P. W. Chan

Reactive pulsed laser deposition of CNx films

Carbon nitride (CNx) films were prepared by reactive pulsed laser deposition at nitrogen partial pressure PN2varying from 0 to 300 mTorr. It is found that the atomic fraction of nitrogen f in the films first increases with increasing PN2, reaches a maximum of 0.32 at PN2=100 mTorr, and then decreases to a saturated value of 0.26 at PN2≳200 mTorr. Because of the absence of energetic particles in reactive pulsed laser deposition, the limited nitrogen content cannot be attributed to preferential sputtering of nitrogen that is generally observed in particle‐assisted deposition of CNx films. Infrared absorption experiments show the existence of C≡N bonds and graphitic sp2 bonds. The sp2 bonds become IR active because of symmetry breaking of graphitic rings as a consequence of nitrogen incorporation. CNx films deposited at low PN2 (e.g., 5 mTorr) are more graphitic than the diamondlike pure carbon sample deposited at PN2=0, so have a slightly narrower electron band gap Eopt and a significantly higher room‐tempe...

Intrinsic resputtering in pulsed‐laser deposition of lead‐zirconate‐titanate thin films

Pulsed‐laser deposition (PLD) of lead‐zirconate‐titanate [Pb(Zrx,Ti1−x)O3] (PZT) thin films under low ambient pressure has been investigated by studying the angular deposition distributions of the constituent elements of the films. Nonstoichiometric profiles are observed and a dip occurs near the target surface normal of the deposition profile of lead. Experimental results show that intrinsic resputtering of the film is important in the PLD process and is responsible for the anomalous distribution of lead.Pulsed‐laser deposition (PLD) of lead‐zirconate‐titanate [Pb(Zrx,Ti1−x)O3] (PZT) thin films under low ambient pressure has been investigated by studying the angular deposition distributions of the constituent elements of the films. Nonstoichiometric profiles are observed and a dip occurs near the target surface normal of the deposition profile of lead. Experimental results show that intrinsic resputtering of the film is important in the PLD process and is responsible for the anomalous distribution of lead.

Effects of substrate temperature on the structure and properties of reactive pulsed laser deposited CNx films

Abstract The effects of substrate temperature (25 ≤ Ts ≤ 437°C) on the structure and properties of reactive pulsed laser deposited (RPLD) carbon nitride (CNx) films prepared at a fixed nitrogen ambient pressure of 200 mTorr were investigated. The structure and composition of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and IR absorption, while the electrical and optical properties were studied by photothermal deflection spectroscopy, optical transmission and electrical conductivity measurements. The results show that the films contain graphitic rings, in which some of the carbon atoms are replaced by nitrogen atoms. The atomic fraction of nitrogen drops from 0.27 to 0.13 as Ts increases from 25 to 437°C, indicating that the incorporation of nitrogen is hindered by a rise in Ts. As a consequence, the optical band gap and the width of electron tail states become narrower, and the room temperature electrical conductivity increases greatly such that the properties of the films deposited at high temperature approach those of graphite.

Physical properties of dual ion beam deposited (B0.5−xSix)N0.5 films

(B0.5−xSix)N0.5 films (0⩽x⩽0.5) were prepared by dual ion beam deposition. Buffer layers were added to improve the film adhesion. The film structure was characterized by x-ray photoelectron spectroscopy, infrared absorption, and x-ray diffraction. The hardness and elastic modulus were measured by a nanoindenter. The I–V curves of the Ti/(B0.5−xSix)N0.5/buffer/p-Si/Ti diodes were investigated. The films are composites of cubic-boron nitride (c-BN), h-BN, and Si–N. When x=0, the film contains 70–75 vol % c-BN and has a hardness ≈38 GPa, but peels off quickly from the substrate after exposure to air. When x increases to 0.013, a small amount of Si–N phase is formed, which serves to release part of the internal stress without affecting the volume fraction of c-BN or the mechanical strength, and good adhesion is achieved. For higher Si content (0.013<x⩽0.067), the c-BN phase is disrupted with simultaneous replacement by h-BN. Rapid drops in the hardness and elastic modulus follow. When the Si content continues...

Structural studies of reactive pulsed laser-deposited CNx films by X-ray photoelectron spectroscopy and infrared absorption

The changes in the structure of reactive pulsed laser-deposited (RPLD) CNx films with nitrogen content from 3.6–22 at% have been investigated by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Fourier transform–infrared (FT–IR) absorption. The films were found to be amorphous, and to consist of a network of rings. The rings that were composed solely of carbon atoms gave rise to an XPS peak located between 284.3 and 284.8 eV (C1 component). The rings containing nitrogen led to another peak located between 285.5 and 286.4 eV (C2 component). When the nitrogen content increased, the relative intensity of the C1 component fell, while that of the C2 component rose, indicating that some carbon atoms in the rings were replaced by nitrogen atoms. C≡N bonds also contributed to the C2 component. The FT–IR data were consistent with this interpretation. No evidence for the existence of a β-C3N4 phase was found in RPLD CNx films.

Thermal stability of pulsed laser deposited diamond-like carbon films

Abstract Pulsed laser deposited diamond-like cabron (PLD DLC) films were prepared with the visible 532 nm Nd:YAG pulsed laser beam of power density Φ from 2.7 × 109 to 2.0 × 1010W cm−2, below the Nagel criterion (5 × 1010W cm−2 for 1064 nm Nd:YAG laser). The temperature dependence of the electrical conductivity, σ(T), the imaginary part of the refractive index, k, and the surface morphology of the films were studied as functions of Φ and post-annealing temperature Ta. Particulates appear on the surface of all samples, with their size increasing with increasing φ. For Φ between 2.7 × 109 and 5.9 × 109W cm−2, the room temperature electrical conductivity σR and k decrease from 1.28 × 10−4 to 3.37 × 10−5 Ω−1 cm−1, and from 0.2 to 0.18, respectively. These results indicate that higher Φ increases the diamond-like content in the films. For Φ from 5.9 × 109 to 2.0 × 1010W cm−2, σR and k increase to reach 3.69 × 10−4 Ω−1 cm−1 and 0.22, respectively. In this power density range the surface graphitic particulates dominate the film properties. Higher Φ generates larger graphite particulates and degrades the film quality, thus leading to increases in σR and k. The as-deposited samples were annealed at temperatures Ta between 100 and 900 °C. In this temperature range, ΦR increases by a factor of 106, while k rises from about 0.2 to 0.5, indicating that a diamond-like-to-graphitic transition has occurred. The degradation process was observable at Ta as low as 100 °C, and became significant for higher Ta. Finally, the films reach a graphitic state when Ta ⩾ 750 °C. Since the surface density and size of the particulates are not influenced significantly by annealing, we suggest that the variation of the films properties arises from changes in the matrix in which the graphitic particulates are embedded.

Effects of carbon incorporation on the structure and mechanical properties of cubic boron nitride films

Abstract Carbon (C) at concentration up to 11.8 at.% was incorporated into ion-beam deposited cubic boron nitride (c-BN) films. Films with C content ≤6.2 at.% were found to contain about 78 vol.% of c-BN, and have high hardness (36–47 GPa) and high elastic modulus (250–320 GPa). Due to the high internal stress in the films they peel off readily from the substrates. At higher C content, the cubic structure is disrupted, and the structural change is accompanied by drops in both the hardness and elastic modulus. However, film adhesion is greatly improved, possibly because of the partial release in internal stresses induced by the incorporated C atoms. The film with 7.2 at.% C exhibits good mechanical properties (hardness ≈ 34 GPa, elastic modulus ≈ 240 GPa) as well as satisfactory adhesion to substrates, and is thus suitable for application as a hard coating material.

The role of ambient gas scattering effect and lead oxide formation in pulsed laser deposition of lead–zirconate–titanate thin films

The angular distribution of lead in films deposited by pulsed laser irradiation of lead–zirconate–titanate and lead targets are studied as a function of ambient gas (argon or oxygen), gas pressure, and substrate temperature. When the substrate is kept in vacuum and at room temperature, a dip in the lead content attributable to the intrinsic resputtering of lead is observed at the position of the target surface normal. In the presence of an ambient gas, the dip disappears and the lead content increases at all angles. These results are attributed to a reduction of resputtering arising from scattering of the ablated species by ambient gas molecules. Under ambient oxygen and at high substrate temperature, the retention of lead content in the deposited films is largely due to the formation of lead oxide.

Relationship between the structure and the optical and electrical properties of ion beam deposited CNx films

Abstract Three series of CNx films were prepared by ion beam sputtering: (i) in N2 ambient (N2-series), (ii) with N2+ ion assist (N2+-series), and (iii) with Ar+ ion assist in N2 ambient (Ar+-series). The substrate temperature Ts was varied from 28 to 337°C. Structural analyses by X-ray photoelectron spectroscopy (XPS) and infrared absorption show that the films of the N2+-series have the highest N content (20–23 at.%). All the films are composed of six-membered ring structures and groups containing C–N, CN and CN bonds. As Ts increases, the fraction of the six-membered rings increases, and some groups containing C–N, CN and CN bonds become volatile and are detached from the film, such that the film structure becomes more graphitic. This leads to an overlap between the conduction band and the valence band, and hence, a higher electrical conductivity σroom. At any given Ts, the films of the Ar+-series have the highest σroom, because they have the highest level of graphitization among the three series. σroom of the N2-series and the N2+-series are lower because the former experiences less graphitization, while the latter contains more N, thus resulting in a lower carrier drift mobility.

Photoluminescence in porous sputtered polysilicon films formed by chemical etching

We have investigated the materials and photoluminescence properties of porous polysilicon films formed by chemical etching. The polysilicon samples were prepared by furnace crystallization of r.f. sputtered silicon films on a crystalline silicon substrate. The materials properties were observed by SEM, TEM, XRD and FTIR. XRD showed that the grains with (111) orientation have the highest etching rate and are probably most efficient in forming porous regions. The photoluminescence intensity depends on the annealing temperature of the sputtered Si film, and has a maximum value at a temperature around . This temperature dependence can be explained from the relative peak intensities of grains of different orientation measured by XRD. Rapid thermal oxidation of porous polysilicon films was found to degrade the photoluminescence intensity.