Wandering principal optical axes in van der Waals triclinic materials.

Nature is abundant in material platforms with anisotropic permittivities arising from symmetry reduction that feature a variety of extraordinary optical effects. Principal optical axes are essential characteristics for these effects that define light-matter interaction. Their orientation - an orthogonal Cartesian basis that diagonalizes the permittivity tensor, is often assumed stationary. Here, we show that the low-symmetry triclinic crystalline structure of van der Waals rhenium disulfide and rhenium diselenide is characterized by wandering principal optical axes in the space-wavelength domain with above π/2 degree of rotation for in-plane components. In turn, this leads to wavelength-switchable propagation directions of their waveguide modes. The physical origin of wandering principal optical axes is explained using a multi-exciton phenomenological model and ab initio calculations. We envision that the wandering principal optical axes of the investigated low-symmetry triclinic van der Waals crystals offer a platform for unexplored anisotropic phenomena and nanophotonic applications.

Reconfigurable VO2 metasurfaces with hybrid electro-optical control: manipulating THz radiation with 0.3 W/cm2 light.

Dynamicallyprogrammable metasurfaces capable of manipulating terahertz (THz) wavefronts in various manners depending on external controls are highly desired for next-generation wireless communication systems and new tools for THz diagnostics. Such metasurfaces may utilize the insulator-to-metal transition in V O 2, which can be induced both electrically and optically. Optical control is especially convenient for individual addressing to each meta-atom, but it is hampered by the high optical switching threshold of V O 2. We experimentally realize V O 2-based THz metasurfaces with hybrid electro-optical control when the metasurface is brought close to the transition point by an almost-threshold current, and then is easily switched by unfocused continuous-wave light. We were able to control the metasurface THz transmission by 0.4W/c m 2 near-IR light, while purely optical switching required tightly focused light with an intensity of >3×105 W/c m 2. After correcting for the fact that a tightly focused spot dissipates heat easier, we estimate that the optical switching threshold reduction due to the electric current alone is ∼2 orders of magnitude. Finally, coating the metasurface with Au nanoparticles further reduced the threshold by 30% due to plasmonic effects.

van der Waals Materials for Overcoming Fundamental Limitations in Photonic Integrated Circuitry.

With the advance of on-chip nanophotonics, there is a high demand for high-refractive-index and low-loss materials. Currently, this technology is dominated by silicon, but van der Waals (vdW) materials with a high refractive index can offer a very advanced alternative. Still, up to now, it was not clear if the optical anisotropy perpendicular to the layers might be a hindering factor for the development of vdW nanophotonics. Here, we studied WS2-based waveguides in terms of their optical properties and, particularly, in terms of possible crosstalk distance. Surprisingly, we discovered that the low refractive index in the direction perpendicular to the atomic layers improves the characteristics of such devices, mainly due to expanding the range of parameters at which single-mode propagation can be achieved. Thus, using anisotropic materials offers new opportunities and novel control knobs when designing nanophotonic devices.

Design of silicone interfaces with antibacterial properties.

Silicone implants are widely used for plastic or reconstruction medical applications. However, they can cause severe infections of inner tissues due to bacterial adhesion and biofilm growth on implant surfaces. The development of new antibacterial nanostructured surfaces can be considered as the most promising strategy to deal with this problem. In this article, we studied the influence of nanostructuring parameters on the antibacterial properties of silicone surfaces. Nanostructured silicone substrates with nanopillars of various dimensions were fabricated using a simple soft lithography technique. Upon testing of the obtained substrates, we identified the optimal parameters of silicone nanostructures to achieve the most pronounced antibacterial effect against the bacterial culture of Escherichia coli. It was demonstrated that up to 90% reduction in bacterial population compared to flat silicone substrates can be achieved. We also discussed possible underlying mechanisms behind the observed antibacterial effect, the understanding of which is essential for further progress in this field.

Dual-Band Coupling of Phonon and Surface Plasmon Polaritons with Vibrational and Electronic Excitations in Molecules.

Strong coupling (SC) between light and matter excitations bears intriguing potential for manipulating material properties. Typically, SC has been achieved between mid-infrared (mid-IR) light and molecular vibrations or between visible light and excitons. However, simultaneously achieving SC in both frequency bands remains unexplored. Here, we introduce polaritonic nanoresonators (formed by h-BN layers on Al ribbons) hosting surface plasmon polaritons (SPPs) at visible frequencies and phonon polaritons (PhPs) at mid-IR frequencies, which simultaneously couple to excitons and molecular vibrations in an adjacent layer of CoPc molecules, respectively. Employing near-field optical nanoscopy, we demonstrate the colocalization of near fields at both visible and mid-IR frequencies. Far-field transmission spectroscopy of the nanoresonator structure covered with a layer of CoPc molecules shows clear mode splittings in both frequency ranges, revealing simultaneous SPP-exciton and PhP-vibron coupling. Dual-band SC may offer potential for manipulating coupling between exciton and molecular vibration in future optoelectronics, nanophotonics, and quantum information applications.

Nanoscale Doping and Its Impact on the Ferroelectric and Piezoelectric Properties of Hf0.5Zr0.5O2.

Ferroelectric hafnium oxide thin films-the most promising materials in microelectronics' non-volatile memory-exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf0.5Zr0.5O2 capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf0.5Zr0.5O2 thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf0.5Zr0.5O2 has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is -0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf0.5Zr0.5O2 via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films.

Late dislocation of the capsular bag-intraocular lens-modified capsular tension ring complex after knotless transscleral suturing using 9-0 polypropylene.

We report a case of late breakage of a 9-0 polypropylene transscleral suture used for fixation of a dislocated capsular bag-intraocular lens-modified capsular tension ring complex in a 52-year-old woman with Marfan syndrome. Breakage occurred despite use of a cow-hitch technique for external and internal fixation. We believe breakage was caused by the suture chafing on the sharp edges of the modified capsular tension ring eyelet. Cross-sectional analysis of Malyugin-modified capsular tension rings from two different manufacturers revealed a difference with respect to radius of curvature. Suturing intraocular implants with relatively sharp edges may cause suture breakage; further studies are needed to identify the critical parameters for the surface quality of sutured intraocular implants.

Five-year results of non-penetrating deep sclerectomy with demineralized cancellous bone xenogenically derived collagen glaucoma implant.

PURPOSE: To investigate the long-term effectiveness of non-penetrating deep sclerectomy (NPDS) with xenogenically derived cancellous bone collagen glaucoma implant (XCB-CGI) implantation in patients with primary open-angle glaucoma (POAG). MATERIALS AND METHODS: Retrospective chart review of patients with POAG stages 2 and 3 was treated with NPDS and XCB-CGI. Follow-up was at 6 months, 1, 2, 3, 4 and 5 years after surgery. Main outcomes were intraocular pressure (IOP) and medication burden. Secondary outcomes were visual acuity, corneal hysteresis (CH), visual field (VF) and optical coherence tomography (OCT) parameter analysis. RESULTS: Among 71 patients (71 eyes), the mean age was 72.7 ± 9.8. Average initial IOP was 27.7 ± 7.9 and average initial med load was 2.36 ± 0.99. At 6 months, 1, 2, 3, 4 and 5 years, the average IOP was 14.9 ± 3.3 mm Hg (46.2% reduction), 15.3 ± 4.0 mm Hg (44.7% reduction), 14.2 ± 3.8 mm Hg (48.7% reduction), 15.2 ± 3.3 mm Hg (45.0% reduction), 15.5 ± 3.3 mm Hg (44.0% reduction) and 14.2 ± 2.8 mm Hg (48.7% reduction), respectively. In 5 years, the success rate was 34% and 67%, without, and with medications (1.8 ± 0.8 meds required), respectively. Visual acuity was not significantly different (P > .05) at all follow-up visits from baseline. Mean CH increased by 2.1 ± 0.8 (P = .05). No glaucomatous deterioration of the VF and OCT parameters was detected in 56 eyes at the 5-year follow-up. CONCLUSION: NPDS with XCB-CGI implantation is an effective procedure to normalize the level of IOP, stabilize glaucomatous changes and decrease the number of meds needed for glaucoma control.

Nanoscale Tailoring of Ferroelectricity in a Thin Dielectric Film.

New opportunities in the development and commercialization of novel photonic and electronic devices can be opened following the development of technology-compatible arbitrary-shaped ferroelectrics encapsulated in a passive environment. Here, we report and experimentally demonstrate nanoscale tailoring of ferroelectricity by an arbitrary pattern within the nonferroelectric thin film. For inducing the ferroelectric nanoregions in the nonferroelectric surrounding, we developed a technology-compatible approach of local doping of a thin (10 nm) HfO2 film by Ga ions right in the thin-film capacitor device via focused ion beam implantation. Local crystallization of the doped regions to the ferroelectric structural phase occurs during subsequent annealing. The remnant polarization of the HfO2:Ga regions reached 13 µC/cm2 at a Ga concentration of 0.6 at. %. Piezoresponse force microscopy over the capacitor device revealed an asymmetrical switching of ferroelectric domains within written HfO2:Ga patterns after capacitor switching, which was attributed to the mechanical stress across the doped film. The lateral spatial resolution of ferroelectricity tailoring is found to be ∼200 nm, which enables diverse applications in switchable photonics and microelectronic memories.

RF-MEMS Monolithic K and Ka Band Multi-State Phase Shifters as Building Blocks for 5G and Internet of Things (IoT) Applications.

RF-MEMS, i.e., Micro-Electro-Mechanical Systems (MEMS) for Radio Frequency (RF) passive components, exhibit interesting characteristics for the upcoming 5G and Internet of Things (IoT) scenarios, in which reconfigurable broadband and frequency-agile devices, like high-order switching units, tunable filters, multi-state attenuators, and phase shifters will be necessary to enable mm-Wave services, small cells, and advanced beamforming. In particular, satellite communication systems providing high-speed Internet connectivity utilize the K and Ka bands, which offer larger bandwidth compared to lower frequencies. This paper focuses on two design concepts of multi-state phase shifter designed and manufactured in RF-MEMS technology. The networks feature 4 switchable stages (16 states) and are developed for the K and Ka bands. The proposed phase shifters are realized in a surface micromachining RF-MEMS technology and the experimentally measured parameters are compared with Finite Element Method (FEM) multi-physical electromechanical and RF simulations. The simulated phase shifts at both the operating bands fit well the measured value, despite the measured losses (S21) are larger than 5-7 dB if compared to simulations. However, such a non-ideality has a technological motivation that is explained in the paper and that will be fixed in the manufacturing of future devices.

Graphene-Supported Thin Metal Films for Nanophotonics and Optoelectronics.

Graphene-metal hybrid nanostructures have attracted considerable attention due to their potential applications in nanophotonics and optoelectronics. The output characteristics of devices based on such nanostructures largely depend on the properties of the metals. Here, we study the optical, electrical and structural properties of continuous thin gold and copper films grown by electron beam evaporation on monolayer graphene transferred onto silicon dioxide substrates. We find that the presence of graphene has a significant effect on optical losses and electrical resistance, both for thin gold and copper films. Furthermore, the growth kinetics of gold and copper films vary greatly; in particular, we found here a significant dependence of the properties of thin copper films on the deposition rate, unlike gold films. Our work provides new data on the optical properties of gold and copper, which should be considered in modeling and designing devices with graphene-metal nanolayers.

Ferroelectricity in Hf0.5Zr0.5O2 Thin Films: A Microscopic Study of the Polarization Switching Phenomenon and Field-Induced Phase Transformations.

Because of their full compatibility with the modern Si-based technology, the HfO2-based ferroelectric films have recently emerged as viable candidates for application in nonvolatile memory devices. However, despite significant efforts, the mechanism of the polarization switching in this material is still under debate. In this work, we elucidate the microscopic nature of the polarization switching process in functional Hf0.5Zr0.5O2-based ferroelectric capacitors during its operation. In particular, the static domain structure and its switching dynamics following the application of the external electric field have been monitored with the advanced piezoresponse force microscopy (PFM) technique providing a nm resolution. Separate domains with strong built-in electric field have been found. Piezoresponse mapping of pristine Hf0.5Zr0.5O2 films revealed the mixture of polar phase grains and regions with low piezoresponse as well as the continuum of polarization orientations in the grains of polar orthorhombic phase. PFM data combined with the structural analysis of pristine versus trained film by plan-view transmission electron microscopy both speak in support of a monoclinic-to-orthorhombic phase transition in ferroelectric Hf0.5Zr0.5O2 layer during the wake-up process under an electrical stress.

Effect of Polarization Reversal in Ferroelectric TiN/Hf0.5Zr0.5O2/TiN Devices on Electronic Conditions at Interfaces Studied in Operando by Hard X-ray Photoemission Spectroscopy.

Because of their compatibility with modern Si-based technology, HfO2-based ferroelectric films have recently attracted attention as strong candidates for applications in memory devices, in particular, ferroelectric field-effect transistors or ferroelectric tunnel junctions. A key property defining the functionality of these devices is the polarization dependent change of the electronic band alignment at the metal/ferroelectric interface. Here, we report on the effect of polarization reversal in functional ferroelectric TiN/Hf0.5Zr0.5O2/TiN capacitors on the potential distribution across the stack and the electronic band line-up at the interfaces studied in operando by hard X-ray photoemission spectroscopy. By tracking changes in the position of Hf0.5Zr0.5O2 core-level lines with respect to those of the TiN electrode in both short- and open-circuit configurations following in situ polarization reversal, we derive the conduction band offset to be 0.7 (1.0) eV at the top and 1.7 (1.0) eV at the bottom interfaces for polarization, pointing up (down), respectively. Energy dispersive X-ray spectroscopy profiling of the sample cross-section in combination with the laboratory X-ray photoelectron spectroscopy reveal the presence of a TiOx/TiON layer at  both interfaces. The observed asymmetry in the band line-up changes in the TiN/Hf0.5Zr0.5O2/TiN memory stack is explained by different origin of these oxidized layers and effective pinning of polarization at the top interface. The described methodology and first experimental results are useful for the optimization of HfO2-based ferroelectric memory devices under development.

Femtosecond Laser-Assisted Intraocular Lens Fragmentation: Low Energy Transection.

PURPOSE: To describe a case of femtosecond laser-assisted hydrophobic intraocular lens transection. METHODS: Case report. RESULTS: Femtosecond laser-assisted transection of a one-piece acrylic hydrophobic intraocular lens for explantation via a small surgical incision was successfully performed with low energy parameters. CONCLUSIONS: This case illustrates a novel and effective clinical application of the femtosecond laser. [J Refract Surg. 2017;33(9):646-648.].

Crossbar Nanoscale HfO2-Based Electronic Synapses.

Crossbar resistive switching devices down to 40 × 40 nm(2) in size comprising 3-nm-thick HfO2 layers are forming-free and exhibit up to 10(5) switching cycles. Four-nanometer-thick devices display the ability of gradual switching in both directions, thus emulating long-term potentiation/depression properties akin to biological synapses. Both forming-free and gradual switching properties are modeled in terms of oxygen vacancy generation in an ultrathin HfO2 layer. By applying the voltage pulses to the opposite electrodes of nanodevices with the shape emulating spikes in biological neurons, spike-timing-dependent plasticity functionality is demonstrated. Thus, the fabricated memristors in crossbar geometry are promising candidates for hardware implementation of hybrid CMOS-neuron/memristor-synapse neural networks.

Ultralow-Loss CMOS Copper Plasmonic Waveguides.

Surface plasmon polaritons can give a unique opportunity to manipulate light at a scale well below the diffraction limit reducing the size of optical components down to that of nanoelectronic circuits. At the same time, plasmonics is mostly based on noble metals, which are not compatible with microelectronics manufacturing technologies. This prevents plasmonic components from integration with both silicon photonics and silicon microelectronics. Here, we demonstrate ultralow-loss copper plasmonic waveguides fabricated in a simple complementary metal-oxide semiconductor (CMOS) compatible process, which can outperform gold plasmonic waveguides simultaneously providing long (>40 µm) propagation length and deep subwavelength (∼λ(2)/50, where λ is the free-space wavelength) mode confinement in the telecommunication spectral range. These results create the backbone for the development of a CMOS plasmonic platform and its integration in future electronic chips.