Substrate Pattern Research Articles

Ultraviolet photodetector based on vertical β-Ga2O3 nanowire array on GaN substrate

Driven by the requirement to ultraviolet detection, β-Ga2O3 UV photodetectors have attracted great attention. Using a metal organic chemical vapor deposition (MOCVD) reactor, we grew β-Ga2O3 nanowires array on a GaN substrate using Ga as catalyst. The density of the nanowires was optimized employing the substrate patterning technology. A UV detector based on the graphene/β-Ga2O3-nanowire-array was realized by micro-fabrication techniques. The device has a wide range of UV response covering UVC-UVA band and the peak response reaches 30.82 mA W−1 at 258 nm corresponding to the band gap of β-Ga2O3. The rapid response speed (<1 s) is comparable to that of most reported Ga2O3 nanowire ultraviolet photodetectors.

Continuum level-set model for anisotropic wet etching of patterned sapphire substrates

We present a continuum modeling approach to simulate anisotropic wet etching of single-crystal sapphire employing mixtures of sulfuric acid and phosphoric acid. Wet etching of sapphire leads to the formation of crystal facets with high Miller–Bravais indices. The resulting complex three-dimensional topographies can be exploited to optimize the patterning of sapphire substrates which are employed for gallium nitride based light-emitting diodes. Due to the strong impact of the three-dimensional sapphire topography on the light extraction efficiency of the final device, precise control over the wet etching process, in particular etchant mixture, etch time, and temperature, is highly important. We present our model in the context of process technology computer-aided design, where we use the level-set method to track the evolution of the three-dimensional etch profile over time. In order to describe the intricate anisotropy of wet etched sapphire, we propose a flexible interpolation method for the etch rate distribution, which incorporates experimentally characterized crystal facets and deduces local extrema in the distribution based on local convexity/concavity considerations. The developed model has been calibrated and evaluated based on scanning electron microscopy and atomic force microscopy characterizations from the literature. Our model enables accurate sapphire etching simulations, where the emerging and disappearing crystal facets show a good agreement with experimental observations for several etchant mixtures and temperatures.

Solid-State Dewetting of Gold on Stochastically Periodic SiO2 Nanocolumns Prepared by Oblique Angle Deposition.

Solid-state dewetting (SSD) on patterned substrates is a straightforward method for fabricating ordered arrays of metallic nanoparticles on surfaces. However, a drawback of this procedure is that the patterning of substrates usually requires time-consuming and expensive two-dimensional (2D) fabrication methods. Nanostructured thin films deposited by oblique angle deposition (OAD) present at the surface a form of stochastically arranged periodic bundles of nanocolumns that might act as a patterned template for fabricating arrays of nanoparticles by SSD. In this work, we explore this concept and investigate the effect of three different types of OAD SiO2 thin films on the SSD of Au deposited on their surface. We demonstrate that the size and spatial distribution of the particles can be tailored through the surface morphology of these OAD film substrates. It has been found that the SSD of the evaporated Au layer gives rise to a bimodal size distribution of particles. A majority of them appeared as mesoparticles with sizes ≳100 nm and the rest as nanoparticles with ∼10 nm, respectively, located either on top of the nanocolumns following their lateral distribution (i.e., resulting from a patterning effect) or incorporated inside the open mesopores existing among them. Moreover, on the SiO2-OAD thin films where interconnected nanocolumnar bundles arrange in the form of discrete motifs, the patterning effect gave rise to the formation of approximately one Au mesoparticle per motif, which is one of the assets of patterned SSD. The morphological, optical (i.e., plasmon resonance), and crystalline structural characteristics of Au mesoparticles suggest that the interplay between a discontinuous nanocolumnar surface acting as a template and the poor adhesion of Au onto SiO2 are key factors for the observed template effect controlling the SSD on the surface of OAD thin films.

Positioning and Aligning Electrospun PAN Fibers by Conductive and Dielectric Substrate Patterns

AbstractDuring electrospinning, the flying nanofibers can be attracted by conductive areas such as copper tape on a nonconductive substrate, especially in case of magnetic nanofibers. The question arises, however, whether the conductivity or any other physical properties of these areas are responsible for this effect. Here, electrospinning polyacrylonitrile (PAN) on nonconductive polypropylene (PP) substrates is reported, modified with conductive copper tape as well as with diverse coatings with varying dielectric constants. The results show that in case of non‐magnetic PAN fibers, especially BaTiO3 with its high dielectric constant strongly, attracts the fibers formed during electrospinning, which can be explained by local modification of the electric field due to the introduced dielectric. This process can be used to tailor the nanofiber mat thickness depending on the position.

The Role of Microenvironmental Cues and Mechanical Loading Milieus in Breast Cancer Cell Progression and Metastasis.

Cancer can disrupt the microenvironments and mechanical homeostatic actions in multiple scales from large tissue modification to altered cellular signaling pathway in mechanotransduction. In this review, we highlight recent progresses in breast cancer cell mechanobiology focusing on cell-microenvironment interaction and mechanical loading regulation of cells. First, the effects of microenvironmental cues on breast cancer cell progression and metastasis will be reviewed with respect to substrate stiffness, chemical/topographic substrate patterning, and 2D vs. 3D cultures. Then, the role of mechanical loading situations such as tensile stretch, compression, and flow-induced shear will be discussed in relation to breast cancer cell mechanobiology and metastasis prevention. Ultimately, the substrate microenvironment and mechanical signal will work together to control cancer cell progression and metastasis. The discussions on breast cancer cell responsiveness to mechanical signals, from static substrate and dynamic loading, and the mechanotransduction pathways involved will facilitate interdisciplinary knowledge transfer, enabling further insights into prognostic markers, mechanically mediated metastasis pathways for therapeutic targets, and model systems required to advance cancer mechanobiology.

Optimized femtosecond laser patterning of organic light-emitting diode substrates for the extraction of substrate guided modes

This work demonstrates the enhancement of the outcoupling efficiency in organic light-emitting diodes via patterning the substrate at the air/glass interface by a femtosecond laser. This patterning technique is completed via a one-step process and thus eliminates the need for complex multi-step fabrication processes, common among outcoupling structures. Comparisons among patterned devices with and without a thick hole injection layer show that intrinsic guided losses can be recovered and extracted into free space, thus achieving an increase in outcoupling efficiency by about 31% and 61%, respectively.

Observation of ordered arrays of endotaxially grown nanostructures from size-selected Cu-nanoclusters deposited on patterned substrates of Si.

We report the first time observation of endotaxial growth during thermal treatment of size-selected nanoclusters on a patterned substrate, when we fabricate highly ordered and partially embedded 3D crystalline Cu nanostructure arrays of controlled size in Si-substrates. For this purpose, we combine low energy cluster deposition on the ripple-patterned substrate with controlled annealing. We have investigated, in detail, the effect of the substrate pattern on the deposited size-selected clusters upon heat treatment. At the annealing temperature of 400 °C, nanosized islands are found to be organized into regular arrays, following the alignment of the substrate pattern exactly. The formed islands are trapped at the specific sites of the substrate where surface curvature is maximum and concave. It is also observed that the size of the produced nanoislands (or particles) in the direction of the ripple wave vector, i.e., across the ripples, are in congruence with the ripple wavelength. All the formed islands are partially buried in the substrate and the growth inside the substrate exhibits endotaxial growth. Such an embedded size-controlled nanoscale system can be very promising as sinter-resistant heterogenous catalyst with strong potential in clean energy technology and industrial chemical synthesis.

Biotemplated Lithography of Inorganic Nanostructures (BLIN) for Versatile Patterning of Functional Materials

Here, we present a highly parallel fabrication method dubbed biotemplated lithography of inorganic nanostructures (BLIN) that enables large-scale versatile substrate patterning of metallic and semi...

Capillary Stamping of Functional Materials: Parallel Additive Substrate Patterning without Ink Depletion

AbstractPatterned substrates for optics, electronics, sensing, lab‐on‐chip technologies, bioanalytics, clinical diagnostics as well as translational and personalized medicine are typically prepared by additive substrate manufacturing including ballistic printing and microcontact printing. However, ballistic printing (e.g., ink jet and aerosol jet printing, laser‐induced forward transfer) involves serial pixel‐by‐pixel ink deposition. Parallel additive patterning by microcontact printing is performed with solid elastomeric stamps suffering from ink depletion after a few stamp‐substrate contacts. The throughput limitations of additive state‐of‐the art patterning thus arising may be overcome by capillary stamping –parallel additive substrate patterning without ink depletion by mesoporous silica stamps, which enable ink supply through the mesopores anytime during stamping. Thus, either arrays of substrate‐bound nanoparticles or colloidal nanodispersions of detached nanoparticles are accessible. Three types of model inks are processed: 1) drug solutions, 2) solutions containing metallopolymers and block copolymers as well as 3) nanodiamond suspensions representing colloidal nanoparticle inks. Thus, aqueous colloidal nanodispersions of stamped drug nanoparticles, regularly arranged ceramic nanoparticles by post‐stamping pyrolysis of stamped metallopolymeric precursor nanoparticles and regularly arranged nanodiamond nanoaggregates are obtained. Capillary stamping may overcome the throughput limitations of state‐of‐the‐art additive substrate manufacturing while a broad range of different inks can be processed.

Uncovering process domains in large rivers: Patterns and potential drivers of benthic substrate heterogeneity in two North American riverscapes

Identifying and understanding functional process domains (sensu Montgomery, 1999) in rivers is paramount for linking the physical habitat template to ecosystem structure and function. To date, efforts to do this have been rare, especially in large rivers, as they require appropriate tools for quantifying habitat heterogeneity with fine-scale resolution across broad spatial extents. In this study, we used side-scan sonar technology to map riverbed substrate at six sites in the Yellowstone and Missouri rivers. Substrate maps were then analyzed and visualized using geospatial analysis to relate fine-grained spatial substrate patterns to process domain structure. Our findings revealed two distinct nested domains of substrate patchiness, suggesting that different factors are responsible for shaping patterns of substrate at different scales. Although small-scale patchiness in substrate was likely driven by internal, or autogenic, physical processes, patterns at larger segment extents (>3 km) were often driven by abrupt transitions in habitat related to exogenous factors such as lateral erosion of talus, tributary inputs, and bank armoring. Additionally, we found that heterogeneity in benthic substrate increased with spatial extent at all of our study sites; however, this relationship was lower in the Missouri River, which is altered by impoundment. Our study represents one of the first efforts to relate benthic habitat heterogeneity to nested process domain structure in large riverscapes, and offers a unique perspective for linking landscape processes, geomorphological habitat heterogeneity, and biological structure and function in large rivers.

Large-Beam Picosecond Interference Patterning of Metallic Substrates

In this paper, we introduce a method to efficiently use a high-energy pulsed 1.7 ps HiLASE Perla laser system for two beam interference patterning. The newly developed method of large-beam interference patterning permits the production of micro and sub-micron sized features on a treated surface with increased processing throughputs by enlarging the interference area. The limits for beam enlarging are explained and calculated for the used laser source. The formation of a variety of surface micro and nanostructures and their combinations are reported on stainless steel, invar, and tungsten with the maximum fabrication speed of 206 cm2/min. The wettability of selected hierarchical structures combining interference patterns with 2.6 µm periodicity and the nanoscale surface structures on top were analyzed showing superhydrophobic behavior with contact angles of 164°, 156°, and 150° in the case of stainless steel, invar, and tungsten, respectively.

Steady states of thin film droplets on chemically heterogeneous substrates

Abstract We study steady-state thin films on chemically heterogeneous substrates of finite size, subject to no-flux boundary conditions. Based on the structure of the bifurcation diagram, we classify the 1D steady-state solutions that exist on such substrates into six different branches and develop asymptotic estimates for the steady states on each branch. Using perturbation expansions, we show that leading-order solutions provide good predictions of the steady-state thin films on stepwise-patterned substrates. We show how the analysis in one dimension can be extended to axisymmetric solutions. We also examine the influence of the wettability contrast of the substrate pattern on the linear stability of droplets and the time evolution for dewetting on small domains. Results are also applied to describe 2D droplets on hydrophilic square patches and striped regions used in microfluidic applications.

Facile Microfluidic Fabrication of 3D Hydrogel SERS Substrate with High Reusability and Reproducibility via Programmable Maskless Flow Microlithography

AbstractIn the field of surface‐enhanced Raman scattering (SERS), advances in nanotechnology and surface chemistry have contributed to fabricating the metal substrates with highly sophisticated architectures and strong binding affinity to target molecules which enhanced the sensitivity to target molecules. However, the elaborate yet complicated steps for the synthesis, patterning, and surface modification of metal substrates have often resulted in compromising the reliability, reproducibility, and reusability as SERS substrates. Here, a fully programmable and automated digital maskless flow microlithography process that spatiotemporally controls the fluid flow, UV irradiation, and the shape and location of SERS polymer matrix is provided to fabricate a reliable, reproducible, and reusable hydrogel‐based 3D SERS substrate. The SERS substrates are located inside the microfluidic device in the form of disk‐shaped hydrogels. By rationally designing the functional group chemistry of the hydrogel microposts, Ag nanoparticles are homogeneously synthesized in situ, a target molecule is amplified by 25‐fold inside the microposts, and an enhancement factor as high as 2.4 × 108 is observed. Furthermore, a highly reusable multitarget sensing capability is demonstrated by a sequential analysis of multiple analytes without the trace of former analytes via the intermittent washing step.

(Invited) Strain Engineering of Si/Ge Heterostructures on Ge-on-Si Platform

Strain engineering of Si/Ge heterostructures with high Ge contents is allowed on the Ge-on-Si platform since a high quality Ge-on-Si has been available owing to the two-step growth method. Detailed studies on initial stages of the partial strain relaxation of strained SiGe layers on Ge-on-Si and bulk-Ge substrates clearly indicate that the strained SiGe grown on the Ge-on-Si reveals lower critical thickness than that on the Ge substrate. On the contrary, it is shown that this reduced critical thickness on the Ge-on-Si can be significantly enhanced beyond that on the Ge substrate by means of the substrate patterning. Additionally, our recent studies including strained Ge-on-Insulator fabrication and its surface passivation toward high-efficient light emitting devices are overviewed.

Role of Thermolysin in Catalytic-Controlled Self-Assembly of Fmoc-Dipeptides

In recent years, short peptide self-assembled materials, prepared under the control of the thermolysin catalyst, have been investigated extensively and shown to acquire various morphologies and fun...

Effects of Density and Diameter on Surface Optical Phonon Modes in GaAs Nanowire Bundles.

We report the systematic investigation of the surface optical phonon modes in Au-catalyzed GaAs nanowires grown on an Au pre-patterned GaAs(111)B substrate using μ-Raman spectroscopy. We employed electron-beam dose rate as a control parameter during the substrate patterning step for adjusting the nanowire base diameter and coverage, which are independent from the nanowire growth conditions. We have experimentally studied the effect of the fill factor and average diameter on the surface optical phonon modes and explained the red-shift and broadening of the surface optical phonon frequencies by employing the dielectric continuum model. The surface optical phonon mode shift is exhibited to be sensitive to fill factor, rather than base diameter. The decrease in the average diameter from 280 nm to 180 nm results in the asymmetric broadening and red-shift of the surface optical phonon frequency (~1.83 cm-1) but the theoretical calculation from the isolated single nanowire-based dielectric continuum model cannot solely explain the behaviors of the surface optical phonon mode. In contrast, the change in the fill factor from 0.01 to 0.83 results in a shift of the surface optical phonon frequency (~6.5 cm-1) from the GaAs bulk value. The red-shift and asymmetric broadening of the surface optical phonons, in an agreement with the Maxwell-Garnett approximation, are consequences of dipolar interaction of randomly aligned neighboring nanowires and the polar nature of GaAs nanowire bundles. This work suggests the pre-patterning parameter dependent surface optical phonon characteristics of GaAs nanowire bundles which are of great importance in the nondestructive characterization of low-dimensional opto-electronic materials and devices.

Periodic surface functional group density on graphene via laser-induced substrate patterning at Si/SiO2 interface

Controlling the spatial distribution of functional groups on 2D materials on a micrometer scale and below represents a fascinating opportunity to achieve anisotropic (opto)electronic properties of these materials. Periodic patterns of covalent functionalization can lead to periodic potentials in the monolayer; however, creating such superstructures is very challenging. Here, we describe an original approach to the periodic functionalization of graphene induced by substrate patterning using a pulsed laser. Laser-induced periodic surface structures (LIPSS) are produced on silicon wafers with thermally-grown oxide layers. The irradiation conditions for the formation of LIPSS confined at the SiO2/Si interface have been unravelled. LIPSS imprint their periodicity to the reactivity of the monolayer graphene placed on the substrate via modulation of its local doping level. This method is clean, straightforward and scalable with high spatial resolution.

A uniquely shaped MIMO antenna on FR4 material to enhance isolation and bandwidth for wireless applications

This paper presents a CPW fed wideband four element multiple input multiple output (MIMO) antenna. The MIMO structure is developed from the analysis of a single wideband CPW fed antenna with −10 dB bandwidth of 1700 MHz. After which a two antenna element structure is analyzed having the same bandwidth range with isolation below −50 dB. Finally, the proposed four element MIMO structure is designed with isolation less than 30 dB between the antenna elements with an Envelope Correlation Coefficient (ECC) below 0.003, measured gain between 2.4 dBi & 5.9 dBi and the radiation efficiency is well above 90% over the entire operating range. The targeted applications lie between 4.3 and 6.0 GHz under the C band spectrum for WLAN and Wi-Fi. The proposed design is printed on a uniquely shaped FR4 substrate to achieve low insertion loss and greater isolation between the antenna elements. The edge-to-edge distance between the adjacent antenna elements is 15 mm keeping which the antenna elements are placed on the arms of the substrate pattern. This also further helps in increasing the number of antenna elements just by extending the armed pattern with constant edge-to-edge distance. The important parameters of the MIMO system such as ECC with a value as low as 0.0002, Diversity Gain (DG) of 9.998 dB, Total Active Reflection Coefficient (TARC), Mean Effective Gain (MEG) measuring the ratio < 3 dB and Channel Capacity Loss (CCL) of 0.0635 bits/s/Hz are observed at the center frequency of 5 GHz. All the necessary simulations are carried out in Ansys HFSS.

Impact of particle arrays on phase separation composition patterns.

We examine the symmetry-breaking effect of fixed constellations of particles on the surface-directed spinodal decomposition of binary blends in the presence of particles whose surfaces have a preferential affinity for one of the components. Our phase-field simulations indicate that the phase separation morphology in the presence of particle arrays can be tuned to have a continuous, droplet, lamellar, or hybrid morphology depending on the interparticle spacing, blend composition, and time. In particular, when the interparticle spacing is large compared to the spinodal wavelength, a transient target pattern composed of alternate rings of preferred and non-preferred phases emerges at early times, tending to adopt the symmetry of the particle configuration. We reveal that such target patterns stabilize for certain characteristic length, time, and composition scales characteristic of the pure phase-separating mixture. To illustrate the general range of phenomena exhibited by mixture-particle systems, we simulate the effects of single-particle, multi-particle, and cluster-particle systems having multiple geometrical configurations of the particle characteristic of pattern substrates on phase separation. Our simulations show that tailoring the particle configuration, or substrate pattern configuration, a relative fluid-particle composition should allow the desirable control of the phase separation morphology as in block copolymer materials, but where the scales accessible to this approach of organizing phase-separated fluids usually are significantly larger. Limited experiments confirm the trends observed in our simulations, which should provide some guidance in engineering patterned blend and other mixtures of technological interest.

Study of indium tin oxide films deposited on colorless polyimide film by magnetron sputtering

Polyimide attracted most interest for its high performance as a flexible substrate of touch panels. Experimental models were built to evaluate production feasibility. The solution with monomer was coated on a glass substrate, cured at 250 °C to form a solid colorless polyimide (CPI) film. Then, a supporting layer with silicon oxide and a conducting layer with indium tin oxide (ITO) were deposited on the CPI film by magnetron sputtering. Composite with a CPI substrate and ITO patterns were prepared via a series of procedures. Test results indicated ITO film thickness and sheet resistance could be controlled by adjusting sputtering power, and the film showed smooth curves on the contour line chart. The transmittance of CPI/ITO film composite was up to 80%. The bending durability of the film was evaluated by two-point bending method, and it could be significantly improved by shielding the ITO pattern with ultraviolet cured resin as an external buffer layer. Samples with buffer layers passed 64,000 cycles bend test, and the minimum fracture radius reached 4 mm. The increase of ITO film thickness had no significant negative impact on the performance of flexible devices.