Glancing Angle Deposition Technique Research Articles

Engineering Light‐Driven Rod‐Shaped Micromotors for Exhibiting Controlled and Tunable Multimode Swimming

AbstractThe recent era of research has been focused on attaining precise and adjustable propulsion modes in micromotors, with remarkable implications in microrobotics and active‐matter applications. This study introduces a novel design of rod‐shaped micromotors featuring light‐driven motion and wavelength‐dependent multimodal swimming behavior. The micromotors are fabricated through the Glancing Angle Deposition (GLAD) technique, which offers a flexible approach to engineering surfaces by incorporating photocatalytic materials (TiO2 and Cu2O) at specific locations. Here, three distinct designs of micromotors (titania, hybrid‐1, and hybrid‐2) are presented that are programmed to showcase diverse behaviors of movements (linear, helical, and axial rotation) when exposed to a specific wavelength. The application of light facilitates convenient control over activity and mode switching by altering between UV and visible ranges. Numerical modeling using a finite element approach is performed to validate the experimental results, demonstrating excellent agreement with the experimental findings. The present study is anticipated to be helpful in tailoring such complex micro/nanoscale advanced functional materials with intricating swimming modes desired for various applications in micro/nanorobotics.

Advancing SERS Diagnostics in COVID‐19 with Rapid, Accurate, and Label‐Free Viral Load Monitoring in Clinical Specimens via SFNet Enhancement

AbstractThis study presents an integrated approach combining surface‐enhanced Raman spectroscopy (SERS) with a specialized deep learning algorithm, SFNet, to offer a rapid, accurate, and label‐free alternative for COVID‐19 diagnosis and viral load quantification. The SiO2‐coated silver nanorod arrays are employed as the SERS substrates, fabricated using a reliable and effective glancing angle deposition technique. A dataset of 4800 SERS spectra from 120 positive and 120 negative inactivated clinical human nasopharyngeal swabs are collected directly on the SERS substrates without any labels. A SFNet algorithm is tailored to adapt to the unique spectral features inherent to SERS data, achieving a test accuracy of 98.5% and a blind test accuracy of 99.04%. Moreover, an optimized SFNet algorithm unveils the capability of estimating SARS‐CoV‐2 viral loads, accurately predicting the cycle threshold values (Ct values) of the three vital gene fragments with a root mean square error (RMSE) of 1.627 (1.3 for blind test). The methodology is substantiated using actual clinical specimens and completed in <15 min, thereby strengthening its real‐world point‐of‐care applicability. This rapid and precise yet label‐free modality competes favorably with classical reverse‐transcription real‐time polymerase chain reaction (RT‐PCR) and marks an advancement in SERS‐based sensor algorithms.

Influence of nanocolumnar electrode geometry on electrochemical sensor performance

The concentration of glucose in sweat recently has been measured with high sensitivity, selectivity, and reproducibility by nanostructured NiO electrodes manufactured by the glancing angle deposition (GLAD) technique. The GLAD technique allows electrode morphological properties such as porosity and film thickness to be tightly controlled, providing ample opportunity to enhance the sensor performance. Currently, the selection of optimal GLAD parameters is determined experimentally by trial and error, at high costs in time and resources. Numerical simulation allows the effects of various parameters on sensor performance to be investigated at a much lower cost compared to experimental studies. In this work, a 2D reaction–diffusion model for the surface-catalyzed reactions in the nanostructured GLAD electrodes is developed, which are then solved using the finite element method. Parametric studies on the nanocolumn thickness and nanocolumn separation of the GLAD structures are then conducted to optimize GLAD-based electrode structures with different adsorption and catalytic rates. This research offers new guidance for rapidly designing highly effective sensors with higher sensitivity and lower limits of detection.

VO2 /MoO3 Heterojunctions Artificial Optoelectronic Synapse Devices for Near-Infrared Optical Communication.

Artificial optoelectronic synapses (OES) have attracted extensive attention in brain-inspired information processing and neuromorphic computing. However, OES at near-infrared wavelengths have rarely been reported, seriously limiting the application in modern optical communication. Herein, high-performance near-infrared OES devices based on VO2 /MoO3 heterojunctions are presented. The textured MoO3 films are deposited on the sputtered VO2 film by using the glancing-angle deposition technique to form a heterojunction device. Through tuning the oxygen defects in the VO2 film, the fabricated VO2 /MoO3 heterojunction exhibits versatile electrical synaptic functions. Benefiting from the highly efficient light harvesting and the unique interface effect, the photonic synaptic characteristics, mainly including the short/long-term plasticity and learning experience behavior are successfully realized at the O (1342nm) and C (1550nm) optical communication wavebands. Moreover, a single OES device can output messages accurately by converting light signals of the Morse code to distinct synaptic currents. More importantly, a 3×3 artificial OES array is constructed to demonstrate the impressive image perceiving and learning capabilities. This work not only indicates the feasibility of defect and interface engineering in modulating the synaptic plasticity of OES devices, but also provides effective strategies to develop advanced artificial neuromorphic visual systems for next-generation optical communication systems.

Improved optical and electrical response by glancing angle synthesized Al2O3 nanorod array device

An Aluminum Oxide (Al2O3) nanorod (NR) array–based device has been synthesized upon an Al2O3 thin film (TF) by electron beam (E-beam) evaporation with a glancing angle deposition technique. The complete fabrication has been done inside a vacuum coating unit. The Al2O3 nanostructures have been fabricated on a silicon substrate. Field emission scanning electron microscopy and transmission electron microscopy show a vertically aligned Al2O3 NR array. From the Tauc plot, the optical band energies are estimated as 5 eV and 5.5 eV for the bare Al2O3 TF and Al2O3 NR/Al2O3 TF devices, respectively. Significant improvement has been observed in photosensitivity by 10 fold, detectivity by 4.2 fold, and noise equivalent power (NEP) by 16.5 fold for the Al2O3 NR/Al2O3 TF device compared with the Al2O3 TF. The Al2O3 NR/Al2O3 TF device exhibits a very fast photoswitching response (rise time = 0.15 s and fall time = 0.13 s). Therefore, the Al2O3 NR/Al2O3 TF device proves to be a prominent candidate for next-generation optoelectronic device applications.

Fabrication of slanted gratings by using glancing angle deposition

Slanted gratings, commonly used for manipulating light in various applications, are typically fabricated using conventional top-down methods. However, these methods have limitations on material choice. This paper explores the use of glancing angle deposition (GLAD) to fabricate slanted gratings with various materials and slant angles on silicon (Si) and quartz (SiO2) substrates. The process involves the first step of creating a template using electron beam lithography, lift-off, and dry etching, and the second step of electron beam evaporation at a glancing angle on the prefabricated template. The template consists of grating structures with very shallow trenches. Different materials, such as chromium (Cr), copper (Cu), aluminum oxide (Al2O3), and titanium oxide (TiO2), were used in the GLAD process to create slanted grating structures on Si or SiO2 substrates, showcasing their versatility. Here, the formation of the slanted grating is due to the shadowing effect that leads to deposition onto the protruded grating lines but not into the trench. Using TiO2 as the source material, the GLAD technique can produce slanted gratings with various angles by adjusting the deposition angle. The optical characteristics of the slanted grating prepared using GLAD were verified through simulations with COMSOL software, confirming its excellent light guide performance.

Continuously variable Fourier filters fabricated using varying angle glancing angle deposition for chip-scale spectroscopy.

Low-cost spectroscopy has received a great deal of attention in recent years in applications such as food inspection, disease detection, and manufacturing. Current spectroscopic systems rely on multiple optical components, making them mechanically fragile systems. In our previous work, we demonstrated the use of Fourier filtering using thin dielectric films. The sampling effect from the cavity resonances can be used to decompose a signal into its Fourier components. Although the thin films were deposited directly on the face of the detectors, filters of varying thicknesses were needed, which required multiple lithographic processes. To overcome this challenge, in this work, we use a continuously variable filters deposited by a single-step electron-beam evaporation technique. We demonstrate a novel, to our knowledge, method that utilizes the glancing angle deposition technique with a continuously varying angle in order to produce tens of variable Fourier filters in a single deposition run. To prove this technique, we deposit this variable filter on a 38-channel linear detector and show the results from this device.

TiO2 nanorod arrays/Ti3C2T x MXene nanosheet composites with efficient photocatalytic activity

Semiconductor photocatalysis holds significant promise in addressing both environmental and energy challenges. However, a major hurdle in photocatalytic processes remains the efficient separation of photoinduced charge carriers. In this study, TiO2 nanorod arrays were employed by glancing angle deposition technique, onto which Ti3C2T x MXene was deposited through a spin-coating process. This hybrid approach aims to amplify the photocatalytic efficacy of TiO2 nanorod arrays. Through photocurrent efficiency characterization testing, an optimal loading of TiO2/Ti3C2T x composites is identified. Remarkably, this composite exhibits a 40% increase in photocurrent density in comparison to pristine TiO2. This enhancement is attributed to the exceptional electrical conductivity and expansive specific surface area inherent to Ti3C2T x MXene. These attributes facilitate swift transport of photoinduced electrons, consequently refining the separation and migration of electron–hole pairs. The synergistic TiO2/Ti3C2T x composite showcases its potential across various domains including photoelectrochemical water splitting and diverse photocatalytic devices. As such, this composite material stands as a novel and promising entity for advancing photocatalytic applications. This study can offer an innovative approach for designing simple and efficient photocatalytic materials composed of MXene co-catalysts and TiO2 for efficient water electrolysis on semiconductors.

Tunable properties of SnOx sputter-deposited by RGPP and GLAD techniques: A potential candidate for photosensing and all-oxide solar cells

In this work, optical and electrical properties of tin-oxide (SnOx) thin-films were investigated for broadband photosensing and photovoltaic applications. The GLancing Angle Deposition (GLAD) and Reactive Gas Pulsing Process (RGPP) techniques were used to study the effects of the oxygen ratio variation and deposition angle on the film optoelectronic and photovoltaic properties. The deposition angle of the particle flux was kept at 80° and the injected oxygen gas concentration was tuned by changing the oxygen pulsing time from 0 to 20 s. It is found that the material band gap increases from 0.9 eV to 3.56 eV when the oxygen content increases. The deposited SnOx films exhibited improved and tuned optoelectronic properties, demonstrating their potential applications for developing alternative broadband photosensing layers and eco-friendly all-oxide solar cells. In this regard, SnOx-based photosensor and all-oxide SnOx solar cell structures were developed using the deposited thin-films. It is revealed that the prepared SnOx photosensor shows the highest responsivity of 32.7 mA/W and improved ION/IOFF ratio of 48 dB. Moreover, the optimized all-oxide SnOx solar cell demonstrates a high efficiency of 3.41 %, a short-circuit current of 14.53 mA/cm2 and an open circuit voltage of 0.49 V. These interesting results make the proposed elaboration process based on combined RGPP and GLAD techniques highly suitable for the development of high-performance optoelectronic and photovoltaic devices based on cost-effective metal oxide materials.

Dynamics and phase behavior of metallo-dielectric rod-shaped microswimmers driven by alternating current electric field.

The ability to move and self-organize in response to external stimuli is a fascinating feature of living active matter. Here, the metallo-dielectric rod-shaped microswimmers are shown to have a similar behavior in the presence of an AC electric field. The silica-copper Janus microrods were fabricated using the physical vapor deposition-based glancing angle deposition technique (GLAD). When the aqueous solution of the microrods was under the influence of an external AC electric field, they were found to exhibit different phases such as clustering, swimming, and vertical standing in response to variation of the applied frequency. The swimming behavior (5-90 kHz) of the rods is attributed to the induced-charge electrophoresis (ICEP) phenomenon, whereas the dynamic clustering (<5 kHz) could be explained in terms of the electrohydrodynamic (EHD) interaction. Interestingly, the rods flip to attain the vertically standing position when responding to the applied electric field above 90 kHz. The reorientation and switching of the major axis of the rod along the field direction is attributed to the electro-orientation phenomenon. This is basically due to the dominance of the electric torque above the upper limit of the characteristic frequency, where the strength of slip flows around the microrods is predicted to be poor. The present study not only offers insight into the fundamental aspects of the dynamics and the phase behavior of rod-shaped microswimmers, but also opens an avenue to design reconfigurable active matter systems with features inspired by biological systems.

Glancing angle intermediate layer deposition approach for CVD diamond coating of high-speed steel substrates

This work demonstrates a new approach to the synthesis of highly adhesive diamond coatings on high-speed steel (HSS) substrates using a glancing angle deposition (GLAD) technique. The parameters of deposition of a molybdenum intermediate layer with a high level of surface roughness at a minimum layer thickness are determined. A maximum roughness of 38.1 nm with a minimum Mo layer thickness of 2 μm was achieved at an incidence angle of 15° and three sample positions. The duration of Mo sputtering at each rotation was 15, 10, 30 min. It is shown that a 2 μm Mo interlayer deposited by GLAD technique increases microcrystalline diamond film adhesion to HSS substrate compared to normally deposited Mo interlayer of the same thickness. The average delimitation area of the diamond film synthesized on a normally deposited molybdenum layer exceeds the corresponding parameter for the coating synthesized on the GLAD Mo layer by more than 8 times. Additionally, the process of diamond-Mo interlayer mechanical interlocking is also considered.

Silver nanosphere array substrates fabricated by glancing angle deposition: Morphology, hot spots and SERS properties

The generation and exploitation of hot spots play a crucial role in the fabrication of highly sensitive surface-enhanced Raman scattering (SERS) substrates. In this work, silver nanosphere (AgNS) array substrates with various morphologies of polystyrene (PS) core/Ag shell were fabricated by reactive ion etching and glancing angle deposition technique on PS sphere templates. The electromagnetic field distribution (hot spots) of AgNS array was calculated by the finite difference time domain method. R6G and MB were used as probe molecules to investigate the effect of structure spacing on electric field enhancement. Under 785 nm excitation, an AgNS substrate with a gap of approximately 20 nm exhibited the best SERS enhancement, and the limit of detection reached 5 × 10−8 M for both analytes. For R6G and MB, the relative standard deviations (RSDs) were 2.39 % and 7.22 %, and the enhancement factors (EFs) were 7.25 × 108 and 7.68 × 107, respectively. These results serve as a reference for the development of new highly sensitive SERS sensors.

Ag nanoparticle assisted vertically aligned β-Ga2O3 nanowire deposited by GLAD technique for ultrafast photodetection

In this study, we report the fabrication of Silver (Ag) nanoparticle (NP) assisted vertically oriented β-Ga2O3 nanowires on Silicon (Si) - substrate by the Glancing angle deposition (GLAD) technique. The fabricated samples were annealed at 900 °C. The optoelectronic properties of both As-deposited and annealed devices are studied thoroughly. The sample shows an increase in average crystallite size upon annealing with a decrease in lattice strain and dislocation density. FEG-SEM image confirms the growth of well-aligned vertically oriented nanowires with Ag NP in the midway of each nanowire. The UV–Vis absorption spectra show that Ag NP's presence results in the appearance of a significant absorption hump in the visible range, thereby broadening the light absorption capability of β-Ga2O3. The improvement in crystalline quality and reduction in defects after annealing resulted in a better response for the annealed device. These results indicate that annealing the Ag NP-assisted β-Ga2O3 NW device could become a feasible option for high-speed photodetectors, as it demonstrates a faster photoresponse time and a lower turn-on voltage.

Full-Control and Switching of Optical Fano Resonance by Continuum State Engineering.

Fano resonance, known for its unique asymmetric line shape, has gained significant attention in photonics, particularly in sensing applications. However, it remains difficult to achieve controllable Fano parameters with a simple geometric structure. Here, a novel approach of using a thin-film optical Fano resonator with a porous layer to generate entire spectral shapes from quasi-Lorentzian to Lorentzian to Fano is proposed and experimentally demonstrated. The glancing angle deposition technique is utilized to create a polarization-dependent Fano resonator. By altering the linear polarization between s- and p-polarization, a switchable Fano device between quasi-Lorentz state and negative Fano state is demonstrated. This change in spectral shape is advantageous for detecting materials with a low-refractive index. A bio-particle sensing experiment is conducted that demonstrates an enhanced signal-to-noise ratio and prediction accuracy. Finally, the challenge of optimizing the film-based Fano resonator due to intricate interplay among numerous parameters, including layer thicknesses, porosity, and materials selection, is addressed. The inverse design tool is developed based on a multilayer perceptron model that allows fast computation for all ranges of Fano parameters. The method provides improved accuracy of the mean validation factor (MVF = 0.07, q-q') compared to theconventional exhaustive enumeration method (MVF = 0.37).

Ag2Se Nanorod Arrays with Ultrahigh Room Temperature Thermoelectric Performance and Superior Mechanical Properties.

Ag2Se is an intriguing material for room-temperature energy harvesting. Herein, we report the fabrication of Ag2Se nanorod arrays by glancing angle deposition technique (GLAD) followed by simple selenization in a two-zone furnace. Ag2Se planar films of different thickness were also prepared. The unique tilted Ag2Se nanorod arrays show excellent zT = 1.14 ± 0.09 and a power factor of 3229.21 ± 149.01 μW/m-K2, respectively, at 300 K. The superior thermoelectric performance of Ag2Se nanorod arrays compared to planar Ag2Se films could be ascribed to the unique nanocolumnar architecture that not only facilitates efficient electron transport but also significantly scatters phonons at the interfaces. Furthermore, the nanoindentation measurements were performed to explore mechanical properties of the as-prepared films. The Ag2Se nanorod arrays showed hardness values of 116.51 ± 4.25 MPa and elastic modulus of 10,966.01 ± 529.61 MPa, which are lowered by 51.8 and 45.6%, compared to Ag2Se films, respectively. The synergetic dependence between the tilt structure and thermoelectric properties accompanied with the simultaneous improvement in mechanical properties opens a new avenue for the practical applications of Ag2Se in next-generation flexible thermoelectric devices.

Tuning of defects in vertical ZnO/CuO axial nanowire for efficient UV-A photodetection

Vertical ZnO/CuO axial nanowire (NW) arrays were fabricated by using glancing angle deposition technique inside the Radio Frequency (RF) magnetron sputtering system. A post annealing treatment of vertical ZnO/CuO axial NWs was performed in air from 200 °C to 900 °C temperature. Field emission scanning electron microscope imaging shows vertically well aligned NW structure. X-ray diffraction analysis showed improvement in crystalline structure, with increasing annealing with 400 °C sample showing the minimum dislocation density. The annealed sample at 400 °C (in air) shows high photoresponse as compared to other samples signifying reduction in defect states as also observed from photoluminescence analysis. The 400 °C sample showed the highest photocapacitance owing to the improvement in the interface. Moreover, the annealed vertical ZnO/CuO axial NW arrays at 400 °C showed a large responsivity (R) of 2.52 A W−1, specific detectivity (D*) of 5.14 × 1011 Jones and noise equivalent power as low as 6.54 pW at +4 V respectively. Furthermore, the annealed 400 °C device showed fast response with equal rise and fall time of 0.02 ms at +4 V.

Vertical nanostructures thin films of CdS and CdTe using low temperatures GLAD

This research develops a distinct method for obtaining of thin films of CdS and CdTe with vertical nanostructure morphology grown at low temperatures on the substrate of about 100 °C, were obtained by RF sputtering and sublimation from a vapor effusion source, respectively, both methods were combined with the glancing angle deposition technique. The CdS thin film exhibited a hexagonal structure with preferential plane orientation (002) under compressive stress and a crystallite size of approximately 45 nm. The CdTe film showed a cubic Zinc-Blende structure with an expansive lattice of the unit cell and with preferential plane orientation (111). The size of the crystallites in CdTe was approximately 56 nm. Scanning electron microscopy showed porous nanocolumn structures with vertical nanorods with a width of approximately 16 nm for the CdS and 80 nm for the CdTe, respectively with thicknesses of approximately 335 nm for the CdS and 1330 nm for the CdTe. Using open-source software ImageJ obtained a porosity measurement of approximately 10.4% for CdS and 9.4% for CdTe, respectively. The bandgap energy of the CdS and CdTe thin films was 2.47 eV and 2.51 eV, respectively. The refractive index was 2.5 for CdS and 3.5 for CdTe, respectively. The Urbach energy of the CdS and CdTe was 146 meV and 62 meV respectively. Our results are optimal for possible applications in photovoltaic devices, especially in solar cells and flexible solar cells.

All-in-One Optoelectronic Logic Gates Enabled by Bipolar Spectral Photoresponse of CdTe/SnSe Heterojunction.

Optoelectronic logic gate devices (OLGDs) have attracted significant attention in high-density information processors; however, multifunctional logic operation in a single device is technically challenging due to the unidirectional electrical transport. In this work, we deliberately design all-in-one OLGDs based on self-powered CdTe/SnSe heterojunction photodetectors. The SnSe nanorod (NR) array is grown on the sputtered CdTe film via a glancing-angle deposition technique to form a heterojunction device. At the interface, the photovoltaic (PV) effect in the CdTe/SnSe heterojunction and the photothermoelectric (PTE) effect from the SnSe NRs are combined together to induce the reversed photocurrent, leading to a unique bipolar spectral response. The competition between PV and PTE in different spectral ranges is thus employed to control the photocurrent polarity, and five basic logic gates of OR, AND, NAND, NOR, and NOT can be performed just with a single heterojunction. Our findings indicate the large potentials of the CdTe/SnSe heterojunctions as logic units in next-generation sensing-computing systems.

Design and development of Fabry–Perot etalon based color filter using ebeam GLAD technique: Simulation and experiment

The design of Spatial Variable Color Filter (SVCF), based on the principle of Fabry–Perot (FP) etalon, has been analyzed in detail considering Ag as reflecting metallic layer and TiO2 as cavity layer. The effect of different thickness ranges of cavity layer for different order of interference peaks and the effect of varying thickness of reflecting layer has been investigated through simulation. A SVCF has been designed in the broad visible wavelength range of 464 to 670 nm based on the 2nd order interference peak of FP etalon for optimized spectral performance and it has been experimentally demonstrated using ebeam evaporation technique. The reflecting Ag layer has been deposited at normal angle and the tapered cavity layer of TiO2 has been deposited at 86° glancing angle. The distribution of thickness and dispersion relationship at various locations of the glancing angle deposited (GLAD) TiO2 thin films has been analyzed by spectroscopic ellipsometry measurements. The effect of lateral variation of dispersion properties of cavity layer caused by GLAD, on the spectral performance of the developed SVCF, has been investigated by both simulation and through spectral transmittance measurement. Overall results demonstrate the potential of the axial glancing angle deposition technique for the first time for development of SVCF in visible wavelength with high peak transmittance (∼67%) and a peak wavelength tunability of ∼4 nm/mm.

An in-depth analysis on the switching response and impedance curves of n-si/In2O3 NW/Ag NPs/In based devices by a double-step glancing angle deposition technique

Silver (Ag) nanoparticles (NPs) were coated upon indium oxide (In2O3) nanowires (NW) by a double-step glancing angle deposition (GLAD) technique. The study focuses on the experimental analysis of current (I) versus voltage (V), current (I) versus time (t), as well as impedance (Zexp) versus voltage (V) curves for n-Si/In2O3 NW/Ag NPs/In based devices with a sweeping voltage of ±10 V at room temperature in different frequency responses varying from 100 Hz to 2 MHz. The n-Si/In2O3 NW/Ag NPs/In based device showed faster rise and fall time of 0.13 s and 0.12 s than the other devices due to oxygen-related defect states. The presence of Ag NPs also improved oxygen related defect states, resulting in high impedance value for n-Si/In2O3 NW/Ag NPs/In based device. The series circuit model (SCM) was used to derive the theoretical investigations of impedances, indicating the n-Si/In2O3 NW/Ag NPs/In based device can be used in nanoelectronics applications.