Double Si Research Articles

Realization of high-capacity coulombic efficiency in sodium alginate/carbon nanotube double network coated Si-anode for lithium-ion batteries

Silicon (Si) is considered as one of the most promising anodes for the next-generation lithium-ion batteries (LIBs) owing to its ultra-high specific capacity, low redox potential and the second abundance of elements in the earth's crust. However, drastic volume change will directly cause electrode pulverization, thus leading to low initial coulombic efficiency (ICE) and terrible cycling stability. In this work, a sodium alginate (SA)‑carbon nanotube (CNT) derived double carbon-coated Si composite (SA-CNT@Si) was prepared through freeze-drying technique followed by high-temperature carbonization, where SA was utilized to encase Si nanospheres, with CNT serving as the conductive framework that interconnects Si spheres. These composites exhibit improved electrical conductivity and stability throughout the charge and discharge cycles when employed as the anodes in LIBs, demonstrating superior electrochemical properties. The SA-CNT@Si electrode with a mass ratio of Si: SA: CNT = 5: 1: 0.75, achieved a first discharge specific capacity of 2200.8 mAh g−1 at a current density of 500 mA g−1 (with the initial three cycles at 100 mA g−1), along with an ICE of 86.2%. Even after 500 cycles, it maintained a capacity of 607 mAh g−1. This study presents a novel approach to designing Si-based anode materials characterized by both high electrical conductivity and structural stability.

Rich essential properties of silicon-substituted graphene nanoribbons: a comprehensive computational study.

The diverse structural, electronic, and magnetic properties of silicon (Si)-substituted armchair and zigzag graphene nanoribbons (AGNRs and ZGNRs) were investigated using spin-polarized density functional theory (DFT) calculations. Pristine AGNRs belong to a nonmagnetic semiconductor with a direct bandgap of 1.63/1.92 eV determined by PBE/HSE06 functionals. Under various Si substitutions, nonmagnetic bandgaps were tuned at 1.49/1.87, 1.06/1.84, 0.81/1.45, 1.04/1.71, 0.89/1.05, and 2.38/3.0 eV (PBE/HSE06) in the single Si edge-, single Si non-edge-, double Si ortho-, double Si meta-, double Si para-, and 100% Si-substituted AGNR configurations, respectively. Meanwhile, pristine ZGNRs displayed antiferromagnetic semiconducting behavior with a spin degenerate bandgap of 0.52/0.81 eV (PBE/HSE06) and becomes a ferromagnetic semimetal in the single Si configurations or an unusual ferromagnetic semiconductor in the 100% Si configuration. Under the developed first-principles theoretical framework, the formation of quasi π (C-2pz and Si-3pz) and quasi σ (C-2s, -2pxy and Si-3s and -3pxy) bands was identified in the Si-substituted configurations. These quasi π and quasi σ bands showed weak separation, resulting in weak quasi sp2 hybridization in Si-C bonds, in which the identified hybridization mechanism was a strong evidence for the formation of stable planar 1D structures in the Si-substituted configurations. Our complete revelation of the essential properties of Si-substituted GNRs can provide a complete understanding of their chemically doped 1D materials for various practical applications.

Double Centrosymmetric Si···π Tetrel Bonds as New Synthons─Evidence from Crystal Structures and DFT Calculations.

The crystal structure of bis((μ2-ethynylsilyloxo)-dichloro-aluminum), BEDCA, and a few related structures are characterized by the occurrence of tetrel bonds that link molecules. Particularly, centosymmetric dimers in such structures occur that are connected by two equivalent Si···π tetrel bonds. The dimer of BEDCA and dimers of other model species that similarly are linked by two equivalent Si···π tetrel bonds are analyzed theoretically. Some of the complexes calculated here are also characterized by the occurrence of triel bonds. Thus, ωB97XD/aug-cc-pVTZ calculations are performed and these DFT results are further supported by calculations with the use of other theoretical approaches: the quantum theory of atoms in molecules, QTAIM; the natural bond orbital, NBO; the energy decomposition analysis, EDA; and the noncovalent interactions method, NCI. The results show that the tetrel bonds analyzed here are rather weak, and they are not detected by the QTAIM approach; however, they are detected by other approaches, like NBO, for example. On the other hand, the triel bonds that occur in a few complexes discussed here are very strong and possess characteristics of covalent bonds.

Kalyuzhnyite-(Ce), NaKCaSrCeTi(Si8O21)OF(H2O)3, a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan: mineral description, crystal structure and a new double (Si8O21) sheet

AbstractKalyuzhnyite-(Ce), ideally NaKCaSrCeTi(Si8O21)OF(H2O)3, is a new mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan. It occurs as equant grains up to 0.05 × 0.07 mm in a quartz–pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and Dcalc. is 3.120 g/cm3. Kalyuzhnyite-(Ce) is monoclinic, P2/c, a = 18.647(4), b = 11.214(2), c = 14.642(3) Å, β = 129.55(3)° and V = 2360.9(11) Å3. The chemical composition of kalyuzhnyite-(Ce) is Nb2O5 0.53, TiO2 0.16, SiO2 43.85, Er2O3 0.13, Ho2O3 0.10, Gd2O3 0.09, Sm2O3 0.47, Nd2O3 6.22, Pr2O3 1.21, Ce2O3 6.34, La2O3 0.82, PbO 4.90, BaO 0.85, SrO 11.39, CaO 1.86, Cs2O 3.80, K2O 1.59, Na2O 2.99, H2O 5.24, F 1.55, O = F –0.65, total 100.31 wt.%. The empirical formula calculated on 26.11 (O + F) apfu is Na1.07K0.37Cs0.30Sr1.21Ca0.37Pb0.24Ba0.06(Ce0.43Nd0.41Pr0.08La0.06Sm0.03Gd0.01Er0.01Ho0.01)Σ1.04(Ti0.97Nb0.04)Σ1.01Si8.06O25.21F0.90H6.42, Z = 4. The simplified formula is (Na,□)(K,Сs)(Ca,Pb,Sr,Na)SrLn3+Ti(Si8O21)OF(H2O)3, where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R1 index of 2.74%. In kalyuzhnyite-(Ce), the main structural units are a heteropolyhedral Na–Sr–Ce–Ti sheet, ideally [NaSrCeTiOF]7+, and a double (Si8O21)10– sheet parallel to (010). In the Si–O sheet, the Si tetrahedra form ten-membered rings. This is the first occurrence of such a double Si–O sheet in a mineral. The two sheets connect via common vertices of Na-, Sr-, Ce- and Ti-polyhedra and SiO4 tetrahedra to form a framework. The interstitial cations and H2O groups, ideally [(CaK)(H2O)3]3+, occur within the Si–O sheet. The mineral is named in honour of Vasily Avksentievich Kalyuzhny (1899–1993) in recognition of his contributions to the geology of ore deposits of Komi Republic (USSR) and the mineralogy of granitic pegmatites (Tajikistan).

Design of Tender X-ray Absorption Spectroscopy Beamline in Taiwan Photon Source

A new tender X-ray absorption spectroscopy beamline for operating over the photon energy range from 1.7 keV to 11 keV is under construction at port 32 of the Taiwan Photon Source (TPS). The TPS 32A beamline uses two back-to-back water-cooled double crystal monochromators (DCMs), InSb(111) and Si(111), for achieving the wide energy tunability. The beamline design takes advantage of the low emittance of the TPS accelerator and a bending magnet (BM) to obtain a high-brightness focussed beam. In order to overcome the issue of poor thermal conductivity of InSb(111) crystals while facing high thermal load, we have implemented the following features : (i) we have controlled the flux and heat load by optimizing the source collection angle of 2 × 0.15 mrad2 (h × v), and (ii) we have installed water cooled double-bounce high harmonic rejection mirrors (HHRMs) with a variable incidence angle upstream of the DCM to reduce the heat load on the first InSb crystal. The DCM is followed by a 2:1 toroidal focusing mirror (TFM) which focuses the beam parallel to the floor of the experimental endstation. The simulated focus beam size is 0.9 × 0.9 mm2 (h × v, FWHM) using the InSb(111) DCM at 1.7 keV, and 0.2 × 0.45 mm2 (h × v, FWHM) using the Si(111) DCM at 4 keV, respectively. The photon flux is 1010 -1012 photons s−1 in the energy range of 1.7 to 11 keV at the sample stage after passing through the Be windows. The design parameters of photon flux and beam spot size will facilitate a tender X-ray source for carrying out high-quality X-ray absorption spectroscopy experiments.

Strain Analysis of High Energy Implanted 4H-SiC Epiwafer By Synchrotron X-Ray Plane Wave Topography

Silicon Carbide (SiC) is a promising wide bandgap semiconductor for power devices. Due to excellent properties of SiC, such as wide band gap, high break down voltage and thermal stability, SiC devices are able to be operated under harsh environment, such as high temperature, high voltage and high frequency environment [1]. 4H-SiC high voltage devices are highly sought for applications, such as hybrid vehicles, shipboard and power grid systems, and high-speed trains. Usually, such medium or high voltage devices are fabricated on 4H-SiC wafers with thick epilayers that will increase the resistance of the device specially at high temperatures. Deep implanted SiC superjunction devices have the potential to replace planar devices for medium voltage applications [2] However, forming deep implanted pillars into thick epilayers is quite challenging. An optimized solution of selective area doping is utilizing multi-steps high energy ion implantation system. Such a system has been developed at the Tandem Van de Graaff accelerator facility at Brookhaven National Laboratory with the capability of multi-steps high energy implantation at energies up to 150 MeV [3]. By employing such a system, medium voltage charge balance devices and 2 kV superjunction structure PIN diode have been demonstrated [4-5]. Implantation employing high energy ions can create lattice strain in the epilayer by displacing the host atoms. Therefore, characterization of strain in as-implanted epilayer is critical to understand the nature of damage introduced by the high energy implantation.Here, we employ synchrotron X-ray plane wave topography (SXPWT), where X-rays with energy of 8 keV is initially monochromatized by double crystal Si (111) monochromator followed by tuning with an asymmetric Si (331) beam conditioner. The effective width of the resultant X-ray beam is lowered to 0.5” due to the asymmetric factor of the beam conditioner [6]. Therefore, the angular resolution of SXPWT is vastly enhanced, enabling miniscule distortions in the lattice to be detected.The diffraction intensity profile from a 4H-SiC epiwafer implanted with Al ions to (concentration) using this effectively plane wave X-ray beam is shown in Fig. 1. Two high intensity peaks and weak intensity fringes in between, with an angular separation of only 2ʹʹ can be observed. This illustrates non-uniform strain in the implanted epilayer. Intensity profile of peaks and fringes is extracted from the topograph then fitted with commercial Rocking-curve Analysis by Dynamical Simulation (RADS) software developed by Bede to obtain the strain profile. The fitted curve and strain profile are shown in Fig.2. The strain profile will be analyzed and compared with doping profile obtained by Secondary Ion Mass Spectrometry (SIMS).[1] J. Guo, Y. Yang, B. Raghothamachar, T. Kim, M. Dudley, J. Kim, J. Cryst. Growth[2] L. C. Yu and K. Sheng, Solid State Electron., vol. 50, no. 6, pp. 1062-1072, 2006.[3] P. Thieberger, C. Carlson, D. Steski, R. Ghandi, A. Bolotnikov, D. Lilienfeld, P. Losee, Nucl. Instrum. Methods Phys. Res. B: Beam Interact. Mater. At.[4] R. Ghandi, C. Hitchcock, S. Kennerly, ECS Transactions 104, 67 (2021)[5] R. Ghandi, A. Bolotnikov, S. Kennerly, C. Hitchcock, P.-m. Tang, T.P. Chow, 2020 32nd International Symposium on Power Semiconductor Devices and ICs (ISPSD), IEEE, 2020, pp. 126-129.[6] H. Peng, Z. Chen, Y. Liu, B. Raghothamachar, X. Huang, L. Assoufid and M. Dudley, J. Appl. Crystallogr. (accepted) Figure 1

Double Heterojunction Crystalline Silicon Solar Cells: From Doped Silicon to Dopant-Free Passivating Contacts

Carrier-selective passivating contacts for effective electron and hole extraction are crucial to the attainment of high efficiency in crystalline silicon (Si) solar cells. In this comprehensive review, the principle of carrier extraction and recombination mechanisms in conventional industrial Si solar cells are discussed first. Passivating contacts based on (i) amorphous hydrogenated Si and (ii) polysilicon/silicon oxide are next reviewed, with emphasis on carrier selectivity mechanisms including contact layer band alignment with silicon, and localized carrier transport in ultrathin oxides. More recent developments in dopant-free passivating contacts deposited by lower-cost fabrication processes with lower thermal budget are then described. This third category of non-Si based electron- and hole-selective passivating contacts include transition metal oxides, alkali/alkali earth metal fluorides and organic conjugated polymers. The photovoltaic performance of asymmetric double heterojunction Si solar cells fabricated using these non-Si passivating contacts and their stability in damp heat conditions are discussed and compared with Si based passivating contacts.

Spectral Simulation of Heat Transfer Across Polytype Interfaces

Polytype nanowires fabricated in both silicon and germanium are particularly attractive for thermoelectric engineering. In this work, the transport of phonons across polytype heterojunctions such as Si 3C/Si 2H and Ge 3C/Ge 2H is theoretically studied by using a particle Monte Carlo simulation for phonons. Full-Band dispersions and phonon-phonon scattering rates are calculated by using the density-functional theory. Phonon transmission across interfaces is implemented by using a Full-Band version of the Diffusive Mismatch Model. First, the different transport regimes (diffusive, ballistic, and intermediate) for homogenous 3C and 2H Si and Ge bars are investigated by using the Knudsen number as well as the spectral contributions of the thermal flux. Then, single and double polytype Si and Ge heterostructures are studied. The variation of the interface thermal conductance as a function of the geometric dimension as well as the effects of the spectral distribution of the flux are investigated. This local indicator of the phonon transport regime can be used as a local indicator of the occurrence of the out of equilibrium transport regime. Finally, it is shown that the polytype interfaces exhibit significant thermal resistances and generate an out of equilibrium phonon transport regime around the interface over several nanometers.

Influence of minority charge carrier lifetime and concentration on crystalline silicon solar cells based on double antireflection coating: A simulation study

In this work, the optoelectrical properties of silver doped zinc oxide (Ag–ZnO)/ZnO double antireflection coating (ARC) layer were investigated by a simulation approach in terms of their minority charge carriers and surface charge carrier concentrations. From the experimental results, the Ag–ZnO/ZnO double ARC layer on Si solar cells presented the reduced average reflectance by 7.58% which was lowered to ZnO and Ag–ZnO single ARC layer. The simulation study demonstrated the reasonable electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 on c-Si solar cells with Ag–ZnO/ZnO double ARC layer. The simulated I–V characteristics evidenced that the performances of Ag–ZnO/ZnO double ARC layer-based Si solar cells gradually increased with the increase of the minority carrier lifetimes. As compared to a single ARC layer, the Ag–ZnO/ZnO double ARC layer-based Si solar cell achieved the highest conversion efficiency 14.32% with a fill factor of 81.35% at a minority carrier lifetime of 10 μs and carrier concentration of 1 × 10 17 cm −3 . The enhanced photovoltaic performance in Ag–ZnO/ZnO double ARC layer-based Si solar cells might be attributed to the high generation of electron-hole pairs, improved minority lifetime, and excellent carrier concentrations. • A simulation study was performed for optoelectrical properties of Ag–ZnO/ZnO double antireflection coating layer > Photovoltaic properties with respect to minority charge carriers/charge carrier concentrations studied > High electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 were observed > Ag–ZnO/ZnO double ARC layer based Si solar cell achieved the highest PCE 14.32%.

Low temperature annealing of nanocrystalline Si paste for pn junction formation

Low temperature annealing of p- and n-type Si paste films consisting of nanocrystal Si particles coated on Al substrates was investigated for application to low cost large-area electronic devices such as solar cells. This process based on aluminum-induced-crystallization enabled one to enhance recrystallization of the Si paste films with reduction of residual tensile stress while suppressing oxidation greatly even at low temperatures (400–550 °C), as confirmed by Raman spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. pn homo-junction diodes were fabricated successfully using a p/n-type double layer Si paste film and even an n-type single layer Si paste film on Al substrates by annealing at temperatures less than 550 °C. The current-voltage characteristic of the diode using a p/n-type double layer Si paste film showed rectification with the on/off current ratio of about 3200 and the reverse current density of the order of 10−9 A/cm2 at room temperature.

Group-IV-semiconductor quantum-dots in thermal SiO2 layer fabricated by hot-ion implantation technique: different wavelength photon emissions

We experimentally studied three types of group-IV-semiconductor quantum-dots (IV-QDs) of Si-, SiC-, and C-QDs in a thermal SiO2 layer that were fabricated using a very simple hot-ion implantation technique for Si+, double Si+/C+, and C+ into the SiO2 layer, respectively, to realize a different wavelength photoluminescence (PL) emission from near-IR to near-UV ranges. TEM analyses newly confirmed both Si- and C-QDs with a diameter of approximately 2–4 nm in addition to SiC-QDs in SiO2. We successfully demonstrated very strong PL emission from three IV-QDs, and the peak photon energies (E PH) (peak PL-wavelength) of Si-, and SiC-, and C-QDs were approximately 1.56 eV (800 nm), 2.5 eV (500 nm), and 3.3 eV (380 nm), respectively. IV-QDs showed that the PL properties strongly depend on the hot-ion doses of Si and C atoms and the post N2 annealing processes. Consequently, it is easy to design peak PL wavelengths by controlling the ion doses of Si+ and C+ implanted into the SiO2 layer.

Graphene quantum dot states near defects

Smoothly confined graphene quantum dots (GQDs) localize Dirac electrons with conserved spin and valley degrees of freedom. Recent experimental realization of such structures using a combination of magnetic fields and a scanning tunneling microscope tip showcased their potential in locally probing and adjusting the valley degree of freedom. The present work models the influence of lattice defects on the level structure of GQDs. We study both the adiabatic level spacing ``landscape''---orbital splitting and valley splitting---as well as transition dynamics between GQD states. The system is modeled using a tight-binding approach with on-site and hopping parameters in the vicinity of the defect region extracted from density functional theory via Wannier orbitals while time propagation is done using Magnus operators. Different defect types, such as double vacancy, Stone-Wales, flower, and Si substitution, are considered. We predict tunable valley splittings of the order of 2--20 meV. The level structure can thus be tailored at will by engineering appropriate defect geometries.

Inversion Boundary Annihilation in GaAs Monolithically Grown on On‐Axis Silicon (001)

AbstractMonolithic integration of III–V materials and devices on CMOS compatible on‐axis Si (001) substrates enables a route of low‐cost and high‐density Si‐based photonic integrated circuits. Inversion boundaries (IBs) are defects that arise from the interface between III–V materials and Si, which makes it almost impossible to produce high‐quality III–V devices on Si. In this paper, a novel technique to achieve IB‐free GaAs monolithically grown on on‐axis Si (001) substrates by realizing the alternating straight and meandering single atomic steps on Si surface has been demonstrated without the use of double Si atomic steps, which was previously believed to be the key for IB‐free III–V growth on Si. The periodic straight and meandering single atomic steps on Si surface are results of high‐temperature annealing of Si buffer layer. Furthermore, an electronically pumped quantum‐dot laser has been demonstrated on this IB‐free GaAs/Si platform with a maximum operating temperature of 120 °C. These results can be a major step towards monolithic integration of III–V materials and devices with the mature CMOS technology.

Efficient and selective alkene hydrosilation promoted by weak, double Si-H activation at an iron center.

Cationic iron complexes [Cp*(iPr2MeP)FeH2SiHR]+, generated and characterized in solution, are very efficient catalysts for the hydrosilation of terminal alkenes and internal alkynes by primary silanes at low catalyst loading (0.1 mol%) and ambient temperature. These reactions yield only the corresponding secondary silane product, even with SiH4 as the substrate. Mechanistic experiments and DFT calculations indicate that the high rate of hydrosilation is associated with an inherently low barrier for dissociative silane exchange (product release).

Electrical Properties of Monocrystalline Thin Film Si for Solar Cells Fabricated By Rapid Vapor Deposition with Nano-Surface Controlling Double Layer Porous Si in H2

Introduction To reduce the Si thickness with maintaining the high quality is a promising approach to reduce the cost of monocrystalline Si solar cell. A major method to fabricate monocrystalline thin Si is epitaxy by Chemical Vapor Deposition (CVD) and Layer Transfer Process (LTP) as shown in Fig. 1. A seed layer and a sacrificial layer such as double layer porous Si (DLPS) which consist of a Low Porous Layer (LPL) and a High Porous Layer (HPL) are fabricated on the surface of a monocrystalline Si wafer, and then Si is epitaxially deposited on the seed layer. This wafer can then be reused in LTP, thus further reducing the material cost of these Si cells. There remain two challenging issues: (ⅰ) crystal defect introduced during epitaxy caused by the roughness of the seed layer1) and (ⅱ) low deposition rate and yield of epitaxy by CVD. To solve problem (ⅰ), we proposed a Zone Heating Recrystallization (ZHR) method2) to smoothen the DLPS surface as shown in Fig.2. The structure of the DLPS surface can be modified by using an upper lamp heater to scan the surface in one direction and a bottom heater to pre-heat Si substrate. To solve problem (ⅱ), we proposed a Rapid Vapor Deposition (RVD) method3) as shown in Fig.3. By depositing Si under a high vapor pressure by heating the source Si to over 2000℃, the deposition rate of over 10 μm/min with a higher yield is achieved. By applying both the ZHR and RVD methods, we successfully reduced the roughness of a DLPS surface and obtained monocrystalline Si with Si wafer level. The critical effect of lowering the roughness of a DLPS surface to Rms < 0.3 nm was confirmed1)4). In this work, to fabricate high quality solar cells, we investigated the key factors in improving the roughness of a DLPS surface and evaluated the semiconductor properties of monocrystalline thin film Si. Experiment DLPS was prepared by 2-step anodization of p-type monocrystalline Si (100) wafers (≦0.005 Ω・cm) with 2 mA/cm2 and 415 s for LPL and 200 mA/cm2 and 5 s for HPL, respectively. The prepared DLPS were thermally treated by ZHR with adjusting the heat levels of both the upper and bottom heater and the scan rate of the upper heater under H2(0～5%)/N2 atmosphere to investigate the effect of surface oxidation. RVD were carried out with using p-type monocrystalline Si (100) (1-10 Ω・cm) wafers as the source. The thickness of Si was required to be >40 μm to obtain the sufficient light absorbance, but in our RVD apparatus, only <10 µm-thick Si can be fabricated in one deposition due to the structure of the source boats, so Si was epitaxially deposited on DLPS by RVD in 5 time depositions and the film (48 μm-thick) (Sample-1) was obtained. To increase the deposition rate, the tungsten boat to put Si was modified and the film with 35 μm-thick was obtained in one time deposition (Sample-2). The roughness of the DLPS surface were analyzed using atomic force microscopy. To measure the mobility and the carrier concentration, Si was epitaxially deposited directly on non-doped Si (100) (≧1000 Ω・cm) wafer and the hall effect measurement was carried out. The lifetime of obtained Si films were measured after passivated with Al2O3 film on both sides by atomic layer deposition. Results and discussion The minimum roughness of DLPS surface and the heating amount which minimize the roughness of DLPS surface was decreased by changing the atmosphere from N2 to H2/N2. It is supposed that the structural change occurs easier by inhibiting the effect of oxidation, possibly due to the presence of H2. The life time of Sample-2 was much higher than that of Sample-1. In the multiple RVD process, a native oxide film seemed to be formed on the surface of a Si film during re-setting sources in air atmosphere. Thus, a thin Si with almost wafer-level quality was obtained by increase the thickness by RVD in one deposition. Conclusion The importance to inhibit the effect of oxidation during ZHR was clarified. Nearly wafer-level, 35 µm-thick Si was obtained by RVD in one time deposition by increasing deposition rate. Acknowledgements The part of this research was supported by KAKENHI (KIBAN A) and Center for Low Carbon Society Strategy (LCS), JST. 1)K.Hasegawa,C.Takazawa,M.Fujita,S.Noda and M.Ihara,CrystEngComm,20(13),1774-1778(2018). 2)A.Lukianov,K.Murakami,C.Takazawa and M.Ihara,Appl.Phys.Lett.,108(213904),1-4(2016). 3)Y.Yamasaki,K.Hasegawa,T.Osawa and S.Noda,CrystEngComm,18,3404-3410(2016). 4)C.Takazawa,M.Fujita,K.Hasegawa,A.Lukianov,X.Zhang,S.Noda and M.Ihara,ECS Transaction,75(31),11-23(2016). Figure 1

Role of Dangling Bond State Occupancy in Adsorption of Copper Phthalocyanine on Si(111)-Sn-√3 × √3

Interaction of organic molecules with solid surfaces reflects the local electronic structure of nonequivalent surface sites. The Si(111)-Sn-√3 × √3 surface with intrinsic defects offers dangling bonds with various electron occupancies. In this study, we report on the interaction of copper phthalocyanine with this surface studied with scanning tunneling microscopy and spectroscopy. Sn atoms in the adlayer contain unpaired electrons in their dangling bonds. The molecules are found to adsorb on Sb and Si substitutional defects instead of the homogenous Sn areas. The symmetry of the molecules is lowered or lost after adsorption, and we find substantial differences in the electronic structure of the molecules adsorbed on either type of defects. Furthermore, the molecules preferentially adsorb on double Si substitutional defects where they can switch between a static and a fuzzy state, for both of which a corresponding bonding model is proposed. Our study shows a pivotal role of substitutional defects in the re...

Silicon nitride as antireflection coating to enhance the conversion efficiency of silicon solar cells

The aim of this work is to investigate the effect of single and double layer antireflection coating (ARC) on the performance of silicon solar cells. In this regard, various previous works on single and double layer ARCs have been consulted. Silicon nitride (Si 3 N 4 ) has been used as ARC material because of its varying refractive index (1.8-3.0). Numerical calculations have been performed to obtain the reflectance for single and double layer Si 3 N 4 using the transfer matrix method. Double layer antireflection coating (DLARC) of Si 3 N 4 is found to have significant advantages over single layer antireflection coating (SLARC). Calculated reflectances have been further used in the PC1D simulator as external reflectance files to study the performance of a silicon solar cell. As a result of the simulation, the reflectance is found to reduce from >30% to <2% with short circuit current of 3.86 mA/cm 2 and conversion efficiency of 20.22% for DLARC. Results obtained for DLARC were further compared with a reference cell (without ARC), a cell with SLARC, and a cell with zero reflectance on the front surface.

Synthesis of a Dichlorodigermasilane: Double Si–Cl Activation by a Ge=Ge Unit

Halogenated oligosilanes and oligogermanes are interesting compounds in oligosilane chemistry from the viewpoint of silicon-based-materials. Herein, it was demonstrated that a 1,2-digermacyclobutadiene derivative could work as a bis-germylene building block towards double Si–Cl activation to give a halogenated oligometallane, a bis(chlorogermyl)dichlorosilane derivative.

Tunnel Transistor-Based Reliable and Energy Efficient Computing Architectures with Circuit and Architectural Co-Design at Low VDD

Tunnel field-effect transistors (TFETs) as low voltage device options have attracted recent attention for energy efficient circuit designs with CMOS technology scaling. This paper presents the circuit and architectural co-design approach for designing reliable and energy efficient architectures (adder cells) for new computing platforms at supply voltages. At circuit level TFET-based 28-transistor static logic design (28T) and 24-transistor transmission gate logic design (24T) have been explored. At architectural level, multiplexer (MUX)-based 22-transistor full adder design (22T) is proposed. Performance of TFET-based architectures have also been benchmarked with 20[Formula: see text]nm double gate Si FinFET technology. It has been seen that with FinFET technology 24T design is not effective in terms of energy efficiency and reliability (due to the large leakage currents in transmission gate logic topology). 28T design is the best in reliability perspective (in terms of reduced over shoots, full logic swing and reduced glitch duration etc.) and 22T design to be energy efficient option. It has been demonstrated in this paper that TFET’s steep slope characteristics enable the 24T design to have similar reliability characteristics like 28T design and energy efficiency like 22T design. TFET-based 22T design has [Formula: see text]91% smaller energy delay product (EDP) and [Formula: see text]84.4% less power delay product (PDP) in comparison to the low threshold voltage (LVT) FinFET 22T design at 0.2[Formula: see text]V VDD.

Monocrystalline Si Thin Film for Solar Cells Grown on Double Layer Porous Si Treated By Zone Heating Recrystallization

The recent development in monocrystalline Si solar cell technology is significant both for reducing the cost and for developing the power generation efficiency. The reduction of Si thickness is one of the key to achieve the further cost reduction. Bottom up technics such as epitaxy and layer transfer process is promising approach to get less than 50 µm-thick Si thin film. Si layer is deposited epitaxially on a seed monocrystalline wafer with a thin sacrificial layer, and then an epitaxial thin film is detached from the seed layer (Fig. 1). This process on double layer porous Si (DLPS), a top low porosity seed layer and a bottom high porosity sacrificial layer, have been widely studied, but there are two challenging issues to be solved. One is the long process time of epitaxy by chemical vapor deposition and another is the quality of the epitaxial film. Rapid vapor deposition (RVD) have been realized to grow epitaxial Si layer at ~10 µm/min deposition rate by the evaporation of Si source with >2000 °C [1]. On the other hand, the crystallographic quality of epitaxial film will depend on the roughness of the seed layer because such roughness will make lattice mismatch during the crystal growth. The effect of the surface roughness is supposed to be larger when the film growth rate get bigger, so to control the roughness become more important to obtain the high quality Si thin film with high speed, low cost process such as RVD. We have developed the zone-heating recrystallization (ZHR) method, the high-speed scanning lamp heating below the melting point of Si, for the selective heat treatment of the Si surface (Fig. 2) [2]. By applying ZHR to the epitaxy and layer transfer process on DLPS by RVD, we obtained the 9 µm-thick monocrystalline Si thin film with only 1-min epitaxy [3]. In this work, we controlled nanometer-size roughness of DLPS surface by ZHR and investigated the properties of Si thin film grown with RVD. To investigate the quality of thin film Si by both XRD and electron spin resonance (ESR), RVD were carried out with intrinsic Si wafer as Si source to avoid the signal of electron from the dopant. ~9 µm intrinsic Si thin films were grown and they could be easily detached by transferring to scotch tape. The Si films with different root mean square roughness (Rms), pore size and pore number density which were grown on DLPS with/without ZHR in several condition were picked up and analyzed. DLPS were formed on p-type monocrystalline Si (100) wafer by two-step anodization. ZHR were carried out with different input power into bottom heater and scanning rate of top lamp heater, and DLPS with different Rms (0.23-0.39 nm) observed by AFM were obtained as described in the previous report [3]. In Si film grown by RVD on the DLPS by each ZHR condition, in-plane XRD Φ-scan of (022) diffraction showed clear four fold symmetry, which proves that the epitaxial monocrystalline film of Si(100) obtained regardless of ZHR conditions. The effect of the surface roughness of DLPS on the crystallographic quality of epitaxial Si films will be discussed. In summary, the epitaxial monocrystalline film by RVD was obtained by the selective heat treatment of Si surface of DLPS by ZHR. The intrinsic monocrystalline film with 9 µm by RVD on DLPS could be easily detached from Si wafer to evaluate crystallographic quality by ESR. [1] Y. Yamasaki et al., CrystEngComm 18, 2016. 3404. [2] A. Lukianov et al., Appl. Phys. Lett. 108, 2016, 1. [3] C. Takazawa et al., ECS Trans. 75, 2017, 11. Figure 1