Mo Underlayer Research Articles

C-axis texture of high-rate-sputtered Nd2Fe14B thin films: independence of sheet texture of Mo underlayer

In this study, we investigated the effects of the sheet texture of the Mo underlayer on the c-axis texture of the high-rate-sputtered Nd2Fe14B phase. The magnetic properties revealed that the squareness of the Nd–Fe–B magnetic layer did not depend on the sheet texture of the Mo underlayer but on the substrate temperature: large squareness was obtained when the magnetic layer was sputtered at high substrate temperature above 500 °C. In-plane X-ray diffraction measurements indicated that the intensity of diffraction from the Nd2Fe14B (410) plane did not depend on the sheet texture of the Mo underlayer but on the substrate temperature: high intensity was obtained when the magnetic layer was sputtered at above 500 °C, which was consistent with magnetic properties. These results support that the c-axis texture of the high-rate-sputtered magnetic layer was driven by the c plane with the lowest surface energy among the crystal planes in the Nd2Fe14B phase.

Fabrication and growth of c-axis textured Nd2Fe14B thin films by high-rate sputtering

To apply Nd–Fe–B thin films for mass-produced heat-assisted magnetic recording media, we investigated the high-rate sputtering conditions required to obtain c-axis textured Nd2Fe14B thin films and analyzed the growth mechanism. Magnetization curves indicated that higher substrate temperatures and sputtering rates resulted in a higher degree of perpendicular magnetic anisotropy; a Nd–Fe–B layer deposited at a substrate temperature (Tsub_0) of 600 °C and a sputtering rate (Rsp) of 2.6 nm/s had the easy axis perpendicular to the film plane. The dependence of the magnetic properties on the sputtering rate was due to a decrease in the substrate temperature during sputtering; there was a threshold for obtaining a high squareness ratio. X-ray diffraction analysis and transmission electron microscopy (TEM) images showed that the c-axis textured Nd2Fe14B crystal phase was formed in the Nd–Fe–B layer deposited at Tsub_0 = 600 °C and Rsp = 2.6 nm/s, which resulted in the highly perpendicular magnetic anisotropy. In addition, the TEM images showed a layer of Nd2Fe14B with no obvious lattice fringes near the interface between the Nd–Fe–B layer and Mo underlayer, while the lattice fringes of the Nd2Fe14B phase were not parallel to this interface but gently curved along the Mo cap layer. We propose that the c-axis orientation was achieved by the rotation of the c plane, which has the lowest surface energy in the Nd2Fe14B phase, toward the vacuum-side surface during sputtering.

Engineering Na-transport to achieve high efficiency in ultrathin Cu(In,Ga)Se2 solar cells with controlled preferred orientation

Although the efficiency of Cu(In, Ga)Se2 (CIGS) solar cells have exceeded 22% for the absorber with thickness more than 2µm, thinning the absorber thickness has attracted attention to save the material costs of indium and gallium as well as to increase manufacturing throughput. However, a trade-off exists between efficiency and thickness of CIGS absorbers. In this work, we report a new insight to promote the efficiency of ultrathin (hundred-nanometer scale) CIGS solar cells by engineering Na-transport in a direct sputtering process with a quaternary CIGS target without post-selenization. We first demonstrate a feasibility to manipulate the preferred orientation of CIGS absorbers via controlled texture growth of the Mo underlayers. Then, we reveal that the amount of Na content within absorbers is strongly related to the preferred orientation and Cu-content of CIGS. The Cu-deficient CIGS absorbers grown on (211)-Mo underlayer show the strongest (220/204) CIGS texture and highest Na content, leading to enhanced efficiency. Through adequate Na-transport engineering and commonly used Ga gradient, we have significantly enhanced the efficiency of ultrathin (550nm) CIGS solar cells to 10.04%. Our results unveil the key factors of Na-transport in nano-scale and provide a strategy to achieve high-efficiency ultrathin CIGS solar cells.

Modification of the Interface Nanostructure and Magnetic Properties in Nd-Fe-B Thin Films.

The effects of Nd2Fe14B grain size and Nd coating on the coercivity in sputter-deposited Nd-Fe-B/Nd thin films have been investigated in order to gain an insight into the coercivity mechanism of Nd-Fe-B magnets. Highly textured Nd2Fe14B particles were grown successfully on the MgO(100) single-crystal substrate with the Mo underlayer. As the Nd-Fe-B layer thickness tNFB was decreased from 70 to 5 nm, the coercivity Hc increased gradually from 6.5 to 16 kOe. By depositing the Nd overlayer onto these films and post-annealing at 500 °C, the Hc value further increased from 17.5 kOe (tNFB=70 nm) to 26.2 kOe (tNFB=5 nm). The amount of Hc increase by the combination of the Nd coating and post-annealing was about 10 kOe irrespective of the tNFB value. These results therefore suggest an independence of size and interface effects on the coercivity of Nd-Fe-B magnets.

Intrinsic Coercivity of SmCo Based Permanent Magnetic Films Prepared on Hot Substrates at 650 °C

The intrinsic coercivity of the SmCo based permanent magnetic films prepared on the hot Si substrate at 650 °C with Al, Cu, Ag, Mo, and Cr underlayer without a subsequent annealing process was investigated. The results show that the films with Mo and Cr underlayer provide an improved intrinsic coercivity. The film thickness presents a complex effect on the intrinsic coercivity of the films with Mo underlayer. When the film thickness is 3.0 μm, the maximum value of the intrinsic coercivity is 281.6 kA·m−1 at room temperature. Furthermore, the temperature dependence of intrinsic coercivity is found to be strongly correlated with the magnetic parameters. In the range from 25 °C to 300 °C, the intrinsic coercivity of the films of above 200 kA·m−1 is obtained.

Magnetic Properties of SmCo7 Permanent Magnetic Films for High Temperature Applications

Abstract High temperature magnetic properties of the SmCo 7 films deposited on Si(100) substrate with Mo underlayer were investigated. The results show that the effects of high temperature aging treatment on the crystal structure and the magnetic properties of the films are not obvious. According to the law of approach to the saturation and high temperature magnetization curves of the films, the temperature dependence of magnetic anisotropy constant K 1 can be obtained, which clearly suggests that the preferred orientation of SmCo crystalline will be destroyed at a certain extent by elevated temperatures. Moreover, the proper temperature dependence of magnetic properties for the films, is suitable for applications in microelectromechanical system (MEMS).

Magnetic properties of SmCo-based permanent magnetic films during 25 to 300 °C

Magnetic properties of the SmCo-based permanent magnetic films prepared on hot substrate with Mo and Cr underlayer without subsequent annealing process were investigated by vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS). The results showed that the film thickness of the SmCo-based films presented complex effect on the intrinsic coercivity Hci. Optimal Hci for the films with Mo underlayer, Cr underlayer, and without underlayer was observed with different film thicknesses. Furthermore, the monotonous temperature dependence of Hci was found to be strongly correlated with the magnetic parameters for the 3.0 μm thick SmCo7 films with Mo underlayer. From 25 to 300 °C, the Hci decreased from 281.6 to 211.2 kA/m with a temperature coefficient of −0.091%/°C, exhibiting good temperature stability.

Effect of rare-earth overlayer on the coercivity in sputter-deposited Nd-Fe-B films

Nd2Fe14B films with the c-axis perpendicular to the film plane were deposited by introducing Mo (110) underlayer on the SiO2 substrates. When the temperature of the substrate during the deposition of the Nd-Fe-B layer was 600 °C, the demagnetization curve exhibited the coercivity of Hc=11 kOe. We observed an Hc increase of up to 14 kOe by capping the film with the Nd overlayer and post-annealing at 500°C. Cross-sectional TEM observation and NBD analysis suggest that the Nd in the overlayer is in the oxide state with either cubic-NdO2 or hcp-Nd2O3 structures.

Characteristic of Copper Films on Molybdenum Substrate by Addition of Titanium in an Advanced Metallization Process

Mo(Ti) alloy and pure Cu thin films were subsequently deposited on <TEX>$SiO_2-coated$</TEX> Si wafers, resulting in <TEX>$Cu/Mo(Ti)/SiO_2$</TEX> structures. The multi-structures have been annealed in vacuum at <TEX>$100-600^{\circ}C$</TEX> for 30 min to investigate the outdiffusion of Ti to Cu surface. Annealing at high temperature allowed the outdiffusion of Ti from the Mo(Ti) alloy underlayer to the Cu surface and then forming <TEX>$TiO_2$</TEX> on the surface, which protected the Cu surface against <TEX>$SiH_4＋NH_3$</TEX> plasma during the deposition of <TEX>$Si_3N_4$</TEX> on Cu. The formation of <TEX>$TiO_2$</TEX> layer on the Cu surface was a strong function of annealing temperature and Ti concentration in Mo(Ti) underlayer. Significant outdiffusion of Ti started to occur at <TEX>$400^{\circ}C$</TEX> when the Ti concentration in Mo(Ti) alloy was higher than 60 at.%. This resulted in the formation of <TEX>$TiO_2/Cu/Mo(Ti)\;alloy/SiO_2$</TEX> structures. We have employed the as-deposited Cu/Mo(Ti) alloy and the <TEX>$500^{\circ}C-annealed$</TEX> Cu/Mo(Ti) alloy as gate electrodes to fabricate TFT devices, and then measured the electrical characteristics. The <TEX>$500^{\circ}C$</TEX> annealed Cu/Mo(<TEX>$Ti{\geq}60at.%$</TEX>) gate electrode TFT showed the excellent electrical characteristics (<TEX>$mobility\;=\;0.488\;-\;0.505\;cm^2/Vs$</TEX>, on/off <TEX>$ratio\;=\;2{\times}10^5-1.85{\times}10^6$</TEX>, subthreshold = 0.733.1.13 V/decade), indicating that the use of Ti-rich(<TEX>$Ti{\geq}60at.%$</TEX>) alloy underlayer effectively passivated the Cu surface as a result of the formation of <TEX>$TiO_2$</TEX> on the Cu grain boundaries.

In-situ Analysis on the Effect of Mo Underlayer on HillockFormation Behavior in Al Thin Films

The in-situ scanning electron microscopy observation of real-time hillock evolution in pure hi thin films on glass substrate during Isothermal annealing was analyzed quantitatively to understand the compressive stress relaxation mechanism by focusing on the effect of Mo interlayer between Al film and glass substrate. There is a good correlation between the hillock-induced stress relaxation by in-situ scanning electron microscopy observation ana the measured stress relaxation by wafer curvature method. It is also clearly shown that the existence of Mo interlayer plays an important role in hillock formation probably due to the large difference in interfacial diffusivity of Al films.

Position-selective growth of vertically aligned carbon nanotubes for application of electronic-measuring nanoprobes

Position-selective growth of carbon nanotubes (CNTs) and vertically aligned CNTs (VACNTs) on patterned metal electrodes have been prepared by thermal chemical vapor deposition (TCVD) and DC plasma enhanced chemical vapor deposition (PECVD). We propose newly a position-controlling method of CNTs by controlling not only a position of Ni as catalysts but also the morphology of Mo as underlayers for the catalysts. The position-selective growth of CNTs was achieved at the edges of the patterned metal by TCVD. The morphologies of the Mo underlayer at the selected area were rough and porous. No CNTs grew on smooth Mo surfaces. The minimum width of selectively grown CNTs, ca. 2.6 μm, was approximately one-eightieth of the patterned metal, 200 μm. VACNTs were synthesized by a PECVD method, however, the VACNTs grew up all over the patterned metal. The Ni catalysts formed into fine particles on rough surfaces of the Mo underlayer. Then the selective growth was achieved by Ni fine particles formed only at the edges of the metal pattern. The results of PECVD suggest that the plasma promoted the Ni catalysts to become fine particles on smooth surfaces of Mo. Conclusively a position-controlling method of CNTs was demonstrated in the optimum conditions of the TCVD.

Growth modes of carbon nanotubes on metal substrates

Growth temperature induced changes in Al∕Fe thin film catalysts are examined for chemical vapor deposition of carbon nanotubes directly on metal substrates. The film thickness, growth temperature, and supporting substrate affect the size and the density of Fe catalyst nanoparticles which in turn control the diameter, length, and single versus multiwalled nature of carbon nanotubes. Growths on two metal substrates, Au and Mo, using sputter deposited Al∕Fe thin films are compared by transmission and scanning electron microscopy, and Raman analyses. Striking differences in the growth modes are observed with Au substrate enhancing multiwalled nanotube growth with metal catalyst particles at the tip away from the substrate and Mo substrate promoting single-walled nanotube growth with the catalyst nanoparticles remaining on the substrate. Oxidative treatment of Mo underlayer (i.e., relatively thick layer Mo sputtered on Au prior to Al∕Fe catalyst deposition) can also induce nanotube growth with catalyst particles at the tips but with single-walled structure. These results suggest the importance of the support catalyst (Al∕AlxOy) adhesion strength on substrates in determining nanotube growth modes.

Preparation and magnetic properties of nanocomposite Nd28Fe66B6 /Fe50Co50 bilayer films

The nanocomposite Nd28Fe66B6/Fe50Co50 bilayer films with Mo underlayer and overlayer have been fabricated on Si substrates. All the samples prepared have perpendicular anisotropy and th e hysteresis loops are simple single loops for fixed Nd-Fe-B layer thickness (10 nm) and different FeCo layer thickness (dFeCo =1—100nm). The shape a nd the behavior of the initial loops and the minor loops suggest that wall pinni ng is the dominant coercivity mechanism in these films. The magnetization of the se samples is found to increase with increasing FeCo layer thickness for a fixed Nd-Fe-B layer thickness and the coercivity of films decrease with increasing Fe Co layer thickness. The sample of maximum energy product is 160×１０３A/m for dFeCo =5nm at room temperature. The enhancement of the rema nence and energy products in nanocomposite bilayer films is attributed to the ex change coupling between the magnetically soft and hard phases.

Semi-epitaxial bcc Ta Growth on Metal Nitride

The crystal structure change of sputtered Ta metal according to the nonmetal underlayer film was studied. The bcc-structure Ta was grown on TaNx, NbNx and bcc Mo underlayer films, whereas tetragonal-structure Ta was grown on glass, Ta2O5 and some metals. The crystal structure of Ta varied from tetragonal to bcc according to the N composition of the TaNx and NbNx underlayer films. The bcc Ta growth on TaNx was explained in terms of crystal structure compatibility of the Ta lattice arrangement between TaNx and bcc Ta, and tetragonal Ta growth on Ta2O5 film could be explained by partial Ta lattice matching between Ta2O5 and Ta crystals. Bcc Ta on the TaNx film gave a low resistivity of 25 µΩcm, in contrast to that of conventional tetragonal Ta of 180 µΩcm. The resistivity of Ta anodic oxide was increased by five orders of magnitude by adding N compared to that of conventional Ta anodic oxide. Low-resistivity bcc Ta on TaNx and high-resistivity TaN anodic oxide are applied as gate bus lines of TFT-LCD.

Effect of underlayer thickness on magnetic properties of SmCo film

It is well known that the Cr underlayer plays significant role in the magnetic properties of Co alloy film. In this study, the effects of the underlayer materials such as Cr, Mo, W, W/Cr, and Al and their thickness on the magnetic properties of SmCo films were studied. In the x-ray diffraction diagrams of the SmCo/Cr film and the SmCo/Mo film, only (110) line of body-centered-cubic crystal structure was observed, while diffraction lines from SmCo phase could not be observed. The oval shaped grains were observed on the surface of Cr underlayer and the Mo underlayer when the thickness was thicker than 100 nm. The coercivity of the SmCo/Cr film and the SmCo/Mo film with thickness over 100 nm was higher than 3 kOe and the squareness ratio and the coercivity squareness ratio was above 0.8 and 0.9, respectively. These results indicate the Cr underlayer and the Mo underlayer are suitable for SmCo layers in order to increase the coercivity and the SmCo/Cr film and the SmCo/Mo film are good candidates for high density recording media.

Adsorption studies on Ar + -sputtered MoS 2(0001)

In this work we report a study of Ar + -sputtered MoS 2(0001) before and after its interaction with gas and metal adsorbates. The study took place in an UHV system with LEED, AES, EELS and WF measurements. The adsorbates were O 2 and Fe. Argon-ion bombardment of MoS 2(0001) caused a displacement of S atoms in the top layer thus exposing areas of the Mo underlayer on the surface. The interaction of deposited oxygen with the Mo areas exposed on the surface of the Ar + -sputtered MoS 2(0001) was quite similar to that of O 2 with Mo metal substrate. The Fe adsorbate was deposited on Ar + -sputtered MoS 2(0001) in two different ways. It formed uniform layers on the Mo areas while on the rest area covered by S, it formed small particles.