Substrate Distance Research Articles

Monte Carlo simulation of the MoS2 sputtering process and the influence of the normalized momentum on residual stresses

The film growth of sputtered MoS2 coatings is highly sensitive to the deposition conditions. Therefore, the effects of the deposition parameters on the resulting film structure have been studied excessively over recent decades. There is wide consensus in the literature that dense and hard MoS2 coatings show the best tribological behavior. Therefore, high-energy particle fluxes are typically favored due to momentum-induced film densification. Although particle flux ϕ and particle energy E are considered to be the most relevant for MoS2 film growth, the relationship between the process parameters and the resulting particle energetics has not yet been investigated. In this study, results from Monte Carlo simulations show the effect of cathode voltage and process pressure on the resulting particle energetics as a function of the target–substrate distance. Due to its relevance for the stress state, the normalized momentum according to Windischmann's intrinsic stress law has been investigated as a function of the deposition parameters. Based on the calculated results, it is assumed that the highest degree of particle induced densification and intrinsic stress formation can be expected at low process pressures, low target–substrate distances and high cathode voltages. However, the intensified densification effect of increased cathode voltages decreases with increasing distances to the target. In this study, the calculated results are compared with experimental residual stress data from literature. For this purpose, different ϕE1/2-factors have been calculated for 13 parameter combinations according to a Box–Behnken design by varying the parameters cathode voltage, process pressure and target–substrate distance on three different levels. A strong correlation between these calculated data and experimentally determined stresses has been found, which confirms the approach of the simulation procedure.

Study of hafnium oxide thin films deposited by RF magnetron sputtering under glancing angle deposition at varying target to substrate distance

Glancing angle deposition of HfO2 thin films by RF magnetron sputtering technique has been explored with respect to two vital deposition parameters visualizing angle of deposition (at 82° and 86° glancing angles) and target to substrate distance, DTS in the range 70–125mm. AFM and spectroscopic ellipsometry measurements show that at optimum DTS of 110mm and glancing angle 82°, the films exhibit nanostructures with an estimated lowest refractive index ∼1.63 at 550nm. For both the deposition angles, with decrease in DTS the round shaped grains of the film surface as obtained from AFM images are found to coalesce and produce films with elliptical shaped grains at shorter target to substrate distance. With increase in DTS the deposition rate first decreases up to DTS=110mm and subsequently increases. The phenomenon has been ascribed to the competition between reduced deposition flux density and increased sticking coefficient due to decrease in adatom kinetic energy with the increase in DTS. GIXRD measurement reveals that all the films exhibit monoclinic crystal structure. At lower DTS, the crystallinity has improved with increase in deposition angle whereas at higher DTS (>90mm) the crystallinity becomes poorer with increase in deposition angle. The fact has been explained in light of variation of shadowing effect and deposition rate.

Surface Plasmon Properties of Silver Nanostructures Fabricated Using Extremely Non-Equilibrium, Hot and Dense Plasma

We present fabrication of silver nanostructures on glass substrates using highly energetic and high fluence material ions generated by one shot of hot, dense and extremely non-equilibrium plasma such as found in modified dense plasma focus (DPF) device. The substrates were first placed at 4.0 cm and 6.0 cm from the top of anode. Nanodots and nanocapsules are observed in the scanning electron microscopy (SEM) images of silver ions deposited with DPF shot on glass. The interparticle distance is found to decrease whereas mean size of nanodots is found to increase slightly when the distance of glass substrate is increased from 4.0 cm to 6.0 cm. The X-ray diffraction (XRD) pattern of the fabricated nanostructures has peaks at 2θ equals 37.90o, 44.24o and 64.20o which correspond to (111), (200) and (220) planes of silver having face-centered cubic structure. The nanostructures obtained on glass placed at 4.0 cm show surface plasmon resonance (SPR) peak at 420 nm whereas nanostructures obtained on glass placed at 6.0 cm has a SPR peak at 428 nm. Redshift of the SPR peak is attributed to increased interaction as a result of decrease in interparticle distance of the nanostructures as well as increase in mean size of nanodots.

Growing LaAlO3/SrTiO3 interfaces by sputter deposition

Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting.

Improvement of mechanical properties of polylactic acid adhesion joints with bio‐based adhesives by using air atmospheric plasma treatment

ABSTRACTThe packaging industry generates a high volume of wastes; so that, there is a high demand of biodegradable materials, which do not damage the environment. Nowadays, there is an interesting consumption of polylactic acid (PLA) due to its biodegradable features. This work focuses on the improvement of mechanical properties of PLA adhesion joints for uses in the packaging industry. In order to achieve that purpose, atmospheric plasma treatment is used to selectively modify PLA surface properties. The obtained experimental results show that the atmospheric plasma treatment is suitable to increase the mechanical performance of PLA–PLA adhesive joints. Optimum conditions for the atmospheric plasma treatment were obtained with a nozzle–substrate distance of 10 mm and an advance rate in the 100–300 mm s−1range; for these particular conditions, the effectiveness of the surface modification is the highest. The main plasma‐acting mechanisms are microetching together with the insertion of polar groups which lead to an interesting synergy that causes a remarkable increase in mechanical properties of adhesion joints. In particular, the shear strength of untreated PLA–PLA adhesion joints is close to 50 N cm−2and this value is increased up to values of about 168.7 N cm−2with optimum plasma treatment conditions. This indicates that atmospheric plasma treatment is both a technical and an environmental friendly technique to improve mechanical performance of PLA adhesive joints. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 42391.

Effect of sputtering conditions on growth and properties of ZnO:Al films

Al-doped zinc oxide (AZO) films were deposited on glass substrates by mid-frequency magnetron sputtering. The effects of substrate rotation speed and target–substrate distance on the electrical, optical properties and microstructure and crystal structures of the resulting films were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), spectrophotometer and Hall-effect measurement system, respectively. XRD results show that all AZO films exhibit a strong preferred c-axis orientation. However, the crystallinity of films decreases with the increase of substrate rotation speed, accompanying with the unbalanced grains grows. For the films prepared at different target–substrate distances, the uniform microstructure and morphology are observed. The highest carrier concentration of 5.9×1020 cm−3 and Hall mobility of 13.1 cm2/(V·s) are obtained at substrate rotation speed of 0 and target–substrate distance of 7 cm. The results indicate that the structure and performances of the AZO films are strongly affected by substrate rotation speed.

Sputtered Ag thin films with modified morphologies: Influence on wetting property

Silver thin films with thickness ranging from 3nm to 33nm were sputter deposited onto silicon wafers and tungsten layers. Those W layers were previously synthesized in the same DC magnetron sputter deposition system with various experimental conditions (argon pressure, target to substrate distance) in order to stabilize different surface morphologies. SEM observations and AFM images showed that the growth mode of Ag films is similar on Si substrates and on the smoothest W layers, whereas it is modified for rough W layers made of sharp grains. The effect of the W layer morphology on Ag film growth was clearly evidenced when the deposition took place at high temperature. It is seen that performing the deposition onto substrates of various morphologies allows tailoring the wetting property of the Ag deposit.

Plasma sputtering robotic device for in-situ thick coatings of long, small diameter vacuum tubes

A novel robotic plasma magnetron mole with a 50 cm long cathode was designed, fabricated, and operated. The reason for this endeavor is to alleviate the problems of unacceptable resistive heating of stainless steel vacuum tubes in the BNL Relativistic Heavy Ion Collider (RHIC). The magnetron mole was successfully operated to copper coat an assembly containing a full-size, stainless steel, cold bore, RHIC magnet tubing connected to two types of RHIC bellows, to which two additional pipes made of RHIC tubing were connected. To increase the cathode lifetime, a movable magnet package was developed, and the thickest possible cathode was made, with a rather challenging target to substrate (de facto anode) distance of less than 1.5 cm. Achieving reliable steady state magnetron discharges at such a short cathode to anode gap was rather challenging, when compared to commercial coating equipment, where the target to substrate distance is 10's cm; 6.3 cm is the lowest experimental target to substrate distance found in the literature. Additionally, the magnetron developed during this project provides unique omni-directional uniform coating. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system is driven by a motorized spool. Excellent coating adhesion was achieved. Measurements indicated that well-scrubbed copper coating reduced secondary electron yield to 1, i.e., the problem of electron clouds can be eliminated. Room temperature RF resistivity measurement indicated that a 10 μm copper coated stainless steel RHIC tube has a conductivity close to that of pure copper tubing. Excellent coating adhesion was achieved. The device details and experimental results are described.

Growth temperature dependent surface plasmon resonances of densely packed gold nanoparticles’ films and their role in surface enhanced Raman scattering of Rhodamine6G

Localized surface plasmon resonance (LSPR) characteristics of gold nanoparticles films grown at different substrate temperatures and mass thicknesses with and without alumina capping were studied. At different film mass thicknesses, the LSPR response was observed mainly in the films grown at high substrate temperatures. About 300°C substrate temperature was found to be optimum for producing narrow and strong LSPR band in both uncapped and alumina capped gold nanoparticles films. The LSPR wavelength could be tuned in the range of 600–750nm by changing either number of ablation pulses or decreasing target to substrate distance (TSD) and alumina layer capping. Though the alumina capping re-sputtered the gold films still these films exhibited stronger LSPR response compared to the uncapped films. Atomic force microscopic analysis revealed formation of densely packed nanoparticles films exhibiting strong LSPR response which is consistent with the package density of the nanoparticles predicted by the theoretical calculations. The average size of nanoparticles increased with substrate temperature, number of ablation pulses and decreasing the TSD. For the same mass thickness of gold films grown at different substrate temperatures the surface enhanced Raman scattering (SERS) intensity of Rhodamine6G dye was found to be significantly different which had direct correlation with the LSPR strength of the films at the excitation wavelength.

Study of Yb-Doped CoSb<sub>3</sub> Thermoelectric Thin Films Prepared by Laser

Thin films of Yb filled CoSb3 were prepared on fused silica substrates using pulsed laser deposition method. The stoichiometric Yb0.19Co4Sb12 target was prepared by hot pressing method. The deposition conditions were changed with the goal to reach layers of smooth morphology. The target-to substrate distance was kept equal to 4 cm. The ambient argon pressure moved from 0.5 Pa to 13 Pa, laser repetition rate from 3 Hz to 10 Hz, and substrate temperature from 250 °C to 400 °C. We tested laser fluencies from 0.8 J·cm-2 to 5 J·cm-2. Films roughness was determined by mechanical profilometer and by atomic force microscopy. The lowest roughness of about 5 nm – 10 nm was reached for low laser fluencies but mechanical quality of films was poor and growth rate low (about 0.1 A/pulse). From WDX analysis follows that there is an excess of Yb and Sb compared to Yb0.19Co4Sb12 target.

Preparation of nanostructured tungsten trioxide thin films by high pressure sublimation and condensation

Thin films of tungsten trioxide (WO3) have gained increasing importance due to their interesting chromogenic properties and for their high application potential in electrochromic devices. It is very well known that their electrochromic switching properties depend very sensitively on their nanostructure. Hence, a vast majority of the research work carried out in this domain at present is dedicated to the various techniques of controlled inducing of a nanostructure in these WO3 thin films in order to enhance their electrochromic performance.In the present work we have carried out a systematic study of the nanostructured WO3 thin films by using a novel technique of varying the source–substrate distance in a high pressure sublimation and condensation method. This technique has been found to be very efficient in controlling the grain size and thus the nanostructure of the deposited films. A correlation is established between the optical and electrochromic properties of the WO3 films and the induced nanostructure. The electrochromic properties are studied by a dry lithiation process developed in our laboratory. The results indicate a strong dependence of the film nanostructure on the source–substrate distance which influences quite sensitively the electrochromic properties. These results are expected to help design electrochromic devices suitable for different applications.

English

We have grown ZnO thin films on glass substrate by R.F magnetron sputtering using metallic zinc target. The influences of some parameters on thin film optical properties were assessed. They exhibited extremely high resistivity of 1012 Ω.cm, an energy gap of 3.3 eV at room temperature. It was found that a R.F power of 50 W, a target to substrate distance of 70 mm, very low gas pressures of 3.35 x 10-3 Torr of argon and oxygen mixed gas atmosphere gave ZnO thin films with a good homogeneity and a high crystallinity. All the films are transparent in the visible region (400 to 800 nm) with average transmittance above 80 %. The optical transmittance and refractive index, calculated from the spectra of optical absorbance, show a significant dependence on the growth parameters. As for the sample grown at 100°C, the average transmittance is about 80% in the visible wavelength range and the refractive index is estimated to be 1.97.      key words: ZnO; R.F sputtering magnetron; X-ray diffraction; transmittance; refractive index.

Macroparticles Reduction Using Filter Free Cathodic Vacuum Arc Deposition Method in ZnO Thin Films.

We report a new method to reduce macroparticles in ZnO thin films using filter free cathodic vacuum arc deposition without using any cooling arrangements operated at low arc current. The detailed mechanism has been proposed to reduce macroparticles during thin film deposition. The successful reduction of macroparticles was confirmed employing FESEM-EDX studies. FESEM images of ZnO thin films deposited with cathode spot to substrate distance from 10 to 20 cm revealed that the population of the macroparticles were reduced with the increase of cathode spot to substrate distances at low arc current. The prepared ZnO films were characterised and showed good structural and optical properties.

Microstructure of ZnO thin films deposited by high power impulse magnetron sputtering

High power impulse magnetron sputtering was used to deposit thin (~100nm) zinc oxide (ZnO) films from a ceramic ZnO target onto substrates heated to 150°C. The resulting films had strong crystallinity, highly aligned (002) texture and low surface roughness (root mean square roughness less than 10nm), as determined by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and atomic force spectroscopy measurements. Deposition pressure and target–substrate distance had the greatest effect on film microstructure. The degree of alignment in the films was strongly dependent on the gas pressure. Deposition at pressures less than 0.93Pa resulted in a bimodal distribution of grain sizes. An initial growth layer with preferred orientations (101) and (002) parallel to the interface was observed at the film–substrate interface under all conditions examined here; the extent of that competitive region was dependent on growth conditions. Time-resolved current measurements of the target and ion energy distributions, determined using energy resolved mass spectrometry, were correlated to film microstructure in order to investigate the effect of plasma conditions on film nucleation and growth.

Laser-induced forward transfer of silver nanopaste for microwave interconnects

We explore the effect of variations in laser fluence and donor-receiver substrate distance on the laser-induced forward transfer technique for high viscosity Ag nanopaste. By transferring 50μm×50μm voxels with thicknesses between 0.8 and 8.7μm at different laser fluences, we are able to systematically determine a thickness-fluence regime for successful transfer that widens with increasing voxel thickness. We use these results to study congruent transfer of square voxels with lateral dimensions spanning 2 orders of magnitude: 5μm×5μm, 50μm×50μm, and 500μm×500μm. We conclude by linking a multitude of voxels together in 1mm and 3mm lines to fabricate the center conductor in coplanar waveguides (CPWs) with relatively low loss up to 10GHz.

Effect of Dip Time on the Structural and Optical Properties of Chemically Deposited CdSe Thin Films

In this study, the effect of dip time on the structural and optical properties of cadmium selenide (CdSe) thin films grown by the chemical bath deposition method is reported. The films were grown with varying dip time in the range of 4 h to 12h, and the other deposition variables (substrate temperature, source to substrate distance, pH, and concentration) were kept constant. X-ray diffractometry (XRD) and optical spectroscopy were used to characterise the layers. The results show that the crystallite size and the film thickness increased with an increase in the dip time up to a “critical value” and then decreased otherwise for the latter. The increase in the crystallite size was more pronounced at the lower dip time ( 8 h. The energy band gap was found to be direct with an optimum value of 1.2 eV obtained for films grown at a dip time of 8 h.

Estimation of Requirements for the Formation of Nanocrystalline Diamond Driven by Electron Beam Ablation

Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.

Angular distribution of species in pulsed laser deposition of LaxCa1−xMnO3

The angular distribution of species from a La0.4Ca0.6MnO3 target irradiated with a 248nm nanosecond pulsed laser was investigated by Rutherford backscattering spectrometry for four different Ar pressures. The film thickness angular distribution was also analyzed using profilometry. Depending on the background gas pressure, the target to substrate distance, and the angular location the film thickness and composition varies considerably. In particular the film composition could vary by up to 17% with respect to the composition of the target material.

Effect of KCN Treatment on Cu-Se Secondary Phase of One-step Sputter-deposited CIGS Thin Films Using Quaternary Target

The structural, optical and electrical properties of sputter-deposited CIGS films were directly influenced by the sputtering process parameters such as substrate temperature, working pressure, RF power and distance between target and substrate. CIGS thin films deposited by using a quaternary target revealed to be Se deficient due to Se low vapor pressure. This Se deficiency affected the overall stoichiometry of the films, causing the films to be Cu-rich. Current tends to pass through the Cu-Se channels which act as the shunting path increasing the film conductivity. The crystal structure of CIGS thin films depends on the substrate orientation due to the influence of surface morphology, grain size and stress of Mo substrate. The excess of Cu was removed from the CIGS films by KCN treatment, achieving a suitable Cu concentration (referred as Cu-poor) for the fabrication of solar cell. Due to high Cu concentrations on the CIGS film surface induced by Cu-Se phases after CIGS film deposition, KCN treatment proved to be necessary for the fabrication of high efficiency solar cells. Also during KCN treatment, dislocation density and lattice parameter decreased as excess Cu was removed, resulting in increase of bandgap and the decrease of conductivity of CIGS films. It was revealed that Cu-Se secondary phase could be removed by KCN wet etching of CIGS films, allowing the fabrication of high efficiency absorber layer.

Photocatalytic hydrogen production by stainless steel@ZnS core–shell wire mesh photocatalyst from saltwater

Ni-doped stainless steel@ZnS core–shell wire mesh photocatalyst for photocatalytic hydrogen production was prepared by a solvothermal method. Effects of wire mesh density, doping, and surface texture on the photocatalytic activity were studied. The photocatalytic activity of the catalyst was evaluated by splitting Na2S/Na2SO3 solution into H2. The effects of surface texture and doping on the surface wettability and photocatalytic activity were investigated. Energy-dispersive X-ray spectroscopy (EDX) analysis and Ni mapping images indicated that a small amount of Ni is loaded on the ZnS. The highest hydrogen evolution is obtained for the Ni-doped core–shell photocatalyst when ZnS is grown on wire mesh substrate (distance between adjacent wires = 60 μm) with precursor solution (Ni(CH3COO)2/Zn(CH3COO)2 = 1%) by a solvothermal reaction for 0.5 h. The enhanced performance results from enhanced separation of the photoinduced carriers by Ni-doping, and effective contact among sacrificial aqueous solution and the ZnS shell. Photocatalytic activity and photocurrent of three repeated tests of recycled photocatalysts were also investigated.