Growth of CNx/BN:C multilayer films by magnetron sputtering

Symmetric CN_x/BN:C multilayer thin films, with nominal compositional modulation periods of Λ=2.5, 5, and 9 nm were deposited by unbalanced dual cathode magnetron sputtering from C (graphite) and B₄C targets in an Ar/N₂ (60/40) discharge. The multilayers and single-layer of the constituent CN_x and BN:C compounds were grown to a total thickness of 0.5 μm onto Si(001) substrates held at 225°C and a negative floating potential of 30 V (E_i≈24 eV). Layer characterizations were performed by TEM, X-ray reflectivity, RBS, and nanoindentation measurements. Results show that CN_0.33 and BN:C (35, 50, and 15 at.% of B, N, and C, respectively) layers were prepared at the above conditions. It is suggested that all films exhibit a three-dimensional interlocked structure with a cylindrical texture in the film growth direction. The structure was continuous over relatively well defined and smooth CN_x/BN:C interfaces. All coatings exhibit extreme elasticity with elastic recoveries as high as 85–90% (10 mN maximum load) attributed to the observed structure. However, the multilayers were stiffer and more elastic compared to that of the single-layers and thus shows promise for improved protective properties.     

Fluorination of CNx Nanotubes

Multiwall CN_x nanotubes have been prepared by thermal decomposition of acetonitrile over Co/Ni catalytic particles. The fluorination of nanotubes was performed at room temperature by using a gaseous mixture of BrF₃ and Br₂. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) indicated that only the outer shells of CN_x nanotubes were fluorinated, whereas the inner shells remained intact. X-ray photoelectron spectroscopy (XPS) showed an oxidation of pyridinic-type nitrogen with tube fluorination.     

Structural characterization of CxByNz (x=0.1 to x=0.2) layers obtained by laser-driven synthesis

C_xB_yN_z layers have been prepared by laser-assisted chemical vapour deposition (CVD) in a gas atmosphere containing C₂H₄, B₂H₆ and NH₃ where the starting composition ratio could vary in a large range. The characterization of these C–B–N materials was made by XRD, EPMA, XPS, optical and scanning electron microscopy. The chemical composition of C–B–N layers tended to a composition C₁B₆N₃ on the line BN–‘B₃C’. The turbostratic structure of C–B–N layers could be influenced and modified as a function of composition. XPS investigations confirmed the single-phase nature and the existence of bonding between all the elements. Some planar structures, containing especially CB₂N groups, were suggested for the ‘unit cell’ of these C–B–N solid solutions, in agreement with EPMA and XPS analysis.     

Random stacking in MoS2−x sputtered thin films

The structure of sputter-deposited MoS_2−x films is investigated by X-ray and electron diffraction. The diffraction spectra show important differences with respect to those of known molybdenite phases. These differences are interpreted in terms of the random-layer model usually applied to turbostratic carbon. Peak profile calculations are performed following an extension of Wilson's model, taking into account the structure factor. They show that the crystal structure of these films consists in a random stacking of S---Mo---S layers, without evidence of 2H or 3R polytypism.     

Hydrophobic CNx thin film growth by inductively-coupled RF plasma enhanced pulsed laser deposition

Interest in carbon nitride as a wear-resistant coating has spurred a large number of attempts at thin film growth using a variety of techniques. Unfortunately, achieving the proper stoichiometry has proven to be surprisingly difficult, and significant effort is typically required to obtain nitrogen contents in excess of 25%. We report the achievement of 38% nitrogen content films deposited on (100) silicon substrates by means of pulsed laser ablation of a graphite target in conjunction with an inductively coupled RF nitrogen plasma source originally designed for molecular beam epitaxy growth of GaN. Quadrupole mass spectroscopy of the plasma source, yields a cracking efficiency of approximately 1.8%, with no significant dependence on RF power. Strong trends in nitrogen incorporation, with both substrate temperature and laser fluence, are observed, the best films being grown at temperatures less than 300°C and fluences of less than 410 mJ/cm². No discernable trend in nitrogen content is observed with either laser repetition rate or the RF power applied to the nitrogen plasma source, and only C---N single bonds are in evidence in FTIR. Contact angle measurements indicate that moderate nitrogen content CN_x films have a slightly hydrophobic character, comparable to pure amorphous carbon films. Coupled with the hardness potential of this material, the hydrophobic behavior makes CN_x a candidate for a number of applications, including alleviating stiction problems in rotating component microelectronic machine (MEMS) systems.     

以钛酸四正丁酯为钛源制备超细Ti粉体

以有机钛源钛酸四正丁酯（Ti（OC₄H₉）₄）与纳米碳黑（C）为反应原料制备超细Ti（C_1-xN_x）粉体。经过计算可知两者理论质量比约为9.4：1,以m（Ti（OC₄H₉）₄）：m（C）=9：1混料,通过溶胶凝胶法制备烧结前驱体。利用高温碳热还原法,在N₂气氛中,分别在不同温度下恒温烧结1 h,直接反应合成超细Ti（C_1-xN_x）粉体。结果发现,随温度升高,x 值逐渐降低,数值区间为0.19~0.72;产物组分中的总碳含量（C_t）逐渐增大,从14.23wt%增大到18.66wt%,游离碳含量（C_f）与氧含量（C_o）均低于0.5wt%;产物平均粒度也呈增大趋势,平均粒度分布区间为220~275 nm。     

Structural, chemical, and electrical characterisation of reactively sputtered WSx thin films

WS_x films were sputter-deposited on Si, SiO₂/Si, and glass substrates from a WS₂ target in an Ar/H₂S atmosphere. Their structure, morphology, chemical composition, and electrical properties were investigated as a function of deposition parameters such as working pressure and H₂S fraction. Films could be grown in the composition range WS_0.3−WS_3.5. Crystallisation was achieved at substrate temperatures T_s > 70 °C and compositions 0.7 ≤ x ≤ 1.95. While the first 5–50 nm near the interface exhibited a basal orientation (c), further growth resulted in the formation of edge-oriented platelets (c) giving rise to a porous, lamellar microstructure. The crystalline structure was mainly turbostratic, while some degree of ordered stacking was present in samples grown at high substrate temperature (600 °C). Resistivity measurements showed a semiconductor-type temperature dependence characterised by activation energies up to 95 meV. Sheet resistance was found to be nearly independent of film thickness, suggesting that the main carrier transport takes place in an interfacial layer of about 20 nm in thickness.     

Structural characterization of TiNxOy/TiO2 single crystalline and nanometric multilayers grown by LP-MOCVD on (110)TiO2

TiO₂/TiN_xO_y superlattices were grown by Low Pressure-Metal-Organic Vapor Phase Epitaxy (LP-MOVPE) technique at deposition temperatures ranking from 650 to 750°C. The growth was performed on top of TiO₂(110) rutile substrates. Intense peaks observed in the X-rays rocking curves and θ-2θ diffraction patterns show the presence of crystalline epilayers. The TiN_xO_y layers were grown in a (200) cubic structure on the (110) quadratic TiO₂ epilayer structure. Transmission electron microscopy confirmed the XRD results and showed the formation of periodic and well structured epilayers.     

Atmospheric plasma discharge chemical vapor deposition of SnOx thin films using various tin precursors

A series of 0.2–0.6 μm thick SnO_x films were deposited onto borosilicate and sodalime silica glass substrates by atmospheric plasma discharge chemical vapor deposition at 80 °C. SnO_x films deposited from monobutyltin trichloride contained a large percentage of SnCl₂:2H₂O, and therefore were partially soluble in water. SnO_x coatings deposited from tetrabutyltin were not soluble in water or organic solvents, had good adhesion even at growth rates as high as 2.3 nm/s, had high transparency of  90% and electrical resistivity of 10⁷ Ω cm. As-grown tin oxide coatings were amorphous with a small concentration of SnO₂, SnO and Sn crystalline phases as determined by grazing angle X-ray diffraction and X-ray photoelectron spectroscopy measurements. Upon annealing in air at 600 °C the resistivity of SnO_x films decreased to 5–7 Ω cm. Furthermore, optical and X-ray measurements indicated that SnO_x was converted into SnO₂ (cassiterite) with a direct band gap of 3.66 eV. Annealing of as-grown SnO_x films in vacuum at 340 °C led to formation of the p-type conductor SnO/SnO_x. The indirect band gap of SnO was calculated from the optical spectra to be 0.3 eV.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Exploring the fracture toughness KIE and KIC of a medium-Strength steel plate using the surface-flaw test

The fracture toughness of a 30 CrMnSiA steel plate of three thicknesses (10,8 and 5 mm) and three widths (110,80 and 56 mm) has been investigated by using surface-flaw method under room temperature. It is not easy to compute the value of K_IE by the maximum applied load. But the values of K_IE and K_IC could be obtained easily, if the computation of the conditional applied load P₁₀ and P₅ based on the relative effective extension Δa/a₀ = 10% and 5% were adopted, together with the conditions of P_max/P₁₀ 1.2 and P_max/P₅ 1.3. The K_R — Δ_a curve, i.e. the resistance-curve described by the parameter K, has been plotted. The values of K_IC and K_IE are then the resistances corresponding to the real extensions of flaws of Δ/a₀ = 2 and 7%, respectively. These values so obtained are in good agreement with the computed values of K_IC and K_IE by using the conditional applied loads. The values of K_IC and K_IE so obtained are also in agreement with the value of K_IC converted from the J-integral and the effective value of K_IE computed by the maximum applied load, respectively.

An approximate relation between K_IC and K_IE has been found to be: K_IC = (0.85˜0.95)K_IE.

The requirements for the dimensions of specimens are: Thickness of plate: B 1.0(K_IC/σ_0.2)² or 1.25(K_ICσ_0.2)²]; Width of plate: 8 W/B 10, 4 W/2c 5; Effective length: l 2W.     

Optical and electrical properties of p-type AgInSnxS2−x (x = 0–0.04) thin films prepared by spray pyrolysis

AgInSn_xS_2−x (x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS₂. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn_xS_2−x (x < 0.2) resemble those of chalcopyrite AgInS₂. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn_xS_2−x (x < 2) thin films.     

Synthesis and characterization of catalysts produced from paper mill sludge. I. Determination Of NOx removal capability

Characteristics and catalytic properties of a series of carbon-based catalysts (CBCs) produced from paper mill sludge were evaluated. The major processes involved in the production of the catalysts were chemical activation, impregnation, pyrolysis, and post pyrolysis rinsing. The porous structure, catalytic activity and thermostability of the catalysts were tailored during the production stage by introducing hetero-atoms (zinc chloride, and ferric nitrate) in the carbon structure. Characterization of the produced CBCs included determination of the surface area, pore size, and pore size distribution (PSD) from standard N₂-adsorption isotherm data. The extent of graphitization and the presence of metal crystals were identified from X-ray diffraction (XRD). The limit of the catalyst gasification was estimated from thermogravimetric analysis (TGA) conducted in an oxidized environment. The NO_x reduction capability of the produced catalysts was evaluated in the presence of carbon monoxide using a fixed bed reactor. The reaction temperature ranged from 300 to 500°C. It was shown that paper mill sludge is an excellent precursor for the production of CBCs with NO_x removal capability of 66–94%. The catalytic capability of the produced CBCs varied according to the method of production, catalyst surface properties (surface area, pore structure, PSD), metal composition and reaction temperature. The highest NO_x removal capacity was observed for the catalytic reactions carried out at 400°C. The mesoporous catalyst produced with a Zn:Fe molar ratio of 1:0.5 exhibited the maximum NO_x removal catalytic activity of 94%.     

Epitaxial growth of strained Si1−yCy films by the hot-wire cell method and its application to metal oxide semiconductor devices

We succeeded in obtaining strained Si_1−yC_y films at a substrate temperature of 200 °C by the hot-wire cell method. The substitutional carbon concentration in films annealed at 700 °C was 0.9%, while it was limited to 0.13% for a sample grown by gas-source molecular beam epitaxy (MBE) at a substrate temperature of 700 °C. We investigated the thermal stability of strained Si_1−yC_y films for device application. Annealing at over 900 °C caused the formation of 3C-SiC and relaxation of the strain occurred. From this result, we found that the process temperature should be lower than 800 °C. A low-temperature MOSFET process, in which all process temperatures after deposition of Si_1−yC_y were lower than 800 °C, was developed and a strained Si_1−yC_y MOSFET was fabricated.     

The preparation and gas sensitivity study of polythiophene/SnO2 composites

Nanocomposites of SnO₂ and polythiophene (PTP) were synthesized by the in situ chemical oxidative polymerization method. These nanocomposites were characterized by FTIR, transmission electron microscope (TEM), X-ray diffraction (XRD) and thermogravimetric and differential thermal analysis (TG–DTA) techniques, which proved the polymerization of thiophene monomer and the strong interaction between polythiophene and SnO₂. The composites were used for gas sensing to methanol (MeOH), ethanol (EtOH), acetone, and NO_x at different working temperature. It was found that PTP/SnO₂ materials with different PTP mass percent (1%, 5%, 10%, 20% and 30%) could detect NO_x with very higher selectivity and sensitivity at much lower working temperature than the reported SnO₂. The PTP/SnO₂ nanocomposites responded to NO_x at concentration as low as 10 ppm. PTP/SnO₂ composite containing 5 mass% PTP showed the highest sensitivity at room temperature. The sensing mechanism of PTP/SnO₂ nanocomposites to NO_x was presumed to be the effects of p–n heterojunction between PTP and SnO₂.     

Y3+掺杂Li4Ti5O12负极材料的电荷输运特性及电化学性能研究

以Li₂CO₃与锐钛矿型TiO₂为原料,六水合硝酸钇（Y（NO₃）₃·6H₂O）为钇源,采用球磨辅助固相法合成了Li₄Ti_5-xY_xO₁₂（x=0,0.05,0.10,0.15,0.20）负极材料。通过X射线衍射分析（XRD）、扫描电镜（SEM）、能谱仪（EDS）与X射线光电子能谱（XPS）分别对材料的物相与形貌进行表征分析,并利用电化学工作站对材料的电化学性能与电荷输运特性进行测试。结果表明,Y³⁺掺杂没有影响尖晶石型Li₄Ti₅O₁₂（LTO）材料的尖晶石结构,x=0.15时,Li₄Ti_4.85Y_0.15O₁₂样品的离子与电子电导率分别为2.68×10^-7 S·cm^-1和1.49×10^-9 S·cm^-1,比本征材料提升了1个数量级,表现出良好的电荷输运特性。电化学测试表明,Li₄Ti_4.85Y_0.15O₁₂样品在0.1 C倍率首次放电比容量可达171 mAh·g^-1,且在10 C与20 C高倍率下仍然拥有102 mAh·g^-1和79 mAh·g^-1的较高比容量,循环200周次后容量保持率分别为92.6%和89.1%,表现出良好的倍率特性。     

锂离子电池正极材料LiNi0.8Co0.15Al0.05O2的制备与性能

采用共沉淀法制备粒径10 μm左右的前驱体Ni_0.8Co_0.15Al_0.05（CO₃）_x（OH）_y,然后采用该前驱体和LiOH·H₂O成功制备了锂离子电池正极材料LiNi_0.8Co_0.15Al_0.05O₂（LiNCA）,并详细研究了煅烧氛围、煅烧温度和煅烧方式等条件对LiNCA电化学性能的影响。研究表明,在O₂中煅烧获得的LiNCA放电容量达到170 mAh·g^-1,50次循环后容量保持率达到95%,性能明显优于空气氛围中煅烧得到的LiNCA。在O₂氛围下,700~750℃温度范围煅烧得到的LiNCA性能最好,煅烧温度过高或过低,LiNCA性能均明显下降。将前驱体在O₂氛围中450℃条件预煅烧,然后与LiOH·H₂O在700~750℃混合煅烧的煅烧方式,得到的LiNCA放电容量明显提高,可达190 mAh·g^-1。     

Growth of high-quality relaxed SiGe films with an intermediate Si1−yCy layer for strained Si n-MOSFETs

High quality and thin relaxed SiGe films were grown on Si (0 0 1) using ultra high vacuum chemical vapor deposition (UHV/CVD) by employing an intermediate Si_1−yC_y layer. The Si_1−yC_y/SiGe bilayer was found to change mechanism of relaxation in the SiGe overlayer. Compared with the samples with a Si layer, the equilibrium critical thickness of top SiGe films with rough surface by introducing an intermediate Si_0.986C_0.014 layer are drastically reduced; this result was attributed to larger tensile stress in the inserted Si_0.986C_0.014 layer. With a 210-nm-thick Si_0.8Ge_0.2 overlayer, this Si_0.8Ge_0.2/Si_0.986C_0.014/Si_0.8Ge_0.2 heterostructure has a threading dislocation density (TDs) less than 1 × 10⁵ cm⁻² and a residual strain of 30%. The root mean square (RMS) of surface roughness for this sample was measured to be about 1.8 nm. In this SiGe/Si_1−yC_y/SiGe structure, C atoms in the intermediate Si layer will improve the relaxation of thin SiGe overlayer, however, the relaxation for the 700-nm-thick SiGe overlayer is independent of the addition of C. The point defects rich Si_0.986C_0.014 layer plays the role to confine the misfit dislocations, which formed at the interface of the top Si_0.8Ge_0.2 and the Si_0.986C_0.014 layer, and blocked the propagation of TDs. Strained-Si n-channel metal-oxide-semiconductor transistors (n-MOSFETs) with a 210-nm-thick Si_0.8Ge_0.2 overlayers as buffer were fabricated and examined. Drain current and effective electron mobility for the strained-Si device with this novel substrate technology was found to be 100 and 63% higher than that of control Si device. Our results show that thin relaxed Si_0.8Ge_0.2 films with the intermediate Si_0.986C_0.014 layer serve as good candidates for high-speed strained-Si devices.     

Preparation of B-doped a-Si1−xCx:H films and heterojunction p–i–n solar cells by the Cat-CVD method

B-doped a-Si_1−xC_x:H films for a window layer of Si thin film solar cells have been prepared by the Cat-CVD method. It is found that C is effectively incorporated into the films by using C₂H₂ as a C source gas, where an only little C incorporation is observed from CH₄ and C₂H₆ under similar deposition conditions. Using a-Si_1−xC_x:H films grown from C₂H₂, heterojunction p–i–n solar cells have been prepared by the Cat-CVD method. The cell structure is (SnO₂ Asahi-U)/ZnO/a-Si_1−xC_x:H(p)/a-Si:H(i)/μc-Si:H(n)/Al. The obtained conversion efficiency was 5.4%.     

Structural and electrochemical characterization of LiMn2−δVδOy spinels

The spinel phase compounds with the composition of LiMn_2−δV_δO_y were prepared by solid reaction of the mixture of LiNO₃·H₂O, MnCO₃ and NH₄VO₃ powders. Evolution of the crystalline phases of the samples versus the vanadium content was analyzed using X-ray diffraction (XRD) technique, EPR and FT-IR spectroscopes. Cubic spinel is the predominant phase in the powders under heat treatment at 550 °C for 5 h. The valence state of manganese ion changed from +4 to +3 with vanadium substitution for charge compensation. The vanadium substitution of manganese leads the decline in capacity and cyclic behavior of the powders. The electrochemical behaviors relating to the variation of structure corresponding to the vanadium substitution were discussed.