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Special Issue "Laser-Based Nano Fabrication and Nano Lithography"

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A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (31 May 2018) | Viewed by 51468

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Special Issue Editors

Dr. Koji Sugioka

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Guest Editor

RIKEN Center for Advanced Photonics, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
Interests: laser processing; micro/nanofabrication; 3D fabrication; biochip
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Ya Cheng

E-Mail Website
Guest Editor

1. State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
2. State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P.O. Box 800-211, Shanghai 201800, China
Interests: ultrafast nonlinear optics and spectroscopy; nonlinear optics at nanometer scale; and super-resolution nanofabrication based on non-perturbative nonlinear optics processes

Special Issue Information

Dear Colleagues,

The improvement of fabrication resolutions is an eternal challenge for miniaturizing and enhancing the integration degrees of devices. Laser processing is one of the most widely-used techniques in manufacturing due to its high-flexibility, high-speed, and environment-friendliness. The fabrication resolution of laser processing is, however, limited by the diffraction limit. Recently, many efforts have been made to overcome the diffraction limit in nano fabrication. Specifically, combinations of multiphoton absorption by ultrafast lasers and the threshold effect associated with a Gaussian beam profile provide fabrication resolutions far beyond the diffraction limit. The use of the optical near-field achieves nano ablation with feature sizes below 100 nm. Multiple pulse irradiation from the ultrafast laser produces periodic nanostructures with a spatial period much smaller than the wavelength. Unlimited diffraction resolutions can also be achieved with shaped laser beams. In the meanwhile, lasers are also widely used for synthesis of nano materials including fullerenes and nano particles. In view of the rapid advancement of this field in recent years, this Special Issue aims at introducing the state-of-the-art in nano fabrication and nano lithography, based on laser technologies, by leading groups in the field.

Laser processing
Ultrafast laser
Nano material synthesis
Nano fabrication
Nano ablation
Nano lithography
Optical near field
Nano ripple formation
Shaped beam processing

Prof. Koji Sugioka
Prof. Ya Cheng
Guest Editors

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Published Papers (12 papers)

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Research

Open AccessArticle

Magnetic [email protected]_x, [email protected] and α-Fe₂O₃ Single-Crystal Nanoblends Synthesized by Femtosecond Laser Ablation of Fe in Acetone

and

Nanomaterials 2018, 8(8), 631; https://doi.org/10.3390/nano8080631 - 20 Aug 2018

Cited by 28 | Viewed by 4804

Abstract

There are few reports on zero-field-cooled (ZFC) magnetization measurements for [email protected]_x or FeO_x particles synthesized by laser ablation in liquids (LAL) of Fe, and the minimum blocking temperature (T_B) of 120 K reported so far is still much higher than those of their counterparts synthesized by chemical methods. In this work, the minimum blocking temperature was lowered to 52 K for 4–5 nm α-Fe₂O₃ particles synthesized by femtosecond laser ablation of Fe in acetone. The effective magnetic anisotropy energy density (K_eff) is calculated to be 2.7–5.4 × 10⁵ J/m³, further extending the K_eff values for smaller hematite particles synthesized by different methods. Large [email protected]α-Fe₂O₃ and [email protected] particles of 10–100 nm in diameter display a soft magnetic behavior with saturation magnetization (M_s) and coercivities (H_c) values of 72.5 emu/g and 160 Oe at 5 K and 61.9 emu/g and 70 Oe at 300 K, respectively, which mainly stem from the magnetism of amorphous Fe cores. Generally, the nanoparticles obtained by LAL are either amorphous or polycrystalline, seldom in a single-crystalline state. This work also demonstrates the possibility of synthesizing single-crystalline α-Fe₂O₃ hematite crystals of several nanometers with (104), (113), (116) or (214) crystallographic orientations, which were produced simultaneously with other products including carbon encapsulated amorphous Fe ([email protected]) and [email protected]_x core-shell particles by LAL in one step. Finally, the formation mechanisms for these nanomaterials are proposed and the key factors in series events of LAL are discussed. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

High Repetition Rate UV versus VIS Picosecond Laser Fabrication of 3D Microfluidic Channels Embedded in Photosensitive Glass

and

Nanomaterials 2018, 8(8), 583; https://doi.org/10.3390/nano8080583 - 31 Jul 2018

Cited by 12 | Viewed by 3341

Abstract

Glass is an alternative solution to polymer for the fabrication of three-dimensional (3D) microfluidic biochips. Femtosecond (fs) lasers are nowadays the most promising tools for transparent glass processing. Specifically, the multiphoton process induced by fs pulses enables fabrication of embedded 3D channels with high precision. The subtractive fabrication process creating 3D hollow structures in glass, known as fs laser-assisted etching (FLAE), is based on selective removal of the laser-modified regions by successive chemical etching in diluted hydrofluoric acid solutions. In this work we demonstrate the possibility to generate embedded hollow channels in photosensitive Foturan glass volume by high repetition rate picosecond (ps) laser-assisted etching (PLAE). In particular, the influence of the critical irradiation doses and etching rates are discussed in comparison of two different wavelengths of ultraviolet (355 nm) and visible (532 nm) ranges. Fast and controlled fabrication of a basic structure composed of an embedded micro-channel connected with two open reservoirs, commonly used in the biochip design, are achieved inside glass. Distinct advantages such as good aspect-ratio, reduced processing time for large areas, and lower fabrication cost are evidenced. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Femtosecond Laser-Based Modification of PDMS to Electrically Conductive Silicon Carbide

and

Nanomaterials 2018, 8(7), 558; https://doi.org/10.3390/nano8070558 - 22 Jul 2018

Cited by 21 | Viewed by 5372

Abstract

In this paper, we experimentally demonstrate femtosecond laser direct writing of conductive structures on the surface of native polydimethylsiloxane (PDMS). Irradiation of femtosecond laser pulses modified the PDMS to black structures, which exhibit electrical conductivity. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) results show that the black structures were composed of β-silicon carbide (β-SiC), which can be attributed to the pyrolysis of the PDMS. The electrical conductivity was exhibited in limited laser power and scanning speed conditions. The technique we present enables the spatially selective formation of β-SiC on the surface of native PDMS only by irradiation of femtosecond laser pulses. Furthermore, this technique has the potential to open a novel route to simply fabricate flexible/stretchable MEMS devices with SiC microstructures. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Extreme Energy Density Confined Inside a Transparent Crystal: Status and Perspectives of Solid-Plasma-Solid Transformations

Eugene G. Gamaly

Saulius Juodkazis

and

Andrei V. Rode

Nanomaterials 2018, 8(7), 555; https://doi.org/10.3390/nano8070555 - 21 Jul 2018

Cited by 8 | Viewed by 4559

Abstract

It was demonstrated during the past decade that an ultra-short intense laser pulse tightly-focused deep inside a transparent dielectric generates an energy density in excess of several MJ/cm

^{3}

. Such an energy concentration with extremely high heating and fast quenching rates leads [...] Read more.

It was demonstrated during the past decade that an ultra-short intense laser pulse tightly-focused deep inside a transparent dielectric generates an energy density in excess of several MJ/cm

^{3}

. Such an energy concentration with extremely high heating and fast quenching rates leads to unusual solid-plasma-solid transformation paths, overcoming kinetic barriers to the formation of previously unknown high-pressure material phases, which are preserved in the surrounding pristine crystal. These results were obtained with a pulse of a Gaussian shape in space and in time. Recently, it has been shown that the Bessel-shaped pulse could transform a much larger amount of material and allegedly create even higher energy density than what was achieved with the Gaussian beam (GB) pulses. Here, we present a succinct review of previous results and discuss the possible routes for achieving higher energy density employing the Bessel beam (BB) pulses and take advantage of their unique properties. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Subwavelength Nanostructuring of Gold Films by Apertureless Scanning Probe Lithography Assisted by a Femtosecond Fiber Laser Oscillator

Ignacio Falcón Casas

and

Wolfgang Kautek

Nanomaterials 2018, 8(7), 536; https://doi.org/10.3390/nano8070536 - 16 Jul 2018

Cited by 13 | Viewed by 3067

Abstract

Optical methods in nanolithography have been traditionally limited by Abbe’s diffraction limit. One method able to overcome this barrier is apertureless scanning probe lithography assisted by laser. This technique has demonstrated surface nanostructuring below the diffraction limit. In this study, we demonstrate how a femtosecond Yb-doped fiber laser oscillator running at high repetition rate of 46 MHz and a pulse duration of 150 fs can serve as the laser source for near-field nanolithography. Subwavelength features were generated on the surface of gold films down to a linewidth of 10 nm. The near-field enhancement in this apertureless scanning probe lithography setup could be determined experimentally for the first time. Simulations were in good agreement with the experiments. This result supports near-field tip-enhancement as the major physical mechanisms responsible for the nanostructuring. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Nanostructure Formation on Diamond-Like Carbon Films Induced with Few-Cycle Laser Pulses at Low Fluence from a Ti:Sapphire Laser Oscillator

and

Nanomaterials 2018, 8(7), 535; https://doi.org/10.3390/nano8070535 - 16 Jul 2018

Cited by 6 | Viewed by 3154

Abstract

This study reports the results of experiments on periodic nanostructure formation on diamond-like carbon (DLC) films induced with 800 nm, 7-femtosecond (fs) laser pulses at low fluence from a Ti:sapphire laser oscillator. It was demonstrated that 7-fs laser pulses with a high power density of 0.8–2 TW/cm² at a low fluence of 5–12 mJ/cm² can form a periodic nanostructure with a period of 60–80 nm on DLC films. The period decreases with increasing fluence of the laser pulses. The experimental results and calculations for a model target show that 7-fs pulses can produce a thinner metal-like layer on the DLC film through a nonlinear optical absorption process compared with that produced with 100-fs pulses, creating a finer nanostructure via plasmonic near-field ablation. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessFeature PaperArticle

Spontaneous Shape Alteration and Size Separation of Surfactant-Free Silver Particles Synthesized by Laser Ablation in Acetone during Long-Period Storage

and

Nanomaterials 2018, 8(7), 529; https://doi.org/10.3390/nano8070529 - 13 Jul 2018

Cited by 25 | Viewed by 4024

Abstract

The technique of laser ablation in liquids (LAL) has already demonstrated its flexibility and capability for the synthesis of a large variety of surfactant-free nanomaterials with a high purity. However, high purity can cause trouble for nanomaterial synthesis, because active high-purity particles can spontaneously grow into different nanocrystals, which makes it difficult to accurately tailor the size and shape of the synthesized nanomaterials. Therefore, a series of questions arise with regards to whether particle growth occurs during colloid storage, how large the particle size increases to, and into which shape the particles evolve. To obtain answers to these questions, here, Ag particles that are synthesized by femtosecond (fs) laser ablation of Ag in acetone are used as precursors to witness the spontaneous growth behavior of the LAL-generated surfactant-free Ag dots (2–10 nm) into different polygonal particles (5–50 nm), and the spontaneous size separation phenomenon by the carbon-encapsulation induced precipitation of large particles, after six months of colloid storage. The colloids obtained by LAL at a higher power (600 mW) possess a greater ability and higher efficiency to yield colloids with sizes of <40 nm than the colloids obtained at lower power (300 mW), because of the generation of a larger amount of carbon ‘captors’ by the decomposition of acetone and the stronger particle fragmentation. Both the size increase and the shape alteration lead to a redshift of the surface plasmon resonance (SPR) band of the Ag colloid from 404 nm to 414 nm, after storage. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the Ag particles are conjugated with COO– and OH– groups, both of which may lead to the growth of polygonal particles. The CO and CO₂ molecules are adsorbed on the particle surfaces to form Ag(CO)_x and Ag(CO₂)_x complexes. Complementary nanosecond LAL experiments confirmed that the particle growth was inherent to LAL in acetone, and independent of pulse duration, although some differences in the final particle sizes were observed. The nanosecond-LAL yields monomodal colloids, whereas the size-separated, initially bimodal colloids from the fs-LAL provide a higher fraction of very small particles that are <5 nm. The spontaneous growth of the LAL-generated metallic particles presented in this work should arouse the special attention of academia, especially regarding the detailed discussion on how long the colloids can be preserved for particle characterization and applications, without causing a mismatch between the colloid properties and their performance. The spontaneous size separation phenomenon may help researchers to realize a more reproducible synthesis for small metallic colloids, without concern for the generation of large particles. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessFeature PaperArticle

Dual THz Wave and X-ray Generation from a Water Film under Femtosecond Laser Excitation

and

Nanomaterials 2018, 8(7), 523; https://doi.org/10.3390/nano8070523 - 13 Jul 2018

Cited by 24 | Viewed by 4212

Abstract

Simultaneous emission of the THz wave and hard X-ray from thin water free-flow was induced by the irradiation of tightly-focused femtosecond laser pulses (35 fs, 800 nm, 500 Hz) in air. Intensity measurements of the THz wave and X-ray were carried out at the same time with time-domain spectroscopy (TDS) based on electro-optic sampling with a ZnTe(110) crystal and a Geiger counter, respectively. Intensity profiles of the THz wave and X-ray emission as a function of the solution flow position along the incident laser axis at the laser focus show that the profile width of the THz wave is broader than that of the X-ray. Furthermore, the profiles of the THz wave measured in reflection and transmission directions show different features and indicate that THz wave emission is, under single-pulse excitation, induced mainly in laser-induced plasma on the water flow surface. Under double-pulse excitation with a time separation of 4.6 ns, 5–10 times enhancements of THz wave emission were observed. Such dual light sources can be used to characterise materials, as well as to reveal the sequence of material modifications under intense laser pulses. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Deformation Behavior of Foam Laser Targets Fabricated by Two-Photon Polymerization

and

Nanomaterials 2018, 8(7), 498; https://doi.org/10.3390/nano8070498 - 06 Jul 2018

Cited by 35 | Viewed by 5289

Abstract

Two-photon polymerization (2PP), which is a three-dimensional micro/nano-scale additive manufacturing process, is used to fabricate component for small custom experimental packages (“targets”) to support laser-driven, high-energy-density physics research. Of particular interest is the use of 2PP to deterministically print millimeter-scale, low-density, and low atomic number (CHO) polymer matrices (“foams”). Deformation during development and drying of the foam structures remains a challenge when using certain commercial acrylic photo-resins. Acrylic resins were chosen in order to meet the low atomic number requirement for the foam; that requirement precludes the use of low-shrinkage organic/inorganic hybrid resins. Here, we compare the use of acrylic resins IP-S and IP-Dip. Infrared and Raman spectroscopy are used to quantify the extent of the polymerization during 2PP vs. UV curing. The mechanical strength of beam and foam structures is examined, particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage is quantified, and finite element analysis is used in order to simulate the resulting deformation. Capillary drying forces during development are shown to be small and are likely below the elastic limit of the foam log-pile structures. In contrast, the substantial shrinkage in IP-Dip (~5–10%) causes large shear stresses and associated plastic deformation, particularly near constrained boundaries and locations with sharp density transitions. Use of IP-S with an improved writing procedure results in a marked reduction in deformation with a minor loss of resolution. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Local Melting of Gold Thin Films by Femtosecond Laser-Interference Processing to Generate Nanoparticles on a Source Target

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Nanomaterials 2018, 8(7), 477; https://doi.org/10.3390/nano8070477 - 28 Jun 2018

Cited by 4 | Viewed by 3949

Abstract

Shape- and size-controlled metallic nanoparticles are very important due to their wide applicability. Such particles have been fabricated by chemosynthesis, chemical-vapor deposition, and laser processing. Pulsed-laser deposition and laser-induced dot transfer use ejections of molten layers and solid-liquid-solid processes to fabricate nanoparticles with a radius of some tens to hundreds of nm. In these processes, the nanoparticles are collected on an acceptor substrate. In the present experiment, we used laser-interference processing of gold thin films, which deposited nanoparticles directly on the source thin film with a yield ratio. A typical nanoparticle had roundness

f_{r} = 0.99

and circularity

f_{c i r c} = 0.869

, and the radius was controllable between 69 and 188 nm. The smallest radius was 82 nm on average, and the smallest standard deviation was 3 nm. The simplicity, high yield, and ideal features of the nanoparticles produced by this method will broaden the range of applications of nanoparticles in fields such as plasmonics. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Formation of Slantwise Surface Ripples by Femtosecond Laser Irradiation

and

Nanomaterials 2018, 8(7), 458; https://doi.org/10.3390/nano8070458 - 22 Jun 2018

Cited by 5 | Viewed by 3249

Abstract

We report on the formation of slantwise-oriented periodic subwavelength ripple structures on chromium surfaces irradiated by single-beam femtosecond laser pulses at normal incidence. Unexpectedly, the ripples slanted in opposite directions on each side the laser-scanned area, neither perpendicular nor parallel to the laser polarization. The modulation depth was also found to change from one ripple to the next ripple. A theoretical model is provided to explain our observations, and excellent agreement is shown between the simulations and the experimental results. Moreover, the validity of our theory is also confirmed on bulk chromium surfaces. Our study provides insights for better understanding and control of femtosecond laser nanostructuring. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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Open AccessArticle

Liquid-Assisted Femtosecond Laser Precision-Machining of Silica

and

Nanomaterials 2018, 8(5), 287; https://doi.org/10.3390/nano8050287 - 28 Apr 2018

Cited by 40 | Viewed by 5625

Abstract

We report a systematical study on the liquid assisted femtosecond laser machining of quartz plate in water and under different etching solutions. The ablation features in liquid showed a better structuring quality and improved resolution with 1/3~1/2 smaller features as compared with those made in air. It has been demonstrated that laser induced periodic structures are present to a lesser extent when laser processed in water solutions. The redistribution of oxygen revealed a strong surface modification, which is related to the etching selectivity of laser irradiated regions. Laser ablation in KOH and HF solution showed very different morphology, which relates to the evolution of laser induced plasma on the formation of micro/nano-features in liquid. This work extends laser precision fabrication of hard materials. The mechanism of strong absorption in the regions with permittivity (epsilon) near zero is discussed. Full article

(This article belongs to the Special Issue Laser-Based Nano Fabrication and Nano Lithography)

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