Direct-bandgap light-emitting germanium in tensilely strained nanomembranes.

Silicon, germanium, and related alloys, which provide the leading materials platform of electronics, are extremely inefficient light emitters because of the indirect nature of their fundamental energy bandgap. This basic materials property has so far hindered the development of group-IV photonic active devices, including diode lasers, thereby significantly limiting our ability to integrate electronic and photonic functionalities at the chip level. Here we show that Ge nanomembranes (i.e., single-crystal sheets no more than a few tens of nanometers thick) can be used to overcome this materials limitation. Theoretical studies have predicted that tensile strain in Ge lowers the direct energy bandgap relative to the indirect one. We demonstrate that mechanically stressed nanomembranes allow for the introduction of sufficient biaxial tensile strain to transform Ge into a direct-bandgap material with strongly enhanced light-emission efficiency, capable of supporting population inversion as required for providing optical gain.

A Dynamic Endonasal Columellar Strut Placement.

The dynamic retrograde intercrural columellar strut graft placement is a novel technique for a columellar strut insertion via a hemi-transfixion incision in patients undergoing endonasal functional or cosmetic surgery. It has a maximally concealed incision and does not disrupt major or minor tip support mechanisms. In our article, we give a detailed description of this unique surgical technique. Laryngoscope, 134:1246-1248, 2024.

Outcomes of endoscopic optic nerve decompression in patients with idiopathic intracranial hypertension.

BACKGROUND: The conventional treatment for idiopathic intracranial hypertension involves weight loss, steroids, diuretics, and/or serial lumbar punctures; however, if the symptoms persist or worsen, surgical intervention is recommended. Surgical options include cerebrospinal fluid diversion procedures, such as ventriculoperitoneal and lumboperitoneal shunts, and optic nerve decompression with nerve sheath fenestration. The latter can be carried out using an endoscopic approach, but the outcomes of this technique have not been firmly established. METHODS: This systematic review examined the outcomes of performing endoscopic optic nerve decompression (EOND) in patients with idiopathic intracranial hypertension (IIH). Six studies were included for a total of 34 patients. RESULTS: The patients presented with visual field disturbances (32 of 32 [100%]), visual acuity disruptions (33 of 34 [97.1%]), papilledema (26 of 34 [76.5%]), and persistent headache (30 of 33 [90.1%]). The mean duration of symptoms ranged from 7 to 32 months. Overall, the patients showed post-EOND improvement in signs and symptoms associated with IIH, specifically visual field deficits (93.8%), visual acuity (85.3%), papilledema (81.4%), and headaches (81.8%). Interestingly, 11 cases showed postoperative improvement in their symptoms with bony decompression of the optic canal alone, without nerve sheath fenestration. There were no major adverse events or complications reported with this approach. CONCLUSION: EOND appears to be a promising and safe surgical alternative for patients with IIH who fail to respond to medical treatment. Further studies are needed before we can attest to the clinical validity of this procedure.

Electronic Transport Properties of Epitaxial Si/SiGe Heterostructures Grown on Single-Crystal SiGe Nanomembranes.

To assess possible improvements in the electronic performance of two-dimensional electron gases (2DEGs) in silicon, SiGe/Si/SiGe heterostructures are grown on fully elastically relaxed single-crystal SiGe nanomembranes produced through a strain engineering approach. This procedure eliminates the formation of dislocations in the heterostructure. Top-gated Hall bar devices are fabricated to enable magnetoresistivity and Hall effect measurements. Both Shubnikov-de Haas oscillations and the quantum Hall effect are observed at low temperatures, demonstrating the formation of high-quality 2DEGs. Values of charge carrier mobility as a function of carrier density extracted from these measurements are at least as high or higher than those obtained from companion measurements made on heterostructures grown on conventional strain graded substrates. In all samples, impurity scattering appears to limit the mobility.

Strained-germanium nanostructures for infrared photonics.

The controlled application of strain in crystalline semiconductors can be used to modify their basic physical properties to enhance performance in electronic and photonic device applications. In germanium, tensile strain can even be used to change the nature of the fundamental energy band gap from indirect to direct, thereby dramatically increasing the interband radiative efficiency and allowing population inversion and optical gain. For biaxial tension, the required strain levels (around 2%) are physically accessible but necessitate the use of very thin crystals. A particularly promising materials platform in this respect is provided by Ge nanomembranes, that is, single-crystal sheets with nanoscale thicknesses that are either completely released from or partially suspended over their native substrates. Using this approach, Ge tensilely strained beyond the expected threshold for direct-band gap behavior has recently been demonstrated, together with strong strain-enhanced photoluminescence and evidence of population inversion. We review the basic properties, state of the art, and prospects of tensilely strained Ge for infrared photonic applications.

Exceptional charge transport properties of graphene on germanium.

The excellent charge transport properties of graphene suggest a wide range of application in analog electronics. While most practical devices will require that graphene be bonded to a substrate, such bonding generally degrades these transport properties. In contrast, when graphene is transferred to Ge(001) its conductivity is extremely high and the charge carrier mobility derived from the relevant transport measurements is, under some circumstances, higher than that of freestanding, edge-supported graphene. We measure a mobility of ∼ 5 × 10(5) cm(2) V(-1) s(-1) at 20 K, and ∼ 10(3) cm(2) V(-1) s(-1) at 300 K. These values are close to the theoretical limit for doped graphene. Carrier densities in the graphene are as high as 10(14) cm(-2) at 300 K.

Translation and manipulation of silicon nanomembranes using holographic optical tweezers.

We demonstrate the use of holographic optical tweezers for trapping and manipulating silicon nanomembranes. These macroscopic free-standing sheets of single-crystalline silicon are attractive for use in next-generation flexible electronics. We achieve three-dimensional control by attaching a functionalized silica bead to the silicon surface, enabling non-contact trapping and manipulation of planar structures with high aspect ratios (high lateral size to thickness). Using as few as one trap and trapping powers as low as several hundred milliwatts, silicon nanomembranes can be rotated and translated in a solution over large distances.