Formation mechanism of ordered stress-relief patterns in a free sustained Cu film system

A nearly free sustained copper （Cu） film system has been successfully fabricated by thermal evaporation deposition of Cu atoms on silicone oil surfaces, and a characteristic ordered pattern has been systematically studied. The ordered pattern, namely, band, is composed of a large number of parallel key-formed domains with different width w but nearly uniform length L; its characteristic values of w and L are very susceptible to the growth period, deposition rate and nominal film thickness. The formation mechanism of the ordered patterns is well explained in terms of the relaxation of the internal stress in the films, which is related to the nearly zero adhesion of the solid-liquid interface. By using a two-time deposition method, it is confirmed that the ordered patterns really form in the vacuum chamber.     

TiO2 chemical vapor deposition on Si(111) in ultrahigh vacuum: Transition from interfacial phase to crystalline phase in the reaction limited regime

The interaction between the metal organic precursor molecule titanium(IV) isopropoxide (TTIP) and three different surfaces has been studied: Si(111)-(7 × 7), SiO_x/Si(111) and TiO₂. These surfaces represent the different surface compositions encountered during TTIP mediated TiO₂ chemical vapor deposition on Si(111). The surface chemistry of the titanium(IV) isopropoxide precursor and the film growth have been explored by core level photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. The resulting film morphology has been imaged with scanning tunneling microscopy. The growth rate depends on both surface temperature and surface composition. The behavior can be rationalized in terms of the surface stability of isopropoxy and isopropyl groups, confirming that growth at 573 K is a reaction limited process.     

Optical properties of quasi-one-dimensional molecular crystals with different polarizations

Quasi-one-dimensional organic compounds in which the acceptor TCNQ molecules form dimers are studied. Site Orbitals describing the electron in half of the TCNQ molecule are introduced. Hubbard's model is generalized so as to take into account the Coulomb repulsion between two electrons at one site. It is shown that the optical excitations of the electron are asssociated with intramolecular vibrations both when the incident light is polarized along the TCNQ chains and when the incident radiation is polarized transverse to the chains. The conductivity of the system with different polarizations is calculated taking into account the electron-vibrational interaction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 74–78, February, 1986.     

Stabilization variation of organic conductor surfaces induced by π—π stacking interactions

The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes (CTCs) including PrQ(TCNQ)₂, MPM(TCNQ)₂, and MEM(TCNQ)₂, have been investigated by scanning tunneling microscopy (STM). The three bulk-truncated surfaces are all ac-surface, which are terminated with TCNQ molecular arrays. On the ac-surface of PrQ(TCNQ)₂, the TCNQ molecules form a tetramer structure with a wavelike row behavior and a γ angle of about 18° between adjacent molecules. Moreover, the dimer structures are resolved on both ac-surfaces of MPM(TCNQ)₂ and MEM(TCNQ)₂. In addition, the tetramer structure is the most stable structure, while the dimer structures are unstable and easily subject to the STM tip disturbance, which results in changeable unit cells. The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the 'π-atom model'.     

Peptide-induced patterning of gold nanoparticle thin films

In this work, the use of patterned proteins and peptides for the deposition of gold nanoparticles on several substrates with different surface chemistries is presented. The patterned biomolecule on the surface acts as a catalyst to precipitate gold nanoparticles from a precursor solution of HAuCl₄ onto the substrate. The peptide patterning on the surfaces was accomplished by physical adsorption or covalent attachment. It was shown that by using covalent attachment with a linker molecule, the influence of the surface properties from the different substrates on the biomolecule adsorption and subsequent nanoparticle deposition could be avoided. By adjusting the reaction conditions such as pH or HAuCl₄ concentration, the sizes and morphologies of deposited gold nanoparticle agglomerates could be controlled. Two biomolecules were used for this experiment, 3XFLAG peptide and bovine serum albumin (BSA). A micro-transfer molding technique was used to pattern the peptides on the substrates, in which a pre-patterned poly(dimethylsiloxane) (PDMS) mold was used to deposit a lift-off pattern of polypropylmethacrylate (PPMA) on the various substrates. The proteins were either physically adsorbed or covalently attached to the substrates, and an aqueous HAuCl₄ solution was applied on the substrates with the protein micropatterns, causing the precipitation of gold nanoparticles onto the patterns. SEM, AFM, and Electron Beam Induced Current (EBIC) were used for characterization.     

Low temperature selective epitaxial growth of SiGe layers using various dielectric mask patterns and process conditions

The SiGe film was deposited at a low temperature of 675-725 °C with various dielectric mask patterns and process conditions using reduced pressure chemical vapor deposition. Pattern shape and process conditions associated with the growth rate and the Ge composition of the selective epitaxial growth (SEG) have been examined for the SiH₄-GeH₄-H₂ system. The objective was to understand the effect of pattern size at low temperature for the feasible device applications. The growth rates showed large non-uniformity of 1.4 depending upon the window width, 2-100 μm, of dielectric mask patterns. From the influence of the pattern shape/size and process parameters, the evolution of growth rates could be explained by the surface migration and the surface topology as well. After the surface migration control appearing dominantly at the initial stage, the surface topology became significant at the last part of the SEG process. The Ge composition is important to form the high quality SEG of SiGe films, so that it is important to optimize the flow rate of SiH₄, GeH₄, and total source gas.     

高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

Characterization of bronze Roman coins of the fifth century called <Emphasis Type="Italic">nummi</Emphasis> through different analytical techniques

Mixing of different organic charge-transfer-complexes (CT-complexes) might allow the adjustment of the optical and morphological properties of the resulting material system. In this work, a study of two CT-complexes, mixed by thermal coevaporation at different concentrations by substituting only the acceptor molecules, is presented. Electron diffraction patterns, which were collected on samples of the ternary system of the prototypical CT-complexes DBTTF-TCNQ and DBTTF-F₄TCNQ do not show any indication of a mixed crystalline phase or novel crystalline order. X-ray diffraction measurements additionally confirm the phase separation in the ternary system. However, upon mixing of the complexes, the degree of crystallinity of the individual phases is reduced. This effect correlates with the mixing ratio of the CT-complexes in the ternary compound. Furthermore, we do not observe a shift or the appearance of new peaks in the infrared spectra of (DBTTF-TCNQ) _x :(DBTTF-F₄TCNQ)_1?x . Hence, there is no indication for a pronounced or novel chemical interaction between the individual CT-complexes in the mixed compound.     

Effect of alcohol sources on synthesis of single-walled carbon nanotubes

The effect of oxidant species forming an alcohol molecule for hot-filament chemical vapor deposition (HFCVD) on single-walled carbon nanotubes (SWCNTs) growth has been investigated. To use a graphite rod as a filament for HFCVD to decompose alcohol sources, contamination-free sample surface can be obtained and SWCNTs are successively and densely grown at a lower temperature than those by conventional thermal CVD. It is found that the higher the molecule number of alcohol among CH₃OH, C₂H₅OH, and 2-C₃H₇OH is, the lower the initial growth rate of SWCNTs is. As for CH₃OH, diameter distribution of SWCNTs is dynamically changed with the growth time passed, and a negative growth rate is observed at the later stage of growth. The growth kinetics depending on the alcohol sources is discussed on the basis of a capability of the oxidant species to burn away SWCNTs and deactivation of Co catalysts used for the growth.     

In situ RHEED monitor of the growth of epitaxial anatase TiO2 thin films

Epitaxial anatase TiO₂ thin films were successfully grown on (0 0 1) SrTiO₃ substrates by the laser molecular-beam epitaxy (laser-MBE) method. The whole growth process is monitored by in situ reflection high-energy electron diffraction (RHEED). RHEED monitoring shows a transition from a streaky pattern to a spot pattern during deposition, indicating different growth modes of TiO₂ film. The RHEED patterns are in consistent with the RHEED intensity oscillation results. The atomic force microscopy (AFM) and X-ray diffraction (XRD) investigation show that the thin films have single crystalline orientation with roughness less than three unit cells.     

Spin resonance of tetramethyltetrathiafulvalene tetracyanoquinodimethane: a comparison with tetrathiafulvalene tetracyanoquinodimethane

Electron spin resonance spectra and linewidth studies of two different phases of tetramethyltetrathiafulvalene (TMTTF) tetracyanoquinodimethane (TCNO) are presented. The linewidth of the solution grown 1:1 phase (TMTTF)(TCNQ), which is the structural analog to tetrathiafulvalene- tetracyanoquinodimethane (TTF) (TCNQ), is shown to have a similar temperature dependence to that of (TTF) (TCNQ) in contrast with earlier reports. The vapor grown phase, identified by X-ray studies as (TMTTF)_1.66 (TCNQ)₂, is shown to have different magnetic and electronic properties. These results are discussed and compared with earlier spin resonance reports on (TMTTF) (TCNQ).     

Spectroscopic investigation of pressure-induced phase transitions in TCNQ complex salts

In most of the TCNQ complex salts, conduction electrons are localized on specific TCNQ sites, so that these salts show nonmetalic behavior. The caesium salt, Cs₂(TCNQ)₃, is one of the 2:3 complex salts. In the crystal, TCNQ molecules form trimeric units, which consist of two TCNQ radical anion sandwiching a neutral TCNQ along the column. The rubidium salt, Rb₂(TCNQ)₃, also has a similar crystal structure to Cs₂(TCNQ)₃. We measured infrared absorption (IR) and Raman spectra for these salts under high pressure by using a diamond anvil cell. In the case of IR spectra, Cs₂(TCNQ)₃ showed a spectral change probably due to a pressure-induced phase transition. Similar feature was not clearly observed in the Rb₂(TCNQ)₃. On the other hand, the Raman spectra, Cs₂(TCNQ)₃ showed two phase transition at 2.5 and 4.1 GPa in the compression stage. The change from localization phase to delocalization phase occurred at latter transition with large hysteresis. Similar phase transition occurred at 3.2 GPa in the Rb₂(TCNQ)₃. The reason for the difference in transition pressure is that the ion radius of Rb⁺ is smaller than that of Cs⁺, because a small ion radius of the counter ion probably favors the charge localization-delocalization transition of the TCNQ column.     

Growth and characterization of indium phosphide single-crystal nanoneedles on microcrystalline silicon surfaces

The epitaxial growth of nanometer-scale structures on non-single crystalline surfaces is proposed and demonstrated. Hydrogenated amorphous silicon was deposited onto an SiO₂ surface by plasma-enhanced chemical vapor deposition. Indium phosphide was deposited on the amorphous silicon by low-pressure metalorganic chemical vapor deposition in the presence of colloidal gold particles as catalysts. Under specific growth conditions, the indium phosphide formed nanoneedles connected to a microcrystalline silicon film nucleated within the amorphous silicon during the growth of the nanoneedles. Transmission electron microscopy revealed the presence of two different crystallographic structures: zinc-blende and wurtzite. Micro-photoluminescence measurements at room temperature showed two peaks with substantial blue-shifts with respect to that of bulk zinc-blende indium phosphide. PACS 81.16.Hc; 81.07.Vb; 68.65.La     

A study on the pulsed laser printing of liquid-phase exfoliated graphene for organic electronics

The aim of this work is the pulsed laser printing of liquid-phase exfoliated graphene in the nanosecond regime and the optimization of the printing process on Si/SiO₂ and flexible polymer substrates (polyethylene naphthalate) via the laser-induced forward transfer technique (LIFT). The laser printing conditions and the optimum energy fluence window for reproducible deposition have been investigated, while the deposited graphene features have been studied morphologically and structurally by means of optical microscopy, micro-Raman spectroscopy and electrical characterization. LIFT experiments were carried out using the fourth harmonic (266 nm) of a pulsed ns Nd:YAG laser combined with a high-power imaging micromachining system to monitor the printing process throughout the experiments. The irradiation of our graphene solution resulted in the deposition of well-resolved patterns on different surfaces, highlighting LIFT as an alternative technique for the printing and patterning of liquid-phase exfoliated graphene for organic electronics applications.     

A multitechnique surface science examination of Sn deposition on Pt(100)

Interfaces prepared by vapor deposition of Sn onto Pt(100) surfaces have been examined using the following techniques: Auger electron and X-ray photoelectron spectroscopy (AES and XPS), low-energy electron diffraction (LEED), and low-energy ion surface scattering (LEISS) with Ne⁺ ions. Tin deposition was conducted at 320 and 600 K, and the surface composition and order was examined as a function of further annealing to 1200 K. The AES uptake plots (signal versus deposition time) indicate that the Sn growth mode can be described by a layer-by-layer process only up to one adayer at 320 K. Some evidence of 3D growth is inferred from LEED and LEISS data for higher Sn coverages. For deposition at 600 K, AES data indicate significant interdiffusion and surface alloy formation. LEED observations (recorded at a substrate temperature of 320 K) show that the characteristic hexagonal Pt(100) reconstruction disappears with Sn exposures of 4.6 × 10¹⁴ atoms cm² (θ_Sn = 0.35 monolayer (ML)). Further Sn deposition results in a c(2 × 2) LEED pattern starting at a coverage of slightly above 0.5 ML. The c(2 × 2) LEED pattern becomes progressively more diffuse with increasing Sn exposure with eventual loss of all LEED features above 2.2 ML. Annealing experiments with various precoverages of Sn on Pt(100) are also described by AES, LEED, and LEISS results. For specific Sn precoverages and annealing conditions, c(2 × 2), p(3√2 × √2)R45°, and a combination of the two LEED patterns are observed. These ordered LEED patterns are suggested to arise from ordered PtSn surface alloys. In addition, the chemisorption of CO and O₂ at the ordered annealed Sn/Pt(100) surfaces was also examined using thermal desorption mass spectroscopy (TDMS), AES, and LEED.     

In situ functionalized self-assembled monolayer surfaces for selective chemical vapor deposition of copper

Recent studies show that the self-assembled monolayer (SAM) is well suited to control the selectivity of chemical vapor deposition (CVD). Here, we reported the selective CVD for copper on the functionalized SAM surfaces (with -SH, -SS-, and -SO₃H terminal groups). The -SS- and -SO₃H terminal group surfaces were obtained through in situ chemical transformation of -SH terminal group surface of a 3-mercaptopropyltrimethoxysilane-SAM (MPTMS-SAM). As a result, the -SS- terminal group surface reduces copper deposition and the -SO₃H terminal group surface enhances copper deposition comparing to the -SH terminal group surface. In addition, the MPTMS-SAM was irradiated by UV-light through a photo mask to prepare SH-group and OH-group regions. Then, copper films were deposited only on the SH-group region of the substrate in chemical vapor deposition. Finally, patterns of copper films were formed in the way of UV-light irradiation. These results are expected for use of selective deposition of copper metallization patterns in IC manufacturing processes.     

Temperature dependent microwave dielectric constant of TTF-TCNQ and related one-dimensional conductors

The results of an experimental study of the low temperature (4.2–40 K) complex dielectric constant of the organic conductors (TTF)(TCNQ), (TMTTF)(TCNQ), (DSeDTF)(TCNQ), (TSeF)(TCNQ), and the alloy (TTF)_0.97(TSeF)_0.03(TCNQ) are described. The similar features observed in these different systems suggest that a common mechanism is involved.     

A photoemission study of molybdenum hexacarbonyl adsorption and decomposition on TiO2(1 1 0) surface

The adsorption and decomposition of molybdenum hexacarbonyl on (1 1 0) TiO₂ surfaces were studied using both core levels and valence band photoemission spectroscopies. It was found that after an adsorption at 140 K, when going back to room temperature, only a small part of molybdenum compounds, previously present at low temperature, remained on the TiO₂ surface. This indicates that the desorption temperature on such a surface is lower than the decomposition one. The use of photon irradiation to decompose the hexacarbonyl molecule was also studied. It was shown that during such a decomposition molecular fragments were chemisorbed on the surface allowing a higher amount of metal to remain on the surface. It was also shown that it was possible to get rid of adsorbed subcarbonyl groups and to organize the metal atoms by thermal treatments at temperatures as low as 400 K, i.e. much lower than the one needed to obtain the same structures using physical vapour deposition (PVD). Moreover, due to lower used temperatures, this chemical way of deposition allows a better control of the interface than during PVD growth.     

Dependence on substrate topography of growth of nanosized dendritic structures in an electron-beam-induced deposition process

Nanometer-sized W-dendrites are fabricated on Al₂O₃ substrates with an electron-beam-induced deposition process. Dependence of growth of nanodendrite on surface topography is investigated with transmission electron microscopy. It is confirmed that the nanodendrite grows on convex surfaces but not around a hole on a substrate. These are attributed to different distribution of charges on surfaces with different topographies during electron beam irradiation when charges are produced on the surface due to emission of second electrons. The charges accumulate on convex surface and do not distribute around a hole. Therefore, the nanodendrite grows on the former and not on the latter.