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RATIONALE: Thin, nanoporous films fabricated using Glancing Angle Deposition (GLAD) technology are demonstrated for solid matrix laser desorption/ionization mass spectrometry (SMALDI-MS). GLAD allows facile engineering of nanoporosity, film thickness, post alignment, and material composition, as demonstrated here by the fabrication of Co-GLAD and Si-GLAD films for SMALDI, and by exploration of the SMALDI performance as a function of thickness, post density, and angle of the post relative to surface normal. METHODS: GLAD films were prepared by electron beam evaporation onto silicon substrates, using steep angles of incidence for the vacuum deposition, with computer controlled substrate rotation. LDI from the GLAD films was evaluated using an MDS-Sciex time-of-flight (TOF) MALDI mass spectrometer. RESULTS: Co-GLAD films give a limit of quantitation of 6 fmol for complex carbohydrate derivatives, and slanted-post Si-GLAD films show up to three times higher sensitivity than vertical post structures. Reproducibility of both Si and Co films is much higher than conventional MALDI methods for m/z below at least 2100 Da. Both reproducibility and detection limits are comparable to or better than other nano-structured materials. Co-GLAD films are significantly better in performance than Co powders or Co thin films on silicon substrates previously evaluated. CONCLUSIONS: The flexibility of GLAD for thin film fabrication of LDI materials is demonstrated by the range of nanoporous materials that can be grown, and the fine control over structural conformation, thickness and porosity. [ABSTRACT FROM AUTHOR]

Abstract: Ultrathin layer chromatography (UTLC) is a relatively new variant of thin layer chromatography, with a 10 m thick monolithic silica sorbent layer that gives faster separations with lower limits of detection and reduced analyte and solvent volumes. We have produced UTLC plates with controllable nanostructure and thickness, and show that the layer separation characteristics depends on the film nanostructure. We also show that layers made with in-plane anisotropic nanostructures will exhibit a decoupling effect, where the analyte spots do not develop in the same direction as the solvent front movement. The added layer morphology and material selection adds a degree of freedom to UTLC, and may have applications in multi-dimensional TLC. [Copyright &y& Elsevier]

Glancing angle deposition (GLAD) is a physical vapour deposition method used to fabricate highly functional thin films with an engineerable columnar morphology. Recent developments in GLAD technology have produced columnar nanostructures of increased complexity, including periodic, nanofibrous, perforated, and graded porosity thin films for use in applications ranging from sensors and actuators to optical filters, microfluidics, and catalysis. A brief review of GLAD methodology and historical developments is followed by a discussion of the latest developments in this field. [ABSTRACT FROM AUTHOR]

Increasing the throughput of the powerful single-step glancing angle deposition (GLAD) method using a prototype simplified roll-to-roll (R2R) system has been explored. While the conventional GLAD technique is popular for fabricating nanostructured devices in a single deposition step, it is not a high-output process. To evaluate the feasibility of large area GLAD deposition, the authors examined the geometrical considerations required to eventually achieve GLAD in a roll-to-roll manufacturing system. Nominal deposition and rotation angles were mathematically translated to their effective R2R counterparts, allowing for deposition recipes of the archetype GLAD nanostructures (slanted posts, vertical posts, and square spirals) and the mechanics of the phi-sweep technique to be converted to this space. Representative structures were then deposited, and the phi-sweep technique successfully applied, in a prototype single barrel roller R2R experimental system. This prototype system provides a foundation for moving GLAD from the laboratory to mass production. [ABSTRACT FROM AUTHOR]

A new technique is developed to fabricate biomimetic antireflection coatings (ARCs). This technique combines a bottom-up fabrication approach (glancing angle deposition, or GLAD) with a top-down engineering process (ion milling). The GLAD technique is first utilized to produce nanopillar arrays (NPAs) with broadened structures, which are subsequently transformed into biomimetic tapered geometries by means of post-deposition ion milling. This structure transformation, due to milling-induced mass redistribution, remarkably decreases reflection over a wide wavelength range (300–1700 nm) and field of view (angle of incidence < 60° with respect to the substrate normal). The milling-induced antireflection enhancement has been demonstrated in the NPAs made of Si, SiOx and TiO2, illustrating that this integrated technique is readily adapted to a wide variety of materials. Good agreement between simulation and experiment indicates that the enhanced antireflection performance is ascribed to a smoother refractive index transition from the substrate to the air, which improves the impedance match and reduces reflection losses. Additionally, ion bombardment tends to alter the stoichiometry and diminish the crystallographic structure of the NPA materials. The broadband and quasi-omnidirectional antireflection observed establishes the strong competitiveness of this technique with the methods previously reported. [ABSTRACT FROM AUTHOR]

Abstract: We report the fabrication, characterisation, and electro-catalytic activity of <0.3 mg cm−2 platinum deposits onto ∼500 nm long nickel nanopillar substrates (NiNP) synthesised by glancing angle deposition (GLAD). This is the first reported study of GLAD-based Pt–Ni electro-catalysts and the first alcohol oxidation study on any GLAD based electro-catalyst. The Pt was deposited onto NiNP via either 1) an unconventional, self-limiting, relatively high current density galvanostatic deposition, with a Pt counter electrode as the source of Pt, or 2) via a conventional potentiostatic deposition from Pt salts dissolved in acidic electrolytes. X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) confirm the successful deposition of Pt onto NiNP, while Scanning Electron Microscopy (SEM) shows that the nanopillar morphology is preserved but the Pt morphology is significantly different between the two methods. The galvanostatic procedure resulted in a conformal Pt deposition over the entire surface of the NiNP. The conventional procedure appeared to be mass-transfer limited, with most of the Pt being deposited on the tops of the NiNP. Cyclic voltammetry in 1 M KOH shows an enhancement of the surface area of the catalysts upon Pt deposition and corroborates the presence of Pt on the NiNP surface. Both prepared catalysts show high electro-catalytic activity towards 2-propanol oxidation in the KOH electrolyte at 60 °C. The activity enhancement below 300 mV vs. RHE (RHE = reversible hydrogen electrode) was attributed to the combined activity of the Pt and Ni components in the catalysts. At higher potentials, a bifunctional mechanism was suggested. Finally, a geometric/composition effect may be at work in the traditionally deposited catalyst, and requires further investigation. [Copyright &y& Elsevier]

Abstract: Fabrication of interdigitated organic photovoltaic (OPV) devices commonly involves filling a nanostructured thin film using solution-based methods. In these cases, the sensitivity of the nanostructured films to the solvents used needs to be studied in order to optimize the interface. Here, we study the ability of chlorobenzene (CB) and dichlorobenzene (DCB) to dissolve and recrystallize zinc phthalocyanine (ZnPc) thin films, while fabricating interdigitated active layers composed of ZnPc and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Using glancing angle deposition (GLAD), we are able to construct slanted nanorod arrays of ZnPc, with nanorod diameters of nominally 40nm and lengths up to 450nm. We find that these films are recrystallized upon direct exposure to CB and DCB, regardless of initial morphology, yielding a variety of possible nanoscale formations. The crystallinity and absorbance of these recrystallized films changes as well, depending on solvent choice and exposure time. Through control of initial ZnPc film morphology and solvent choice for PCBM casting, we exploit the sensitivity of ZnPc to these organic solvents to optimize the photovoltaic performance of ZnPc/PCBM devices. Optimal OPV device performance is achieved with a 30nm thick GLAD-textured ZnPc film while using DCB as the PCBM solvent. In this case, power conversion efficiencies are up to 3.0%, compared to an average of 2.3% when using CB as the solvent on the same film, and 2.3% also for bilayer devices when using DCB as the solvent. A higher degree of material mixing at the ZnPc/PCBM interface is shown when using DCB over CB as the PCBM solvent, which may be the primary mechanism for the photovoltaic improvements seen in these devices. [Copyright &y& Elsevier]

Abstract: The porous nature of high surface area and large aspect ratio nanorods arrays make them strong candidates for a range of applications from catalyst supports to energy scavenging devices. The glancing angle deposition (GLAD) technique is a straightforward and flexible method for ensuring control of morphology and porosity in nanorod arrays. Quantifying the porous nature of nanostructured columnar arrays, fabricated using the GLAD technique, is critical for understanding and optimizing the performance of devices fabricated using this method. The mesoporosity and pore volume of these GLAD nanorod arrays have thus been characterized using gas adsorption (krypton adsorption at 87.3K) and scanning electron microscopy (SEM) image analysis techniques. To characterize the obliquely deposited amorphous titanium dioxide (TiO2) and silicon dioxide (SiO2) samples, top-down SEM images of the films were also analyzed which allowed us to determine the mean distance between columns. SEM image analysis permitted for estimation of inter-column porosity of films deposited at angles from 65° to 85°, while krypton analysis allowed for the identification of mesoporosity in films from 45° to 85°. Our results provide a comprehensive characterization of GLAD film porosity which will be vital for the design of devices for a diverse set of applications from photonics to sensing to microfluidics. [Copyright &y& Elsevier]

Ni nanopillar structures were fabricated on glassy carbon electrodes (Ni GLAD /GC) using glancing angle deposition (GLAD). Thin, conformal layers of Pt were deposited by a rotating substrate, self-limiting, high current density galvanostatic deposition to form Ni GLAD {Pt}/GC deposits. The Pt loading in the Ni GLAD {Pt}/GC deposits was systematically varied by interrupting the deposition at various coverages, and the series of the Ni GLAD {Pt}/GC deposits were evaluated as catalysts for the oxygen reduction reaction (ORR) in O 2 saturated, 0.1 M HClO 4 at room temperature. The optimum amount of Pt (initial wt. ratio ∼ Pt 0.22 Ni 0.78 ) was deposited over 800 to 1500 seconds. These deposits, after dealloying, were about 30 times more active by mass and by surface area than a {Pt}/GC electrode prepared by deposition of Pt onto GC under the same conditions. [ABSTRACT FROM AUTHOR]

Glancing Angle Deposition (GLAD) was used to prepare 500 nm long Ni nanopillars directly on glassy carbon disc electrodes (Ni GLAD /GC). Ni GLAD {Pt}/GC core-layer nanopillars were prepared by depositing Pt on the Ni GLAD substrate via a novel rotating disc electrode galvanostatic deposition, where a stationary blackened Pt counter electrode served as the Pt source. Scanning electron microscopy, cyclic voltammetry, and inductively-coupled mass spectrometry were employed to characterize the deposits. Results indicated that the Pt was deposited in a conformal manner on the Ni GLAD giving a loading of 11.6 μg. The Ni GLAD {Pt}/GC electrode was ca. three fold more active than a {Pt}/GC (made with the same deposition in the absence of Ni) towards the oxygen reduction reaction (ORR) in 1.0 M KOH. As well, long term potentiostatic ORR studies showed the Ni GLAD {Pt}/GC deposit was more durable than the {Pt}/GC, with the former completely retaining its initial performance after 5000 s polarization at 0.85 V vs. RHE, while {Pt}/GC lost 38% of its activity. Subsequent control experiments in the absence of O 2 showed that such decay was not due to loss of Pt over the prolonged ORR. [ABSTRACT FROM AUTHOR]

Abstract: Nb-doped TiO2 (TNO) has been widely explored as an alternative transparent conductor. TNO thin films have been fabricated by various deposition methods, and here we demonstrate fabrication by evaporation of sol–gel synthesized TNO source material. A range of Nb x Ti1− x O2 (x =0, 0.03, 0.06, 0.12, 0.24) compositions were synthesized, pressed into pellets, and deposited as thin films via electron beam evaporation. The thin films were characterized for composition by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy and for crystallinity by X-ray diffraction for the different Nb contents explored. Transparency, conductivity, and Haacke transparent conductor figure of merit values are reported for the evaporated TNO films as a function of Nb content, substrate heating temperature, and post deposition annealing conditions. Glancing angle deposition (GLAD) is used to demonstrate nanostructuring of evaporated TNO based on physical shadowing. Nanostructured GLAD TNO films of increased morphological complexity can be produced using this method, and could lead to unique transparent conductor device architectures. [Copyright &y& Elsevier]

Abstract: Metal oxides such as niobium oxides have been demonstrated as alternative support materials for Pt and non-precious metal catalysts in fuel cells. High surface area and columnar niobium oxide catalyst support structures were produced by the glancing angle deposition (GLAD) technique on 5mm diameter glassy carbon disks. The columnar structures have lengths of about 500nm, diameters of 50nm and an areal density of about 109 cm−2. Annealing under different gas mixtures (Ar/H2) led to the formation of various oxides (Nb2O5, NbO2, or NbO+NbO2). Pt catalyst, with a loading of 0.1mgPt cm−2, was deposited onto these structures by magnetron sputter deposition. Rotating disk electrode characterization of the samples, performed in 0.1M HClO4 electrolyte at room temperature, revealed surface enhancement factors of up to 11 and oxygen reduction specific activities of ≥1mAcm−2 Pt at 0.9V (vs. RHE). The impact of annealing on Nb-O phase formation, conductivity, oxygen reduction activity and stability are discussed. [Copyright &y& Elsevier]

Abstract: Nanopillar metal oxide thin films offer versatility as ultra high surface area supports and conductors. Metal oxide properties (e.g. stability, conductivity) can be tuned via phase and composition control to achieve desired application-specific functionality. Here we demonstrate phase control of high surface area thin films grown by glancing angle deposition and transformed to desired phases through high temperature annealing in a reducing environment. The post-annealed properties such as stoichiometry, phase, and morphology are shown to be largely dependent on initial film structure and hydrogen forming gas flow rate. Initially amorphous films of approximate stoichiometry Nb2O5 are transformed to NbO2 or NbN x O1−x through annealing. Transformation to oxygen-deficient phases is more easily achieved for films of higher initial porosity. Higher forming gas flow rates result in both increased oxygen removal and significantly less physical degradation of nanostructures. A phase map is included as a guide to phase formation and morphology control in annealed nanopillar niobium oxide films. [Copyright &y& Elsevier]

Abstract: Glancing angle deposition was used to fabricate TiO2 thin film relative humidity sensors. These sensors have been shown to have an extremely high capacitive response along with sub-second response times. However, the thin film morphology that gives rise to the strong performance also renders the film vulnerable to ageing processes which can degrade sensor performance over a period of days. In this paper, the evolution of sensor response in time was studied. The response of our sensors to ultraviolet irradiation was investigated, and shown to not only reverse the ageing of our sensors, but also increase the overall device response. [Copyright &y& Elsevier]

Abstract: A high-speed optical humidity sensor was fabricated from a nanostructured titanium dioxide thin film. A refractive index depth profile designed to yield a narrow-bandpass optical interference filter was obtained through nanoscale porosity variations produced by a physical vapor deposition technique known as glancing angle deposition (GLAD). The GLAD process provides film morphology control on the 10nm scale through a combination of deposition at highly oblique vapor incidence angles and controlled substrate motion. Under varying humidity conditions the transmittance spectrum of the filter shifts due to effective index changes of the porous structure resulting from water vapor adsorption/desorption. Performance analysis has shown that this device is highly sensitive, exhibits minimal hysteresis, and is extremely fast. The adsorption and desorption response times were measured to be 270ms and 160ms, respectively. [Copyright &y& Elsevier]