Muharrem Bayraktar

Method to calculate the far field of three-dimensional objects for computer-generated holography

Here, a new method for calculating the computer-generated holograms of three-dimensional (3D) objects is presented along with a review of current techniques. The method, the planar layers method (PLM), is established on the idea of representing 3D objects in discrete planar layers perpendicular to the observation plane, then calculating the total far field pattern by summing up the far field patterns of each layer. Simulation results, computational complexity, and error comparisons reveal that this new method can be used to calculate far field patterns--hence, the holograms--of computer-synthesized objects very efficiently.

Nanosheet controlled epitaxial growth of PbZr0.52Ti0.48O3 thin films on glass substrates

Integration of PbZr0.52Ti0.48O3 (PZT) films on glass substrates is of high importance for device applications. However, to make use of the superior ferro- and piezoelectric properties of PZT, well-oriented crystalline or epitaxial growth with control of the crystal orientation is a prerequisite. In this article, we report on epitaxial growth of PZT films with (100)- and (110)-orientation achieved by utilizing Ca2Nb3O10 (CNO) and Ti0.87O2 (TO) nanosheets as crystalline buffer layers. Fatigue measurements demonstrated stable ferroelectric properties of these films up to 5 × 109 cycles. (100)-oriented PZT films on CNO nanosheets show a large remnant polarization of 21 μC/cm2 that is the highest remnant polarization value compared to (110)-oriented and polycrystalline films reported in this work. A piezoelectric response of 98 pm/V is observed for (100)-oriented PZT film which is higher than the values reported in the literature on Si substrates.

Spectral purification and infrared light recycling in extreme ultraviolet lithography sources

We present the design of a novel collector mirror for laser produced plasma (LPP) light sources to be used in extreme ultraviolet (EUV) lithography. The design prevents undesired infrared (IR) drive laser light, reflected from the plasma, from reaching the exit of the light source. This results in a strong purification of the EUV light, while the reflected IR light becomes refocused into the plasma for enhancing the IR-to-EUV conversion. The dual advantage of EUV purification and conversion enhancement is achieved by incorporating an IR Fresnel zone plate pattern into the EUV reflective multilayer coating of the collector mirror. Calculations using Fresnel-Kirchhoffs diffraction theory for a typical collector design show that the IR light at the EUV exit is suppressed by four orders of magnitude. Simultaneously, 37% of the reflected IR light is refocused back the plasma.

Digital holography image reconstruction methods

In recent years the field of digital holography became an attractive research area following the developments of CCD-arrays and an ever increasing computational power of computers. Here we investigate digital holography reconstruction methods and compare them for the accuracy and the computational speed. In addition, possible discrepancies in the calculation of the diffraction integral via fourier transform is clarified and it is compared to convolution methods. The proper evaluation of discrete Fresnel diffraction equation is demonstrated by creating artificial holograms and numerically reconstructing them. Simulation results and experimental work is presented.

Active multilayer mirrors for reflectance tuning at extreme ultraviolet (EUV) wavelengths

We propose an active multilayer mirror structure for extreme ultraviolet (EUV) wavelengths, which can be adjusted to compensate for reflectance changes. The multilayer structure tunes the reflectance via an integrated piezoelectric layer that can change its dimension due to an externally applied voltage. Here, we present design and optimization of the mirror structure for maximum reflectance tuning. In addition, we present preliminary results showing that the deposition of piezoelectric thin films with the requisite layer smoothness and crystal structure is possible. Finally piezoelectric coefficient measurement (d33 = 60 pm V −1 ) of the film is presented. (Some figures may appear in colour only in the online journal)

Wavefront correction in the extreme ultraviolet wavelength range using piezoelectric thin films

A new scheme for wavefront correction in the extreme ultraviolet wavelength range is presented. The central feature of the scheme is the successful growth of crystalline piezoelectric thin films with the desired orientation on an amorphous glass substrate. The piezoelectric films show a high piezoelectric coefficient of 250 pm/V. Using wavefront calculations we show that the grown films would enable high-quality wavefront correction, based on a stroke of 25 nm, with voltages that are well below the electrical breakdown limit of the piezoelectric film.

Narrowband and tunable anomalous transmission filters for special monitoring in the extreme ultraviolet wavelength region

We present the first experimental demonstration of a novel type of narrowband and wavelength-tunable multilayer transmission filter for the extreme ultraviolet (EUV) region. The operating principle of the filter is based on spatially overlapping the nodes of a standing wave field with the absorbing layers within the multilayer structure. For a wavelength with a matching node pattern, this increases the transmission as compared to neighboring wavelengths where anti-nodes overlap with the absorbing layers. Using Ni/Si multilayers where Ni provides strong absorption, we demonstrate the proper working of such anomalous transmission filter. The demonstration is carried out at the example of 13.5 nm wavelength and at normal incidence, providing a 0.27 nm-wide transmission peak. We also demonstrate wavelength tunability by operating the same Ni/Si filter at different wavelengths by varying the angle of incidence. As the multilayer filter is directly deposited on the active area of an EUV-sensitive photodiode, this provides an extremely compact device for easy spectral monitoring in the EUV. The transmission spectrum of the filter is modeled and found to be in good agreement with the experimental data. The agreement proves that such filters and compact monitoring devices can be straightforwardly designed and fabricated, as desired, also for other EUV wavelengths, bandwidths and angles of incidence, thereby showing a high potential for applications.

Tuning of large piezoelectric response in nanosheet-buffered lead zirconate titanate films on glass substrates

Renewed interest has been witnessed in utilizing the piezoelectric response of PbZr0.52Ti0.48O3 (PZT) films on glass substrates for applications such as adaptive optics. Accordingly, new methodologies are being explored to grow well-oriented PZT thin films to harvest a large piezoelectric response. However, thin film piezoelectric response is significantly reduced compared to intrinsic response due to substrate induced clamping, even when films are well-oriented. Here, a novel method is presented to grow preferentially (100)-oriented PZT films on glass substrates by utilizing crystalline nanosheets as seed layers. Furthermore, increasing the repetition frequency up to 20 Hz during pulsed laser deposition helps to tune the film microstructure to hierarchically ordered columns that leads to reduced clamping and enhanced piezoelectric response evidenced by transmission electron microscopy and analytical calculations. A large piezoelectric coefficient of 250 pm/V is observed in optimally tuned structure which is more than two times the highest reported piezoelectric response on glass. To confirm that the clamping compromises the piezoelectric response, denser films are deposited using a lower repetition frequency and a BiFeO3 buffer layer resulting in significantly reduced piezoelectric responses. This paper demonstrates a novel method for PZT integration on glass substrates without compromising the large piezoelectric response.

Polarizaton recovery in lead zirconate titanate thin films deposited on nanosheets-beffered Si (oo1)

Fatigue behavior of Pb(Zr,Ti)O3 (PZT) films is one of the deterrent factors that limits the use of these films in technological applications. Thus, understanding and minimization of the fatigue behavior is highly beneficial for fabricating reliable devices using PZT films. We have investigated the fatigue behavior of preferentially oriented PZT films deposited on nanosheets-buffered Si substrates using LaNiO3 bottom and top electrodes. The films show fatigue of up to 10% at 100 kHz, whereas no fatigue has been observed at 1 MHz. This frequency dependence of the fatigue behavior is found to be in accordance with Dawber–Scott fatigue model that explains the origin of the fatigue as migration of oxygen vacancies. Interestingly, a partial recovery of remnant polarization up to 97% of the maximum value is observed after 4 109 cycles which can be further extended to full recovery by increasing the applied electric field. This full recovery is qualitatively explained using kinetic approach as a manifestation of depinning of domains walls. The understanding of the fatigue behavior and polarization recovery that is explained in this paper can be highly useful in developing more reliable PZT devices

Adaptive multilayer optics for extreme ultraviolet wavelengths

In this thesis we describe the development of a new class of optical components to enhance the imaging performance by enabling adaptations of the optics. When used at extreme ultraviolet (EUV) wavelengths, such ‘adaptive optics’ offers the potential to achieve the highest spatial resolution in imaging known to date, i.e., a resolution down to several nanometers. These optics are discussed, e.g., in the field of photolithography for the fabrication of more energy efficient and faster electronic equipment. The topics in this thesis can be subdivided into two parts. The first part includes a mirror design that can be used to enhance the spectral quality of EUV light sources. Our design consists of a diffractive Fresnel zone plate patterned in the surface of a curved mirror to achieve spectral purification, i.e., removing undesired wavelengths of the EUV light sources. The removed light is recycled to produce more EUV light. This design achieves four orders of magnitude purification and provides a 35% improvement in efficiency. The second part of the thesis describes a new class of adaptive multilayer mirrors that can be used to correct wavefront distortions, reflectance degradations or wavelength deviations. These adaptive optics contain integrated crystalline piezoelectric thin films of which the film thickness can be adjusted by an externally applied voltage. Because the optics substrates typically have an amorphous structure, so far it was not possible to grow high quality crystalline piezoelectric films on them. We utilized crystalline nanosheets on these substrates to grow the highest quality, i.e., epitaxial, piezoelectric films (PbZr0.52Ti0.48O3, PZT). The PZT films show a record high piezoelectric coefficient of 98 pm/V, although the piezoelectric response in this case is still reduced due to clamping by the substrate. We minimized the clamping effect by depositing films with a columnar structure, which enhances the voltage-controlled change in film thickness. In these films we measured a piezoelectric response of 280 pm/V, the highest value reported on glass substrates. Importantly, the developed films can produce a stroke of 25 nm. This order of magnitude is useful when considering to correct EUV wavefront distortions.