Thick Soda-lime Glass Research Articles

(Invited) Optical Probes for Resonance-Enhanced Gold Growth on Nanooptical Substrates

We investigate light-stimulated growth of gold metal lines to technically mimic the growth of long-range axonal connections for neuromorphic computing architectures. Photocatalytic gold growth from an aqueous gold chloride precursor solution (HAuCl4) on a photoactive titanium dioxide layer is used. It is known that local gold growth may be obtained by UV illumination through a shadow mask [1]. To obtain a wavelength and angle dependent growth of metal lines – and thus stimulus-dependent resistances – we suggest to employ a nanooptical template. Inspired by the typical number of 2 to 10 connections to a node found, e.g., in the neuronal system of the biological species Hydra, we decided on the implementation of a hexagonal design. The edges are formed by periodic grating nanostructures with 10 to 20 periods and a grating pitch of 170 nm to 210 nm for excitation in the UV. In order to investigate the resonant optical enhancement, we employ optical probes. It is well known that colloidal quantum dots show enhanced fluorescence emission on photonic crystal surfaces due to resonant excitation and resonant outcoupling [2]. In our initial experiments for investigation of the resonant enhancement, we use 4,4’-Bis(2,2-diphenylvinyl)-1,1’-biphenyl (DBVBi) as the emitter material. Its absorption maximum matches the excitation laser at 355 nm and fluorescence in the visible spectrum around 455 nm may be monitored with our camera and spectrometer setup.The nanostructure master was fabricated by electron-beam lithography (Kelvin Nanotechnology Ltd.) according to our design. We transfer the nanostructure pattern onto 1.1 mm thick soda-lime glass substrates by UV-nanoimprint lithography. Subsequently, a 100 nm titanium dioxide layer is deposited. The 150 nm emissive DBVBi layer is then added by thermal evaporation. The samples are characterized optically with a camera setup and magnifying optics on an in-plane rotatable xy-stage. We use a Cobolt Zouk 355 nm 10 mW laser to excite the emissive layer. The output power of the laser is set to 2 mW and its output beam is widened with a collimating lens setup to a diameter of approximately 1.5 mm². The widened beam is essential to obtain a homogeneous excitation. We observe the successful resonant excitation by the higher emission intensity of DPVBi in specific regions of the nanostructure at specific excitation angles. Already for 10 periods of the grating structure resonance effects are observed. A stronger enhancement is obtained for 20 periods. Further, the enhancement depends on the grating pitch as connections with nanograting pitches below 190 nm are no longer visible. They do not meet the criteria for resonant excitation.This method of using optical probes on the nanooptical template works well for initial characterization of the resonance enhancement at different excitation angles. Now the setup is ready for performing gold growth under different excitation conditions. Without the additional emissive layer, the waveguide thickness change needs to be compensated with an increased titanium dioxide layer thickness. For online monitoring of the resonant enhancement during growth optical probes may be employed below the photoactive titanium dioxide layer. It is expected that the resonance enhancement is reduced with the addition of gold due to the increased absorption and thus reduced quality factor as was previously studied in the context of nanostructured OLEDs [3].We acknowledge funding by the DFG (German Research Foundation) with the CRC 1461- Neurotronics (Project-ID 434434223 – SFB 1461).[1] S. Veziroglu et al. (2018). Photocatalytic growth of hierarchical au needle clusters on highly active TiO2 thin film. Advanced Materials Interfaces, 5(15), 1800465.[2] N. Ganesh et al. (2007). Enhanced fluorescence emission from quantum dots on a photonic crystal surface. Nature nanotechnology, 2(8), 515-520.[3] J. Buhl et al. (2023). Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings. Advanced Photonics Research, 4(2), 2200143. Figure 1. (Left) Fluorescence image of optical probe layer on nanooptical substrate for 355 nm laser excitation. (Middle) Schematic of nanooptical substrate with grating pitch (in nm) and number of periods given. Same colors represent identical grating features. (Right) Field emission scanning electron microscopy (FESEM) image of one node with 6 connections. Figure 1

Microcutting of glass with high ablation efficiency by means of a high power ps-pulsed NIR laser

Microcutting of glass through ultrafast lasers represents a process more and more employed in many industrial fields, among which touchscreen displays for electronic devices. The main disadvantage is the low processing speed that does not meet the industrial requirements. In this work, a ps-pulsed NIR laser with 200 W average power was employed for cutting of thick soda-lime glass with a relatively high thickness of 1 mm submerged in water. The cut evolution with respect to the number of passes and the quality of cut kerf were analysed by considering different levels of pulse repetition rate, pulse energy and scan speed. The results show a considerable influence of the scan speed on the ablation efficiency and surface roughness, because of the thermal accumulation given by the pulse overlap. Complete cut of 1 mm-thick glass was achieved at 400 kHz, 360 μJ, with speed from 0.5 m/s to 3 m/s and number of scans from 300 to 1900 respectively. The results showed that the use of high power ps-pulsed NIR laser can provide high material removal efficiency up to 600 µm3/pulse at 0.5 mm thickness and up to 300 µm3/pulse at 1 mm thickness.

Influence of Exposure Parameters on Nanoliquid-Assisted Glass Drilling Process Using CO2 Laser

Liquid-assisted laser processing (LALP) is implemented using a 10.6 μm continuous-wave (CW) CO2 laser to drill holes in 1.1 mm thick soda-lime glass substrates fully immersed in a nanoliquid bath. The nanoliquid bath consisted of de-ionized water and carbon nano-particles (CNPs) of different wt.%. The study focuses on the influence of exposure time (TE, [s]), laser beam power (P, [W]) and number of pulses (NP) on resulting geometrical features, namely, crack length (CL, [mm]), inlet diameter (DINLET, [mm]) and exit diameter (DEXIT, [mm]). The processed samples were characterized using an optical microscope. Findings show that LALP with investigated ranges of control parameters TE (0.5–1.5 s), P (20–40 W) and NP (1–6 pulses) led to successful production of drilled holes having CL range (0.141 to 0.428 mm), DINLET range (0.406 to 1.452 mm) and DEXIT range (0.247 to 1.039 mm). It was concluded that increasing TE alone leads to increasing CL, DINLET and DEXIT, while keeping a good balance among the control parameters, especially TE and NP, will result in reduced CL values. Moreover, process statistical models were developed using statistical analysis of variance (ANOVA). These models can be used to further understand and control the process within the investigated ranges of control and response parameters.

Simultaneous spatial and temporal focusing optical vortex pulses for micromachining through optically transparent materials.

We introduce the optical vortex beam into simultaneous spatial and temporal focusing (SSTF) technique, and theoretically and experimentally demonstrate the local control of peak intensity distribution at the focus of a simultaneous spatiotemporally focused optical vortex (SSTF OV) beam. To avoid nonlinear self-focusing in the conventional focusing scheme, a spatiotemporally focused femtosecond laser vortex beam was employed to achieve doughnut-shaped ablation and high aspect ratio (∼28) microchannels on the back surface of 3 mm thick soda-lime glass and fused silica substrates.

Adjustable multifocus laser separation scheme for thick glass with flexibly controllable thermal stress distribution

As a high-quality thick glass separation method, multifocus technology has proven its superiority. For a certain thickness of glass, there must be an optimal multifocus distance. But, the positions of the foci cannot be adjusted flexibly in current multifocus schemes without changing the energy proportions; the influence of thermal stress distribution on the quality of thick glass separation has not been systematically studied. An adjustable multifocus laser scheme has been proposed in this paper and proved by optical design, ray tracing, and experiment. First, finite element simulations have been performed to analyze the thermal stress distribution inside 20 mm glass. The simulation results show that thermal tensile stress exceeds the fracture threshold only at the upper and lower sides of the glass but not in the middle; the maximum thermal tensile stress reduces inside the glass when the symmetrical focal distance increases. Then, a series of separation experiments of 20, 22, and 25 mm thick soda lime glass have been carried out, which have adjusted foci positions to control the thermal stress distribution. The experimental results show that the deviation length decreases with an increase of the foci distances, and the optimal symmetrical foci distances reduce as the glass thickness increases.

Comparative analysis of ultrasonic drilling process using static and rotary tools

Ultrasonic drilling (USD) is widely used for drilling of glass. A comparative study of USD for 2.0 mm diameter hole in 3.0 mm thick soda lime glass has been performed using static (USD-ST) and rotary tool (USD-RT) of mild steel. To make the process more cost effective and productive, statistical models of material removal rate (MRR), hole circularity at entry and exit (HCentry, HCexit) and hole taper (Ht) have been developed using Box–Behnken approach of response surface methodology. The effect of abrasive size, frequency, ultrasonic power and tool rotational speed have been investigated and it was observed that abrasive size is the most significant factor to control MRR during USD-ST. In USD-RT, MRR, HCentry, HCexit and Ht are significantly affected by frequency. The combination of low frequency and small grain size produces high MRR in USD-RT. Increase of frequency from 22 to 24 kHz increases HCentry by 4.3% in USD-ST, whereas for rotating tool the increase of frequency from 22 to 25 kHz decreases the value by 2%. HCentry increases with the rise of frequency at constant ultrasonic power, USD-ST provides 7.14% more circular hole at entry compared to USD-RT for a combination of frequency and grit size. In multi-objective optimization of USD-ST, a desirability value of 0.8589 was obtained at ultrasonic power of 90%, frequency 23.47 kHz and abrasive grit no 60, whereas for USD-RT the desirability value of 0.8499 were correspondingly obtained at 78.48%, 25.5 kHz, 770.20 rpm and 60.

Single-pass laser separation of 8 mm thick glass with a millijoule picosecond pulsed Gaussian–Bessel beam

Efficient micromachining of glass with thicknesses of up to several millimeters can be enabled by using picosecond laser pulses with energies in the order of millijoules. In the experiments presented in this article, we investigated in-volume modifications in different thicknesses of borosilicate and soda lime glass using an axicon-generated Gaussian–Bessel beam. The main objective of the study was to demonstrate the separation of 8 mm thick soda lime glass within a single pass of the laser beam.

Improving efficiencies of Cu2ZnSnS4 nanoparticle based solar cells on flexible glass substrates

In spite of its mechanically inflexible structure, millimeter thick soda-lime glass is generally used for fabrication of Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells; improvements in sintering of the chalcogenide absorber layer from intrinsic sodium doping and subsequent higher device efficiency make soda-lime glass the preferred substrate. Thin and flexible Corning® Willow® Glass provides a unique advantage in contaminant-free fabrication of flexible solar cells, as it can be processed at the elevated temperatures (c.a. 500°C–550°C) needed for high performance thin film solar cells. In this study, we report successful lab-scale fabrication of CZTSSe solar cells on flexible glass substrates from nanoparticle inks of Cu2ZnSnS4 (CZTS), and identify necessary process changes to bridge device performance to standard devices fabricated with soda-lime glass (SLG).Since the sodium concentration in Willow Glass is negligibly small, supply of sodium to the absorber film during selenization was explored. Soaking coated CZTS films in sodium chloride prior to selenization was found to have a detrimental effect on power conversion efficiency (PCE). Alternatively, sodium doping with a thin NaF film on top of the CZTS nanoparticles films prior to selenization resulted in slightly improved device performance. The addition of a 10nm thick NaF layer slightly increased the average device efficiency from 6.2±0.3% to 6.4±0.4% with a record 6.9% PCE based on total cell area. The increased efficiency results from higher Voc due to the sodium doping. While these initial results demonstrate the potential of Willow Glass as a flexible support for nanoparticle based photovoltaic devices, there is a need to continue developing improved processing methods to further enhance PCE values.

Fracture features in soda-lime glass after testing with a spherical indenter

A thick soda-lime glass plate was indented with a spherical indenter at high indentation forces up to 1.839 kN. A systematisation of the fracture figures showed a basic structure, consisting of four individual zones. The detailed characteristics of these zones depended on indentation force. Existing models for the assessment of contact diameter and radial and lateral vent cracks length were proven. The appearance of fracture lances was observed and discussed. It was found that these lances formed during the intersection of conchoidal (lateral) fractures, and that their formation was bound to the elastic-plastic period of the indentation process. Features of fracture lances, namely the formation of numerous symmetric lance fronts, periodically occurring lance fronts, lance front statistics, and lance dimensions were described and discussed in detail. It was also shown that the formation of fracture lances showed elements of self-similarity and fractal geometry.

CIGS thin films, solar cells, and submodules fabricated using a rf-plasma cracked Se-radical beam source

Coevaporated Cu(In,Ga)Se 2 (CIGS) film growth using a rf-plasma cracked Se-radical beam (R–Se) source leads to a significant reduction in the amount of raw Se source material wasted during growth and exhibits unique film properties such as highly dense, smooth surfaces and large grain size. R–Se grown CIGS solar cells also show concomitant unique properties different from conventional evaporative Se (E–Se) source grown CIGS cells. In the present work, the impact of modified surfaces, interfaces, and bulk crystal properties of R–Se grown CIGS films on the solar cell performance was studied. When a R–Se source was used, Na diffusion into CIGS layers was enhanced while a remarkable diffusion of elemental Ga and Se into Mo back contact layers was observed. Improvements in the bulk crystal quality as manifested by large grain size and increased Na concentration with the use of a R–Se source is expected to be effective to improve photovoltaic performance. Using a R–Se source for the growth of CIGS absorber layers at a relatively low growth temperature, we have successfully demonstrated a monolithically integrated submodule efficiency of 15.0% (17 cells, aperture area of 76.5 cm 2) on 0.25-mm thick soda-lime glass substrates.

Electric field and force modeling for electrostatic levitation of lossy dielectric plates

Electrostatic levitation holds great promise for the semiconductor, solar panel, and flat-panel display industry where the handling of dielectrics in a contact-free manner can bring many advantages and solve long-standing contamination and particulate control problems. In this work an analytical model is developed for the electrostatic levitation field between a lossy dielectric plate and a generic stator electrode structure consisting of a regular planar array of parallel bar electrodes. Time-varying voltages of differing polarities are alternatingly applied to the bar electrodes. Atmospheric humidity-related surface conduction on the plate is explicitly taken into account in the model since it has a profound effect on the field dynamics. Based on this model, the electrostatic levitation force is calculated using the Maxwell stress tensor formulation. The levitation force dynamics are investigated by evaluating the transient response of the field under a step in the applied voltages. In this context, the rate of electric charge build up on the plate is characterized by the suspension initiation time (TSI), which is defined as the time elapsed between applying step voltages to the stator electrodes and start of lift-off of the dielectric plate from its initial position. TSI is theoretically predicted for 0.7 mm thick soda-lime glass substrates, typically used in the manufacturing of liquid crystal displays (LCDs), as a function of electrode geometry, air gap separation, ambient humidity, and step voltage magnitudes. The predicted results are shown to be in good agreement with previously published experimental data for soda-lime glass substrates.

Fabrication of Simple Diode Structure FED Device with Connecting Plate

By using the thick soda-lime glass plate and the flat thin glass, the connecting plates were formed easily. The carbon nanotube materials were prepared to form the field emitters. The simple small diode structure field emission display device with connecting plate was developed. The detailed fabrication technology for the whole device was also presented. The sealing of the vacuum room was performed by means of glass frit and the gas in the vacuum room could be evacuated out through the exhaust tube. The developed diode structure FED sample exhibited large field emission current, better field emission properties and image display performance.

Laser etching of glass substrates by 1064 nm laser irradiation

Glass substrates are transparent to 1064 nm laser irradiation and cannot be etched directly by 1064 nm pulsed laser. By placing the glass substrate in contact with copper sulphate (CuSO4) solution and irradiating 1064 nm laser light through the glass, etching of the glass is observed on the downside of the glass, the contact side with the copper sulphate solution. The etching mechanism is proposed to be a two-step process. The first step is the deposition of copper from copper sulphate solution upon 1064 nm irradiation. It is followed by the absorption of the 1064 nm laser irradiation by the deposited copper, resulting in the etching of the glass. Using this technique, 1 mm thick soda lime glass slides can be cut through. Furthermore, various arbitrary shapes can be diced out from glass substrates. The formation of copper deposits is observed and characterized.

Competing Fracture Modes in Brittle Materials Subject to Concentrated Cyclic Loading in Liquid Environments: Monoliths

The competition between fracture modes in monolithic brittle materials loaded in cyclic contact in aqueous environments with curved indenters is examined. Three main modes are identified: conventional outer cone cracks, which form outside the maximum contact; inner cone cracks, which form within the contact; and median–radial cracking, which form below the contact. Relations describing short-crack initiation and long-crack propagation stages as a function of number of cycles, based on slow crack growth within the Hertzian field, are presented. Superposed mechanical driving forces—hydraulic pumping in the case of inner cone cracks and quasiplasticity in the case of median–radials—are recognized as critically important modifying elements in the initial and intermediate crack growth. Ultimately, at large numbers of cycles, the cracks enter the far field and tend asymptotically to a simple, common relation for center-loaded pennylike configurations driven by slow crack growth. Crack growth data illustrating each mode are obtained for thick soda-lime glass plates indented with tungsten carbide spheres in cyclic loading in water, for a range of maximum contact loads and sphere radii. Generally in the glass, outer cone cracks form first but are subsequently outgrown in depth as cycling proceeds by inner cones and, especially, radial cracks. The latter two crack types are considered especially dangerous in biomechanical applications (dental crowns, hip replacements) where ceramic layers of finite thickness are used as load-bearing components. The roles of test variables (contact load, sphere radius) and material properties (hardness, modulus, toughness) in determining the relative importance of each fracture mode are discussed.

Unloading fractures in indented glass

Abstract The failure sequence of thick soda—lime glass plates under indentation from tungsten carbide spheres at high loads is described. Failure shows a combination of features normally associated with either blunt or sharp indentation, and most occurs during unloading. In particular the effects of irreversible processes of flow, densification, fracture and interfacial slip during loading on the initiation and propagation of failure during unloading are described and discussed.

An experimental study of the elastic rebound of spheres

Accurate measurements have been made of the impact and rebound behaviour of 5-mm aluminium oxide spheres impacting a thick soda–lime glass anvil, for impact angles from normal to very near glancing incidence. Speed, angle and rotation before and after impact have been measured with a strobe and single-frame digital camera. Reproducibility and precision are considerably better than in any previously published work, and have been achieved by careful attention to all aspects of the experiment, including the mechanical and optical systems, illumination, electronic control, computer-based image measurement, and the geometry and condition of the impacting surfaces. All aspects of the rebound dynamics of the elastic spheres, including the motion of the centre of mass and of the contact patch, the spin and the partition of energy, are fully described by the measured variation of the normal and tangential restitution coefficients over the range of impact angles. These measurements show very close agreement with the numerical work of Maw et al. which takes into account the effects of sticking, microslip and tangential compliance. For impacts with a greater obliqueness than about 30° from the normal, the results also agree closely with the classical theory of rigid body sliding.

The measurement of particle rebound characteristics

Accurate measurements have been made of the rebound behaviour of 5 mm aluminium oxide spheres impacting a thick soda–lime glass anvil (fully elastic response) and an aluminium alloy anvil (involving some plastic deformation). Speed, angle and rotation before and after impact have been measured with a strobe and single-frame digital camera, for a range of impact angles from normal to very near glancing. High levels of reproducibility and precision have been achieved by careful attention to all aspects of the measurement, including the mechanical and optical systems, illumination, electronic control, and computer-based image measurement. Rebound parameters from the elastic and plastic impacts are analysed and compared in the context of the numerical work of Maw et al. for near-normal angles when sticking, micro-slip and tangential compliance are the major factors, and of rigid body sliding for more oblique angles.

Characteristics of indium tin oxide films deposited by r.f. magnetron sputtering

Highly conductive indium tin oxide (ITO) films were deposited by r.f. magnetron sputtering using ITO targets. The composition of the ITO targets was 90% indium oxide and 10% tin oxide. ITO films were deposited on 1 mm thick soda lime glass. Films deposited at substrate temperature of 300 °C, exhibited resistivities as low as 1.3 × 10 −4ohm cm −1. Annealing of the ITO films in air for 2 h was necessary for achieving low resistivities. X-ray diffraction and transmissivity tests were carried out to study the effects of annealing. Lowest resistivity and highest transmission were found to occur at an annealing temperature of 350 °C. X-ray diffraction measurements revealed that the as deposited film had a strongly (222) oriented cubic structure. Annealing relieved the as deposited tensile strain and increased crystal perfection.

Enhanced failure of ceramics irradiated by combined pulse and c.w. lasers

Several ceramic materials were subjected to the combined irradiation of a 1.06μ pulse and a 10.6μ continuous wave (c.w.) laser. The duration of c.w. irradiation required to cause failure from the combined exposure is compared to that from c.w. irradiation alone. For example, thin Pyroceram and soda-lime glass plates burned through when exposed to the c.w. laser followed by the single pulse laser, in about one half the time required to cause fracture during exposure to the c.w. laser alone. Also, enhanced catastrophic fracture of thick soda-lime glass plates resulted when the c.w. irradiation followed the pulse within 0.3 sec. Finally, the effects of the combined pulse and c.w. exposure are compared with the effects of single or multiple pulses, and the apparent enhancement is discussed in terms of beam size and power.