Root Mean Square Roughness Research Articles

Silicon nitride shadowed selective area growth of low defect density vertical GaN mesas via plasma-assisted molecular beam epitaxy

Ion bombardment during inductively coupled plasma reactive-ion etching and ion-implantation introduces irreparable crystalline damage to gallium nitride (GaN) power devices, leading to early breakdown and high leakage current. To circumvent this, a bi-layer selective area growth mask was engineered to grow up to 3.0 µm thick epitaxy of GaN using plasma-assisted molecular beam epitaxy as an ion-damage-free alternative to standard epitaxial processing routes. The masks and regrown architectures are characterized via SEM, conductive-atomic force microscopy (AFM), x-ray photo electron spectroscopy, Raman, and cathodoluminescence. Mask deposition conditions were varied to modulate and minimize the stress induced during thermal cycling. The resulting mesas exhibit low leakage, attributed to naturally terminated sidewalls as measured by an innovative perpendicular AFM measurement of the regrown sidewall. The regrown sidewall exhibited RMS (root mean square) roughness of 1.50 (±0.34) nm and defect density of 1.36 × 106 (±1.11 × 106) cm−2. This work provides a method to eliminate defect-inducing steps from GaN vertical epitaxial processing and stands to enhance GaN as a material platform for high-efficiency power devices.

Rolling mechanism profundities on material removal mechanism of surface-textured GaN using Molecular dynamics simulation

Molecular dynamics simulation examines how the polishing tool's rotating velocity and axes affect surface nanotribological properties and material removal mechanism of patterned gallium nitride (GaN) substrates. Frictional coefficient and average contact area affect material removal rate (MRR) variance. Rotating speed increases the frictional coefficient and contact area, elevating MRR. Anticlockwise abrasives have substantially higher root-mean-square roughness (RMS) than clockwise ones. After polishing, increasing the rotating angle increases the frictional coefficient, average contact area, MRR, and RMS. MRR enhancement is maximum at −15 rad/ns, the only spinning velocity that improves MRR. RMS improvement ratio is highest when the polishing tool spins clockwise or the rotational axis orientation is lowered. Particularly, the MRR and RMS improvements after the polishing process can reach 103.8 % and 223.5 %, respectively. These findings help explain atomic-scale GaN-based material removal and deformation with frictional resistance and erosion by polishing.

TXRF capability of metallic contamination analysis on rough silicon wafers

AbstractTotal X-Ray Fluorescence (TXRF) is a non-destructive technique for the characterization of metallic contaminants on bare silicon wafers. TXRF is sensible to roughness leading to a diffraction phenomenon. In this study, the effects of roughness on TXRF analysis were evaluated with various rough silicon wafers produced by microelectronic processes of grinding, wet cleaning and chemical mechanical polishing. TXRF parameters rise as roughness increases, starting from 3 nm RMS (Root Mean Square) roughness. On spectra, characteristic Si (silicon wafer) and W (TXRF anode) peaks widen. Secondary peaks, sum/escape peaks appear, inducing interferences with Al, Cu, Zn and background noise increases as well. Through intentionally contaminated grinded wafers (RMS 12 nm) by spin-coating at selected concentrations, it was observed that most of the elements are quantified at 1 × 1012 at/cm2. At concentrations of 1 × 1010 at/cm2 and 1 × 1011 at/cm2, only few elements are quantified due to the elevated background noise and interferences. Graphical abstract

Investigation of structural and optical properties of ZnTiO3 thin films irradiated with 50 MeV oxygen ions

This paper aims to investigate the effects of high-energy ion irradiation on the structural, morphological, optical, and luminescent characteristics of ZnTiO3 (ZTO) films. ZTO films were grown on silicon and quartz substrates via RF magnetron sputtering in pure argon ambiance and annealed at 800 °C for crystallization. The annealed (pristine) samples were irradiated with 50 MeV oxygen ions at three distinct fluences: 1 × 1012, 5 × 1012, and 1 × 1013 ions/cm2. X-ray diffraction (XRD) data demonstrates that the intensity of highly oriented (311) peak first increases with fluence up to 5 × 1012 and then decreases at 1 × 1013 ions/cm2. The root mean square roughness (RMS) increases initially from 8.22 (pristine) to 9.10 nm (1 × 1012 ions/cm2) and decreases to 8.25 nm for 1 × 1013 ions/cm2 fluence. Transmittance spectra indicate an enhancement in the transmission of irradiated films. The calculated band gap of pristine and irradiated films lies in the range of 3.93–3.84 eV. X-ray photoelectron spectroscopy (XPS) analysis reveals a reduction in oxygen vacancies up to a fluence of 5 × 1012 and then rises at 1 × 1013 ions/cm2. The enhancement of peak intensity is observed in photoluminescence (PL) spectra on increasing the ion fluence due to a reduction in the non-radiative recombination centers.

Computational and experimental investigation of anticorrosive potential of Panthenol for mild steel in 1 M hydrochloric acid solution

An investigation into how Panthenol affects the corrosion of mild steel in 1 M hydrochloric acid was carried out, specifically its adsorption behaviour and the mechanism by which it inhibited corrosion and for this electrochemical analysis techniques, weight loss, scanning electron microscopy, atomic force microscopy, contact angle measurements has been used. Also, the theoretical study which includes study of global reactivity descriptors EHOMO, ELUMO, energy gap (∆E) etc. and molecular dynamics (MD) simulations in aqueous phase have been used to simulate the real situation. This study confirmed a high inhibition efficacy of 90 % at a concentration of 400 ppm. The electrochemical analysis demonstrated that as the concentration of Panthenol increased, there was an apparent reduction in the value of jcorr and an upsurge in the value of Rct. In case of potentiodynamic polarization, the value of jcorr came out to be 144 μA cm−2 and in electrochemical impedance spectroscopy, the value of Rct came out to be 125.32 Ω cm2 at 400 ppm. The surface morphological investigations revealed the deposition of an extensively protective coating on the mild steel surface. Calculated values of roughness (average and root mean square in nm) in the present study shows a reduction in roughness (in the acid the values were 401 nm, 518 nm respectively and acid with Panthenol, the values were 56.9 nm and 82.5 nm, respectively). In quantum chemical calculations, the calculated value of ΔE came out to be 5.098, validating the strong tendency of inhibitor to retard the corrosion. The investigation revealed that Panthenol is an effective and environmentally friendly inhibiting agent of corrosion for mild steel in a 1 M HCl solution. Additionally, the theoretical findings reiterated the experimental results obtained in this study.

Highly transparent and highly hydrophobic coating for outdoor camera window glass: Fabrication, transparency, and hydrophobicity

Highly transparent, superhydrophobic coatings are highly desirable for maintaining long-lasting clarity for outdoor camera windows. In this study, the authors present a simple approach to create a wide–range anti-reflective and highly hydrophobic layer on a glass surface. This is accomplished through a hydrothermal alkali etching process combined with a dip-coating process using 1 H, 1 H, 2 H, 2 H-Perfluorooctyltrimethoxysilane (POTS). The sample, etched for 20 h and modified by POTS, exhibiting an average transmittance of 96.5 %, a water contact angle (WCA) of 140° and a sliding angle (SA) of 40°. The results of the water spray experiment indicate this surface exhibits excellent water repellent performance, preventing water droplets larger than 0.01 mm in size. The relationship between optical transmittance and etching depth was thoroughly studied, revealing that an etched depth ranging from 200 nm to 600 nm yields optimal wide-spectrum anti-reflective properties. Furthermore, the influence of surface roughness on apparent WCA and SA was investigated. It was found that root mean square (RMS) roughness can be an effective factor to predict the apparent WCA of a surface, while both the RMS roughness and morphological structure affect the SA.

Correlation between structural, morphological, and electrical transport properties of nano-dimensional Tellurium thin film by low energy ion beam irradiation

Tellurium (Te), an emerging semiconductor material, exhibits intriguing physical properties in low-dimensional forms. This study investigates the structural, morphological, and transport properties of low-dimensional Te thin film deposited by physical vapor deposition after 400 keV Kr2+ ion irradiation with varying fluences of 1 × 1013, 5 × 1013, and1 × 1014 ions-cm−2. The X-ray diffraction (XRD) pattern reveals the hexagonal phase of pristine Te. As ion fluence increases, intensity of the XRD peaks decreases and the full-width half maxima (FWHM) increases, indicating a reduction in crystallinity. The intensity of the Raman peak decreases upon irradiation, resulting in a red shift in the spectra of the irradiated sample. The evolution of morphology at different fluences has been examined with atomic force microscopy (AFM) measurements. The results indicate the segregation of grains and an increase in root mean square (RMS) roughness from 2.59 pm to 5.11 pm with ion fluence up to 5 × 1013 ions-cm−2. At the highest fluence, i.e., 1 × 1014 ions-cm−2, there is an agglomeration of grains, and hence a decrease in RMS roughness to 3.92 pm is observed. The DC resistivity measurement indicates the semiconducting nature of all films. Additionally, this measurement signifies the rapid decrease in activation energy at both band-to-band conduction and nearest neighbour hopping (NNH) conduction. Following irradiation, Hall measurement demonstrates a decrease in the concentration of charge carriers and an increase in resistivity due to scattering originating from grain boundaries. However, when the fluence is increased to 1 × 1014 ions-cm−2, there is a reduction in resistivity and an increase in carrier concentration with enhanced Hall mobility in comparison to pristine Te. Therefore, this study showcases that low-energy ion irradiation has a significant impact on the modification of the structure, morphology, and electrical transport properties of semiconducting Te thin film.

Relationship between topographic parameters and BRDF for tungsten surfaces in the visible spectrum

In metallic fusion devices, parasitic light originating from multiple reflections on the wall is a major problem for the interpretation of optical diagnostics. Strong stray light affects several optical diagnostics in ITER. One possibility to cope with this reflected light is to use photonic simulation, which can accurately predict the behavior of light within complex 3D geometry. A prerequisite is to get a good description of the reflection model, represented by the Bidirectional Reflectance Distribution Function (BRDF), based on optical measurements of in-vessel materials. To avoid complicated measurements using goniophotometer to get the BRDF, one possibility is to link surface optical properties and topography characteristics, such as roughness measurements, for example, using the classical Bennett’s formula. Measurements were performed using two experimental goniophotometers to fully characterize the BRDF of tungsten samples with different roughness values. Surface topography was measured using a three-dimensional laser scanning confocal microscope. Several parameters were extracted from these measurements including the arithmetic average roughness (Ra), the root mean square roughness (RMS), the Surface Inclination Angle Distribution and furthermore its mean value δm and the power spectral density (PSD). The correlations of BRDF model parameters deduced from the measurements are compared with the previous topographic parameters. The initial results on several tungsten samples show that Ra, which is the usual measure of surface roughness, is not the most suitable metric to link with the reflection behavior of the surface. In contrast, the PSD and the surface inclination angle are interesting metrics for describing the reflected light.

Structural and Morphological Characterization of MEH-PPV/Ag Composite

In this study, spin coating was used to prepare thin films of poly (2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylene vinylene) and silver (MEH-PPV/Ag) in this study. The physical characteristics of MEH-PPV/Ag thin films with various weight ratios (0.01, 0.02, 0.03, and 0.04%) were investigated by Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction analysis (XRD), and thermal testing. FTIR analysis showed that there were occurrences of the polymer's predicted chemical bonds. AFM tests show that when different amounts of silver are added to a polymer matrix, the film's surface roughness (root mean square) goes up from an average of 83.51 to 511.3 nm. FE-SEM analysis showed that a pure sample of the polymer formed evenly. However, when different amounts of Ag were added, clear balls or circles formed, showing the energy of mixing between the MEH-PPV and Ag. As silver addition transformed the polymer from amorphous to polycrystalline, XRD analysis revealed both phases. In tests comparing pure MEH-PPV to MEH-PPV/Ag, the polymer containing silver showed higher thermal conductivity.

Experimental Study on Dispersion Stability and Polishing Performance of Polishing Solution Based on Micro-Abrasive Water Jet Polishing

In micro-abrasive water jet polishing (MAWJP) technology, where abrasive particles serve as polishing tools, particles tend to form large clusters, leading to increased nozzle wear and diminished material polishing quality. Achieving a polishing solution with good dispersion stability is crucial for enhancing polishing accuracy and minimizing nozzle wear. Therefore, this study employed three dispersants with distinct dispersion mechanisms to examine the impact of each dispersant’s concentration on the dispersion stability of the polishing solution across various abrasive concentrations. Through experimentation, the optimal dispersant type and concentration ratio of abrasive to dispersant were determined, and the effect of the selected dispersant on jet polishing performance was validated. The results of the dispersion stability experiment indicated that, in comparison to Na(PO3)6 and polyethylene glycol (PEG), the polishing solution containing 1.0–2.0 wt% phosphoric ester compounds exhibited a more stable dispersion effect (zeta potential < −50 mV) and superior dispersibility, characterized by a smaller average particle size. Furthermore, K9 optical glass was subjected to fixed-point and local polishing using phosphoric ester compounds as the dispersant. The fixed-point polishing experiment revealed that, at a dispersant concentration of 1.0 wt% and an abrasive concentration of 20 wt%, a smooth and symmetrical material removal profile could be achieved. In the local polishing experiment, the reduction rate of the root mean square of the surface roughness (RMS) increased from 54.33% to 82.24%, and the reduction rate of peak-to-valley height difference in surface (PV) increased from 38.84% to 68.97%. In conclusion, the incorporation of a dispersant proves effective in enhancing the dispersion stability of the polishing solution and dispersibility of the abrasive particles, thereby improving the surface quality of the materials in MAWJP.

CO2 gas-triggered wettability control of silylation-modified CNC films by manipulating the surface structure and introducing tertiary amino groups

Here, cellulose nanocrystal (CNC) films were chemically modified in a two-stage process to realize surface wettability control through the introduction of CO2 gas. In addition to controlling the surface structure of the silylation-modified CNC film, functional groups derived from silane compounds were installed, and the corresponding effects on the resulting chemical modification were investigated. In the first stage, methyltriethoxysilane (MTES) and hexyltriethoxysilane (HTES) combined with tetraethoxysilane (TEOS) were subjected to condensation under alkaline conditions. In the second stage, (3-(N,N-dimethylamino)propyl)trimethoxysilane (DMAPS) generated an amino group to control the surface wettability by adsorption CO2 gas. Then, the silylation-modified CNC film was fabricated on a glass substrate by spin coating. Fourier transform infrared (FT-IR), nuclear magnetic resonance (29Si-NMR), and X-ray photoelectron spectroscopy (XPS) inspection indicated that the silane compounds were bonded to the CNC film surface and that tertiary amino groups were successfully introduced. The surface structure of the silylation-modified CNC film was analyzed by atomic force microscopy (AFM), and the surface roughness calculating indicated a root-mean-square roughness (RMS) of 4.2 nm. The water contact angles before and after the CO2 gas treatment were evaluated as 73o and 22o, respectively.

Two-step ion beam treatment for superhydrophilic fluorinated polymers

Plasma treatment is a widely used simple and ecofriendly method to improve the surface wettability of polymers. However, this is challenging for fluorinated polymers because of their robust CF bonds with low surface energies. Here, we demonstrated a simple approach, involving Ar-H2 and O2-H2 two-step ion beam treatments, to achieve superhydrophilic fluorinated polymer surfaces. The effects of surface roughness and chemical composition on the water contact angle (WCA) were studied using X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. After the single H2 ion beam treatment on fluorinated ethylene propylene films, the WCA decreased from 110.2° to 35.2° due to defluorination and oxidation effects. However, the H2 ion beam treatment alone has a limited effect on the root-mean-square (RMS) roughness, which hinders achieving superhydrophilicity. In contrast, the WCA significantly decreased to 1.3° and 1.2°, respectively after the Ar-H2 and O2-H2 two-step ion beam treatments. Although the chemical composition after these treatments was similar to that after the single H2 ion beam treatment, the RMS roughness increased upon the Ar and O2 ion beam treatments because of the formation of nanostructures. Our results show that nanostructures with abundant polar oxygen bonds are required to obtain superhydrophilic surfaces in fluorinated polymers.

The role of the areal parameters on turbulent flow over 2D Gaussian roughness

In the past decades, numerous efforts have been dedicated to establishing a direct correlation between a geometric parameter that represents wall roughness and the corresponding velocity reduction, known as the Roughness Function ΔU+. This reduction is influenced by various statistical measures of roughness height, including average roughness height, peak-to-valley roughness distance, roughness root mean square, and Effective Slope, among others. It has been demonstrated that a singular measure of roughness height cannot sufficiently predict the Roughness Function across all turbulent regimes. Consequently, many studies have concentrated on identifying a universal correlation between roughness geometry and the downward shift of the mean velocity profile. In this study, we investigated the correlation between various geometrical parameters and the Roughness Function using Large Eddy Simulation (LES) techniques in channel flows at a friction Reynolds number of Reτ=400. Given the complexity introduced by the random nature of irregular roughness, we explored specific aspects of the relationship between wall irregularities and the roughness function by studying 2D geometries. This approach allowed us to systematically investigate the impact of geometrical properties on the roughness function and isolate the effects of roughness density and coverage area. Several irregular rough surfaces, characterized by different average oscillations height, different distributions and different densities, were designed throughout 2D Gaussian functions. With the aim to find a universal correlation between the roughness geometry and the Roughness Function, new geometrical quantities were investigated, based on the global area occupied by the roughness A∗. The prediction of the roughness function can be thus obtained using apriori data. To predict the roughness function, we introduced a parameter called Effective Area (EA), which is derived from the correlation between the Effective Slope (ES) and the roughness area A∗. Our findings indicate that a single geometric parameter, whether ES or Area A, is insufficient to predict the roughness effect. Conversely, combining these two parameters enhances predictive accuracy, at least for the proposed roughness model. This improvement can be attributed to the ability of ES to interpret the roughness distribution and height, while the coverage area is effective in predicting roughness density over a flat plate.

Covalent crosslinking chemistry for controlled modulation of nanometric roughness and surface free energy.

Smooth interfaces embedded with low surface free energy allow effortless sliding of beaded droplets of selected liquids-with homogeneous wettability. Such slippery interfaces display low or moderate contact angles, unlike other extremely liquid repellent interfaces (e.g. superhydrophobic). These slippery interfaces emerged as a promising alternative to extremely liquid repellent hierarchically rough interfaces that generally suffer from instability under severe conditions, scattering of visible light because of the hierarchically rough interface, entrapment of fine solid particulates in their micro-grooves and so on. However, a controlled and precise modulation of surface free energy and nanometric roughness is essential for designing a more compelling solid and dry antifouling interface. Here, we have unprecedentedly demonstrated the ability of covalent cross-linking chemistry for precise and simultaneous modulation of both essential surface free energy (∼49 mN m-1 to ∼22 mN m-1) and roughness (root mean square roughness from 30 nm to 3 nm) of a solid interface for achieving liquid, substrate, and process independent, robust slippery properties. The strategic selection of β-amino-ester linkage through a 1,4-conjugated addition reaction between amine and acrylate groups of a three component reaction mixture (dominated by a 61% (w/w) crosslinker) under ambient conditions provided a facile basis for associating various important and relevant properties-including self-cleaning ability, anti-smudge properties (against both water and oil-based inks), thermal stability (>300 °C), chemical stability, physical durability, optical transparency (∼95%) and so on. The embedded slippery properties of the coating remained unaffected at both low (0 °C) and high (100 °C) temperatures. Thus, the prepared coating would be appropriate to maintain the unperturbed performance of commercially available solar cell modules and other relevant objects under outdoor conditions.

(First Best Student Paper Award) Polymer to Silicon Direct Bonding for Microelectronics

Direct bonding consists in spontaneously bringing into contact two solid surfaces without any intermediate liquid. A liquid is defined here as a being thick enough to have fluid characteristics. Silicon direct bonding is widely used in microelectronics, for instance for the production of silicon-on-insulator substrates (for transistor manufacturing). Direct bonding can be performed between identical surfaces, for example, two silicon substrates. However, direct bonding is also feasible with two different surfaces such as silicon and metal.Direct bonding of two solid materials requires very strict surface conditions such as planarity, particle cleanliness and low surface roughness. The surface Root Mean Square (RMS) roughness should be lower than 0.5 nm for hydrophilic silicon bonding and 0.3 nm for hydrophobic silicon bonding [1].We will focus here on direct bonding with polymer films. It is a quite innovative bonding as polymers are materials with very different properties compared to silicon. They are indeed not crystalline, much less rigid and most of the time hydrophobic.Five different polymers thin films are used to evaluate direct bonding with polymers: LOR2A, BARC AR26N, SOC HM8102, TOK TDMR and LTC9310. Thicknesses are between 32 nm and 6 µm. Those polymers are deposited on 200 or 300 mm diameter Si substrates.First of all, polymers are characterized by Fourier-Transform Infrared Spectroscopy (FTIR), spectroscopic ellipsometry and Thermogravimetric Analysis (TGA). Contact angles of the different polymers are in the 58° to 77° range, a feature which is a characteristic of hydrophobic surfaces. For comparison, the contact angle is lower than 5° for hydrophilic silicon (SiO2) and 78° for hydrophobic H-passivated silicon (Si). The surface roughness of the five different polymers is evaluated by Atomic Force Microscopy (AFM), with RMS roughness ranging from 0.29 to 0.40 nm found. Such values are in-between the 0.3 nm and 0.5 nm thresholds for hydrophobic and hydrophilic surface bonding, respectively. However, direct bonding is feasible between polymers and hydrophilic or hydrophobic silicon surfaces in all cases. Bonding waves are observed and characterized by infrared imaging. Adhesion energies for bonding with the five different polymers are between 40 and 70 mJ/m². Meanwhile, the bonding wave velocity is in the 10-19 mm/s range. Data for polymer to hydrophilic silicon bonding are provided in Table 1. They can be compared to Table 2 data for hydrophilic and hydrophobic silicon bonding (i.e. ceramic bonding) as they have equivalent water contact angles. Polymer to Si direct bonding has higher adhesion energy and bonding wave velocity than SiO2 to Si ceramic direct bonding. The bonding interface, characterized by Scanning Acoustic Microscopy (SAM), does not reveal any bonding defects. Bonded stacks can be annealed at different temperatures. Acoustic images of bonding with BARC are shown in Figure 1 for different annealing temperatures. It is possible to measure their adherence energy after annealing using the DCB (Double Cantilever Beam) technique [2]. BARC adherence energies are given in Figure 2. As with ceramic bonding, bonding strengthens as the temperature increases. The covalent bonds density should increase during the annealing. The bonding degradation at 250°C and especially 300°C evidenced by Scanning Acoustic Microscopy (SAM) is in line with TGA findings on polymer degradation, with a threshold at 280°C. X-ray Photoelectron Spectroscopy is being used to identify interactions between the silicon surface and the polymer. A mechanism will be proposed for these innovative bondings.[1] H. Moriceau et al., « Overview of recent direct wafer bonding advances and applications », Adv. Nat. Sci. Nanosci. Nanotechnol., vol. 1, no 4, p. 043004, févr. 2011, doi: 10.1088/2043-6262/1/4/043004.[2] W. P. Maszara, G. Goetz, A. Caviglia, et J. B. McKitterick, « Bonding of silicon wafers for silicon‐on‐insulator », J. Appl. Phys., vol. 64, no 10, p. 4943-4950, nov. 1988, doi: 10.1063/1.342443. Figure 1

Enhancing photocatalysis through annealing: Unveiling the role of physical properties in photocatalytic behavior

Using spray pyrolysis, silver-doped In2S3 thin films were deposited on pre-heated glass substrates, with varying doping concentrations. Subsequently, these films underwent vacuum annealing at 400 °C for a duration of 2 h. A comprehensive study of their structural, morphological, and optical properties was conducted, revealing homogeneous, compact, crack-free films with polycrystalline tetragonal-phase of In2S3. Among the set of the analyzed films the best parameter values, including crystallite size, dislocation density, micro-strain, grain size, and root mean square (RMS) roughness, were achieved when maintaining a Silver-to-indium (|Ag|/|In|) ratio of 4 % in the precursors for both as-deposited and annealed samples. The annealing process had a discernible impact on the grain size distribution, resulting in a significant increase in crystallite and grain size, along with RMS roughness, for most doped films. The optical analysis of these films unveiled their transparency in the visible and near-infrared regions, coupled with substantial absorption in the UV region. Higher Ag concentration in the as-deposited films led to an increased band gap energy in the annealed samples. The roughness peaked at |Ag|/|In| = 4 %, resulting in a noteworthy enhancement of photocatalytic activity, achieving 95 % photodegradation of a methylene blue aqueous solution. This underscores the critical role of surface properties in determining performance. Future research intends to explore other applications for these thin films, including potential usage in gas sensors, capitalizing these films' promising characteristics.

Influence of diamond matrix morphology on ZnO surface morphology and preferred orientation

The signal propagation loss and conversion efficiency are two critical performances of diamond/ZnO film-based surface acoustic wave (SAW) device, and depend on roughness and preferred orientation degree (POD) of ZnO surface layer at plane (002). In-situ improvement of operational performance of ZnO layer is achieved by adjusting morphology of diamond matrix layer via diamond particle size. Diamond layer is deposited on silicon substrate using hot-filament chemical vapor deposition (HFCVD) technique by varying Ar/(Ar+H2) ratio. The ZnO layer is then deposited on the diamond film using radio-frequency magnetron sputtering (RFMS). The results show that, by regulating the diamond particle size, it is possible to adjust morphology of the diamond layer and facilitate variation in morphology and preferred orientation of ZnO layer for a better operational performance of SAW device. When the diamond particle size is decreased from 1.38 to 0.12 µm, the root-mean-square (RMS) roughness of ZnO layer initially drops and then rises, and the lowest roughness is 6.4 nm. Also, POD of ZnO (002) increases from 2.61 to 2.89, and then drops to 2.83. For a diamond particle size of 0.35 µm, the RMS roughness of ZnO layer has minimum value of 6.4 nm, and the POD of ZnO (002) approaches the maximum of 2.89 with a half-peak width of 0.36˚. The influence of diamond layer morphology on ZnO morphology and POD is thus proposed.

Machine learning study on organic solar cells and virtual screening of designed non-fullerene acceptors

Machine learning (ML) is effective to establish the complicated trilateral relationship among structures, properties, and photovoltaic performance, which is fundamental issue in developing novel materials for improving power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, we constructed the database of 397 donor–acceptor pairs of OSCs with photovoltaic parameters and descriptor sets, which include donor–acceptor weight ratio within the active layer of the OSCs, root mean square of roughness, and 1024-bit Morgan molecular fingerprint for donor (Fp-D) and acceptor (Fp-A). The ML models random forest (RF), adaptive boosting (AdaBoost), extra trees regression, and gradient boosting regression trees were trained based on the descriptor set. The metrics determination coefficient (R2), Pearson correlation coefficient (r), root mean square error, and mean absolute error were selected to evaluate ML model performances. The results showed that the RF model exhibits the highest accuracy and stability for PCE prediction among these four ML models. Moreover, based on the decomposition of non-fullerene acceptors L8-BO, BTP-ec9, AQx-2, and IEICO, 20 acceptor molecules with symmetric A–D–A and A–π–D–π–A architectures were designed. The photovoltaic parameters of the designed acceptors were predicted using the trained RF model, and the virtual screening of designed acceptors was conducted based on the predicted PCE. The results indicate that six designed acceptors can reach the predicted PCE higher than 12% when P3HT was adopted as a donor. While PM6 was applied as a donor, five designed acceptors can achieve the predicted PCE higher than 16%.

Condition assessment of cycle path texture and evenness using a bicycle measurement trailer

ABSTRACT Cyclists’ riding comfort, related to pavement texture and unevenness, has not been thourougly investigated, partly due to the lack of condition assessment methods specifically adapted to the speed and space limits on cycle paths. Metrics that better describe the perceived comfort of cyclists, rather than that of car users, are needed. In this paper a novel method, the Bicycle Measurement Trailer (BMT), is proposed to bridge this gap. Eight different cycle path surface types have been assessed with regards to pavement texture and for four of these surfaces the longitudinal evenness was assessed. The accuracy and repeatability of the BMT were evaluated. Finally, five different metrics (Dynamic Comfort Index, Evenness Coefficient, 0.5 m Straight Edge, International Roughness Index and Root Mean Square), were calculated from the collected data and assessed. The main findings suggest that the BMT has a high accuracy at normal and high cycling speeds and a high level of repeatability at normal cycling speed. The surfaces could be ranked according to texture, and the evenness was successfully analysed. In conclusion, the BMT could be a valuable tool to assess the cycle path surface condition in relation to bicycle riding comfort.

Study on mixed elastohydrodynamic lubrication performance of point contact with non‐Gaussian rough surface

AbstractA numerical method is proposed to evaluate the effect of non‐Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non‐Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro‐contact model. The influence of non‐Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis.