Carbon-stimulated self-organization of Ge nanoislands during molecular beam epitaxy of Ge/CaF<Subscript>2</Subscript>/Si(111) heterostructures

The self-organization of germanium nanoislands on the surface of calcium fluoride was studied using atomic-force microscopy and reflection electron diffraction. A Ge/CaF₂/Si(111) structure was grown by molecular beam epitaxy. The surface of the calcium fluoride film was modified by submonolayer carbon coverage to stimulate the formation of germanium nanoislands. The parameters of an array of nanoislands were found to depend on the coverage.     

Formation and structural features of silicon quantum dots in germanium

The formation of Si quantum dots on Ge is studied. Fundamental differences were found between the nucleation and growth of quantum dots on substrates with different orientations, related to both the formation of a SiGe solid solution layer and the shape of quantum dots. The temperature interval of formation of Si nanocrystals on Ge (111) is determined. It is shown that a change in the epitaxy temperature from 480 to 400 °C increases the silicon content in quantum dots from 58 to 75%. The effect of surfactants (in particular, hydrogen) on the nucleation and growth of silicon nanoislands is analyzed, showing that the use of hydrogen as a surfactant leads to a decrease in the size of quantum dots and a substantial increase in their density. The observed effects are attributed to the suppression of surface diffusion of atoms in the presence of hydrogen.     

Formation of ordered groups of quantum dots during Ge/Si heteroepitaxy

A new approach to the creation of circularly ordered Ge nanoislands by epitaxy on the surface of a heterophase structure consisting of a Si(100) substrate with premade seeds in the form of SiGe nanodisks or SiGe nanorings is developed. It is shown that the spatial configuration of islands in the group is due to the nucleation of the islands in the area of local minima of the elastic energy density on the surface of a circular seed. On the basis of this approach, a number of multilayer structures with vertically aligned ring groups of quantum dots were grown. The elemental composition and luminescent properties of the ordered structures are studied.     

Effect of Zn doping on the sublimation rate of pentaerythritol tetranitrate using atomic force microscopy

A series of Zn ion‐doped pentaerythritol tetranitrate (PETN) nanoislands in the form of thin films were prepared on Si substrates using spin coating. The effect of Zn concentrations on the sublimation energy was investigated by atomic force microscopy (AFM). The pure and Zn‐doped nanoislands are imaged by AFM in contact mode at room temperature after annealing isothermally for a given time. The volume of the islands starts to decrease after annealing at 45°C for pure PETN, whereas Zn‐doped nanoislands start to decrease in height and volume after annealing at 55–58°C. The minimum activation energy is found to be 29.7 Kcal/mol for 1,000 ppm Zn concentration. These studies are important for the long‐term stabilization of PETN. SCANNING 31: 181–187, 2009. © 2009 Wiley Periodicals, Inc.     

Arsenic-terminated silicon and germanium surfaces studied by scanning tunnelling microscopy

The epitaxial growth of As on the (111) and (100) faces of Si and the (111) face of Ge has been studied with vacuum tunnelling microscopy. The (111) faces of both semiconductors display a principally 1×1 termination, but differ with the presence of point defects on the Si(111): As-1×1 surface and trenches separating large (～ 100 Å) domains on the Ge(111): As-1×1 surface. I-V characteristics of the tunnel junction show a surface energy gap of approximately 1·9 eV for the Si(111): As-1×1 surface and 0·9 eV for the Ge(111): As-1×1 surface, in good agreement with recent theoretical calculations for these systems. As deposition on Si(001) results in a nominal 2×1 reconstruction of symmetric As dimers and elimination of missing dimer defects characteristic of the native Si(001) 2×1 surface. Further studies on vicinal, double-stepped substrates shows the orientation of the dimers with respect to the substrate depends critically on the substrate temperature during the growth phase, with destruction of the single principle domain surface order occurring at temperatures in excess of 700°C.     

Dislocation nucleation in SiGe nanoscale islands formed during heteroepitaxial growth

A model is proposed to predict the critical parameters (shape, size, element composition) of nanoislands for dislocation nucleation. The onset of plastic relaxation of three-dimensional islands formed during heteroepitaxy in the Stranski-Krastanov mode are considered theoretically for the Ge/Si(100) heterosystem as an example. The study is based on a combination of numerical and analytical approaches to the calculation of strains in three-dimensional island containing a dislocation. It is confirmed that dislocation nucleation in three-dimensional SiGe islands is not limited by the kinetic barrier.     

A new method of scanning tunneling spectroscopy for study of the energy structure of semiconductors and free electron gas in metals

In this study, anew method for the scanning tunneling spectroscopy (STS) of direct and indirect gap semiconductors and free electron gas in metals is proposed. Band structures of Si, porous Si, and Ge were studied. The tunneling current-voltage characteristics of Si and porous Si surfaces were measured over different voltage intervals from tens of mV to 20 V under incident light from an Xe lamp and those of a Ge surface in the dark. The correlation between the shapes of the I-V curves and band structure of the materials was calculated. It was found that the curves are linear if measured in the voltage range V₀ E_g/(2e) and nonlinear when V₀ α E_g/(2e) (in the measurements the applied voltage was changed from -V₀ to V₀). The method was used for the observation of a new effect of tunneling of free electron gas having thermal energies from a metal tip to a band gap state of the semiconductor. The energy spectrum of free electron gas was measured.     

Measurement of elastic strains and small lattice rotations using electron back scatter diffraction

A method is presented for the determination of elastic strains from electron back scatter diffraction patterns, which are obtained at high spatial resolution, from bulk specimens in a scanning electron microscope. It is estimated that the method is sensitive to strains of the order of 0.02%. Strains in Si(1-x)Ge(x) epitaxial layers grown on planar Si substrates were measured for x from 0.2 to 0.015, there being excellent agreement with X-ray diffraction results. Small lattice rotations can also be measured, the technique being sensitive to rotations of 0.01 degrees, which offers an improvement of approximately two orders of magnitude from the more usual EBSD measurements of misorientation. Small lattice rotations were measured in Si(0.85)Geo(0.15) grown on a patterned Si substrate and were consistent with elastic relaxation of the epilayer strain energy.     

Improved quantitative electron probe X-ray microanalysis of biological cryosections using an EDS germanium detector and a super-atmosphere thin window (SuperATW)

A new Link energy-dispersive GEM detector with SuperATW window was tested for quantitative electron probe microanalysis of low calcium and sodium concentrations ([Ca], [Na]) in intracellular compartments of cardiac myocytes. We compare Ca profiles with high count statistics and similar peak area collected under the same conditions with either a Be-windowed Si and a Ge SuperATW detector. The height of the Ca peak was increased by 7%, the full width at half-maximum height was reduced by 9% with the Ge detector. The counts statistics of the Ca Kα peak improved by 9% and the partial overlap with the K Kβ peak was better deconvoluted. We calculate [Ca] and errors of the single measurement in mitochondria of guinea-pig cardiac myocytes from spectra acquired with a Si or Ge detector. For identical analysis conditions, the [Ca] were identical; however, with the Ge SuperATW detector, the calculated error of the single measurement was only 1/2.7 of that calculated from measurements with the Si detector. We compare the peak area of identical [Na] in spectra collected with the Be-windowed Si detector and Ge SuperATW detector. The peak area was significantly higher with the SuperATW Ge than with the Si detector and Be window, whereas the continuum in the range 4–10 keV was comparable, demonstrating the improved sensitivity for low atomic elements such as Na of the Ge SuperATW detector. [Na] and errors of the single measurement in mitochondria of quiescent guinea-pig cardiac myocytes were calculated from spectra acquired with the Si or the Ge detector. The use of the Ge SuperATW detector improved the detectability limit for sodium by more than 80% and reduced the error of the single measurement by a factor of 7–8.     

蒸馏水润滑下Si_3N_4-白口铸铁摩擦面上表面膜形成过程的观察

为了观察蒸馏水润滑下的Ｓｉ３Ｎ４—白口铸铁摩擦面上表面膜的形成过程,在环—块磨损试验机上进行了不同磨程的磨损试验,通过扫描电镜（ＳＥＭ）对不同磨程的铸铁磨面进行了观察,对表面膜的形成机理进行了初步探讨。结果表明,当Ｓｉ３Ｎ４与白口铸铁配副摩擦时,由于铸铁中碳化物的剥落而形成剥落坑,Ｓｉ３Ｎ４磨屑嵌入剥落坑并氧化和水解,其反应产物富集于剥落坑中,脱水聚合后形成硅胶,从而在磨面形成了含硅胶的表面膜。表面膜的形成保护了陶瓷和铸铁磨面,使其变得很光滑,从而使摩擦系数降至０．０２,并使陶瓷和铸铁的磨损几乎接近于零。     

EFFECT OF SURFACE ENERGY ON THE GROWTH OF DIAMOND-LIKE CARBON/AMORPHOUS SILICON FILMS ON VARIOUS SUBSTRATES

Diamond-like carbon/amorphous silicon bilayer films were deposited on SiO₂, Ge, and Ta₂O₅ substrates using a pulsed filtered cathodic arc (PFCA) system. Amorphous silicon (a-Si) layer was firstly deposited on three substrates using DC magnetron sputtering, then diamond-like carbon (DLC) film was deposited on a-Si layer via pulsed filtered cathodic arc. The thicknesses of a-Si layer and DLC film as monitored by in-situ ellipsometry during the film deposition were 7 and 10 nm, respectively. The surface energy of SiO₂, Ge, and Ta₂O₅ substrates was determined by measuring the contact angle of water on these substrates. It was found that the contact angles of water on SiO₂, Ge, and Ta₂O₅ substrates were 53°, 63°, and 75°, respectively. This result indicates that SiO₂ has the highest surface energy while Ta₂O₅ has the lowest surface energy. The thickness of the a-Si layer and DLC film was determined from the cross-section transmission electron microscopy (TEM) images. The thinnest a-Si layer of 5.64 nm was obtained from SiO₂ substrate which has the highest surface energy. The thickest a-Si layer of 6.97 nm was obtained from Ta₂O₅ corresponding to the lowest surface energy. This study shows that the thickness of the growth film strongly depends on the surface energy of the substrate. However, the DLC films deposited on each a-Si layer of three substrates have the same thickness approximately of 9.9 nm, because all of them were deposited on a-Si layers having the same surface energy.     

Wave-dispersive x-ray spectrometer for simultaneous acquisition of several characteristic lines based on strongly and accurately shaped Ge crystal

Si and Ge are widely used as analyzing crystals for x-rays. Drastic and accurate shaping of Si or Ge gives significant advance in the x-ray field, although covalently bonded Si or Ge crystals have long been believed to be not deformable to various shapes. Recently, we developed a deformation technique for obtaining strongly and accurately shaped Si or Ge wafers of high crystal quality, and the use of the deformed wafer made it possible to produce fine-focused x-rays. In the present study, we prepared a cylindrical Ge wafer with a radius of curvature of 50 mm, and acquired fluorescent x-rays simultaneously from four elements by combining the cylindrical Ge wafer with a position-sensitive detector. The energy resolution of the x-ray fluorescence spectrum was as good as that obtained using a flat single crystal, and its gain was over 100. The demonstration of the simultaneous acquisition of high-resolution x-ray fluorescence spectra indicated various possibilities of x-ray spectrometry, such as one-shot x-ray spectroscopy and highly efficient wave-dispersive x-ray spectrometers.     

Randomization of heavily damaged regions in annealed low energy Ge(+)-implanted (001)Si

Apparent growth of amorphous layers during low temperature annealing was observed in low energy Ge(+)-implanted (001)Si by high-resolution transmission electron microscopy. The occurrence of abnormal growth is due to the randomization of heavily damaged regions beneath the original amorphous/crystalline interfaces. The randomization process is attributed to the strain, incurred by the presence of a high density of large Ge atoms in the heavily damaged Si substrate, relaxation to lower the free energy of the systems. The randomization upon annealing may be fruitfully applied to minimize the transient enhanced diffusion in shallow junction formation.     

Dislocations in CdTe heteroepitaxial structures on GaAs(301) and Si(301) substrates

Initial stages of ZnTe growth on GaAs(301) and Si(301) substrates by the method of molecular beam epitaxy are investigated by means of in situ one-wave ellipsometry. Layer-by-layer growth of the ZnTe film is observed on GaAs(301) substrates, whereas 3D nucleation occurs during epitaxy on Si(301) substrates. Misfit dislocations (MDs) are inserted into the ZnTe film during the growth of the first monolayers. Owing to MDs, the film lattice turns with respect to the substrate lattice, which is confirmed by X-ray measurements. Threading segments of MDs in CdTe/ZnTe/GaAs(301) and CdTe/ZnTe/Si(301) heterostructures are subjected to etching. The etch dislocation pits are found to have different shapes, which testifies to different types of threading dislocations. In the case of layer-by-layer etching, the dislocation density is found to increase inward the CdTe film, which testifies to annihilation of dislocations in the course of growth of CdTe films. The dislocation annihilation rate is higher in films grown on GaAs(301) than in those grown on Si(301). A possible reason is the higher mobility of dislocations in CdTe films on GaAs(301) substrates.     

原子力显微镜在GaN研究中的应用

本文采用原子力显微镜(AFM)对Si基外延GaN的形貌及出现的V缺陷进行研究。实验结果表明,GaN外延层厚度为0.5μm时粗糙度最低且没有裂纹出现;厚度为0.4μm的GaN表面出现小坑———V缺陷,密度约为108cm-2。     

Formation of Ge/Si and Ge/Ge x Si1−x /Si nanoheterostructures by molecular beam epitaxy

A kinetic diagram of Ge growth on Si is constructed by methods of fast electron diffraction and scanning electron microscopy. Activation energies of morphological transitions from two-dimensional to three-dimensional growth and from hut-clusters to dome-type islands are determined. The curve of the 2D–3D transition has two segments that follow the Arrhenius law and refer to different mechanisms of two-dimensional growth: two-dimensional island mechanism in the temperature range of 300–525 °C with the activation energy of ?0.11 eV and step motion in the temperature range of 525–700 °C with the activation energy of 0.15 eV. Transitions from hut-islands to dome-islands are also observed. The curve constructed for the hut-dome transition is approximated by two exponential segments that obey the Arrhenius law. The hut-dome transition activation energy is 0.11 eV in the temperature range of 350–550 °C and 0.24 eV in the temperature range of 550–700 °C. The maximum density of islands in the case of Ge growth on a Ge _x Si_1?x layer reaches 4 · 10¹¹ cm^?2. An increase in the composition leads to an increase in the density of Ge islands owing to a decrease in the length of migration of Ge adatoms on the Ge _x Si_1?x surface, as compared to the case of Ge growth on Si. The periodicity N, which is manifested as a (2 × N) superstructure, decreases during the reconstruction from 14 to 8 with increasing Ge content in the Ge _x Si_1?x layer. An increase in thickness or temperature leads to a decrease in periodicity and testifies to Ge segregation; in this case, stress relaxation occurs, which reduces the Ge diffisivity.     

Si(111)和Si(100)衬底上AlN薄膜的激光分子束外延生长特征

采用激光分子束外延技术在Si(111)和Si(100)衬底上制备了AlN薄膜,研究了衬底温度和激光能量对薄膜物相结构和形貌的影响。结果表明:低的激光能量和高的衬底温度有益于薄膜的取向度和表面质量;激光能量为100mJ时,Si(111)衬底上的AlN薄膜呈单一的h-AlN(002)取向,Si(100)衬底上的薄膜在600℃时出现小的h-AlN(100)衍射峰,在700℃时呈微弱的h-AlN(002)取向;在Si(111)衬底上更易生长出取向度高的AlN薄膜。     

Unlubricated wear of Si/SiC and its composite with nickel Si/SiC-Ni

Using a pin-on-disk tribometer, dry friction and wear properties at different temperatures were investigated for reaction-sintered silicon carbide Si/SiC and its composites with nickel Si/SiC-Ni. The friction and wear properties of the composites are improved by the addition of nickel. The analysis on the worn surfaces and sub-surfaces by SEM suggest that shallow grooves are the main wear feature at 15°C. At 600°C, surface cracking and fracture is the predominating wear mechanism for Si/SiC, and the formation of flake pits on the surface due to crack propagation at subsurface is the main wear mechanism for Si/SiC-Ni. Finally the relationships between wear resistance and mechanical properties are discussed.     

Transmission Electron Microscope Investigations Of Defects Produced By Individual Displacement Cascades In Si And Ge

Monocrystalline {111} Si and Ge specimens have been irradiated with atomic and molecular heavy ions in order to study the influence of the cascade energy density and the interaction between displacement cascades on the defect production. Transmission electron microscope (TEM) studies were performed to investigate the defect parameters. After atomic irradiation of Si and Ge the defects analysed (typical size 3–5 nm) are of interstitial type. Both defects with three-dimensional strain centres and defects with a strongly asymmetric strain field were observed. An analysis of the yield and the defect size in Si as a function of ion dose suggests that the defects are formed within individual cascades rather than by a process involving overlapping cascades. Changes of the energy density locally deposited in the lattice do not affect yield and size significantly. Under otherwise similar experimental conditions, the average defect depth is significantly larger for Bi₂+ irradiations than for Bi+ irradiations.     

Reinvestigation of the alkali-metal-induced Ge(111)3 × 1 reconstruction on the basis of boundary structure observations

We have investigated the surface atomic structure of boundary area of Li- and Na-induced Ge(1 1 1)3×1 reconstruction using scanning tunneling microscope. On Li/Ge(1 1 1)3×1, the 3×1 phase was found to be terminated with a single row in the filled-state image and with dimer-like features in the empty-state image. The images of both interior and boundary of the Li/Ge(1 1 1)3×1 surface are compatible with the honeycomb-chain-channel (HCC) model, which has substrate atoms with double bonds and is well established as the structure of AM/Si(1 1 1)3×1 surfaces. In contrast, termination with zigzag double rows at the domain boundary edges was observed in the filled-state images of the Na/Ge(1 1 1)3×1 phase, which is not reconcilable with the HCC structure. The filled-state STM feature of the boundary region of the Na/Ge(1 1 1)3×1 phase supports a structural model not having Ge=Ge double bonds, which was proposed to interpret its empty-state images. The trend of bondings between atoms in the surface layer of the AM-induced 3×1 reconstruction of Si and Ge is discussed in terms of electronegativity differences.