Silicon Band Research Articles

Single-Electron Structures Based on Solitary Dopant Atoms of Arsenic, Phosphorus, Gold, and Potassium in Silicon

Here we present CMOS compatible fabrication methods and the results of an experimental study of single-atom single-electron transistors made from silicon on insulator and based on various dopant atoms. Transistors with channels doped with arsenic (As), phosphorus (P), gold (Au) and potassium (K) atoms were fabricated and studied. Two methods for fabricating of experimental transistor structures are presented. The first method (As, P transistors) used a inhomogeneously doped in depth silicon layer and controlled reduction of the size of the transistor channel in several cycles of isotropic reactive-ion etching. The second method (Au and K transistors) used an undoped silicon layer and the subsequent implantation of dopant atoms into a preformed transistor channel. Dopant electron and hole levels of Au and K atoms in silicon are located near the middle of the silicon band gap, which provides a small effective size of the dopant charge center and, as a result, a high value of the charge energy and operating temperature of the transistor compared to the traditional dopants (P, As, Sb, B). The values of the charge energy of the Au and K transistors, which were estimated from the measurements (Ec ≥ 150 meV), are much higher than those of the As and P transistors (Ec < 30 meV). Important advantages of the proposed methods are: controlled implantation of various impurities and possibility to combine etching and implantation cycles during sample preparation.

Historical, Current and Future Approaches to Surgery for Rhegmatogenous Retinal Detachment.

Rhegmatogenous retinal detachment (RRD) is a serious condition that can cause blindness without surgical treatment. RRD occurs when a retinal tear or hole allows fluid to accumulate below the retinal surface, causing the retina to separate from the underlying layers. RRD is difficult to treat because each case is unique, varying with the location, size, and duration of the detachment, as well as patient age. The first successful methods to reattach the retina in RRD used thermocautery to repair the detachment. Many renowned ophthalmologists continued to study RRD and developed many new surgical approaches, notably: scleral buckling (SB), in which a silicone band is placed around the eye to reduce traction on the retina caused by the vitreous humor that fills the eye; pars plana vitrectomy (PPV), which eliminates traction on the retina by removing the vitreous; and pneumatic retinopexy (PR), in which the retina is reattached by pushing it back into place with an expanding gas bubble injected into the eye. However, no consensus has been reached on which approach is ideal. Furthermore, recent surgical and non-surgical breakthroughs, such as artificial vitreous substitutes and neuroprotective drugs, must also be considered. Thus, this review provides a guide for ocular specialists and non-specialists on the historical background of RRD, summarizes the three current main techniques (SB, PR and PPV) compares these three techniques, and provides an overview of new technologies that promise to greatly improve outcomes after RRD surgery.

Utilizing a Previous Silicone Band Track in Recurred Retinal Detachment

Utilizing a Previous Silicone Band Track in Recurred Retinal Detachment

EPA's non-targeted analysis collaborative trial (ENTACT): genesis, design, and initial findings.

In August 2015, the US Environmental Protection Agency (EPA) convened a workshop entitled "Advancing non-targeted analyses of xenobiotic chemicals in environmental and biological media." The purpose of the workshop was to bring together the foremost experts in non-targeted analysis (NTA) to discuss thestate-of-the-science for generating, interpreting, and exchanging NTA measurement data. During the workshop, participants discussed potential designs for a collaborative project that would use EPA resources, including the ToxCast library of chemical substances, the DSSTox database, and the CompTox Chemicals Dashboard, to evaluate cutting-edge NTA methods. That discussion was the genesis of EPA's Non-Targeted Analysis Collaborative Trial (ENTACT). Nearly 30 laboratories have enrolled in ENTACT and used a variety of chromatography, mass spectrometry, and data processing approaches to characterize ten synthetic chemical mixtures, three standardized media (human serum, house dust, and silicone band) extracts, and thousands of individual substances. Initial results show that nearly all participants have detected and reported more compounds in the mixtures than were intentionally added, with large inter-lab variability in the number of reported compounds. A comparison of gas and liquid chromatography results shows that the majority (45.3%) of correctly identified compounds were detected by only one method and 15.4% of compounds were not identified. Finally, a limited set of true positive identifications indicates substantial differences in observable chemical space when employing disparate separation and ionization techniques as part of NTA workflows. This article describes the genesis of ENTACT, all study methods and materials, and an analysis of results submitted to date. Graphical abstract ᅟ.

Two-dimensional semiconductors pave the way towards dopant-based quantum computing.

Since the proposal in 1998 to build a quantum computer using dopants in silicon as qubits, much progress has been made in the nanofabrication of semiconductors and the control of charge and spins in single dopants. However, an important problem remains unsolved, namely the control over exchange interactions and tunneling between two donors, which presents a peculiar oscillatory behavior as the dopants relative positions vary at the scale of the lattice parameter. Such behavior is due to the valley degeneracy in the conduction band of silicon, and does not occur when the conduction-band edge is at k = 0. We investigate the possibility of circumventing this problem by using two-dimensional (2D) materials as hosts. Dopants in 2D systems are more tightly bound and potentially easier to position and manipulate. Moreover, many of them present the conduction band minimum at k = 0, thus no exchange or tunnel coupling oscillations. Considering the properties of currently available 2D semiconductor materials, we access the feasibility of such a proposal in terms of quantum manipulability of isolated dopants (for single qubit operations) and dopant pairs (for two-qubit operations). Our results indicate that a wide variety of 2D materials may perform at least as well as, and possibly better, than the currently studied bulk host materials for donor qubits.

Energy filtering in silicon nanowires and nanosheets using a geometric superlattice and its use for steep-slope transistors

This paper investigates energy filtering in silicon nanowires and nanosheets by resonant electron tunneling through a geometric superlattice. A geometric superlattice is any kind of periodic geometric feature along the transport direction of the nanowire or nanosheet. Multivalley quantum-transport simulations are used to demonstrate the manifestation of minibands and minibandgaps in the transmission spectra of such a superlattice. We find that the presence of different valleys in the conduction band of silicon favors a nanowire with a rectangular cross section for effective energy filtering. The obtained energy filter can consequently be used in the source extension of a field-effect transistor to prevent high-energy electrons from contributing to the leakage current. Self-consistent Schrödinger-Poisson simulations in the ballistic limit show minimum subthreshold swings of 6 mV/decade for geometric superlattices with indentations. The obtained theoretical performance metrics for the simulated devices are compared with conventional III-V superlatticeFETs and TunnelFETs. The adaptation of the quantum transmitting boundary method to the finite-element simulation of 3-D structures with anisotropic effective mass is presented in Appendixes A and B. Our results bare relevance in the search for steep-slope transistor alternatives which are compatible with the silicon industry and can overcome the power-consumption bottleneck inherent to standard CMOS technologies.

Ocular movement disorders following scleral buckling surgery: A case series study

PurposeTo evaluate ocular movement disorders after scleral buckling surgery (SBS) for retinal detachment. MethodsIn this prospective, observational, case series, 206 patients (206 eyes) with rhegmatogenous retinal detachment who underwent SBS and investigated at the strabismus ward of Farabi Eye Hospital in Iran between November 2011 and November 2014 were assessed. Patients were followed from 6 to 36 months after SBS to evaluate for strabismus. Logistic regression analysis test and SPSS software version 20 were used for statistical analysis. ResultsFrom 206 patients, 56.8% were male, and 33.2% were female. For scleral buckle in 44.7% of patients, silicone band and tire (SBT) was used, and in 55.3%, a sponge. Among all patients, seven (3.39%) exhibited ocular movement disorder. There was no significant relation between type of buckle (P = 0.65) or the location of buckle (P = 0.56) and movement disorder. ConclusionOcular movement disorder is one of the main complications after SBS without specific association between the type and location of exoplanet.

Raman spectroscopy of porous silicon substrates

We have investigated the effect of the etching time on the Raman spectra of porous silicon prepared by anodic etching. Electrochemical destruction of the substrate increasing with the etching time and the correlation between the microstructure of the silicon wafer and the shape and position of their Raman spectra have been observed. Raman analysis has shown that the intensity of the Raman dominant silicon band decreases and the bandwidth is shifted to lower frequencies, depending on the morphology of the sample. Therefore we believe that the electrochemical destruction of the surface of Si substrates leads to surface amorphization.

Lifetime Imaging on Silicon Bricks Using the Ratio of Photoluminescence Images With Different Excitation Wavelengths

The efficiency of silicon solar cells is eventually limited by the bulk lifetime of minority carriers in the wafer. The characterization of the bulk quality, measured on silicon bricks early in the production process, provides an immediate indication of the efficiency potential of the material, the feedstock purity, and the quality of the crystallization process. Previously, the intensity ratio of two photoluminescence images that are acquired with different spectral filters (i.e., the two-filter method) has been used to measure the bulk lifetime of silicon bricks. In this paper, we report on a similar approach, which uses the ratio of two photoluminescence images each acquired with a different illumination wavelength (915 and 1064 nm); one of which is within the photoluminescence emission band of silicon. We demonstrate with modeling that this two-laser method is more robust against uncertainties that affect the spectrum of photoluminescence emission and its detection, while the two-filter method is more robust against uncertainties in the carrier density profile and the illumination system properties. Experimentally, both the two-laser and two-filter methods show good agreement across a monocrystalline and multicrystalline silicon brick. However, challenges using the two-laser method arose when a brick with strongly injection-dependent lifetime was measured.

Down-shifting emission by charge transfer band in porous silicon infiltrated with Eu3+ and Gd3+ ions

Down-shifting emission properties of europium (Eu3+) and gadolinium (Gd3+) ions incorporated in porous silicon (PS) layers are presented. Different samples were prepared by electrochemical etching of p+-type crystalline silicon wafers followed by simple impregnation with rare earth ions from nitrate solutions of europium and gadolinium and subsequent high temperature annealing in air. The samples exhibited room temperature photoluminescence (PL) and the excitation spectra present a wide excitation band around 233 nm which can be associated to the charge transfer band transitions. This band is attributed to O2−(2p)→Eu3+(4f) ligand-to-metal charge transfer. The down-shifting emission for Gd+3:Eu3+ was analyzed by a simple rate equation model to study the interaction between the O2− ions and Eu3+ ions. The exact solution of this model agrees very well with the experimental results.

Electron-selective quinhydrone passivated back contact for high-efficiency silicon/organic heterojunction solar cells

Interfacial properties play a critical role in the dynamic process of carrier transport in dopant-free silicon (Si) heterojunction solar cells (HSCs), based on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). In this study, we use quinhydrone (QHY) to engineer the interfacial properties by grafting the semiquinone (QH) on Si surface at low temperature. The QH monolayer provides effective chemical and field-effect passivation by the surface dangling-bond saturation and its interface dipole, respectively, and results in a large minority carrier lifetime of 477 μs. At the front Si/PEDOT:PSS interface, the QH-terminated Si surface presents higher wettability for the improved contact at the Si/PEDOT:PSS junction. At the rear Al/Si interface, the work function of Al film is reduced significantly to form ohmic contact for electron-selective transport. The dark current-voltage and capacitance-voltage measurements show the improved electric characteristics with a higher carrier collection efficiency. Furthermore, the silicon band bending generated by the QH dipoles enhances the overall built-in potential of Si/PEDOT:PSS HSCs for a larger open-circuit voltage. As a result, the QHY modified Si/PEDOT:PSS HSC yields a power conversion efficiency of 13.29%. This approach demonstrates that the organic grafting is a simple, effective and low-cost method for the interface engineering to achieve high-efficiency HSCs.

A new instrument to simplify encircling buckle placement.

The purpose of this study is to describe a new surgical instrument that simplifies 360° silicone band placement, alone or in combination with pars plana vitrectomy, for the treatment of rhegmatogenous retinal detachment. The instrument has a straight shank and a curved component in the form of a partial helix, whose purpose is to encircle the perimeter of the eye globe below the rectus muscles. The distal tip of the helix is inserted through a small conjunctival incision in the superior temporal quadrant, and the shank is rotated 360° on its axis until the tip emerges from the insertion point. One end of the silicone band is sutured to the tip, and the instrument is rotated in the opposite direction until both ends of the band are positioned in the same scleral quadrant. The band is sutured to the sclera and the conjunctival incision is closed. Pars plana vitrectomy can then be performed using transconjunctival microincision techniques through the intact conjunctiva. Our experience using the instrument in more than 100 procedures has shown that the new technique considerably reduces surgical trauma: wide opening of the conjunctiva is obviated, there is little manipulation of the extraocular musculature, and only a few sutures are needed. The duration of the procedure is considerably shorter because of the smaller number of surgical maneuvers. We describe a new scleral technique facilitated by this surgical instrument, whose objective is safe and effective placement of an encircling silicone band with minimum trauma and a reduction in operating time.

Immersion and electrochemical deposition of Ru on Si

The stability of the aquapentachlororuthenate (III) complex has been monitored in ultrapure water, hydrochloric acid, and sulphuric acid using UV–vis spectroscopy. When a Si – H terminated surface is exposed to an acidic solution containing Ru3+, metallic Ru nuclei are deposited and the surface is oxidized due to hole injection by Ru3+ into the valence band of silicon. The self-limiting mechanism was investigated by electrochemical methods (voltammetry and open-circuit potential transients). For the electrochemical deposition of Ru on n-Si(100), the nuclei size and density were determined using atomic force microscopy. The impact of applied current density was studied, for which it was found that hydrogen evolution strongly reduces the nuclei density. The Ru|Si interface has been characterized using transmission electron microscopy and elemental mapping. It was observed that hemispherical nuclei are deposited on an interfacial silicon oxide layer.

Deep level transient spectroscopic analysis of p/n junction implanted with boron in n-type silicon substrate

For P-i-N diodes implanted and activated with boron ions into a highly-resistive n-type Si substrate, it is found that there is a large difference in the leakage current between relatively low temperature furnace annealing (FA) and high temperature laser annealing (LA) for activation of the p-layer. Since electron trap levels in the n-type Si substrate is supposed to be affected, we report on Deep Level Transient Spectroscopy (DLTS) measurement results investigating what kinds of trap levels are formed. As a result, three kinds of electron trap levels are confirmed in the region of 1–4 μm from the p-n junction. Each DLTS peak intensity of the LA sample is smaller than that of the FA sample. In particular, with respect to the trap level which is the closest to the silicon band gap center most affecting the reverse leakage current, it was not detected in LA. It is considered that the electron trap levels are decreased due to the thermal energy of LA. On the other hand, four kinds of trap levels are confirmed in the region of 38–44 μm from the p-n junction and the DLTS peak intensities of FA and LA are almost the same, considering that the thermal energy of LA has not reached this area. The large difference between the reverse leakage current of FA and LA is considered to be affected by the deep trap level estimated to be the interstitial boron.

Preparation and characterization of the Si:Co layer for intermediate band solar cell applications

Abstracts The Co-implanted silicon layers with rapid thermal process (RTP) have been prepared for intermediate band materials. The characterization of the Si:Co layer has been analyzed and discussed. The results show that the Co concentrations in effective implanted region of the Si layers exceed the Mott limit, satisfying the requirement for the formation of intermediate band in silicon. The Co-implanted samples are well crystallized by RTP treatment. The effective lifetime of the carriers in the samples increases with the Co dose implanted. This indicates that the non-radiative recombination has been suppressed in the post-annealed samples. Furthermore, the optical absorptance of the samples is much enhanced in the wavelength range of above 1100 nm. It can be concluded that the Si:Co layer can be prepared by Co implantation in Si followed by RTP method, and it is a promising material that can be used for intermediate band solar cells.

Comparison of Two Tourniquets on a Mid-Thigh Model: The Israeli Silicone Stretch and Wrap Tourniquet vs. The Combat Application Tourniquet.

Experience from recent conflicts underlines the dramatic impact of effective tourniquet use on combat casualty mortality. Although the Combat Application Tourniquet (CAT) is replacing the silicone band tourniquets (IST; "Israeli Silicone Tourniquet") in the Israeli Defense Forces, no direct comparison was made between them. The purpose of this study is to compare the performance of the two tourniquets on a mid-thigh model. Participants were Israeli military recruits who previously had the military first aid course. Each participant applied both the CAT and the IST. Applications were assessed by the HapMed Leg Tourniquet Trainer, which measured the applied pressure and the time required to reach it. IST application resulted in higher rates of effective occlusion pressure compared with the CAT (91% vs. 73.1%, p < 0.01), and a higher mean occlusion pressure (41 mmHg, p < 0.01) was recorded using the IST. Among effective attempts, application time did not differ significantly between the tourniquets. The IST was superior to the CAT in producing effective occlusion pressure while not prolonging application time. These results may indicate that the IST remains a valid option for controlling mid-thigh bleeding.

Amorphous Submicron Layer in Depletion Region: New Approach to Increase the Silicon Solar Cell Efficiency

The insertion of a thin amorphized layer (AL) in the space charge region of a silicon solar cell is proposed as a way to improve the conversion efficiency due to the impurity photovoltaic effect. Previously, this approach had been applied to a cell with a layer inserted in the emitter by the ion implantation. The insertion of such layer in the space charge region is founded to be preferable, because a better control over the recombination (via energy levels in the band gap and local states of interfaces) can be achieved. The parameters of a modified device are investigated by the numerical simulation, and it is concluded that the layer parameters have a crucial influence on the cell conversion efficiency. Based on our simulation results, the optimal AL and the height of barriers are determined. In such a case, the short circuit current density is improved due to the absorption of photons with energy less than a silicon band gap of 1.12 eV in AL, whereas the open circuit voltage and fill factor remain unchanged. Theoretically, the increase in the efficiency by 1–2% is achievable. In the non-optimal case, the degradation of a short circuit current and the fill factor eliminate the positive effect of an additional photogeneration in AL.

Clinical histopathology of intrachoroidal splitting in open-globe injury: A retrospective case series of four patients.

PURPOSE:The purpose of this study is to observe the characteristics of intrachoroidal splitting (ICS) associated with choroidal detachment due to open-globe injury.METHODS:A retrospective, observational case series study of four eyes diagnosed with choroidal detachment exhibited ICS. The in vivo pathologic changes of the ICS were recorded during surgery. Four specimens were obtained from the inner part of the ICS region. One specimen was stained with hematoxylin and eosin; one specimen was examined under scanning electron microscopy, and the other two specimens were examined under transmission electron microscopy.RESULTS:All four patients presented with vortex vein rupture associated with large-scaled mid-peripheral ICS. The histopathologic observations indicated that ICS occurred between the medium-sized and large-sized choroidal vessel layers. Large vascular indentations and medium-sized choroidal vessels were observed on the inner part of the split interface. Postoperative outcomes of the four patients were poor. Vision in all four patients was no light perception before or after surgery. Three eyes became atrophic with silicon oil tamponade and band keratopathy, one eye was eventually enucleated for cosmetic reason.CONCLUSION:Intrachoroidal tissue has the potential to split during trauma. The outcome of ICS with choroidal detachment in open-globe injury was poor.

Valley spin polarization of Tl/Si(111)

Metal/semiconductor hybrid systems are attractive for integrating spintronic devices on current semiconductor technology. This paper investigates the potential of Tl/Si(111), a system with an unoccupied surface state within the silicon band gap, which forms fully spin-polarized valleys at the $\overline{\mathrm{K}}$ and ${\overline{\mathrm{K}}}^{\ensuremath{'}}$ points close to the Fermi level. Our key findings are the robustness of the system against contamination and the possibility to dope the system such that the fully spin-polarized valleys become metallic. This establishes Tl/Si(111) as possessing all necessary key properties for spintronic applications.

Characterization of silicon surface states at clean and copper contaminated condition via transient capacitance measurement

Silicon surface is one of the dominant recombination sites for silicon solar cells. Generally, the recombination ability of silicon surface is characterized in terms of surface recombination velocity. However, silicon surface actually contain a series of donor and acceptor levels across the silicon band gap, and therefore the surface recombination velocity is too general to provide detailed information of the silicon surface states. In this paper, we used the measured transient capacitance data to extract the detailed information (like defect energy levels, defect densities, and capture cross sections) of the silicon surface states. Furthermore, the influence of copper contamination on silicon surface states was examined, and it was found that copper contamination can change the localized energy levels of “clean” silicon surface states to the band-like energy levels, meanwhile the defect densities and capture cross sections were both enlarged.