Xing-Min Cai

Shenzhen University, Bao'an, Guangdong, China

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Publications (21)33.13 Total impact

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    ABSTRACT: A series of Zn-Sb thin films were deposited by direct current (DC) magnetron co-sputtering through fixing the sputtering power of Zn target while varying the sputtering power of Sb target. The deposited thin films were annealed at 673 K under Ar atmosphere for 1 h. X-ray diffraction (XRD) results show that the prepared thin film gradually transforms from β phase Zn4Sb3 to ZnSb phase with increasing Sb sputtering power. It is found that the thermoelectric properties of the prepared Zn-Sb thin films are related to the phase transformation. Firstly, the carrier concentration decreases while the Hall mobility increases with increasing Sb sputtering power until 20 W, and then with further increasing Sb sputtering power, the carrier concentration increases while Hall mobility decreases. The thin films prepared by the Sb sputtering power of 20 W shows a mixed phase of ZnSb and Zn4Sb3 and its Seebeck coefficient has a higher value than the samples with single β-Zn4Sb3 or ZnSb phase. Through optimizing the ratio of β-Zn4Sb3 to ZnSb phase in the mixed Zn-Sb thin film, an enhanced power factor of 1.91 × 10-3 W/m K2 can be obtained with a high Seebeck coefficient of 360 μV K-1 and a low resistivity of 6.79 × 10-5 Ω m at 573 K. X-ray photoelectron spectroscopy (XPS) was used to investigate the binding energy of Zn and Sb in the thin film with a power factor of 1.91 × 10-3 W/m K2 and it is suggested that the weak bonding of the thin film could be one of the reasons resulting in enhanced thermoelectric performance.
    01/2014;
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    ABSTRACT: To study the effect of Cu doping, In2O3 and Cu-doped In2O3 films were deposited on K9 glass and Si substrates with the same experimental parameters. All the films were found to be body centered cubic and have the same preferred orientation. No secondary phases were detected in Cu-doped In2O3. The atomic ratio of Cu to Cu plus In was approximately 18% in Cu-doped In2O3 films where were found to be n-type. After Cu doping, the resistivity of the films increased by 3 to 4 orders of magnitude and film with higher Cu content had larger resistivity, due to compensation. Cu doping is found to widen the optical band gap of In2O3 films, possibly due to a metal-insulator transition.
    Thin Solid Films 01/2014; · 1.87 Impact Factor
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    ABSTRACT: Bismuth antimony tellurium is one of the most important tellurium-based materials for high-efficient thermoelectric application. In this paper, ion beam sputtering was used to deposit Bi2Te3 and Sb2Te3 bilayer thin films on borosilicate substrates at room-temperature. Then the bismuth antimony tellurium thin films were synthesized via post thermal treatment of the Bi2Te3 and Sb2Te3 bilayer thin films. The effect of annealing temperature and compositions on the thermoelectric properties of the thin films was investigated. After the thin films were annealed from 150 °C to 350 °C for 1 h in the high vacuum condition, the Seebeck coefficient changed from a negative sign to a positive sign. The X-ray diffraction results showed that the synthesized tellurium-based thermoelectric thin film exhibited various alloys phases, which contributed different thermoelectricity conductivity to the synthesized thin film. The overall Seebeck coefficient of the synthesized thin film changed from negative sign to positive sign, which was due to the change of the primary phase of the tellurium-based materials at different annealing conditions. Similarly, the thermoelectric properties of the films were also associated with the grown phase. High-quality thin film with the Seebeck coefficient of 240 μV K− 1 and the power factor of 2.67 × 10− 3 Wm− 1 K− 2 showed a single Bi0.5Sb1.5Te3 phase when the Sb/Te thin film sputtering time was 40 min.
    Thin Solid Films 01/2014; 562:181–184. · 1.87 Impact Factor
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    ABSTRACT: N-type bismuth telluride (Bi2Te3) thermoelectric thin films were deposited by co-sputtering simple substance Te and Bi targets. The deposited films were annealed under various temperatures. The composition ratio, micro-structure and thermoelectric properties of the prepared films were systematically investigated by energy dispersive spectrometer, X-ray diffraction, four-probe method and Seebeck coefficient measurement system. When the annealing temperature is 400 °C, the stoichiometric N-type Bi2Te3 film is achieved, which has a maximum thermoelectric power factor of 0.821 × 10-3 W m-1 K-2. Furthermore, the dependence of Seebeck coefficient, electrical conductivity and power factor of the stoichiometric N-type Bi2Te3 film annealed at film 400 °C on the applied temperature ranging from 25 °C to 315 °C was investigated. The results show that a highest power factor of 3.288 × 10-3 W m-1 K-2 is obtained at the applied temperature of 275 °C. The structural and thermoelectric properties of the deposited bismuth telluride thin films are greatly improved by annealing and the Seebeck coefficient, electrical conductivity and power factor increase with the applied temperature rising, which are helpful and could be guidance for preparing the high-performance thin film thermoelectric materials for thermoelectric application.
    Applied Surface Science 09/2013; · 2.11 Impact Factor
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    ABSTRACT: In conventional thin film thermoelectric generators, heat flow running vertical to film surface is used. The hot side and the cold side are just separated by the thickness of the films and to maintain the temperature difference between both sides remains a key challenge. Here, we demonstrate the properties of our designed thin film thermoelectric generators with heat flow running parallel to film surface, where a larger temperature difference between both sides is maintained. The maximum output power of our generator can reach 19.13 μW at the temperature difference of 85 K.
    Applied Physics Letters 01/2013; 102(3). · 3.79 Impact Factor
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    ABSTRACT: Cu-doped ZnO films were deposited by direct current magnetron sputtering at room temperature in an atmosphere of argon and oxygen. The properties of Cu-doped ZnO films were characterized and their field emission was studied. The field emission is related to the defect energy levels of Zn interstitials. Cu doping can weaken the field emission by reducing the number of Zn interstitials, deteriorating the crystalline quality and forming electron traps. The content of Cu has to be carefully controlled to achieve a field emission with a large current density and a low threshold voltage.
    physica status solidi (b) 03/2012; 249(3):596-599. · 1.49 Impact Factor
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    ABSTRACT: Indium doped ZnO film was fabricated at room temperature by co-sputtering a zinc target and an indium plate under the flow of oxygen and argon. The film was then characterized and the field emission of the film was studied. The indium composition x in the film (Zn1−xInxO) is 5%. The film is hexagonal without any secondary phases or precipitates. The film has two major emission peaks, one related to the band edge emission and another possibly related to the electron acceptor transition. The possible acceptor is nitrogen occupying oxygen site in ZnO. The film is n-type and very resistive. The turn on field of the film at an emission current density of 10μA/cm2 is 17.5V/μm. The relatively weak field emission property is due to the unintentional incorporation of acceptors such as substitutional nitrogen and oxygen vacancies, which increase the work function of ZnO by reducing the electron density and lowering the Fermi level position of the ZnO:In film.
    Physica B Condensed Matter 01/2012; · 1.33 Impact Factor
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    ABSTRACT: Cu–In–O composite thin films were deposited by reactive DC magnetron sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV/vis spectrophotometer, four-probe measurement and Seebeck effect measurement, etc. The samples contain Cu, In and O. The ratios of Cu to In and O to In increase with increase in O2 flow rates. The ratio of Cu to In is over 1 and this suggests that Cu is in excess. The obtained Cu–In–O thin films are very possibly made of rhombohedral In2O3 and monoclinic CuO. Transmittance of the films decreases with increase in O2 flow rate. The decrease in transmittance results from increase in Cu content in the films. The optical band gap of all the samples is estimated to be 4.1–4.4 eV, which is larger than those of In2O3 and CuO. The sheet resistance of the films decreases with increase in O2 flow rate. Conductivity of the films is a little low, due to the addition of Cu and the poor crystalline quality of the film. The conduction behavior of the films is similar to that of In2O3 and the conduction mechanism of Cu–In–O thin films is through O vacancy.
    Physica B Condensed Matter 02/2011; 406(3):516–519. · 1.33 Impact Factor
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    ABSTRACT: To evaluate the influence of film thickness on the structural, electrical, and optical properties of Al-doped ZnO (AZO) films, a set of polycrystalline AZO samples with different thickness were deposited on glass substrates by ion-beam sputtering deposition (IBSD). X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS), four-point probe measurements, and spectrophotometry were used to characterize the films. XRD showed that all the AZO films had preferred c-axis orientation. The ZnO (110) peak appeared, and the intensity increased, with increasing thickness. All the samples exhibited compressive intrinsic stresses. AFM showed that the grain size along with the root-mean-square (RMS) roughness increased with increasing thickness. The decrease of resistivity is due to the corresponding change in grain size, surface morphology, and chemical com-position. The average optical transmittance of the AZO films was over 80%, and a sharp fundamental absorption edge with red-shifting was observed in the visible region. The optical band gap decreased from 3.95 eV to 3.80 eV when the AZO film thickness increased from 100 nm to 500 nm.
    Journal of Electronic Materials 01/2011; 40(3). · 1.64 Impact Factor
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    ABSTRACT: CuInSe2 (CIS) thin films were prepared by ion beam sputtering deposition of copper layer, indium layer and selenium layer on BK7 glass substrates followed by annealing at different temperatures for 1h in the same vacuum chamber. The influence of annealing temperature (100–400°C) on the structural, optical and electrical properties of CIS thin films was investigated. X-ray diffraction (XRD) analysis revealed that CIS thin films exhibit chalcopyrite phase and preferential (112) orientation when the annealing temperature is over 300°C. Both XRD and Raman show that the crystalline quality of CIS thin film and the grain size increase with increasing annealing temperature. The reduction of the stoichiometry deviation during the deposition of CIS thin films is achieved and the elemental composition of Cu, In and Se in the sample annealed at 400°C is very near to the stoichiometric ratio of 1:1:2. This sample also has an optical energy band gap of about 1.05eV, a high absorption coefficient of 105cm−1 and a resistivity of about 0.01Ωcm.
    Thin Solid Films 01/2011; 519(16):5348-5352. · 1.87 Impact Factor
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    ABSTRACT: Ion beam sputtering was used to deposit Sb2Te3 thin films on BK7 glass substrates at room temperature. The effect of annealing on the thermoelectric properties of the Sb2Te3 thin films was investigated. After the stoichiometric films were annealed at 100°C to 400°C for one hour, the Seebeck coefficient decreases from 190μVK−1 to 106μVK−1, and the conductivity increases from 1.1×102Scm−1 to 2.01×103Scm−1. The Power Factor is enhanced greatly from 0.40×10−3Wm−1K−2 to 2.26×10−3Wm−1K−2 after annealing at 400°C. The positive Seebeck coefficient α suggests the films to be p-type. X-ray diffraction (XRD) shows that the major diffraction peaks of the films match those of Sb2Te3 and high crystalline films are achieved after annealing. These results indicate that high-quality Sb2Te3 thin films are achieved and annealing greatly improves the thermoelectric properties of the films.
    Journal of Alloys and Compounds 01/2010; 505(1):278-280. · 2.39 Impact Factor
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    ABSTRACT: Ion beam sputtering process was used to deposit n-type fine-grained Bi2Te3 thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400°C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400°C. Thermoelectric properties of Bi2Te3 thin films were investigated at room temperature. The Bi2Te3 thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168μVK−1 and the electrical conductivities of 3.92×102–7.20×102Scm−1 after annealing. The Bi2Te3 film with a maximum power factor of 1.10×10−3Wm−1K−2 is achieved when annealed at 300°C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.
    Journal of Physics and Chemistry of Solids 01/2010; 71(12):1713-1716. · 1.53 Impact Factor
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    ABSTRACT: The optimization of ion beam sputtering deposition process for Sb2Te3 thin films deposited on BK7 glass sub-strates is reported. The influence of composition ratio on the thermoelectric properties is investigated. X-ray diffraction shows that the major diffraction peaks of the films match with those of Sb2Te3. Hall effect and See-beck coefficient measurement reveal that all the samples are of p-type. The Sb2Te3 thin films exhibit the Seebeck coefficient of 190 íµí¼‡Vk −1 and the electrical conductivity of 1.1 × 10 3 Scm −1 when the atomic ratio of Sb to Te is 0.65. Carrier concentration and motility of the films increase with the increasing atomic ratio of Sb to Te. The Sb2Te3 film with a maximum power factor of 2.26 × 10 −3 Wm −1 K −2 is achieved when annealed at 400 ∘ C. Raman measurement shows that the main peaks are at about 120 cm −1 , 252 cm −1 and 450 cm −1 , in agreement with those of V-VI compound semiconductors. Alloys based on V-VI compound semiconductors, with A 2 B 3 -type, have been extensively studied be-cause of their excellent thermoelectric properties and potential applications in efficient thermoelectric de-vices such as thermoelectric generators, coolers and optical storage systems. [1,2] The research results indi-cate that thin films and nanowires would have a higher figure of merit (ZT) [3] due to their stronger quantum confinement. [4] Therefore, various techniques, includ-ing flash evaporation, [5] sputtering, [6] electrochemi-cal deposition [7−9] and chemical-vapor deposition [10] have been used to grow thermoelectric thin films and nanowires. Antimony telluride (Sb 2 Te 3) is an important V-VI thermoelectric material at room temperature due to its narrow-band gap and lager figure of merit (ZT) value. [11−13] Compared with bulk Sb 2 Te 3 ma-terials, the ZT value of Sb 2 Te 3 thin films has been enhanced greatly. However, only a few studies have been conducted on fabricating Sb 2 Te 3 thin films and nonawires. [12−14] The most difficult task for preparing Sb 2 Te 3 thin films is controlling the composition of the thin films. Because the vapor pressure of Te is so high and re-evaporation of Te prevents the formation of Sb 2 Te 3 . Actually, ion beam sputtering deposition is a very attractive technique since it combines a high de-position rate with a great versatility in the deposition of films by adjusting the target composition and con-trolling the sputtering energy. In addition, preparing Sb 2 Te 3 thin films by ion beam sputtering deposition (IBSD) is rarely reported. In this work, high quality Sb 2 Te 3 thin films are prepared by IBSD. The struc-tural and electrical properties of the films are investi-gated. Sb 2 Te 3 thin films were deposited on BK7 glass substrates by IBSD in argon ambience. The tar-get was made of fan-shaped high purity Sb (99.99%) and Te(99.99%) plates. The Sb/Te proportion was controlled by adjusting the ratio of the correspond-ing plate areas. The background pressure was 7.0 × 10 −4 Pa and the work pressure was 6.1×10 −2 Pa. The substrates were ultrasonically cleaned in acetone and alcohol for 10 min, respectively. Prior to Sb/Te de-position, a 15-min sputter cleaning process was per-formed to remove the native oxides and contami-nants on the target surfaces. Four samples (named as S1 ∼ S4) with different Sb/Te compositions were prepared at room temperature. The deposition time was 60 min. The sample with the best power factor (PF = íµí»¼ 2 íµí¼Ž) was annealed at 400 ∘ C for one hour in the vacuum chamber (named as S5). More details on sample preparation are given in Table 1 where íµí±… ato is the atomic ratio of Sb to Te.
    Chinese Physics Letters 01/2010; 27(73). · 0.81 Impact Factor
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    ABSTRACT: CuInSe2 (CIS) films were prepared by ion beam sputtering depositing Cu, In and Se layers sequentially on BK7 glass substrates and annealing the 3-layer film in the same vacuum chamber. The adjustment of the Se amount in the film was achieved by controlling the sputtering time of the Se target. X-ray diffraction pattern shows CIS films have chalcopyrite structure and preferential (112) orientation when the sputtering of the Se layer is between 60 and 180min. It also can be seen that the most intense and narrow peak indicates the highest crystallinity for the sample with sputtering Se of 60min, which is in agreement with the Raman measurement. The content of Cu, In and Se in the film deviates from 1, 1 and 2 with increasing the sputtering time of the Se target. Direct band gap energy between 0.96 and 1.05eV, depending on the Se amount, and a high absorption coefficient of 105cm−1 are found. The measured film resistivities vary from 0.01 to 0.05Ωcm. Thus, the structural, optical and electrical characteristics of the CIS thin films were dependent on the Se amount during the fabrication of films and after fitting the sputtering time of Se, an optimization of the properties and a saving of Se consumption were achieved.
    Journal of Materials Science Materials in Electronics 01/2010; 21(9):897-901. · 1.49 Impact Factor
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    ABSTRACT: In this paper, InN thin films were deposited on Si (100) and K9 glass by reactive direct current magnetron sputtering. The target was In metal with the purity of 99.999% and the gases were Ar (99.999%) and N2 (99.999%). The properties of InN thin films were studied. Scanning electron microscopy (SEM) shows that the film surface is very rough and energy dispersive X-ray spectroscopy (EDX) shows that the film contains In, N and very little O. X-ray diffraction (XRD) and Raman scattering reveal that the film mainly contains hexagonal InN. The four-probe measurement shows that InN film is conductive. The transmission measurement demonstrates that the transmission of InN deposited on K9 glass is as low as 0.5% from 400nm to 800nm.
    Applied Surface Science 01/2009; 256(1):43-45. · 2.11 Impact Factor
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    ABSTRACT: InN thin films were fabricated by reactive direct current magnetron sputtering. Different Ar and N2 flow rates were tried in order to tune the properties of the obtained films. Scanning electron microscopy (SEM) shows that growth of InN on Si (100) follows island growth mode. Energy dispersive X-ray spectroscopy (EDX) shows that the film contains In, N and O. When Ar flow rate is 75sccm and N2 changes from 25sccm to 150sccm, the atomic ratio of N increases while that of In and O decreases. X-ray diffraction (XRD) and Raman scattering reveal that the film contains hexagonal InN and cubic In2O3. The XRD peak intensity related to cubic In2O3 decreases with the increase of N2 flow rate. The four probe measurement shows that all the samples have very low sheet resistances. The transmission of InN deposited on K9 glass is very low.
    Journal of Alloys and Compounds 01/2009; 484(1):677-681. · 2.39 Impact Factor
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    ABSTRACT: CuInSe2 (CIS) thin films were prepared by ion-beam sputtering at different substrate temperatures. The films prepared at room temperature were annealed at different temperatures. Films annealed at appropriate temperatures are dense, uniform and of single-phase.
    01/2009;
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    ABSTRACT: HfNxOy thin films were deposited on Si substrates by direct current sputtering at room temperature. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). SEM indicates that the film is composed of nanoparticles. AFM indicates that there are no sharp protrusions on the surface of the film. XRD pattern shows that the films are amorphous. The field electron emission properties of the film were also characterized. The turn-on electric field is about 14V/μm at the current density of 10μA/cm2, and at the electric field of 24V/μm, the current density is up to 1mA/cm2. The field electron emission mechanism of the HfNxOy thin film is also discussed.
    Applied Surface Science 01/2008; 254(10):3074-3077. · 2.11 Impact Factor
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    ABSTRACT: Zirconia films were prepared by e-beam evaporation, and oxygen plasma treatment was used to modify film properties. Spectrophotometry, x-ray diffractometry (XRD), and atomic force microscopy were used to characterize refractive index, extinction coefficient, microstructure, and surface roughness, respectively. The experimental results indicate that both refractive index and extinction coefficient of the films were reduced slightly after oxygen plasma treatment, with the decrease of intrinsic stress and surface roughness. From XRD spectra, the intensity decrease of the T(110) diffraction peak was clearly observed after the treatment, which was caused by the restructuring of the film atoms.
    Solid State Communications 01/2008; 148(1):22-24. · 1.53 Impact Factor
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    ABSTRACT: Laser-induced damage of optical thin films is one of the main obstacles, which prevents laser technology from being developed toward high power. Many experimental results indicated that microdefect and absorption of films are the two major factors that influence laser induced damage threshold (LIDT). To reduce microdefect density and absorption, and improve LIDT of thin films, researchers have developed not only novel film deposition techniques, but also novel film post-treatment techniques. Though film deposition techniques have been highly developed, microdefect still remains to be the main limited factor of LIDT. Because of this, posttreatment techniques as a novel way to reduce defect density and improve LIDT has (been) attracted much attentions. One of the most frequently used posttreatment methods is laser conditioning and another is ion posttreatment. By comparing the treatment mechanism of two posttreatment techniques, it is easy to find their similarities and differences. Though laser conditioning is a classical posttreatment technique, its shortages such as low efficiency, rigorous requirement of equipment stability, and uncertain treatment results are inevitable. As a novel technique, ion posttreatment has great potential to improve LIDT of thin films. This technique not only has high treatment efficiency, but also has convenience and easily adjusted parameters. So it should be a promising posttreatment technique in improving LIDT of optical thin films.
    Proc SPIE 12/2007;