Publication database
The industrial advancement of high-efficiency silicon solar cells increasingly depends on precise laser patterning and reliable silver-free metallization. For tunnel oxide passivated contact (TOPCon) devices, laser contact opening on the rear side faces a critical trade-off: achieving sufficient surface roughening for robust electroplated adhesion while minimizing thermal damage to the sensitive passivating stack. Here, we demonstrate a transformative ultraviolet femtosecond laser strategy that effectively decouples these conflicting requirements for damage-free rear-side metallization. Atomic-resolution transmission electron microscopy systematically reveals the single-pulse ablation behavior, identifying an effective SiNx removal threshold of 0.105 J/cm2 and a passivating contact damage threshold above 0.17 J/cm2, thus defining a viable processing window for selective dielectric opening with preserved electrical integrity. Building on this, we introduce a novel twin-pulse irradiation approach that exploits nonlinear energy accumulation to generate functional laser-induced periodic surface structures (LIPSS) for potential enhanced mechanical anchoring, while highly confining substrate damage to a depth of ∼30 nm. This enables ultra-narrow grid fingers (7.1 μm) and exceptionally low specific contact resistivity (0.35 mΩ cm2) in Ni electroplated contacts. These results highlight ultraviolet femtosecond lasers as a scalable, high-precision tool for next-generation silver-free TOPCon metallization, paving the way for cost-effective mass production and further efficiency gains in silicon photovoltaics.
Laser-induced graphene (LIG) enables rapid conversion of polymer substrates into conductive carbon materials. In this study, nitrogen-containing carbon nanomaterials were fabricated on polyetherimide (PEI) substrates using empirical screening of two specific process points. The resulting materials were characterized using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy to correlate structural features with electron-transfer behavior. Raman and XPS analyses showed different structure and morphology depending on irradiation regime. The carbon materials with a higher sp3 fraction (≈55–59%), larger in-plane crystallite size (La up to 8.0 nm), and pronounced π–π* shake-up satellites indicated enhanced graphitic ordering when a shorter nanosecond laser was used. These structural differences resulted in substantially lower charge-transfer resistance (0.53–0.79 kΩ·cm3) and larger electroactive surface areas for the porous electrodes compared with foam structured carbon nanomaterials. The results show that, under the selected fabrication conditions, variations in laser processing parameters correspond to differences in graphitic ordering and electron-transfer properties in PEI-derived laser-induced carbon materials.
Photoacoustic tomography is a contrast agent-free imaging technique capable of visualizing blood vessels and tumor-associated vascularization in breast tissue. While sophisticated breast imaging systems have been recently developed, there is yet much to be gained in imaging depth, image quality and tissue characterization capability before clinical translation is possible. In response, we have developed a hybrid photoacoustic and ultrasound tomographic system (PAM3). The photoacoustic component has for the first time, in a full-view hemispherical breast system, three-dimensional multi-wavelength imaging capability and implements substantial technical advancements in critical hardware and software sub-systems. The ultrasound component enables three-dimensional ultrasound (computed) tomography from both reflected and transmitted signals from which we currently extract an image of the sound speed. For the first time, in vivo sound speed images were reconstructed using a fully 3D full-waveform inversion (FWI) algorithm, which demonstrated excellent quantitative as well as spatial accuracy. The sound speed image of the breast was then incorporated in photoacoustic reconstruction to correct for acoustic inhomogeneities, enabling accurate target recovery. The results demonstrate identification of blood vessels to depths of up to 48 mm, with a more uniform field of view than hitherto, and an isotropic spatial resolution comparable to the in-plane resolution of clinical breast Magnetic Resonance Imaging. The in vivo performance achieved, and the complementary diagnostic value of interrogating angiogenesis-driven optical contrast as well as tumor mass sound speed contrast, gives confidence in the system’s clinical potential.
Breast cancer screening with mammography is less effective in women with dense breast tissue, prompting the use of ultrasound (US) imaging. While two- (2D) and three-dimensional (3D) US improve cancer detection, their low specificity leads to frequent unnecessary biopsies. Operator dependence on 2D US has led to the development of 3D automated breast volume scanners (ABVS), but challenges remain in distinguishing benign from malignant lesions. We developed a 3D photoacoustic and ultrasound (PAUS)–ABVS system that integrates a large field-of-view, 768-element transducer to improve diagnostic accuracy. In a clinical study of 61 patients with 36 benign and 30 malignant lesions, multispectral photoacoustic imaging was used to measure blood volume and oxygen saturation within lesions. When combined with standard US BI-RADS (breast imaging reporting and data system) scores, the system achieved a sensitivity of 96.7% and specificity of 66.7%. This performance matched the best outcomes of 2D PAUS and outperformed conventional US. Our results suggest that the PAUS-ABVS can support more accurate breast cancer diagnosis while reducing unnecessary biopsies.
Direct-writing submicron copper circuits on glass with laser precision – without lithography, vacuum deposition, or etching – represents a transformative step in next-generation microfabrication. We present a high-resolution, maskless method for metallizing glass using ultrashort pulse Bessel beam laser processing, followed by silver ion activation and electroless copper plating. The laser-modified glass surface hosts nanoscale chemical defects that promote the in situ reduction of Ag+ to metallic Ag0 upon exposure to AgNO3 solution. These silver seeds act as robust catalytic and adhesion sites for subsequent copper growth. Using this approach, we demonstrate circuit traces as narrow as 0.7 µm, featuring excellent uniformity and adhesion. Compared to conventional redistribution-layer (RDL) and under-bump-metallization (UBM) techniques, this process eliminates multiple lithographic and vacuum-based steps, significantly reducing process complexity and production time. The method is scalable and adaptable for applications in transparent electronics, fan-out packaging, and high-density interconnects.
Image-guided phototheranostics, including photothermal therapy and photoacoustic imaging using plasmonic nanoparticles, has attracted attention due to its remarkable photothermal conversion effects. In particular, considering the several benefits of biocompatibility, unique plasmon resonance, and tunable optical properties, gold nanoparticles of various shapes have been widely utilized as phototheranostic agents. However, applications in the near-infrared window have been limited due to the tendency of anisotropic gold nanoparticles to transform into spherical shapes under repetitive laser irradiation, which cause a shift in the localized surface plasmon resonance peak and reduces photothermal stability. To address these limitations, we introduce an Fe layer between Au nanodiscs to synthesize Au/Fe/Au trilayer uniform structured nanodiscs (AuFeAuNDs) using nanoimprint lithography. This approach aims to improve photostability and endow a magnetic targeting ability, enabling more accurate spatiotemporal regulation. The AuFeAuNDs primarily function as photothermal therapy agents and also serve as chemodynamic agents via the Fenton reaction specifically within the tumor microenvironment, which induces ferroptosis. Moreover, the AuFeAuNDs trigger immunogenic cell death following photothermal therapy. This study demonstrates applications of magnetic-targeted AuFeAuNDs for photoacoustic imaging-guided, spatiotemporal-controlled photothermal therapy, chemodynamic therapy, and immune modulation to bolster anti-tumor immune responses in cancer treatment.
This paper presents the precipitation of copper (Cu) from a surfactant-added glyoxylic acid copper (GACu) complex ink, in femtosecond laser multiple pulse-induced thermochemical processes to achieve high-resolution Cu direct writing. The study specifically examines the impact of the surfactant, n-decanoylsarcosine sodium, (NDSS), on the nonlinear optical absorption properties of GACu complex ink. Findings reveal that the addition of NDSS did not alter the molecule binding and single-photon absorption properties of the ink. However, nonlinear optical absorptions evaluated through the open aperture z-scan method displayed differences between the NDSS-added and non-added GACu complex inks when subjected to femtosecond laser pulse irradiation. These results suggest that Cu nanoparticles were generated from the GACu complex ink via nucleation and surfactant-mediated growth, leading to the saturable absorption of the subsequent irradiated laser pulses. By employing a pulse repetition frequency of 5 MHz and a pulse number of 2 × 104, a minimum dot diameter of 1.6 ± 0.1 μm with stable reproductivity was attained with NDSS-added ink, corresponding to the laser spot diameter, without excessive precipitation due to thermal diffusion. This comprehensive understanding of the surfactant NDSS and pulse number effects on the Cu precipitation process holds potential for the direct writing of various materials. Furthermore, this insight offers a novel approach for affordable and scalable manufacturing with minimized environmental impact.
Teflon, or polytetrafluoroethylene (PTFE), is popular for high-frequency applications due to its low dielectric constant and high chemical resistance, but these properties also make it difficult to metallize for electronic uses because its inertness impedes metal adhesion and deposition. We present the design, simulation, and measurement of Sierpinski antenna for radio frequency energy harvesting, manufactured using the Selective Surface Activation by Laser (SSAIL) technique on flexible Teflon sheet. The results demonstrate that SSAIL is an excellent method for fabricating antennas on flexible surfaces, offering high performance and reliability. Electromagnetic simulations and experimental validations confirm the effectiveness of this approach for next-generation flexible communication devices and electronics.
The increasing demand for miniaturized and high-performance consumer electronics has driven advancements in packaging solutions, including the transition to glass interposers. One of the critical aspects of the development is the fabrication of high-density through-glass vias (TGVs). This article presents the formation of TGVs in various glass substrates using an industrial femtosecond laser FemtoLux 30 operating in different operation modes – single-pulse, MHz burst, GHz burst and MHz+GHz burst modes. By employing burst mode and advanced machining methods such as bottom-up milling – TGVs fabrication is possible. With specific parameter sets TGVs with aspect ratios exceeding 1:80 was achieved, with drilling times as low as 350 ms. Additionally, to address current challenges in making electric traces on substrates, it introduces Selective Surface Activation Induced by Laser (SSAIL) as a unique complementary metallization technology, enabling direct copper deposition on different materials like ceramic, plastics and most importantly – glass, for complete packaging workflows. The findings demonstrate the potential of the FemtoLux femtosecond laser as a high-throughput and precise solution not only for TGV fabrication, but also for Selective Surface Activation Induced by Laser (SSAIL) based metallization - supporting next-generation semiconductor advanced packaging solutions.
Femtosecond lasers have proven themselves in processing various materials with high precision and quality. Glass is one of the materials that benefits most from ultra-short pulses, which process it without the significant thermal effects that would otherwise cause catastrophic damage. This application note shows how the FemtoLux 30 combines various processing modes to manufacture free-form micro-optical elements with high precision and high throughput.