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Nanocapsules that collapse in response to guanosine triphosphate (GTP) have the potential as drug carriers for efficiently curing diseases caused by cancer and RNA viruses because GTP is present at high levels in such diseased cells and tissues. However, known GTP-responsive carriers also respond to adenosine triphosphate (ATP), which is abundant in normal cells as well. Here, we report the elaborate reconstitution of microtubule into a nanocapsule that selectively responds to GTP. When the tubulin monomer from microtubule is incubated at 37 °C with a mixture of GTP (17 mol%) and nonhydrolysable GTP* (83 mol%), a tubulin nanosheet forms. Upon addition of photoreactive molecular glue to the resulting dispersion, the nanosheet is transformed into a nanocapsule. Cell death results when a doxorubicin-containing nanocapsule, after photochemically crosslinked for properly stabilizing its shell, is taken up into cancer cells that overexpress GTP.

During injured tissue regeneration, the extracellular matrix plays a key role in controlling and coordinating various cellular events by binding and releasing secreted proteins in addition to promoting cell adhesion. Herein, we develop a cell-adhesive fiber-forming peptide that mimics the jigsaw-shaped hydrophobic surface in the dovetail-packing motif of glycophorin A as an artificial extracellular matrix for regenerative therapy. We show that the jigsaw-shaped self-assembling peptide forms several-micrometer-long supramolecular nanofibers through a helix-to-strand transition to afford a hydrogel under physiological conditions and disperses homogeneously in the hydrogel. The molecular- and macro-scale supramolecular properties of the jigsaw-shaped self-assembling peptide hydrogel allow efficient incorporation and sustained release of vascular endothelial growth factor, and demonstrate cell transplantation-free regenerative therapeutic effects in a subacute-chronic phase mouse stroke model. This research highlights a therapeutic strategy for injured tissue regeneration using the jigsaw-shaped self-assembling peptide supramolecular hydrogel., The extracellular matrix contributes to tissue regeneration by binding and releasing growth factors. Here the authors present the jigsaw-shaped self-assembling peptide JigSAP as an artificial ECM and show that VEGF-JigSAP has therapeutic effects on the subacute-chronic phase of brain stroke.

A simple method to form ultra-thin (2 and Si3N4. We found that decreasing the Ge thickness reduces the grain size and increases the grain boundary barrier height, causing carrier mobility degradation. We examined two methods, known effective to enhance the grain size in the thicker Ge (>100 nm). As a result, a relatively high Hall hole mobility (59 cm2 V−1 s−1) has been achieved with a 20 nm thick polycrystalline Ge layer on Si3N4, which is the highest value among the previously reported works.

Silicon growth using chemical vapor deposition (CVD) is omnipresent in electronic device technology. CVD reactions of different precursor molecules on Si have been the focus of research for decades. Renewed interest in the CVD growth of silicon films has been spurred by the need for high-quality, ultrathin films for fabrication of novel electronic devices. In this work, we have formulated an experimental nanoscale approach to analyze the modification of wet-prepared Si(0 0 1) surfaces by dichlorosilane (SiH2Cl2, DCS) reactions at low pressure and 500–650 °C performed in a thermal CVD reactor connected to a scanning tunneling microscopy and spectroscopy (STM/STS) system. The DCS dissociation reaction resulted in a decrease of the Si surface potential due to the creation of chlorine-induced electric dipoles. Employing the ability of the scanning tunneling spectroscopy (STS) to recognize specific adsorption sites, we have carried out a comparative analysis of the relative coverage by Cl and Si as a function of exposure conditions. The existence of an intermediate reaction state of the DCS molecule was confirmed by the STS spectra and further supported by Si XPS data and ab initio calculations. This experimental nanoscale approach shows great promise for the CVD growth of ultrathin films.

This paper describes the use of flash lamp annealing (FLA) to fabricate high-Sn content GeSn n-MOSFETs. We exploit FLA processing for both impurity activation and for the solid-phase growth (SPG) of the GeSn channel. High-Sn incorporation of up to 12% is achieved by overcoming the solid-solubility limit of Sn in Ge (1%), and high-quality n+-source/drain junctions were obtained by P implantation and subsequent FLA. Consequently, we achieved well-behaved transistor operation of the SPG-Ge0.88Sn0.12 n-MOSFETs, with an on/off current ratio one order of magnitude higher than for conventional rapid thermal annealing processing.

The effect of flash lamp annealing on the crystal growth of amorphous germanium-tin (GeSn) layer deposited on Ge-on-insulator wafer was investigated. It was found that the presence of Sn in the amorphous Ge significantly promoted solid-phase growth (SPG). The diffusion of Sn during the SPG of GeSn was completely suppressed owing to milli-second thermal processing, providing a high-quality GeSn layer with Sn content of 13%, which far exceeds the equilibrium solid solubility limit (∼1%). The fabricated GeSn/Ge-on-insulator wafer exhibited improved infrared absorption beyond 2000 nm, which would be a suitable platform for near-infrared image sensors based on group-IV materials.

The capacitance–voltage characteristics of MOS capacitors and ab initio theoretical calculations revealed that an amorphous film composed of WSin clusters (n = 6−12) had a low effective work function of 4.0 eV on SiO2 with excellent thermal stability up to 600oC. In Si Schottky diodes with WSin insertion, the electron Schottky barrier height (SBH) was 0.58 eV for n = 6 and reduced to 0.45 eV when n = 12. The n-dependency of SBH was attributed to the surface passivation of WSin becoming more effective as n increased, with annealing leading to a lower value of 0.32 eV.

Ab initio molecular orbital calculations are performed for B13−, Al13−, B12H122−, Al12H122−, Si10, and Si10H16 clusters. The highest occupied molecular orbital (HOMO) of stable and unstable clusters is bonding and antibonding orbitals, respectively. The cluster size dependences of the orbital energies are almost the same for B13− and Al13− icosahedral clusters, when the size and the energy are properly normalized. The normalized factors for size and energy are almost coincident with the ratios of those of the atomic outer s orbitals. On the other hand, the most stable size of B13− is smaller than that of Al13−, and this ratio of the stable size seems to be affected by the ratio of the sizes of the atomic outer p orbitals. As a result, B13− and Al13− icosahedral clusters have antibonding and bonding orbitals for HOMOs and so are unstable and stable, respectively. The situation for B13− and Al13− planar clusters is opposite to that discussed above for the icosahedral clusters. The orbital energies for the metallic bonding Al13− icosahedral and Si10 clusters can be reproduced by the Woods–Saxon model; however, those for the unstable B13− icosahedral and covalent bonding B12H122−, Al12H122−, and Si10H16 clusters cannot be reproduced by the Woods–Saxon model. After optimization of the parameters of the Woods–Saxon model for the Al13− icosahedral and Si10 clusters, the orbital energies are reproduced very well and the sizes and shapes of the potential are reasonable.

Thin-film transistors (TFTs) on insulator substrates are widely used in applications from liquid crystal displays to sensor devices. However, insulator substrates with low heat conductivity lead to unfavorable self-heating effects in the channel regions. Herein, the carrier and heat transport properties of polycrystalline GeSn films on SiO2/Si substrates were improved by suppressing Sn segregation in the films to fabricate GeSn channel TFTs. Alloying with 5.5% Sn enabled the formation of larger grains than those in poly-Ge films after low-temperature annealing (below 520 °C) without Sn segregation. In addition, the films had a hole mobility of 40 cm2 V−1 s−1 at a hole density of 1.1 × 1018 cm−3 and a thermal conductivity of 12.1 Wm−1 K−1 at room temperature. The temperature dependences of the carrier and heat transport properties of the poly-GeSn films were investigated to accurately simulate a device with a poly-GeSn channel TFT. This was achieved by using the carrier transport measurements and numerical simulations of the heat transport in the Debye model. The simulated device allowed an accurate assessment of the self-heating effects of the TFT and thus provides a design guide for TFTs.

Submicrometer-sized high-index Mie resonators attract significant interest in photonic applications due to their capabilities to manipulate light. 2-dimensional metamaterials or metasurfaces consisting of arrays of such resonators on a device surface can be used in the flat optics, sensors, and other applications. Here, we report on the comprehensive nanoscale characterization and optical properties of nearly regular SiGe Mie resonator arrays on a Si surface fabricated using a simple and low-cost method. We achieved control on the surface morphology by depositing Ge on the Si(100) surface at elevated temperatures 890–960 °C and obtained arrays of submicrometer/micrometer low-Ge-content SiGe lenslike islands via dewetting when the Ge content was >4%. At the lower Ge content, we observed the formation of a continuous SiGe film via wetting. We used Raman microscopy not only for the Ge content and stress control but also for studying photonic properties of the islands and their coupling with the Si substrate. In contrast to the elastic light scattering, we clearly distinguished visible light Raman signals from the islands themselves and from the substrate areas under the islands enhanced compared to the signal from the open substrate. Calculation of the light electric field distribution in the islands and the substrate demonstrate how the islands trap the light and forward it into the high-index substrate. This explains the island-induced reflection suppression and Si substrate Raman enhancement, which we observe experimentally. Such an SiGe-island array is a promising metasurface for the improvement of Si photosensors and solar-energy device performance.

We elucidate the comprehensive mechanism of gas-phase reactions of WF6 with SiH4 for deposition of high-density W silicide (WSi n , 0 ~10, less reactive fluorine-deficient molecules are formed by the reduction reaction, inhibiting the powder formation. Only when the gas-phase reaction with SiH4 is sufficiently promoted under the condition of an extremely high R S/W > 103, the W-atom-encapsulated Si n cage clusters are formed without fluorine content, leading to the powder-free deposition of the dense WSi n film of n ≥ 6 with a homogeneously smooth surface.

© 2016 Author(s). Strained Ge1-xSnx thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge0.94Sn0.06 films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge0.94Sn0.06 films grown by molecular beam epitaxy. ispartof: Journal of Applied Physics vol:120 issue:8 pages:1-11 status: published

Thermally induced crystallization processes for amorphous GeSn thin films with Sn concentrations beyond the solubility limit of the bulk crystal Ge-Sn binary system have been examined by X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, and (scanning) transmission electron microscopy. We paid special attention to the behavior of Sn before and after recrystallization. In the as-deposited specimens, Sn atoms were homogeneously distributed in an amorphous matrix. Prior to crystallization, an amorphous-to-amorphous phase transformation associated with the rearrangement of Sn atoms was observed during heat treatment; this transformation is reversible with respect to temperature. Remarkable recrystallization occurred at temperatures above 400 degrees C, and Sn atoms were ejected from the crystallized GeSn matrix. The segregation of Sn became more pronounced with increasing annealing temperature, and the ejected Sn existed as a liquid phase. It was found that the molten Sn remains as a supercooled liquid below the eutectic temperature of the GeSn binary system during the cooling process, and finally, beta-Sn precipitates were formed at ambient temperature. ispartof: Journal of Applied Physics vol:120 issue:24 status: published

We have developed a new type of ion trap, an external multipole static attraction ion trap (EMSIT) for use as a cluster-ion source. The EMSIT consists of 36 linear pole electrodes of nearly equal length arranged in a 6×6 square lattice and a cylindrical cage electrode surrounding the pole edges. An ion-trapping field is generated between the multipole and the cage electrode by applying ac and dc voltages to the pole electrodes. Simulation results indicated that the EMSIT can confine the ions with a wide range of mass values in the ion-trapping field and act as a mass-selective ion source using the central four poles as an ion extraction guide. In fact, we observed that Xe+ ions were confined in the EMSIT for more than 1 s in the presence of He buffer gas of 5.0×10-2 Pa. Hydrogenated Si cluster ions, SinHx+ (n=2–6), were grown from SiH4 gas and extracted with mass selection, indicating that the EMSIT acts as a cluster-ion source.

We studied how Si6Hx clusters behave on Si (111)-(7×7) surfaces depending on hydrogen content x by scanning tunneling microscopy. The Si6Hx+ ions were synthesized in an ion trap and deposited onto the (7×7) surfaces with an impact kinetic energy of 3 eV, i.e., 0.5 eV/Si atom, without decomposition. Deposited Si6H10–13 clusters favorably adsorbed on faulted halves of the (7×7) surfaces while Si6H0–5 clusters were randomly distributed. A clear difference of the electronic structure between Si6H0–5 and Si6H10–13 clusters was found in the tunneling spectra of the clusters.

Kinetic energy distribution of ion beams was measured by a retarding field energy analyzer for a mass-selective cluster ion beam deposition system that uses a quadrupole ion trap as a cluster ion beam source. The results indicated that the system delivers a cluster-ion beam with energy distribution of ~2 eV, which corresponded well to the calculation results of the trapping potentials in the ion trap. Using this deposition system, mass-selected hydrogenated Si cluster ions SinHx+ were actually deposited on Si(111)-(7×7) surfaces at impact kinetic energy Ed of 3–30 eV. Observation by using a scanning tunneling microscope (STM) demonstrated that Si6Hx+ cluster ions landed on the surface without decomposition at Ed=3 eV, while the deposition was destructive at Ed18 eV.

Metasurfaces consisting of arrays of high-index Mie resonators concentrating/redirecting light are important for integrated optics, photodetectors, and solar cells. Herein, we report the optical properties of low-Ge-content SiGe lens-like Mie resonator island arrays fabricated via dewetting during Ge deposition on a Si(100) surface at approximately 900 °C. We observe enhancement of the Si interaction with light owing to the efficient island-induced light concentration in the submicron-depth Si layer, which is mediated by both near-field Mie resonance leaking into the substrate and far-field light focusing. Such metasurfaces can improve the Si photodetector and solar-cell performance.

We demonstrate the excellent thermal stability of an amorphous film composed of W-atom-encapsulated Si (WSin) clusters with n ≥ 8, formed by thermal deposition using WF6 and SiH4 gas sources. To determine how the structure of the constituting clusters affects the thermal stability of the film, we also prepared films containing unencapsulated WSin clusters in which the W atom was not fully encapsulated in the Sin cage, with n ≤ 7. The effect of annealing was investigated by Raman scattering and optical absorption measurements with repeated 10-min isochronal annealing in a N2 atmosphere at temperatures ranging from 500 to 1100 °C. The films, composed of WSin clusters completely encapsulating W atoms with a uniform composition of n = 12, remained in the same amorphous structure up to 1000 °C, although partial crystallization of Si began at 1100 °C. The stability decreased when the film contained unencapsulated WSin clusters, even with an average film composition of n ≤ 10; partial crystallizations of Si and ...

We structurally and electrically characterize sub-10-nm-thick heteroepitaxial Ge films on Si(001), formed by heated sputtering and subsequent rapid thermal annealing (RTA). After RTA treatment at 720 °C, we find the heteroepitaxial Ge films to have smooth surfaces with a roughness root mean square value of 0.54 nm. Raman measurement reveals that the 720 °C RTA improves the crystallinity of Ge films while maintaining abrupt Ge/Si interfaces. Cross-sectional transmission electron microscopy confirms that the 720 °C RTA step effectively reduces stacking faults and dislocations in the Ge films. The Richardson plot of the TaN/Ge/n-Si diode indicates a Schottky barrier height (SBH) of 0.33 V, which is close to the height of 0.37 V measured from the capacitance–voltage measurement. These values are reasonable compared with the reported SBH of the TaN/bulk Ge Schottky barrier diode, indicating that the method involving heated sputtering and subsequent RTA provides adequate thin Ge films for Ge/Si heterostructures.

In this study, the temperature-dependent thermoelectric properties of p-type single-crystal Ge, which is a useful material for thermoelectric applications owing to its significantly high carrier mobility, were investigated. The thermoelectric properties of Ga-doped (5.7 × 1016, 3.4 × 1018, and 1.0 × 1019 cm−3) p-type single-crystal Ge were measured from room temperature to 770 K. The sample with a carrier concentration of 1.0 × 1019 cm−3 showed the highest thermoelectric figure of merit, ZT, over the entire measured temperature range. The maximum ZT value was 0.06 at 650 K. A theoretical model based on the Boltzmann transport equation with relaxation-time approximation was developed and quantitatively reproduced the experimentally observed data. The optimal impurity concentration predicted by this model was 3 × 1019 cm−3 at 300 K and increased with temperature.

We formed Si-rich W silicide films composed of Sin clusters, each of which encapsulates a W atom (WSi(n) clusters with 8 < n ≤ ∼ 12), by using a gas-phase reaction between WF6 and SiH4 in a hot-wall reactor. The hydrogenated WSi(n)H(x) clusters with reduced F concentration were synthesized in a heated gas phase and subsequently deposited on a substrate heated to 350-420 °C, where they dehydrogenated and coalesced into the film. Under a gas pressure of SiH4 high enough for the WSi(n)H(x) reactant to collide a sufficient number of times with SiH4 molecules before reaching the substrate, the resulting film was composed of WSi(n) clusters with a uniform n, which was determined by the gas temperature. The formed films were amorphous semiconductors with an optical gap of ∼0.8-1.5 eV and an electrical mobility gap of ∼0.05-0.12 eV, both of which increased as n increased from 8 to 12. We attribute this dependence to the reduction of randomness in the Si network as n increased, which decreased the densities of band tail states and localized states.

We report the formation of icosahedral B(12)H(8) (+) through ion-molecule reactions of the decaborane ion [B(10)H(x)(+) (x=6-14)] with diborane (B(2)H(6)) molecules in an external quadrupole static attraction ion trap. The hydrogen content n of B(12)H(n)(+) is determined by the analysis of the mass spectrum. The result reveals that B(12)H(8)(+) is the main product. Ab initio calculations indicate that B(12)H(8)(+) preferentially forms an icosahedral structure rather than a quasiplanar structure. The energies of the formation reactions of B(12)H(14)(+) and B(12)H(12)(+) between B(10)H(x)(+) (x=6,8) ions, which are considered to be involved in the formation of B(12)H(n)(+), and a B(2)H(6) molecule are calculated. The calculations of the detachment pathway of H(2) molecules and H atoms from the product ions, B(12)H(14)(+) and B(12)H(12) (+), indicate that the intermediate state has a relatively low energy, enabling the detachment reaction to proceed owing to the sufficient reaction energy. This autodetachment of H(2) accounts for the experimental result that B(12)H(8)(+) is the most abundant product, even though it does not have the lowest energy among B(12)H(n)(+).

We have studied the electronic states of shallow P-doped n-type Si(100) with hydrofluoric acid (HF) treatment using high-resolution electron energy loss spectroscopy (HREELS). Upon HF treatment, HREELS measurements confirmed the formation of hydride on the Si surface. The surface plasmon energy was measured as an indicator of the change in carrier density near the surface region (12 nm). We observed a blueshift of the plasmon peak after annealing at 300 °C, indicating the reactivation of the P dopant atoms neutralized by hydrogen near the Si surface. Further annealing at 600 °C removed hydrogen from the Si surface, resulting in surface states due to dangling bonds. The electron transfer towards the surface states induces the reduction in electron density, forming a depletion layer, and band bending. The activation efficiency of the P dopant near the surface was estimated to be 55–59% on the basis of the relationship between surface plasmon energy and carrier density.

Carrier distributions near n-type epitaxially-grown Ge(100) surfaces with high impurity concentrations (1 × 1020 cm−3) were studied using high resolution electron energy loss spectroscopy (HREELS) upon surface treatments in aqueous solutions of HF and HCl. After surface treatments with HCl and HF, the molecular vibration modes distinctly showed either chloride or hydride terminations of Ge surfaces with negligible oxidation. The free-carrier concentration profile was inferred from the conduction band plasmon measurements as a function of the incident electron energies employing a dielectric theory simulation with a 4-layer structure and an effective electron mass of 0.02m0. A carrier-free layer of 40 and 24 Å were derived for HCl- and HF-treated Ge(100), respectively. The surface band bending was estimated to be 0.32 eV for HF-treated Ge. HCl-treated Ge surfaces showed a band bending of 0.91 eV attributed to the strong effect of the surface Cl-Ge dipole.

In recent years, nanostructured thermoelectric materials have attracted much attention. However, despite this increasing attention, available information on the thermoelectric properties of single-crystal Si is quite limited, especially for high doping concentrations at high temperatures. In this study, the thermoelectric properties of heavily doped (1018–1020 cm−3) n- and p-type single-crystal Si were studied from room temperature to above 1000 K. The figures of merit, ZT, were calculated from the measured data of electrical conductivity, Seebeck coefficient, and thermal conductivity. The maximum ZT values were 0.015 for n-type and 0.008 for p-type Si at room temperature. To better understand the carrier and phonon transport and to predict the thermoelectric properties of Si, we have developed a simple theoretical model based on the Boltzmann transport equation with the relaxation-time approximation.

We investigated a device isolation process for MoS2-based devices and fabricated high-k/metal-gate MoS2 MOSFETs. An Ar-ion etching process was utilized for the device isolation process. It circumvents damage in the device channel, as confirmed by Raman spectroscopy. A top-gate MoS2 MOSFET was fabricated with a HfO2 thin film 16 nm thick as the gate insulator. Utilizing capacitance–voltage (C–V) measurements, the capacitance equivalent thickness (CET) was estimated to be 5.36 nm, which indicates that a gate stack with the sufficiently thin insulator was successfully realized. The device exhibited a mobility of 25.3 cm2/(Vs), a subthreshold swing (SS) of 86.0 mV/decade, and an ON/OFF ratio of 107. This satisfactory device performance demonstrates the feasibility of the proposed device isolation process.

Ultrathin GeSn layers with a thickness of 5.5 nm are fabricated on a Si(111) substrate by solid phase epitaxy (SPE) of amorphous GeSn layers with Sn concentrations up to 6.7%. We demonstrate well-behaved depletion-mode operation of GeSn p-channel metal–oxide–semiconductor field-effect transistors (pMOSFETs) with an on/off ratio of more than 1000 owing to the ultrathin GeSn channel layer (5.5 nm). It is found that the on current increases significantly with increasing Sn concentration at the same gate overdrive, attributed to an increasing substitutional Sn incorporation in Ge. The GeSn (6.7%) layer sample shows approximately 90% enhancement in hole mobility in comparison with a pure Ge channel on Si.

We investigated the electrical properties and derived the energy band structures of amorphous Si-rich W silicide (a-WSin) films and approximately 1-nm-thick crystalline WSin epitaxial films (e-WSin) on Si (100) substrates with composition n = 8–10, both composed of Sin clusters each of which encapsulates a W atom (WSin clusters). The effect of annealing in the temperature range of 300–500 °C was also investigated. The Hall measurements at room temperature revealed that a-WSin is a nearly intrinsic semiconductor, whereas e-WSin is an n-type semiconductor with electron mobility of ∼8 cm2/V s and high sheet electron density of ∼7 × 1012 cm−2. According to the temperature dependence of the electrical properties, a-WSin has a mobility gap of ∼0.1 eV and mid gap states in the region of 1019 cm−3 eV−1 in an optical gap of ∼0.6 eV with considerable band tail states; e-WSin has a donor level of ∼0.1 eV with sheet density in the region of 1012 cm−2 in a band gap of ∼0.3 eV. These semiconducting band structures are ...

We demonstrate an electron excitation effect in silicon nanocrystals (SiNCs) embedded in a SiO2 layer treated with hydrogen atoms for passivation of interface defects. Using electron spin resonance (ESR) measurements of quasi-conduction electrons (QCE) excited at lower temperatures, we observed the enhancement of the number of QCE in SiNCs by light irradiation. The electron excitation effect is retained at temperatures lower than 250 K after stopping the light irradiation. The dependence on the size of SiNCs and on excitation laser wavelength suggest that the main memory process is caused by photo-induced electron charging induced through electron excitation of interface states between SiNCs and SiO2.

In this study, we have developed highly efficient thermoelectric materials based on p-type and n-type composite films of Si nanocrystals and Ni silicide nanocrystals. The heavy doping of the films with boron or phosphorus and thermal annealing of the films caused formation of nanocrystals with high electrical conductivities, low thermal conductivities, and high Seebeck coefficients, consequently leading to the high dimensionless figures of merit (ZT). For the p-type (B-doped) and n-type (p-doped) films, ZT is 0.13 and 0.06, respectively, which were much higher than that of bulk Si (

We demonstrate tensile-strained GeSn metal–oxide–semiconductor field-effect transistor (MOSFET) devices on Si(111) substrates using solid phase epitaxy of amorphous GeSn layers. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single-crystalline GeSn by solid phase epitaxy. Single-crystalline GeSn layers with 4.5% Sn and 0.33% tensile strain are fabricated on Si(111) substrates. To verify the structural quality of thin-film GeSn as a channel material, we fabricate ultrathin GeSn p-channel MOSFETs (pMOSFETs) on Si(111). We demonstrate junctionless depletion-mode operation of tensile-strained GeSn(111) pMOSFETs on Si substrates.

We have fabricated thin films composed of W-encapsulated Si clusters (WSi10) on Si substrates and investigated their electronic properties using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). An epitaxial layer was observed at the interface with the Si substrate, and an amorphous layer was on top. The bulk plasmon of the WSi10 cluster film was measured and compared with those of crystalline Si (c-Si) and WSi2 films. We found similar plasmon energies in the epitaxial and amorphous layers of the WSi10 cluster film. The plasmon peak of the WSi10 cluster film is shifted to higher energy compared with that of c-Si, which is related to the electron density increase in the valence band. The Si-L23 absorption edge spectra show that the conduction-band density of states in Si was modified by hybridization between Si and W atoms.

We present the formation of hydrogen-content-controlled B(12)H(n) (+) clusters through the decomposition and ion-molecule reactions of the decaborane (B(10)H(14)) and diborane (B(2)H(6)) molecules in an external quadrupole static attraction ion trap. The hydrogen- and boron-contents of the B(10-y)H(x) (+) cluster are controlled by charge transfer from ambient gas ions. In the process of ionization, a certain number of hydrogen and boron atoms are detached from decaborane ions by the energy caused by charge transfer. The energy caused by the ion-molecule reactions also induces H atom detachment. Ambient gas of Ar leads to the selective generation of B(10)H(6) (+). The B(10)H(6) (+) clusters react with B(2)H(6) molecules, resulting in the selective formation of B(12)H(8) (+) clusters. Ambient gas of Ne (He) leads to the generation of B(10-y)H(x) (+) clusters with x=4-10 and y=0-1 (with x=2-10 and y=0-2), resulting in the formation of B(12)H(n) (+) clusters with n=4-8 (n=2,4-8). The introduction of ambient gas also increases the production of clusters. PBE0/6-311+G(d)//B3LYP/6-31G(d)-level density functional theory calculations are conducted to investigate the structure and the mechanism of formation of B(10-y)H(x) (+) and B(12)H(n) (+) clusters.

We found a new filtering effect of hydrogen (H) and deuterium (D) isotope atoms for penetration process into crystal silicon (Si) through the interface between a Si and SiO2 native oxide layer. More H atoms are introduced into Si than D for mixing gases. It was determined from H and D mixed-atom treatment of Si wafer with the native oxide and the systematic measurements of Raman scattering of hydrogen molecules (H2, HD, or D2) and secondary ion mass spectrometry. This phenomenon can be tentatively explained in terms of an isotope filtering model of H and D via an intermediate cluster state formed at the interface between the native SiO2 layer and crystal Si.

Si nanocrystals (SiNCs) embedded in formed amorphous SiO2 layer and P nanoscale doping have been investigated by electron spin resonance (ESR) measurements at low temperatures. Hydrogen atom treatment is found to be required to determine the proper doping effects and electronic states of doped donors and quasi-conduction electrons in SiNCs. The dependences of microwave power and temperature for the ESR hyperfine structure of isolated P donors indicate that the spin–lattice relaxation time T1 becomes longer with decreasing size of SiNCs. From the experimental results of donor concentration and temperature dependence, we propose a novel model that the spin property of SiNCs of approximately 5.8 nm size is strongly dependent on the number of donors doped in a SiNC, i.e., odd or even. Using this model, we also estimate the numbers of P donors included in each SiNC to be 1 to at most 6, which are less than 1/10 of the average P doping concentrations.

application/pdf, We have investigated phosphorus ion (P+) implantation in Si nanocrystals (SiNCs) embedded in SiO2, in order to clarify the P donor doping effects for photoluminescence (PL) of SiNCs in wide P concentrations ranging in three orders. Some types of defects such as Pb centers were found to remain significantly at the interfaces between SiNCs and the surrounding SiO2 even by high-temperature (1000 °C) annealing of all the samples. Hydrogen atom treatment (HAT) method can efficiently passivate remaining interface defects, leading to significant increase in the intensity of PL arising from the recombination of electron-hole pairs confined in SiNCs, in addition to significant decrease in interface defects with dangling bonds detected by electron spin resonance. From both the results of the P dose dependence before and after HAT, it is found that the amount of remaining defects is higher for samples with SiNCs damaged by implantation with relatively lower P+ doses and then annealed, and that through HAT the observed PL intensity increases surely as the P concentration increases up to a critical concentration. Then it begins to decrease due to Auger nonradiative recombination above the critical concentration which depends on the size of SiNCs. These results suggest an effect of relatively low concentration of P atoms for the enhancement of PL intensity of SiNCs and we present an unconventional idea for explaining it.

We synthesized amorphous films composed of transition-metal-encapsulating Si clusters (MSin: M=Mo or Nb) by deposition of hydrogenated MSinHx clusters onto silica substrates followed by annealing at 500 ?C for dehydrogenation. The MoSin (n=7?16) cluster films are semiconductors with an optical gap >0.6 eV and resistivity >1 ? cm. In particular, the MoSi12 cluster film has a large gap of 1.1 eV and resistivity of 120 ? cm with high hole mobility of 32 cm2/(V s). In these films, Si atoms form amorphous networks similar to those in hydrogenated amorphous Si but the electronic disorder is reduced by the use of MSin clusters as the building blocks.

We have studied the charge transfer between various fullerenes (C60, C78, C84, C60F36, and C60F48) and oxidized Si surfaces in order to evaluate their capability of charge-transfer doping to form ultrashallow junctions in Si. Although the lowest unoccupied molecular orbitals of these fullerene molecules in isolated states are higher in energy than the valence band maximum (VBM) of Si, the fullerenes C60F36 and C60F48, which were deposited on oxidized Si substrates, captured electrons from the Si surfaces; this generated hole inversion layers. C60, C78, and C84 did not induce such electron transfer. From the densities of the generated holes, we estimated the acceptor levels of C60F36 and C60F48, which were condensed on the oxidized Si surface, to be 5.6–5.7 and 5.2eV below the vacuum level, respectively; these values are lower than the VBM of Si.

Undoped 0.2-µm-thick polycrystalline Si (poly-Si) films were deposited on fused quartz substrates by plasma-enhanced chemical vapor deposition from a SiH4–H2 mixture. All films were prepared under the same deposition conditions, just after the substrates were exposed for 1 min to CF4–He plasma excited with various rf powers. Poly-Si films with improved crystallinity and large grains were obtained when the films were deposited on substrates with the proper degree of surface roughness of uniform size and shape. These films were also found to have lower values of stress and higher values of g, as compared with those of poly-Si films on substrates with a flat surface or an extremely rough surface. The X-ray diffraction (XRD) spectra exhibited only the texture, and the intensity was proportional to the third power of the average grain size estimated from the width values of the XRD spectra. These results suggested that the growth of grains is three-dimensionally controlled and depends on the surface morphology of the substrates, while the concentration of grains per unit area is roughly independent of the morphology of the substrates.