Spin-coating Speed Research Articles

Effect of Annealing Temperature and Spin Coating Speed on Mn-Doped ZnS Nanocrystals Thin Film by Spin Coating

ZnS:Mn nanocrystals thin film was fabricated at 300°C and 500°C via the spin coating method. Its sol-gel was spin coated for 20 s at 3000 rpm and 4000 rpm with metal tape being used to mold the shape of the thin film. A different combination of these parameters was used to investigate their influences on the fabrication of the film. Optical and structural characterizations have been performed. Optical characterization was analyzed using UV-visible spectroscopy and photoluminescence spectrophotometer while the structural and compositional analysis of films was measured via field emission scanning electron microscopy and energy dispersive X-ray. From UV-vis spectra, the wavelength of the ZnS:Mn was 250 nm and the band gap was within the range 4.43 eV–4.60 eV. In room temperature PL spectra, there were two emission peaks centered at 460 nm and 590 nm. Under higher annealing temperature and higher speed used in spin coating, an increase of 0.05 eV was observed. It was concluded that the spin coating process is able to synthesize high quality spherical ZnS:Mn nanocrystals. This conventional process can replace other high technology methods due to its synthesis cost.

The synthesis, characterization and ZnS surface passivation of polycrystalline ZnO films obtained by the spin-coating method

This study describes the facile synthesis of ZnO nanolayers by the sol-gel process and evaluates their subsequent surface passivation with ZnS by gas-phase sulfidation. The ZnO nanolayers were formed by a spin-coating technique following calcination in air in the temperature range 500–900 °C to obtain a polycrystalline wurtzite structure of ZnO. The layer thickness was optimized by adjusting the spin-coating speed and concentration of polymer in the starting solution. The continuity and formation of the films was influenced by ZnO crystal size, which was found to increase with increasing calcination temperature. The ZnO nanostructure was covered by a thin ZnS layer in a one-step passivation process carried out at room temperature in the presence of H2S. This thin coating of ZnS was found to have a sphalerite structure. The cathodoluminescence intensity of near-band-gap emission of the coated crystal was one order of magnitude greater following the passivation of surface defects.

Controllable thin-film morphology and structure for 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8BTBT) based organic field-effect transistors

Organic field-effect transistors (OFETs) based on organic semiconductor material 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8BTBT) as the active layer were fabricated by using organic molecular beam deposition (OMBD) and solution-processed methods, in which the C8BTBT thin-film morphology could be well controlled. In OMBD method, C8BTBT thin-film morphology could be controlled by the thickness of organic semiconductor layer and the deposition rate, of which the high-quality C8BTBT thin film was obtained at a thickness of about 20 nm and at a deposition rate of 1.2 nm/min, resulting in an obvious mobility improvement from 2.8 × 10−3 cm2 V−1 s−1 to 1.20 cm2 V−1 s−1. While in the solution-processing, C8BTBT thin-film morphology and thickness are related to the spin-coating speed and the substrate position in spin coater, i.e., in-centre and off-centre position. The off-centre spin-coating with an optimized speed produced large-size domain C8BTBT thin film and accordingly resulted in a mobility of 1.47 cm2 V−1 s−1. Furthermore, an additive polystyrene (PS) was added into C8BTBT solution could further improve the thin-film morphology with more metal-stable phase as well as improve the interface contact with the substrate SiO2, resulting in the highest mobility up to 3.56 cm2 V−1 s−1. The research suggested that C8BTBT-based OFETs with the mobility over 1.20 cm2 V−1 s−1 could be fabricated by using both OMBD and solution-processed methods through the thin-film morphology and structure optimization, which shows the potential applications in high-performance flexible and printed electronics.

Phase Separation of Silicon-Containing Polymer/Polystyrene Blends in Spin-Coated Films.

In this Article, two readily available polymers that contain silicon and have different surface tensions, polydimethylsiloxane (PDMS) and polyphenylsilsequioxane (PPSQ), were used to produce polymer blends with polystyrene (PS). Spin-coated thin films of the polymer blends were treated by O2 reactive-ion etching (RIE). The PS constituent was selectively removed by O2 RIE, whereas the silicon-containing phase remained because of the high etching resistance of silicon. This selective removal of PS substantially enhanced the contrast of the phase separation morphologies for better scanning electron microscope (SEM) and atomic force microscope (AFM) measurements. We investigated the effects of the silicon-containing constituents, polymer blend composition, concentration of the polymer blend solution, surface tension of the substrate, and the spin-coating speed on the ultimate morphologies of phase separation. The average domain size, ranging from 100 nm to 10 μm, was tuned through an interplay of these factors. In addition, the polymer blend film was formed on a pure organic layer, through which the aspect ratio of the phase separation morphologies was further amplified by a selective etching process. The formed nanostructures are compatible with existing nanofabrication techniques for pattern transfer onto substrates.

Statistical Modelling of the Conductivity Performance of Poly(3,4- ethylene- dioxythiophene/poly(Styrene Sulfonic Acid) Films

This paper presents a comprehensive statistical evaluation of the conductivity performance of PEDOT/PSS films generated at various spin coating speeds (1000 to 5000 rpm) by correspondence analysis (CA), regression and ANOVA models. Poly(3,4-ethylenedioxythiophene) (PEDOT) is a highly conducting insoluble polymer which, when doped with poly(styrene sulfonic acid) (PSS) in water, results in a dispersion with good film forming properties. Our interest in PEDOT/PSS is in its application as an interfacial layer and gate electrode in organic photovoltaic and organic field effect transistor devices, respectively. The generation of a homogeneous spun-cast layer of PEDOT/PSS over the entire substrate for these intended applications is a function of the spin-coating speed which, in turn, affects the thickness of the film and, consequently, its conductivity measured by the four point probe. From correspondence analysis, we find that only the 1000 rpm spin-coating speed is strongly associated with high thickness and high resistivity (i.e. low conductivity), although further analysis of speeds 2000 - 5000 rpm shows that the spin-coating speed is still associated with the thickness of the films, and subsequently, their conductivities, such that the thinnest and most conductive films result from the highest spin-coating speed (5000 rpm). We also observed the phenomenon of the horseshoe effect from the CA displays and discussed the reasons for not resorting to detrending solutions for dealing with its presence. From multiple and nonlinear regression models, spin-coating speeds 1000 and 2000 rpm were found to produce films of less precise conductivity values as reflected in the absolute value of mean of residuals of nonlinear regression models while more precise and optimal conductivity values are obtained when the films are generated between 3000 and 5000 rpm. The ANOVA models showed that the means of conductivity of films obtained at 1000 rpm is statistically significantly different to those from higher spin coating speeds and that there is no significant difference between the conductivity of films generated using spin coating speeds 2000 and 3000 rpm and between spin coating speeds 4000 and 5000 rpm. Further, the conductivity of films from spin coating speeds 4000-5000 rpm are higher and more precise than those obtained at 2000-3000 rpm. Based on the results of this study, we have standardised conductivity measurements of PEDOT/PSS films using the four-point probe by spin-coating at 4000-5000 rpm in order to obtain optimal and reproducible conductivity values.

Effects of spin-coating speed on the morphology and photovoltaic performance of the diketopyrrolopyrrole-based terpolymer

Polymer solar cells (PSCs) were fabricated by combining a diketopyrrolopyrrole-based terpolymer (PTBT-HTID-DPP) as the electron donor, and [6,6]-phenyl C 61 butyric acid methyl ester (PC 61 BM) as the electron acceptor, and the power conversion efficiency (PCE) of 4.31% has been achieved under AM 1.5 G (100 mW cm -2 ) illumination condition via optimizing the polymer/PC 61 BM ratio, the variety of solvent and the spin-coating speed. The impact of the spin-coating speed on the photovoltaic performance of the PSCs has been investigated by revealing the effects of the spin-coating speed on the morphology and the absorption spectra of the polymer/PC 61 BM blend films. When the thickness of the blend films are adjusted by spin-coating a fixed concentration with different spin-coating speeds, the blend film prepared at a lower spin-coating speed shows a stronger absorption per unit thickness, and the correspond device shows higher IPCE value in the longer-wavelength region. Under the conditions of similar thickness, the blend film prepared at a lower spin-coating speed forms a more uniform microphase separation and smaller domain size which leads to a higher absorption intensity per unit thickness of the blend film in long wavenumber band, a larger short-circuit current density ( J sc ) and a higher power conversion efficiency (PCE) of the PSC device. Noteworthily, it was found that spin-coating speed is not only a way to control the thickness of active layer but also an influencing factor on morphology and photovoltaic performance for the diketopyrrolopyrrole-based terpolymer.

Effect of Spin Coating Speed on Some Optical Properties of ZnO Thin Films

This paper reports the synthesis and characterization of ZnO thin films prepared by sol-gel spin coating technique. The sol-gel was prepared from zinc acetate dehydrate as a precursor, 2-me- thoxyethanol as a solvent and di-ethanolamine as a stabilizer, and then deposited on glass substrate using spin coater at the coating speed of 1000 rpm, 2000 rpm, 3000 rpm, 4000 rpm, 5000 rpm and 6000 rpm. After pre-heated at 150℃, the samples were post-heated at 250oC and also annealed at 400℃. X-ray diffraction (XRD) of the films showed polycrystalline hexagonal structure, with (002) orientation as most intense peak having a grain size of 28.1 nm. The absorbance of the film decreases with increasing wavelength and the transmittance was generally high between visible regions from 280 nm - 1200 nm. The ZnO films deposited at a spinning speed of 2000 rpm had highest transmittance of 88% in the visible region from 280 nm - 1200 nm. The energy band gap was found to be in the range of 3.23 - 3.40 eV. The thicknesses of the films decreased with increase in coating speed. Based on these results, ZnO thin films obtained could have useful application in transparent conducting oxide electrode in solar cells.

The Effect of the Sol-gel Spincoating Deposition Technique on the Memristive Behaviour of ZnO-based Memristive Device

This paper presents the memristive behavior of zinc oxide thin films deposited on ITO substrate by sol-gel spin coating technique. The spin coating speed was varied from 1000 rpm to 5000 rpm to study the effect it has on the memristive device fabricated. The electrical properties were characterized by using a two-point probe IV (current-voltage) measurement system (Keithley 2400). The thicknesses of the thin films were measured by Veeco Dektak 150 Surface Profiler and it shows that the thickness decreased with the spin coat speed. The lowest thickness was obtained from thin film deposited at 5000 rpm which is 17.47 nm. The highest resistance Roff/Ron ratio was obtained from thin film spin coated at 3000 rpm which is 1.346 with visible ZnO nanoparticle characterized by FESEM (JEOL JSM 6701F). This indicated that the optimum spin coat speed for the zinc oxide-based memristive device is 3000 rpm as it exhibited the best switching behavior.

A New Strategy of Lithography Based on Phase Separation of Polymer Blends.

Herein, we propose a new strategy of maskless lithographic approach to fabricate micro/nano-porous structures by phase separation of polystyrene (PS)/Polyethylene glycol (PEG) immiscible polymer blend. Its simple process only involves a spin coating of polymer blend followed by a development with deionized water rinse to remove PEG moiety, which provides an extremely facile, low-cost, easily accessible nanofabrication method to obtain the porous structures with wafer-scale. By controlling the weight ratio of PS/PEG polymer blend, its concentration and the spin-coating speed, the structural parameters of the porous nanostructure could be effectively tuned. These micro/nano porous structures could be converted into versatile functional nanostructures in combination with follow-up conventional chemical and physical nanofabrication techniques. As demonstrations of perceived potential applications using our developed phase separation lithography, we fabricate wafer-scale pure dielectric (silicon)-based two-dimensional nanostructures with high broadband absorption on silicon wafers due to their great light trapping ability, which could be expected for promising applications in the fields of photovoltaic devices and thermal emitters with very good performances, and Ag nanodot arrays which possess a surface enhanced Raman scattering (SERS) enhancement factor up to 1.64 × 108 with high uniformity across over an entire wafer.

Shear stress-induced enhancement of the piezoelectric properties of PVDF-TrFE thin films

Material properties of PVDF-TrFE related to dipole alignment and crystallinity, such as surface potential, polarization direction, piezoelectric coefficient, and remnant polarization, have been systematically examined to explain the improvement in the piezoelectric properties of PVDF-TrFE formed at a high spin-coating speed. The correlations between the distribution of the dipole moment vector and the degree of crystallinity were studied as a function of strain rate using a computational molecular dynamic simulation.

Tuning the Interfacial Thermal Conductance between Polystyrene and Sapphire by Controlling the Interfacial Adhesion.

In polymer-based electric microdevices, thermal transport across polymer/ceramic interface is essential for heat dissipation, which limits the improvement of the device performance and lifetime. In this work, four sets of polystyrene (PS) thin films/sapphire samples were prepared with different interface adhesion values, which was achieved by changing the rotation speeds in the spin-coating process. The interfacial thermal conductance (ITC) between the PS films and the sapphire were measured by time domain thermoreflectance method, and the interfacial adhesion between the PS films and the sapphire, as measured by a scratch tester, was found to increase with the rotation speed from 2000 to 8000 rpm. The ITC shows a similar dependence on the rotation speed, increasing up to a 3-fold from 7.0 ± 1.4 to 21.0 ± 4.2 MW/(m(2) K). This study demonstrates the role of spin-coating rotation speed in thermal transport across the polymer/ceramic interfaces, evoking a much simpler mechanical method for tuning this type of ITC. The findings of enhancement of the ITC of polymer/ceramic interface can shed some light on the thermal management and reliability of macro- and microelectronics, where polymeric and hybrid organic-inorganic nano films are employed.

In-situ fabrication of dual porous titanium dioxide films as anode for carbon cathode based perovskite solar cell

We develop a dual porous (DP) TiO2 film for the electron transporting layer (ETL) in carbon cathode based perovskite solar cells (C-PSCs). The DP TiO2 film was synthesized via a facile PS-templated method with the thickness being controlled by the spin-coating speed. It was found that there is an optimum DP TiO2 film thickness for achieving an effective ETL, a suitable perovskite/TiO2 interface, an efficient light harvester and thus a high performance C-PSC. In particular, such a DP TiO2 film can act as a scaffold for complete-filling of the pores with perovskite and for forming high-quality perovskite crystals that are seamlessly interfaced with TiO2 to enhance interfacial charge injection. Leveraging the unique advantages of DP TiO2 ETL, together with a dense-packed and pinhole-free TiO2 compact layer, PCE of the C-PSCs has reached 9.81% with good stability.

Study of Optical and Electrical Properties of Organic Thin Films for Photovoltaic Applications

The paper deals with the study of optical, electrical and dielectric properties of thin film organic materials suitable for the preparation of optoelectronic devices (e.g. photodiodes, phototransistors, photovoltaic cells). As active layers palladium phthalocyanine (PdPc[t-Bu] 4 ), fullerene (acceptor material, PCBM) and their mixture (9:5 mass %) were used. Thin films were prepared by two methods: by spin coating (Chemat technology Spin Coater) and by material inkjet printing (Dimatix Materials Printer DMP-2800). UV-VIS spectroscopy and ellipsometry were used to study the optical properties. The paper also presents results of electrical and dielectric measurements. We found out that the properties of all structures prepared by spin coating depend on the rotational speed of spin coater, on the mode of solution casting (static, dynamic) and in the case of material inkjet printing they are too much influenced by the substrate. Samples prepared on the substrate at 60 °C showed a photovoltaic effect with fill factor about 0.25 and the conversion efficiency about 0.2 %. DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7278

High performance planar p-i-n perovskite solar cells with crown-ether functionalized fullerene and LiF as double cathode buffer layers

Double cathode buffer layers (CBLs) composed of fullerene derivative functionalized with a crown-ether end group in its side chain (denoted as PCBC) and a LiF layer were introduced between the PCBM acceptor layer and the top cathode in planar p-i-n perovskite solar cells (pero-SCs) based on CH3NH3PbI3−XClX. The devices with the PCBC/LiF double CBLs showed significant improvements in power conversion efficiency (PCE) and long-term stability when compared to the device with LiF single CBL. Through optimizing the spin-coating speed of PCBC, a maximum PCE of 15.53% has been achieved, which is approximately 15% higher than that of the device with single LiF CBL. The remarkable improvement in PCE can be attributed to the formation of a better ohmic contact in the CBL between PCBC and LiF/Al electrode arising from the dipole moment of PCBC, leading to the enhanced fill factor and short-circuit current density (Jsc). Besides the PCE, the long-term stability of the devices with PCBC interlayer is also superior to that of the device with LiF single CBL, which is due to the more effective protection for the perovskite/PCBM interface.

Crystallisation behaviours of ferroelectric P(VDF-TrFE) ultrathin films on different substrates

A series of ferroelectric polymer ultrathin films on different substrates were fabricated by spin coating. Thickness of the ultrathin films was easy to manipulate through tuning the polymer concentration or spin-coating speed. Crystallisation behaviours of these ferroelectric films on different substrates such as bare silicon, silicon coated with Cr or Au, were investigated by atomic force microscopy. The substrates had remarkable effect on the morphologies of the ferroelectric ultrathin films after annealing. Ferroelectric polymer ultrathin film on bare silicon grew to lamellar crystals, while the ultrathin film on silicon coated with Au came into being ‘ball-like’ crystals which were aggregated by smaller ones. The crystallisation behaviour of ferroelectric ultrathin film on silicon coated with Cr was closely related with its heat history. The film annealed immediately after fabrication generated rodlike crystals, which connected with each other. However, the one annealed after storage for a week in desiccator created spherulites, and these spherulites collided with each other and generated curved lamellae which were twisted. The different crystallisation behaviours of the ultrathin films may be due to the surface energy of different substrates. Moreover, P(VDF-TrFE) ultrathin film showed ferroelectricity although its thickness is about 10 nm.

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells.

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n+ emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion.

Interpretation of Ostwald ripening of catalytic nanoparticles based on the radial breathing mode in single-walled carbon nanotubes

Catalytic nanoparticle (NP) size is the crucial factor that determines carbon nanotube (CNT) diameter. Therefore, we explored the Ostwald ripening phenomenon of catalytic NPs from the radial breathing modes in resonant Raman spectra of synthesized single-walled CNTs (SWCNTs). SWCNTs were synthesized using chemically derived monodisperse Fe oxide catalytic NPs by a conventional thermal chemical vapor deposition system. The density of the NPs was manipulated by simply adjusting the spin-coating speed and cycle. The diameter distribution and tube type (SWCNTs or multi-walled CNTs) were thereby determined, which can be understood by density-dependent Ostwald ripening of the NPs. As a result, the diameter-selective growth of SWCNTs was successfully achieved, which will be useful for SWCNTs-based electronic applications.

Solution-Processed Copper Iodide as an Inexpensive and Effective Anode Buffer Layer for Polymer Solar Cells

In this work, a CuI anode buffer layer prepared from a facile solution-processed method was introduced in polymer solar cells (PSCs). The CuI films obtained under different spin-coating speeds and anneal treatments, and the performances of corresponding device fabricated with these CuI films were systematically investigated. The results showed that the devices based on CuI anode buffer layer displayed superior performance than conventional devices using poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) sulfonic acid (PEDOT/PSS). The highest power conversion efficiency of the PSCs based on CuI layer reached 4.15% under the illumination of AM 1.5G, 100 mW/cm2. Furthermore, the pristine CuI layer could be applied in PSCs immediately, which shortened the production time of PSCs.

Micro-Gap Electrodes Fabrication by Low Cost Conventional Photo Lithography Technique and Surface Characterization by Nanoprofiler

The fabrication of sensitive and selective nanodevices is one of the important challenges for future detection of low concentration single bio molecule. The current research article is one of the attempts to achieve such sensitive and selective micro-gap electrodes by simple, low cost controllable process. Therefore high sensitive chrome mask was designed for micro-gap design transformation to wafer samples. At first the positive photoresist namely PR-1 2000A was spin coated on the samples wafer at different rotation speed. Then by implementation of low cost conventional photolithography technique an initial structure of micro-gap was patterned on wafer sample. Finally by using surface Nanoprofiler the thickness of resist coated wafer samples were investigated. The obtained results show that the thickness of the resist is directly related with spin coating speed of spin coater.

Study of an antireflection surface constructed of controlled ZnO nanostructures

Zinc oxide (ZnO) nanostructures were fabricated on Si wafers using a hydrothermal method. By adjusting the spin-coating speed and annealing time for the zinc acetate thin films used as a seed layer, the density of ZnO nanorods (NRs) was controlled. In addition, it was found that the morphology of the NRs evolved from a wire-like geometry to a tower-like geometry with an increasing concentration of ascorbic acid. The surface reflectance of the ZnO NR layers with various textures was investigated. The results indicated that NRs effectively enhanced light trapping and further reduced Fresnel reflection due to the significant grading in the refractive index, avoiding the abrupt transition at the air/Si interface. The total reflectance on the coated surface can be as low as 11%, which is 3 times lower than that of polished Si. The optimized design of nanostructured ZnO surfaces for antireflection coatings will greatly improve the performance of optoelectronic devices.