Porphyrins and their associated derivatives have been widely used as photosensitizers for photodynamic therapy (PDT) of tumors. To overcome the limitations of porphyrin photosensitizers in PDT, the marriage of porphyrins and nanotechnology offers a new perspective to improve the efficacy and safety of porphyrin-based PDT. To date, various organic and inorganic nanoparticles have been developed for porphyrin delivery for high payload photosensitizers, protection from premature release of photosensitizers, and tumor-selective targeting. In this article, we summarize the strategies for porphyrin photosensitizer delivery, including encapsulation, covalent conjugation, self-assembly for PDT, and characterization methods of singlet oxygen (1O2) generation. We focus on the summarized strategies of improving cancer PDT efficacy by nanotechnology. Finally, the challenges and outlook for porphyrin-based nanocomposites-mediated PDT are discussed.

We detail a method to produce graphite materials with a three-dimensional, flexible and porous structure obtained from the exposure to CO2 laser radiation. One of them is Laser Induced Graphene (LIG) grown from an insulating polyimide as raw material, and the other is laser reduced graphene oxide (lrGO), obtained from a graphene oxide (GO) thin film. For both materials, we describe their morphology, crystalline structure and electrical characterizations. These materials have important applications in organic electronics technology.

Ultrafast electron diffraction has been employed for the study of structural dynamics at surfaces in the time domain. Experiments were performed in a pump-probe setup with femtosecond-laser excitation and subsequent probing through diffraction of a femtosecond electron pulse at a temporal resolution of 350 fs. The system of interest is one atomic layer of indium atoms on a Si(111) surface. Through self-assembly, indium atomic wires form and exhibit a Peierls-like, insulator-to-metal phase transition that can be driven nonthermally through a femtosecond laser pulse. The transient intensity of the diffraction spots indicates the lifting of the Peierls transition and melting of a charge-density wave in only 700 fs, heating of the surface in 6 ps, and formation of a metastable and supercooled phase, which exists for nanoseconds.

In the quest for dynamic multimodal probing of a material’s structure and functionality, it is critical to be able to quantify the chemical state on the atomic-/nanoscale using element-specific electronic and structurally sensitive tools such as electron energy-loss spectroscopy (EELS). Ultrafast EELS, with combined energy, time, and spatial resolution in a transmission electron microscope, has recently enabled transformative studies of photoexcited nanostructure evolution and mapping of evanescent electromagnetic fields. This article aims to describe state-of-the-art experimental techniques in this emerging field and its major uses and future applications.

Ultrafast measurement technology provides essential contributions to our understanding of the properties and functions of solids and nanostructures. Atomic-scale vistas with ever-growing spatial and temporal resolution are offered by methods based on short pulses of x-rays and electrons. Time-resolved electron diffraction and microscopy are among the most powerful approaches to investigate nonequilibrium structural dynamics. In this article, we discuss recent advances in ultrafast electron imaging enabled by significant improvements in the coherence of pulsed electron beams. Specifically, we review the development and first application of ultrafast low-energy electron diffraction for the study of structural dynamics at surfaces, and discuss novel opportunities for ultrafast transmission electron microscopy facilitated by laser-triggered field-emission sources. These and further developments will render coherent electron beams an essential component in future ultrafast nanoscale imaging.

LIBS is a developing analytical technique, which is used to perform qualitative and semi-quantitative elemental analysis of materials (solid, liquid and gas). Recently LIBS became an attractive technique to be used for geological samples, due to its advantages such as fast data collection and the lack of sample preparation. This study is done to improve analytical methods for geochemical analysis of samples during different exploration phases (Mining, filed analysis, etc.), to be used in the future as a real-time analysis method to save money and time spent in labs. In this work, LIBS has been used to differentiate between some geological samples gathered from different areas: South Africa and Namibia. Using principal component analysis (PCA), it was found that LIBS was able to differentiate between the samples even those of the same area. The results from the LIBS technique were correlated with subsequent analysis of the same samples by Particle-Induced X-ray emission (PIXE).

Recently, a laboratory-scale method for measuring the rapid energy release from milligram quantities of energetic material has been developed based on the high-temperature plasma chemistry induced by a focused, nanosecond laser pulse. The ensuing exothermic chemical reactions result in an increase in the laser-induced shock wave velocity compared to inert materials. Laser-induced air shock from energetic materials (LASEM) provides a method for estimating the detonation performance of novel organic-based energetic materials prior to scale-up and full detonation testing. Here, the extension of LASEM to non-organic energetic materials is discussed. The laser-induced shock velocities from reactive materials such as Al/PTFE, Al/CuO, Al/Zr alloys, Al/aluminum iodate hexahydrate, and porous silicon composites have been measured; in many cases, the high sensitivity of the samples resulted in propagation of the reaction to the surrounding material, producing significantly higher shock velocities than conventional energetic materials. Methods for compensating for this effect will be discussed. Despite this limitation, the relative comparison of the shock velocities, emission spectra, and combustion behavior of each type of material provides some insight into the mechanisms for increasing the energy release of the material on a fast (μs) and/or slow (ms) timescale.

The synthesis of Y2Ti2O7-Al2O3 compositional (multiphase) ceramics from powder mixtures Al2O3-Y2O3-TiO2 was carried out in two stages: 1) under the traditional sintering and then 2) in regime of directed laser heating. It was established that the sintering of mixtures with different content of components and the ratio of TiO2/Y2O3 = 2.34 in ceramic specimens the main phases are Y2Ti2O7 and α-Al2O3. The content of the main phases in ceramic materials also depends upon the oxide content in the initial mixtures. In ceramics the Y3Al5O12 is formed only at sufficiently high content of titanium and yttrium oxides in initial mixtures. In laser remelting, the phase composition is substantially different from that obtained at the traditional sintering, and depends on the mode of laser heating: irradiation power and the moving speed of the laser beam (i.e., heating temperature). Under certain conditions of laser remelting can be obtained superficial ceramic layer with crystallographic directional crystallization of Y2Ti2O7 and Al2O3 crystallites. The size of crystallites and the coefficient texturing also depend on the mode of laser treatment.

We propose a new technique suitable for on-line monitoring of gas phase synthesis of nanoparticles. It is based on aerodynamic focusing of nanoparticles followed by Laser-Induced Breakdown Spectroscopy (LIBS) under vacuum. The laser crosses a beam of particles at low pressure so that the plasma-produced photons to be analyzed are emitted only from the particles. Unlike previous experiments, the background from interaction with the gaseous component is totally eliminated from the collected spectra. Vacuum allows also for easier spectra collection in the UV range. Moreover, as the nanoparticle beam is highly collimated, the optical interface windows are not obstructed by particle deposition and the system can be kept running for hours.

Ultrafast laser synthesis and processing of materials is a burgeoning field that is still in its infancy. This article and the theme articles in this issue review recent developments in the fundamental physics of ultrafast laser–solid interactions as well as the state of our understanding of ultrafast laser-driven surface morphology, modification of transparent media, 3D photo-polymerization and additive fabrication, spallation of graphene, and biological interactions. Also reviewed is the current state of emerging commercial high average power lasers, central to the widespread adoption of ultrafast laser synthesis and processing of materials. It is remarkable that ultrafast lasers with 20 to 600 femtosecond pulse duration can have such a dramatic impact on materials. As we learn more about the fundamental mechanisms that drive the ultrafast laser-material response, even more applications are anticipated to emerge. This revolutionary approach to materials synthesis and processing has already spawned several commercial technologies and promises to create many more in the near future.

The present work accentuates the effect of UV laser irradiation on theconductivity of nickel oxide (NiO) thin films, deposited at various temperaturesby radio-frequency reactive sputtering of Ni in oxygen containing atmosphere.The effect of UV irradiation on zinc oxide – nickel oxideheterostructures, obtained by sputtering, was examined as well. It was foundthat the resistivity of NiO changes from 12 Ω-cm to 0.62Ω-cm, and the majority carrier concentration from3.95x1017 holes/cm3 to 4.22x1020electrons/cm3. The current-voltage (I-V) characteristics of theZnO/NiO heterostructure shows an improved p-n diode behavior with the forwardbias current increasing for the laser-irradiated ZnO/NiO compared to theas-deposited stack. The observed improvement in diode-like behavior suggeststhat laser irradiation can be an important technique to controllably change thestructural, electrical and optical properties of metal oxide thin films.

The photo-structural changes in a 2 μm thick amorphous selenium (a-Se) thin film, thermally evaporated on Si substrate, have been studied by micro-Raman spectrometer with 532 nm laser at different laser power densities (1 to 64 W/mm2) and exposure times (15 – 60 s). In addition, the nanoscale photo-structural changes/photo-thermodynamic phase changes are examined on 90 nm a-Se film coated on SiO2 cladding of the optical Fiber Bragg Grating (FBG) sensor on prolonged exposure to a low power (1 mW/mm2, 10 mW/mm2) 532 nm laser, which is measured by means of photo-striction (light induced strain) in the material.

Graphene-based field effect transistors (GFETs) were assessed when interfaced with well separated and precisely placed core/shell CdSe/ZnS semiconductor quantum dot (QD) arrays. The QDs were imbedded in a hexagonal hole-array, which was formed in a layer of anodized aluminum oxide on Si/SiO2 substrates. Graphene (single, or two layers), grown by chemical vapor deposition (CVD) on Cu foils, was transferred and placed on top of the QDs imbedded films and served as the transistor channel. Electrical characteristics under white-light illumination at various biasing conditions revealed that the photo current was decreasing upon increasing biasing. The device's photoluminescence (PL) as a function of both the drain-source and gate-source potentials also reduced as a function of the potential biases. We observed two maxima in the PL data while tilting the sample with respect to the incident laser beam. We attributed it to the optimal coupling between the incident and the emission wavelengths to resonating surface modes.

New material phases formed under non-equilibrium conditions at pressures above 100 GPa and temperatures exceeding 104K, the conditions of the warm dense matter (WDM), have become accessible using micro-explosions triggered by ultra-short sub-1 ps pulses tightly focused into micro-volume with cross sections comparable with the wavelength of light. Laser-induced micro-explosions convert a material in a focal volume into a non-equilibrium disordered plasma state confined inside the bulk of pristine crystal. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable high pressure phases, which are preserved in the surrounding pristine crystal for following recovery and exploitation. Direct laser writing was used to pattern large areas by closely packed arrays of the microexplosion modified sites for structural characterisation of the minute volumes of nano-materials with transmission electron microscopy, diffraction and synchrotron X-ray diffraction. The method of ultrafast-laser induced confined microexplosion is demonstrated for modification and creation of new phases in case of bcc-Al inside sapphire, valence change of Fe-ions in olivine, formation of new tetragonal bt8 and st12 phases of silicon, Ge and O separation in GeO2 glass and molecular oxygen formation inside voids at the site of microexplosion inside glasses.

This work studies the nitridation of Ta by laser irradiation by means of x-ray photoelectron spectroscopy. The study has been carried out under “in situ” conditions by controlling the nitrogen partial pressure, the presence of traces of oxygen, and the irradiance of the laser. It is found that a thin layer of Ta2O5 is directly obtained when irradiating in the presence of oxygen, while a Ta3N5 surface compound and some minor contributions of nonstoichiometric phases are formed in the presence of nitrogen. For O2:N2 mixtures at 0.1 Pa, preferential nitride formation occurs up to a ratio of 1:4, while Ta2O5 starts to be predominant for ratios above this value. The air stability of the tantalum nitride layer formed by laser irradiation and the surface topography of the irradiated metal are also studied. The possible factors determining this behavior are discussed.

Metallized polyimide polymer films are of interest owing to their wide scope of applications including adaptive optical mirrors, solar dynamic power generation, radiation shielding, and thermal control coatings. Palladium-based polyimide films have proven to be unique in terms of thermal reduction, photochemistry and nanoparticulate distribution within the polymer matrix. When Pd polyamic acid is exposed to lamp radiation for 15 hours prior to curing, an additional nanoscale metallic interlayer is created within the surface-metallized polyimide matrix. This photo-process creates alternating nanoparticulate layers of palladium metal. Whilst previous efforts have produced metallic interlayer in 15 hours, we show that an excimer laser reduces this time to 4-8 minutes. Preliminary results using a femtosecond laser show that a metal interlayer can be formed with as little as 8 seconds of exposure time. Transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) are used to characterize the layers. In addition to Pd, surface metallization and interlayer formation using other metals is discussed.

We provide a general description of the operating principle of the photo-induced force microscope (PiFM), which probes the optically induced changes in the dipolar interactions between a sharp polarizable tip and the sample, in terms of classical fields and forces. We rigorously calculate the photo-induced force behavior and compare the predicted profile with experimental results obtained from a gold nanowire.

Laser processing of thin-film silicon is a promising approach for the realization of polycrystalline silicon for large area electronics and solar cell applications. In this study we investigate the material modification of amorphous hydrogenated silicon (a-Si:H) with different hydrogen content (30%, 13% and <1%) by means of femtosecond (fs) laser pulses. Depending on the peak fluence applied, hydrogen diffusion/effusion, layer crystallization or material ablation can be achieved. Despite the low absorption coefficient of a-Si:H at the center wavelength of an amplified Titanium Sapphire laser at 790 nm a high local energy deposition close to the surface of the a-Si:H layer is observed, which can be attributed to a nonlinear absorption process.

Femtosecond near IR laser irradiation is explored as a general methodology to produce metal nanoparticles from metal precursor solutions. Initial studies of the formation and transformations of gold nanoparticles in aqueous solution are used as model processes to evaluate the effects of laser parameters, reaction medium and surfactants in controlling metal nanoparticle formation. The addition of polymer surfactants such as poly(ethylene glycol) (PEG) was found to significantly accelerate Au(III) reduction as compared to surfactant-free systems. Photo-reduction for aqueous solutions of Au(III) in the presence of PEG results in relatively small narrowly dispersed spherical gold nanoparticles compared to relatively large well-formed crystalline nanoparticles that are observed in the absence of surfactants. Varying the concentration of PEG is an effective approach to tune the diameter and size distribution from 3.9±0.7 nm to 11±2.4 nm for Au nanoparticles produced by laser processing.

Laser is used to produce graphene nanoribbons (GNRs) by unzipping carbon nanotubes (CNTs). It is found that laser can not only unzip CNTs, but also join GNRs through covalent reconnections. Because the CNTs are aligned in a freestanding CNT sheet, the laser irradiation process results in a freestanding GNR network. Experimental results show that the expected results can be achieved by controlling the delivery of laser beam energy to the sheet. Moreover, this process is a solid-state process and a scalable manufacturing process.