Search

We report on a very compact desk-top transmission extreme ultraviolet (EUV) microscope based on a laser-plasma source with a double stream gas-puff target, capable of acquiring magnified images of objects with a spatial (half-pitch) resolution of sub-50 nm. A multilayer ellipsoidal condenser is used to focus and spectrally narrow the radiation from the plasma, producing a quasi-monochromatic EUV radiation (λ = 13.8 nm) illuminating the object, whereas a Fresnel zone plate objective forms the image. Design details, development, characterization and optimization of the EUV source and the microscope are described and discussed. Test object and other samples were imaged to demonstrate superior resolution compared to visible light microscopy.

An Nd:YAG pulsed laser was employed to irradiate a nitrogen gas-puff target. The interaction gives rise to the emission of soft X-ray (SXR) radiation in the ‘water window’ spectral range (λ= 2.3÷4.4 nm). This source was already successfully employed to perform the SXR microscopy. In this work, a Silicon Carbide (SiC) detector was used to characterize the nitrogen plasma emission in terms of gas-puff target parameters. The measurements show applicability of SiC detectors for SXR plasma characterization.

Application of a compact laser plasma source of soft X-rays in radiobiology studies is demonstrated. The source is based on a laser produced plasma as a result of irradiation of a double-stream gas puff target with nanosecond laser pulses from a commercially available Nd:YAG laser. The source allows irradiation of samples with soft X-ray pulses in the “water window” spectral range (wavelength: 2.3–4.4 nm; photon energy: 280–560 eV) in vacuum or a helium atmosphere at very high-dose rates and doses exceeding the kGy level. Single-strand breaks (SSB) and double-strand breaks (DBS) induced in DNA plasmids pBR322 and pUC19 have been measured. The different conformations of the plasmid DNA were separated by agarose gel electrophoresis. An exponential decrease in the supercoiled form with an increase in linear and relaxed forms of the plasmids has been observed as a function of increasing photon fluence. Significant difference between SSB and DSB in case of wet and dry samples was observed that is connected with the production of free radicals in the wet sample by soft X-ray photons and subsequent affecting the plasmid DNA. Therefore, the new source was validated to be useful for radiobiology experiments.

Extreme ultraviolet (EUV) surface modification of polytetrafluoroethylene (PTFE) was performed in order to enhance the degree of biocompatibility. Polymer samples were irradiated by different number of EUV shots using a laser–plasma based EUV source in the presence of nitrogen gas. The physical and chemical properties of EUV modified PTFE samples were studied using Atomic Force Microscopy, X-ray photoelectron spectroscopy and water contact angle (WCA) methods. Pronounced wall type micro and nano-structures appeared on the EUV treated polymer surfaces resulting in increased surface roughness and hydrophobicity. Stronger cell adhesion and good cell morphology were observed on EUV modified surfaces by in-vitro cell culture studies performed using L929 fibroblasts.

We present a few examples of imaging experiments, which were possible using a compact laser-plasma extreme ultraviolet (EUV) and soft X-ray (SXR) source, based on a double stream gas puff target. This debris-free source was used in full-field EUV imaging to obtain magnified images of test samples, ZnO nanofibers and images of the membranes coated with salt crystals. The source was also employed for SXR microscopy in the “water-window” spectral range using grazing incidence Wolter type-I objective to image test samples and to perform the initial studies of biological objects. Gas puff target EUV source, spectrally tuned for 13.5 nm wavelength with multilayer mirror and thin film filters, was also used in variety of shadowgraphy experiments to study the density of newly developed modulated density gas puff targets. Finally, the source was also employed in EUV tomography experiments of low density objects with the goal to measure and optimize the density of the targets dedicated to high harmonic generation.

A desk-top laser-produced plasma (LPP) source of soft X-rays (SXR) has been developed for radiobiology research. The source is based on a double-stream gas puff target, irradiated with the focused beam of a commercial Nd:YAG laser. The source has been optimized to get a maximum photon emission from LPP in the X-ray “water window” spectral wavelength range from 2.3 nm (i.e., an absorption edge of oxygen) to 4.4 nm (i.e., an absorption edge of carbon) (280–540 eV in photon energy units) by using argon gas-puff target and spectral filtering by free-standing thin foils. The present source delivers nanosecond pulses of soft X-rays at a fluence of about 4.2 × 103 photons/μm2/pulse on a sample placed inside the vacuum chamber. In this paper, the source design, radiation output characterization measurements and initial irradiation experiments are described. The source can be useful in addressing observations related to biomolecular, cellular and organisms’ sensitivity to pulsed radiation in the “water window”, where carbon atoms absorb X-rays more strongly than the oxygen, mostly present in water. The combination of the SXR source and the radiobiology irradiation layout, reported in this article, make possible a systematic investigation of relationships between direct and indirect action of ionizing radiation, an increase of a local dose in carbon-rich compartments of the cell (e.g., lipid membranes), an experimental estimation of a particular role of the Auger effect (in particular in carbon atoms) in the damage to biological systems, and the study of ionization/excitation-density (LET – Linear Energy Transfer) and dose-rate effects in radiobiology.

We present a 2-D mapping of a sample thickness with nanometer accuracy employing a compact arrangement of near-edge X-ray absorption fine structure (NEXAFS) technique. A NEXAFS spectrum coupled with a scanning system was used to generate a 2-D thickness map of the TiO2 sample (anatase form) deposited on the top of a SiN membrane. The thickness values were retrieved from the experimental data by applying different methods of data processing. In the paper, the detailed analysis of the data processing methods and the identified sources of the errors show that the proposed procedure based on averaging two imperfect estimates reduces the error caused by the uncontrolled bias of the measured signals. This procedure was termed as the average one. The estimates from the proposed average approach and the standard absorption-jump ratio in the absorption edge vicinity were compared with the direct results obtained by applying scanning electron microscopy (SEM). The experimental arrangement of the NEXAFS spectroscopy system, the data acquisition method, as well as the possible error sources, are presented and discussed in detail.

We report oxygen K-shell photoabsorption measurements in CO2 plasmas, using a table-top laser produced plasma soft X-ray and extreme ultraviolet (EUV) source. Significant differences are observed between the photoabsorption spectra of the neutral CO2 molecule and photoionized CO2 plasmas, as new spectral features emerge in the case of the latter. These features are attributed to 1s → 2p photoexcitation in O, O+ , O 2+ species identified with the aid of calculations performed with the Cowan suite of atomic structure codes. Such signatures of atomic ions in the photoionized plasma point to the fragmentation of the parent molecule upon absorption of a soft X-ray photon.

In the paper new experimental techniques for nano-imaging and nano-spectroscopy operating with electromagnetic radiation in the nanometer wavelength range (soft X-rays - SXR and extreme ultraviolet – EUV) are presented. SXR and EUV radiation is generated using laser plasma sources in which a laser plasma is produced by irradiation of a gas puff target with nanosecond laser pulses at intensities of about 1011-1012 Wcm-2 in the interaction region. Commercially available Nd:YAG lasers (EXPLA) generating 4 ns pulses with energy up to 0.8 J at 10 Hz repetition rate are used to irradiate the targets that are formed by pulsed injection of working gas (Xe, Kr, Ar, N2) in an additional annular stream of He gas under high-pressure using a double-nozzle set up (a double-stream gas puff target approach [1]). Laboratory microscopy systems with the use of compact laser plasma sources of soft X-rays and EUV, operating in the ‘water window’ spectral range (wavelength: 2.3–4.4 nm; photon energy: 280–560 eV) or the EUV range at the wavelength of 13.8 nm have been developed [2]. Application of these microscopes for nano-imaging of hydrated and dry biological samples with spatial resolution from 50 nm to 100 nm and relatively short exposition time is presented. Moreover, a recently developed laboratory system for the near-edge X-ray absorption fine structure (NEXAFS) spectroscopy [3] is also presented. The new NEXAFS system has been used for elemental composition analysis of polymer samples. [1] H. Fiedorowicz et al. Appl. Phys. B 70 (2000) 305 [2] P. Wachulak et al. Appl. Sci. 7 (2017) 548 [3] P. Wachulak et al. (2018) - submitted

In this work a laser-produced plasma (LPP) source was used to create low temperature plasmas. An extreme ultraviolet and soft X-ray (EUV/SXR) radiation pulse was used for ionization of molecular gases, injected into a vacuum chamber synchronously with the EUV/SXR pulse. Energies of photons exceeding 100 eV were sufficient for dissociative ionization, ionization of atoms or even ions. The resulting photoelectrons had also enough energy for further ionizations or excitations. Time resolved UV/VIS spectra, corresponding to single charged ions, molecules and molecular ions, were recorded. For spectral lines, corresponding to radiative transitions in F II and S II ions, electron temperature was calculated based on a Boltzmann plot method. Numerical simulations of the molecular spectra were fitted to the experimental spectra allowing for determination of vibrational and rotational temperatures.

A laser-plasma double stream gas-puff target source coupled with Fresnel zone plate (FZP) optics, operating at He-like nitrogen spectral line λ=2.88nm, is capable of acquire complementary information in respect to optical and electron microscopy, allowing to obtain high resolution imaging, compared to the traditional visible light microscopes, with an exposition time of a few seconds. The compact size and versatility of the microscope offers the possibility to perform imaging experiments in the university laboratories, previously restricted to large-scale photon facilities. Source and microscope optimization, and examples of applications will be presented and discussed.

Application of a compact laser plasma source of soft X-rays and extreme ultraviolet (EUV) in imaging with nanometer resolution is demonstrated. The source is based on a gas puff target irradiated with nanosecond laser pulses from a small commercial Nd:YAG laser. Soft X-ray radiation in the ‘water window’ spectral range and EUV near 10 nm are generated efficiently without production of target debris. Nanoscale imaging of biological samples as well as micro- and nanostructures using transmission soft X-ray and EUV microscopy based on Fresnel optics and soft X-ray contact microscopy is demonstrated.

In this study, surface modification of fluoropolymer Polyvinyl fluoride (PVF) films was performed using Extreme Ultraviolet (EUV) radiations to induce patterned structures on surface and to provide control over the surface wettability. Specially developed laser produced plasma based EUV source was used for surface structuring. The double stream gas-puff target was produced by injection of krypton and xenon (KrXe) gas mixture into a hollow stream of helium. Commercially available EKSPLA Nd:YAG 1.06 micron laser was used to irradiate the KrXe gas puff target with 3 nanosecond pulse duration having 0.8 J energy. The PVF films were irradiated with 50 and 200 EUV pulses. The surface characterisation of the pristine and EUV modified PVF polymer films was performed by Atomic Force Microscopy (AFM) for morphological modifications. To investigate chemical modifications, X-ray Photoelectron Spectroscopy was used. The wettability of the sample surfaces was examined by Water Contact Angle (W CA) measurements. EUV surface modification of PVF films resulted in formation of wall type rippled structures on the polymer surfaces. The surface roughness of the EUV treated surfaces was increased up to 287 nm and 21° reduction was observed in the WCA of the PVF films. Successful surface structuring and wettability control was obtained using EUV surface modification of PVF films.

Short illumination wavelength allows an extension of the diffraction limit toward nanometer scale; thus, improving spatial resolution in optical systems. Soft X-ray (SXR) radiation, from “water window” spectral range, λ=2.3–4.4 nm wavelength, which is particularly suitable for biological imaging due to natural optical contrast provides better spatial resolution than one obtained with visible light microscopes. The high contrast in the “water window” is obtained because of selective radiation absorption by carbon and water, which are constituents of the biological samples. The development of SXR microscopes permits the visualization of features on the nanometer scale, but often with a tradeoff, which can be seen between the exposure time and the size and complexity of the microscopes. Thus, herein, we present a desk-top system, which overcomes the already mentioned limitations and is capable of resolving 60 nm features with very short exposure time. Even though the system is in its initial stage of development, we present different applications of the system for biology and nanotechnology. Construction of the microscope with recently acquired images of various samples will be presented and discussed. Such a high resolution imaging system represents an interesting solution for biomedical, material science, and nanotechnology applications.

The results of formation of elongated krypton/helium plasma channels are presented. Two laser pulses were used: one to produce plasma channels and the second one for conversion to soft X rays. The soft X-ray radiation was in turn used for backlighting the channels and their visualization. The study of their formation and uniformity was performed using a combination of soft X-ray shadowgraphy and pinhole camera imaging. The plasma channels, with various lengths and various densities, were visualized and the results of their characterization are presented. Using moderate laser pulse energy quite uniform channels, up to 9 mm in length, were demonstrated.

In this work, two laser-produced plasma (LPP) sources – extreme ultraviolet (EUV) and a LPP soft X-ray (SXR) source were used to create Ne photoionized plasmas. A radiation beam was focused onto a gas stream, injected into a vacuum chamber synchronously with the radiation pulse. EUV radiation spanned a wide spectral range with pronounced maximum centered at λ≈11 nm, while in case of the SXR source spectral maximum was at λ≈1.4 nm. Emission spectra of photoionized plasmas created this way were measured in a wide spectral range λ = 10–100 nm. The dominating spectral lines originated from singly charged ions (Ne II) and neutral atoms (Ne I). For the highest radiation fluence, spectral lines originating from Ne III and even Ne IV species were detected. Differences between the experimental spectra, obtained for all irradiation conditions, were analyzed. They were attributed either to different fluence or spectral distribution of driving photons.

A compact soft X-ray microscope based on a nitrogen double-stream gas puff target soft X-ray source, operating at He-like nitrogen spectral line at the wavelength of λ = 2.88 nm is presented. The desk-top size microscope was successfully demonstrated in transmission mode using the Fresnel zone-plate objective and it is suitable for soft X-ray source microscopy in the "water window" spectral range (λ = 2.3 ÷ 4.4 nm). Details about the soft X-ray source source, the microscope and an example of application in the biomedical field are shown and discussed.

In this work different kinds of reflective optical systems were used for creation and investigation of low temperature, photoionized plasmas. The plasmas were created in gases, irradiated with a focused beam of extreme ultraviolet (EUV) or soft X-ray (SXR) radiation, from laser-plasma sources employing 10 Hz Nd:YAG laser systems (0.8 J/ 4 ns and 10 J/ 1-10 ns). In both cases, the EUV radiation was focused using a gold-plated grazing incidence ellipsoidal collector in the wavelength range λ = 9÷70 nm or a gold-plated grazing incidence multifoil collector in the wavelength range λ = 5 ÷ 70 nm. Additionally, in case of the 10 J Nd:YAG laser with the pulse duration 1 ns, a paraboloidal collector optimized for the wavelength range λ ≥ 1 nm was employed. Different gases were injected into the vacuum chamber, perpendicularly to an optical axis of the irradiation system at the focal region, using an auxillary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms/molecules. Spectra in SXR/EUV range were measured using a grazing incidence, flat-field spectrometer (McPherson Model 251), equipped with a 450 lines/mm toroidal grating or a home-made spectrograph based on the 5000 l/mm transmission grating. Optical spectra were recorded using the Echelle Spectra Analyzer ESA 4000. In all cases the most intense emission lines were assigned to singly charged ions, however, lines corresponding to ions with higher charge were also recorded. Based on spectral lines originating from ions electron temperature was estimated.

A silicon carbide (SiC) detector was calibrated in terms of quantum efficiency (QE) as well as its spectral responsivity at two different wavelength radiations ( $\lambda _{N_{2}} = 2.88$ nm and $\lambda _{N_{e}}= 1.35$ nm), using two different calibrated Si detectors, sensitive to the soft X-ray radiation ( $\lambda = 0.1\div 10$ nm). An Nd:YAG laser was employed to irradiate a nitrogen and a neon gas-puff target, producing a plasma, which is emitting radiation used for estimation of the detector parameters. A possibility to characterize a new generation of not commercial SiC detectors, with a higher band gap with respect to Si, employing a gas-puff target source, will be presented. Measurements show the SiC detectors QE, equal to 3.4 and 7.1 e/ph for 2.88- and 1.35-nm wavelength radiations, respectively. Calculations and results are reported and discussed.

Experimental measurements and numerical modeling of emission spectra in photoionized plasma in the ultraviolet and visible light (UV/Vis) range for noble gases have been investigated. The photoionized plasmas were created using laser-produced plasma (LPP) extreme ultraviolet (EUV) source. The source was based on a gas puff target; irradiated with 10ns/10J/10Hz Nd:YAG laser. The EUV radiation pulses were collected and focused using grazing incidence multifoil EUV collector. The laser pulses were focused on a gas stream, injected into a vacuum chamber synchronously with the EUV pulses. Irradiation of gases resulted in a formation of low temperature photoionized plasmas emitting radiation in the UV/Vis spectral range. Atomic photoionized plasmas produced this way consisted of atomic and ionic with various ionization states. The most dominated observed spectral lines originated from radiative transitions in singly charged ions. To assist in a theoretical interpretation of the measured spectra, an atomic code ...

A compact, desktop size microscope, based on laser-plasma source and equipped with reflective condenser and diffractive Fresnel zone plate objective, operating in the extreme ultraviolet (EUV) region at the wavelength of 13.8 nm, was developed. The microscope is capable of capturing magnified images of objects with 95-nm full-pitch spatial resolution (48 nm 25–75% KE) and exposure time as low as a few seconds, combining reasonable acquisition conditions with stand-alone desktop footprint. Such EUV microscope can be regarded as a complementary imaging tool to already existing, well-established ones. Details about the microscope, characterization, resolution estimation and real sample images are presented and discussed.

A compact microscope based on nitrogen double stream gas puff target soft X-ray source, which emits radiation in the water-window spectral range, at the wavelength of λ = 2.88 nm, is presented. The microscope, employing ellipsoidal grazing incidence condenser and a Fresnel zone plate objective, is capable of capturing images with a 60 nm spatial resolution and exposure time as low as a few seconds. Examples of different applications of the SXR microscopy, and its applicability for various fields of science, are presented and discussed.

Surface roughness control of polymeric materials is often desirable in various biomedical engineering applications related to biocompatibility control, separation science and surface wettability control. In this study, Polyethylene terephthalate (PET) polymer films were irradiated with Extreme ultraviolet (EUV) photons in nitrogen environment and investigations were performed on surface roughness modification via EUV exposure. The samples were irradiated at 3 mm and 4 mm distance from the focal spot to investigate the effect of EUV fluence on topography. The topography of the EUV treated PET samples were studied by AFM. The detailed scanning was also performed on the sample irradiated at 3 mm. It was observed that the average surface roughness of PET samples was increased from 9 nm (pristine sample) to 280 nm and 253 nm for EUV irradiated samples. Detailed AFM studies confirmed the presence of 1.8 mm wide period U-shaped channels in EUV exposed PET samples. The walls of the channels were having FWHM of about 0.4 mm. The channels were created due to translatory movements of the sample in horizontal and transverse directions during the EUV exposure. The increased surface roughness is useful for many applications. The nanoscale channels fabricated by EUV exposure could be interesting for microfluidic applications based on lab-on-a-chip (LOC) devices.

We present our recent results, related to nanoscale imaging in the extreme ultraviolet (EUV) and soft X-ray (SXR) spectral ranges and demonstrate three novel imaging systems recently developed for the purpose of obtaining high spatial resolution images of nanoscale objects with the EUV and SXR radiations. All the systems are based on laser-plasma EUV and SXR sources, employing a double stream gas puff target. The EUV and SXR full field microscopes—operating at 13.8 nm and 2.88 nm wavelengths, respectively—are currently capable of imaging nanostructures with a sub-50 nm spatial resolution with relatively short (seconds) exposure times. The third system is a SXR contact microscope, operating in the “water-window” spectral range (2.3–4.4 nm wavelength), to produce an imprint of the internal structure of the investigated object in a thin surface layer of SXR light sensitive poly(methyl methacrylate) photoresist. The development of such compact imaging systems is essential to the new research related to biological science, material science, and nanotechnology applications in the near future. Applications of all the microscopes for studies of biological samples including carcinoma cells, diatoms, and neurons are presented. Details about the sources, the microscopes, as well as the imaging results for various objects will be shown and discussed.

In the last 30 years much effort was made in order to develop compact laser-produced plasma sources emitting short wavelength radiation, from the soft X-ray (SXR, λ = 0.1–10 nm), especially in the so-called “water window” (λ = 2.3–4.4 nm) and in the extreme ultraviolet (EUV, λ = 10–120 nm) spectral ranges. Investigations in the nanometer scale, employing short wavelengths, drive the need for developing table-top microscopes, to overpass the limitations imposed by large facilities, such as their high complexity, maintenance costs and the limited user access. In this paper we present our recent results related to nanoscale imaging using such table-top and desk-top EUV/SXR microscopes. Their construction is based on a double stream gas puff target laser plasma source. The double stream gas puff target EUV and SXR sources, coupled with Fresnel zone plates (FZPs) represent a suitable platform for microscopy experiments in transmission mode, employing SXR and EUV radiation. It represents a possible complementary technique to synchrotrons and free-electron laser facilities. The sources, which are very easy to be used by a single user, allow for efficient generation of plasma radiation with high SXR/EUV flux. Presented herein compact microscopes, based on that source, allow one to capture SXR and EUV images of various samples, with 50–60 nm half-pitch spatial resolution (corresponding to a Rayleigh resolution of 100–120 nm) and exposure time of the order of few seconds. Thus, herein, we would like to present our recent developments and progress in compact desk-top SXR/EUV microscopy employing laser plasma gas puff target sources, showing examples of acquired images and possible applications.

A comparative study of photoionized plasmas created by soft X-ray (SXR) and extreme ultraviolet (EUV) laser plasma sources was performed. The sources, employing high or low energy laser systems, utilized double-stream Xe/He gas-puff targets irradiated with laser pulses of different parameters. The SXR/EUV beams were used for irradiation of a gas stream, injected into a vacuum chamber synchronously with the radiation pulse. Photoionized plasmas produced this way in Ne gas emitted radiation in the SXR/EUV range. The corresponding spectra were dominated by emission lines originating from singly charged ions. Significant differences between spectra obtained in different experimental conditions concern specific transitions in Ne II ions. Creation of photoionized plasmas by SXR or EUV irradiation resulted in K-shell or L-shell emissions respectively. In case of the low energy system absorption spectra were measured additionally. In case of the high energy system, the electron density measurements were performed by laser interferometry, employing a femtosecond laser system. A maximum electron density reached the value of 2·1018cm-3. For the low energy system, a detection limit was too high for the interferometric measurements, thus only an upper estimation for electron density could be made.

A compact size microscope based on nitrogen double stream gas puff target soft X-ray source, which emits radiation in water-window spectral range at the wavelength of λ = 2.88 nm is presented. The microscope employs ellipsoidal grazing incidence condenser mirror for sample illumination and silicon nitride Fresnel zone plate objective for object magnification and imaging. The microscope is capable of capturing water-window images of objects with 60 nm spatial resolution and exposure time as low as a few seconds. Details about the microscopy system as well as some examples of different applications from various fields of science, are presented and discussed.

We present a possibility of reaching higher energy absorption edges of organic materials, beyond the carbon K-edge, in the near edge X-ray absorption fine structure (NEXAFS) spectroscopy technique using a compact laser-produced plasma soft X-ray (SXR) source based on a double-stream gas puff target. The source was optimized for emission in the SXR spectral range from 1.5 to 5 nm wavelength using the krypton/helium target. The emission spectrum of the source and the absorption spectrum of the investigated sample were measured simultaneously by means of a grazing incidence spectrometer, equipped with a single, large aperture diffractive element. Based on both spectra, the optical density was computed for the silicon nitride membranes in a transmission mode, to reveal the NEXAFS features near the nitrogen K-edge. Moreover, due to spectral narrowing of the SXR emission by the use of titanium filter, reaching the titanium L-edge was also possible. Multiple SXR pulse data were compared to single SXR pulse (single-shot) data as well as to the numerical simulations. In this paper, the detailed information about the source, spectroscopy system, and the results of NEXAFS measurements is presented and discussed.

New developments in nanoscience and nanotechnology require nanometer scale resolution imaging tools and techniques such as an extreme ultraviolet (EUV) and soft X-ray (SXR) microscopy, based on Fresnel zone plates. In this paper, we report on applications of a desk-top microscopy using a laser-plasma EUV source based on a gas-puff target for studies of morphology of thin silicon membranes coated with NaCl crystals and samples composed of ZnO nanofibers.

In this work helium and neon photoionization experiments, using a laser-plasma EUV (extreme ultraviolet) source were performed. The EUV radiation was focused onto a gas stream, injected into a vacuum chamber synchronously with the EUV pulse. The most intense emission from the source spanned a relatively narrow spectral region centered at λ =11±1 nm, however, spectrally integrated intensity at longer wavelengths was also significant. Additionally Zr and Al filters were used to narrow the irradiation spectrum and to change the irradiation conditions. Irradiation of gases resulted in EUV luminescence, acquired by a toroidal grating spectrometer. The dominating spectral lines originate from singly charged ions, however, Ne III lines were also detected. Significant differences were observed between spectra obtained for different irradiation conditions. The differences were mainly due to various possibilities of photoexcitation of corresponding states depending on energy distribution of irradiating photons.

Polymeric biomaterials are being widely used for the treatment of various traumata, diseases and defects in human beings due to ease in their synthesis. As biomaterials have direct interaction with the extracellular environment in the biological world, biocompatibility is a topic of great significance. The introduction or enhancement of biocompatibility in certain polymers is still a challenge to overcome. Polymer biocompatibility can be controlled by surface modification. Various physical and chemical methods (e.g., chemical and plasma treatment, ion implantation, and ultraviolet irradiation etc.) are in use or being developed for the modification of polymer surfaces. However an important limitation in their employment is the alteration of bulk material. Different surface and bulk properties of biomaterials are often desirable for biomedical applications. Because extreme ultraviolet (EUV) radiation penetration is quite limited even in low density mediums, it could be possible to use it for surface modification without influencing the bulk material. This article reviews the degree of biocompatibility of different polymeric biomaterials being currently employed in various biomedical applications, the surface properties required to be modified for biocompatibility control, plasma and laser ablation based surface modification techniques, and research studies indicating possible use of EUV for enhancing biocompatibility.

We report for the first time on a compact, desk-top size, laboratory-type microscopy setup, based on nitrogen gas puff target soft X-ray source, which emits radiation in “water-window” spectral range. The microscope employs Wolter type-I objective and allows capturing magnified images of objects with 850 nm spatial resolution and exposure time as low as a few seconds. Details about the source and the microscope as well as imaging results for test and biological objects are presented and discussed.

We report on a very compact desk-top transmission extreme ultraviolet (EUV) microscope based on a laser-plasma source with a double stream gas-puff target, capable of acquiring magnified images of objects with a spatial (half-pitch) resolution of sub-50 nm. A multilayer ellipsoidal condenser is used to focus and spectrally narrow the radiation from the plasma, producing a quasi-monochromatic EUV radiation (λ = 13.8 nm) illuminating the object, whereas a Fresnel zone plate objective forms the image. Design details, development, characterization and optimization of the EUV source and the microscope are described and discussed. Test object and other samples were imaged to demonstrate superior resolution compared to visible light microscopy.

Using a table-top size soft X-ray (SXR) microscope, based on a laser plasma source with a double stream gas-puff target and a Fresnel zone plate objective, series of images of test samples were acquired. Characterization and optimization of the acquisition parameters were studied and evaluated in terms of signal to noise ratio (SNR). Conclusions for the optimization of SXR imaging were reached. Similar SNR measurements might be performed to characterize other SXR imaging systems as well. Software enabling live calculation of the SNR during the image acquisition might be introduced in future in the compact imaging systems for optimal image acquisition or for benchmarking purposes.

Laser-produced plasma sources of short-wavelength radiation offer an interesting alternative to synchrotron and free-electron laser installations. Recently, we reported on a newly developed desktop EUV microscope based on plasma generated from a gas-puff target and diffractive optics. The half-pitch resolution of the microscope approached 50 nm. Compared to analogous microscopes based on synchrotron sources, our system is compact and cost-effective. In this paper, we present the results of imaging experiments on a thin polycrystalline object that was carried out in order to further examine the applicability of the microscope. We have demonstrated here that EUV microscopy can provide structural information that cannot be accessed by conventional optical microscopy or SEM.

A slit-shaped elongated nozzle, capable of forming an extended gas density profile, is presented and studied in detail. Argon and xenon target density backlighting measurements revealed the elongated density profiles with gas density that can be tuned by changing valve backing pressure and valve timing. Two dimensional density maps for Ar and Xe targets, obtained at soft X-ray wavelengths around 7 A, are shown and spatially characterized. Moreover the influence of valve backing pressure and valve timing on gas puff target density is studied. This geometry of the nozzle has potential applications in high harmonic generation for an efficient conversion of femto-second duration, intense infrared pulses to extreme ultraviolet (EUV) region.

Various imaging methods and techniques capable of reaching a nanometer spatial resolution are currentlyunder development. One of them is an extreme ultraviolet microscopy, based on the Fresnel zone plates. Inthis paper a compact, high-repetition, laser-plasma EUV source, with a gas puff target, capable of emittingquasi-monochromatic radiation at 13.8 nm wavelength was used in the first demonstration of a desk-top EUVtransmissionmicroscopywithaspatial(half-pitch)resolutionof50nm. EUVmicroscopyimagesofobjectswithvariousthicknessesandthespatialresolutionmeasurementsusingtheknife-edgetestarepresented.PACS:52.38.Ph,52.50.Dg,41.50.+h,42.30.Va,42.79.Ci

Imaging systems with nanometer resolution are instrumental to the development of the fast evolving field of nanoscience and nanotechnology. Decreasing the wavelength of illumination is a direct way to improve the spatial resolution in photon-based imaging systems and motivated a strong interest in short wavelength imaging techniques in the extreme ultraviolet (EUV) region. In this review paper, various EUV imaging techniques, such as 2D and 3D holography, EUV microscopy using Fresnel zone plates, EUV reconstruction of computer generated hologram (CGH) and generalized Talbot self-imaging will be presented utilizing both coherent and incoherent compact laboratory EUV sources. Some of the results lead to the imaging with spatial resolution reaching 50 nm in a very short exposure time. These techniques can be used in a variety of applications from actinic mask inspection in the EUV lithography, biological imaging to mask-less lithographic processes in nanofabrication.

In this paper an efficient micromachining of poly(vinylidene fluoride) (PVDF) by direct photo-etching with a laser-plasma EUV (extreme ultraviolet) source was demonstrated for the first time. Mass spectroscopy was employed to investigate the ablation products and revealed emission of numerous molecular species of C-containing fragments of the polymer chain. Chemical surface changes after irradiation were investigated using X-ray photoelectron spectroscopy (XPS). The XPS spectra obtained for PVDF samples, irradiated with low and high EUV fluence, indicate significant differences between chemical structures in near-surface layers. It was shown that irradiation with low fluence results in defluorination and thus carbon enrichment of the polymer in near-surface layer. In contrary, irradiation with high fluence leads to intense material ablation and hardly modifies the chemical structure of the remaining material.

In this work, a 10 Hz laser-plasma extreme ultraviolet (EUV) source built for surface processing of polymers is presented. The source is based on a double-stream gas puff target created in a vacuum chamber synchronously with the pumping laser pulse. The target is formed by pulsed injection of Kr, Xe or a KrXe gas mixture into a hollow stream of helium. The EUV radiation is focused using a grazing incidence gold-plated ellipsoidal collector. Spectrum of the reflected radiation consists of a narrow feature with intensity maximum at 10–11 nm wavelength and a long-wavelength spectral tail up to 70 nm. The exact spectral distribution depends on a gas applied for plasma creation. To avoid strong absorption of the EUV radiation in a residual gas present in the chamber during the source operation a two step differential pumping system was employed. The system allows for polymer processing under relatively high vacuum conditions (10−5 mbar) or in a reactive gas atmosphere. Polymer samples can be irradiated in a focal plane of the EUV collector or at some distance downstream the focal plane. This way fluence of the EUV beam at the polymer surface can be regulated.

In this work a laser-plasma EUV source based on a gas puff target was used for micro- and nanostructuring of polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and poly-oxydiphenylene-pyromellitimide (Kapton HN) foils. The plasma radiation was focused using a gold-plated grazing incidence ellipsoidal collector. The collector allowed for effective focusing of Kr plasma radiation from the wavelength range λ = 9–70 nm. The polymer foils were irradiated in the focal plane or at some distance downstream the focal plane of the EUV collector. The surface morphology of the irradiated polymer samples was investigated using a scanning electron microscope (SEM) and the chemical changes by X-ray photoelectron spectroscopy (XPS). Different kinds of micro- and nanostructures created in near-surface layers of the polymers were obtained. The form of the structures depends on the type of polymer and the EUV exposure. In case of PEN even a single shot was sufficient to obtain visible changes in surface morphology. In case of Kapton clearly visible surface modification requires tens of EUV pulses. To investigate the changes in the chemical structure XPS spectra, corresponding to the valence band of the polymer samples, were measured. Significant differences were revealed in the XPS spectra of irradiated and not-irradiated polymers showing decrease of functional groups containing oxygen was indicated.

In this paper a new approach to a laser-produced plasma EUV source based on a tin target is presented. A thin layer of pure tin and composite layers consisting of Sn with Si, SiO and LiF are investigated. The target composed of several thin layers produces less debris than the other targets and provides a conversion efficiency (CE) in the 13.5-nm±1% band at least comparable to the CE for the pure tin slab target. The largest CE was observed for the target composed of a mixture of Sn and LiF, due to the fact that lithium, similarly to tin, is a strong emitter at 13.5 nm.

In this work, the radiation from a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target was used for surface modification of polyethylene terephthalate (PET). The spectrum of the wide band radiation focused with a gold-coated ellipsoidal collector consisted of a narrow feature with maximum at 10 nm and a long-wavelength tail up to 70 nm. The PET samples were mounted in the focal plane of the EUV collector or at some distance downstream this plane and irradiated for 0.1 s–2 min with 10-Hz repetition rate. The polymer samples after irradiation were rinsed in acetone. Surface morphologies of the PET samples after irradiation were investigated using a scanning electron microscope and atomic force microscope. Different kinds of surface micro- and nanostructures were created as a result of irradiation depending on the EUV fluence and number of pulses. Acetone treatment of the polymer samples after irradiation resulted in formation of additional nanostructures. In this case the nanostructures were revealed even after exposure with a single EUV pulse.

We have investigated the influence of oriented microstructures at modified polyethylene terephthalate (PET) on the adhesion and alignment of Chinese hamster ovary (CHO) cells. For surface modification, the PET foils were exposed to the radiation of a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target. The emission of the plasma was focused onto the samples by means of a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated with the EUV pulses at a repetition rate of 10 Hz in a high vacuum. For control experiments, PET samples were also irradiated in air with the light of a 193 nm ArF-excimer laser. Different kinds of surface microstructures were obtained depending on the EUV or laser fluence and pulse number, including oriented wall- and ripple-type structures with lateral structure periods of a few µm. The surface morphology of polymer samples after the irradiation was investigated using a scanning electron microscope (SEM). Changes in chemical surface structure of the irradiated samples were investigated using X-ray photoelectron spectroscopy (XPS). We demonstrated that the cells show good adhesion and align along oriented wall- and ripple-type microstructures on PET surfaces produced by the EUV irradiation.

We have developed compact, high repetition, table-top soft-X-ray sources, based on a gas puff target, emitting in “water window” spectral range at λ = 2.88 nm from nitrogen gas target or, in 2–4 nm range of wavelengths, from argon gas target. Double stream gas puff target was pumped optically by commercial Nd:YAG laser, energy 0.74 J, pulse time duration 4 ns. Spatial distribution of laser-produced plasma was imaged using a pinhole camera. Using transmission grating spectrometer, argon and nitrogen emission spectra were obtained, showing strong emission in the “water window” spectral range. Using AXUV100 detector the flux measurements of the soft-X-ray pulses were carried out and are presented. These debris free sources are table-top alternative for free electron lasers and synchrotron installations. They can be successfully employed in microscopy, spectroscopy and metrology experiments among others.

Extreme ultraviolet (EUV) radiation is the electromagnetic radiation ranging from vacuum ultraviolet to soft X-rays. A single EUV photon carries enough energy to ionize any atom or molecule. The penetration depth of the radiation in any material is very short, ranging from tens to hundreds nanometers. Intense EUV pulses can remove material from the surface or modify its morphology or/and chemical structure. In this work, the radiation from a laser-plasma EUV source based on a double-stream gas-puff target was used for surface modification of polyethylene terephthalate (PET). The PET samples were irradiated with the EUV pulses emitted from krypton plasma and focused with a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated for 1 s–2 min at a 10-Hz repetition rate. Surface morphology of polymer samples after irradiation was investigated using a scanning electron microscope. Changes in chemical surface structure of the irradiated samples were investigated using an X-ray photoelectron spectroscopy. Different kinds of surface microstructures were obtained depending on the EUV fluence in a single pulse and the total EUV fluence. XPS measurements also revealed a modification of the chemical structure.

Extreme ultraviolet (EUV) covers wavelength range from about 5 nm to 50 nm. That is why EUV isespeciallyapplicableforimagingandpatterningonnanometerscalelength. Inthepaperperiodicnanopatterningrealized by interference lithography and high resolution holographic nanoimaging performed in a Gabor in-lineschemearepresented. IntheexperimentsacompacttabletopEUVlaserwasused. PreliminarystudiesonusingalaserplasmaEUVsourcefornanoimagingarepresentedaswell.PACSnumbers:42.25.Hz,42.40.Ht,42.40.