Marchywka Effect
Encyclopedia
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
cleaning of diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
using an electric field induced with remote electrodes.
Discovery and development
It was first observed by accident by Mike Marchywka while trying to find a selective means to etch non-diamond carbon and fabricate simple astronomical UV detection devices. These devices required a few specific features such as clean surfaces and patterned areas of non-diamond carbon but the approach has subsequently been explored as a more general means to terminate carbon surfaces and selectively clean and etch various other materials or structures. The term "Marchywka Effect" is not used consistently and sometimes the term "bipolar surface treatment" is used as the substrate is induced to become a bipolar electrodeElectrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
. Various phrases such as "non-contacted electrochemical" process may also be used( see any references cited herein) or it may be mentioned as just an "electrochemical etch".
While this is easily confused with various common electrochemical cells, and may appear to be a trivial and obvious extension of well known methods, recent patents continue to reference prior work that cites non-contactedness as a feature. The use of a low conductivity medium as used in Marchywka et al.'s original paper is sometimes noted when it is used and may produce new effects.
The apparatus to create the effect is similar to the well-known electroporation
Electroporation
Electroporation, or electropermeabilization, is a significant increase in the electrical conductivity and permeability of the cell plasma membrane caused by an externally applied electrical field...
system except that the biological specimen is replaced with an inorganic substrate, although, in some cases, organic films can be etched with this process using a surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
solution as the electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
.
Surface effects
As a "non-contact" process, the effect differs from traditional electrochemical processes where carrier flow through the surface is achieved by connection to a current source with highly conductive materials such as copper wire. It is well known that materials contacted to an anode can be modified in a variety of ways including anodizing and electropolishingElectropolishing
Electropolishing, also known as electrochemical polishing or electrolytic polishing , is an electrochemical process that removes material from a metallic workpiece. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating...
. Electrochemistry was quickly recognized as an important related field in the popular press once the first synthetic diamonds were made. However, the use of an induced field created by remote electrodes allows discontinuous areas on an insulating substrate to be cleaned, modified, or etched (similar to electroetching
Electroetching
Electroetching is a metal etching process that involves the use of a solution of an electrolyte, an anode and a cathode. The metal piece to be etched is connected to the positive pole of a source of direct electric current. A piece of the same metal is connected to the negative pole of the...
), greatly expanding the role of electrochemical methods.
The mechanism is presumed to be due to the induced field but little in the way of exhaustive analysis has been done, as the actual processes do not appear to differ from traditional approaches. For example, "identified as the ‘Marchywka Effect’ in the literature. The etching may be due to the galvanic coupling of diamond and non-diamond carbon". The applied field apparently creates directed surface modifications on polished diamond surfaces with little or no actual removal of material. This may be desirable for making various devices, or simply studying the properties of the diamond surface. The induced field deposits or replaces a single layer of some molecule and this could be thought of as a monolayer electroplating
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
method. It has been elucidated in more fully in many works.
Earlier related approaches
Many prior technologies exist for preparing wide-gap diamond for use in electronic devices or as a substrate for single-crystal diamond growth. The more stable forms of carbon have lower gaps and different crystal structures, and their presence must be carefully controlled. The Marchywka Effect has been characterised and compared to alternative means to create a desired surface for several applications.Removal of non-diamond carbon with wet chemicals had been accomplished by boiling in mixtures of sulphuric and chromic acid
Chromic acid
The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the...
. When applied to a diamond substrate with an ion implantation
Ion implantation
Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into another solid. This process is used to change the physical, chemical, or electrical properties of the solid...
damage profile as may be used for basic science, crystal growth, or device fabrication, the electrochemical approach makes it easier to preserve the thin film of less damaged diamond lying above the implant range, and it has been used in annealing
Annealing
Annealing may refer to:*Annealing , a heat treatment that alters the microstructure of a material causing changes in properties such as strength and hardness and ductility*Annealing , heating a piece of glass to remove stress...
experiments to fix the diamond after implantation damage has occurred. In some cases, thermal cycling may be an issue and selectivity to various masks may be important, so the lower temperatures and more flexible chemistry may offer benefits over prior art.
The method does not require the use of non-volatile materials such as chrome, possibly reducing contamination problems in some applications. The ability to control the etching direction and speed with an applied voltage or electrode configuration, as with electrochemical machining, gives additional capabilities not available with isotropic chemical-only approaches. Dry processing methods such as hot oxygen or plasmas can also burn off the graphite faster than the diamond, as can a simple acetylene torch. These require higher temperatures and do not have the same high selectivity that can be achieved with the electrochemical approach.
Surface termination is often an issue with both solid state and vacuum devices, and the details of final surface band structure have been compared with alternatives in various device structures.
Applications
While the original effort failed to produce useful products, follow-on work in Europe did produce usable astronomical detectorsbut without apparent use of this technology. In other areas, however, the approach seems to be competitive, with prior art for making various end-products, since it has been used as a fabrication step for experimental devices and structures. Many groups have used the approach to grow homoepitaxial diamond and subsequently release the thin-films with a variety of "lift-off" processes.
It has also been considered in contexts such as carbon microelectromechanical systems
Microelectromechanical systems
Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...
production and different materials applications, for example with non-contacted palladium deposition and extensions. While not citing Marchywka et al.'s original paper, these continue to cite non-contactedness as a feature,
"The electrode assembly and the conductive surface may be positioned in close proximity to, but without contacting, one another". references a much earlier patent covering related attempts to achieve non-contacted electro-etching, "The present invention relates to a method of and apparatus for electrochemically processing metallic surfaces of workpieces arranged in a contact-free manner with regard to the cathode and anode[...]."
The effect has been mentioned in passing with regard to novel devices such
as quantum coherent devices while patents on emerging uses for amorphous carbon
and
diamond thermal conductors by manufacturers of high density electronic chips reference the related lift-off technology.