Inside Silicon Research Articles

Direct observation and quantification of nanosecond laser induced amorphization inside silicon

The nature of structural changes of nanosecond laser modification inside silicon is investigated. Raman spectroscopy and transmission electron microscopy measurements of cross sections of the modified channels reveal highly localized crystal deformation. Raman spectroscopy measurements prove the existence of amorphous silicon inside nanosecond laser induced modifications, and the percentage of amorphous silicon is calculated based on the Raman spectrum. For the first time, the high-resolution transmission electron microscopy images directly show the appearance of amorphous silicon inside nanosecond laser induced modifications, which corroborates the indirect measurements from Raman spectroscopy. The laser modified channel consists of a small amount of amorphous silicon embedded in a disturbed crystal structure accompanied by strain. This finding may explain the origin of the positive refractive index change associated with the written channels that may serve as optical waveguides.

Practical Challenges in Nanofluid Convective Heat Transfer Inside Silicon Microchannels

Despite numerous studies on nanofluids in microchannel heat sinks (MCHSs), they are not yet commercialized due to long-term stability issues and high maintenance costs. Therefore, this study explores the impact of nanofluids and nanoparticle clustering on single-phase convective heat transfer inside microchannels under laminar conditions. Water and commercially available water-based nanosuspensions, including Al2O3-water (30–60 nm), TiO2-water (5–30 nm), and polystyrene-water (50 nm), are circulated through silicon MCHS having rectangular channels integrated into a closed flow loop. To assess the in situ and real-time nanoparticle clustering during heat transfer experiments, Light Extinction Spectroscopy (LES) is applied as a non-intrusive measurement technique on nanofluids without any fluid sampling. Our findings reveal the appearance of nanofluid discoloration with no measurable increase in heat transfer coefficient. This unexpected change is attributed to the interplay of abrasion, erosion, and corrosion phenomena, likely triggered by the clustering of nanoparticles within the silicon microchannels—a novel insight into the complex dynamics of nanofluid behavior (an increase in the De Brouckere mean diameter from 11 nm to 107.3 nm over a 2.5 h period for TiO2 nanoparticles). The resulting material loss could not be mitigated by altering the nanoparticle material, which may impede heat transfer enhancement under tested conditions.

(Invited) Modeling Aging Induced Volume Change of Porous Electrodes

Automotive battery manufacturers are improving individual cell and overall battery pack design by focusing on increasing performance, durability, and range while reducing cost. However, the coupled mechano-electrochemical phenomena caused by lithiation-based active material volume change significantly complicates the adoption and design of advanced battery systems, especially those with a high degree of volume change. Battery pack engineers mitigate the effects of volume change using a variety of methods, though, these mitigation strategies rely on extensive testing with anytime a change in chemistry or pack design is made. Therefore, it is critical to understand the link between active material volume change and the effect on multiple scales.In this work, we add to a previously developed mechano-electrochemical model to more practically understand the impact of irreversible active material volume change, primarily assigned to SEI layer growth. Initially, a representative volume element model was incorporated into the model geometry to more realistically understand how cell components mechanically interact with each other. This allows for a better understanding of how individual components, including foam added to mitigate volume change, and the overall cell reacts to the active material volume change at the anode electrode during lithiation to generate realistic predictions of pressure and porosity changes. Second, the volume change tied to structural changes for graphite was tied to cell level volume change. Then, a mechano-electrochemical measurement apparatus was developed and used to verify simulation results. This work improves on past efforts and considers the impact of aging on volume change at the particle level, and extends the growth as an irreversible source term to impact the overall cell expansion.References Pereira, D. J., Aleman, A. M., Weidner, J. W., & Garrick, T. R. (2022). “A Mechano-Electrochemical Battery Model that Accounts for Preferential Lithiation Inside Blended Silicon Graphite (Si/C) Anodes.” Journal of The Electrochemical Society, 169(2), 020577.Pereira, D. J., Fernandez, M. A., Streng, K. C., Hou, X. X., Gao, X., Weidner, J. W., & Garrick, T. R. (2020). “Accounting for Non-Ideal, Lithiation-Based Active Material Volume Change in Mechano-Electrochemical Pouch Cell Simulation.” Journal of The Electrochemical Society, 167(8), 080515.Pereira, D. J., Weidner, J. W., & Garrick, T. R. (2019). “The effect of volume change on the accessible capacities of porous silicon-graphite composite anodes.” Journal of The Electrochemical Society, 166(6), A1251.Garrick, T. R., Higa, K., Wu, S. L., Dai, Y., Huang, X., Srinivasan, V., & Weidner, J. W. (2017). “Modeling battery performance due to intercalation driven volume change in porous electrodes.” Journal of The Electrochemical Society, 164(11), E3592.Garrick, T. R., Huang, X., Srinivasan, V., & Weidner, J. W. (2017). “Modeling volume change in dual insertion electrodes.” Journal of The Electrochemical Society, 164(11), E3552.Garrick, T. R., Dai, Y., Higa, K., Srinivasan, V., & Weidner, J. W. (2016). “Modeling battery performance due to intercalation driven volume change in porous electrodes.” Ecs Transactions, 72(11), 11.Garrick, T. R., Kanneganti, K., Huang, X., & Weidner, J. W. (2014). “Modeling volume change due to intercalation into porous electrodes.” Journal of The Electrochemical Society, 161(8), E3297.

Enhanced Catalytic Palladium Embedded Inside Porous Silicon for Improved Hydrogen Gas Sensing

In this work, we reported on room temperature porous silicon (PS) and embedding PS using simple and economical techniques of electrochemical etching and thermal evaporation. The PS substrate was prepared using the technique of electrochemically etching the n-type Si (100) wafer at a constant current density of 10 mA/cm2 for 10 min under the illumination of incandescent white light. After PS formation, Ge pieces were thermally evaporated onto the two PS substrates in a vacuum condition. This was then followed by the deposition of the ZnO layer onto the Ge/PS substrate by the same method using commercial 99.9% pure ZnO powders. The three samples were identified as PS, Ge/PS and ZnO/Ge/PS samples, respectively. Pd finger contacts were deposited on the PS and embedding PS (Ge/PS and ZnO/Ge/PS) to form Pd on PS hydrogen sensors using RF magnetron sputtering. SEM and EDX suggested the presence of substantial Ge and ZnO inside the uniform circular pores for Ge/PS and ZnO/Ge/PS samples, respectively. Raman spectra showed that good crystalline Ge and ZnO nanostructures embedded inside the pores were obtained. For hydrogen sensing, Pd on ZnO/Ge/PS Schottky diode exhibited a dramatic change of current after exposure to H2 as compared to PS and Ge/PS devices. It is observed that the sensitivity increased exponentially with the hydrogen flow rate for all the sensors. The ZnO/Ge/PS showed more sensitivity towards H2 than that of PS and Ge/PS especially at high flow rate of H2 with higher current gain (69.11) and shorter response (180 s) and recovery times (30 s).

Cascading shocks and heated electrons probability distributions on the surface and inside silicon target irradiated by femto-second laser pulse

The femtosecond laser effects on shock cascades at the surface as well as inside the silicon target are studied by using the two temperature method (TTM) for simulating the non-equilibrium system. The laser wavelength is varied from 500 to 1500 nm and significant modifications are noted in the shock cascades, an electron temperature probability distributions, cumulative probability distributions, and electron-lattice equilibration temperature. It is found that the highest and lowest electron temperatures occurred for 500 and 1500 nm lasers respectively. To explain silicon heating sensitivity to the interacting laser wavelength, fundamental parameters including reflection coefficient, absorption, extinction coefficients, refractive index, specific heat, thermal conductivity, electron-hole collision frequency, and lattice-electron coupling coefficient are comprehensively studied. The temperature distributions included non-Gaussian tails and cumulative probability distributions included shock-like jumps at distinctly different temperatures for considered five types of laser wavelengths. The findings of this study can be helpful for understanding silicon crystals interaction with an ultra-short and an intense femtosecond laser pulses.

Targeted Positioning of Quantum Dots Inside 3D Silicon Photonic Crystals Revealed by Synchrotron X-ray Fluorescence Tomography.

It is a major outstanding goal in nanotechnology to precisely position functional nanoparticles, such as quantum dots, inside a three-dimensional (3D) nanostructure in order to realize innovative functions. Once the 3D positioning is performed, the challenge arises how to nondestructively verify where the nanoparticles reside in the 3D nanostructure. Here, we study 3D photonic band gap crystals made of Si that are infiltrated with PbS nanocrystal quantum dots. The nanocrystals are covalently bonded to polymer brush layers that are grafted to the Si–air interfaces inside the 3D nanostructure using surface-initiated atom transfer radical polymerization (SI-ATRP). The functionalized 3D nanostructures are probed by synchrotron X-ray fluorescence (SXRF) tomography that is performed at 17 keV photon energy to obtain large penetration depths and efficient excitation of the elements of interest. Spatial projection maps were obtained followed by tomographic reconstruction to obtain the 3D atom density distribution with 50 nm voxel size for all chemical elements probed: Cl, Cr, Cu, Ga, Br, and Pb. The quantum dots are found to be positioned inside the 3D nanostructure, and their positions correlate with the positions of elements characteristic of the polymer brush layer and the ATRP initiator. We conclude that X-ray fluorescence tomography is very well suited to nondestructively characterize 3D nanomaterials with photonic and other functionalities.

A Mechano-Electrochemical Battery Model that Accounts for Preferential Lithiation Inside Blended Silicon Graphite (Si/C) Anodes

Automotive manufacturers are currently working to produce commercially-viable electric trucks, driving the need to develop batteries that are higher in energy density and lower in cost. To realize this, cell designers have introduced blended silicon-graphite anodes to combine the high energy density of silicon with the stability and relatively lower mechanical degradation of graphite. As more blended anodes with high lithiation-based volume change are considered, the need to simultaneously account for mechanical and electrochemical phenomena increases. In this study, the focus is to learn how preferential lithiation (caused by differing equilibrium potentials and other intercalation kinetics of the two blended active materials) impact the coupled electrochemical performance and mechanical phenomenon at the electrode and cell scales. To do this, adaptations of previous modeling methods are proposed that treat the active materials as separate particles, representing the mixing of two active materials powders within a slurry. For comparison, the historically-used assumption is shown, where the blended active materials lithiate uniformly. The resulting simulations show that preferential lithiation of the blended materials will have a significant impact on both electrochemical and mechanical phenomena. Discussion is also provided with regard to C-rate, blended electrode composition, and other mechano-electrochemical behavior.

Transverse ultrafast laser inscription in bulk silicon

In-volume ultrafast laser direct writing of silicon is generally limited by strong nonlinear propagation effects preventing the production of modifications. By using advantageous spectral, temporal, and spatial conditions, we demonstrate that modifications can be repeatably produced inside silicon. Our approach relies on irradiation at $\ensuremath{\approx}2$ $\ensuremath{\mu}\mathrm{m}$ wavelength with temporally distorted femtosecond pulses. These pulses are focused in a way that spherical aberrations of different origins mutually balance, as predicted by point spread function analyses and in good agreement with nonlinear propagation simulations. We also establish the laws governing modification growth on a pulse-to-pulse basis, which allows us to demonstrate transverse inscription inside silicon with various line morphologies depending on the irradiation conditions. We finally show that the production of single-pulse repeatable modifications is a necessary condition for reliable transverse inscription inside silicon.

Development of the ReaxFF Reactive Force Field for Cu/Si Systems with Application to Copper Cluster Formation during Cu Diffusion Inside Silicon

Development of the ReaxFF Reactive Force Field for Cu/Si Systems with Application to Copper Cluster Formation during Cu Diffusion Inside Silicon

Aluminum modified silicon surfaces: Optical and electrical characterization

A set of silicon substrates was treated depositing aluminum on its polished surface and then sintered for a long time up to 8 h. After aluminum removal, the formation of rectangular pits like inverted pyramids was observed. The analysis made by Rutherford backscattering spectroscopy reveals that during the sintering process aluminum and oxygen diffuses inside silicon and the amount of the first one inside silicon is practically proportional to the sintering time, but oxygen achieves its maximum concentration for the sample sintered during four hours. According to the electrical characterization made by fitting the current–potential and the impedance electrochemical curves, oxygen is a key factor in the diminution of the Schottky barrier height, which in the framework of the impedance analysis, is interpreted as a lowering of the surface resistance for charge transfer. According to the X-ray diffraction, this fact is associated with the surface lattice modification which yields surface strain due to oxygen presence, whereas aluminum was identified as an important factor in reducing the silicon complex refractive index insofar aluminum increases.

Modeling interactions of dsDNA inside single-walled nanotubes

Nanotubes (NTs) have unique physicochemical properties, and therefore, they have found various applications, especially in medicine and electronics. This study models the interaction of a double-stranded deoxyribonucleic acid (dsDNA) molecule inside carbon, boron nitride, silicon, molybdenum disulphide (MoS2), and tungsten disulphide (WS2) single-walled NTs by using the Lennard-Jones potential and a continuum approach. Explicit analytical expressions for the interaction energy are obtained to determine the preferred minimum-energy position of the dsDNA molecule inside the NTs. Furthermore, the encapsulation behavior of the dsDNA molecule inside these five types of NTs is compared. The results indicate that the encapsulation of the dsDNA molecule inside the NTs depends on the NT diameter. The results also indicate that DNA can be encapsulated inside NTs for applications in biosensors, drug and gene delivery systems, and biomaterials as well as for detecting biomolecules for biotechnology and medical science applications.

Inscribing diffraction grating inside silicon substrate using a subnanosecond laser in one photon absorption wavelength

Using focused subnanosecond laser pulses at 1.064,upmu hbox {m} wavelength, modification of silicon into opaque state was induced. While silicon exhibits one-photon absorption at this wavelength, the modification was induced inside 300,upmu hbox {m}-thick silicon substrate without damaging top or bottom surfaces. The depth range of the focus position was investigated where inside of the substrate can be modified without damaging the surfaces. Using this technique, diffraction gratings were inscribed inside silicon substrate. Diffraction from the gratings were observed, and the diffraction angle well agreed with the theoretical value. These results demonstrate that this technique could be used for fabricating infrared optical elements in silicon.

Optical modulation at the interface between silicon and a phase change material

Thin layers of phase change materials are investigated theoretically and experimentally as way to modulate the properties of light interacting with silicon at a planar interface. By inducing a phase transition in vanadium dioxide films, the resulting changes in refractive index modulate the injection of light into silicon and the ejection out of it. Internal reflection of light propagating inside silicon causes the polarization state to be altered during the phase transition. Possible applications to silicon photonics are discussed.

Improved Evaluation of Magnetic Loss Inside Silicon Steel Laminations Under 3-D Multi-Harmonic Magnetizations

An improved method is presented to study the efficient numerical modeling of stray-field loss in magnetic shielding excited by a 3-D harmonic magnetic field. The experimental platform is established to obtain the magnetic properties and loss model of the silicon steel lamination under harmonic magnetizations. Experimental determination is improved for more accurate stray-field loss based on the engineering-oriented model TEAM Problem 21c-M1. Prediction and evaluation of stray-field loss and additional iron loss due to harmonic excitations are achieved by special treatment of material properties in the numerical calculation of the harmonic magnetic field.

Ultrafast Laser Writing Deep inside Silicon with THz-Repetition-Rate Trains of Pulses.

Three-dimensional laser writing inside silicon remains today inaccessible with the shortest infrared light pulses unless complex schemes are used to circumvent screening propagation nonlinearities. Here, we explore a new approach irradiating silicon with trains of femtosecond laser pulses at repetition rates up to 5.6 THz that is order of magnitude higher than any source used for laser processing so far. This extremely high repetition rate is faster than laser energy dissipation from microvolume inside silicon, thus enabling unique capabilities for pulse-to-pulse accumulation of free carriers generated by nonlinear ionization, as well as progressive thermal bandgap closure before any diffusion process comes into play. By space-resolved measurements of energy delivery inside silicon, we evidence changes in the interplay between detrimental nonlinearities and accumulation-based effects. This leads to a net increase on the level of space-time energy localization. The improvement is also supported by experiments demonstrating high performance for 3D laser writing inside silicon. In comparison to repeated single pulses, irradiation with trains of only four-picosecond pulses with the same total energy leads to an apparent decrease of the energy threshold for modification and drastic improvements on the repeatability, uniformity, and symmetricity of the produced features. The unique benefits of THz bursts can provide a new route to meet the challenge of 3D inscription inside narrow bandgap materials.

Three-dimensional laser writing inside silicon using THz-repetition-rate trains of ultrashort pulses

Three-dimensional laser writing inside silicon remains today inaccessible with the shortest infrared light pulses unless complex schemes are used to circumvent screening propagation nonlinearities. Here, we explore a new approach irradiating silicon with trains of femtosecond laser pulses at repetition rates up to 5.6 THz. This extremely high repetition rate is faster than laser energy dissipation from microvolume inside silicon, thus enabling unique capabilities for pulse-to-pulse accumulation of free carriers generated by nonlinear ionization, as well as progressive thermal bandgap closure before any diffusion process comes into play. By space-resolved measurements of energy delivery inside silicon, we evidence a net increase on the level of space-time energy localization. The improvement is also supported by experiments demonstrating an apparent decrease of the energy threshold for modification and drastic improvements on the repeatability, uniformity, and symmetricity of the produced features. The unique benefits of THz bursts can provide a new route to meet the challenge of 3D inscription inside narrow bandgap materials.

Competing Nonlinear Delocalization of Light for Laser Inscription Inside Silicon with a 2- µ m Picosecond Laser

Recent advances in ultrafast laser 3D writing offer direct fabrication of in-chip silicon microsystems, but this technique remains extremely challenging, because of propagation nonlinearities that limit energy localization inside narrow-band-gap materials. This study examines the complex energy flux and subsequent unusual modification of silicon due to intense picosecond pulses from a thulium-doped fiber laser. The best conditions for reliable data inscription deep inside silicon are identified, which is a critical step toward engineering solutions to this problem. Also, the wavelength used here points to facing the next challenges associated with materials of even narrower band gap.

Far-Field Superoscillatory Metamaterial Superlens

We demonstrate a metamaterial superlens: a planar array of discrete subwavelength metamolecules with individual scattering characteristics tailored to vary spatially to create subdiffraction superoscillatory focus of, in principle, arbitrary shape and size. Metamaterial free-space lenses with previously unattainable effective numerical apertures – as high as 1.52 – and foci as small as 0.33λ in size are demonstrated. Super-resolution imaging with such lenses is experimentally verified breaking the conventional diffraction limit of resolution and exhibiting resolution close to the size of the focus. Our approach will enable far-field label-free super-resolution nonalgorithmic microscopies at harmless levels of intensity, including imaging inside cells, nanostructures, and silicon chips, without impregnating them with fluorescent materials.

Characterization and control of laser induced modification inside silicon

Internal modification of silicon is important for wafer stealth dicing. In this paper, the authors report experimental and simulation results of three-dimensional modification inside silicon wafers using laser pulses with 1.55 μm wavelength and 3.5 ns pulse duration. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without damaging the front and back surface. Cross sections of these modifications are observed after cleaving the samples and are further analyzed after mechanical polishing followed by chemical etching. The shape of the modification is found to depend on the input beam shape, laser power, and scanning speed. With proper conditions, a nearly circular modification is obtained, which has potential application for waveguide writing inside silicon.

Laser-written depressed-cladding waveguides deep inside bulk silicon

Laser-written waveguides created inside transparent materials are important components for integrated optics. Here, we demonstrate that subsurface modifications induced by nanosecond pulses can be used to fabricate tubular-shaped “in-chip” or buried waveguides inside silicon. We first demonstrate single-line modifications, which are characterized to yield a refractive index depression of ≈2×10−4 compared to that of the unmodified crystal. Combining these in a circular geometry, we realized 2.9-mm-long, 30-μm core-diameter waveguides inside the wafer. The waveguides operate in a single-mode regime at a wavelength of 1300 nm. We use near- and far-field imaging to confirm waveguiding and for optical index characterization. The waveguide loss is estimated from scattering experiments as 2.2 dB/cm.