Enhancing the thermal conductivity of polymer-assisted deposited Al_2O_3 film by nitrogen doping

Polymer-assisted deposition technique has been used to deposit Al2O3 and N-doped Al2O3 （AION） thin films on Si（100） substrates. The chemical compositions, crystallinity, and thermal conductivity of the as-grown films have been characterized by X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and 3-omega method, respectively. Amorphous and polycrystalline Al2O3 and AlON thin films have been formed at 700 ℃ and 1000 ℃. The thermal conductivity results indicated that the effect of nitrogen doping on the thermal conductivity is determined by the competition of the increase of Al-N bonding and the suppression of crystallinity. A 67% enhancement in thermal conductivity has been achieved for the samples grown at 700 ℃, demonstrating that the nitrogen doping is an effective way to improve the thermal performance of polymer-assisted-deposited Al2O3 thin films at a relatively low growth temperature.

Synthesis of free-standing Ga_2O_3 films for flexible devices by water etching of Sr_3Al_2O_6 sacrificial layers

Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.

Effect of Al_2O_3 Buffer Layers on the Properties of Sputtered VO_2 Thin Films

VO_2 thin films were grown on silicon substrates using Al_2O_3 thin films as the buffer layers. Compared with direct deposition on silicon, VO_2 thin films deposited on Al_2O_3 buffer layers experience a significant improvement in their microstructures and physical properties. By optimizing the growth conditions, the resistance of VO_2 thin films can change by four orders of magnitude with a reduced thermal hysteresis of 4 °C at the phase transition temperature. The electrically driven phase transformation was measured in Pt/Si/Al_2O_3/VO_2/Au heterostructures. The introduction of a buffer layer reduces the leakage current and Joule heating during electrically driven phase transitions. The C–V measurement result indicates that the phase transformation of VO_2 thin films can be induced by an electrical field.

Electron Cyclotron Resonance Plasma-Assisted Atomic Layer Deposition of Amorphous Al_2O_3 Thin Films

Without extra heating, Al2O3 thin films were deposited on a hydrogen-terminated Si substrate etched in hydrofluoric acid by using a self-built electron cyclotron resonance （ECR） plasma-assisted atomic layer deposition （ALD） device with Al（CH3）3 （trimethylaluminum; TMA） and O2 used as precursor and oxidant, respectively. During the deposition process, Ar was in- troduced as a carrier and purging gas. The chemical composition and microstructure of the as-deposited Al2O3 films were characterized by using X-ray diffraction （XRD）, an X-ray photo- electric spectroscope （XPS）, a scanning electron microscope （SEM）, an atomic force microscope （AFM） and a high-resolution transmission electron microscope （HRTEM）. It achieved a growth rate of 0.24 nm/cycle, which is much higher than that deposited by thermal ALD. It was found that the smooth surface thin film was amorphous alumina, and an interfacial layer formed with a thickness of ca. 2 nm was observed between theAl2O3 film and substrate Si by HRTEM. We conclude that ECR plasma-assisted ALD can growAl2O3 films with an excellent quality at a high growth rate at ambient temperature.

Research of Trap and Electron Density Distributions in the Interface of Polyimide/Al2O3 Nanocomposite Films Based on IDC and SAXS

The distributions of traps and electron density in the interfaces between polyimide （PI） matrix and Al2O3 nanoparticles are researched using the isothermal decay current and the small-angle x-ray scattering （SAXS） tests. According to the electron density distribution for quasi two-phase mixture doped by spherical nanoparticles, the electron densities in the interfaces of PI/Al2O3 nanocomposite films are evaluated. The trap level density and carrier mobility in the interface are studied. The experimental results show that the distribution and the change rate of the electron density in the three layers of interface are different, indicating different trap distributions in the interface layers. There is a maximum trap level density in the second layer, where the maximum trap level density for the nanocomposite film doped by 25 wt% is 1.054 × 10^22 eV·m^-3 at 1.324eV, resulting in the carrier mobility reducing. In addition, both the thickness and the electron density of the nanocomposite film interface increase with the addition of the doped Al2O3 contents. Through the study on the trap level distribution in the interface, it is possible to further analyze the insulation mechanism and to improve the performance of nano-dielectric materials.

The microwave response of MgB2 /Al2O3 superconducting thin films

Microwave characteristics of MgB2/Al2O3 superconducting thin films were investigated by coplanar resonator technique. The thin films studied have different grain sizes resulting from different growth techniques. The experimental results can be described very well by a grain-size model which combines coplanar resonator theory and Josephson junction network model. It was found that the penetration depth and surface resistance of thin films with smaller grain sizes are larger than those of thin films with larger grain sizes.

KH550修饰Al_2O_3及其对PI/Al_2O_3薄膜性能的影响

通过调整KH550的含量对Al2O3粉体表面进行改性,并用红外光谱(FT-IR)和X射线衍射(XRD)对改性后的粉体进行表征,表征结果显示KH550成功的键合到Al2O3粉体表面。然后分别使用Al2O3以及改性Al2O3制备了一系列无机粉体含量为16%(质量分数)的PI复合薄膜,通过扫描电子显微镜(SEM)对复合薄膜的断面微观形貌进行表征,并对复合薄膜的力学性能和击穿场强进行测试。测试结果显示KH550的含量对无机粉体分散情况有较大影响。当KH550含量为2%(质量分数)时,PI/KH550-Al2O3复合薄膜的拉伸强度和断裂伸长率最优,分别为130 MPa,12%,与PI/Al2O3薄膜相比,拉伸强度和断裂伸长率分别提高了22.8%,44.5%,击穿场强与其相近。

Some Studies on Wear and Corrosion Properties of Al5083/Al₂O₃/Graphite Hybrid Composites

Advanced technology has put an increasing demand on the composite materials, particularly more in the areas of dynamic structures. Among the several types of aluminum alloys being used, Al5000 series are widely used in marine and aerospace applications due to their superior corrosion resistance, excellent formability and good welding characteristics. Al5083, a non-heat treatable high Mg-Al wrought alloy, is extensively used for the marine applications. Hence, an attempt has been made in the proposed work to study the effects of Graphite (Gr) and Aluminium oxide (Al2O3) on aluminum hybrid composites involving both hard and soft reinforcements on wear and corrosion properties. The synthesis of hybrid metal matrix composite used in the present study has been carried out by stir casting method. The effects of reinforcement, time duration and particle size on prepared samples of composites have been studied on slurry erosive wear. The static and accelerated corrosion tests have been performed and the microhardness of the developed composites was also investigated. The experimental results on Al5083-Al2O3-Gr hybrid composites revealed that the addition of reinforcement improves the hardness and reduces corrosion and wear rates.

用于含阴离子型聚丙烯酰胺废水处理的硅藻土基Al_2O_3膜

为了有效地分离污水中具有线型结构的阴离子型聚丙烯酰胺(APAM),通过AlCl_3的水解制备出硅藻土基Al_2O_3膜,分别用红外光谱(FT-IR)、X射线衍射(XRD)和扫描电子显微镜(TEM)对样品进行测试。结果表明,在硅藻土的表面已成功组装上Al_2O_3涂层。另外,将硅藻土基Al_2O_3膜用于处理中性废水(APAM和固体悬浮物的浓度分别为60 mg/L和90 mg/L)结果表明,经处理后,滤液中APAM和固体悬浮物的浓度分别为0和34 mg/L,达到了回用的要求(APAM≤5 mg/L、固体悬浮物≤70 mg/L)。因此,硅藻土基Al_2O_3膜在处理含APAM废水时具有显著的优势和应用前景。

Evaluation on Microstructure and Mechanical Behaviour of Al6061-Al₂O₃-Gr Hybrid Composites

Metal matrix composites (MMCs) are gaining widespread recognition in numerous technological fields owing to its superior mechanical properties when compared with conventional metals/alloys. The aluminium based hybrid composites are increasingly being used in the transport, aerospace, marine, automobile and mineral processing industries, owing to the improved strength, stiffness and wear resistance properties. In the present research work, the composites were prepared using the liquid metallurgy technique, in which 2 - 10 weight percentage of Al2O3 particulates and 1 weight percentage of Graphite were dispersed in the base Al6061 alloy. The Casted hybrid composites were subjected to machining process to prepare the specimens according to ASTM standards. Then, the prepared specimens are subjected for assessing the Microstructure followed by its Mechanical behaviors such as, Hardness, Tensile strength, Compressive strength respectively. The microstructure analysis confirms that homogenous distribution of Al2O3 and Gr in the Al6061 matrix alloy and there was a momentous enhancement in decisive tensile strength, compressive strength and hardness properties of the hybrid composite. However, a substantial increase in the compressive strength was noticed in graphite reinforced composites as the graphite content was increased and there was a significant diminution in hardness coupled with monotonic increases in the ductility. Further, the ultimate tensile strength and compressive strength of the composite was noticed;thus the outcome of the study will provide explicit rationalizations for these observable facts. Therefore, the proposed way out in the study can provide ample of approaches to minimize the existing problem by employing this newer hybrid composites.

Plasma-Assisted ALD of an Al_2O_3 Permeation Barrier Layer on Plastic

Atomic layer deposition （ALD） technique is used in the preparation of organic/inorganic layers, which requires uniform surfaces with their thickness down to several nanometers. For film with such thickness, the growth mode defined as the arrangement of clusters on the surface during the growth is of significance. In this work, Al2O3 thin film was deposited on various interfacial species of pre-treated polyethylene terephthalate （PET, 12 μm） by plasma assisted atomic layer deposition （PA-ALD）, where trimethyl aluminium was used as the Al precursor and O2 as the oxygen source. The interracial species, -NH3, -OH, and -COOH as well as SiCHO （derived from monomer of HMDSO plasma）, were grafted previously by plasma and chemical treatments. The growth mode of PA-ALD Al2O3 was then investigated in detail by combining results from in-situ diagnosis of spectroscopic ellipsometry （SE） and ex-situ characterization of as-deposited layers from the morphologies scanned by atomic force microscopy （AFM）. In addition, the oxygen transmission rates （OTR） of the original and treated plastic films were measured. The possible reasons for the dependence of the OTR values on the surface species were explored.

Structure and oxidation resistance of W_(1-x)Al_xN composite films

A series of W1?xAlxN films(0<x<38.6%,mole fraction)were deposited by reactive magnetron sputtering.The composition,microstructure,mechanical properties and oxidation resistance of the films were characterized by EPMA,XRD,XPS,nano-indentation,SEM and HRTEM.The effect of Al content on the microstructure and oxidation resistance of W1?xAlxN films was investigated.The results show that WN film has a face-centered cubic structure.The preferred orientation changes from(111)to(200).The W1?xAlxN films consist of a mixture of face-centered cubic W(Al)N and hexagonal wurtzite structure AlN phases.The hardness of the W1?xAlxN films first increases and then decreases with the Al content increasing.The maximum hardness is36GPa,which is obtained at32.4%Al(mole fraction).Compared with WN film,the W1-xAlxN composite films show much better oxidation resistance because of the formation of dense Al2O3oxide layer on the surface.

双离子束溅射Al_(2)O_(3)高温绝缘薄膜的氧分压研究

采用双离子束溅射沉积法(DIBSD)制备了用作高温绝缘层的Al_(2)O_(3)薄膜,分析了所制备Al_(2)O_(3)薄膜的表面和截面形貌,研究了溅射氧分压对薄膜氧铝元素比的影响,并进一步探讨了氧铝元素比对Al_(2)O_(3)薄膜高温绝缘性能的影响。研究结果表明:双离子束溅射沉积法制备的Al_(2)O_(3)薄膜表面平整度高,粗糙度约为2.86 nm,截面形貌致密,没有微裂纹、空隙等缺陷;溅射氧分压的提高可以增加所制备Al_(2)O_(3)薄膜的氧铝元素比例,18%溅射氧分压下制备的Al_(2)O_(3)薄膜O∶Al约为1.44,接近Al_(2)O_(3)化合物的元素比;18%氧分压溅射的Al_(2)O_(3)薄膜,在1000℃具有6.5 MΩ的绝缘电阻值,高温绝缘性能良好。

Fluorescence spectra of colloidal self-assembled CdSe nano-wire on substrate of porous Al2O3/Au nanoparticles

We present a self-assembly method to prepare array nano-wires of colloidal CdSe quantum dots on a substrate of porous Al2 O3 film modified by gold nanoparticles. The photoluminescence(PL) spectra of nanowires are in situ measured by using a scanning near-field optical microscopy(SNOM) probe tip with 100-nm aperture on the scanning near-field optical microscope. The results show that the binding sites from the edge of porous Al2 O3 nanopores are combined with the carboxyl of CdSe quantum dots’ surface to form an array of CdSe nanowires in the process of losing background solvent because of the gold nanoparticles filling the nano-holes of porous Al2 O3 film. Compared with the area of nonself-assembled nano-wire, the fluorescence on the Al2 O3/Au/CdSe interface is significantly enhanced in the self-assembly nano-wire regions due to the electron transfer conductor effect of the gold nanoparticles’ surface. In addition, its full width at half maximum(FWHM) is also obviously widened. The method of enhancing fluorescence and energy transfer can widely be applied to photodetector, photocatalysis, optical display, optical sensing, and biomedical imaging, and so on.

Fabrication of Homogenous Dispersion TiB_2-Al_2O_3 Composites

In order to get a homogenous mixture and compact of TiB2-Al2O3, hybridization as a surface modification method was used to prepare nano-scale Al2O3 coated TiB2 particles. PE-wax particles were first coated onto TiB2 particles by hybridization, and then the nano-scale Al2O3 particles were coated onto the surface of TiB2 coated by PE-wax particles again. SEM, TEM and EDS were used to characterize the microstructure of as-received core/shell particles and its compacts. The experimental results show that a particle-scale homogenous dispersion of TiB2 and Al2O3 can be formed not only in mixed powder but also in dewaxed compacts. The compacts then were sintered by gas-pressing sintering （GPS）. Finial products show improved mechanic properties comparing with reference samples fabricated by normal ways.

Effects of Atomic Oxygen Irradiation on Transparent Conductive Oxide Thin Films

Transparent conductive oxide （TCO） thin film is a kind of functional material which has potential applications in solar cells and atomic oxygen （AO） resisting systems in spacecrafts. Of TCO, ZnO：Al （ZAO） and In2O3：Sn （ITO） thin films have been widely used and investigated. In this study, ZAO and ITO thin films were irradiated by AO with different amounts of fluence. The as-deposited samples and irradiated ones were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and Hall-effect measurement to investigate the dependence of the structure, morphology and electrical properties of ZAO or ITO on the amount of fluence of AO irradiation. It is noticed that AO has erosion effects on the surface of ZAO without evident influences upon its structure and conductive properties. Moreover, as the amount of AO fluence rises, the carrier concentration of ITO decreases causing the resistivity to increase by at most 21.7%.

Taguchi approach to influence of processing parameters on erosive wear behaviour of Al7034-T6 composites

Taguchi technique was used to predict the influence of processing parameters on the erosive wear behavior Al7034-T6composite reinforced with SiC and Al2O3particles in different mass fractions.These hybrid metal matrix composites(HMMCs)werefabricated by using a simple technique called stir casting technique.Scanning electron microscope(SEM)was used to study thesurface morphology of the composite and its evolution according to processing time.The design of experiment(DOE)based onTaguchi’s L16orthogonal array was used to identify various erosion trials.The most influencing parameter affecting the wear rate wasidentified.The results indicate that erosion wear rate of this hybrid composite is greatly influenced more by filler content and impactvelocity respectively compared to other factors.This also shows the significant wear resistance with the increase in the filler contentsof SiC and Al2O3particles,respectively.

Fabrication of GaN epitaxial films on Al_2O_3/Si (001) substrates

Single crystal GaN films of hexagonal modification have been fabricated on Al2O3/Si （001） substrates via a low pressure metalorganic chemical deposition （LP-MOCVD） method. The full width at half-maximum of （0002） X-ray diffraction peak for the GaN film 1.1 μm thick was 72 arcmin, and the mosaic structure of the film was the main cause of broadening to the X-ray diffraction peak. At room temperature, the photoluminescence （PL） spectrum of GaN exhibited near band edge emission peaking at 365 nm.

Reliable high temperature, high humidity flexible thin film encapsulation using Al2O3/MgO nanolaminates for flexible OLEDs

Since most organic materials are very sensitive to moisture and oxygen, organic light emitting diodes (OLEDs) require an encapsulation layer to protect the active layer from these gases. Since light, flexible and portable OLEDs are being employed in more diverse climates and environmental conditions, the OLED encapsulation layer must retain robust mechanical properties and stability in high temperature/high humidity conditions. Al2O3 films have demonstrated excellent barrier performance, but they readily hydrolyze when exposed to prolonged harsh environments. In this study, we fabricated a thin film encapsulation (TFE) film that was resistant to hydrolysis, using Al2O3/MgO (AM) nanolaminates. MgO has superior resistance to harsh environments, and the aluminate phase generated by the chemical reaction of Al2O3 and MgO provided excellent barrier performance, even after storage in harsh conditions. A multi-barrier fabricated using the AM nanolaminate showed excellent barrier performance, close to the level required by OLEDs. It did not significantly deteriorate even after a bending test of 1,000 iterations at 0.63% strain. After 1,000 cycle of bending, the electrical properties of the passivated OLEDs were not significantly degraded at shelf-lifetime test where the fabricated device was stored for 50 days in a harsh environment of 60℃, 90% relative humidity. The multi-barrier shows the best performance compared to previous studies on flexible encapsulation that can be used in harsh environments.

Atomic-layer-deposited （ALD） Al2O3passivation dependent interface chemistry, band alignment and electrical properties of HfYO/Si gate stacks

In this work, the effects of atomic-layer-deposited(ALD) Al2O3 passivation layers with different thicknesses on the interface chemistry and electrical properties of sputtering-derived HfYO gate dielectrics on Si substrates have been investigated. The results of electrical measurements and X-ray photoelectron sepectroscopy(XPS) showed that 1-nm-thick Al2O3 passivation layer is optimized to obtain excellent electrical and interfacial properties for HfYO/Si gate stack. Then, the metal-oxide-semiconductor capacitors with HfYO/1-nm Al2O3/Si/Al gate stack were fabricated and annealed at different temperatures in forming gas(95% N2+5% H2). Capacitance-voltage(C-V) and current density-voltage(J-V) characteristics showed that the 250℃-annealed HYO high-k gate dielectric thin film demonstrated the lowest border trapped oxide charge density(-3.3 × 1010 cm-2), smallest gate-leakage current(2.45 × 10-6 A/cm2 at 2 V)compared with other samples. Moreover, the annealing temperature dependent leakage current conduction mechanism for Al/HfYO/Al2O3/Si/Al MOS capacitor has been investigated systematically. Detailed electrical measurements reveal that Poole-Frenkle emission is the main dominant emission in the region of low and medium electric fields while direct tunneling is dominant conduction mechanism at high electric fields.