To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure email@example.com is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Rapid growth of single-layer graphene using laser-induced chemical vapor deposition (LCVD) with a visible CW laser (λ = 532 nm) irradiation at room temperature was investigated. In this study, an optically-pumped solid-state laser with a wavelength of 532 nm irradiates a thin nickel foil to induce a local temperature rise, thereby allowing the direct writing of graphene patterns about ~10 μm in width with high growth rate on precisely controlled positions. It is demonstrated that the fabrication of graphene patterns can be achieved with a single scan for each graphene pattern using LCVD with no annealing or preprocessing of the substrate. The scan speed reaches to about ~50 um/s, which indicates that the graphene pattern with 1:1 aspect ratio (x:y) can be grown in 0.2 sec. The patterned graphene on nickel was transferred to SiO2/Si substrate for fabrication of electrical circuits and sensor devices.
A feedback control mechanism based on infrared radiation monitoring coupled with reflectivity information was developed to control the temperature of a laser assisted chemical vapor deposition process for the growth of carbon nanotube forests. An infrared laser operating at 808 nm is focused on a silicon substrate containing a 20 nm-aluminum-oxide layer and a 1.5 nm-iron catalyst layer. The growth takes place in an argon/ hydrogen/ ethylene gaseous environment. SEM and Raman spectroscopy analysis show that good controllability and reproducibility is achieved over multiple experiments.
Numerous applications based on CNTs have been conceived and developed at laboratory scale. However, only a handful of applications have been successfully implemented due to the difficulties in controlled growth, manipulation, and integration of CNTs. In spite of countless efforts having been devoted into this field, high-performance-on-demand solution packages are still absent. In this study, we investigated applications of lasers in the controlled growth and integration of CNTs, and developed laser-based strategies to achieve nano-fabrication of CNTbased devices. By making use of unique features of lasers, we achieved 1) parallel integration of CNTs into pre-designed micro/nano-architectures in a single-step laser-assisted chemical vapor deposition (LCVD) process, 2) selective removal of metallic CNTs in open air, 3) growing CNTs of controlled-alignments, and 4) diameter modulation in individual CNTs. The laser-based strategies developed in this study suggest a laser-based solution-package to meet the challenges for the nano-fabrication of CNT-based devices and promises a reliable and scalable approach to achieve CNT-integrated devices.
This study describes the fabrication of hybrid micro- and nanostructures of semiconductor nanocrystals arranged in microscopic lines inside of a borosilicate glass doped with CdSxSe1-x. This was performed using a two step process of (1) ultrafast laser modification and (2) heat treatment. The glass was photomodified using focused sub-picosecond infra-red pulses with 1 MHz repetition rate to create linear domains with local compositional variations. Heat treating the sample at temperatures near glass transition preferentially precipitated semiconductor in the modified regions, as evidenced by confocal fluorescence microscopy. The optical properties of the precipitated nanocrystals varied with heat treatment duration.
Fabrication of nanoscale devices by assembling individual carbon nanotubes (CNTs) remains challenging despite enormous effort made in this field. Fulfilling the promise of CNTs requires more efficient assembly techniques. In this study, we have developed an in-situ assembly method for precise and cost-effective integration of CNTs using a laser-assisted chemical vapor deposition (LCVD) process. Results show that CNTs can be trapped between sharp tip-shaped electrodes due to the optical gradient forces around the tip apexes generated by a CO2 laser irradiation. This method enables the precise assembly of CNT-based field-effect transistors (FETs) and paves the way for the successful implementation of the CNT-based nanoelectronics.
Classically, the limit for optical machining is on the order of the wavelength of the incident light. However, by taking advantage of precise, nonlinear damage mechanisms that occur for femtosecond laser pulses, damage can be achieved on a scale an order of magnitude lower, allowing precise removal of very small amounts of material to produce holes mere tens of nanometers wide. Femtosecond laser nanomachining can be carried out in a variety of dielectrics, and in transparent substrates machining can be sub-surface, in contrast to other nanomachining techniques such as using an electron beam or focused ion beam. We focus on the use of glass, as it is in many ways an ideal material for use in biological applications due to its chemical, optical, electrical and mechanical properties. By precisely placing laser pulses in glass, three dimensional nano and microfluidic channels and devices can be formed including nozzles, mixers, and separation columns. Recent advances in this technique allow the formation of high aspect ratio nanochannels from single pulses, thus helping address the fabrication speed limitations presented by serial processing. These nanochannels have a range of applications including the fabrication of nanoscale pores and nanowells that may serve as vias between fluidic channels, or from channels to a surface. These nanochannels have applications as a standalone technique for fabrication of nanopores and nanowells, but can also complement other fabrication techniques by allowing precisely placed jumpers that can connect channels that are out of plane. We discuss applications for diagnostic microfluidic devices, and basic cell biology research.
Electrode thin films made of LiCoO2, Li-Mn-O and SnO2 were synthesized by rf magnetron sputtering on silicon and stainless steel substrates. In order to increase the active surface direct laser structuring methods using ns- and ps-laser sources were applied. A laser system operating at a wavelength of 248 nm with a pulse length of 4-6 ns and repetition rates up to 500 Hz enabled the formation of high aspect ratio micro- and sub-micron structures with feature sizes down to less than 400 nm. Subsequent to the laser structuring process, laser annealing of LiCoO2 and Li-Mn-O was performed in order to achieve an appropriate crystalline phase which shows improved electrochemical cycling performance. Laser annealing was applied via a high power diode laser system operating at a wavelength of 940 nm. In case of LiCoO2 the high temperature phase was obtained through laser-annealing while for Li-Mn-O the spinel phase was formed. For both LiCoO2 and Li-Mn-O thin films appropriate annealing parameters were temperatures of up to 680 °C and an annealing time of 100 s.
Laser direct polymerization has been proven as a powerful tool to generate microstructures. Often photosensitive polymer materials are used because they can be tuned by photoactive molecules to be susceptible to a specific wavelength of light to initiate the polymerization process. One of the main drawbacks of this technique is the lack of functional polymers, e.g. conductive, magnetic, mechanical, optical or bioactive materials. Nanocomposites (nanocompounds), i.e. polymers with inorganic nanomaterials incorporated in the matrix offer a huge variety of new functionalities. A new approach will be presented how functional nanocomposite polymers can be generated and used for laser direct writing techniques. This can open the door for completely new MEMS and MOEMS devices comprising active and passive subcomponents.
A femtosecond (fs) pulse duration is shorter than many physical/chemical characteristic times, such as the electron-photon relaxation time, which makes it possible to control electron dynamics. This paper reviews our recent progress which proposes to change electron dynamics (selective excitation/ionization) and electron densities/temperatures in materials to control the following properties and processes: 1) the transient (femtosecond-to-picosecond time scale), localized (nanometer-to-micrometer length scale) material properties, 2) the corresponding photon absorption process, and 3) phase change mechanisms, by manipulating fs pulse-train number/delay for high-precision micro/nanoscale manufacturing.
Using high-sensitivity confocal time-resolved photoluminescence (PL) techniques, we found an ultrafast PL (40 ps-5 ns) from impurity-free surface flaws on fused silica. This PL is excited by the single-photon absorption of sub-band gap light. Regions which exhibit this PL are strongly absorptive well below the band gap, as evidenced by a propensity to damage with 3.5 eV nanosecond-scale laser pulses. Very high defect densities are needed to explain the damage thresholds observed. For such high defect densities, significant interactions between defects may strongly affect the temporal characteristics of the emission of electronic excitations. We propose that the distribution in lifetimes observed is not simply due to a large variety of defect states, but due to a variety of energy transfer interactions between defect states.
We present data on micrometer-scale localized single-pulse laser irradiation of Au, Cu, Al, or Ti films on borosilicate glass substrates. These metals represent a range of thermal properties, chemical reactivity levels, and relevance to specific applications. A mask projection technique employing a Q-switched Nd:YAG laser, emitting at its fourth harmonic of 266nm, was used to produce the irradiation spots in this work. The metal films, deposited by RF-sputtering, had thicknesses of several hundred nanometers. Sample irradiation was performed in either vacuum or ambient air, and the resulting microstructures were examined by electron microscopy. The results indicate that irradiation of Cu films can lead to the formation of bumps, sharp cones or protrusions. However, the controllability of these structures on Cu films is limited, compared to those formed on Au or Si. The results, upon irradiation of Ti films, are limited to melting and surface roughening or ablation openings, regardless of the conditions of irradiation, film thickness, substrate or ambient gas. The modifications that occur within Al films are reproducible, but limited in shape and size.
We present a scalable, continuous manufacturing method of nanoparticle production based on laser ablation of an aerosol generated from an aqueous precursor solution. A Collison nebulizer is used to generate a mist of ~10 μm diameter water droplets containing dissolved transition metal salts, suspended in 1 atmosphere of buffer gas. Water from the droplets quickly evaporates, leaving solid particles ~2 μm in diameter for a typical solution concentration. These microparticles are then ablated by a pulsed KrF excimer laser (10 ns, λ = 248 nm, 2 J/cm2 at focus). Ablation results in plasma breakdown of the microparticle and photothermal decomposition of the precursor material. Following ablation, nanoparticles 5-20 nm in diameter are formed and collected. For AgNO3 ablated in He gas, metal Ag nanoparticles were produced. For Cu(NO3)2 ablated in He, crystalline Cu2O nanoparticles were produced. For Ni(NO3)2 ablated in He, crystalline NiO nanoparticles were produced. A combination of AgNO3 and Cu(NO3)2 ablated in a reducing atmosphere of 10% H2 and 90% He yielded Ag-Cu alloy nanoparticles. In contrast to conventional wet-chemical synthesis processes, our nanoparticles are formed ‘bare,’ without surfactants or organic material contaminating the surface. Owing to their small size and high free surface area, nanoparticles produced by this process are ideally suited for applications that include catalysis and facilitated transport membranes.
A study of the formation mechanisms of foamy coatings on the surface of glass-ceramic substrates produced by laser ablation is presented. Three laser systems emitting at 1064, 532 and 355 nm with pulse-widths in the nanosecond range were used. In the NIR range the formation of the coating is only possible when the temperature of the surface is higher than 300 ºC. In this case, the generation is related to an increase of the layer in liquid-phase produced in the interaction zone. However, when the sample is machined at 532 or 355 nm, it is not necessary to heat the whole surface to be processed. In this case, the local temperature and the pressure exerted over the interaction zone produce the generation of this coating, obtaining the layer at room temperature. Furthermore, the coating can be produced at higher speeds. In this way, it is possible to reduce the energetic cost improving the efficiency of the process.
Morphology, microstructure, composition and thermal properties of the layer are described.
Two-Photon initiated polymerization (TPIP) has shown great promise for fabrication of complex micro- and nano-structures. The method has been used to fabricate such structures over small areas (< 1 mm2) because of slow fabrication speeds and resulting long fabrication times. In order for TPIP to reach practical application in a commercial setting fabrication times need to be reduced by orders of magnitude. We report results on a highly photosensitive initiation system for photoresists based on free radical and cationic polymerization, where photosensitivity is increased 102- to 103-fold compared to previously reported photoinitiation systems. Threshold writing speeds are determined for critical exposure conditions, including laser power, type and concentration of photoinitiation system, and photoresist type. Surface roughness, a critical parameter in applications such as optics and microfluidics, for example, is also used to determine threshold writing speed. The utility of the approach is demonstrated by making a cell phone keypad light guide from a microreplication tool fabricated using the highly photosensitive photoresist.
Processing of transparent materials by non-linear absorption mechanisms induced by short pulse lasers has been applied in many fields. Silicon (Si) is widely used materials in microelectronics, MEMS and photonics. It is, however, not transparent for commonly used processing lasers in near infrared to ultraviolet spectral range and has not been a subject for the non-linear processing by lasers so far. In this paper, possibilities and capabilities of non-linear processing of Si by 900 fs, 1552nm laser radiation are described with special emphasis on application to frequency adjustment of a crystal oscillator in a package made from Si.
We have demonstrated and studied polymeric solid-state dye lasers (SSDLs) fabricated by three-dimensional (3D) polystyrene colloidal crystals and tert-butyl roadamine B (t-Bu RhB) doped Poly (methyl methacrylate) (PMMA) films with different film thickness. The sandwich-typed resonator cavities with different active layer thickness display single-mode lasing oscillations in the reflection bandgap of the colloidal crystals. The lasing thresholds could be optimized by changing the thickness of t-Bu RhB doped PMMA films, which is as low as 7.43 W/cm2. Adjusting active layer thickness would provide an opportunity to accelerate the development of fabricating polymeric SSDLs with low threshold.
Laser welding of transparent high performance polymer foils requires an additional absorption layer at the interface of both foils. This paper demonstrates that metallic nano-particles, e.g. gold, silver or copper, can act as such an absorption layer. Silver nanoparticles were deposited on the surface of 200 μm thick ethylene tetrafluoroethylene (ETFE) polymer foils by evaporation processes or by magnetron sputtering. For their additional mechanical stabilization, thin films produced by plasma polymerisation of hexamethyldisilazane or PTFE-polymer sputtering were deposited on top of the metal nanoparticles. Laser irradiation of the coated foil together with the untreated joining partner was performed by a continuous wave diode laser at a wavelength of 808 nm. With the defocused laser, the foils were welded and finally a nearly transparent welding seam was achieved. The nanostructure and the optical properties of the nanoparticle layer before laser irradiation were determined and compared with the nanostructure and the optical properties of the polymer metal nanocomposite after laser welding.