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Effects of background gases and pressure in pulsed laser deposition of Al-doped ZnO
摘要： Background gases (O2, He or Ar) with the pressure from ~ 10?3 Pa to 133.3 Pa are used in 355 nm laser deposition of Al-doped ZnO at room temperature. The effects of these gases and pressure on plasma formation are studied by optical emission spectroscopy (OES) and time of flight (TOF) measurement. The OES results show that the emission intensity of the species in O2 and Ar decrease slightly and then increase exponentially above ~ 5 Pa. The emission intensity in Ar is the highest, followed by emission in O2 whilst the emission in He is low and weakly depend on background gas pressure. TOF measurements indicate that the ion velocity decrease with increasing O2 and Ar pressure at about 5–10 Pa. The ion velocity is highest in He while the ion velocities in O2 and Ar are similar. Thin-film samples deposited in different gas at 2.6 Pa are amorphous, but those deposited at 133.3 Pa are crystalline and exhibit different morphologies and optical properties depending on type of gas. Samples deposited in O2 are highly transparent but those deposited in He and Ar contain nano and micron-sized structures with <50% transmittance. In addition, Zn crystallites are detected by X-ray diffraction.
关键词： Pulsed laser deposition,Background gases,Aluminum-doped zinc oxide,Pressure,Laser produced plasma,Nanostructured films
更新于2025-09-23 15:21:01
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Molecular beam homoepitaxy on bulk AlN enabled by aluminum-assisted surface cleaning
摘要： We compare the effectiveness of in situ thermal cleaning with that of Al-assisted cleaning of native surface oxides of bulk AlN for homoepitaxial growth by molecular beam epitaxy. Thermal deoxidation performed at 1450 (cid:2)C in vacuum results in voids in the AlN substrate. On the other hand, Al-assisted deoxidation at (cid:3)900(cid:2)C results in high-quality AlN homoepitaxy, evidenced by clean and wide atomic terraces on the surface and no extended defects at the growth interface. This study shows that Al-assisted in situ deoxidation is effective in removing native oxides on AlN, providing a clean surface to enable homoepitaxial growth of AlN and its heterostructures; furthermore, it is more attractive over thermal deoxidation, which needs to be conducted at much higher temperatures due to the strong bonding strength of native oxides on AlN.
关键词： surface cleaning,homoepitaxy,molecular beam epitaxy,aluminum-assisted cleaning,AlN
更新于2025-09-23 15:21:01
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Influence of the Wire Feeding on the Wetting Process during Laser Brazing of Aluminum Alloys with Aluminum-Based Braze Material
摘要： The wetting behavior in laser brazing can be designated as inconstant, caused largely by external process discontinuities such as the wire feeding. To reveal periodic melt pool propagation effects that occur during laser brazing of aluminum and for a better understanding of those effects in laser brazing in general, this paper analyzes high-speed recordings of the brazing process with aluminum alloy. It is demonstrated that two main effects of periodic melt pool behavior in different frequency scales occur during the process, related directly to the wire feeding.
关键词： laser brazing,aluminum,process frequencies,melt pool behavior,process dynamics
更新于2025-09-23 15:21:01
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Novel cathode buffer layer of Al(acac)3 enables efficient, large area and stable semi-transparent organic solar cells
摘要： Electrode buffer layer plays a more crucial in semi-transparent organic solar cells (ST-OSCs) than that of the opaque devices due to the additional requirements of the average visible transmittance (AVT) and color rendering index (CRI) besides the power conversion efficiency (PCE). Herein, we developed a novel cathode buffer layer Aluminum(III) acetylacetonate (Al(acac)3) via mild spin-coating with post low temperature heat treatment process. Studies show that Al(acac)3 film possess outstanding optical features and suitable energy level. Namely, the absorption of Al(acac)3 film with thickness of 10 nm is as low as 1% and the transmittance is high up to 95% in the visible and near infrared regions, guarantying full absorption of the photoactive layer and high CRI for ST-OSCs; and the suitable energy level ensures a smooth electron transport and collection process. By introducing Al(acac)3 film in ST-OSCs, the devices based on PM6:Y6 yield an efficiency of 12.41%, an AVT of 25.33% (from 370 nm to 740 nm) and a CRI of 94.6. Encouragingly, the large-area ST-OSC of 100 mm2 with Al(acac)3 buffer layer yields an efficiency of 11.28%. Further long-term stability of ST-OSCs show that the device with encapsulation retains its 60% of the initial PCE over 60 hours continuous illumination. The results indicate that Al(acac)3 is a promising cathode buffer layer for fabricating efficient, large area and stable semi-transparent organic solar cells.
关键词： Semitransparent organic solar cells,cathode buffer layer,stability,Aluminum(III) acetylacetonate,large-area device
更新于2025-09-23 15:21:01
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[Laser Institute of America ICALEO?? 2014: 33rd International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - San Diego, California, USA (October 19a??23, 2014)] International Congress on Applications of Lasers & Electro-Optics - Possibilities of improving weld seam quality in laser welding of aluminum die cast
摘要： The process of aluminum die-casting produces near-net-shape, complex and thin-walled prefabricated parts of aluminum that is more widely applied in all areas of the industry because it has economic advantages compared to other processes in productivity. The technique mostly used in the molding process of aluminum die-casting products is fusion welding, which shows multiple problems: The safe production of pore free welding seams requires an expensive optimization all over the die-casting process as well as the choice of a qualified welding process. Compared to arc welding, the beam welding processes are characterized by high welding speeds, low heat input and consequently by small heat-affected zones and minimal distortion. Thus, the beam procedures are suitable in particular for components in which narrow and deep weld seams are required. Exemplary, aluminum die cast housings are such parts. However, the welds have to meet the desired requirements on the tightness there. This is a great challenge because aluminum die cast tends to pore formation and melt ejection due to its production-related gas content. Respect to the achievable weld seam quality, in particular, electron beam welding exhibits best results. This is due to the process management under vacuum in the range of p = 10-3 hPa, which makes it possible to eliminate atmospheric influences and generally contributes to better degassing. An alternative beam welding procedure is laser beam welding. Compared to the EB welding, however, laser beam weldings of aluminium die cast have an increased porosity. In this paper, different possibilities are presented by which an improvement of weld seam quality in laser beam welding of aluminum die casting can be achieved. Experiments with different laser optical configurations, as well as varying process parameters influence the formation of pores in a considerable extent. In addition, the ambient pressure is a decisive parameter to improve the weld quality. The welding process is more and more stable and the formation of pores is clearly suppressed by decreasing pressure.
关键词： weld seam quality,aluminum die cast,porosity,vacuum,laser welding
更新于2025-09-23 15:21:01
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Directed energy deposition of Al 5xxx alloy using Laser Engineered Net Shaping (LENS??)
摘要： Here, we present directed energy deposition (DED) of wrought-like Al 5xxx AlMg alloy by Laser Engineered Net Shaping (LENS?). A transition from an Al 5083 gas atomized powder feedstock to Al 5754 characteristics of the as-deposited material due to selective evaporation of Mg was observed. Density values obtained by X-ray micro-computed tomography (μ-CT) were compared to those obtained by the Archimedes method. The latter indicated a relative density as high as 99.26%. Possible origins of porosity are discussed. The as-deposited material was comprised of both equiaxed and columnar grains with no preferred crystallographic orientation and mean grain size of 36 μm. The Young's modulus, yield stress, ultimate tensile strength, fracture strain, Poisson's ratio, and total ultimate strain energy (toughness) were determined by uniaxial tensile tests combined with digital image correlation (DIC). Fractography complemented the mechanical testing. A pulse-echo ultrasonic non-destructive test was used to obtain more accurate values of the Young's and shear moduli and to adjust the value of the yield strength accordingly. The measured mechanical properties meet the requirements of international standards for wrought Al 5754 in its annealed condition.
关键词： Additive manufacturing (AM),Mechanical properties,Micro-computed tomography (μ-CT),Laser Engineered Net Shaping (LENS?),Directed energy deposition (DED),Aluminum alloys
更新于2025-09-23 15:21:01
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Rapid laser fabrication of long-term stable superhydrophilic aluminum surface
摘要： A simple method for fabricating stable superhydrophilic aluminum surface is reported in this paper. Controllable micro-nanostructures were prepared on the surface of aluminum plate by nanosecond laser and then soaked in boiled 45% ethanol solution for 2 h as the post-treatment. It is demonstrated that the laser-ablated aluminum plate surface is hydrophilic and then switch to superhydrophilic after a 45% ethanol solution post-treatment. The treated superhydrophilic structure has good hydrophilic stability in a certain period of time. The mechanism of superhydrophilic behavior of aluminum surface treated with laser and ethanol solution was discussed. A new method for preparing stable superhydrophilic surface is proposed in this paper, which is of great significance for the preparation of superhydrophilic surface and the application of superhydrophilic surface in industrial production.
关键词： Superhydrophilic surface,Ethanol solution,Nanosecond laser,Aluminum,Contact angle
更新于2025-09-23 15:21:01
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The relation between magnesium evaporation and laser absorption and weld penetration in pulsed laser welding of aluminum alloys: Experimental and numerical investigations
摘要： It is observed that in laser welding of aluminum alloys, magnesium can evaporate, and the weld penetration is dependent on Mg content of the alloy and Mg loss from the weld pool. In this research, it is proposed that the presence of Mg not in the base metal alloy, but rather the presence of Mg vapor in the plasma plume over the weld pool affects the laser absorption, and it is through this phenomenon that the weld profile and penetration is affected. Numerical simulation was performed to determine the relationship between the weld profile to estimate the effective laser absorption coefficient of four Al alloys and in parallel EPMA technique was used to determine the Mg losses of the weld metals. The combined analysis of the results showed that increasing the laser pulse energy (decreasing laser pulse frequency), Mg evaporation is increased, and that, in turn, increased the effective laser absorption coefficient. However, more laser power absorption does not necessarily mean more weld penetration. Laser absorption results in weld penetration, once the threshold Mg evaporation rate of 200 × ?10 6g/cm2 is passed.
关键词： Pulsed laser welding,Effective absorption coefficient,Aluminum alloys,Evaporation,Magnesium content,Penetration depth
更新于2025-09-23 15:21:01
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Aluminum foil as a substrate for metal enhanced fluorescence of bacteria labelled with quantum dots, shows very large enhancement and high contrast
摘要： Very high surface/metal enhanced fluorescence was observed for E. coli single bacteria cells labeled with composite CdSeS/ZnS quantum dots (QDs) on three substrates: aluminum foil, aluminum film and gold film. The enhancement factors relative to maximum fluorescence intensity on glass for those substrates were in the range of several hundred (up to 500) for two-excitation wavelengths 532 and 633 nm. Contrast as a ratio of signals from QD labeled to signals of QD unlabeled (control) cells was also in the range of 100 s for those substrates and the highest contrast of 370 was observed on Al film. When CdTe QDs were used for labelling cells on all substrates or when fluorescence from cells with both QDs was measured on silver film, low or no enhancement was observed. Overall, untreated aluminum foil demonstrated great potential as low-cost substrate for surface/metal enhanced fluorescence, which delivers even more reproducible signal than gold film.
关键词： E. coli,Bacteria,Enhancement facor,Quantum dots,Single bacterial cell detection,Metal enhanced fluorescence,Contrast,Surface enhanced fluorescence,Aluminum foil,QD toxicity
更新于2025-09-23 15:21:01
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Young’s modulus and fatigue investigation of aluminum nitride films deposited on 304 stainless steel foils using micro-fabricated cantilevers
摘要： Aluminum nitride based (AlN-based) piezoelectric vibration energy harvesters (PVEHs) have been received much attention in the power generation for the device in microelectromechanical systems (MEMS). During the long-time vibration, PVEHs are suffering cyclically dynamic stress. This may result in the defect of the materials, and finally cause the failure of the device. To achieve a reliable design of the device that can work for a long time without failure, the investigation on the mechanical properties of Young’s modulus and fatigue were conducted for AlN films deposited on 304 stainless steel (SUS 304) foils in this study. Two kinds of materials were tested, SUS 304 foils with a thickness of 50 μm (SUS 304 (50 μm)) and a composite material of AlN films deposited on both sides of SUS 304 foils (AlN (1 μm)/ SUS 304 (50 μm)/ AlN (1 μm) structure). The samples were micro-fabricated to cantilevers. Young’s modulus was measured by the micro-cantilever resonance method. The resonant bending fatigue testing method was used to investigate the fatigue properties of the materials. The displacement amplitude of the samples was recorded during the tests. A new criterion by using the change of amplitude versus number of cycles was proposed to define the fatigue life. As results, the Young’s modulus was 184.9 and 342.9 MPa, for SUS 304 foil and AlN film, respectively. Stress-cycle (S-N) curves were plotted by using the proposed criterion successfully. The fatigue strength of SUS 304 foils and the material with AlN/ SUS 304/ AlN structure was estimated to be 294 and 327 MPa, respectively. Fatigue failures of stable crack, intrusions and extrusions, and slip bands, appeared on the surface of SUS 304 foils after the long time vibration. No fatigue failure or surface defect was observed on AlN films.
关键词： 304 stainless steel foil,aluminum nitride film,Young’s modulus,fatigue,micro-fabricated cantilever
更新于2025-09-23 15:21:01