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90-586: Thin-film deposition has plated objects as small as an atom, therefore plating finds uses in nanotechnology . There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate ). Other plating techniques include electroplating , vapor deposition under vacuum and sputter deposition . Recently, plating often refers to using liquids. Metallizing refers to coating metal on non-metallic objects. In electroplating, an ionic metal

180-671: A [ 1 − exp ⁡ ( − t τ a ) ] n = J σ τ a [ exp ⁡ ( − t τ a ) ] {\displaystyle n=J\sigma \tau _{a}\left[1-\exp \left({-t \over \tau _{a}}\right)\right]n=J\sigma \tau _{a}\left[\exp \left({-t \over \tau _{a}}\right)\right]} Adsorption can also be modeled by different isotherms such as Langmuir model and BET model . The Langmuir model derives an equilibrium constant b {\displaystyle b} based on

270-438: A halide or hydride of the element to be deposited. In the case of metalorganic vapour phase epitaxy , an organometallic gas is used. Commercial techniques often use very low pressures of precursor gas. Plasma Enhanced Chemical Vapor Deposition uses an ionized vapor, or plasma , as a precursor. Unlike the soot example above, this method relies on electromagnetic means (electric current, microwave excitation), rather than

360-414: A noble gas , such as argon ) to knock material from a "target" a few atoms at a time. The target can be kept at a relatively low temperature, since the process is not one of evaporation, making this one of the most flexible deposition techniques. It is especially useful for compounds or mixtures, where different components would otherwise tend to evaporate at different rates. Note, sputtering's step coverage

450-412: A 10- μm layer over an underlying nickel plate. When plating on iron or steel, an underlying plating of copper allows the nickel to adhere. The pores (tiny holes) in the nickel and chromium layers work to alleviate stress caused by thermal expansion mismatch but also hurt the corrosion resistance of the coating. Corrosion resistance relies on what is called the passivation layer , which is determined by

540-427: A chemical-reaction, to produce a plasma. Atomic layer deposition and its sister technique molecular layer deposition , uses gaseous precursor to deposit conformal thin film's one layer at a time. The process is split up into two half reactions, run in sequence and repeated for each layer, in order to ensure total layer saturation before beginning the next layer. Therefore, one reactant is deposited first, and then

630-410: A film of non-ionic metal. Electroless deposition , also known as chemical or auto- catalytic plating, is a non- galvanic plating method that involves several simultaneous reactions in an aqueous solution , which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite (Note: the hydrogen leaves as

720-805: A final finish or as a paint base. If environmental concerns matter, in most aspects cadmium plating can be directly replaced with gold plating as it shares most of the material properties, but gold is more expensive and cannot serve as a paint base. Nickel is electroplated by using a Watts bath , an electrolytic cell having a nickel anode and electrolyte containing nickel sulfate , nickel chloride , and boric acid . Other nickel salts such as nickel ammonium sulfate are sometimes used instead of nickel sulfate. Electroless nickel plating, also known as enickel and NiP , offers many advantages: uniform layer thickness over most complicated surfaces, direct plating of ferrous metals (steel), superior wear and corrosion resistance compared to electroplated nickel or chrome. Much of

810-422: A fluid precursor undergoes a chemical change at a solid surface, leaving a solid layer. An everyday example is the formation of soot on a cool object when it is placed inside a flame. Since the fluid surrounds the solid object, deposition happens on every surface, with little regard to direction; thin films from chemical deposition techniques tend to be conformal , rather than directional . Chemical deposition

900-472: A high level of ionization (30–100%), multiply charged ions, neutral particles, clusters and macro-particles (droplets). If a reactive gas is introduced during the evaporation process, dissociation , ionization and excitation can occur during interaction with the ion flux and a compound film will be deposited. Electrohydrodynamic deposition (electrospray deposition) is a relatively new process of thin-film deposition. The liquid to be deposited, either in

990-443: A hydride ion) or thiourea , and oxidized, thus producing a negative charge on the surface of the part. The most common electroless deposition method is electroless nickel plating , although silver, gold and copper layers can also be applied in this manner, as in the technique of angel gilding . Gold plating is a method of depositing a thin layer of gold on the surface of glass or metal, most often copper or silver. Gold plating

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1080-470: A large source of silver at the time. This can cause confusion when talking about silver items; plate or plated. In the UK it is illegal to describe silver-plated items as "silver". It is not illegal to describe silver-plated items as "silver plate", although this is ungrammatical. The earliest form of silver plating was Sheffield Plate , where thin sheets of silver are fused to a layer or core of base metal, but in

1170-417: A liquid precursor, or sol-gel precursor deposited onto a smooth, flat substrate which is subsequently spun at a high velocity to centrifugally spread the solution over the substrate. The speed at which the solution is spun and the viscosity of the sol determine the ultimate thickness of the deposited film. Repeated depositions can be carried out to increase the thickness of films as desired. Thermal treatment

1260-453: A moisture-free environment will not undergo this type of corrosion. Copper plating is the process of electrolytically forming a layer of copper on the surface of an item. It is commonly used as an even cheaper alternative to silver plating as it is much cheaper than silver. Rhodium plating is occasionally used on white gold, silver or copper and its alloys. A barrier layer of nickel is usually deposited on silver first, though in this case it

1350-450: A result of tin whisker formation. In some cases, it is desirable to co-deposit two or more metals resulting in an electroplated alloy deposit. Depending on the alloy system, an electroplated alloy may be solid solution strengthened or precipitation hardened by heat treatment to improve the plating's physical and chemical properties. Nickel-Cobalt is a common electroplated alloy. Metal matrix composite plating can be manufactured when

1440-425: A substrate is plated in a bath containing a suspension of ceramic particles. Careful selection of the size and composition of the particles can fine-tune the deposit for wear resistance, high temperature performance, or mechanical strength. Tungsten carbide , silicon carbide , chromium carbide , and aluminum oxide (alumina) are commonly used in composite electroplating. Cadmium plating is under scrutiny because of

1530-456: A substrate, which is also heated via a laser beam. The vast range of substrate and deposition temperatures allows of the epitaxial growth of various elements considered challenging by other thin film growth techniques. Cathodic arc deposition (arc-physical vapor deposition), which is a kind of ion beam deposition where an electrical arc is created that blasts ions from the cathode. The arc has an extremely high power density resulting in

1620-693: A thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering . Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media , electronic semiconductor devices , integrated passive devices , light-emitting diodes , optical coatings (such as antireflective coatings), hard coatings on cutting tools, and for both energy generation (e.g. thin-film solar cells ) and storage ( thin-film batteries ). It

1710-417: A variety of shapes without damage to the surface tin layer. It provides sacrificial protection for copper, nickel and other non-ferrous metals, but not for steel . Tin is also widely used in the electronics industry because of its ability to protect the base metal from oxidation thus preserving its solderability. In electronic applications, 3% to 7% lead may be added to improve solderability and to prevent

1800-433: Is glucose (an aldehyde) for such applications. Clean glassware is required for a high quality mirror. To increase the speed of deposition, the glass surface may be pre-treated with tin(II) chloride stabilised in hydrochloric acid solution. For applications requiring the highest optical quality, such as in telescope mirrors , the use of tin(II) chloride is problematic, since it creates nanoscale roughness and reduces

1890-480: Is a chemical reagent used to distinguish between aldehydes and ketones along with some alpha-hydroxy ketones which can tautomerize into aldehydes. The reagent consists of a solution of silver nitrate , ammonium hydroxide and some sodium hydroxide (to maintain a basic pH of the reagent solution). It was named after its discoverer, the German chemist Bernhard Tollens . A positive test with Tollens' reagent

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1980-673: Is a relative term, but most deposition techniques control layer thickness within a few tens of nanometres . Molecular beam epitaxy , the Langmuir–Blodgett method , atomic layer deposition and molecular layer deposition allow a single layer of atoms or molecules to be deposited at a time. It is useful in the manufacture of optics (for reflective , anti-reflective coatings or self-cleaning glass , for instance), electronics (layers of insulators , semiconductors , and conductors form integrated circuits ), packaging (i.e., aluminium-coated PET film ), and in contemporary art (see

2070-442: Is also being applied to pharmaceuticals, via thin-film drug delivery . A stack of thin films is called a multilayer . In addition to their applied interest, thin films play an important role in the development and study of materials with new and unique properties. Examples include multiferroic materials , and superlattices that allow the study of quantum phenomena. Nucleation is an important step in growth that helps determine

2160-604: Is also known as the sol-gel method because the 'sol' (or solution) gradually evolves towards the formation of a gel-like diphasic system. The Langmuir–Blodgett method uses molecules floating on top of an aqueous subphase. The packing density of molecules is controlled, and the packed monolayer is transferred on a solid substrate by controlled withdrawal of the solid substrate from the subphase. This allows creating thin films of various molecules such as nanoparticles , polymers and lipids with controlled particle packing density and layer thickness. Spin coating or spin casting, uses

2250-468: Is an environmentally safe option. Hexavalent chromate has been classified as a human carcinogen by the EPA and OSHA. The tin -plating process is used extensively to protect both ferrous and nonferrous surfaces. Tin is a useful metal for the food processing industry since it is non-toxic, ductile and corrosion resistant. The excellent ductility of tin allows a tin coated base metal sheet to be formed into

2340-418: Is associated with the highest atomic mobility and deposition temperature. There is also a possibility of developing a mixed Zone T/Zone II type structure, where the grains are mostly wide and columnar, but do experience slight growth as their thickness approaches the surface of the film. Although Koch focuses mostly on temperature to suggest a potential zone mode, factors such as deposition rate can also influence

2430-409: Is characterized by low grain growth in subsequent film layers and is associated with low atomic mobility. Koch suggests that Zone I behavior can be observed at lower temperatures. The zone I mode typically has small columnar grains in the final film. The second mode of Volmer-Weber growth is classified as Zone T, where the grain size at the surface of the film deposition increases with film thickness, but

2520-433: Is expensive because the process is complex. Moreover, the process is lengthy even for thin layers. When only corrosion resistance or surface treatment is of concern, very strict bath composition and temperature control is not required and the process is used for plating many tons in one bath at once. Electroless nickel plating layers are known to provide extreme surface adhesion when plated properly. Electroless nickel plating

2610-406: Is formed in this case. Another test relies on reaction of the furfural with phloroglucinol to produce a colored compound with high molar absorptivity. It also gives a positive test with hydrazines , hydrazones , α-hydroxy ketones and 1,2-dicarbonyls . Both Tollens' reagent and Fehling's reagent give positive results with formic acid . In anatomic pathology , ammonical silver nitrate

2700-440: Is further categorized by the phase of the precursor: Plating relies on liquid precursors, often a solution of water with a salt of the metal to be deposited. Some plating processes are driven entirely by reagents in the solution (usually for noble metals ), but by far the most commercially important process is electroplating . In semiconductor manufacturing, an advanced form of electroplating known as electrochemical deposition

2790-520: Is indicated by the precipitation of elemental silver, often producing a characteristic "silver mirror" on the inner surface of the reaction vessel. This reagent is not commercially available due to its short shelf life , so it must be freshly prepared in the laboratory. One common preparation involves two steps. First a few drops of dilute sodium hydroxide are added to some aqueous 0.1  M silver nitrate . The OH − {\displaystyle {\ce {OH-}}} ions convert

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2880-427: Is made up of about 250 g/L of CrO 3 and about 2.5 g/L of SO 4 . In solution, the chrome exists as chromic acid, known as hexavalent chromium . A high current is used, in part to stabilize a thin layer of chromium(+2) at the surface of the plated work. Acid chrome has poor throwing power, fine details or holes are further away and receive less current resulting in poor plating. Zinc coatings prevent oxidation of

2970-411: Is more or less conformal. It is also widely used in optical media. The manufacturing of all formats of CD, DVD, and BD are done with the help of this technique. It is a fast technique and also it provides a good thickness control. Presently, nitrogen and oxygen gases are also being used in sputtering. Pulsed laser deposition systems work by an ablation process. Pulses of focused laser light vaporize

3060-419: Is non-magnetic and amorphous. Electroless nickel plating layers are not easily solderable, nor do they seize with other metals or another electroless nickel-plated workpiece under pressure. This effect benefits electroless nickel-plated screws made out of malleable materials like titanium. Electrical resistance is higher compared to pure metal plating. "Aluminum plating" can refer to either plating on aluminum or

3150-407: Is not to prevent migration of silver through rhodium, but to prevent contamination of the rhodium bath with silver and copper, which slightly dissolve in the sulfuric acid usually present in the bath composition. Chrome plating is a finishing treatment using the electrolytic deposition of chromium . The most common form of chrome plating is the thin, decorative bright chrome , which is typically

3240-483: Is now used to create the copper conductive wires in advanced chips, replacing the chemical and physical deposition processes used to previous chip generations for aluminum wires Chemical solution deposition or chemical bath deposition uses a liquid precursor, usually a solution of organometallic powders dissolved in an organic solvent. This is a relatively inexpensive, simple thin-film process that produces stoichiometrically accurate crystalline phases. This technique

3330-451: Is often carried out in order to crystallize the amorphous spin coated film. Such crystalline films can exhibit certain preferred orientations after crystallization on single crystal substrates. Dip coating is similar to spin coating in that a liquid precursor or sol-gel precursor is deposited on a substrate, but in this case the substrate is completely submerged in the solution and then withdrawn under controlled conditions. By controlling

3420-442: Is often used in electronics, to provide a corrosion -resistant electrically conductive layer on copper, typically in electrical connectors and printed circuit boards . With direct gold-on-copper plating, the copper atoms have the tendency to diffuse through the gold layer, causing tarnishing of its surface and formation of an oxide/sulfide layer. Therefore, a layer of a suitable barrier metal , usually nickel, has to be deposited on

3510-490: Is one of the best corrosion resistant finishes available offering over 5 times the protection of conventional zinc plating and up to 1,500 hours of neutral salt spray test performance. This plating is a combination of a high-nickel zinc-nickel alloy (10–15% nickel) and some variation of chromate. The most common mixed chromates include hexavalent iridescent, trivalent or black trivalent chromate. Used to protect steel, cast iron, brass, copper, and other materials, this acidic plating

3600-598: Is placed in an energetic , entropic environment, so that particles of material escape its surface. Facing this source is a cooler surface which draws energy from these particles as they arrive, allowing them to form a solid layer. The whole system is kept in a vacuum deposition chamber, to allow the particles to travel as freely as possible. Since particles tend to follow a straight path, films deposited by physical means are commonly directional , rather than conformal . Examples of physical deposition include: A thermal evaporator that uses an electric resistance heater to melt

3690-458: Is reformed: Alternatively, aqueous ammonia can be added directly to silver nitrate solution. At first, ammonia will induce formation of solid silver oxide, but with additional ammonia, this solid precipitate dissolves to give a clear solution of diamminesilver(I) coordination complex , [ Ag ( NH 3 ) 2 ] + {\displaystyle {\ce {[Ag(NH3)2]+}}} . Filtering

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3780-415: Is sometimes used for plating copper, as its electrical resistance is lower (see Resistivity of various materials ); more so at higher frequencies due to the skin effect . Variable capacitors are considered of the highest quality when they have silver-plated plates. Similarly, silver-plated, or even solid silver cables, are prized in audiophile applications; however some experts consider that in practice

3870-413: Is supplied with electrons to form a non-ionic coating on a substrate . A common system involves a chemical solution with the ionic form of the metal, an anode (positively charged) which may consist of the metal being plated (a soluble anode) or an insoluble anode (usually carbon, platinum, titanium, lead, or steel), and finally, a cathode (negatively charged) where electrons are supplied to produce

3960-401: Is the applied vapor pressure of adsorbed adatoms: θ = X p ( p e − p ) [ 1 + ( X − 1 ) p p e ] {\displaystyle \theta ={Xp \over (p_{e}-p)\left[1+(X-1){p \over p_{e}}\right]}} As an important note, surface crystallography and differ from

4050-481: Is the net flux, τ a {\displaystyle \tau _{a}} is the mean surface lifetime prior to desorption and σ {\displaystyle \sigma } is the sticking coefficient: d n d t = J σ − n τ a {\displaystyle {dn \over dt}=J\sigma -{n \over \tau _{a}}} n = J σ τ

4140-394: Is the vapor pressure of adsorbed adatoms: θ = b P A ( 1 + b P A ) {\displaystyle \theta ={bP_{A} \over (1+bP_{A})}} BET model where p e {\displaystyle p_{e}} is the equilibrium vapor pressure of adsorbed adatoms and p {\displaystyle p}

4230-507: Is used in the Fontana–Masson Stain , which is a silver stain technique used to detect melanin , argentaffin and lipofuscin in tissue sections. Melanin and the other chromaffins reduce the silver nitrate to metallic silver. Tollens' reagent is also used to apply a silver mirror to glassware; for example the inside of an insulated vacuum flask. The underlying chemical process is called silver mirror reaction . The reducing agent

4320-409: The environmental toxicity of the cadmium metal. Cadmium plating is widely used in some applications in the aerospace, military, and aviation fields. However, it is being phased out due to its toxicity. Military and Aerospace components manufacturers, such as Amphenol Aerospace , have recently been exploring drop-in electroplating replacements for use with currently fielded equipment in order to support

4410-442: The silver aquo complex form into silver(I) oxide , Ag 2 O {\displaystyle {\ce {Ag2O}}} , which precipitates from the solution as a brown solid: In the next step, sufficient aqueous ammonia is added to dissolve the brown silver(I) oxide. The resulting solution contains the [Ag(NH 3 ) 2 ] complexes in the mixture, which is the main component of Tollens' reagent. Sodium hydroxide

4500-520: The 18th century to provide cheaper versions of household items that would otherwise be made of solid silver, including cutlery , vessels of various kinds, and candlesticks. In the UK the assay offices , and silver dealers and collectors, use the term "silver plate" for items made from solid silver, derived long before silver plating was invented from the Spanish word for silver "plata", seizures of silver from Spanish ships carrying silver from America being

4590-442: The 19th century new methods of production (including electroplating) were introduced. Britannia metal is an alloy of tin, antimony and copper developed as a base metal for plating with silver. Another method that can be used to apply a thin layer of silver to objects such as glass, is to place Tollens' reagent in a glass, add glucose/dextrose, and shake the bottle to promote the reaction. For applications in electronics, silver

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4680-401: The adsorbate-surface interactions are stronger than adsorbate-adsorbate interactions. Volmer–Weber ("isolated islands"). In this growth mode the adsorbate-adsorbate interactions are stronger than adsorbate-surface interactions, hence "islands" are formed right away. There are three distinct stages of stress evolution that arise during Volmer-Weber film deposition. The first stage consists of

4770-407: The adsorption reaction of vapor adatom with vacancy on the substrate surface. The BET model expands further and allows adatoms deposition on previously adsorbed adatoms without interaction between adjacent piles of atoms. The resulting derived surface coverage is in terms of the equilibrium vapor pressure and applied pressure. Langmuir model where P A {\displaystyle P_{A}}

4860-407: The aldehyde to a carboxylate ion and in the process is reduced to elemental silver and aqueous ammonia. The elemental silver precipitates out of solution, occasionally onto the inner surface of the reaction vessel, giving a characteristic "silver mirror". The carboxylate ion on acidification will give its corresponding carboxylic acid . The carboxylic acid is not directly formed in the first place as

4950-412: The bulk to minimize the overall free electronic and bond energies due to the broken bonds at the surface. This can result in a new equilibrium position known as “selvedge”, where the parallel bulk lattice symmetry is preserved. This phenomenon can cause deviations from theoretical calculations of nucleation. Surface diffusion describes the lateral motion of adsorbed atoms moving between energy minima on

5040-679: The chemical composition and processing, and is damaged by cracks and pores. In a special case, micropores can help distribute the electrochemical potential that accelerates galvanic corrosion between the layers of nickel and chromium. Depending on the application, coatings of different thicknesses will require different balances of the aforementioned properties. Thin, bright chrome imparts a mirror -like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to 1000 μm, are called hard chrome and are used in industrial equipment to reduce friction and wear. The traditional solution used for industrial hard chrome plating

5130-399: The chrome plating done in aerospace industry can be replaced with electroless nickel plating, again environmental costs, costs of hexavalent chromium waste disposal and notorious tendency of uneven current distribution favor electroless nickel plating. Electroless nickel plating is self-catalyzing process, the resultant nickel layer is NiP compound, with 7–11% phosphorus content. Properties of

5220-424: The copper substrate, forming a copper-nickel-gold sandwich. Metals and glass may also be coated with gold for ornamental purposes, using a number of different processes usually referred to as gilding . Sapphires, plastics, and carbon fiber are some other materials that are able to be plated using advance plating techniques. The substrates that can be used are almost limitless. Silver plating has been used since

5310-402: The evaporant flux. Typical deposition rates for electron beam evaporation range from 1 to 10 nanometres per second. In molecular beam epitaxy , slow streams of an element can be directed at the substrate, so that material deposits one atomic layer at a time. Compounds such as gallium arsenide are usually deposited by repeatedly applying a layer of one element (i.e., gallium ), then a layer of

5400-412: The film. Molecular beam epitaxy is a particularly sophisticated form of thermal evaporation. An electron beam evaporator fires a high-energy beam from an electron gun to boil a small spot of material; since the heating is not uniform, lower vapor pressure materials can be deposited. The beam is usually bent through an angle of 270° in order to ensure that the gun filament is not directly exposed to

5490-675: The final film microstructure. A subset of thin-film deposition processes and applications is focused on the so-called epitaxial growth of materials, the deposition of crystalline thin films that grow following the crystalline structure of the substrate. The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an ordered manner". It can be translated as "arranging upon". Tollens%27 reagent Tollens' reagent (chemical formula Ag ( NH 3 ) 2 OH {\displaystyle {\ce {Ag(NH3)2OH}}} )

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5580-404: The final structure of a thin film. Many growth methods rely on nucleation control such as atomic-layer epitaxy (atomic layer deposition). Nucleation can be modeled by characterizing surface process of adsorption , desorption , and surface diffusion . Adsorption is the interaction of a vapor atom or molecule with a substrate surface. The interaction is characterized the sticking coefficient ,

5670-467: The form of nanoparticle solution or simply a solution, is fed to a small capillary nozzle (usually metallic) which is connected to a high voltage. The substrate on which the film has to be deposited is connected to ground. Through the influence of electric field, the liquid coming out of the nozzle takes a conical shape ( Taylor cone ) and at the apex of the cone a thin jet emanates which disintegrates into very fine and small positively charged droplets under

5760-475: The fraction of incoming species thermally equilibrated with the surface. Desorption reverses adsorption where a previously adsorbed molecule overcomes the bounding energy and leaves the substrate surface. The two types of adsorptions, physisorption and chemisorption , are distinguished by the strength of atomic interactions. Physisorption describes the Van der Waals bonding between a stretched or bent molecule and

5850-402: The grain size in the deposited layers below the surface does not change. Zone T-type films are associated with higher atomic mobilities, higher deposition temperatures, and V-shaped final grains. The final mode of proposed Volmer-Weber growth is Zone II type growth, where the grain boundaries in the bulk of the film at the surface are mobile, resulting in large yet columnar grains. This growth mode

5940-442: The growth of metallic "whiskers" in compression stressed deposits, which would otherwise cause electrical shorting. However, RoHS (Restriction of Hazardous Substances) regulations enacted beginning in 2006 require that no lead be added intentionally and that the maximum percentage not exceed 1%. Some exemptions have been issued to RoHS requirements in critical electronics applications due to failures which are known to have occurred as

6030-497: The influence of Rayleigh charge limit. The droplets keep getting smaller and smaller and ultimately get deposited on the substrate as a uniform thin layer. Frank–van der Merwe growth ("layer-by-layer"). In this growth mode the adsorbate-surface and adsorbate-adsorbate interactions are balanced. This type of growth requires lattice matching, and hence considered an "ideal" growth mechanism. Stranski–Krastanov growth ("joint islands" or "layer-plus-island"). In this growth mode

6120-430: The material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate without reacting with or scattering against other gas-phase atoms in the chamber, and reduce the incorporation of impurities from the residual gas in the vacuum chamber. Only materials with a much higher vapor pressure than the heating element can be deposited without contamination of

6210-590: The morphology of the film’s surface is unchanging with film thickness. During this stage, the overall stress in the film can remain tensile, or become compressive.   On a stress-thickness vs. thickness plot, an overall compressive stress is represented by a negative slope, and an overall tensile stress is represented by a positive slope. The overall shape of the stress-thickness vs. thickness curve depends on various processing conditions (such as temperature, growth rate, and material). Koch states that there are three different modes of Volmer-Weber growth. Zone I behavior

6300-467: The newly formed grain boundaries. The magnitude of this generated tensile stress depends on the density of the formed grain boundaries, as well as their grain-boundary energies. During this stage, the thickness of the film is not uniform because of the random nature of the island coalescence but is measured as the average thickness. The third and final stage of the Volmer-Weber film growth begins when

6390-445: The nucleation of individual atomic islands. During this first stage, the overall observed stress is very low. The second stage commences as these individual islands coalesce and begin to impinge on each other, resulting in an increase in the overall tensile stress in the film. This increase in overall tensile stress can be attributed to the formation of grain boundaries upon island coalescence that results in interatomic forces acting over

6480-413: The other (i.e., arsenic ), so that the process is chemical, as well as physical; this is known also as atomic layer deposition . If the precursors in use are organic, then the technique is called molecular layer deposition . The beam of material can be generated by either physical means (that is, by a furnace ) or by a chemical reaction ( chemical beam epitaxy ). Sputtering relies on a plasma (usually

6570-552: The overall free energy. These stable sites are often found on step edges, vacancies and screw dislocations. After the most stable sites become filled, the adatom-adatom (vapor molecule) interaction becomes important. Nucleation kinetics can be modeled considering only adsorption and desorption. First consider case where there are no mutual adatom interactions, no clustering or interaction with step edges. The rate of change of adatom surface density n {\displaystyle n} , where J {\displaystyle J}

6660-515: The phaseout of the dangerous finish. Cadmium plating (or cad. plating ) offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, softness and malleability , freedom from sticky and/or bulky corrosion products, galvanic compatibility with aluminum, freedom from stick-slip thus allowing reliable torquing of plated threads, can be dyed to many colors and clear, has good lubricity and solderability, and works well either as

6750-441: The plating is often poorly implemented, making the result inferior to similarly priced copper cables. Care should be used for parts exposed to high humidity environments because in such environments, when the silver layer is porous or contains cracks, the underlying copper undergoes rapid galvanic corrosion , flaking off the plating and exposing the copper itself; a process known as red plague . Silver plated copper maintained in

6840-409: The plating of aluminum on other materials. Thin-film deposition A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer ) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many applications. A familiar example is the household mirror , which typically has

6930-518: The polymer chains. Physical deposition uses mechanical, electromechanical or thermodynamic means to produce a thin film of solid. An everyday example is the formation of frost . Since most engineering materials are held together by relatively high energies, and chemical reactions are not used to store these energies, commercial physical deposition systems tend to require a low-pressure vapor environment to function properly; most can be classified as physical vapor deposition . The material to be deposited

7020-499: The potential energy as a function of distance. The equilibrium distance for physisorption is further from the surface than chemisorption. The transition from physisorbed to chemisorbed states are governed by the effective energy barrier E a {\displaystyle E_{a}} . Crystal surfaces have specific bonding sites with larger E a {\displaystyle E_{a}} values that would preferentially be populated by vapor molecules to reduce

7110-469: The premise that aldehydes are more readily oxidized compared with ketones; this is due to the carbonyl-containing carbon in aldehydes having attached hydrogen. The diamine silver(I) complex in the mixture is an oxidizing agent and is the essential reactant in Tollens' reagent. The test is generally carried out in a test tube in a warm water bath. In a positive test, the diamine silver(I) complex oxidizes

7200-544: The protected metal by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide ) does not cause a breakdown of the substrate's surface integrity as it is formed. Indeed, the zinc oxide, if undisturbed, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminum and stainless steels by their oxide layers. The majority of hardware parts are zinc-plated, rather than cadmium-plated . Zinc-nickel plating

7290-472: The reaction takes place under alkaline conditions. The ionic equations for the overall reaction are shown below; R refers to an alkyl group. Tollens' reagent can also be used to test for terminal alkynes ( R − C 2 H {\displaystyle {\ce {R-C2H}}} ). A white precipitate of the acetylide ( AgC 2 − R {\displaystyle {\ce {AgC_2-R}}} )

7380-413: The reagent before use helps to prevent false-positive results. Once the presence of a carbonyl group has been identified using 2,4-dinitrophenylhydrazine (also known as Brady's reagent or 2,4-DNPH or 2,4-DNP), Tollens' reagent can be used to distinguish ketone vs aldehyde . Tollens' reagent gives a negative test for most ketones, with alpha-hydroxy ketones being one exception. The test rests on

7470-481: The resultant layer hardness and wear resistance are greatly altered with bath composition and deposition temperature, which should be regulated with 1 °C precision, typically at 91 °C. During bath circulation, any particles in it will become also nickel-plated; this effect is used to advantage in processes which deposit plating with particles like silicon carbide (SiC) or polytetrafluoroethylene (PTFE). While superior compared to many other plating processes, it

7560-448: The second reactant is deposited, during which a chemical reaction occurs on the substrate, forming the desired composition. As a result of the stepwise, the process is slower than chemical vapor deposition; however, it can be run at low temperatures. When performed on polymeric substrates, atomic layer deposition can become sequential infiltration synthesis , where the reactants diffuse into the polymer and interact with functional groups on

7650-659: The substrate surface. Diffusion most readily occurs between positions with lowest intervening potential barriers. Surface diffusion can be measured using glancing-angle ion scattering. The average time between events can be describes by: τ d = ( 1 / v 1 ) exp ⁡ ( E d / k T s ) {\displaystyle \tau _{d}=(1/v_{1})\exp(E_{d}/kT_{s})} In addition to adatom migration, clusters of adatom can coalesce or deplete. Cluster coalescence through processes, such as Ostwald ripening and sintering, occur in response to reduce

7740-495: The surface characterized by adsorption energy E p {\displaystyle E_{p}} . Evaporated molecules rapidly lose kinetic energy and reduces its free energy by bonding with surface atoms. Chemisorption describes the strong electron transfer (ionic or covalent bond) of molecule with substrate atoms characterized by adsorption energy E c {\displaystyle E_{c}} . The process of physic- and chemisorption can be visualized by

7830-419: The surface of the target material and convert it to plasma; this plasma usually reverts to a gas before it reaches the substrate. Thermal laser epitaxy uses focused light from a continuous-wave laser to thermally evaporate sources of material. By adjusting the power density of the laser beam, the evaporation of any solid, non-radioactive element is possible. The resulting atomic vapor is then deposited upon

7920-445: The total surface energy of the system. Ostwald repining describes the process in which islands of adatoms with various sizes grow into larger ones at the expense of smaller ones. Sintering is the coalescence mechanism when the islands contact and join. The act of applying a thin film to a surface is thin-film deposition – any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. "Thin"

8010-419: The withdrawal speed, the evaporation conditions (principally the humidity, temperature) and the volatility/viscosity of the solvent, the film thickness, homogeneity and nanoscopic morphology are controlled. There are two evaporation regimes: the capillary zone at very low withdrawal speeds, and the draining zone at faster evaporation speeds. Chemical vapor deposition generally uses a gas-phase precursor, often

8100-425: The work of Larry Bell ). Similar processes are sometimes used where thickness is not important: for instance, the purification of copper by electroplating , and the deposition of silicon and enriched uranium by a chemical vapor deposition -like process after gas-phase processing. Deposition techniques fall into two broad categories, depending on whether the process is primarily chemical or physical . Here,

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