Ion irradiation effects on WNxOy thin films
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The present article demonstrated that pseudo surface wave (PSW) should exist on a slightly anisotropic crystal sapphire. PSW velocity dispersions on the three principal planes of sapphire were numerically calculated. The existence possibility of PSW on the water-sapphire (101̄2) plane was experimentally examined by using acoustic spectromicroscopy. Numerical analysis reveals that the two-component surface wave should be activated on the sapphire (101̄2) plane along direction angle φ0=17.18631°. This also verified the existence possibility of PSW on the slightly anisotropic crystal sapphire.
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Abstract The formation mechanism of AlN whiskers on sapphire substrates during heat treatment in a mixed flow of H 2 and N 2 was investigated in the temperature range of 980–1380 °C. AlN whiskers grew above 1030 °C after covering the sapphire surface with a thin AlN layer. The existence of pits on the sapphire surface beneath the thin AlN layer was observed. Both AlN whisker and pit densities of samples were on the same order of 10 8 cm −2 . These results suggested the following mechanism. First, the sapphire surface reacts with H 2 , and the generated Al gas reacts with N 2 to form a thin AlN layer on sapphire. Then, the sapphire surface reacts with H 2 diffusing to the AlN/sapphire interface. The Al gas escapes through dislocations in the AlN layer to leave pits on the sapphire surface, and finally reacts with N 2 to form AlN whiskers on the top surface.
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Infrared antireflective double layer films of SiO2/Si3N4 were prepared on sapphire(α-Al2O3) by radio frequency magnetron reactive sputtering.The high temperature strength and transmission of sapphire are measured.The results show that the high temperature strength of sapphire coated with the double layer films of SiO2/Si3N4 on both sides and transmission of sapphire have been improved greatly.The high strength of sapphire coated with SiO2/Si3N4 films is 41.0% higher than uncoated sapphire sample at 800 ℃;the transmission of sapphire coated with SiO2/Si3N4 films on both sides is 8.0% higher than uncoated sapphire sample at wavelengths from 3 to 5 μm at room temperature.Double layer films of SiO2/Si3N4 have high heat-stability and high adhesion with sapphire.
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Orientation dependent decomposition of sapphire substrates and resultant AlN formation during heat treatment in an atmospheric-pressure mixed gas flow of H 2 and N 2 (H 2 /N 2 = 3/1) was investigated within the temperature range 980–1480 °C. AlN was formed on sapphire in the temperature range 1030–1430 °C for c -, a -, and m -plane sapphire, and 980–1430 °C for the r -plane sapphire. At 1480 °C, AlN was not formed, and only sapphire was decomposed by H 2 with the ranking of m - > r - > a - > c -plane. The ranking was contrary to that of the amount of AlN formation at 1380 °C, which occurred by the reaction of gaseous Al generated by the sapphire decomposition and N 2 . This discrepancy was due to the shape of AlN formed on sapphire; whisker-like AlN does not protect c - and a -plane sapphire from decomposing, while layer-like AlN protects r - and m -plane sapphire from decomposing.
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The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and planar energy fluence and absorbed dose has been calculated in 5 and 20 MeV electron beams in water. The shape of these distributions has been compared with analytic expressions for fluence and absorbed dose and the general mechanisms governing the shape of the depth dose curve have been explained. In particular it is demonstrated that the depth dependence of planar energy fluence and mean energy is very similar, and so is the case for fluence and absorbed dose and primary fluence and absorbed dose from primaries with inclusion of fast secondaries. The results are useful for dosimetry and dose planning in high energy electron beams.
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Synchrotron x-ray diffraction was employed to measure the lattice constants a and c of GaN films grown with an AlN buffer layer on sapphire (0001) over a thickness range of 50 Å to 1 μm. We used multiple reflections and a least-squares fit method for high reliability. As the thickness increased, the lattice constant a increased from 3.133 Å to 3.196 Å and c decreased from 5.226 Å to 5.183 Å. The expected trend was fitted to an equilibrium theory, allowing the critical thickness of GaN on AlN to be estimated at 29 Å ± 4 Å in good agreement with a theoretical prediction.
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InGaN/Sapphire LED에서 기판 제거와 패키지 방식이 광출력 특성에 미치는 영향을 분석하였다. Sapphire 기판의 제거는 반도체 접합에서 발생된 열의 방출에 도움이 되지만, 반대로 광추출효율이 손상되는 문제점이 수반된다. Sapphire 기판이 제거된 칩을 열전도율이 좋은 금속의 마운트 위에 부착하면, 최대 구동전류는 현저히 증가하고 광출력도 상당히 증가됨으로써, 광추출효율이 손상되는 문제점이 어느 정도 보상된다. 하지만, sapphire 기판이 제거된 칩을 상대적으로 열전도율이 낮은 유전체의 마운트 위에 부착하는 경우에는, 거의 모든 입력전류 범위에서 sapphire 기판이 남아 있는 일반형 칩보다 낮은 광출력을 나타낸다. 따라서, 작은 광출력이 요구되는 응용분야에서는 사용된 칩 마운트의 종류에 무관하게, 일반형 칩이 sapphire 기판이 제거된 칩 보다 유리한 것으로 분석된다.
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The authors report on the plasma-assisted molecular-beam epitaxy of semipolar AlN(112¯2) films on (11¯00) m-plane sapphire. AlN deposited on m sapphire settles into two main crystalline orientation domains, AlN(112¯2) and AlN(101¯0), whose ratio depends on the III/V ratio. The in-plane epitaxial relationships of AlN(112¯2) on m-plane sapphire are [112¯3¯]AlN‖[0001]sapphire and [11¯00]AlN‖[112¯0]sapphire. In the case of AlN(101¯0), the in-plane epitaxial relationships were [12¯10]AlN‖[0001]sapphire and [0001]AlN‖[112¯0]sapphire. Growth under moderate nitrogen-rich conditions enables them to isolate the (112¯2) orientation and to improve the surface morphology of the layers.
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