Oblique Deposition Research Articles

Low temperature dependence of electrical resistivity in obliquely sputter-deposited transition metal thin films

Transition metals exhibiting hcp (Ti, Zr, Hf) and bcc (V, Nb, Ta, Cr, Mo, W) crystalline structures are DC sputter-deposited by oblique angle deposition. A constant film thickness of 400 nm is prepared, whereas the deposition angle α is systematically changed from 0 to 85° A columnar structure is produced with column angle reaching β = 50° for the highest deposition angle. Crystallinity and grain size are both reduced with an increasing deposition angle, especially for α higher than 60° DC electrical resistivity vs. temperature in the range 7–300 K shows a typical metallic-like behavior with films becoming more resistive for high deposition angles. For temperatures higher than 100 K, the linear temperature dependence of resistivity is obtained for films prepared with deposition angles lower than 60° The electron-phonon is the main interaction acting on electronic transport mechanism. Oblique deposition angles give rise to an enhancement of electron-phonon interactions with a saturation effect of electrical resistivity for some metals. Resistivity measurements at low temperatures (down to 7 K) show the predominance of electron-defect interactions. Electron-phonon-defect interaction effect is particularly investigated as a function of the deposition angle and a shift of the crossover temperature is brought to the fore.

Chiral Thin Film Structures Based on Arrays of Cobalt Nanohelices Obtained By Oblique Deposition

Chiral Thin Film Structures Based on Arrays of Cobalt Nanohelices Obtained By Oblique Deposition

Physics of microscale freeform 3D printing of ice

Ice is emerging as a promising sacrificial material in the rapidly expanding area of advanced manufacturing for creating precise 3D internal geometries. Freeform 3D printing of ice (3D-ICE) can produce microscale ice structures with smooth walls, hierarchical transitions, and curved and overhang features. However, controlling 3D-ICE is challenging due to an incomplete understanding of its complex physics involving heat transfer, fluid dynamics, and phase changes. This work aims to advance our understanding of 3D-ICE physics by combining numerical modeling and experimentation. We developed a 2D thermo-fluidic model to analyze the transition from layered to continuous printing and a 3D thermo-fluidic model for the oblique deposition, which enables curved and overhang geometries. Experiments are conducted and compared with model simulations. We found that high droplet deposition rates enable the continuous deposition mode with a sustained liquid cap on top of the ice, facilitating smooth geometries. The diameter of ice structures is controlled by the droplet deposition frequency. Oblique deposition causes unidirectional spillover of the liquid cap and asymmetric heat transfer at the freeze front, rotating the freeze front. These results provide valuable insights for reproducible 3D-ICE printing that could be applied across various fields, including tissue engineering, microfluidics, and soft robotics.

Asymmetrical Absorption and Surface‐Enhanced Raman Scattering Enhancement by Silver Nanoflower Metasurface

A metasurface composed of silver nanoflower arrays, which exhibit asymmetrical absorption and surface‐enhanced Raman scattering (SERS) due to hybrid plasmonic effects, is reported. The silver nanoflowers are fabricated by oblique deposition of silver on a polymer nanohole array on a glass substrate, forming petal‐like semicontinuous thin films on the inner walls of the holes. Depending on the deposition angle, three‐ or five‐petal nanoflowers are obtained. The nanoflower arrays show strong reflection from the air side and broadband and wide‐angle absorption from the glass side, as a result of transmission surface plasmon resonance and localized surface plasmon resonance, respectively. The three‐petal structure, which absorbs most of the incident light from the glass side, induces a localized enhancement of electric field in the center of each nanohole, providing a high‐sensitivity SERS substrate. The SERS performance of the metasurface by direct measurement and near‐field simulation is demonstrated.

Spatially selective narrow band and broadband absorption in Ag/SiO2/Ag based trilayer thin films by oblique angle deposition of SiO2 layer

We have experimentally demonstrated spatially selective absorption in Ag-SiO2-Ag based trilayer thin films by tuning the deposition angle of SiO2 layer. These structures generate cavity resonance which can be tuned across the substrate locations due to spatially selective thickness and refractive index of silicon oxide (SiO2) film sandwiched between metallic silver (Ag) mirrors. Spatially selective property of SiO2 film is obtained by oblique angle deposition technique using an electron beam evaporation system. The resonance wavelength of absorption in this trilayer structure shifts across the substrate locations along the direction of oblique deposition. The extent of shift in resonance increases with increase in angle of deposition of SiO2 layer. 4.14 nm mm−1 average shift of resonance wavelength is observed when SiO2 is deposited at 40° whereas 4.76 nm mm−1 average shift is observed when SiO2 is deposited at 60°. We observed that the width of resonance increases with angle of deposition of the cavity layer and ultimately the resonant absorption disappears and becomes broadband when SiO2 is deposited at glancing angle deposition (GLAD) configuration. Our study reveals that there is a suitable range of oblique angle of deposition from 40° to 60° for higher spatial tunability and resonant absorption whereas the absorption becomes broadband for glancing angle deposition.

Perpendicular magnetic properties and field-free current-induced switching in W/CoFeB/MgO trilayers with a compensating oblique W underlayer

Zero-field magnetization switching (ZFS) driven by current-induced spin–orbit torque (SOT) holds significant importance in spintronic applications. The introduction of a lateral asymmetric structure (LAS) through oblique deposition proves to be an effective strategy for breaking inversion symmetry, thereby enabling SOT-driven ZFS. However, the coexistence of wedge thickness structure and slanted columnar microstructure in the obliquely deposited films poses challenges in distinguishing their respective effects. In this study, we conducted a comparative investigation of the perpendicular magnetic properties and current-induced switching in W/Co40Fe40B20/MgO films by oblique sputtering of the W underlayer at a fixed tilting angle and at two opposite tilting angles with its wedge thickness compensated. We have found that the perpendicular magnetic properties of the Co40Fe40B20 layer are significantly altered at large tilting angles, irrespective of whether the W wedge thickness is compensated. Notably, at a tilting angle of 50°, ZFS is realized for both the conventional oblique sample and the compensating oblique sample, with the switching polarity contingent on the final tilting direction of the W layer. We have identified a gradient in perpendicular magnetic anisotropy in these samples, attributed to the laterally varying roughness associated with the slanted columnar microstructure of the W underlayer. This study underscores the dominant role of microscopic LAS in obliquely deposited films in breaking SOT symmetry. Our research sheds light on the impact of the slanted columnar microstructure on the magnetic and magneto-transport properties of films, offering valuable insights for advancing spintronic device research.

Enhanced magnetic anisotropy and its thermal stability in obliquely deposited Co-Film on the nanopatterned substrate

The deliberate manipulation of magnetic anisotropy through controlled adjustments to surface and interface morphology has become important due to its potential applications in spintronics and magnetic memory devices. In the present work, oblique angle deposition (OAD) at 65° to the surface normal on a rippled substrate, keeping nanopatterns on the SiO2 substrate perpendicular to the OAD projection, has been used to induce in-plane uniaxial magnetic anisotropy (UMA) and its thermal stability in cobalt (Co) thin film. Prior to film preparation, the patterned substrate of wavelength 68 ± 4 nm and amplitude 3.4 ± 0.2 nm was prepared separately using a low-energy ion beam erosion (IBE) process. Grazing incidence small-angle X-ray scattering (GISAXS) and magneto-optical Kerr effect (MOKE) techniques have been used for film characterization. While GISAXS provided information about film structure and morphology, MOKE provided information about magnetic properties, thus making it possible to correlate the temperature-dependent evolution of morphology with that of UMA in the film. A clear anisotropy in the growth of Co film is found to result in strong UMA. Unlike previous studies, which typically observe a reduction in UMA strength with thermal annealing, the present work demonstrates a 31 % increase in UMA strength after annealing up to 200 °C, underscoring the importance of oblique angle deposition on nano-rippled substrates for achieving high UMA and ensuring its thermal stability up to moderate temperatures. The appearance of large UMA and its unusual temperature dependence is understood in terms of the shadowing effects and column coalescence, resulting in more robust shape anisotropy. This work provides insights into morphological anisotropy, elucidating the interplay of shadowing effects, shape anisotropy, and dipolar interactions within interacting column and ripple structures. This method gives rise to morphology-induced anisotropy, which can also be applied to other ferromagnetic films to enhance the magnetic anisotropy and ensure thermal stability.

Effect of TiN thin films deposited by oblique angle sputter deposition on sol-gel coated TiO2 layers for photocatalytic applications

TiO2 monolayer and TiN/TiO2 bilayer coatings were deposited on soda-lime glass prepared by mixing two techniques, TiO2 was deposited by sol-gel dip-coating and TiN film was deposited by oblique angle deposition using reactive magnetron sputtering at α=45° Structural analysis showed typical peaks of TiO2 anatase phase and cubic (Na-Cl type) structure of TiN. Roughness value of 3 nm was obtained for the TiN/TiO2 bilayer film with a rise and elongated grains size. It was found that the optical band gap energy decreases after coupling the TiN sub-layer which is explained by the incorporation of N atoms into TiO2 structure. At constant UV irradiation time, the photo-degradation of methylene blue rate increased for TiN/TiO2 film by 4 % compared to TiO2 film.

Improvement of high-frequency magnetic properties of CoFeB thin film using oblique deposition for spin wave electronic devices

Improvement of high-frequency magnetic properties of CoFeB thin film using oblique deposition for spin wave electronic devices

Atomic force microscopy observation of surface morphologies and measurements of local contact potential differences of amorphous solid water samples deposited at 15 and 100 K.

We use an ultra-high vacuum cryogenic atomic force microscope to investigate the surface morphology of amorphous solid water (ASW) prepared by oblique deposition of water vapor onto Si(111)7 × 7 substrates at temperatures of 15 and 100 K. Height-height correlation function analysis of topographic images suggests that ASW at 15 K has a columnar structure and that the typical diameter of the column is 5-10 nm. At 100 K, the typical diameter is 10-30 nm, although columnar features are less prominent. The surface roughness (i.e., deviation of the height) is greater at 15 K than at 100 K, indicating that the surface at 100 K exhibits a relatively flat morphology. This result implies that transient diffusion of deposited water molecules affects the surface morphology at 100 K. In addition, measurements of the local contact potential difference between the tip and the ASW surface suggest that the magnitude of the negative surface potential at the microscopic scale, which is attributed to spontaneous polarisation, cannot simply be scaled by the thickness of ASW as predicted in previous experiments with Kelvin probes.

Magnetic Anisotropy of FeNi Multilayer Films with Different Orientations of the Magnetic Anisotropy Axes in Adjacent Layers

FeNi films were prepared using the DC magnetron sputtering technique with an oblique deposition arrangement. Multilayers with different orientations of the magnetic anisotropy axes were obtained thanks to a rotary sample holder inside the vacuum chamber. Magnetic properties were studied using magneto–optical Kerr microscopy and a vibrating sample magnetometer. Single-layered FeNi films having thicknesses as high as 10 nm and 40 nm show in-plane uniaxial easy magnetization axes produced by the oblique incidence of incoming components of the beams. Magnetic anisotropy field for four-layered samples with orthogonal uniaxial magnetic anisotropy axes in the adjacent layers and the thickness of individual layers of 10 nm and 40 nm turned out to be less than in single-layered films. The magnetic properties peculiarities of the eight-layered sample FeNi (10 nm) × 8 obtained by rotation of the sample holder by 45° before deposition of each subsequent layer suggest the formation of a helix-like magnetic structure through the thickness of the multilayered sample similar to the magnetization arrangement in the Bloch-type magnetic domain wall.

Role of CdTe Interface Structure on CdS/CdTe Photovoltaic Device Performance.

Glancing angle deposition (GLAD) of CdTe can produce a cubic, hexagonal, or mixed phase crystal structure depending upon the oblique deposition angles (Φ) and substrate temperature. GLAD CdTe films are prepared at different Φ at room temperature (RT) and a high temperature (HT) of 250 °C and used as interlayers between the n-type hexagonal CdS window layer and the p-type cubic CdTe absorber layer to investigate the role of interfacial tailoring at the CdS/CdTe heterojunction in photovoltaic (PV) device performance. The Φ = 80° RT GLAD CdTe interlayer and CdS both have the hexagonal structure, which reduces lattice mismatch at the CdS/CdTe interface and improves electronic quality at the heterojunction for device performance optimization. The device performance of HT CdS/CdTe solar cells with Φ = 80° RT with 50 to 350 nm thick GLAD CdTe interlayers is evaluated in which a 250 nm interlayer device shows the best device performance with a 0.53 V increase in open-circuit voltage and fill-factor product and a 0.73% increase in absolute efficiency compared to the HT baseline PV device without an interlayer.

Texture evolution of obliquely deposited Au thin films

Understanding the formation and evolution of the texture of obliquely deposited films is of great significance for improving their performance. Among these films, Au films have many advantages and wide application prospects. However, a systematic study of texture evolution of Au films has not been reported. In this study, Au films were prepared by magnetron sputtering oblique deposition. The pole figures of films deposited with various oblique angles (γ) and thicknesses were measured by X-ray diffraction. The morphology and size of the grains on the surface and in the cross-section of the films were observed by scanning electron microscopy. The surface topography of the films was determined by atomic force microscopy. During the growth process of the films, the increase rate of roughness was faster than the transverse broadening rate of grains. The samples deposited at γ ≤ 60° were composed of densely arranged grains with inclined (111) plane fiber texture whose tilt angle increased with the increase of γ and thickness. In the films deposited at γ ≥ 70°, the grain structure evolved into highly porous nanorods, and the (111) plane texture was more slanted and dispersed. The mechanism of film texture formation during oblique deposition is discussed.

Deposition of nanometer-thick amorphous carbon films by filtered cathodic vacuum arc under oblique ion incidence conditions

Filtered cathodic vacuum arc (FCVA) is a promising technique for synthesizing extremely thin carbon films exhibiting highly tetrahedral (sp3) carbon atom hybridization. However, most FCVA studies are for incident ions impinging perpendicular to the substrate surface. In this study, the effects of the ion incidence angle on the thickness, structure, and surface roughness of amorphous carbon (a-C) films deposited under different substrate bias voltages were examined in the light of computational and experimental results. Dynamic simulations and film thickness measurements showed a decrease in film thickness with increasing ion incidence angle, attributed to the decrease in carbon ion fluence on the film surface. Carbon atom hybridization analysis revealed a critical ion incidence angle for a given substrate bias voltage. Simulation and experimental results demonstrated that the enhancement of sp3 hybridization resulted from carbon-carbon collision cascades on the growing film surface and densification induced by direct and recoil implantation processes controlled by the ion incidence angle and substrate bias voltage. The strong dependence of a-C film growth on the carbon ion incidence angle exemplified by the results of this study has direct implications in the oblique deposition of ultrathin a-C films with predominant tetrahedral carbon atom hybridization. The present study provides a framework for optimizing the ion incidence angle to achieve the deposition of a-C ultrathin films with high sp3 contents.

Tailoring the in-plane magnetic anisotropy and permeability spectra of obliquely deposited Fe40Co40B20 films for 5G communications

Ferromagnetic films are widely used in magnetic devices owing to their high saturation magnetization, high magnetic permeability, and low coercivity. However, it is extremely challenging to apply ferromagnetic films to high-frequency communication applications due to the low resonant frequency of permeability spectra. Here, ferromagnetic Fe40Co40B20 films are prepared using oblique magnetron sputtering deposition and the static and dynamic magnetic properties are comprehensively investigated. The self-shadowing effect caused by the tilted growth of columnar grains introduces in-plane magnetic anisotropy to the films, thereby increasing the natural resonant frequency. As the sputtering angle increases from 24° to 30°, the resonant frequency increases from 4.09 to 4.87 GHz, resulting in an approximate liner tunability of 0.13 GHz/degree. Compared to the normally sputtered films, the figure of merit in regard to the microwave magnetic performance of the obliquely sputtered films is significantly enhanced by more than 50%. These results reveal the effectiveness of the oblique sputtering deposition to tailor the in-plane magnetic anisotropy and permeability spectra of ferromagnetic films for the high-frequency film inductor application of 5G communications.

Impact of Silver on the Structural and Wettability Properties of ZnO Films Grown by Oblique Angle Magnetron Sputtering

Un-doped (uZO) and silver-doped zinc oxide (SZO) films were prepared by oblique incidence sputtering deposition under different process parameters. The crystalline structure, chemical composition, and surface morphology were correlated with the optical properties, as well as with the wettability of the films. In the case of uZO films, the orientation, inclination, and morphology of the columnar structure determined the wettability of the layer, moving from a hydrophilic- to hydrophobic-like character. In the case of SZO films, although almost all of them displayed hydrophobic behavior, the hydrophobic character increased with the Ag content. The most hydrophobic surface was obtained when the Ag content in the layers was greater than 7 at.% and, in these cases, the structural results indicate that the layers were formed by a disordered mixture of Zn and Ag oxides.

Plasmonic Photoresistor Based on Interconnected Metal‐Semiconductor Grating

AbstractMetal‐semiconductor nanostructures in various configurations are extensively used in photodetection, photocatalysis, and photovoltaics. For photodetection purposes, the working principle is straightforward; on illumination, generated charge carriers in excess lead to a decrease in resistance. Notably, using an interconnected metal‐semiconductor grating, it is observed and now reported an opposite response, an increase in the resistance. Such photoresistors are fabricated through wrinkle structuring and oblique angle material deposition methods. It is found that the controlled wrinkling leads to large‐area 1D periodic structures with coexisting cracking perpendicular to the grating direction—such cracks are used as connections between the two‐point contact measurement through the associated gold layer deposition. An enhanced current reduction is further observed on photoexcitation for an additional deposition of an amorphous titania layer. Subsequently, a discussion on the mechanisms and interaction between hot electron injection, charge carrier recombination, and thermalization is presented. Supported by numerical modeling, the angle‐resolved plasmonic modes with the photoresistance can be correlated. The ease of layered deposition of the materials allows one to extend the studies on cavity‐based structures with sandwiched titania layers as hotspots. This simple, scalable, and robust fabrication method thus promises an efficient routeway toward photosensor development in which plasmon‐mediated hot electrons play a crucial role.

Micromorphology and uniaxial magnetic anisotropy of oblique-sputtered Ni80Fe20 films on periodically rippled Al2O3 substrates

Ni80Fe20 (NiFe) films were deposited on periodically rippled Al2O3 substrates by two different template oblique angle deposition (OAD) processes at various oblique deposition angles α (0° ≤ α ≤ 60°). The disparate in-plane uniaxial magnetic anisotropy (UMA) caused by the two template deposition processes of films was revealed by magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) measurements. The analysis of Transmission electron microscopy images indicated that this was related to the different micromorphology of the films due to the two template deposition processes. The angle between substrates’ ripple direction and the material flow incident direction would strongly influence the micromorphology and the induced in-plane UMA field of films. The values of the UMA field of these films can be much larger than those of the films oblique deposited on the plane Al2O3 substrates at the same α by choosing the template deposition direction. The results would help further modulate the UMA of magnetic films deposited on rippled substrates, which would be beneficial for the applications of these films in spintronic, magnetic memory and magnetic microwave devices.

Spin-structured multilayer THz emitters by oblique incidence deposition

State-of-the-art THz spintronic emitters require a constant magnetic field to saturate their magnetization. We demonstrate that depositing the ferromagnetic layers at oblique incidence confines the magnetization to a chosen in-plane easy axis and maintains the saturation in the absence of an external magnetic field. We use this method to build THz emitters structured as spin valves, for which we use an external magnetic field to turn on and off the emission of THz radiation as well as to change its polarization. We are able to reproduce the THz waveforms by modeling the spin current and the THz propagation through the multilayer system.

Ultimate figures of merit broadband self-powered obliquely deposited antimony thin film laser detectors

Fabrication of a fast and high detectivity infrared detector operating at room temperature represents a big challenge. Due to the small energy gap of the semiconducting materials used for infrared detectors, the noise becomes considerable factor and the possibility of operating the detector at room temperature is very limited. A study of the figures of merit antimony thin films detector grown by oblique angle deposition technique is presented. Polycrystalline antimony thin films were thermally evaporated on the glass substrates at a angles of 0, 10, 30, and70°. The aim was to develop a wideband (0.649–10.6) µm self-powered laser detectors; operating at room temperature. The deposition angle had a decisive role in the detector specifications, namely, its detectivity, responsivity, linearity, and response time. At θ = 70° deposition angle; maximum detectivity and fastest response were achieved. The variation of rise time with deposition angle was linear, and the rise time was around 50 ns at 70°. The antimony detectors showed about the same specific detectivity ~ 109 Jones at 300 k for the wavelength range of 1.064–10.6 µm.