Film Growth Direction Research Articles

Effect of nitrogen partial pressure on the structure, physical and mechanical properties of CrB 2 and Cr–B–N films

The investigation of structure and properties of Cr–B and Cr–B–N films deposited by direct current magnetron sputtering of CrB 2 target in argon and argon–nitrogen environments, respectively is presented. The nitrogen partial pressure was kept at 10, 15, and 25% of the total pressure. The microstructure, phase and chemical composition of Cr–B–(N) films were studied by means of X-ray diffraction, transmission- and scanning-electron microscopy, X-ray photoelectron spectroscopy, electron probe microanalysis and secondary neutral mass-spectrometry. The films were characterized in terms of their electrical resistivity, optical reflectivity and transmittance. Measurements of hardness and elastic modulus were performed by depth sensing nanoindentation. The results obtained show that the films deposited in pure Ar had a hexagonal AlB 2-type structure with crystallites, 15–17 nm in lateral size, elongated in the direction of film growth. The Cr–B–N films consisted of nanocrystalline nc-CrB 2 and amorphous a-BN phases. As the nitrogen content in films was raised, the volume fraction of the nc-CrB 2 phase decreased and a-BN phase increased. When nitrogen was added to the gas discharge during deposition, the nc-CrB 2 crystallite size decreased down to 3–5 nm. Without nitrogen, the films exhibited a columnar morphology. Nitrogen introduction suppressed the columnar growth of films because formation of a-BN intergranular layers. The films deposited under optimal parameters showed hardness in the range of 36–43 GPa and Young's modulus below 300 GPa. For all films, electrical resistivity values between approximately 200 and 700 µΩ cm were recorded.

Ti-30Ta-(3~15)Nb 합금에 HA/Ti 복합 코팅한 표면의 교류임피던스 특성

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-()Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at . Ti-30Ta-()Nb alloys showed the phase, and phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at , whereas, the growth direction of film was (110) for Ti coating. The polarization resistance () of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at . Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

Characterization of crystallinity of a large self-standing homoepitaxial diamond film

We have investigated the crystallinity of a self-standing homoepitaxial diamond film grown at a high rate using a polarized optical microscope, X-ray rocking curves and X-ray topographs. The self-standing film was made by removing a synthetic type-Ib(001) substrate after the film growth using a “lift-off process”. The cross-nicol optical microscope image demonstrated that there exists strain spreading at a relatively large area in the film and the strain inherits over that in the substrate. From cross-sectional X-ray topographs, the dominant defects, observed as dotted patterns in plan-view topographs and micrographs, are dislocations extending along the film growth direction 〈001〉 and generating at the interface between the film and the substrate. The density of such defects counted from these measurements was ~ 1 × 10 3 cm − 2 . The dotted patterns observed in X-ray topographs of (220), (− 220) and (400) diffraction planes are almost the same with each other, suggesting that dominant line defects along 〈001〉 are mixed dislocations with a burgers vector directing between 〈001〉 and in-plane of the sample. The high resolution X-ray rocking curve showed that the peak is very sharp with full width at half maximum of 7.56″, which indicates that imperfection of our single-crystal diamond plate is almost the same as that of high-quality high-pressure high-temperature, synthetic type-Ib diamond.

Substrate effect on texture properties of nanocrystalline TiO2 thin films

Abstract Titanium oxide (TiO 2 ) nanocrystalline thin films have been grown on different substrates LaAlO 3 (0 0 1) and α-Al 2 O 3 (0 0 0 1) by dc magnetron sputtering in an Ar+O 2 gas mixture. Pure rutile or anatase or mixed (rutile and anatase) phase of TiO 2 can be grown at fixed sputtering pressure and substrate temperature on various substrates. XRD and TEM studies of the films deposited at fixed pressure of 2×10 −2 Torr and substrate temperature of 650 °C revealed that preferred (0 0 4) oriented anatase phase was observed in case of films grown over LaAlO 3 substrates and rutile phase with preferred (2 0 0) orientation was observed in case of films deposited over the sapphire substrate. The results indicate that the film growth direction is highly affected with nature of substrate and substrate orientation. Further, AFM and FESEM images showed that nanostructured TiO 2 films could be grown on all substrates.

Laser processed protonic ceramics

High temperature protonic conductors of SrCe 0.9Y 0.1O 3− δ , Sr 3Ca 1+ x Nb 2− x O 9− δ and BaCe 0.85Y 0.15O 3− δ were fabricated by laser processing. Laser float zone method and pulse laser deposition were used to fabricate dense high temperature protonic ceramic rods and films. Melt growth processing by laser float zone produced textured microstructures with cellular characteristics. Directional solidified SrCe 0.9Y 0.1O 3− δ contained an aluminium rich inter-granular phase, whereas Sr 3Ca 1+ x Nb 2− x O 9− δ exhibits a cellular microstructure with a decreasing Ca/Nb ratio from the cell center to the cell boundary. A low Ca/Nb ratio is detrimental to proton transport. Nano-domains caused by oxygen cage tilting were observed in both compositions. Sr 3Ca 1+ x Nb 2− x O 9− δ also exhibits stoichiometric domains with an ordered distribution of Nb 5+ and Ca 2+ cations. These domains were surrounded by non-stoichiometric domains containing a random cation distribution, which preserves the global stoichiometry and charge neutrality. Electrical impedance spectroscopy revealed similar protonic transport to published data for sintered compositions. Crystalline BaCe 0.9Y 0.1O 3− δ films were fabricated on porous substrates at deposition temperatures ranging from 400 to 950 °C. Crystalline films 1–10 μm thick were deposited by excimer laser on porous Al 2O 3 and BaZrO 3 substrates. Single-phase BaCe 0.85Y 0.15O 3− δ films with a columnar growth morphology are observed with preferred crystal growth along the [1 0 0] or [0 0 1] direction. The film electrical conductivity was measured perpendicular to the film growth direction. Impedance measurements show the importance of matching crystal symmetry between substrate and film. High protonic conducting films were achieved by deposition on BaZrO 3.

Highly Aligned Epitaxial Nanorods with a Checkerboard Pattern in Oxide Films

One of the central challenges of nanoscience is fabrication of nanoscale structures with well-controlled architectures using planar thin-film technology. Herein, we report that ordered nanocheckerboards in ZnMnGaO4 films were grown epitaxially on single-crystal MgO substrates by utilizing a solid-state method of the phase separation-induced self-assembly. The films consist of two types of chemically distinct and regularly spaced nanorods with mutually coherent interfaces, approximately 4 x 4 x 750 nm3 in size and perfectly aligned along the film growth direction. Surprisingly, a significant in-plane strain, more than 2%, from the substrate is globally maintained over the entire film thickness of about 820 nm. The strain energy from Jahn-Teller distortions and the film-substrate lattice mismatch induce the coherent three-dimensional (3D) self-assembled nanostructure, relieving the volume strain energy while suppressing the formation of dislocations.

Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films

ABSTRACTBy using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.

Structural Homogeneity of nc-Si Films Grown by Low-Energy PECVD

Nanocrystalline silicon is considered one of the most promising materials for thin-film solar cells. For such an application, one of the critical issues yet unsolved is to obtain a good structural uniformity along the film growth direction to yield high fill factors and open-circuit voltages. In this article, Raman spectroscopy was used to obtain crystallinity in-depth profiles of samples grown at a high growth rate by low-energy plasma-enhanced chemical vapor deposition (PECVD) using different SiH 4 and H 2 fluxes, all yielding the same dilution factor. The results showed that the total flow rate strongly affects the structural uniformity of nanocrystalline silicon films.

Mediation of room temperature ferromagnetism in Co-doped SnO2 nanocrystalline films by structural defects

Co-doped SnO2 nanocrystalline films have been fabricated by magnetron sputtering to investigate the effects of structural defects on mediating ferromagnetism in this system. X-ray photoelectron spectroscopy analysis reveals that Co element is incorporated into SnO2 lattice and is in 2+ oxidation state in all samples. High-resolution transmission electron microscopy observation indicates that along the film growth direction, Sn1−xCoxO2 films change from amorphous structure to columnar grain except for the film deposited at room temperature. With the decrease of film thickness, deposition rate, and deposition temperature, a relative proportion of structural defects in films increases, resulting in an enhancement of the saturated magnetic moment of Sn1−xCoxO2 film. Bound magnetic polaron mechanism is adopted to explain the mediation effect of structural defects on ferromagnetism in this system.

The Structural and Mechanical Properties of Ti Films Fabricated by Using RF Magnetron Sputtering

Titanium films were deposited on various substrates, such as pure Si(100), oxide/Si(100), nitride/Si(100), TiOxNy/Si(100), PI(polyimide) and glass, by using r.f. magnetron sputtering. X-ray diffraction (XRD) data showed a distinct change in major film growth direction with the substrate. In the case of Ti film growth on pure Si(100), oxide/Si(100) and nitride/Si(100) surfaces, the film was strongly grown in the (100) direction while Ti films with growth preferentially in the (002) direction were observed on TiOxNy/Si(100), PI and glass surfaces. The surface morphologies were observed using atomic force microscopy (AFM). The mechanical properties were observed by using a nano-indenter.

Probing fatigue in ferroelectric thin films with subnanometer depth resolution

The authors report the study of polarization fatigue in Pb(Zr,Ti)O3 (PZT) ferroelectric thin films using in situ high-resolution grazing incidence x-ray specular reflectivity of synchrotron radiation. The results demonstrate that there is no formation of a region of different electron densities in the film growth direction with subnanometer depth resolution during fatigue. The upper bounds on the theoretically predicted interfacial accumulation of oxygen vacancies at the interfaces between PZT and Pt electrodes are determined by the comparison of experimental results and theoretical simulations.

Microstructure and Interface Phase Formation in ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ Prepared by an MOD Process

Understanding the evolution of microstructure in YBCO (YBa2Cu3O7-zeta) is critical to optimizing the process for production of high quality superconducting wire for commercial applications. Therefore, microstructure and interfaces have been investigated in fully reacted YBa2Cu3O7-zeta, prepared by the metalorganic deposition (MOD) process, and deposited on CeO2/YSZ/Y2O3/NiW. YBCO nucleates on CeO2 with a specific orientation relationship where [011] CeO2 || [100] YBCO and (200) CeO2 || (002) YBCO, and with the [001] YBCO axis parallel to the film growth direction. A 25-50 nm thick reaction layer of BaCeO3 was observed at the YBCO : CeO2 interface. Formation of this layer releases a considerable amount of Cu and Y into the YBCO matrix. Details of the interfacial phase formation in the MOD-processed YBCO films are presented in this paper.

Ge nanoclusters in PECVD-deposited glass after heat treatment and electron-beam irradiation

This paper reports the formation of Ge nanoclusters in silica glass thin films deposited by plasma-enhanced chemical vapor deposition (PECVD). We studied the samples by transmission electron microscopy (TEM) and Raman spectroscopy after annealing. TEM investigation shows that the Ge nanoclusters at two areas were formed by different mechanisms. The Ge nanoclusters formed in a single row along the interface of a silicon substrate and the silica glass film by annealing during high-temperature heat treatment. Ge nanoclusters did not initially form in the bulk of the film but could be subsequently formed by the electron-beam irradiation. The interface between the silicon substrate and the silica glass film was investigated by Raman spectroscopy. The shift of the Raman peaks around 286.8 cm-1 and 495 cm-1 suggests that the interface is a Si1-xGex alloy film and that the composition x varies along the film growth direction.

Spin polarization of electrons in a quantum film based on a narrow-gap semiconductor

The size-quantized spectrum of a film (quantum well) with a variable band gap based on Pb1−xSnxSe compounds has been studied. It is shown that an asymmetric modulation of the band gap in the film growth direction leads to the spin splitting of the electron subbands of a uniform quantum well. The effect of the state of the film surface on spontaneous polarization of the electron gas is discussed.

Characteristics of Ni6Fe94 films deposited on SiO2/Si(100) by an oblique target co-sputtering

Ni6Fe94 films were deposited on SiO2/Si(100) substrates at room temperature by oblique target co-sputtering and then annealed in vacuum at 573 K, 673 K and 753 K for 1 h, respectively. The as-deposited and annealed films mainly have a body-centered cubic structure and a [110]-crystalline orientation in the film growth direction. The [110]-orientation of the film enhances with increasing annealing temperature. A face-centered cubic phase coexists in the body-centered cubic phase of the Ni6Fe94 films annealed at 673 K and 753 K. The as-deposited film grows with thin columnar grains and has a void network at the grain boundaries. The grain size does not change markedly with annealing temperature, whereas the voids decrease with increasing annealing temperature. Furthermore, wide and short void network is formed upon annealing. The resistivity of the film decreases with annealing temperature. The temperature coefficient of resistance of the film annealed at 753 K is larger than that of the as-deposited film. The as-deposited film shows a hard magnetization requiring a saturation field of 3.34×105 A/m. The film annealed at 753 K shows an easy magnetization characteristic and its coercivity is 2.51×104 A/m. The saturation magnetization of the film increases with annealing temperature. The as-deposited and annealed films have an isotropic magnetization characteristic.

Microstructure of Homoepitaxial SrTiO3 Films Deposited by Laser Ablation

Homoepitaxial strontium titanate thin films have been grown by pulsed laser deposition on (001) SrTiO3 (STO) substrates with pulse rates ranging from 0.15 Hz to 100 Hz. The microstructure of the as-deposited films has been characterised by cross-sectional transmission electron microscopy. It is found that the growth mode and microstructure of the films are strongly influenced by the intervals between the laser pulses. Films have homogeneous microstructure under a critical thickness, above which the film breaks into toothlike columns. The growth is unstable against the formation of low angle boundaries which result in the formation of grains elongated in the direction of film growth. These become toothlike structures and the size of the tooth depends on the pulse rate and the growth time. The diffusion of point defects in films grown over a long time can lead instead to the development of elongated vacancy clusters directed normal to the film-vacuum interface. All films grow with a high density of point defects which may be related to deviation from the stoichiometry of the ceramic ablation target. Microanalysis suggests that there is strontium loss in the film, which causes defect formation inside the STO films.

Time-resolved Photoconductivity as a Probe of Carrier Transport in Microcrystalline Silicon

AbstractThe use of transient photoconductivity techniques in the investigation of carrier transport in microcrystalline silicon is described. Results are presented which highlight variations in transport parameters such as carrier mobility and density of states with structure composition. Hole mobility is significantly enhanced by crystalline content in the film of 10% or less. The density of states inferred from transport measurements parallel to and at right angles to the direction of film growth differ somewhat, suggesting that transport may be anisotropic.

Refractive index gradients in TiO2 thin films grown by atomic layer deposition

Transmission spectra of TiO2 films grown by atomic layer deposition on fused silica have been analysed by using Lorentz dispersion and a model consisting of two sublayers inside a film. It has been shown that the deposition process parameters significantly influenced the refractive index gradient in the film growth direction. The films grown at a lower flow of the carrier gas showed a 35 nm thick sublayer with low refractive index at the silica substrate and a layer with a higher refractive index at the film surface. The films deposited at higher carrier gas flow had a higher refractive index at the substrate and a lower refractive index at the film surface. The results also demonstrate that by using a parameter modelling one can obtain some information about the internal structure of a film even if there are no clearly defined interference fringes in a transmission spectrum.

Complexity of the microstructure evolution for optimization cBN growth in a four-step ion-assisted deposition process

The changes in microstructure of a specially prepared boron nitride (BN) film as a function of film depth were studied by high resolution transmission electron microscopy (HRTEM) and other materials analysis tools. These changes were then correlated to the changes in processing parameters during film growth. The analyzed film was fabricated by the four-step ion-assisted deposition procedure known to be effective in film-stress engineering for the formation and retention of a thick cubic BN (cBN) layer with a three-step buffer-layer deposition. In this deposition, the energy of the ions assisting cBN formation was increased stepwise from 200 to 280, and then to 360 eV [ S.F. Wong, C. W. Ong, G.K.H. Pang, K.Z. Baba-Kishi, W. M. Lau, J. Vac. Sci. Technol. A 22 (2004) 676]. The nominal thickness of the cBN layer was 650 nm and that for each of the three buffer layers was about 160 nm. Both the HRTEM and electron diffraction results confirmed that the top cBN layer, with a thickness of 643 nm, consisted of cBN grains with a preferred orientation of their c-axis along the film growth direction. In comparison, the three-step buffer layer deposition yielded complex and intriguing microstructures. In the first buffer layer adjacent to the substrate, grains containing sp 2 planes with a preferred orientation of their basal planes parallel to the film growth direction were the main constituents. The increase of ion energy from 200 to 280 eV for the formation of the second buffer layer first led to an enrichment of the concentration of these sp 2 grains with the preferred orientation. Then, bending of some of the sp 2 planes into curved microstructures was evident. The microstructure became very complex and displayed multiple phases including some amorphous structures. The presence of a cBN-like phase was indeed detected by electron energy loss spectroscopy. This complex microstructure persisted until it was replaced by the cBN structure, without abrupt change when the ion energy was increased from 280 to 360 eV for the deposition of the third buffer layer. It is proposed that small grains with cBN-like sp 3 bonding configurations are present in the 2nd and 3rd buffer layers, probably with crystalline domains less than 5 nm and thus difficult for direct detection even by HRTEM. A sufficient accumulation of these cBN nuclei transformed the buffer layer to the cBN layer.

Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin films

ABSTRACTThis paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in‐plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement–amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions.