Morphology of periodic nanostructures for photonic crystals grown by glancing angle deposition

An enhancement of the glancing angle deposition (GLAD) technique called PhiSweep was used to grow slanted columns of silicon and titanium dioxide onto patterned substrates. The PhiSweep technique involves periodically rotating the substrate back and forth during the deposition process, which reduces column fanning caused by anisotropy in the shadowing conditions. The patterned substrates consisted of a tetragonal array of hillocks with 100, 200, and 300 nm periodicities and were fabricated using electron beam lithography. The PhiSweep method alters the tilt angle of the slanted columns compared with those grown using traditional GLAD. We present a derivation of the tilt angle of the slanted columns as a function of the parameters of the PhiSweep technique. The tilt angles of the silicon and titanium dioxide films were measured and agree with the predicted values. The films fabricated using the PhiSweep method are compared with similar films grown using traditional GLAD. The PhiSweep technique produced films with substantially less column fanning than those grown by traditional GLAD. This reduction in column fanning has extended the size range over which periodic GLAD structures, such as square spiral photonic crystals, can be grown.     

Gold coated metal nanostructures grown by glancing angle deposition and pulsed electroplating

Nickel based nanostructures are grown by glancing angle deposition (GLAD) on flat and pre-patterned substrates. These fabricated porous thin films were subsequently coated by pulsed electroplating with gold. The morphology and conformity of the gold coating were investigated by scanning electron microscopy and X-ray diffraction. Controlled growth of closed gold layers on the nanostructures could be achieved, while the open-pore structure of the nanosculptured thin films was preserved. Such gold coated nanostructures are a candidate for optical sensing and catalysis applications. The demonstrated method can be applied for numerous material combinations, allowing to provide GLAD thin films with new surface properties.     

Structure and optical properties of ZnS thin films grown by glancing angle deposition

The glancing angle deposition (GLAD) technique was used to deposit ZnS films by electron beam evaporation method. The cross sectional scanning electron microscopy (SEM) image illustrated a highly orientated microstructure composed of slanted column. The atomic force microscopy (AFM) analysis indicated that incident flux angle had significant effects on the nodule size and surface roughness. Under identical nominal thickness, the actual thickness of the GLAD films is related to the incident flux angle. The refractive index and in-plane birefringence of the GLAD ZnS films were discussed, and the maximum birefringence Δn = 0.036 was obtained at incident flux angle of α = 80°. Therefore, the glancing angle deposition technique is a promising way to create a columnar structure with enhanced birefringent property.     

ZrO2 films with variable refractive index by glancing angle deposition

When optical film is deposited at oblique angle incidences, the film becomes porously, and the film effective refractive index will decrease. Six porous ZrO2 films are fabricated by the glancing angle deposition (GLAD) technique with the different incidence angles. By changing the substrate tilt angle from 0° to 85°, the film refractive index varies from 1.92 to 1.27.     

Characterization of CoPt nanowire fabricated by glancing angle deposition

CoPt and Co nanowire films were deposited by the Glancing Angle Deposition(GLAD) method. All samples are deposited on Si substrates that were covered by polystyrene spheres to assist the alignment of nanowires. SEM observation results show that the length and diameter of nanowires are uniform for all samples. According to the result of XRD, the crystal structure of CoPt is fcc. The angular dependence of magnetization of the nanowires shows that the easy axis of magnetization is along the growth direction of the nanowires.     

斜角入射沉积法制备渐变折射率薄膜的理论探讨

从理论上分析了单一膜料倾斜入射沉积时的折射率与填充密度的关系,给出了三种不同的表达式;然后从正变和负变、完整周期和存在半周期以及不同的周期数等几个方面探讨了膜层的填充密度按照线性变化时的渐变折射率薄膜的光学特性,并将折射率的不同理论表达式对光学特性的影响进行了对比,最后讨论了单一膜料倾斜入射沉积渐变折射率薄膜的方法、填充密度线性变化时的渐变折射率薄膜的应用及制备中需要进一步解决和处理的问题. 关键词： 斜角入射沉积 渐变 填充密度     

Porosity engineering in glancing angle deposition thin films

We present a new technique for the fabrication of thin films at highly oblique flux incidence angles, in which the direction of film growth and the direction of incoming deposition flux are decoupled. The technique offers a high level of control over the porosity of thin films, and has been used to make thin films with a uniform and highly porous microstructure of tightly interwoven nanoscale fibres. The nanofibrous films have been analysed using scanning and transmission electron microscopy, and will be useful for thin film applications relying on high porosity, such as humidity sensors and super-capacitors. PACS 68.55.Jk; 68.55.Ac; 81.05.Rm; 61.46.+w; 81.15.Ef     

Nanostructure fabrication by glancing angle ion beam assisted deposition of silicon

Glancing angle deposition by utilizing an ion beam sputter process and a controlled substrate rotation is used to deposit silicon nanostructures with different structure varieties. The structures are grown on seeded and plain [100] silicon substrates at room temperature. The ratio of deposition rate to substrate angular frequency and the substrate surface properties determine the nanostructure geometry, size and assembly. PACS 61.46.+w; 81.05.Gc; 81.15.Cd     

斜角入射沉积法制备渐变折射率薄膜的折射率分析

斜角入射沉积法是一种制备薄膜的新颖方法,它可以用来制备渐变折射率薄膜.本文首先探讨了膜料的沉积入射角为α,薄膜柱状生长倾斜角为β时的薄膜的填充系数;之后利用drude理论,分析研究了斜角入射沉积法制备渐变折射率薄膜的折射率与薄膜的入射角和生长方向的关系. 关键词： 斜角入射沉积 渐变折射率 填充系数     

Rugate filters prepared by rapidly alternating deposition

A methodology for the fabrication of composite (Nb₂O₅)_1-x(SiO₂)_x thin-film rugate filters by using pulsed direct current magnetron sputtering is presented. The two materials are mixed using rapidly alternating deposition technology. The optical properties of the composite films varying with the composition of the material are studied in detail. Refractive indices between 1.50 and 2.14 can be realized in our coating system. Two designed rugate filters with a reflection band at the wavelength of 532 nm are fabricated using an automatic deposition process. The microstructure of the rugate filter is investigated by using scanning electron microscopy. The calculated and the measured transmittance spectra are in good agreement with each other. The causes of the slight differences between them are also analysed.     

Deposition of quaternary sputtered CIGS nanorods via glancing angle deposition

Nanostructured materials have become an attractive alternative to their thin film and bulk counterparts in photovoltaic and photoconductivity research. This is mainly attributed to their superior optical and electrical properties. Light trapping in vertically aligned nanostructures results in high optical absorption and provides enhanced carrier collection by utilizing a fully depleted p–n‐junction between the anode and cathode via an isolated ”capping” construction. The combination of these two features can potentially lead to the development of high efficiency nanostructured devices including solar cells, photodiodes, and photodetectors. Optical absorption proper ties of nanorod arrays of CuIn_x Ga_1–xSe₂ (CIGS), a p‐type semiconductor with a wide band gap ranging from 1.0 eV to 1.7 eV, are compared to their thin film counterpart. Utilizing an RF sputtering system, a quaternary target, and glancing angle deposition (GLAD) technique, vertical arrays of CIGS nanorods were fabricated while conventional films were fabricated by normal incidence deposition. Scanning electron microscopy (SEM) images indicated a successful growth of CIGS nanorods. Optical absorption was found to be strongly altered by the presence of the nanorod structures through spectroscopic reflectometry. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Graded index broadband antireflection coating prepared by glancing angle deposition for a high-power laser system

This paper reports that SiO₂ is selected to fabricate broadband antireflection (AR) coatings on fused silica substrate by using glancing angle deposition and physical vapour deposition. Through accurate control of the graded index of the SiO₂ layer, transmittance of the graded broadband AR coating can achieve an average value of 98% across a spectral range of 300--1850~nm. Moreover, a laser-induced damage threshold measurement of the fabricated AR coating is performed by using a one-on-one protocol according to ISO11254-1, resulting in an average damage threshold of 17.2~J/cm$^{2}$.     

Fabrication of 2D–3D photonic crystal heterostructures by glancing angle deposition

We fabricate 2D–3D photonic crystal heterostructures based on the silicon [001]-diamond:1 square spiral geometry using glancing angle deposition. We compare the normal incidence reflection properties of the fabricated 2D–3D heterostructures to simulated spectra generated using finite-difference time-domain calculations. Reflection peaks are observed, resulting from the presence of a photonic band gap, and defect modes are created by the 2D layer. Deterioration of the reflectance peaks with increased number of vertical spiral periods is observed. A series of square spiral structures are fabricated with a varying number of vertical periods to quantify the degradation of reflection peaks. At normal light incidence, a maximum reflection peak is observed from the film with three vertical periods. Beyond three spiral rotations, deterioration of the substrate-plane periodicity causes scattering losses.     

Photocatalytic properties of TiO2 thin films obtained by glancing angle deposition

Titanium dioxide (TiO₂) thin films with different nanostructures such as nano-particles and separated vertical columns were grown by glancing angle deposition (GLAD) in an electron beam evaporation system. The photocatalytic properties of grown TiO₂ films with different deposition angles and different annealing temperatures were evaluated by following decomposition of methyl orange under ultraviolet (UV) light irradiation. The results suggest that increased surface area due to the GLAD process could improve the photocatalytic properties of TiO₂ films.     

Controllable nanostructure and optical properties of ZrO2 thin films by glancing angle deposition

In this paper, nanostructured ZrO₂ films were prepared by electron beam evaporation with the glancing angle deposition (GLAD) technique. Columnar films with voids in between formed owing to the self-shadowing effect and the limited diffusion of deposited atoms. The microstructure evolves from slanted columnar structure to helical and pillar structures as the substrate rotational speed increases. The diameter of the columns is in the range of 30–50 nm. A higher rotational speed favors a larger nodule size and a greater surface roughness. Due to the porous structure, the refractive index n of GLAD ZrO₂ films varies from 1.75 to 1.80, lower than that of bulk material. A maximum value of birefringence (Δn=0.03) is obtained in a slanted columnar structure, and the relationship between birefringence and microstructure orientation is discussed. Our results demonstrate that glancing angle deposition is a feasible approach for designing the nanostructure and optical properties of thin films.     

Morphology control of tungsten nanorods grown by glancing angle RF magnetron sputtering under variable argon pressure and flow rate

Morphologically novel tungsten nanorods (WNRs) with the co-existence of two crystalline phases, α-W (thermodynamically stable) and β-W, were fabricated by glancing angle RF magnetron sputtering technique under various Ar pressures and flow rates. For these nanorods, a significant variation in their morphology and surface roughness was observed. These structures could be useful in a wide range of applications such as field emission, robust superhydrophobic coatings, energy, and medicine.     

Homogeneity analysis of sculptured thin films deposited in symmetric style through glancing angle deposition technique

The symmetric deposition technique is often used to improve the uniformity of sculptured thin film （STF）. In this paper, optical properties of STF with the columnar angles 4-/3 are analyzed theoretically, based on the characteristic matrix method for extraordinary waves. Then, the transmittances of uniformity monolayer and bilayer STF in symmetrical style are calculated to show the effect of the bilayer structure on the optical properties of STF. The inhomogeneity of STF is involved in analyzing the differences in transmittance and phase retardation between monolayer and bilayer STF deposited in symmetric style. The results show that optical homogeneity of STF can be improved by depositing in symmetric style at the normal incidence, but it is not the same case as the oblique incidence.     

用于补偿增益窄化效应的Rugate滤波器设计

采用Rugate膜系理论,分别根据钛宝石和钕玻璃介质增益窄化的特点,合理选择补偿增益窄化的调制函数,优化设计出了分别用于补偿钛宝石系统和钕玻璃系统增益窄化效应的Rugate滤波器.由普通均匀多层膜的特征矩阵方法近似分析了设计出的Rugate滤波器的光谱响应,数值模拟了Rugate滤波器的光谱补偿效果.结果显示,能比较好的符合光谱补偿的要求,可以用作补偿增益窄化效应的光谱调制滤波器. 关键词： 超短脉冲 增益窄化 光谱补偿 Rugate滤波器     

Ultrahigh supercapacitance in cobalt oxide nanorod film grown by oblique angle deposition technique

Nanorod films of cobalt oxide (Co₃O₄) have been grown by a unique oblique angle deposition (OAD) technique in an e-beam evaporator for supercapacitor electrode applications. This technique offers a non-chemical route to achieve large aspect ratio nanorods. The fabricated electrodes at OAD 80° exhibited a specific capacitance of 2875 F/g. The electrochemically active surface area was 1397 cm⁻², estimated from the non-Faradaic capacitive current region. Peak energy and power densities obtained for Co₃O₄ nanorods were 57.7 Wh/Kg and 9.5 kW/kg, respectively. The Co₃O₄ nanorod electrode showed a good endurance of 2000 charge-discharge cycles with 62% retention. The OAD approach for fabricating supercapacitor nanostructured electrodes can be exploited for the fabrication of a broad range of metal oxide materials.     

Defect reduction in GaAs/Si film with InAs quantum-dot dislocation filter grown by metalorganic chemical vapor deposition

The growth of GaAs epilayers on silicon substrates with multiple layers of InAs quantum dots(QDs) as dislocation filters by metalorganic chemical vapor deposition(MOCVD) is investigated in detail.The growth conditions of single and multiple layers of QDs used as dislocation filters in GaAs/Si epilayers are optimized.It is found that the insertion of a five-layer InAs QDs into the GaAs buffer layer effectively reduces the dislocation density of GaAs/Si film.Compared with the dislocation density of 5×10~7 cm~(-2) in the GaAs/Si sample without QDs,a density of 2×10~6 cm~(-2) is achieved in the sample with QD dislocation filters.