject onto the target substrate, or a combination of both. Nanoparticles of sizes as small as 160nm have been printed to a precision of 50nm.