Holographic Lithography Technique Research Articles

High diffraction efficiency varied-line-space concave gratings for the Lyman ultraviolet explorer

In this paper we present the design and fabrication of the reflection varied-line-space concave grating (VLSCG) for the project of CAFE (the Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer), which aims to detect and map the warm-hot circumgalactic medium via OVI emission at 103.2 nm and 103.8 nm, using two off-Rowland-circle spectrograph channels. High diffraction efficiency at LUV is supposed for the VLSCG, and an aperture ratio as small as is desired for a compact design. The gratings are fabricated by holographic lithography and ion beam etching techniques. We introduce an additional lens into the normal holographic exposing system to generate the varied-line-space grating patterns. Grooves with triangle profiles are obtained to increase the diffraction efficiency by oblique ion beam bombardment during the etching process. Finally, several VLSCGs with a central line density of 3300 lines/mm have been fabricated successfully. The measured results show that the groove efficiency reaches 51% at 106.4 nm and 31% at 127.4 nm. We imitated the working optical path of the spectrometer and used the order of the VLSCG to measure the image near the exit slit. The results showed that the image of the point source has a vertical extent of 0.68 mm, and the aberrations have been corrected.

Wafer-scale hysteresis-free plasmonic hydrogen sensors based on Pd–Au alloy nanoarrays

The prospective market of hydrogen energy has dramatically boosted the demand for accurate and stable detection of ambient hydrogen. In this work, we fabricated wafer-scale plasmonic hydrogen sensors consisting of periodically distributed Pd–Au alloy nanodiscs by holographic lithography and other semiconductor-compatible techniques, thus obtaining reliable and low-cost sensing devices. Light transmittance measurements at specific light wavelength close to the plasmonic absorption peak position are conducted to investigate the hydrogen sensing performance on account that optical signals afford spark-free operation and high tolerance. Upon alloying Pd with appropriate content of Au, the hysteresis between hydrogen absorption and desorption curves is completely suppressed which greatly improves the sensing accuracy throughout the hydrogen pressure range of 102–105 Pa. Moreover, the precisely defined Pd–Au alloy nanodiscs provide satisfactory stability and device-to-device reproducibility. This work demonstrates an attractive route into practical applications of hydrogen detection for the facile fabrication method and satisfactory performance.

Sub-wavelength microstructures on lithium triborate surface with high transmittance and laser-induced damage threshold at 1064 nm

This paper presents a sub-wavelength moth-eye-like antireflective structure on lithium triborate (LiB3O5, LBO) surface that can effectively promote the transmittance and maintain high laser-induced damage threshold (LIDT). Fabricated by holographic lithography and reactive ion-beam etching techniques, sub-wavelength periodic arrays can be obtained on the crystal surface. The surface morphology and transmittance were measured with atomic force microscope and spectrophotometer respectively. Single-sided transmittance of the LBO with moth-eye-like structure was confirmed to exceed 98% in the wavelength range of 1028–1300 nm, while is 98.73% at 1064 nm. For 1064 nm laser with the pulse width of 12 ns, the measured 1-on-1 LIDT is 42.57 J/cm2, which is about 2.28 times that of LBO compared with traditional antireflection (AR) coatings.

Nanobowtie arrays with tunable materials and geometries fabricated by holographic lithography.

We introduce a highly efficient method for the fabrication of large area nanobowtie arrays (NBAs) based on a home-built tunable holographic lithography (THL) technique. By elaborately designing pattern templates, NBAs with different materials and geometric parameters can be easily obtained by a two-step approach. Both the plasmonic and semiconductor NBAs with tunable gap sizes and a high uniformity over an area of one square centimetre can be conveniently fabricated. Surface-enhanced Raman spectroscopy (SERS) performance and photoelectric properties have been demonstrated on the gold and TiO2 NBAs, respectively. This THL technique shows unique advantages in fabricating well-defined and large-area nanostructures in a high throughput way, facilitating practical applications in a broad range of fields of optoelectronics.

Second-harmonic generation from plasmon polariton excitation on silver diffraction gratings: comparisons of theory and experiment

We present a comparison between experimental and theoretical results for the diffraction efficiencies of the second-harmonic light produced in the orders of silver diffraction gratings. The gratings considered are sinusoidal, have depths of a few nanometers, and can produce significant surface plasmon polariton excitation at fundamental and second-harmonic frequencies. The calculations are based on a general expression for the nonlinear polarization of the surface of a homogeneous and isotropic medium, and the diffraction problems at the fundamental and harmonic frequencies are solved using a Rayleigh method. The silver gratings were fabricated using holographic lithography and evaporative metal deposition techniques. The samples were illuminated with picosecond pulses of wavelength 1064 nm, and photon-counting techniques were used to study the diffracted orders at 532 nm, with absolute normalization provided by a quartz reference. The diffracted orders exhibit anomalies and other features, many of which are related to plasmon polariton excitation at both fundamental and second-harmonic frequencies. Employing previously measured values for the nonlinear susceptibilities of a flat silver surface, remarkably good comparisons of theory and experiment are obtained for the second-harmonic order efficiencies.

Optical activities of large-area SU8 microspirals fabricated by multibeam holographic lithography.

We report on the fabrication of large-area microspirals in SU8 photoresist using a 6+1 beam holographic lithography (HL) technique involving the interference of six linearly polarized side beams and one circularly polarized central beam. In contrast to common photoresist-substrate (glass) configuration, the spirals are fabricated on a substrate with a precured thin SU8 photoresist. This SU8-SU8-glass configuration strengthens the attachment of the spirals to the substrate, and hence enhances the quality of the fabricated spirals. The fabricated SU8 microspirals exhibit large optical activities with a polarization rotation close to 10deg and a circular dichroism of about 0.5 in the visible range. Our precured substrate method could lift the limitations of the HL method in fabricating large and uniform microstructures or nanostructures.

Broad area single mode operation of quantum cascade lasers by integrating porous waveguide and distributed feedback grating

Quantum cascade laser (QCL) emitting at 4.8 \(\upmu \)m with a single-longitudinal mode and small divergence was achieved by integrating porous (PS) waveguide structure and distributed feedback (DFB) grating. The PS waveguide is fabricated in highly doped InP cladding layer by electro-chemical etching process. The DFB grating was defined above the active region by holographic lithography technique. A fundamental transverse mode of single-lobed radiation far-field pattern with full width at half maximum of 7.8\(^{\circ }\) was obtained. Single-longitudinal mode emission with a high peak power of 1.2 W was achieved. Our work is useful for many potential applications of the QCL.

Fabrication of two kinds of eight-fold photonic quasi-crystals assisted by a specially designed prism

We demonstrate that two kinds of 2D eight-fold photonic quasi-crystals (PQCs) can be fabricated by a specially designed prism via single-exposure holographic lithography. The prism with five continuous side surfaces out of common eight symmetrical side surfaces, plus a top surface, is well designed for PQC fabrication. Compared with the traditional method of setting up eight free-space beams in the half-space for an eight-fold PQC fabrication, our specially designed prism reduces the number of beams, avoids the differences of beam-to-beam phases, and simplifies the fabrication process. The theory and computer simulation confirm the patterns of two kinds of PQCs by a single prism illumination recording. Further, these quasi-crystal patterns are successfully verified by experimental results under a scanning electron microscope. In addition, these samples show some good properties, such as uniformity over large area, the implementation of a single defect by underexposure, and symmetry break of the eight dots. Our special prism-assisted holographic lithography technique provides a base for further investigating the optical properties of these novel structures.

Fabrication of periodic micro-structures by holographic lithography

The principles of the holographic lithography technique are reviewed, and the ability in the formation of structures with different periods by the holographic lithography technique in SZ2080 is demonstrated. The influence of laser exposure, phase shift between interfering laser beams, and the used laser wavelength on the structures fabricated by the four-beam interference technique has been studied. It is shown that by using the − interfering beams with a different phase is it possible to reduce the period of the structure √2 times compared to the four interfering beams of the same phase. Fabrication of micro-structures by the holographic lithography technique can be realized via multi-photon and single-photon polymerization processes. The structures created by these two techniques are compared. Finally, in the experiments with the five-beam interference, the doubleperiod effect was observed by adding the zero-order beam with a low intensity. The fabricated periodic microstructures have the potential to be used as a scaffold for cell growth and micro-optics.

Multicolor patterning using holographic woodpile photonic crystals at visible wavelengths

High-quality woodpile structures with photonic band gaps in the visible wavelength range were fabricated using a single prism holographic lithography technique. Woodpile structures were prepared to have a rod diameter of 160 nm, a lateral periodicity of 240 nm, and an axial periodicity of 300 nm, which is the smallest feature size for three-dimensional nanopatterned structures. A multicolor patterning method was used to vary the degree of crosslinking in the negative photoresist. These woodpile structures showed enhanced fluorescence due to a large surface area and the presence of bicontinuous interconnected pores.

Hierarchically Ordered Arrays of Noncircular Silicon Nanowires Featured by Holographic Lithography Toward a High‐Fidelity Sensing Platform

AbstractA novel, highly uniform and tunable hybrid plasmonic array is created via ion‐milling, catalytic wet‐etching and electron‐beam evaporation, using a holographically featured structure as a milling mask. A simple and low‐cost prism holographic lithography (HL) technique is applied to create an unprecedentedly coordinated array of elliptic gold (Au) holes, which act as the silicon (Si) etching catalyst in the reaction solution used to fabricate an elliptic silicon nanowire (SiNW) array; here, the SiNWs are arrayed hierarchically in such a way that three SiNWs are triangularly coordinated, and the triangles are arranged hexagonally. After removing the polymeric mask and metal thin film, the highly anisotropic thick Au film is deposited on the SiNW arrays. This hybrid substrate shows tunable optical properties in the near‐infrared (NIR) region from 875 nm to 1030 nm and surface‐enhanced Raman scattering (SERS) activities; these characteristics depend on the catalytic wet etching time, which changes the size of the vertical gap between the Au thick films deposited separately on the SiNWs. In addition, lateral interparticle coupling induces highly intensified SERS signals with good homogeneity. Finally, the Au‐capped elliptical SiNW arrays can be hierarchically patterned by combining prism HL and conventional photolithography, and the highly enhanced fluorescence intensity associated with both the structural effects and the plasmon resonances is investigated.

Fabrication of micro-tube arrays in photopolymer SZ2080 by using three different methods of a direct laser polymerization technique

In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of several tens of micrometers in the photopolymer SZ2080 by three different methods: direct laser writing, using the optical vortex beam and holographic lithography. The flexibility of direct laser writing and dramatic increase of production efficiency by applying the vortex-shaped beam and four-beam interference approaches are presented. Sample arrays of micro-tubes were successfully manufactured applying all three methods and the fabrication quality as well as efficiency of the methods is compared. The processing time of a single micro-tube with 60 µm height and 3 µm inner radius is reduced 400 times for the holographic lithography technique and 500 times for the optical vortex method compared with the direct laser writing technique. The processing time of a micro-tube array containing 400 micro-tubes is the shortest for the holographic lithography method but not for the optical vortex method as in the case of a single micro-tube, because the holographic lithography method does not require time for sample translation. Additionally, the holographic lithography enables manufacturing of the whole micro-tube array by a single exposure. Although point-by-point photo-structuring ensures unmatched complexity of manufactured microstructures, employing nowadays high repetition rate amplified femtosecond lasers combined with beam shaping or several beam interference can envisage industrial applications for practical demands.

Growth and characterization of periodically polarity-inverted ZnO structures on sapphire substrates

We report on the fabrication and characterization of periodically polarity inverted (PPI) ZnO heterostructures on (0001) Al2O3 substrates. For the periodically inverted array of ZnO polarity, CrN and Cr2O3 polarity selection buffer layers are used for the Zn- and O-polar ZnO films, respectively. The change of polarity and period in fabricated ZnO structures is evaluated by diffraction patterns and polarity sensitive piezo-response microscopy. Finally, PPI ZnO structures with subnanometer scale period are demonstrated by using holographic lithography and regrowth techniques.

Omnidirectional emission from top-emitting organic light-emitting devices with microstructured cavity

We demonstrate optimized viewing-angle characteristics from top-emitting organic light-emitting devices by integrating a periodic microstructure into the cavity. A holographic lithography technique combined with filling process of the groove by spin coating of a polymer film has been employed to enable its periodically and gradually changed cavity length and suppress the viewing-angle dependence of the peak emission wavelength and intensity. The theoretical and experimental results support that the proposed microstructured cavity can resolve the angular-dependence effect in a very simple and effective way, and a desired omnidirectional emission has been obtained.

Simultaneous fabrication of line defects-embedded periodic lattice by topographically assisted holographic lithography

We have demonstrated simultaneous fabrication of designed defects within a periodic structure. For rapid fabrication of periodic structures incorporating nanoscale line-defects at large area, topographically assisted holographic lithography (TAHL) technique, combining the strength of hologram lithography and phase-shift interference, was proposed. Hot-embossing method generated the photoresist patterns with vertical side walls which enabled phase-shift mask effect at the edge of patterns. Embossing temperature and relief height were crucial parameters for the successful TAHL process. Periodic holes with a diameter of 600 nm at a 1 μm-pitch incorporating 250 nm wide line-defects were obtained simultaneously.

Holographic fabricated continuous wave operation of distributed feedback quantum cascade lasers at λ ≈ 8.5 μm

The fabrication and characterization of distributed feedback (DFB) quantum cascade lasers emitting at λ ≈ 8.5 μm are reported. The first-order DFB grating structure was defined using the holographic lithography technique. Reliable dynamic single-mode emission with a side-mode suppression ratio of 20 dB and a tuning coefficient of −0.277 cm−1/K from 93 to 210 K is obtained in continuous wave mode by using high-reflectivity coating on the rear facet. The output power is over 100 mW at a temperature of 80 K.

Enhanced Light Extraction in GaN-Based Light-Emitting Diodes with Holographically Fabricated Concave Hemisphere-Shaped Patterning on Indium–Tin-Oxide Layer

The enhanced light extraction of the GaN-based light-emitting diode (LED) with a two-dimensional concave hemisphere-shaped indium–tin-oxide (ITO) layer, fabricated using laser holographic lithography and inductively-coupled plasma etching techniques were studied. Compared to the LED with a planar ITO layer, it is found that the light output power of LEDs with concave hemisphere patterned ITO layers is improved by ∼34%. This enhanced light output power is attributed to the increase of light extraction by effective photon escape and self-divergence effect at the concave hemisphere-shaped ITO surface.

Holographic fabrication of photonic crystals using multidimensional phase masks

This paper reports the experimental approaches to the fabrication of two-layer integrated phase masks and the fabrication of photonic crystal templates using the phase mask based on holographic lithography technique. The photonic crystal template is formed by exposing photoresist mixtures to five-beam interference patterns generated through the phase mask. The fabricated phase mask consists of two layers of orthogonally oriented gratings produced in a liquid crystal and photoresist mixture. A polymerization-induced phase separation preserves the grating structure during the exposure. The vertical spatial separation between two layers of gratings produces a phase difference among diffracted laser beams, which enables the holographic fabrication of diamondlike photonic crystal structures. The fabricated photonic crystal structure is consistent with simulations based on the five-beam interference. The two-layer phase mask opens up an opportunity of direct printing photonic structures.

3-D holographic lithography of organic–inorganic hybrids

Fabrications of ordered three-dimensional structures with submicron lattice constants were performed on organic–inorganic hybrids using a holographic lithography technique recently reported in the literature. The possibility of such a patterning has previously been demonstrated from single nanosecond laser pulse irradiation of thin films of epoxy photoresist and mixtures of methacrylate-alkoxy-silane with Zr or Ti alkoxides. In the present work, UV irradiation of similar hybrid resins were carried out through repeated laser pulses of low energy with a twofold objective: (i) to study the interference stability for future chemical gas phase decomposition experiments and (ii) to obtain patterning through large film thickness (e.g. 1 mm). The influence of several parameters on the structuration was examined from observations by scanning electron microscopy and optical diffraction. Many interdependent parameters were considered in different steps of the process, namely (i) hybrid resin preparations with required properties of stability, transparency and viscosity, (ii) film coating on different substrates, (iii) UV irradiation (energy and number of laser pulses), (iv) ultrasonic dissolution of monomer, and (v) sample drying. As results, different structuration resolutions were observed as a function of these parameters. But if the influence of a few parameters was easily understood and controlled, it has also appeared that it was not the case of all of them.

Extreme ultraviolet holographic lithography: Initial results

The authors report the initial results from a holographic lithography technique using extreme ultraviolet (EUV) radiation. This approach removes the need for complex EUV reflective masks and optics, replacing them with a binary, nanopatterned transmission mask. Computer generated holograms were fabricated on 100nm thick silicon nitride membranes with a 100nm thick chromium absorber layer. Reconstructed images have been recorded in an 80nm thick polymethylmetacrylate photoresist using 13nm wavelength EUV radiation from an undulator source. The pattern was characterized by optical and atomic force microscopies, and compared with simulation results from the TOOLSET diffraction simulation program, yielding excellent agreement.