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Abstract

Two sapphire substrates are tightly bonded through a fresnoite-glass thin film, by irradiation with a 1,064 nm nanosecond laser. The composition of the glass solder at the bond interface changes, due to incorporation of Al from the upper substrate. The oxidic solder remains amorphous after laser irradiation, but after annealing (850 °C for 1 h) crystalline structures are observed in different morphologies, which are attributed not only to fresnoite, but also to Ba–Ti–Al–O phases, which lead to a strong luminescence of the laser irradiated region under UV excitation.

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... In our previous publications [29][30][31], we applied a fresnoitic glass (2BaO-TiO 2 -2SiO 2 , BTS) thin film as an absorber for the laser light, acting as a solder between two transparent substrates. In this way, silica glass-to-silica glass and sapphire-to-sapphire joints were formed. ...
... Ti 4+ ions hosted in a square-pyramidal TiO 5 are responsible for blue fluorescence when irradiated in the UV range [34]. In our previous contributions [29][30][31], we reported the damage of bond interface with the upper substrate by the laser irradiation. Upon UV excitation the solder strongly emits in the blue spectral range. ...
... The uncoated silica glass substrate was then placed over the BTS·3SiO 2 -coated sapphire substrate leaving the BTS·3SiO 2 thin film acting as glass solder (Fig. 1). The set-up for the laser bonding is the same shown previously in [29,31], in which a custom-made arrangement fixture was used in order to bring both substrates in close proximity. ...
Article
Laser welding of dissimilar materials is challenging, due to their difference in coefficients of thermal expansion (CTE). In this work, fused silica-to-sapphire joints were achieved by employment of a ns laser focused in the intermediate Si-enriched fresnoitic glass thin film sealant. The microstructure of the bonded interphase was analyzed down to the nanometer scale and related to the laser parameters used. The crystallization of fresnoite in the glass sealant upon laser process leads to an intense blue emission intensity under UV excitation. This crystallization is favored in the interphase with the silica glass substrate, rather than in the border with the sapphire. The formation of SiO2 particles was confirmed, as well. The bond quality was evaluated by scanning acoustic microscopy (SAM). The substrates remain bonded even after heat treatment at 100 °C for 30 min, despite the large CTE difference between both substrates.
... 23 In our previous works, different combinations of transparent materials and BTS-based thin films acting as sealants were investigated. [24][25][26][27][28] One of the novelties of those works was that the BTS glass sealant was employed as thin film (1-2 µm thickness) obtained from Pulsed Laser Deposition (PLD) process, and not as paste from glass powders (Table 1). In Ref. (26), we reported on the laser welding of two transparent dissimilar substrates, being sapphire and fused silica. ...
... The employed set-up and analysis parameters are similar to our previous works. [24][25][26][27][28] Bonded samples were examined with an optical microscope (Leica DM RXE-650H). Fluorescence maps were recorded in the same optical microscope by locating an UV Lamp Camag (254 nm excitation wavelength with excitation density of 1.2 mW/cm 2 ) in front of the package. ...
... The BTS.xSiO 2 thin film is completely molten ( Figure 7C), welding both substrates when resolidified. From our previous works, 6,[24][25][26] it is well-known that the ablation of the upper substrate upon laser irradiation leads to its partial incorporation (in this case silica) in the thin film. Hence, the composition of the glass sealant changes with the course of the laser welding, incorporating constituents of the upper wafer. ...
Article
The present paper embraces two different approaches for the joining of materials through glass sealants. First, the conventional method of furnace sealing in which paste technology is normally employed. The glass sealant is applied in powder form mixed with agglomerant and with the help of dispenser robots, tape casting or screen printing. Glass‐ceramics for sealing of solid oxide fuel cells (SOFC) are described as an example of this type of processing. Glass composition, thermal properties, particle size of the glass powder, sintering and crystallization competition and final crystalline phases together with a suitable chemical compatibility with the metallic and ceramic elements to be sealed need to be carefully adjusted for this specific application. Second, laser welding is presented as an alternative sealing technology. A general overview about laser welding through glass sealants is presented. Particularly, the welding of sapphire and fused silica glass through a BTS.2SiO2 thin film glass sealant by employment of a ns pulsed laser is detailed. Laser parameters (frequency, power, scan speed, number of passes) were optimized to get the best molten conditions of the BTS thin film, while allowing its crystallization. BTS crystallization upon laser welding leads to a strong blue emission upon UV excitation. Finally, both processing technologies are compared.
... Among transparent materials, sapphire is widely used in the field of optical components and micromechanical devices. In our previous publications [10,11], we reported the laser soldering of two sapphire substrates through a fresnoite (2BaO-TiO 2 -2SiO 2 ) glass thin film. It was stated that the laser soldering procedure leads to the ablation of the upper sapphire substrate in the interface and aluminum was incorporated into the fresnoite glass thin film. ...
... The uncoated substrate was then placed over the BaTiAl 6 O 12 (BTAO) coated substrate leaving the BaTiAl 6 O 12 thin film in between acting as an absorber first and glass solder later ( Fig. 1a and b). The set-up for the laser bonding is the same shown previously in [10], in which a custom-made sample holder was used in order to bring both sapphire substrates in close proximity. ...
... After exposure to a heat treatment (at 950°C for 30 minutes) the bonded sample exhibits a visible strong optical emission. The temperature was selected based on a high melting temperature of 1450°C and from the assumption from our previous results [10,11] concerning the inclusion of Al 2 O 3 from both substrates, which would increase the crystallization temperature. Fig. 5 shows a photograph of the bonded sample heat treated at 950°C for 30 minutes upon 254 nm excitation. ...
Article
Two sapphire substrates are tightly bonded through a BaTiAl6O12-glass thin film, by irradiation with a nanosecond laser. After the laser process, the composition of the glass sealant changes, due to incorporation of Al2O3 from the upper substrate. After annealing of the bonded samples (950 °C for 30 minutes) crystalline structures are observed by TEM which are attributed to crystalline BaTiAl6O12. These crystals together with Al2O3:Ti centers are the responsible of the observed strong blue luminescence of the laser irradiated region upon UV excitation. The structural and optical characterizations of the bonded samples clarify the laser soldering procedure as well as the origin of the luminescence. Bond quality and bond strength were evaluated by scanning acoustic microscopy (SAM) and tensile tests, which results in a tensile stress of nearly 13 MPa, which is an acceptable value for glass sealants.
... Among transparent materials, sapphire is widely used in the field of optical components and micromechanical devices. In our previous publications [10,11], we reported the laser soldering of two sapphire substrates through a fresnoite (2BaO-TiO 2 -2SiO 2 ) glass thin film. It was stated that the laser soldering procedure leads to the ablation of the upper sapphire substrate in the interface and aluminum was incorporated into the fresnoite glass thin film. ...
... The uncoated substrate was then placed over the BaTiAl 6 O 12 (BTAO) coated substrate leaving the BaTiAl 6 O 12 thin film in between acting as an absorber first and glass solder later (Fig. 1a and b). The set-up for the laser bonding is the same shown previously in [10], in which a custom-made sample holder was used in order to bring both sapphire substrates in close proximity. The irradiation source was a pulsed 5 ns 532 nm nanosecond Nd: YAG laser (Xiton Photonics laser implemented into a microSTRUCT C laser micromachining workstation by 3D-Micromac AG), operated at 50 kHz. ...
... After exposure to a heat treatment (at 950 °C for 30 minutes) the bonded sample exhibits a visible strong optical emission. The temperature was selected based on a high melting temperature of 1450 °C and from the assumption from our previous results [10,11] concerning the inclusion of Al 2 O 3 from both substrates, which would increase the crystallization temperature.Fig. 5 shows a photograph of the bonded sample heat treated at 950 °C for 30 minutes upon 254 nm excitation. ...
... Ti 4 þ ions hosted in a squarepyramidal TiO 5 are responsible for blue fluorescence when irradiated in the UV range [11]. In our previous contributions [12,13], two sapphire substrates were joined through a fresnoite glass thin film. It was reported that the upper sapphire substrate was ablated by the laser irradiation and part of the Al from the sapphire was incorporated into the glass solder. ...
... After annealing the stack and upon UV excitation the solder strongly emits in the blue spectral range. This fluorescence was attributed to fresnoite crystals together with Si-deficient and Ba-Ti-Al-O containing phases [12]. The ablation of the upper sapphire substrate and the incorporation of the aluminum in the glass solder have motivated the replacement of sapphire for fused silica substrates and thus, the study of the influence on the composition of the glass solder. ...
... The uncoated substrate was then placed over the BTScoated substrate leaving the BTS thin film in between acting as glass solders (Fig. 1a). The set-up for the laser bonding is the same shown previously in Ref. [12,13], in which a custom-made arrangement fixture was used in order to bring both fused silica substrates in close proximity. ...
... , especially as glass frit bonding layers (Knechtel 2005). In our previous study, we reported the joining of two sapphire substrates through a fresnoite glass (2BaO-TiO 2 -2SiO 2 ) (BTS) thin film by laser welding technique (de Pablos-Martín et al. 2014). BTS is known to exhibit luminescence (Blasse 1979;Takahashi et al. 2012), pyro-, piezo-and ferroelectric properties (Shen et al. 2014Zhang et al. 1999), as well as non-linear optical properties, in particular a strong blue luminescence from UV excitation more intense in the crystalline frensnoite than in the glass (Bechthold et al. 1978;Takahashi et al. 2005). ...
... Concerning solder materials, glasses and glass-ceramics are suitable for sealing wafers (Donald et al. 2011; 1 3 Pablos-Martín et al. 2014). The mechanical characterization of the bond is analyzed in terms of fracture toughness K IC , based on the widely used micro-chevron-test (MCT) (Naumann et al. 2013). ...
... The bond sandwich consists of two 11 × 13 mm 2 sapphire wafers, one of them being coated with a fresnoite thin film acting as glass solder. The set-up for the laser bonding is the same as shown previously in (de Pablos-Martín et al. 2014). A self-made sample holder was employed in order to bring both sapphire wafers in close proximity, resulting in a contact pressure of ~7 MPa. ...
Article
Two sapphire substrates were bonded using a fresnoite glass thin film as a sealant, by irradiation with a 1,064 nm ns laser. The sapphire close to the interface was examined by TEM, showing some structural defects due to the laser processing. Bond quality and strength were evaluated by scanning acoustic microscopy (SAM) and micro-chevron testing, respectively. Optimization of laser parameters lead to an improved processing speed (>1 mm/s) as well as an enhanced fracture toughness to 1.23 MPa m1/2.
... Table 1 shows that fresnoite glass-ceramics are mainly studied using surface crystallization , electrochemically induced nucleation (EiN) [150][151][152][153][154][155][156][157][158][159][160][161][162] or laser induced processes [163][164][165][166][167][168][169][170][171][172][173][174]. Fresnoite has also been crystallized in cathode ray tube (CRT) glasses [175], via a sol-gel process [176] and synthesized in the form of thin films [177][178][179][180][181][182][183][184][185][186][187][188][189] or powders [190,191]. ...
... Due to the high nucleation rates and crystal growth velocities achievable in fresnoite glass-ceramics, glasses in the BTS system are interesting for applications as welds and sealants, especially if rapid processes are to be applied. Laser welding utilizing fresnoite thin films has already been performed [187][188][189]. ...
Article
The crystallization of fresnoite from glasses enables to produce a wide variety of materials including piezoelectric glass-ceramics due to the aligned growth of these crystals in the amorphous matrix. The crystal structure of fresnoite leads to interesting pyroelectric, piezoelectric and nonlinear optical properties and is one of the few known non-ferroelectrics which can be easily produced as polycrystalline but polar materials. This review provides a summary of the properties of fresnoite crystals as well glass-ceramics containing fresnoite crystals. A special focus is the preparation of oriented and polar glass-ceramics and the resulting properties. The literature concerning the complete process from the amorphous glass to crystal nucleation and the subsequent growth is reviewed.
... Glass sealants has been used to join similar or dissimilar materials [13] in the fields of solid oxide fuel cells [14,15] and microelectronics [16,17]. In our previous works, sapphire substrates were welded through a 50 nm titanium thin film [18], as well as through a glass thin film [19,20]. Silica glass substrates were also welded through glass thin films [21] acting as absorbers, by employing a ns pulsed laser. ...
... From EDX line scan analysis (Fig. 10), the incorporation of the glass components into the solder can be deduced. This behavior has been observed in previous publications, as well [20,21]. Interfacial reactions between titanium and glass have been reported [44,45]. ...
... In order to fulfill these conditions, rapidly crystallizing glasses are required. Choosing a homogeneous glass as sealing material is not suitable, because all glass compositions with that CTE usually show softening temperatures much lower than 900°C [14,15]. Hence, for high temperature seals with the required CTE, a glass which can be densified at temperatures below 1250°C is necessary and from which subsequently a phase with high CTE can be crystallized. ...
Article
Full-text available
A glass with the composition 61 CaO·30 Al2O3·9 SiO2 was studied with respect to its crystallization behavior and its suitability as a rapidly crystallizing material for laser sealing. The glass was studied by differential scanning calorimetry; from the profiles recorded, Avrami activation energies and Avrami coefficients were calculated. The latter are in the range between 0.99 and 1.55 which is supposedly attributed to sole surface crystallization. During thermal treatment as well as during laser sealing, Ca12Al14O33, CaAl2O4 and Ca3Al2O6 are formed. These phases were also observed in SEM micrographs as evidenced by electron backscatter diffraction from the attributed Kikuchi patterns. Transmission electron microscopy showed a crystallized CaO- and SiO2-enriched interface which strongly adhered to the Al2O3 ceramic. The porosity of the crystallized seal was in the order of few percent. The studied glass proved suitable as crystallizing seal for rapid laser sealing.
Article
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The crystallization of fresnoite (Ba2TiSi2O8) in supercooled melts can be triggered by the reduction of Ti4+ to Ti3+. We address the question of whether Ti3+ is incorporated into the fresnoite crystal structure during such electrochemically induced crystallization. Fresnoite crystals grown from a variety of highly reduced melts were studied by electron energy-loss spectroscopy in order to distinguish between Ti3+ and Ti4+ contents in the corresponding phases. Although the presence of Ti3+ strongly promotes crystallization, Ti3+ is not incorporated into the fresnoite crystal lattice in a significant amount (less than 10 at.%) but, at sufficiently high Ti3+ concentrations, forms a previously unreported barium oxotitanate(III) containing trivalent titanium only. Since, in the fresnoite crystal structure, Ti4+ solely adopts an unusual fivefold coordination, we also discuss the energy-loss near-edge structure (ELNES) of the Ti L2,3 ionization edge and compare it with the Ti L2,3 ELNES of tetrahedrally and octahedrally coordinated Ti4+.
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Fresnoite (Ba2TiSi2O8–BTS) thin films were grown on fused quartz, silicon (100), MgO (100), and a-plane sapphire by pulsed laser deposition, and crystallized by subsequent thermal or flash lamp annealing. The corresponding texture evolution of the BTS thin films was studied by X-ray diffraction. The preferential (001) texture of the crystallised BTS films was found to be most pronounced on sapphire substrates. The broad photoluminescence band of the BTS thin films depends only weakly on temperature. The intensity of the BTS luminescence can be as high as that of the most efficient oxide scintillator materials. In order to qualify the fresnoite thin films for photonic applications, we demonstrate infrared-laser direct writing in amorphous BTS films which allows a local crystallisation and patterning. A subsequent considerable enhancement of luminescence intensity can be applied for UV-sensitive marking of nearly any object.
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The crystallization of fresnoite (Ba2TiSi2O8) in supercooled melts can be triggered by the reduction of Ti4+ to Ti3+. We address the question of whether Ti3+ is incorporated into the fresnoite crystal structure during such electrochemically induced crystallization. Fresnoite crystals grown from a variety of highly reduced melts were studied by electron energy-loss spectroscopy in order to distinguish between Ti3+ and Ti4+ contents in the corresponding phases. Although the presence of Ti3+ strongly promotes crystallization, Ti3+ is not incorporated into the fresnoite crystal lattice in a significant amount (less than 10at.%) but, at sufficiently high Ti3+ concentrations, forms a previously unreported barium oxotitanate(III) containing trivalent titanium only. Since, in the fresnoite crystal structure, Ti4+ solely adopts an unusual fivefold co-ordination, we also discuss the energy-loss near-edge structure (ELNES) of the Ti L2,3 ionization edge and compare it with the Ti L2,3 ELNES of tetrahedrally and octahedrally coordinated Ti4+.
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Authors tried to butt-weld a mild steel plate to a magnesium alloy plate by the solid state welding using a rotating pin. This study investigated the effects of a pin rotating speed, the position for the pin axis to be plunged (pin offset) on the strength and the microstructure of the joint. The main results obtained are as follows. Butt-welding of a steel plate to a magnesium alloy plate was easily and successfully achieved. The maximum tensile strength of a joint reached about 70% of the magnesium base metal tensile strength and the fracture path was along the joint interface. When a pin rotating speed was slow, some defects appeared in the magnesium matrix due to the insufficient plasticization of the magnesium. The joint strength increased with the pin rotating speed. This seems to be because the plasticization of the magnesium was increased and the pressure for pushing the plasticized magnesium onto an activated faying surface of the steel increased. However, the excessive increase of the pin rotating speed caused the ignition of the magnesium, resulting in the decrease of a joint strength. At the pin offset of 0.1mm toward steel, steel fragments scattered in the magnesium matrix in the form of a small piece that had no influence to the joint strength. By contrast, larger offsets over 0.2mm produced the steel fragment continuous and parallel to the weld interface in the magnesium matrix, and the joint strength decreased.
Conference Paper
In this paper, we report a method to bond silicon and glass wafers directly using localized laser heating (pulsed Nd:YAG laser, 1064 nm, 12 ns). Laser energy was transmitted through the glass wafer and absorbed by the silicon wafer, resulting in a localized high temperature area. Pressure was applied upon the silicon and glass wafers to ensure immediate contact and good heat conduction between them. Scanning electron microscope (SEM) and chemical analysis were used to study bonding area and bonding mechanism. Numerical simulation was carried out in parallel using finite element method to predict the local temperature change of both the glass wafer and the silicon wafer during laser heating. The simulation was validated to some extent by the matching of melting time, which was obtained by using an additional probing laser (He-Ne, 633 nm, 20 mW) during the transient melting and re-solidification of the silicon. This bonding process is conducted locally while the entire wafer is maintained at room temperature, making it advantageous over traditional anodic bonding or fusion bonding.
Article
BaTiAl 6O 12 crystallizes in the orthorhombic system with unit-cell dimensions a = 4.862(1), b = 7.136(2), c = 13.598(3) Å and space group Pnnm with z = 2. The structure was solved by Patterson and Fourier methods. Of the 714 unique reflections measured by counter techniques, 253 with I > 3 σ( I) were used in the least-squares refinement of the model to a conventional R of 0.042 ( Rw = 0.037). The structure of BaTiAl 6O 12 consists of octahedra (mixed Ti and Al occupancy) and tetrahedra (all Al) in a three-dimensional array forming tunnels in which barium ions are located. The octahedra form ribbons or strings by edge-sharing to one another, and are corner-shared to tetrahedra. The corner-shared array of tetrahedra links the ribbons of octahedra. Ba 3TiAl 10O 20 crystallizes in the monoclinic system with unit-cell dimensions a = 15.631(4), b = 11.373(2), and c = 4.981(1) Å, β = 107.77(2)°, and space group {C2}/{m} with z = 2. The structure was solved by Patterson and Fourier methods and of the 2909 unique reflections measured by counter techniques, 1561 with I > 3 σ( I) were used in the least-squares refinement of the model to a conventional R of 0.046 ( Rw = 0.042). The structure consists of sheets of corner-shared tetrahedra linked by parallel ribbons of edge-shared octahedra. (The octahedra are of mixed Ti and Al occupancy.) The barium ions are located in tunnels of two different types.
Article
Fresnoite Ba2TiSi2O8 (BTS) thin films were grown and crystallized in situ using pulsed laser deposition (PLD) with CO2 laser direct heating of the a-plane sapphire (1 1 0) substrates up to 1250 °C. Starting with 775 °C growth temperature, (0 0 1)- and (1 1 0)-textured BTS and BaTiO3 phases, respectively, could be assigned in the films, and the typical fern-like BTS crystallization patterns appear. For higher process temperatures of 1100 to 1250 °C, atomically smooth, terraced surface of the films was found, accompanied by crystalline high-temperature phases of Ba–Ti–Si oxides. HAADF micrographs taken in both scanning transmission electron microscopy and energy-dispersive x-ray spectrometry mode show details of morphology and elemental distribution inside the films and at the interface. To balance the inherent Si deficiency of the BTS films, growth from glassy BTS × 2 SiO2 and BTS × 2.5 SiO2 targets was considered as well. The latter targets are ideal for PLD since the employed glasses possess 100% of the theoretical density and are homogeneous at the atomic scale.
Article
The Ba2TiSi2O8 (BTS) is a well known piezoelectric, ferroelectric and non-linear crystal. In this work, nanocrystals of BTS have been obtained by different thermal treatments of precursor glasses. The glasses were fabricated from BaO–TiO2–SiO2 and doped with Dy2O3 using the melt quenching method. Thermal treatment in an electrical furnace at 740 °C was used to obtain transparent glass ceramic samples, which are formed by an amorphous matrix containing BTS nanocrystals, with an average size of 35 nm confirmed by X-ray diffraction. Moreover, a localized area in the precursor glass has been irradiated by continuous wave (c.w.) Ar-laser or femtosecond (fs) pulsed laser. Evidence of the changes induced by laser irradiation is confirmed by spectroscopic comparison of irradiated regions with the precursor glass and glass ceramic samples. The emission spectra corresponding to the Dy3+: 4F9/2 → 6H13/2 (578 nm), 4F9/2 → 6H11/2 (670 nm) and 4F9/2 → 6H9/2 (757 nm) transitions were obtained under laser excitation at 473 nm. These measurements confirm the incorporation of the Dy3+ ions into the BTS nanocrystals which produces an enhancement of luminescence and makes it an attractive material for optical amplification.
Article
The amperometric glucose biosensor utilizing glucose oxidase immobilized in polymerized polypyrrole film was constructed on multi-walled carbon nanotube (CNT) modified C-MEMS electrode. Dense coverage of CNTs was successfully integrated on the surface of the C-MEMS, which greatly increased the effective electro-active surface area thus resulting in higher loading of enzyme. Electrochemical studies reveal that the C-MEMS/CNT based glucose sensor displays linear response for glucose concentrations from 5 to 80 mM with a sensitivity of 97.3 mA M−1 cm−2 with the response time less than 10 s. The detecting sensitivity was proved to be increased more than 50 times compared with 1.7 mA M−1 cm−2 for the blank C-MEMS one.
Article
Sapphire and hot-pressed 99% Al2O3 ceramic were joined using Ag70.5Cu27.5Ti2 bracing filler metal in a vacuum electric furnace. The interface reaction between Ag70.5Cu27.5Ti2 alloy and sapphire, hot-pressed Al2O3 ceramic during brazing is reported. The joining strength and the airtight of the specimen are influenced by the surface condition of Al2O3 ceramic and the factor of active brazing condition.
Article
Ablation of sapphire on different crystallographic facet planes by single and multiple laser pulses irradiation was carried out with a femtosecond pulsed laser operating at a wavelength of 780 nm and a pulse width of 164 fs. The quality and morphology of the laser ablated sapphire surface were evaluated by scanning electron microscopy and atomic force microscopy. For single laser pulse irradiation, two ablation phases were observed, which have a strong dependency on the pulse energy. The volume of the ablated craters kept an approximately linear relationship with the pulse energy. The threshold fluences of the two ablation phases on different crystallographic facet planes were calculated from the relationship between the squared diameter of the craters and pulse energy. With multiple laser pulses irradiation, craters free of cracks were obtained in the ‘gentle’ ablation phase. The threshold fluence for N laser pulses was calculated and found to decrease inversely to the number of laser pulses irradiating on the substrate surface due to incubation effect. The depth of the craters increased with the number of laser pulses until reaching a saturation value. The mechanism of femtosecond laser ablation of sapphire in two ablation phases was discussed and identified as either phase explosion, Coulomb explosion or particle vaporization. The choice of crystallographic facet plane has little effect on the process of femtosecond laser ablation of sapphire when compared with the parameters of the femtosecond laser pulses, such as pulse energy and number of laser pulses. In the ‘gentle’ ablation phase, laser-induced periodic surface structures (LIPSS) with a spatial period of 340 nm were obtained and the mechanism of the LIPSS formation is discussed. There is a potential application of the femtosecond laser ablation to the fabrication of sapphire-based devices.
Article
The Al/Ni multilayers were characterized and diffusion bonding of TiAl intermetallics to TiC cermets was carried out using the multilayers. The microstructure of Al/Ni multilayers and TiAl/TiC cermet joint was investigated. The layered structures consisting of a Ni3(AlTi) layer, a Ni2AlTi layer, a (Ni,Al,Ti) layer and a Ni diffusion layer were observed from the interlayer to the TiAl substrate. Only one AlNi3 layer formed at the multilayer/TiC cermet interface. The reaction behaviour of Al/Ni multilayers was characterized by means of differential scanning calorimeter (DSC) and X-ray diffraction. The initial exothermic peak of the DSC curve was formed due to the formation of Al3Ni and Al3Ni2 phases. The reaction sequence of the Al/Ni multilayers was Al3Ni → Al3Ni2 → AlNi → AlNi3 and the final products were AlNi and AlNi3 phases. The shear strength of the joint was tested and the experimental results suggested that the application of Al/Ni multilayers improved the joining quality.
Article
Emerging technologies embrace the very early stages of socio-technological evolution. Despite their appealing nature, they have been loosely defined and operationalized. In particular, operationalization approaches based on bibliometric methods have often tended to emphasize the exponential growth and the potential impacts of emerging technologies while overlooking their inherent uncertainty and ‘fluidity’. The purpose of this paper is to contribute to the operationalization of emerging technologies by presenting an approach for quantitatively interpreting technologies of an emerging nature along both dimensions. We do so by looking into the dynamic properties of scientific knowledge bases in terms of their rates and directions of change. Our approach integrates bibliometric indicators, social network analysis and multivariate statistical methods on scientific publications, and their citing and cited references. The empirical case of micro/nanoelectromechanical systems technologies (MEMS/NEMS), which embrace micro- and nano-sensors and actuators, is used. A total of thirteen MEMS/NEMS technologies are evaluated. Overall, our results provide a quantitative framework for discerning technological emergence through the evaluation of the dynamics of scientific knowledge bases. These results highlight the coupled intense patterns of growth and cognitive fluidity characterizing emerging technologies. We also provide a glimpse into the difficulties encountered by specific nanotechnology fields in bringing forward nano-enabled devices.
Article
The nonlinear optical susceptibilities of fresnoite, relative to d36 of KH2PO4, have been determined to be: d31=±9.3,d33=∓1.63,d15=±10.3(λ=1.064 microm). The double refraction in the visible spectrum is too small to allow phase matched second harmonic generation.
Article
Three new ternary compounds, BaTi5Al2O14, BaTiAl6O12, and Ba3TiAl10O20 have been identified in the system BaO-TiO2-Al2O3 and were characterized by X-ray powder diffraction. BaTi5Al2O14 has a tetragonal unit-cell with a = 7.025 Å, c = 10.156 Å, and Z = 2. The compound melts incongruently at 1500°C. BaTiAl6O12 also has a tetragonal unit-cell with a = 10.07 Å, c = 9.107 Å, and Z = 4. The compound melts incongruently at 1560°C. Ba3TiAl10O20 has an orthorhombic unit-cell with a = 14.854 Å, b = 11.356 Å, c = 4.986 Å, and Z = 2. The compound dissociates in the solid state at 1440°C to yield BaTiAl6O12 and BaAl2O4.
Article
We present a novel room temperature bonding technique using reactive multilayer Ni/Al foils as local heat sources to heat intermediate adhesion layers and thus bond silicon wafers to form wafer level package. Exothermic reactions in Ni/Al multilayer foils were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD measurements showed that the dominant product after the exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be -57.9 kJ/mol. Two bonding approaches were realized. One used AuSn solder as an intermediate layer to bond two silicon wafers together; the other approach conducted bonding between Parylene-C and silicon wafers with a thin Parylene-C coating. Either silicon or Parylene-C was torn when the bond was forcefully broken, indicating a strong bond was achieved. Moreover, leakage test in isopropanol alcohol (IPA) showed that the joints possessed good hermeticity to liquid. Numerical simulation results demonstrated that both localized heating and rapid cooling occurred during the bonding process, which made reactive foil bonding an ideal method for MEMS wafer level packaging applications.
Article
A reliable composite metal seal comprising both intermetallic compounds (IMC) and solder joints, which are formed by transient liquid phase bonding and soldering respectively, is proposed and demonstrated in wafer level bonding experiments. Hermetic sealing is demonstrated on 8-in. wafers using low volume Cu/Sn materials at process temperatures as low as 280°C. It is shown that the composite seal is stable when subjected to temperatures of 250°C, and that it provides better hermeticity and reliability than an IMC seal alone.
Article
Nanocrystallized glasses with the composition of (50-x)BaO-xTiO 2-50SiO2 (x=10, 15, 16.7 and 20) have been prepared by heattreatment at Tx (crystallization onset temperature) for 3 h, and their optical properties, photoluminescence (PL), XRD and Raman spectra have been examined. The absorption edges of the glasses were red-shifted and the absorption coefficient increased with an increase of TiO2. The glass subjected to the heat-treatment showed a dense formation of Ba 2TiSi2O8 crystals. The XRD and Raman results show that the nanocrystallized glasses formed fresnoite phase up to TiO 2 concentrations of 15 mol%. Furthermore, blue luminescence with a peak at the wavelength of around 470 nm was observed in the nanocrystallized glass, demonstrating the optical multifunctional nanocrystallized material such as non-linear optics and photo-luminescence. It is thought that the blue luminescence from the Ba2TiSi2O8 nanocrystallized glass originated from the presence of Ti1+ incorporated into the fresnoite-type structure.
Article
We have developed an innovative rapid laser direct joining process of metal and plastic lap plates without adhesives or glues. The joints made between a Type 304 stainless steel plate and a polyethylene terephthalate (PET) plastic sheet of 30 mm width possessed tensile shear loads of about 3000 N. Transmission electron microscope photographs of the joint demonstrated that Type 304 and the PET were bonded on the atomic, molecular or nanostructural level through a Cr oxide film. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Article
A femtosecond laser with 800nm, 250kHz and 150fs has been used to irradiate Eu3+-doped BaO–TiO2–SiO2 glasses. It is found from micro-Raman spectra and optical microscope that crystalline dots and lines are formed around the focal point of the femtosecond laser beam. Both blue emission at 400nm due to the second harmonic generation and red emission due to the transitions of Eu3+ are observed from the irradiation region with the precipitation of Ba2TiSi2O8 crystal. The mechanism of the observed phenomenon is discussed.
Article
Sapphire single crystal [α-Al2O3(0001)] samples were treated by irradiation with Ti+ ions in the energy range 0.5-7.0 keV at 25°C and 750°C under UHV conditions for total doses of 1016 Ti+/cm2. These Ti treated sapphire samples were studied by ex situ X-ray photoelectron spectroscopy (XPS) depth profiling and by atomic force microscopy (AFM). Aluminum in the oxidation states Al0,3+,x+, where 0 < x < 3, and titanium in the oxidation states Ti0,2+,3+,4+ were found to coexist throughout the implanted region, with variation of their relative amounts along the depth distribution. The AFM measurements showed that there was minimal change in surface morphology following implantation at all conditions, indicating that the sapphire surface has enough resiliency to retain its original surface morphology despite the keV ion impacts.
Article
Fresnoite is a pyrosilicate containing a pyramidal TiO5 group. From vibrational spectroscopy the axial TiO distance is shown to be short. The luminescence of the TiO5 group shows a very long decay time (3.5 ms) which is ascribed to the spin selection rule and lack or orbital overlap.
Article
The SrO–Al2O3–B2O3–SiO2 glasses doped with different concentrations of MnO were synthesized and their spectroscopic studies were carried out. The UV–vis absorption spectrum of these glasses exhibited a broad band centered at about 428 nm identified as being due as being to 6A1(S) → 4T2 (G) tetrahedral transition of Mn2+ ions. With the increase in the concentration of manganese oxide, a new band at about 525 nm corresponding to 6A1g(S) → 4T1g(G) octahedral transition of Mn2+ ions is developed. The photoluminescence spectra of these glasses excited at 420 nm exhibited two luminescence bands at about 540 (green emission) and 632 nm (red emission). As the concentration of MnO is increased up to 1.5 mol%, the red emission band is observed to grow at the expense of green band. The analysis of these results coupled with FT-IR and ESR spectral results has indicated that in the glass containing 1.5 mol% of MnO, the manganese ions predominantly occupy octahedral positions and are found to be responsible for rich red emission.
Article
Crystalline fresnoite (Ba2TiSi2O8), attributed glasses and glass ceramics of the systems Ba2TiSi2O8+xSiO2 (x=0, 0.75) and Sr2TiSi2O8 have been studied by X-ray photoelectron spectroscopy (XPS). To understand the process of crystallization, changes in coordination of the constituting elements have been studied in glassy and crystalline samples. It was observed that changes in coordination took place at the Ti-sites. It is shown that in fresnoite glass (Ba2TiSi2O8), fivefold coordinated Ti predominates (≈60%) while fourfold (≈25%) and sixfold (≈15%) coordinated Ti is present as well. In another series of experiments, the effect of reducing Ti(IV) to Ti(III) by adding carbon to the glass batches was studied. It was shown that XPS could resolve the two valency states and gave Ti(IV)/Ti(III) ratios equal to that obtained from thermogravimetry. By comparison of all samples measured, XPS-line positions for different coordinations and valencies of Ti in these samples are given.
Article
In this paper we describe compounds A3BC10O20 (A = Sr, Ba, Pb; B = Ti, Ge, Sn; and C = Al, Ga). The crystal structure of Ba3TiAl10O20 has been determined by neutron powder profile refinement. The luminescence of these compounds has been investigated. Apart from the titanate luminescence of Ba3TiAl10O20, these compounds show a semiconductor type of luminescence.
Article
Crystallization behavior of the fresnoite-type Ba2TiGe2O8 (BTG) with a large optical nonlinearity has been examined in the BaO-TiO2-GeO2 glass thin film fabricated by a RF sputtering technique and the corresponding glass (same composition of thin film, i.e., 28BaO-22TiO2-50GeO2). Both the glass thin film and the corresponding glass were crystallized by the heat-treatment, keeping a good transparency. Initial formation of BTG phase followed by the BaGe4O9 phase was confirmed in the both glass samples. In addition, the BTG crystallites in the both glass samples indicated the preferential (211) orientation. Crystallization behavior confirmed in this study was quite different from the previous study about the 30BaO-15TiO2-55GeO2 glass.
Article
We examined the laser-induced crystallization to form the fresnoite type Ba2TiGe2O8 crystal line patterns in transition metal ion doped BaO–TiO2–GeO2 glass. Ba2TiGe2O8 crystal line was written in 0.6FeO–33.3BaO–16.7TiO2–50GeO2 glass by continuous wave yttrium–aluminum–garnet (YAG) laser irradiation. We obtained polarization dependence of Raman spectra in crystal line pattern. Second harmonic generation (SHG) indicated unique fringe patterns from Ba2TiGe2O8 crystal lines.
Article
Polar, nonferroelectric (BaxSr2-x)TiSi2O8 glass ceramics with highly oriented crystallites were prepared by a gradient temperature heat treatment technique. The crystallization mechanism and microstructures of (BaxSr2-x)TiSi2O8 glass ceramics were investigated by means of differential thermal analysis, x-ray diffraction and scanning electron microscopy, and the dielectric, piezoelectric and pyroelectric properties were investigated for various compositions. The results show that polar (BaxSr2-x)TiSi2O8 glass ceramics have a low dielectric constant and a high hydrostatic figure of merit dh×gh=~2500. This high hydrostatic figure of merit, along with other unique characteristics, such as no aging or depoling problems and good stability at high temperatures, high pressure, and in harsh environments, makes (BaxSr2-x)TiSi2O8 glass ceramics attractive for use as hydrophones and high temperature infrared detectors.
Article
Amorphous thin films of Hf–Al–O (with atomic ratio of Al/Hf of about 1.4) were deposited on (100) p-Si substrates by pulsed-laser deposition using a HfO2 and Al2O3 composite target. Transmission electron microscopy was employed for a detailed study of the interfacial reaction between the Hf–Al–O films and the Si substrates. Islands of Hf silicide formed from interfacial reaction were observed on the surface of the Si substrate. The formation of Hf silicide is attributed to the presence of Al oxide in the films that triggers the reaction between Hf atoms in the amorphous Hf–Al–O films and Si under an oxygen deficient condition. The impact of silicide formation on the electrical properties was revealed by high-frequency capacitance–voltage (C–V) measurements on metal–oxide–semiconductor capacitors. The observed abnormal C–V curve due to interfacial reaction was discussed. © 2003 American Institute of Physics.
Article
We report on the joining of dissimilar transparent materials based on localized melting and resolidification of the materials only around the focal volume due to nonlinear absorption of focused femtosecond laser pulses. We demonstrate the joining of borosilicate glass and fused silica, whose coefficients of thermal expansion are different. The joint strength and the transmittance through joint volume were investigated by varying the translation velocity of the sample and the pulse energy of the irradiated laser pulses.
Article
A glass of the composition 2SrO?TiO2?2.75SiO2 was melted. Cooled samples were polished and thermally annealed at 970 uC for 10 min to 20 h to achieve surface crystallisation of Sr2TiSi2O8 fresnoite. At the surface, the crystals were immediately oriented with their crystallographic c-axes perpendicular to the surface. Crystal growth occurred in the form of similarly oriented structures. Very homogeneous structures were also observed but they fray into areas of higher orientation diversity at some distance from the surface. The crystallised areas were highly permeated by nanoscale inclusions of residual glass. Kinetic selection occurs and leads to a preferred orientation with the crystallographic c-axis tilted by about 43 ¡ 5u from the surface normal after about 300 mm. Crystal growth is not governed by the fastest growing crystallographic direction or the formation of a diffusion barrier, but rather by the ability to circumvent the residual glass.
Article
Innovation in implantable drug delivery devices is needed for novel pharmaceutical compounds such as certain biologics, gene therapy, and other small molecules that are not suitable for administration by oral, topical, or intravenous routes. This invasive dosing scheme seeks to directly bypass physiological barriers presented by the human body, release the appropriate drug amount at the site of treatment, and maintain the drug bioavailability for the required duration of administration to achieve drug efficacy. Advances in microtechnologies have led to novel MEMS-enabled implantable drug infusion pumps with unique performance and feature sets. In vivo demonstration of micropumps for laboratory animal research and preclinical studies include acute rapid radiolabeling, short-term delivery of nanomedicine for cancer treatment, and chronic ocular drug dosing. Investigation of MEMS actuators, valves, and other microstructures for on-demand dosing control may enable next generation implantable pumps with high performance within a miniaturized form factor for clinical applications.
Article
We synthesized spinel ZnAl2O4 film on α-Al2O3 substrate using a solid-phase reaction between the pulsed-laser-deposited ZnO film and α-Al2O3 substrate. Auger electron spectroscopy showed that the atomic distribution in the spinel ZnAl2O4 was inhomogeneous, which indicated that the reaction was diffusion controlled. Based on X-ray fluorescence measurements, the apparent growth activation energy of ZnAl2O4 was determined as 504 kJ/mol. X-ray diffractometry spectra showed that, as the growth temperature increased, the ZnAl2O4 film became disoriented from the single (111) orientation. The ZnAl2O4 (333) diffraction peak shifted toward a small angle, and its full-width at half-maximum decreased from 1.30° to 0.37°. At the growth temperature of 1100°C, the morphology of the ZnAl2O4 was initially transformed from islands to stick structures, then to bulgy-line structures with increased growth time. X-ray diffractometry spectra showed that these transformations were correlated with changes of ZnAl2O4 orientation.
Article
BaTi2O5 thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (Tsub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on Tsub, and the b-axis oriented BaTi2O5 thin film could be obtained at Tsub = 973–1023 K. The surface morphology of the films was different with changing Tsub, which showed a dense surface with an elongated granular texture at Tsub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi2O5 thin films were highly transparent with an optical transmittance of ∼70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for Tsub = 923 K to 3.56 eV for Tsub = 1023 K.
Article
Al2O3:Si,Ti, prepared under oxidizing condition at high temperature, gives PL emission around 430 nm when excited with 240 nm. The Al2O3:C, TL/OSL phosphor, also shows emission around 430 nm, which corresponds to characteristic emission of F-center. Thus, to identify the exact nature of luminescent center in Al2O3:Si,Ti, fluorescence lifetime measurement studies were carried out along with the PL,TL and OSL studies. The PL and TL in Al2O3:Si,Ti show emission around 430 nm and the time-resolved fluorescence studies show lifetime of about 43 μs for the 430 nm emission, which is much smaller than the reported lifetime of ∼35 ms for the 430 nm emission (F-center emission) in Al2O3:C phosphor. Therefore, the emission observed in Al2O3:Si,Ti phosphor was assigned to Ti4+ charge transfer transition. Fluorescence studies of Al2O3:Si,Ti do not show any traces of F and F+ centers. Also, Ti4+ does not show any change in the charge state after gamma-irradiation. On the basis of the above studies, a mechanism for TSL/OSL process in Al2O3:Si,Ti is proposed.
Chapter
As far back as the tenth century BC , sapphires and rubies were valued as gems on the level of diamonds. Artificial sapphires were first used in jewelry art as well, but from the beginning of the twentieth century sapphire has played an increasingly significant role in engineering. At present one can hardly find a branch of science or technology where this crystal is not used. Demand for sapphire grows year after year, almost exponentially. Devices and their components applied in aviation and space industries, in chemical processing, and in many other fields are simultaneously subjected to the action of aggressive media, radiation, high temperatures, pressures, and mechanical loads. Under such extreme conditions any material is prone to intense corrosion and erosion. High-strength alloys have reached the practical limits of their capabilities. The structure of polycrystalline materials and consequently their mechanical properties essentially change under extreme conditions due to recrystallization, corrosion of the grain boundaries, and so forth The rate of diffusion via the grain boundaries grow with increasing temperature, radiation dose, and operation time. As a result, the material breaks down. Such drawbacks are inherent in sapphire components and assemblies to a considerably lesser extent.