Heavily P-doped (≥1021 cm-3) Si and SiGe films grown by photo-CVD at 250° C

A novel photo-CVD process has been successfully applied to a low-temperature heavy-doping technique using SiH₄ + SiH₂F₂ + H₂ or SiH₄ + SiH₂F₂ + GeH₄ + H₂ gas mixture at a very low-temperature of 250° C with PH₃ as a doping gas. A maximum electron concentration of 2.3 × 10²¹ cm^-3 and 1.3 × 10²¹ cm^-3 was achieved for Si and Si_0.9Ge_0.1 epitaxial layer on a single-crystal silicon substrate. The resistivity of the sample monotonously decreased with decreasing the sample temperature, which implies that the carriers were not frozen out in low temperature regions (4K) and that the obtained samples were “metallic” semiconductors.     

Halide-hydrogen vapor transport for growth of ZnO single crystals with controllable electrical parameters

The advantages of HCl+H₂ gas mixture as a chemical vapor transport agent for ZnO single crystals growth in the closed growth chambers are shown in comparison with Cl₂, HCl and H₂ by the thermodynamic analysis. The influence of the growth temperature, density of HCl+H₂ transport agent and undercooling were investigated experimentally on the rate of ZnO mass transport. It was shown that HCl+H₂ gas mixture provides (i) a rather high growth rate (up to 1 mm per day), (ii) a minimization of wall adhesion effect and deformations during a post-growth cooling, (iii) stable and reproduced seeded growth of the void-free single crystals with controllable conductivity and charge carrier concentration varied in the range of 2–22 (Ω cm)⁻¹ and (1–31)·10¹⁷ cm⁻³, respectively. The characterization by the photoluminescence spectra, the transmission spectra and the electrical properties, as well as energy spectra of stable Cl-containing defects are analyzed.     

Texture and electromigration lifetime improvements in layered Al-alloy metallization with underlying Ti by controlling water adsorption on SiO2 substrates

The effect of residual gas constituents and substrate temperature during Ti sputtering on the texture of TiN/Ti films deposited on SiO₂/Si substrates has been investigated. The Ti(002) and TiN(111) preferred texture of the films deposited at 350°C was found to be improved drastically by increasing the H₂O partial pressure from 1×10⁻⁹ to 3×10⁻⁸ Torr. Both of the Ti(002) and TiN(111) textures showed a similar H₂O partial pressure and substrate temperature dependence because of the epitaxial transfer between these planes. The improved Ti(002) texture was attributed to the self-assembly of Ti atoms on the SiO₂ surface, which had a low surface free energy due to the formation of surface OH groups. Two kinds of layered Al-alloy interconnects, AlSiCu/Ti/TiN/Ti and AlCu/TiN/Ti, were fabricated with the highly textured TiN/Ti film, and their Al(111) texture and electromigration lifetime were then evaluated. It was confirmed that both of the interconnects have strong Al(111) texture and longer EM lifetimes.     

Electrical properties of Pb1−xCdxS epitaxial films

We have measured the resistivity ρ and Hall coefficient R_H at 300, 77, and 4.2 K of p-type Pb_1−XCd_XS epitaxial films as a function of substrate temperature T_s, film thickness d, and composition x. The films were vapor deposited on cleaved (111) BaF₂ (111) SrF₂ , and (001) NaCl and polished (001) BaF₂ substrates. The Hall mobility μ_H at 77 K of p-type PbS films increased approximately linearly from 1 × 10⁴ to 2 × 10⁴ cm² V⁻¹ sec⁻¹ as T_s was varied from 400 to 500°C, respectively. Both μ_H and R_H increased with d due to the presence of a strong p-type surface layer on the exposed surface. The x of the films was controlled by the x of the source material and T_s. The mole fraction of CdS could be varied between 0.002 < x < 0.06 by varying T between 513 and 410°C, respectively, and using source material with x = 0.06. The electrical properties of samples grown on freshly cleaved (111) BaF₂ and (111) SrF₂ were essentially identical even though the lattice constant of SrF₂ is a better match to Pb_1−XCd_XS than BaF₂. The R_H and μ_H at 77 K were independent of thickness for low substrate temperatures and were observed to increase with increasing thickness for high substrate temperatures. The μ_H increased with decreasing temperature and became temperature independent below about 30 K, which is similar to the behavior observed in other lead salt compounds. However, the magnitude of μ_H was considerable lower throughout the 300 to 4.2 K temperature range than for PbS films. The R_H showed little temperature variation, which is typical lead salt behavior. Supported by Naval Surface Weapons Center Independent Research Funds.     

The influence of hydrogen gas on the characteristics of amorphous silicon deposited by RF sputtering

The electrical and optical properties of a-Si depend greatly on the fill gas and substrate temperature during RF sputtering. From the measured absorption coefficient, it was estimated that after the introduction of H₂ gas during sputtering the gap state density reduces from 3.2 × 10¹⁹ cm^?3 to 4.8 × 10¹⁷ cm^?3. As a consequence the optical band gap was found to increase from 1.74 to 1.82 eV. The d.c. conductivity measurement shows three distinct conducting mechanisms at different temperature regions. The SiH bonds in RF sputtered samples are persistant to higher temperature treatment than the CVD prepared ones.     

The equilibrium constant for the reaction of ZnO + H2 and the chemical vapor transport of zno via the Zn + H2O reaction

Using a gas transpiration method, the equilibrium constant for the reaction ZnO(s) + H₂(v)⇄ Zn(v) + H₂O(v) was determined directly in the temperature interval 592–950°C. The data are described by the equation log₁₀K = [-11.794 × 10³/T] + 8.040 with ΔH° = 53.97 Kcal/mole and ΔS° = 36.79 e.u. Based on this Information, vapor-solid gas concentration curves useful for defining conditions for the chemical vapor transport of ZnO via the reverse of the above reaction have been computer calculated.     

Kinetics of vaporization of lead sulfide

The kinetics of vaporization of lead sulfide were investigated in the temperature range 785 to 993 °C using a thermogravimetric balance. The effect of nonreactive ambient atmosphere on the vaporization kinetics was examined in some detail. Under He-rich He-N₂ atmosphere the rate of vaporization was found to be about four times as large as that under N₂-atmosphere. A mathematical model was developed taking into consideration the chemical kinetic and mass-transfer factors. It was found that faster vaporization rates obtained with He-rich atmosphere are due to the higher diffusivity of PbS(g) in He(g). The chemical kinetic aspects of vaporization appear to be unaffected by the ambient atmosphere. The activation energy for vaporization has a value of 198.95 kJ · mole⁻¹ in the temperature range investigated. The evaporation coefficient was found to have values ranging from 0.05 to 0.14.     

Layered Growth of Lattice-Mismatched Ga x In1−x P on GaP Substrates by Liquid Phase Epitaxy

We report layered growth of Ga _x In_1?x P on GaP substrates using single-step liquid phase epitaxy (LPE) with a Sn-based melt when the lattice mismatch is greater than 0.4 % (x < 0.95). Compositional control was observed by (1) varying the cooling rate and (2) changing the melt-back temperature at the beginning of the growth. Possible growth mechanisms are proposed to explain the principles of both approaches of compositional control. Smooth epilayers have been observed. High resolution x-ray diffraction was used to characterize the composition of the epilayers, and room temperature photoluminescence was reported for one of the samples with the composition of x = 0.11. Plan-view TEM measurements revealed threading dislocation densities on the order of 10⁸ cm^?2 in the upper regions of the Ga _x In_1?x P epilayers. In contrast, when using In-based melts, LPE of Ga _x In_1?x P on GaP (100) substrates exhibited island growth at large misfits, whereas edge growth dominated when using GaP (111B) substrates under equivalent growth conditions.     

Biodegradable Fe(III)@WS2‐PVP Nanocapsules for Redox Reaction and TME‐Enhanced Nanocatalytic,Photothermal, and Chemotherapy

In this study, biocompatible Fe(III) species‐WS₂‐polyvinylpyrrolidone (Fe(III) @ WS₂‐PVP) nanocapsules with enhanced biodegradability and doxorubicin (DOX) loading capacity are one‐pot synthesized. In this nanocapsule, there exists a redox reaction between Fe(III) species and WS₂ to form Fe²⁺ and WO₄^2?. The formed Fe²⁺ could be oxidized to Fe³⁺, which reacts with Fe(III) @ WS₂‐PVP again to continuously produce Fe²⁺ and WO₄^2?. Such a repeated endogenous redox reaction leads to an enhanced biodegradation and DOX release of DOX @ Fe(III) @ WS₂‐PVP. More strikingly, the Fe²⁺ generation and DOX release are further accelerated by the overexpressed H₂O₂ and the mild acidic tumor microenvironment (TME), since H₂O₂ and H⁺ can accelerate the oxidation of Fe²⁺. The continuously generated Fe²⁺ catalyzes a fast Fenton reaction with the innate H₂O₂ in tumor cells and produces abundant highly toxic hydroxyl radicals for nanocatalytic tumor therapy. Together with the high photothermal transforming capability, the DOX @ Fe(III) @WS₂‐PVP nanocapsules successfully achieve the endogenous redox reaction and exogenous TME‐augmented tumor photothermal therapy, chemo and nanocatalytic therapy outcome. The concept of material design can be innovatively extended to the synthesis of biodegradable Fe(III) @ MoS₂‐PVP nanocomposite, thus paving a promising novel way for the rational design of intelligent theranostic agents for highly efficient treatment of cancer.     

Luminescent Metal‐Organic Frameworks for Selectively Sensing Nitric Oxide in an Aqueous Solution and in Living Cells

Cu²⁺‐based metal‐organic framework (Cu? TCA ) (H₃ TCA = tricarboxytriphenyl amine) having triphenylamine emitters was assembled and structurally characterized. Cu? TCA features a three‐dimensional porous structure consolidated by the well‐established Cu₂(O₂CR)₄ paddlewheel units with volume of the cavities approximately 4000 nm³. Having paramagnetic Cu²⁺ ions to quench the luminescence of triphenylamine, Cu? TCA only exhibited very weak emission at 430 nm; upon the addition of NO up to 0.1 mM , the luminescence was recovered directly and provided about 700‐fold fluorescent enhancement. The luminescence detection exhibited high selectivity – other reactive species present in biological systems, including H₂O₂, NO₃^?, NO₂^?, ONOO^?, ClO^? and ¹O₂, did not interfere with the NO detection. The brightness of the emission of Cu? TCA also led to its successful application in the biological imaging of NO in living cells. As a comparison, lanthanide metal‐organic framework Eu? TCA having triphenylamine emitters and characteristic europium emitters was also assembled. Eu? TCA exhibited ratiometric fluorescent responses towards NO with the europium luminescence maintained as the internal standard and the triphenylamine emission exhibited more than 1000‐fold enhancement.     

Hydrogen Selective NH2‐MIL‐53(Al) MOF Membranes with High Permeability

Hydrogen‐based energy is a promising renewable and clean resource. Thus, hydrogen selective microporous membranes with high performance and high stability are demanded. Novel NH₂‐MIL‐53(Al) membranes are evaluated for hydrogen separation for this goal. Continuous NH₂‐MIL‐53(Al) membranes have been prepared successfully on macroporous glass frit discs assisted with colloidal seeds. The gas sorption ability of NH₂‐MIL‐53(Al) materials is studied by gas adsorption measurement. The isosteric heats of adsorption in a sequence of CO₂ > N₂ > CH₄ ≈ H₂ indicates different interactions between NH₂‐MIL‐53(Al) framework and these gases. As‐prepared membranes are measured by single and binary gas permeation at different temperatures. The results of singe gas permeation show a decreasing permeance in an order of H₂ > CH₄ > N₂ > CO₂, suggesting that the diffusion and adsorption properties make significant contributions in the gas permeation through the membrane. In binary gas permeation, the NH₂‐MIL‐53(Al) membrane shows high selectivity for H₂ with separation factors of 20.7, 23.9 and 30.9 at room temperature (288 K) for H₂ over CH₄, N₂ and CO₂, respectively. In comparison to single gas permeation, a slightly higher separation factor is obtained due to the competitive adsorption effect between the gases in the porous MOF membrane. Additionally, the NH₂‐MIL‐53(Al) membrane exhibits very high permeance for H₂ in the mixtures separation (above 1.5 × 10^?6 mol m^?2 s^?1 Pa^?1) due to its large cavity, resulting in a very high separation power. The details of the temperature effect on the permeances of H₂ over other gases are investigated from 288 to 353 K. The supported NH₂‐MIL‐53(Al) membranes with high hydrogen separation power possess high stability, resistance to cracking, temperature cycling and show high reproducibility, necessary for the potential application to hydrogen recycling.     

Microporous Metal–Organic Frameworks with High Gas Sorption and Separation Capacity

The design, synthesis, and structural characterization of two microporous metal–organic framework structures, [M(bdc)(ted)_0.5]·2 DMF·0.2 H₂O (M = Zn ( 1 ), Cu ( 2 ); H₂bdc = 1,4‐benzenedicarboxylic acid; ted = triethylenediamine; DMF: N,N‐dimethylformamide) is reported. The pore characteristics and gas sorption properties of these compounds are investigated at cryogenic temperatures, room temperature, and higher temperatures by experimentally measuring argon, hydrogen, and selected hydrocarbon adsorption/desorption isotherms. These studies show that both compounds are highly porous with a pore volume of 0.65 ( 1 ) and 0.52 cm³ g^{– 1} ( 2 ). The amount of the hydrogen uptake, 2.1 wt % ( 1 ) and 1.8 wt % ( 2 ) at 77 K (1 atm; 1 atm = 101 325 Pa), places them among the group of metal–organic frameworks (MOFs) having the highest H₂ sorption capacity. [Zn(bdc)(ted)_0.5]·2 DMF·0.2 H₂O adsorbs a very large amount of hydrocarbons, including methanol, ethanol, dimethylether (DME), n‐hexane, cyclohexane, and benzene, giving the highest sorption values among all metal–organic based porous materials reported to date. In addition, these materials hold great promise for gas separation.     

Gd43+[AlPCS4]34− Nanoagent Generating 1O2 for Photodynamic Therapy

Gd₄³⁺[AlPCS₄]₃^4? (AlPCS₄: aluminium(III) chlorido phthalocyanine tetrasulfonate) inorganic–organic hybrid nanoparticles (IOH‐NPs) are presented as a novel photosensitizer for singlet oxygen (¹O₂) generation with potential use in localized photodynamic therapy. The saline nanoparticles contain an unprecedented high phthalocyanine content of 81 wt% AlPCS₄; they show red emission (680 nm), and efficient ¹O₂ generation. In vitro studies (HepG2 and HeLa cells) demonstrate excellent uptake, low cytotoxicity, and a remarkable induced phototoxicity. Most interestingly, Gd₄³⁺[AlPCS₄]₃^4? IOH‐NPs (in suspension) significantly outperform the clinically approved H₄AlPCS₄ (in solution) in terms of photostability, reactive oxygen species generation, phototoxic effect in cells (i.e., Gd₄³⁺[AlPCS₄]₃^4?: LD₅₀ < 5 × 10^?6 m ; H₄AlPCS₄: LD₅₀ > 20 × 10^?6 m , both illuminated 10 min at 670 nm), as well as suppression of microcapillary networks and vascular cord formation. According to in vivo studies, IOH‐NP‐pretreated HeLa‐GFP cells injected into zebrafish larvae can be easily colocalized based on the red emission of the IOH‐NPs and the green emission of the tumor cells. Upon light exposure (0–20 min at 635 nm), the transgenic HeLa‐GFP cells show drastically reduced viability in vivo due to the induced phototoxicity of the Gd₄³⁺[AlPCS₄]₃^4? IOH‐NPs.     

Electrophoretic Nuclei Assembly for Crystallization of High‐Performance Membranes on Unmodified Supports

Metal–organic framework (MOF) films have recently emerged as highly permselective membranes yielding orders of magnitude higher gas permeance than that from the conventional membranes. However, synthesis of highly intergrown, ultrathin MOF films on porous supports without complex support‐modification has proven to be a challenge. Moreover, there is an urgent need of a generic crystallization route capable of synthesizing a wide range of MOF structures in an intergrown, thin‐film morphology. Herein, a novel electrophoretic nuclei assembly for crystallization of highly intergrown thin‐films (ENACT) approach, that allows synthesis of ultrathin, defect‐free ZIF‐8 on a wide range of unmodified supports (porous polyacrylonitrile, anodized aluminum oxide, metal foil, porous carbon and graphene), is reported. As a result, a remarkably high H₂ permeance of 8.3 × 10^?6 mol m^?2 s^?1 Pa^?1 and ideal gas selectivities of 7.3, 15.5, 16.2, and 2655 for H₂/CO₂, H₂/N₂, H₂/CH₄, and H₂/C₃H₈, respectively, are achieved from an ultrathin (500 nm thick) ZIF‐8 membrane. A high C₃H₆ permeance of 9.9 × 10^?8 mol m^?2 s^?1 Pa^?1 and an attractive C₃H₆/C₃H₈ selectivity of 31.6 are obtained. The ENACT approach is straightforward, reproducible and can be extended to a wide range of nanoporous crystals, and its application in the fabrication of intergrown ZIF‐7 films is demonstrated.     

The epitaxial growth of ZnO on sapphire and MgAl spinel using the vapor phase reaction of Zn and H2O

The gas phase reaction of Zn and H₂O in a He carrier gas has been used as the basis for the chemical vapor deposition of ZnO on sapphire and MgAl spinel. Deposit characteristics were studied as a function of reactor linear gas stream velocity, Zn/H₂O vapor phase ratio, temperature and substrate preparation. It was round that the substrate support can influence the surface morphology significantly and that in situ pretreatment can affect epitaxial relationships between deposit and substrate. Transparent, visually smooth deposits of (11–24) ZnO can be obtained on chemically polished (0001) sapphire at 815°C using average linear gas stream velocities, ν, of 6-12 cm/sec referenced to room temperature in conjunction with a Zn/H₂O reactor input-pressure ratio of 0.02–0.09 (using Zn reactor pressures of 1.2–5.0 × 10⁻³ atm) . The substrates are given an H₂O in situ pretreatment at 900°C prior to deposition at ν = 3 cm/sec with the partial pressure of H₂O in He = 5.7 × 10 atm.     

Effect of growth conditions on incorporation of Si into Ga and As sublattices of GaAs during molecular-beam epitaxy

The effect of dopant concentration and growth-surface crystallographic orientation on the incorporation of Si into Ga and As sublattices was investigated during GaAs molecular-beam epitaxy. The epitaxial layers (epilayers) were grown on GaAs substrates with (100), 2°(100), 4°(100), and 8°(100) orientations at a temperature of 520°C and with (111)A, 2°(111)A, 2°(111)A, 5°(111)A, 6°(111)A, and 8°(111)A (where A = Ga) orientations at a temperature of 480°C. The Sidopant concentration was varied within 10¹⁷–10¹⁹ cm^?3. Through electrical and photoluminescent methods of investigation, the Si impurity was found to occur at the sites of both GaAs-layer sublattices not only as simple donors and acceptors (Si_Ga and Si_As), but also as Si_Ga-Si_As, Si_Ga-V_Ga, and Si_As-V_As complexes. The concentration of Si impurity in various forms depends on the doping level of the layers and on the growth-surface orientation. Amphoteric properties of Si manifest themselves more prominently on the (111)A face than on the (100) one. It is shown that impurity defects form at the stage of layer crystallization and depend on the growth-surface structure.     

Lpe growth of Hgl−xCdxTe using conventional slider boat and effects of annealing on properties of the epilayers

The epitaxial layers of Hg_1−xCd_xTe (0.17≦×≦0.3) were grown by liquid phase epitaxy on CdTe (111)A substrates using a conventional slider boat in the open tube H₂ flow system. The as-grown layers have hole concentrations in the 10¹⁷− 10¹⁸ cm⁻³ range and Hall mobilities in the 100−500 cm²/Vs range for the x=0.2 layers. The surfaces of the layers are mirror-like and EMPA data of the layers show sharp compositional transition at the interface between the epitaxial layer and the substrate. The effects of annealing in Hg over-pressure on the properties of the as-grown layers were also investigated in the temperature range of 250−400 °C. By annealing at the temperature of 400 °C, a compositional change near the interface is observed. Contrary to this, without apparent compositional change, well-behaved n-type layers are obtained by annealing in the 250−300 °C temperature range. Sequential growth of double heterostructure, Hg_l−xCd_xTe/Hg_l−yCd_yTe on a CdTe (111)A substrate was also demonstrated.     

Superparamagnetic Fe3O4 nanoparticles,synthesis and surface modification

Magnetite nanoparticles have been synthesized through a co-precipitation of iron (Fe³⁺ and Fe²⁺), and were characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and superconducting quantum interference device magnetometer (SQUID). The particles have been modified by several types of stabilizers such as polyethylene glycol (PEG 4000), sodium citrate, and ethylenediaminetetraacetic acid (Na₂H₂Y·2H₂O). These nanoparticles are nearly spherical with an average diameter 12 nm. The capping agents have been successfully anchored to the surface, as revealed by the absorption bands in infrared, and the adsorbed quantities are evaluated by TGA analysis. Magnetization of these magnetic nanoparticles was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Such NPs magnetite could serve as a magnetic core to an eventual core-shell structure when coated with various materials.     

Low pressure MOVPE of InP from trimethylindium and phosphine

Epitaxial layers of InP have been grown by MOVPE at reduced chamber pressures from trimethylindium (TMI) and phosphine (PH₃) in a horizontal reactor. Growth rates and deposition efficiency show an increase of about 2 times as the pressure is reduced from 760 Torr (1 atm) to 9 Torr. Background impurities decrease to a minimum at 38 Torr (0.05 atm) for growth at 650° C. At 38 Torr the growth rates are linear with TMI flow above a threshold minimum and correlate to the carrier gas thermal conductivity in mixtures of H₂ + N₂. Uniformity of the layer thicknesses is influenced by pressure, temperature, gas flow rate and position of the substrate on the susceptor.     

Microstructure and properties of aluminum contacts formed on GaAs(100) by low pressure chemical vapor deposition with dimethylethylamine alane source

We report on a low pressure chemical vapor deposition of metallic thin aluminum films on GaAs (001) with a dimethylethylamine alane (DMEAA) source and H₂ as a carrier gas. The deposition temperatures varied in the range 130–360°C. Integrated volumes for Al (111), (100), (110)R, and (110) grains were estimated by the x-ray diffraction technique and the growth temperature values preferred for every type of grains were observed. The experimentally observed dominance of Al(110)R over Al(110), irrespective of the substrate miscut direction, supports the GaAs(100) inner anisotropy effect on the Al grain orientation. Electrical resistivity was 5 ·cm for the best Al films. The Schottky barrier heights were near a 0.7 eV level and the ideality factor n=1.1. Nonalloyed ohmic contacts were fabricated on an n-type GaAs epitaxial layer with an additional set of Si-layers near the Al/GaAs interface. Specific contact resistance, c=7 cm², was measured. Best contacts were obtained at a deposition temperature lower than 250°C.