Far-Infrared Near-Field Optical Imaging and Kelvin Probe Force Microscopy of Laser-Crystallized and -Amorphized Phase Change Material Ge3Sb2Te6.

Chalcogenide phase change materials reversibly switch between non-volatile states with vastly different optical properties, enabling novel active nanophotonic devices. However, a fundamental understanding of their laser-switching behavior is lacking and the resulting local optical properties are unclear at the nanoscale. Here, we combine infrared scattering-type scanning near-field optical microscopy (SNOM) and Kelvin probe force microscopy (KPFM) to investigate four states of laser-switched Ge3Sb2Te6 (as-deposited amorphous, crystallized, reamorphized, and recrystallized) with nanometer lateral resolution. We find SNOM to be especially sensitive to differences between crystalline and amorphous states, while KPFM has higher sensitivity to changes introduced by melt-quenching. Using illumination from a free-electron laser, we use the higher sensitivity to free charge carriers of far-infrared (THz) SNOM compared to mid-infrared SNOM and find evidence that the local conductivity of crystalline states depends on the switching process. This insight into the local switching of optical properties is essential for developing active nanophotonic devices.

In3SbTe2 as a programmable nanophotonics material platform for the infrared.

The high dielectric optical contrast between the amorphous and crystalline structural phases of non-volatile phase-change materials (PCMs) provides a promising route towards tuneable nanophotonic devices. Here, we employ the next-generation PCM In3SbTe2 (IST) whose optical properties change from dielectric to metallic upon crystallization in the whole infrared spectral range. This distinguishes IST as a switchable infrared plasmonic PCM and enables a programmable nanophotonics material platform. We show how resonant metallic nanostructures can be directly written, modified and erased on and below the meta-atom level in an IST thin film by a pulsed switching laser, facilitating direct laser writing lithography without need for cumbersome multi-step nanofabrication. With this technology, we demonstrate large resonance shifts of nanoantennas of more than 4 µm, a tuneable mid-infrared absorber with nearly 90% absorptance as well as screening and nanoscale "soldering" of metallic nanoantennas. Our concepts can empower improved designs of programmable nanophotonic devices for telecommunications, (bio)sensing and infrared optics, e.g. programmable infrared detectors, emitters and reconfigurable holograms.

Advanced Optical Programming of Individual Meta-Atoms Beyond the Effective Medium Approach.

Nanometer-thick active metasurfaces (MSs) based on phase-change materials (PCMs) enable compact photonic components, offering adjustable functionalities for the manipulation of light, such as polarization filtering, lensing, and beam steering. Commonly, they feature multiple operation states by switching the whole PCM fully between two states of drastically different optical properties. Intermediate states of the PCM are also exploited to obtain gradual resonance shifts, which are usually uniform over the whole MS and described by effective medium response. For programmable MSs, however, the ability to selectively address and switch the PCM in individual meta-atoms is required. Here, simultaneous control of size, position, and crystallization depth of the switched phase-change material (PCM) volume within each meta-atom in a proof-of-principle MS consisting of a PCM-covered Al-nanorod antenna array is demonstrated. By modifying optical properties locally, amplitude and light phase can be programmed at the meta-atom scale. As this goes beyond previous effective medium concepts, it will enable small adaptive corrections to external aberrations and fabrication errors or multiple complex functionalities programmable on the same MS.

Highly Confined and Switchable Mid-Infrared Surface Phonon Polariton Resonances of Planar Circular Cavities with a Phase Change Material.

Mid-infrared (MIR) photonics demands highly confined optical fields to obtain efficient interaction between long-wavelength light and nanomaterials. Surface polaritons excited on polar semiconductor and metallic material interfaces exhibit near-fields localized on subwavelength scales. However, realizing a stronger field concentration in a cavity with a high quality ( Q) factor and a small mode volume is still challenging in the MIR region. This study reports MIR field concentration of surface phonon polaritons (SPhPs) using planar circular cavities with a high Q factor of ∼150. The cavities are fabricated on a thin film of the phase change material Ge3Sb2Te6 (GST) deposited on a silicon carbide (SiC) substrate. Scattering-type scanning near-field optical microscopy visualizes the near-field distribution on the samples and confirms directly that the SPhP field is strongly concentrated at the center of the centrosymmetric cavities. The smallest concentrated field size is 220 nm in diameter which corresponds to 1/50 of the wavelength of the incident light that is far below the diffraction limit. The thin GST film enhances the SPhP confinement, and it is used to switch the confinement off by tuning the cavity resonance induced by the phase change from the amorphous to the crystalline phase. This subwavelength and switchable field concentration within a high- Q polariton cavity has the potential to greatly enhance the light-matter interaction for molecular sensing and emission enhancement in MIR systems.

Reversible optical switching of highly confined phonon-polaritons with an ultrathin phase-change material.

Surface phonon-polaritons (SPhPs), collective excitations of photons coupled with phonons in polar crystals, enable strong light-matter interaction and numerous infrared nanophotonic applications. However, as the lattice vibrations are determined by the crystal structure, the dynamical control of SPhPs remains challenging. Here, we realize the all-optical, non-volatile, and reversible switching of SPhPs by controlling the structural phase of a phase-change material (PCM) employed as a switchable dielectric environment. We experimentally demonstrate optical switching of an ultrathin PCM film (down to 7 nm, <λ/1,200) with single laser pulses and detect ultra-confined SPhPs (polariton wavevector kp > 70k0, k0 = 2π/λ) in quartz. Our proof of concept allows the preparation of all-dielectric, rewritable SPhP resonators without the need for complex fabrication methods. With optimized materials and parallelized optical addressing we foresee application potential for switchable infrared nanophotonic elements, for example, imaging elements such as superlenses and hyperlenses, as well as reconfigurable metasurfaces and sensors.

Hyperbolic phonon-polaritons in boron nitride for near-field optical imaging and focusing.

Hyperbolic materials exhibit sub-diffractional, highly directional, volume-confined polariton modes. Here we report that hyperbolic phonon polaritons allow for a flat slab of hexagonal boron nitride to enable exciting near-field optical applications, including unusual imaging phenomenon (such as an enlarged reconstruction of investigated objects) and sub-diffractional focusing. Both the enlarged imaging and the super-resolution focusing are explained based on the volume-confined, wavelength dependent propagation angle of hyperbolic phonon polaritons. With advanced infrared nanoimaging techniques and state-of-art mid-infrared laser sources, we have succeeded in demonstrating and visualizing these unexpected phenomena in both Type I and Type II hyperbolic conditions, with both occurring naturally within hexagonal boron nitride. These efforts have provided a full and intuitive physical picture for the understanding of the role of hyperbolic phonon polaritons in near-field optical imaging, guiding, and focusing applications.

Near-field imaging and spectroscopy of locally strained GaN using an IR broadband laser.

Scattering-type scanning near-field optical microscopy (SNOM) offers the possibility to analyze material properties like strain in crystals at the nanoscale. In this paper we introduce a SNOM setup employing a newly developed tunable broadband laser source with a covered spectral range from 9 µm to 16 µm. This setup allows for the first time optical analyses of the crystal structure of gallium nitride (GaN) at the nanometer scale by excitation of a near-field phonon resonance around 14.5 µm. On the example of an artificially induced stress field within a GaN wafer, we present a method for a 2D visualization of small deviations in the crystal structure, which allows for fast qualitative characterizations. Subsequently, the stress levels at chosen points were quantified by recording complex near-field spectra and correlating them with theoretical model calculations. Applied to the cross-section of a heteroepitaxially grown GaN wafer, we finally demonstrate the capability of our setup to analyze the relaxation of the crystal structure along the growth axis with a nanometer spatial resolution.

Femoral arterial thrombosis after cardiac catheterization in infancy: impact of Doppler ultrasound for diagnosis.

Femoral arterial thrombosis (FAT) is a nonnegligible complication after cardiac catheterization (CC) in infancy. The aim of this study was to evaluate the impact of Doppler ultrasound (US) for diagnostic work-up after catheterization. We compared standard follow-up (FU) without Doppler US by relying on clinical signs of FAT with advanced FU using Doppler US of the femoral vessels. Between January and December 2009, we evaluated the rate of FAT in infants <12 months of age using a multicenter, prospective observational survey. We analysed 171 patients [mean age 4.1 ± 3.3 (SD) months; mean body weight 5.3 ± 1.8 kg] from 6 participating centres. The mean duration of catheter studies was 57.7 ± 38.0 min. The overall rate of FAT based on clinical diagnosis was 4.7% and was comparable in both groups [3.4% undergoing standard FU vs. 7.4% undergoing advanced FU (p = 0.15)]. However, the overall rate of thrombosis as screened by Doppler US was greater at 7.1 %, especially in patients after advanced FU [18.5% advanced vs. standard FU 1.7% (p < 0.01)]. In conclusion, FAT remains a relevant and underestimated complication after catheterization in young infants when relying only on clinical signs of FAT. Therefore, to start effective treatment as soon as possible, we recommend Doppler US to be performed the day after CC.

Autonomic function testing in children and adolescents with diabetes mellitus.

Cardiac autonomic neuropathy (CAN) is a common complication in type 1 diabetes mellitus (T1DM) and associated with an increased mortality. Early detection of CAN would be desirable for a better individual risk stratification. The aim of this study was to determine whether autonomic dysfunction can be diagnosed in young patients with a recent history of T1DM. Autonomic function was assessed in 20 pediatric patients with T1DM, aged 10-19 yr, and a control group of 136 non-diabetic patients using four cardiorespiratory reflexes: heart rate and blood pressure response in standing position, deep breathing, and Valsalva maneuver. Furthermore, power spectral analyses of the low- and high-frequency band of heart rate variability (HRV) and baroreflex sensitivity (BRS) were tested with the non-invasive Task force monitor (CNSystems, Graz, Austria). Cardiorespiratory reflexes were pathologic for at least one item in 75% of the diabetic and 60% in the healthy control group. A reduced BRS was always combined with abnormal HRV. We found this pattern in 30% of diabetic patients and never in the control group. In patients with impaired BRS, mean hemoglobin A1c (HbA1c) was 7.7% and duration of diabetes 6.5 yr. This did not differ from the overall value of the diabetic group: HbA1c level 8.4% and diabetes duration 7.3 yr. In conclusion, signs of autonomic dysfunction are not uncommon in an early stage of diabetes in young patients. Classical cardiorespiratory reflexes seem to be less specific than HRV and BRS as testing methods.

Common patterns of response to the head-up tilt test in children and adolescents.

Testing using the head-up tilt table is performed regularly as a diagnostic tool in the evaluation of syncope. Recommendations for protocols, and interpretation of the results, however, are mainly based on experience in adults. We evaluated the results of tilt table testing in 100 consecutive children and adolescents aged from 6 to 18 years and referred for investigation of syncope. Over half the patients, 55%, proved impossible to classify using the criterions established by the European Society of Cardiology. Based on our data, we propose a modified classification for responses to tilt table testing in the young.

Successful management of an extreme example of neonatal hyperprostaglandin-E syndrome (Bartter's syndrome) with the new cyclooxygenase-2 inhibitor rofecoxib.

OBJECTIVE: To describe the successful treatment of an unusual case of severe neonatal Bartter's syndrome refractory to treatment with indomethacin. DESIGN: Case report, clinical. SETTING: Tertiary care intensive care unit. PATIENTS: A patient with neonatal hyperprostaglandin-E syndrome and excessive requirements of intravenous (via central venous catheter) water and salt supplementation, failure to thrive, vomiting, and massive growth retardation, despite adequate treatment with indomethacin. MAIN RESULT: Four weeks after induction of the new cyclooxygenase-2 inhibitor rofecoxib, the patient was well, on full enteral feeds, thriving, and had gained 600 g in weight. A lower supplementary potassium, magnesium, and sodium intake was required. Reinstitution of indomethacin therapy resulted in severe deterioration, despite high indomethacin doses; symptoms improved again after rofecoxib administration. No side effects have been seen thus far. CONCLUSION: This report shows that in selected patients with a severe form of neonatal Bartter's syndrome, the new cyclooxygenase-2 inhibitor rofecoxib may control the clinical symptoms of hyperprostaglandin-E syndrome after ineffective indomethacin therapy.

Longitudinal stent fracture 11 months after implantation in the left pulmonary artery and successful management by a stent-in-stent maneuver.

Fracture of a 12 mm Palmaz stent after implantation in the left pulmonary artery for palliation of postoperative stenosis in a 9-year-old child is described. Successful management by implantation of a second Palmaz stent revealed immediate stabilization and no signs of significant restenosis during 1-year follow-up.

Successful management of a resistant renal artery stenosis in a child using a 4 mm cutting balloon catheter.

Percutaneous transluminal renal angioplasty (PTRA) is a well-established method to treat renal artery stenosis (RAS) in children and adults. However, a significant number of stenoses might not be treated by interventional techniques due to the inability to dilate the RAS. Conventional balloon angioplasty with a high-pressure coronary angioplasty balloon at 20 atm was unable to dilate a significant RAS in a 12-year-old child with severe renovascular hypertension (RR 195/125 mm Hg). After using a 4 mm cutting balloon, we achieved wide patency of the renal artery and an instant normalization of blood pressure without further need of antihypertensive therapy. PTRA using the cutting balloon technique may offer an additional therapeutic option for selected patients in whom conventional balloon angioplasty was not able to dilate RAS.

The spectrum of subdivided left atrium: diagnosis, treatment and outcome in eight patients.

From January 1996 to April 2001, we treated eight patients with subdivided left atrium. Their ages at diagnosis ranged from newborn to 6.4 years. Prominent clinical symptoms were failure to thrive, respiratory symptoms, demand for oxygen, and congestive cardiac failure. Diagnosis was made by transthoracic echocardiography in all cases. Cardiac catheterization was necessary only in those patients who had associated cardiac anomalies, or suspected signs of pulmonary hypertension. In 7 patients, surgery was performed immediately after diagnosis, but one preterm infant died before operation due to neonatal sepsis and respiratory distress syndrome. In the postoperative period, one patient developed a severe capillary leak syndrome, and died due to irreversible congestive cardiac failure. The other 6 patients have all been followed up, with good results in the short- and intermediate-term at a mean of 34.3+/-20.2 months. The infants were thriving, had a reduction in the frequency of infections of the respiratory tract, no significant arrhythmias, and showed early recovery from pulmonary hypertension and right ventricular hypertrophy.