Evaporated Metal Atoms Research Articles

Screening of a flow of evaporated metal atoms by the Langmuir layer formed at the point of contact of hot plasma with metal

We have theoretically analyzed conditions under which the screening of a flow of evaporated metal atoms by the Langmuir layer formed due to ionization of atoms in this layer can significantly influence the dynamics of hot plasma in contact with a metal surface. It is established that allowance for the screening of evaporated atomic flow by this Langmuir layer is necessary in many cases, in particular, in simulations of laser-plume dynamics.

Ab Initio Thermodynamics of Surface Oxide Structures under Controlled Growth Conditions

Having a robust and predictive ab initio thermodynamic model to examine and describe the interplay of the oxygen gas and evaporated metal atoms on another metal substrate may prove to be very helpful in understanding the surface phase diagrams of these oxygen/metal systems. In this work, we examine the O/Cu/Au(111) system and provide a refined atomistic thermodynamic model which takes different definitions of the chemical potential of the less abundant metal, Cu into account. We argue that the latter highly depends on the various surface structures (overlayers and alloys) that forms on the metal substrate under growth conditions. We demonstrate that our improved thermodynamic model rationalizes new experimentally observed oxide structures and may pave a systematic way to predict new surface structures of reduced stoichiometries, which would otherwise be missed by the common practice of taking only the bulk limits.

Damaging Effect of Hot Metal Atoms on Organic Semiconducting Films during Top Contact Formation

The formation of a high quality interface between metallic and organic semiconducting thin films is critically important in achieving high-performance organic electronics devices. In this regard, the importance of understanding the multifaceted issue of structure damage incurred to organic films by the evaporated metal atoms cannot be overstated. In the present study, we have investigated the change of a structurally ordered, organic semiconducting (o.s.) thin film of 5,11-bis(triethylsilylethynyl)anthradithiophene (TESADT) effected by gold atoms by means of synchrotron-based soft X-ray spectroscopies including ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopies (XPS) with imaging capability, near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and atomic force microscopy (AFM). This work shows that gold atoms readily diffuse into the organic films and nucleate into nanometer-size clusters, damage chemical structure, destroy structural ordering of the organic fi...

Conductive carbon paint as an anode buffer layer in inverted CdS/Poly(3-hexylthiophene) solar cells

Hybrid solar cells have been prepared by deposition of thin films of cadmium sulfide (CdS) on transparent conductive glass substrates, followed by the formation of poly(3-hexylthiophene) (P3HT) coatings. Conductive carbon paint (CP) layer was applied on top of P3HT before the evaporation of gold (Au) as metal contact. When the P3HT film thickness (d) was smaller than 600nm, photovoltaic (PV) performance of the CdS/P3HT solar cells was enhanced with CP layer. In the case of d=305nm, the presence of CP layer increased the open-circuit voltage (Voc) from 335 to 710mV and the short-circuit current density (Jsc) from 1.23 to 1.42mA/cm2 as well. The analysis of current–voltage (I–V) curves in the dark of the same type of cells indicates that CP reduced the leakage current and metal contact resistance, and increased the rectification ratio. I–V curves of hole-only Metal-1/P3HT/Metal-2 devices suggest that the presence of CP facilitates hole-extraction from P3HT. The comparison of charge recombination times at CdS/P3HT interface suggests that without CP layer, Au atoms could reach areas near the interface and facilitates charge recombination process. It is concluded that conductive carbon not only improves the ohmic contact between P3HT and top metal but also impedes the diffusion of the evaporated metal atoms deep inside the polymer films. This leads to better PV performance of the CdS/P3HT solar cells.

Thermal metal deposition induces segregation in polymer thin films: a demonstration on OPVs

Interfacial interactions between thermally evaporated metal atoms and a polymer can induce its segregation to the polymer blend/metal interface. This segregation effectively modifies the surface composition, originally directed by surface energy considerations during film formation, and can be utilized to enhance device performances as demonstrated here for polymer solar cells.

Effects of pressure on metal atom transport and plasma properties during arc ion plating of TiAlN

Arc ion plating is used to deposit titanium and aluminum nitrides as wear and corrosion resistant layers on the surface of steel tools. In this study, the deposition efficiency for the evaporated metal atoms in arc ion plating was obtained by a view factor solution for the collisionless transport and a diffusion solution for the continuum transport. In the diffusion solution, the deposition efficiency decreases rapidly with pressure. A global nitrogen plasma model with a set of simplified plasma chemistry was used to investigate the plasma properties at pressures ranging from several mTorr up to 50 mTorr. The results indicate that the electron temperature, the ratio of electric field to gas density, and the nitrogen atom density all decrease with increasing pressure, while the plasma density increases. Based on the combined considerations of deposition efficiency and effective ion bombardment of the films on the substrate, an operating pressure range from 20 to 30 mTorr is recommended for highly efficient (Ti, Al)N coating during film deposition.

Disorder formation in rutile during ion assisted deposition

Ion assisted deposition (IAD) is a well-known method for obtaining dense and well adhering surface layers. Conventional IAD operates with evaporated metal atoms and energetic gaseous ions whereas metal plasma immersion ion implantation and deposition (MePIIID) draws energetic metallic ions from a cathodic arc which may additionally ionise the background gas. TiO 2 is a widely investigated material for biomedical, optical and catalysis applications. MePIIID is employed to deposit TiO 2 films onto Si substrates at different pulse voltages up to 10 kV. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies are performed to investigate the changing film properties as a function of pulse voltage and to estimate the barrier efficiency against diffusion through the layer.

Matrix studies of the thermal and photolytic reactions of Zn, Cd and Hg (M) atoms with H2O: formation and characterisation of the adduct M⋯OH2and photoproduct HMOH

IR spectra have been used to chart the thermal and photolytic reactions occurring during or after the codeposition of Zn, Cd or Hg (M) vapour with an excess of H2O-doped Ar. Following the formation of the contact pair M⋯OH2, detected after deposition of a matrix including thermally evaporated metal atoms, UV irradiation (200 ≤ λ/nm ≤ 400) causes M⋯OH2 to rearrange with insertion of the metal atom into an O–H bond in forming the M(II) hydride HMOH. Characterisation of the molecules has been underpinned by reference (i) to the effects of isotopic change (1,2H) and (ii) to the results of density functional theory (DFT) calculations. The properties of the molecules are compared with those of related species, and the mechanism of the photochemical change is discussed.

Quantitative laser mass spectroscopy of sputtered versus evaporated metal atoms

We demonstrate that the presence of excited states in sputtered surface atoms after ion bombardment affects the measured ion yield of a subsequent post multiphoton-ionization processes. This effect was investigated using an advanced time-of-flight mass-spectroscopic technique. This work reports a comparison of two-photon ionization spectra of metallic atoms obtained from solid samples via sputtering and thermal evaporation that reveals the role of excited states. Furthermore we experimentally determine the cross sections for the two photon ionization processes of evaporated Mg, Zn, and In through quantitative ion yield measurement. Numerical configuration interaction calculations for Mg and Zn are presented and the resulting theoretical two-photon ionization cross sections are compared with the measured ones.

Optical response of cesium coated C $_{60}$

Photoabsorption spectra are reported for Csn+ and C60Csn+ + clusters for n=40, 60, 120 and 310. The spectra were obtained by heating the mass selected clusters in a beam by means of photoabsorption until they evaporated metal atoms. The resulting mass loss was observed in a time-of-flight mass spectometer. The plasmon-like resonance in pure Cs clusters shifts to lower energies with decreasing cluster size. The collective electronic excitations in clusters containing C60 are split in energy as would be expected for fullerene molecules coated with layers of metal.

Transition and rare-earth metal ion sources

The design and operation of an original transition and rare-earth metal ion source are described. Ions were produced during collisions of evaporated metal atoms with fast electrons. The source delivered the following parameters: (1) an ion energy of (1–20) keV; (2) a total ion current of (1–25)× 10−6 A; (3) an ion current stability of 0.1%; (4) a beam cross-section diameter of (1–12) mm; and (5) a period of 30–60 h of uninterrupted operation on a charge of 1 g of metal under UHV conditions. The peculiarity of the source is the creation of multiple-charged ions Mq+(q=1–6), and some part of these ions are metastable-excited. The testing results and practical applications of a proposed source are demonstrated.

Origin of low Z impurities in TEXTOR with an “all carbon” surrounding

The carbonization of the metallic liner and limiters of TEXTOR led to plasmas which contained less than 10 −5 metal, and, in best cases, (0.6 ± 0.4)% low Z ions per D +. However disruptions damaged some of the carbon film and evaporated metal atoms. These were redeposited on the carbon layer and became a source of impurities. Graphite limiters have been used since mid-1985. The metal pollution is not a problem for more than 1000 discharges after one carbonization. However the low Z contamination was initially five times larger than earlier. Surprisingly, the oxygen concentration had considerably increased. Experiments were performed to identify the sources of C and O and to improve the conditioning methods in this “all carbon” surrounding. The main tools used were: RG (radiofrequency assisted DC glow) discharges in H 2, D 2, and their mixtures with CH 4 and CD 4, the study of the H/D ratio in water and hydrocarbons and of the CO and CO 2 released during the ramp heating and cooling of limiters, liner, vessel and main portholes, and the modulation of the deuterium fluxes to the liner and limiters during tokamak discharges. The quality of tokamak plasmas measures the progress of the wall conditioning. We describe the optimized conditioning procedure which was applied after the most probable oxygen source had been drastically reduced.

Effect of Dissolved Oxygen on the Rates of Evaporation of Molten Iron and Copper

The evaporation rates of liquid iron and copper under reduced pressure of 0.001-600mmHg Ar were measured at several temperatures by using a micro balance.In the pressure range of less than 0.1mmHg Ar, rates of evaporation are independent of argon pressure, although evaporation rates under argon atmosphere of more than 0.1mmHg decrease with increasing pressure of argon, probably because of the collision between the evaporated metal atoms and argon molecules as described already by previous investigators.It is also found that evaporation rates for both metals decrease with increasing oxygen concentration in molten metals. Considering that oxygen dissolved in liquid metal is a surface active element, it seems reasonable to consider that rates are controlled by the evaporation reaction at metal surface where oxygen adsorbs. Namely, the present results suggest that most of metal atoms vaporize at oxygen free sites.Moreover, it is found that the values of surface tensions of molten metals estimated from the present work agree well with those in literatures.

Magnetic Properties of Ferromagnetic Thin Films Prepared by Ion Plating

Thin films of Fe, Co and their alloys were prepared by ion plating. Metals were evaporated in the argon gas atmosphere of about 0.01 Torr, by applying a dc electric field of 2 kV/15 cm between the substrate and the evaporation source. Since evaporated metal atoms, which were given large kinetic energies by the gas plasma, impinged on the surface of the substrate, a strong adhesion between the ferromagnetic thin films and the substrate could be obtained. Due to the granular structure of the thin film, a higher coercive force and the squareness ratio could be obtained: i.e. by changing the Ar gas pressure, the coercive force and the squareness ratio could be controlled up to 500 Oe and 0.6, respectively, and also they were controlled by choosing the constituents of the mother alloys.

Investigation of the Reaction of Compound Formation in the Reactive Evaporation Process

The reactions in the reactive evaporation process have been studied by using a quadrupole mass analyser. Experiments were carried out in systems of Ti-C2H4 and Al-NH3. Films of the various composition have been obtained by changing the ratio of the incident frequency of both active gas molecules and evaporated metal atoms onto the substrate. By taking account of the results of mass analysis and the effects of the substrate temperature on the composition of products, it may be concluded that the formation processes have dominantly proceeded on the substrate. The reactions seem to be taking place between the adsorbed molecules and/or atoms on a substrate. At relatively higher substrate temperatures, above about 300°C, the main processes are simple reactions caused by the direct collisions between metal atoms and gas molecules during the migration on the growing film surface.