Periodic submicrometer structures by sputtering

The existence of three-dimensional photonic bandgaps in square spiral thin films, made using the Glancing Angle Deposition (GLAD) method, was recently verified. We further demonstrate the flexibility of the GLAD process to fabricate silicon photonic bandgap crystals with customizable bandgap centre frequencies. GLAD combines physical vapor deposition at highly oblique flux incidence angles with dual axis substrate motion control, creating porous thin films with three-dimensional submicrometer topographies. This makes it a near-ideal approach for diamond lattice based photonic crystal fabrication, with manipulation of the photonic properties through the deposition parameters. We have produced a range of different square spiral thin films, and present characterization results indicating bandgaps at wavelengths close to 2 micrometers. Such low wavelength bandgaps have not previously been achieved for square spiral architectures. Ongoing work towards optimization of the process holds the promise of square spiral photonic crystals with even lower bandgap centre wavelengths, approaching the telecommunications windows. In addition to its flexibility and mass-production suitability, we present how GLAD can be used to engineer defects inside the photonic crystals during the one-step growth process. Such defects may potentially be employed as stand-alone waveguides, or as elements of more complex photonic device and circuitry designs involving subsequent micromachining of the GLAD thin films.

Omnidirectional anti-reflection coating nanostructure film have attracted enormous attention for the developments of the optical coating, lenses, light emitting diode, display and photovoltaic. However, fabricated of the omnidirectional antireflection nanostructure film on glass substrate in large area was a challenge topic. In the past two decades, the invention of glancing angle deposition technique as a growth of well-controlled two and three-dimensional morphologies has gained significant attention because of it is simple, fast, cost-effective and high mass production capability. In this present work, the omnidirectional anti-reflection nanostructure coating namely silicon dioxide (SiO 2 ) nanorods has been investigated for optimized high transparent layer at all light incident angle. The SiO 2 nanorod films of an optimally low refractive index have been fabricated by electron beam evaporation with the glancing angle deposition technique. The morphological of the prepared sampled were characterized by field-emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM). The optical transmission and omnidirectional property of the SiO 2 nanorod films were investigated by UV-Vis-NIR spectrophotometer. The measurement were performed at normal incident angle and a full spectral range of 200 – 2000 nm. The angle dependent transmission measure were investigated by rotating the specimen, with incidence angle defined relative to the surface normal of the prepared samples. The morphological characterization results showed that when the glancing angle deposition technique was applied, the vertically align SiO 2 nanorods with partially isolated columnar structure can be constructed due to the enhanced shadowing and limited addtom diffusion effect. The average transmission of the vertically align SiO 2 nanorods were higher than the glass substrate reference sample over the visible wavelength range at all incident angle due to the transition in the refractive index profile from air to the nanostructure layer that improved the anti-reflection characteristics.

Preparation and characterization of nanostructured ZrO 2 thin films by glancing angle deposition

Evaporated epitaxial chromium films

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.

Structure and optical properties of Nb 2O 5 sculptured thin films by glancing angle deposition

This study investigated the multilayer growth and properties of ZnS and MgF2 using glancing angle deposition. We used deposition angles of 85°–89° for ZnS and 70°–88° for MgF2 to obtain the structural properties. The film properties primarily followed Tait’s rule with a deposition angle of less than 87° in the vapor flux. However, film growth with a vapor flux angle of 88°–89° followed the tangent rule. Mathematical and cross-sectional scanning electron microscopy examinations found a transition point for the growth mechanisms at 87°, which comes from an extreme angle property for glancing angle deposition. We also performed mathematical derivations for the well-known empirical formula of the tangent rule and its generalized version. To stabilize the interface structure and surface roughness of multilayer structures, film growth at slightly tilted angles is recommended. Based on these results, an optical structure was designed, fabricated, and analyzed for a 550 nm wavelength pass filter on a glass substrate.

ABSTRACTPhotonic Band Gap (PBG) crystals are artificially engineered structures of periodically alternating dielectric materials that enable manipulation of light in unique ways. As proposed by O. Toader and S. John, large bandwidth PBG crystals based on the diamond lattice can be constructed by fabricating a two-dimensional periodic array of silicon square spirals. Furthermore, an improved photonic crystal can be constructed by fabricating the inverse of this structure, such that void square spirals are situated in a silicon backfill. This structure yields a theoretical maximum PBG of 24%, while the direct silicon square spiral structure yields a theoretical maximum of 16%. [1]The direct silicon square spiral structure has previously been successfully fabricated using the glancing angle deposition (GLAD) process [2]. The GLAD fabrication process uses advanced substrate motion and oblique incidence deposition to engineer precise nanostructures such as helices, chevrons, or polygonal spirals. These nanostructures are grown with lateral and longitudinal periodicity using a pre-patterned substrate consisting of a tetragonal array of relief structures.Upon successful fabrication of the direct silicon square spiral structure, it was proposed that fabrication of the inverse structure could be completed using a backfill process with a silica template [2]. A periodic array of silica square spirals would be fabricated using the GLAD technique. The template would then be filled with amorphous silicon using low-pressure chemical vapour deposition (LPCVD). To reveal the inverse silicon structure, the silica template would be removed by means of chemical etching with an isotropic chemical etchant. Creation of a suitable template for the inversion of silicon square spirals is an important step in the realization of the inverse silicon square spiral PBG crystal. However, we have seen empirically that silica square spiral films grown directly via the GLAD technique are structurally inferior to silicon films. We present an intermediate step for the fabrication of a suitable template, whereby a silicon structure is fabricated with appropriate geometries and subsequently oxidized. The procedure has been optimized to ensure a thorough oxidization of the silicon posts, while minimally distorting the structure of the square spiral template.

The growth dynamics of 1D nanorods (NRs) composed of noble metals is ambiguous during glancing angle deposition (GLAD). The continuum equation (CE) model describes ballistic deposition limited by adatom diffusion, not verified in GLAD of noble metal NRs. In this work, GLAD is operated at Ts (substrate temperature) below room temperature to create inclined Ag NRs, and the CE fits the growth orientation of NRs with deposition angles at fixed Ts well. The CE fitting evaluates the diffusion activation energy (Ed) as 0.23 eV, showing that Ag NRs are poly-crystalline with dominant (111), as confirmed by XRD. This work introduces an effective approach to study the growth thermodynamics of 1D nanostructures and evaluate the Ed of adatoms with relatively low melting points.

Broadband and antireflective characteristics of glancing angle deposited titanium dioxide nanostructures for photovoltaic applications

We developed a three-terminal ion-sensitive device (TTISD) as a proton (H+) and arsenic (As3+) sensor for the detection of glucose and As(III) dissolved in water. The TTISD was fabricated using the e-beam evaporation and glancing angle deposition (GLAD) technique. The TiO2 nanowires (NWs) were grown by GLAD on the conducting nafion channel of the TTISD to immobilize the test specimens. Arsenic (As) contamination in drinking water is a burning issue as it’s a threat to human health beyond the safe limit of As(III) in drinking water (0.005 mg/dL). Glucose concentration within the limit of 0–200 mg/dL in various body fluids, such as blood, sweat, and saliva is also a necessary parameter to monitor. Early detection of high As(III) concentration in water and regular monitoring of glucose concentration in the human body are essential for human health and safety. This work presents a common nano-hybrid platform for the detection of low-concentration glucose (40–200 mg/dL) and high-concentration arsenic (0.02–2 mg/dL) in drinking water. The device exhibits a rapid response time of ~1 s, enabling real-time detection of glucose and As(III).

Tailoring the structural and magnetic properties of Ni zigzag nanostructures using different deposition angles

Co-sputtering is a simple yet effective technique for fabricating a thin film of composite materials and different compositions by adjusting the electrical power of each sputtering target. However, practical issues arise when depositing cermet materials such as Ni-YSZ and Ni-GDC because of the contrasting characteristics of metal and ceramic sputtering targets. For example, the surface binding energy of GDC is significantly higher than that of Ni, resulting in a considerably lower sputtering yield of GDC. The difference in sputtering yield is further exacerbated by the low power density limit of the GDC target, which is set by its unfavorable material properties such as brittleness and low thermal conductivity. In contrast, due to its magnetic property, Ni requires sufficiently high sputtering power during magnetron sputtering.This work combines co-sputtering with advanced sputtering techniques such as glancing angle deposition (GLAD) and oblique angle deposition (OAD) to fabricate otherwise unobtainable Ni-GDC anode microstructure with various compositions. Reduced flux capture area of Ni caused by the high incident angle of GLAD allowed control of thin-film compositions, and optimal composition was determined based on fuel cell performance and electrochemical impedance spectroscopy (EIS) analysis. A sufficient amount of GDC was necessary to expand the triple-phase boundary (TPB) and suppress the thermal agglomeration of highly mobile Ni.The effect of electrode nanostructure on fuel cell performance was also investigated. The ballistic shadowing effect during OAD was utilized to produce thin-film electrodes with various porosities. With the increase of the deposition angle, the porosity increased, whereas the in-plane electrical conductivity decreased due to the reduced density. The columnar structure was also manipulated by managing the substrate position through azimuthal rotation. As a result, various columnar structures such as vertical posts, slanted posts, and zig-zag were fabricated, and the optimal microstructure was determined via electrochemical examinations.

Growth and roughness dependent wetting properties of CeO2 films prepared by glancing angle deposition

The structural and wetting properties of as‐deposited, annealed, and UV‐exposed TiO2‐slanted nanorods grown on different substrates have been studied. The slanted nanorods of 250 nm thickness are deposited on silicon, fluorine‐doped tin oxide, and glass at 80° using glancing angle deposition (GLAD) by employing e‐beam evaporation. The structural evolution shows that the prior seeding on the substrate affects the morphology dramatically, while a different angle of deposition can tune a plane substrate for exciting morphologies by GLAD technique. Annealing and UV exposure redefine the grown material and change the structural and wetting behavior of the TiO2 films. Notably, annealing the sample at 500 °C for 1 h has decreased the contact angle, and all the annealed samples become hydrophilic. Further, the UV radiation exposure makes all the samples super‐hydrophilic. It is demonstrated that by choosing an appropriate substrate, controlled properties of our interest with or without external stimuli can be achieved. Nevertheless, these samples will find interesting applications in self‐cleaning, photocatalysis, gas sensing, antireflection coating, etc.