Laser Exfoliation Research Articles

Synergistic effects of 1T–2H MoS2 and laser-reduced graphene Oxide–ZnO scaffold composite catalyst for efficient hydrogen evolution reaction

A composite catalyst, zinc-doped laser-reduced graphene oxide (LrGO), is synthesized with highly dispersed molybdenum disulfide (MoS2) nanolayers using laser exfoliation followed by a hydrothermal process. The resultant LrGO–ZnO/1T–2H MoS2 (GZM3) catalyst exhibits enhanced hydrogen evolution reaction (HER) catalytic performance and improved stability. It achieves small overpotentials of 94 and 191.5 mV at a current density of 10 mA cm−2, under acidic and alkaline conditions, respectively. This superior catalytic activity is attributed to the high electrical conductivity and large electrochemical surface area of graphene, along with efficient charge transfer facilitated by Zn ions between LrGO–ZnO and 1T–2H MoS2.

Use of non-intrusive laser exfoliation to improve substance uptake into citrus leaves.

Background: Despite the presence of stomata in leaves, foliar application of agrochemicals can be extremely inefficient due to the low permeability of leaf cuticular surfaces to polar compounds. Methods: This study introduced a laser-based "wax exfoliation" method to facilitate the penetration of substances into the leaf and, together with enhancing their uptake into the phloem and subsequent transport across tissue. This investigation demonstrated the effectiveness and non-invasive properties of laser exfoliation to improve the penetration of foliar-applied substances into citrus leaves. Results: This work presents the use of laser energy to exfoliate the cuticle of a leaf, with the highest energy density of 0.76 J/ cm2 resulting in 85-90% exfoliation across the entire laser-spot area. The infrared wavelength of the erbium laser is specifically chosen to target the wax cuticle without causing damage to the underlying epidermal cells. This selective ablation allows for increased penetration of therapeutic compounds into the leaf and transportation throughout the plant's vasculature. This is demonstrated using a fluorescent glucose analog applied to the laser treated leaves, showing increased penetration and transport throughout the leaf. Conclusions: Our findings demonstrate that the use of laser technology for the foliar application of agrochemicals provides significant advantages, including improved foliage uptake of therapeutic compounds. The method of cuticle exfoliation presented in this study is highly effective and non-intrusive, limiting its effects to the cuticle only. Future work should focus on the development of prototypes for in-field applications, including testing at longer distances as the Er:YAG laser does not require a lens for this application.

Use of non-intrusive laser exfoliation to improve substance uptake into citrus leaves.

Background: Despite the presence of stomata in leaves, foliar application of agrochemicals can be extremely inefficient due to the low permeability of leaf cuticular surfaces to polar compounds. Methods: This study introduced a laser-based "wax exfoliation" method to facilitate the penetration of substances into the leaf and, together with enhancing their uptake into the phloem and subsequent transport across tissue. This investigation demonstrated the effectiveness and non-invasive properties of laser exfoliation to improve the penetration of foliar-applied substances into citrus leaves. Results: This work presents the use of laser energy to exfoliate the cuticle of a leaf, with the highest energy density of 0.76 J/ cm2 resulting in 85-90% exfoliation across the entire laser-spot area. The infrared wavelength of the erbium laser is specifically chosen to target the wax cuticle without causing damage to the underlying epidermal cells. This selective ablation allows for increased penetration of therapeutic compounds into the leaf and transportation throughout the plant's vasculature. This is demonstrated using a fluorescent glucose analog applied to the laser treated leaves, showing increased penetration and transport throughout the leaf. Conclusions: Our findings demonstrate that the use of laser technology for the foliar application of agrochemicals provides significant advantages, including improved foliage uptake of therapeutic compounds. The method of cuticle exfoliation presented in this study is highly effective and non-intrusive, limiting its effects to the cuticle only. Future work should focus on the development of prototypes for in-field applications, including testing at longer distances as the Er:YAG laser does not require a lens for this application.

Use of non-intrusive laser exfoliation to improve substance uptake into citrus leaves.

Background: Despite the presence of stomata in leaves, foliar application of agrochemicals can be extremely inefficient due to the low permeability of leaf cuticular surfaces to polar compounds. Methods: This study introduced a laser-based "wax exfoliation" method to facilitate the penetration of substances into the leaf and, together with enhancing their uptake into the phloem and subsequent transport across tissue. This investigation demonstrated the effectiveness and non-invasive properties of laser exfoliation to improve the penetration of foliar-applied substances into citrus leaves. Results: This work presents the use of laser energy to exfoliate the cuticle of a leaf, with the highest energy density of 0.76 J/ cm2 resulting in 85-90% exfoliation across the entire laser-spot area. The infrared wavelength of the erbium laser is specifically chosen to target the wax cuticle without causing damage to the underlying epidermal cells. This selective ablation allows for increased penetration of therapeutic compounds into the leaf and transportation throughout the plant's vasculature. This is demonstrated using a fluorescent glucose analog applied to the laser treated leaves, showing increased penetration and transport throughout the leaf. Conclusions: Our findings demonstrate that the use of laser technology for the foliar application of agrochemicals provides significant advantages, including improved foliage uptake of therapeutic compounds. The method of cuticle exfoliation presented in this study is highly effective and non-intrusive, limiting its effects to the cuticle only. Future work should focus on the development of prototypes for in-field applications, including testing at longer distances as the Er:YAG laser does not require a lens for this application.

Phase-Reversed MoS2 Nanosheets Prepared through Femtosecond Laser Exfoliation and Chemical Doping

Metallic 1T MoS2 nanosheets are highly desirable for application in catalysis, energy storage, and energy production due to their high electrical conductivity and abundant active sites. Here, this ...

Ultra-sensitive nanometric flat laser prints for binocular stereoscopic image

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with tantalizing layer-dependent electronic and optical properties have emerged as a paradigm for integrated flat opto-electronic devices, but their widespread applications are hampered by challenges in deterministic fabrication with demanded shapes and thicknesses, as well as light field manipulation in such atomic-thick layers with negligible thicknesses compared to the wavelength. Here we demonstrate ultra-sensitive light field manipulation in full visible ranges based on MoS2 laser prints exfoliated with nanometric precisions. The nontrivial interfacial phase shifts stemming from the unique dispersion of MoS2 layers integrated on the metallic substrate empower an ultra-sensitive resonance manipulation up to 13.95 nm per MoS2 layer across the entire visible bands, which is up to one-order-of-magnitude larger than their counterparts. The interlayer van der Waals interactions and the anisotropic thermal conductivity of layered MoS2 films endow a laser exfoliation method for on-demand patterning MoS2 with atomic thickness precision and subwavelength feature sizes. With this, nanometric flat color prints and further amplitude-modulated diffractive components for binocular stereoscopic images can be realized in a facile and lithography-free fashion. Our results with demonstrated practicality unlock the potentials of, and pave the way for, widespread applications of emerging 2D flat optics.

Highly ambient-stable few-layer black phosphorene by pulsed laser exfoliation and HEMM.

Pulsed laser exfoliation was successfully applied to fabricate few-layer phosphorene from high energy mechanical milling (HEMM) synthesized black phosphorus (BP) powders and crystals. The results show that the polycrystalline phosphorene laser-exfoliated from the HEMM-synthesized BP powders is highly stable in ambient environments, providing proof-of-concept for the low-cost fabrication of highly stable few-layer phosphorene for large-scale applications.

Influence of laser wavelength on two-dimensional carbon nanosheet formation from laser-induced exfoliation of naphthalene

Abstract Pulsed Nd:YAG (532 nm) and Excimer (248 nm) lasers were employed to produce freestanding, two-dimensional (2D), carbon nanosheets (CNSs) from naphthalene, through laser-induced exfoliation. The polymer-to-carbon transition was investigated in terms of laser wavelengths, fluences, as well as target preparations. Continuous and porous CNSs of several nanometers in thickness and micrometers in size were obtained from 532 and 248 nm pulsed laser exfoliation of spin-coated naphthalene films, respectively. The porous morphology is ascribed to the photon-induced dissociation of chemical bonds dominated in 248 nm laser interaction with ablated naphthalene. With the increase of laser fluences from 1 to 5 J cm−2, amorphous carbon and ultrathin CNS structures were obtained in sequence. This work revealed a general mechanism of producing 2D structured carbon materials from pulsed laser exfoliation.

Rapid reproduction of complex images in graphite by laser etching and exfoliation

We describe a means to produce thin layers of carbon, graphene multilayers, using laser etching followed by exfoliation. Complex macroscopic images can be produced in minutes. The laser need only mark the top-most layers of graphene for the image to become permanent down to the glass substrate. We use the technique to produce artwork for proof of principle results. With refinement the methodology should also enable patterning of novel graphene electronic and optoelectronic devices.

Ultrafast Method for Selective Design of Graphene Quantum Dots with Highly Efficient Blue Emission.

Graphene quantum dots (GQDs) have attractive properties and potential applications. However, their various applications are limited by a current synthetic method which requires long processing time. Here, we report a facile and remarkably rapid method for production of GQDs exhibiting excellent optoelectronic properties. We employed the pulsed laser ablation (PLA) technique to exfoliate GQDs from multi-wall carbon nanotube (MWCNTs), which can be referred to as a pulsed laser exfoliation (PLE) process. Strikingly, it takes only 6 min to transform all MWCNTs precursors to GQDs by using PLE process. Furthermore, we could selectively produce either GQDs or graphene oxide quantum dots (GOQDs) by simply changing the organic solvents utilized in the PLE processing. The synthesized GQDs show distinct blue photoluminescence (PL) with excellent quantum yield (QY) up to 12% as well as sufficient brightness and resolution to be suitable for optoelectronic applications. We believe that the PLE process proposed in this work will further open up new routes for the preparation of different optoelectronic nanomaterials.

Laser exfoliation of 2D black phosphorus nanosheets and their application as a field emitter

Highly crystalline two dimensional (2D) few layered black phosphorus (BP) nanosheets have been synthesized via a one step facile laser irradiation technique under optimized experimental conditions. The BP material shows promising field emission performance.

Few-layer graphene film fabricated by femtosecond pulse laser deposition without catalytic layers

The films of few-layer graphene are formed through laser exfoliation of a highly ordered pyrolytic graphite (HOPG), without a catalytic layer for the growth process. The femtosecond (fs) laser exfoliation process is investigated at different laser fluences and substrate temperature. For fs laser exfoliation of HOPG, the few-layer graphene is obtained at 473 K under an optimal laser fluence. The formation of few-layer graphene is explained by removal of intact graphite sheets occurred by an optimal laser fluence ablation. The new insights may facilitate the controllable synthesis of large area few-layer graphene.

ChemInform Abstract: Laser Flash Synthesis of Graphene and Its Inorganic Analogues: An Innovative Breakthrough with Immense Promise

AbstractReview: 109 refs.

Nanosecond Pulsed Laser Processing of Ion Implanted Single Crystal Silicon Carbide Thin Layers

Abstract The attractiveness of single crystal SiC in a variety of high power, high voltage, and high temperature device applications such as electric vehicles and jet engines is counteracted by the very high cost of substrates. Precision cutting of multiple micrometre thick SiC layers and transferring them to lower cost substrates would drive the cost down and allow expanding the use of single crystal SiC. In this study, laser beam processing has been utilized to exfoliate thin layers from a surface of single crystal SiC that was prepared with hydrogen and boron ion implantation. The layer thickness of 1 μm has been achieved by ion implantation that formed voids and microcracks under the surface at a layer of 150 nm thick. High energy laser pulses provided the layer removal and its transfer to bonded Si substrate has been shown. Exfoliated surfaces and topography have been evaluated with Scanning Electron Microscopy. Furthermore, thermal modelling of pulse laser irradiation of implanted multi-layer SiC material has been conducted and temperature profiles are obtained at different peak pulse intensity settings to optimize exfoliation process parameters. It was found that laser exfoliation mechanism can be further improved by higher optical absorptance of defect rich layer obtained with boron ion implantation.

Femtosecond laser ablation of highly oriented pyrolytic graphite: a green route for large-scale production of porous graphene and graphene quantum dots

Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm(-2), no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm(-2) range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.

Laser flash synthesis of graphene and its inorganic analogues: An innovative breakthrough with immense promise

Laser-based green synthetic approaches for 2D atomic sheets of graphene, graphene nanoribbons and inorganic analogues of graphene are relatively new techniques. There are several significant laser-based approaches for graphene synthesis such as (a) laser exfoliation, (b) intercalation and exfoliation in liquid nitrogen, (c) pulsed laser deposition, (d) laser induced ultrafast chemical vapour deposition, (e) laser induced catalyst-free growth of graphene from solid carbon sources, (f) epitaxial graphene growth on a Si rich surface of SiC by laser sublimation of surface silicon atoms, (g) reduction of graphene oxide and (h) unzipping of carbon nanotubes. Apart from the deoxygenation of graphene, lasers have also been employed for the dehydrogenation and dehalogenation of graphene surfaces. Such laser induced bond dissociation paves the way for achieving the desired band gap in graphene by adequately controlling the extent of such surface bonds. Such photochemical transformations can be exploited for patterning and nanolithography of graphene and related materials. Laser exfoliation has successfully been extended to synthesize inorganic analogues of graphene such as 2D atomic sheets of hexagonal BN and metal dichalcogenides such as MoS2, MoSe2, WS2, WSe2etc. It is noteworthy that the emerging novel laser-based approaches have tremendously simplified the synthesis of 2D atomic sheets and are capable of yielding impurity-free device quality 2D materials in a scalable manner and consequently inspiring various commercial applications of such materials. An overview of the progress made into laser based approaches is presented.

Production of few-layer graphene through liquid-phase pulsed laser exfoliation of highly ordered pyrolytic graphite

Graphene suspension was obtained through liquid-phase pulsed laser exfoliation of highly ordered pyrolytic graphite (HOPG). The liquid-phase pulsed laser process leaded to the compression and expansion of HOPG surface, resulting in the exfoliation of graphene sheets. Graphene sheets of ∼1nm in thickness and micrometers in size were obtained. Transparent conductive graphene films were fabricated by vacuum filtration, showing an electrical conductivity of ∼1000S/m and an optical transparency of ∼75% at 550nm. This study demonstrated the growth of few-layer graphene by pulsed laser exfoliation of HOPG in liquid and explored its applications in transparent conductive films.

Update on the Effect of Botulinum Toxin Pretreatment on Laser Resurfacing Results

Background: Facial laser resurfacing and chemodenervation with botulinum toxin type A are used independently as means of nonsurgical facial rejuvenation. Recent reports in the literature have described combining these 2 therapies, claiming improved and longer-lasting laser resurfacing results. To date, no scientific investigation has been undertaken to prove or disprove this theory. Design: Institutional review board–approved, prospective, randomized, blinded study at university-affiliated outpatient cosmetic surgery offices. Intervention: Patients had one side of their face injected, at specific anatomic subsites (crow’s feet, horizontal forehead furrows, and glabellar frown lines), with botulinum toxin 1 week before laser resurfacing. After receiving an injection, patients underwent cutaneous laser exfoliation on both sides of the face with either a carbon dioxide or an erbium dual-mode laser. Main Outcome Measures: Patients’ injected (experimental) and noninjected (control) sides were compared after laser resurfacing. Follow-up was documented at 6 weeks, 3 months, and 6 months after laser resurfacing. Subjective evaluation, based on a visual analog scale, was performed in person by a blinded observer. Furthermore, a blinded panel of 3 expert judges (1 facial plastic surgeon, 1 oculoplastic surgeon, and 1 cosmetic dermatologist) graded 35-mm photographs taken during postoperative follow-up visits. Results: Ten female patients were enrolled in the study. A 2-tailed t test showed that all sites that were pretreated with botulinum toxin showed statistically significant improvement (P .05) over the nontreated side, with the crow’s feet region showing the greatest improvement. Comparing results between the carbon dioxide and erbium lasers did not result in any statistically significant differences. Conclusions: Hyperdynamic facial lines, pretreated with botulinum toxin before laser resurfacing, heal in a smoother rhytid-diminished fashion. These results were clinically most significant in the crow’s feet region. We recommend pretreatment of movement-associated rhytids with botulinum toxin before laser resurfacing. For optimum results, we further recommend continued maintenance therapy with botulinum toxin postoperatively.

Formation of graphene sheets through laser exfoliation of highly ordered pyrolytic graphite

Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation.

The Efficacy of Topical Silicone Gel Elastomers in the Treatment of Hypertrophic Scars, Keloid Scars, and Post–Laser Exfoliation Erythema

The Efficacy of Topical Silicone Gel Elastomers in the Treatment of Hypertrophic Scars, Keloid Scars, and Post–Laser Exfoliation Erythema