Single Crystal Silicon Substrates Research Articles

Growth Kinetics of Magnesium Silicide Formation Via Reaction of Mg Gas and Si Substrates

The thermal, electrical, optical, and chemical properties of magnesium silicide (Mg2Si) have led to consideration of this semiconducting material for use in thermoelectric, optical, sensor, corrosion mitigation, and other applications. The relative non-toxicity and earth-abundant nature of the constituent elements of this silicide are also attractive characteristics. One approach for generating patterned magnesium silicide structures for use in devices is the direct conformal reaction of patterned silicon structures with magnesium gas. The kinetic mechanism controlling such conformal gas/solid reaction will be discussed in this presentation. The rate of thickening of magnesium silicide films, via the reaction of magnesium gas with planar silicon single crystal substrates, has been examined via measurements of mass change (∆m/A) and film thickness (∆X from SEM analyses of reacted cross-sections) as a function of time at 600oC. To avoid oxidation during such reaction, experiments were conducted within metal ampoules that had been carefully sealed in an argon atmosphere. Upon heating of the sealed ampoules to 600oC within an argon atmosphere tube furnace, magnesium gas (generated from solid magnesium within the ampoule) migrated to, and underwent reaction with, the planar silicon substrate. Measurements of ∆m/A vs. time and ∆X vs. time were both consistent with a parabolic rate law for the thickening of the Mg2Si layer, with the rate constants from both types of measurements in good agreement. Variations in the magnesium gas diffusion distance, and in the orientation of the starting silicon single crystal, were found to have negligible influence on the reaction kinetics. Such kinetic data were consistent with Mg2Si formation controlled by solid-state diffusion through the Mg2Si product layer. Inert marker experiments (using MgO particles) were used to determine the dominant interface at which new Mg2Si formed, and to evaluate the associated diffusing species controlling such formation. Kinetic analyses from this solid/gas reaction study will be compared to prior work on the formation of Mg2Si via solid-state reaction of magnesium with silicon. Figure 1

MODIFICATION OF THE STRUCTURAL-PHASE STATE AND ELECTRICAL PROPERTIES OF COPPER-CONTAINING FULLERITE FILMS DURING THERMAL ANNEALING IN VACUUM

Abstract—Scanning electron and atomic force microscopy, X-ray diffraction, X-ray spectral microanalysis, and diffraction of reflected electrons were used to study changes in the structure, elemental, and phase composition of fullerite–copper films with an atomic metal fraction of 0.5, 1, 2 and 4%, deposited on oxidized single-crystal silicon substrates and subjected to thermal exposure in vacuum at different temperatures (470, 520, 570 and 620 K). It was found that thermal annealing at T = 520 K (t = 1 h) leads to the formation of a nanocrystalline structure with an average structural elements size of 33, 42, 50, and 65 nm for fullerite–copper films with an atomic fraction of metal of 0.5, 1, 2, and 4% respectively. An increase in temperature and annealing time leads to an increase in the size of structural elements and the formation of a new of CuxC60 phase, which belongs to the monoclinic space group P2/m. Electric force microscopy and the four-probe method were used to study changes in the local electrical properties and electrical resistivity of copper-containing fullerite films during vacuum annealing.

Doping induced tailoring of exchange bias effect in granular Ni1-xZnxO film

Significant exchange bias effect is observed in the granular Ni1-xZnxO film prepared by sol-gel dip-coating technique on a silicon single crystal (100) substrate. Atomic force microscopy reveals the crystallite size which is commensurate with that obtained from the analysis of X-ray diffraction studies. Magnetization measurement reveals the blocked state of Ni0.95Zn0.05O below 155 K. On the other hand, the uncompensated spin is inferred for Ni0.97Zn0.03O from the low temperature up turn of the magnetization. The systematic shift of the magnetic hysteresis loop of Ni1-xZnxO film is measured in field cooled mode. This is the fingerprint of exchange bias (EB) effect which is found to depend strongly on x. The pinning mechanism at the interface between antiferromagnetic core and shell consisting of uncompensated spins in the granular Ni1-xZnxO film is proposed for interpreting the EB effect.

Second-generation Micro-Spec: A compact spectrometer for far-infrared and submillimeter space missions

Micro-Spec is a direct-detection spectrometer which integrates all the components of a diffraction-grating spectrometer onto a ≈10-cm2 chip through the use of superconducting microstrip transmission lines on a single-crystal silicon substrate. The second generation of Micro-Spec is being designed to operate with a spectral resolution of at least 512 in the far-infrared and submillimeter (420–540 GHz, 714–555 μm) wavelength range, a band of interest for NASA's experiment for cryogenic large-aperture intensity mapping called EXCLAIM. EXCLAIM will be a balloon-borne telescope that is being designed to map the emission of redshifted carbon monoxide and singly-ionized carbon lines over a redshift range 0<z<3.5 and it will be the first demonstration of the Micro-Spec technology in a space-like environment. This work reviews the status of the Micro-Spec design for the EXCLAIM telescope, with emphasis on the spectrometer's two-dimensional diffractive region, through which light of different wavelengths is focused on kinetic inductance detectors along the instrument focal plane. An optimization process is used to generate a geometrical configuration of the diffractive region that satisfies specific requirements on size, operating spectral range and performance. An initial optical design optimized for EXCLAIM is presented in terms of geometric layout, spectral purity and efficiency.

Individual layer thickness-dependent microstructures and mechanical properties of fcc/fcc Ni/Al nanolaminates and their strengthening mechanisms

Individual layer thickness-dependent nanoindentation hardness (H) and reduced elastic modulus (E) were measured for face-centered cubic/face-centered cubic (fcc/fcc) nickel (Ni)/aluminum (Al) nanolaminates deposited via magnetron sputtering onto a single-crystal silicon (Si) substrate with a wide, equal individual layer thickness (h) ranging from 5 to 100 nm. The microstructures of the fabricated nanolaminates varied due to the variation in h and these microstructural changes affected the mechanical properties of the Ni/Al nanolaminates. The microstructural changes in the nanolaminates have been characterized using different microscopy analysis. H gradually increased to a plateau of ∼5.07 GPa with a reduction in h down to 10 nm, while the further reduction in h caused H to remain unchanged. Interestingly, E exhibited a monotonic increase to attain a maximum of ∼134.65 GPa with a reduction in h to a critical value of 20 nm, while it started to reduce with further reduction in h. This unusual reduction of E below the 20 nm individual layer thickness may be related to the formation of disordered amorphous layers as well as broken and intermixed interfaces in the Ni/Al nanolaminates. This individual layer thickness-dependent strengthening mechanism in Ni/Al nanolaminates suggests that the dislocation-based Hall–Petch (H–P) strengthening mechanism governs the strength of the Ni/Al nanolaminates from 100 nm down to 20 nm, while the confined layer slip (CLS) strengthening mechanism takes place below 20 nm, and the strengthening mechanism becomes independent of h when it decreases from 10 nm to a few nanometers. The results offer a method for design-engineering ductile Ni/Al nanolaminates with high strength and low reduced elastic modulus.

ZnO@Si(100) and ZnO@Si(111): Hydrothermal Synthesis, Morphology, and Lasing Characteristics

Microstructures have been formed on single-crystal silicon substrates of different crystallographic orientations, (111) and (100), under “soft” hydrothermal conditions. Well-faceted ZnO microcrystallites were obtained on the Si(111) surface, whereas the Si(100) substrate surface was covered with willemite (Zn2SiO4) crystallites, and zinc oxide microcrystallites were observed in only a narrow region ∼1 mm wide over the substrate edge. These results indicate clear influence of the crystallographic orientation of silicon substrates on the processes of crystal formation and microstructure growth under conditions of low-temperature hydrothermal synthesis. Low-threshold effective lasing has been detected on well-faceted zinc oxide crystallites under optical excitation.

Effect of Thickness of Molybdenum Nano-Interlayer on Cohesion between Molybdenum/Titanium Multilayer Film and Silicon Substrate.

Titanium (Ti) film has been used as a hydrogen storage material. The effect of the thickness of a molybdenum (Mo) nano-interlayer on the cohesive strength between a Mo/Ti multilayer film and a single crystal silicon (Si) substrate was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nano-indenter. Four groups of Si/Mo/Ti multilayer films with different thicknesses of Mo and Ti films were fabricated. The XRD results showed that the introduction of the Mo layer suppressed the chemical reaction between the Ti film and Si substrate. The nano-indenter scratch results demonstrated that the cohesion between the Mo/Ti film and Si substrate decreased significantly with increasing Mo interlayer thickness. The XRD stress analysis indicated that the residual stress in the Si/Mo/Ti film was in-plane tensile stress which might be due to the lattice expansion at a high film growth temperature of 700 °C and the discrepancy of the thermal expansion coefficient between the Ti film and Si substrate. The tensile stress in the Si/Mo/Ti film decreased with increasing Mo interlayer thickness. During the cooling of the Si substrate, a greater decrease in tensile stress occurred for the thicker Mo interlayer sample, which became the driving force for reducing the cohesion between the Mo/Ti film and Si substrate. The results confirmed that the design of the Mo interlayer played an important role in the quality of the Ti film grown on Si substrate.

Dispersion-Engineered Guided-Wave Resonators in Anisotropic Single-Crystal Substrates - Part I: Concept and Analytical Design.

This paper presents an analytical approach for implementation of high quality-factor (Q) resonators with arbitrary cross-sectional vibration mode-shapes in anisotropic single-crystal substrates. A closed-form dispersion relation is analytically derived to characterize the dynamics of guided waves in rectangular waveguides. Three categories of waves with propagating, standing-evanescent and propagating-evanescent dynamics are identified and used for energy localization of acoustic excitations with arbitrary cross-sectional vibration patterns. An analytical design procedure is presented for dispersion engineering of waveguides to realize high-Q resonators without the need for geometrical suspension through narrow tethers or rigid anchors. The effectiveness of the dispersion engineering methodology is verified through development of experimental test-vehicles in 20㯌m-thick single-crystal silicon substrate with 500nm aluminum nitride transducers. Various proof-of-concept resonators, representing guided waves with different dispersion types, are presented and compared to highlight the optimum design procedures for Q enhancement and spurious mode suppression. Part I of this paper presents the operation principle of guided wave resonators based on analytical derivation of dispersion relation followed by a systematic resonator design procedure. Numerical and experimental characterization for verification of the proposed design procedure and extensive measurement data on proof-of-concept resonators are presented in Part II.

Approximations of reflection and transmission coefficients of inhomogeneous thin films based on multiple-beam interference model

A multiple-beam interference model is used to derive approximate formulae for the reflection and transmission coefficients of inhomogeneous thin films exhibiting large gradients of refractive index profiles. It is shown that these formulae are constituted by series containing the Wentzel-Kramers-Brillouin-Jeffreys term and correction terms with increasing order corresponding to number of considered internal reflections inside the films. A numerical analysis enabling us to show the influence of a degree of inhomogeneity on spectral dependencies of reflectance and ellipsometric parameters of inhomogeneous films is performed. Advantages and disadvantages of our approach compared with other approximate approaches are discussed. The optical characterization of a selected non-stoichiometric silicon nitride film prepared by reactive magnetron sputtering onto silicon single crystal substrate is performed for illustration of using our formulae in practice.

Influence of a por-Si Buffer Layer on the Optical Properties of Epitaxial InxGa1 –xN/Si(111) Heterostructures with a Nanocolumnar Film Morphology

Integrated heterostructures exhibiting a nanocolumnar morphology of the InxGa1 –xN film are grown on a single-crystal silicon substrate (c-Si(111)) and a substrate with a nanoporous buffer sublayer (por-Si) by molecular-beam epitaxy with the plasma activation of nitrogen. Using a complex of spectroscopic methods of analysis, it is shown that the growth of InxGa1 –xN nanocolumns on the por-Si buffer layer offer a number of advantages over growth on the c-Si substrate. Raman and ultraviolet spectroscopy data support the inference about the growth of a nanocolumn structure and agree with the previously obtained X-ray diffraction (XRD) data indicative of the strained, unrelaxed state of the InxGa1 –xN layer. The growth of InxGa1 –xN nanocolumns on the por-Si layer positively influences the optical properties of the heterostructures. At the same half-width of the emission line in the photoluminescence spectrum, the emission intensity for the heterostructure sample grown on the por-Si buffer layer is ~25% higher than the emission intensity for the film grown on the c-Si substrate.

Влияние буферного слоя por-Si на оптические свойства эпитаксиальных гетероструктур In-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-N/Si(111) с наноколончатой морфологией пленки

AbstractIntegrated heterostructures exhibiting a nanocolumnar morphology of the In_ x Ga_1 –_ x N film are grown on a single-crystal silicon substrate ( c -Si(111)) and a substrate with a nanoporous buffer sublayer ( por -Si) by molecular-beam epitaxy with the plasma activation of nitrogen. Using a complex of spectroscopic methods of analysis, it is shown that the growth of In_ x Ga_1 –_ x N nanocolumns on the por -Si buffer layer offer a number of advantages over growth on the c -Si substrate. Raman and ultraviolet spectroscopy data support the inference about the growth of a nanocolumn structure and agree with the previously obtained X-ray diffraction (XRD) data indicative of the strained, unrelaxed state of the In_ x Ga_1 –_ x N layer. The growth of In_ x Ga_1 –_ x N nanocolumns on the por -Si layer positively influences the optical properties of the heterostructures. At the same half-width of the emission line in the photoluminescence spectrum, the emission intensity for the heterostructure sample grown on the por -Si buffer layer is ~25% higher than the emission intensity for the film grown on the c -Si substrate.

Влияние адсорбированных молекул СО на электронное состояние нанопленок иттербия, выращиваемых на кремниевых подложках

Adsorption of carbon monoxide (CO) molecules on ytterbium nanofilms with the thickness of 16 – 200 monolayers (6.1 – 76 nm) has been studied. The films are grown on single-crystal silicon substrates with the (111) surface orientation. It is shown that before the adsorption of CO molecules, ytterbium is divalent with the electronic configuration of [Xe]4f146s2. Upon the adsorption of gas molecules, a layer of trivalent ytterbium (the electronic configuration is [Xe]4f135d16s2), which is adjacent to the film surface, is formed. Evaluations of the thickness of the layer modified by adsorbed CO molecules are performed. Such evaluations have given rise to the values within 9 – 22 monolayers (3.4 – 8.4 nm).

Focus on photonics, spectrometry, and spectroscopy

Focus on photonics, spectrometry, and spectroscopy

The influence of photo-stimulated adsorption of polyelectrolyte molecules on electro-physical characteristics of structures based on single crystal silicon substrates

The effect of photo-stimulated adsorption of cationic (polyethylenimine, PEI) and anionic (glucose oxidase, GOx) polyelectrolyte molecules on C-V characteristics of a electrolyte/insulator/semiconductor structure was investigated. We obtained that illumination of semiconductor during the adsorption of PEI increases a shift of the flat band potential by 29% and 45% for n-Si and p-Si, respectively. Furthermore, depending on a Si conductivity type, the photo-stimulated adsorption of GOx molecules either increases (for n-Si/PEI) or decreases (for p-Si/PEI) the C-V shift, which was explained by corresponding changes of enzyme molecules on the surface, respectively. Our research is useful in fabrication of potentiometric biosensors since the growth of enzyme molecules density on the surface of the semiconductor transducer increases the threshold sensitivity of the sensor.

Effect of a por-Si Buffer Layer on the Structure and Morphology of Epitaxial InxGa1 – xN/Si(111) Heterostructures

Integrated heterostructures exhibiting nanocolumnar morphology of the InxGa1 – xN/Si(111) film are grown on a single-crystal silicon substrate (c-Si(111)) and a substrate with a nanoporous buffer sublayer (por-Si) by molecular-beam epitaxy with the plasma activation of nitrogen. Using a complex of structural and microscopic methods of analysis, it is shown that the growth of InxGa1 – xN nanocolumns on a nanoporous buffer layer offers a number of advantages over growth on c-Si. The por-Si substrate predetermines the preferential orientation of the growth of InxGa1 – xN nanocolumns closer to the Si(111) orientation direction and makes it possible to produce InxGa1 – xN nanocolumns with a higher degree of crystallographic uniformity and with a nanocolumn lateral size of ~40 nm unified over the entire surface. The growth of InxGa1 – xN nanocolumns on a por-Si layer yields a decrease in the strain components exx and ezz and in the density of edge and screw dislocations compared to the corresponding parameters for InxGa1 – xN nanocolumns grown on c-Si. The InxGa1 – xN nanocolumnar layer fabricated on por-Si exhibits a 20% higher charge-carrier concentration compared to the layer grown on c-Si as well as a higher intensity of the photoluminescence quantum yield (+25%).

Research on material removal model and processing parameters of cluster magnetorheological finishing with dynamic magnetic fields

Based on fluid mechanics and Preston equation, the influences of various technological parameters (including rotational speeds of workpieces, magnetic poles, and polishing disk and the machining gap) on polishing pressure on workpiece surfaces were investigated. On this basis, a material removal rate (MRR) model of cluster magnetorheological finishing (CMRF) with dynamic magnetic fields was established. Moreover, three pieces of single-crystal silicon substrates were subjected to synchronous polishing on the CMRF devices with dynamic magnetic fields in order to analyze the influence of different technological parameters on the MRR. It is showed that the theoretical simulation results favorably agree with the experimental results. The single-crystal silicon substrates with the initial surface roughness (Ra) of 0.48 μm were polished for 5 h on the optimal technological conditions: the machining gap and the eccentricity of magnetic poles are 0.9 mm and 6 mm, respectively; the workpieces are oscillated in Y direction for 40 mm at the oscillation speed of 600 mm/min; the rotational speeds of the polishing disk, magnetic poles, and workpieces are 50 r/min, 90 r/min, and 350 r/min, respectively. In this way, the super-smooth uniform surfaces with the roughness of Ra 2.4 nm were acquired.

Crystallographically Defined Silicon Macropore Membranes

Abstract Laser ablation with nanosecond-pulsed Nd:YAG laser irradiation combined with anisotropic alkaline etching of Si wafers creates 4-20 μm macropores that extend all the way through the wafer. The walls of these macropores are crystallographically defined by the interaction of the anisotropy of the etchant with the orientation of the single-crystal silicon substrate: rectangular/octagonal on Si(001), parallelepiped on Si(110), triangular/hexagonal on Si(111). Laser ablation can create pillars with peak-tovalley heights of over 100 μm. However, with nanosecondpulsed irradiation at 532 nm, the majority of this height is created by growth above the original plane of the substrate whereas for 355 nm irradiation, the majority of the height is located below the initial plane of the substrate. Repeated cycles of ablation and alkaline etching are required for membrane formation. Therefore, irradiating with 355 nm maintained better the crystallographically defined nature of the through-pores whereas irradiation at 532 nm led to more significant pore merging and less regularity in the macropore shapes. Texturing of the substrates with alkaline-etching induced pyramids or near-field modulation of the laser intensity by diffraction off of a grid or grating is used to modulate the growth of ablation pillars and the resulting macropores. Texturing causes the macropores to be more uniform and significantly improves the yield of macropores. The size range of these macropores may make them useful in single-cell biological studies.

Growth mechanism of polycrystalline CsI(Tl) films on glass and single crystal Si substrates

The microstructure morphology and crystal quality of CsI(Tl) films are influenced by the crystal properties of substrates. In this work, CsI(Tl) films on the glass and single crystal silicon substrates are fabricated by vacuum thermal evaporation at a low deposition rate. The microstructure morphology, crystalline quality and scintillation properties of the films were examined by using scanning electron microscopy, X-ray diffraction, photoluminescence and radioluminescent spectrum. To study the growth mechanism of CsI(Tl) films on amorphous and monocrystalline substrates, a growth model based on the classical Volmer-Weber (VW) growth mode are proposed. During the film growing, the wetting and not-wetting phenomena of the clusters appear on the glass and Si(1 1 1) substrates respectively. In addition, the microcrystalline columns with different orientations are modeled to explain the surface morphology deteriorate of the CsI(Tl) film with 3 μm thickness on Si(1 1 1) substrate.

Contact Melting of Aluminum-Silicon Structures under Conditions of Thermal Shock

The work is devoted to the study of contact melting in the Al-Si system, which is an aluminum film deposited on a silicon single-crystal substrate. The impulse action of high-density currents (j&gt; 8.1010 A / m2) passing through an aluminum film is analyzed. It was found that under the considered electric heat loads in the system, the degradation processes associated with the appearance of a molten aluminum zone and subsequent contact melting in the metal-semiconductor system develop. From the analysis of contact melting processes, a technique for estimating the coefficients of multiphase diffusion in the system under consideration is a thin aluminum film-single-crystal silicon substrate.

Formation of Axially Aligned Polydisperse Nanocarbon Structures via Chemical Vapor Deposition from Cyclohexane with Ferrocene

Axial polydisperse carbon microstructures composed of vertically aligned arrays of multiwalled carbon nanotubes (MWCNTs) are synthesized via chemical vapor deposition (CVD) of cyclohexane with ferrocene onto a single-crystal silicon substrate. Their structural peculiarities are examined via scanning electron microscopy on a Tescan Lyra3 FEG system, atomic force microscopy on an Ntegra Spectra NT-MDT probe microscopy, by Raman spectroscopy. The abilities to purify synthesized carbon structures from amorphous carbon through oxidation with atomic oxygen and ozone are studied in order to achieve significant enlargement of specific surface area of nanotubes. The routes of application of polydisperse structures as catalyst supports, solid electrolytes, and chemical sensor supports, as well as absorption techniques of gas and liquid storage, are proposed.