Sensors and Actuators A 254 (2017) 89–94
Contents lists available at ScienceDirect
Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna
Non-magnetic thin films for magnetic field position sensor Rizwan Ur Rehman Sagar a,b , Awais Siddique Saleemi c , Khurram Shehzad d , Sachin T. Navale a,b , Rajaram S. Mane e , Florian J. Stadler a,∗ a College of Materials Science and Engineering, Shenzhen Key Laboratory of Polymer Science and Technology, Guangdong Research Center for Interfacial Engineering of Functional Materials, Nanshan District Key Lab for Biopolymers and Safety Evaluation, Shenzhen University, Shenzhen 518060, PR China b Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, PR China c Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China d College of Information and Electronic Engineering, Zhejiang University, Hangzhou, 310027, PR China e School of Physical Sciences, Swami Ramanand Teerth Marathwada University, Nanded 431606, India & Department of Chemistry, College of Science, Bld-5, King Saud University, Riyadh, Saudi Arabia
a r t i c l e
i n f o
Article history: Received 18 July 2016 Received in revised form 1 December 2016 Accepted 1 December 2016 Available online 5 December 2016 Keywords: Anisotropic magnetotransport Magnetoresistance and amorphous carbon
a b s t r a c t Herein, for the first time, anisotropic magnetotransport phenomenon in amorphous carbon (a-C) thin films has been examined on the basis of Brysksin – Klein (B-K) model. The sign of magnetoresistance turns negative at (, ) = (0◦ , 90◦ ) to positive at (, ) = (90◦ , 90◦ ) where and are the angle between applied magnetic field and normal to the plane and the angle between applied magnetic field and current, respectively. The sign of magnetoresistance of a-C thin films varies continuously at = 0–360◦ and =0–90◦ , suggesting good potential for the position sensing of large magnetic field. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Compared to the Hall-effect-based sensors, magnetoresistance (MR)-based sensors offer the advantages of high sensitivity at room temperature [1], as well as exhibit the angle-dependent magnetoresistance (AMR) phenomenon [2]. AMR is a typical feature of ferromagnetic class of materials, which is a result of quantum scattering due to the applied magnetic field [3,4]. The magnitude and sign of MR is highly dependent on the angle between electrical current and magnetization direction (i.e. 1 ) of the ferromagnetic material. The sign of MR changes with 1 , which can be described mathematically as [5];
(1 ) = ⊥ + − ⊥ cos2 1
(1)
where (1 ) is the total resistivity, ⊥ is the resistivity at 1 = 90◦ , is the resistivity at 1 = 0◦ . One drawback that limits the use of magnetic material-based AMR-sensors is that the magnitude of MR saturates above a particular applied magnetic field, i.e. magnetic sensors cannot detect magnetic fields above certain magnetic field, largely depending upon the type of magnetic materials used
∗ Corresponding author at: College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, P. R. China. E-mail address:
[email protected] (F.J. Stadler). http://dx.doi.org/10.1016/j.sna.2016.12.001 0924-4247/© 2016 Elsevier B.V. All rights reserved.
[6]. Unlike ferromagnetic materials, magnetotransport properties of non-magnetic materials have the great advantage over magnetic materials due to absence of a saturation level in MR, even at large magnetic fields [6]. However, no report exists in literature about anisotropic magnetotransport phenomenon in undoped non-magnetic amorphous carbon (a-C) thin films [7]. In this article, we found an anisotropic magnetotransport behavior in undoped non-magnetic a-C thin films for the first time to the best of our knowledge. The sign and magnitude of magnetoresistance vary with the variation of , while does not play any role in AMR phenomenon (i.e. is the angle between applied magnetic field and normal to the plane, while is the angle between applied magnetic field and current). This anisotropic transport can be examined with the help of Brysksin – Klein (B-K) model [8–10]. 2. Experimental details 2.1. Fabrication of a-C thin films The fabrication of a-C thin films on top of 300 nm thick SiO2 was performed using the method reported earlier (Fig. 1) [11–13]. Three gases viz. hydrogen, argon, and ethylene (i.e. carbon donor) were utilized for this purpose. Insulating substrates (i.e. SiO2 ) were heated to 1050 ◦ C under hydrogen and argon atmosphere (i.e. Heating Regime – Fig. 1) at flow rates of 40 and 160 standard cubic
90
R.U.R. Sagar et al. / Sensors and Actuators A 254 (2017) 89–94
Fig. 1. Growth conditions for a-C thin films fabricated via Chemical Vapor Deposition (CVD).
centimeters per minute (sccm), respectively. Ethylene (C2 H4 ) was mixed with hydrogen and argon at a flow rate of 40 sccm (i.e. Fabrication Regime – Fig. 1). The mixture of the three gases was allowed to flow through the chemical vapor deposition-furnace until one achieved the required thickness. The mixture of argon and hydrogen was continuously provided until the furnace cooled down to a room temperature (i.e. Cooling Regime – Fig. 1). The specimens were taken out of the furnace when naturally cooled down.
2.2. Transfer of a-C thin films The as-grown a-C films on SiO2 were dipped into hydrofluoric acid (HF) solution to remove SiO2 by etching, followed by immersing them into acetone for several hours to remove residues, if there is any. These a-C films were transferred on a copper grid for structural characterization and onto insulating substrate for magnetotransport measurements.
3. Results & discussion High-resolution image of a-C thin film was obtained via HRTEM where two atomic spacings i.e. d = 0.21 nm & d = 0.34 nm (measured via Gatan DigitalMicrograph software) corresponding to graphitic grains and graphene nano-sized layers (Fig. 3(a)) are obtained [14]. Selected area diffraction pattern (SAED) of thin film was measured several times over the micron size area of film and found a diffusedtype rings, instead of broad milky band or regular spots, at the center, suggesting the presence of nanocrystalline phase (inset of Fig. 3(a)) [12]. Moreover, two rings correspond to (001) and (002) atomic planes were corroborated from the respective interplanar spacing values. The thickness of a-C thin films, obtained via AFM taping mode, was in the range of 20–30 nm (Fig. 3(b)). Raman signatures confirmed four peaks; D, G, 2D and D + D’ at 1350, 1596, 2700, and 2930 cm−1 , respectively (Fig. 4). The intensity ratio of D and G band as well as G and 2D band gives information in the packing structure of the carbon atoms [15–17]. The defects are responsible for the activation of D band. The ratio between D and G (ID /IG ) can be used to estimate the distance crystallite size [18];
I −1
2.3. Measurement configuration
La = 2.4 × 10−10 × 4 ×
Four rectangular shaped (i.e. area: 1 × 2 mm2 ) gold electrodes were deposited in a line on the top of a-C thin films (Fig. 2(a)). The distance between two electrodes was fixed to ∼2 mm. The current was applied between first (I) and fourth (IV) metal electrodes. The voltage drop was detected across second (II) and third (III) electrodes (Fig. 2(a)). The angle between applied magnetic field (B) & normal to the plane (n) was termed as , while was the angle between current (I) and applied magnetic field (B) (Fig. 2(b)).
where, La (nm) is distance between defects, (nm) is wavelength of laser used in Raman (∼514 nm). The estimated La values for different thin specimens were within ∼15–20 nm (Fig. 4). The intensity ratio (ID /IG ) changed in fractions with the variation of thickness, indicating that the crystallite size changes in fractions with the thickness of the specimen (Fig. 4).
2.4. Characterization details High-resolution transmission electron microscope (HRTEM, JEOL-2010) images and Raman spectroscopy (Renishaw-HR800) measurements were used for structural elucidation. Atomic force microscopy (AFM, Shimadzu SPM-9700) was utilized to determine the thickness of transferred a-C thin films. The magnetotransport properties of a-C thin films were measured by using Physical Property Measurement System (PPMS-9T, Quantum design) in the temperature range from 2 to 300 K.
D
IG
(2)
3.1. Magnetoresistance at fixed angle The magnetotransport properties of a-C thin films were studied at low temperature (i.e. 2–40 K) under applied magnetic fields up to 7 T at fixed = 0◦ and = 90◦ while = 90◦ was fixed through the measurements (i.e. : angle between applied magnetic field (B) & normal to the plane (n), : angle between current (I) and applied magnetic field (B)). MR was calculated by using the following relation [13]; MR (%) =
R − R B 0 R0
× 100%
(3)
where, RB is the resistance under applied magnetic field and R0 is the resistance without applied magnetic field. Negative magnetore-
R.U.R. Sagar et al. / Sensors and Actuators A 254 (2017) 89–94
91
Fig. 2. (a) Configuration of metal electrodes on the top of a-C thin films, (b) Locations of and in present work.
Fig. 3. (a) HRTEM image of a-C thin film (inset: SAED), (b) thickness (∼ 20 nm) of a-C thin films via AFM.
sistance (NMR) was observed in the temperature range of 2–10 K, at = 0◦ (Fig. 5(a)). The MR was positive in the temperature range of 2–7 K, at = 90◦ (i.e. applied magnetic field was perpendicular to the normal to the plane) and switched to negative for T > 7 K (Fig. 5(b)). The magnitudes of MR under different magnetic fields (i.e. 0–7 T) vs. temperature at = 0◦ and = 90◦ are presented in Fig. 5(c) and (d), while = 90◦ . The magnitude of NMR increased with increasing applied magnetic field at = 0◦ (Fig. 5(c)), while magnitude of positive magnetoresistance (PMR) increases with decreasing applied magnetic field at = 90◦ (Fig. 5(d)). The magnitudes of PMR and NMR at 2 K were 1.6 and 2%, respectively, suggesting a change of the magnitudes of PMR and NMR change along similar lines under applied magnetic field. The sign of MR changed from positive to negative at T ∼7 K and at = 90◦ (Fig. 6(a)). The sign switching occurred at a transition temperature of 7 K. Fig. 6(a) clearly shows that the NMR remained negative in the entire temperature range of 2–10 K for = 0◦ , while at = 90◦ , PMR switched from positive to negative with increasing temperature. The sign of MR did not change till room temperature afterwards, as shown in previous report [11]. To further analyze resistance vs. temperature (RT) curve at low temperature range (i.e. 2–10 K) three different cases were analyzed (Fig. 6(b)). In the first case, RT was measured at B = 0 T ( = 0◦ = 90◦ ). In the second case, RT was measured at B = 7 T and = 0◦ . In the third case, RT was measured under B = 7 T and = 90◦ , = 90◦ . It was found that both temperature and direction of magnetic field play an important role in switching the sign of MR. The variations in sample resistance under the applied magnetic field might cause
Fig. 4. Raman signatures of specimens fabricated at different fabrication time.
variation in the sign of MR, increase of the resistance results into PMR and decrease of the resistance results into NMR. 3.2. Magnetoresistance at variable angle The specimen can be rotated along short and long axis rotation in which both and changing continuously (Fig. 7(a)). Firstly, was varied from 0 to 360◦ at fixed = 90◦ as a result of short axis rotation (Fig. 7(b)). Secondly, was varied from 0 to 360◦ at variable from 0 to 90◦ , respectively (Fig. 7(c)).
92
R.U.R. Sagar et al. / Sensors and Actuators A 254 (2017) 89–94
Fig. 5. MR-B curves at; (a) = 0◦ = 90◦ , and (b) = 90◦ = 90◦ . MR vs. temperature curves at; (c) = 0◦ = 90◦ , and (d) = 90◦ = 90◦ .
Fig. 6. (a) MR vs. temperature (2 ∼ 10 K) curves at = 90◦ and = 0◦ while = 90◦ under 7 T, (b) Comparison of RT curves at = 90◦ , and 0◦ when = 90◦ under 7 T and under 0 T.
The change of the resistance in both rotations (i.e. short axis or long axis) remained similar, indicating that in this case does not play any role in angle dependent change in the resistance, which makes these results more interesting. The disorder in the a-C thin films plays an important role for magnetotransport properties. The small and large disorder in amorphous material identified via KF 1 and KF 1, respectively (i.e.KF is Fermi wave vector and is the mean free path) [8]. However, B-K model does not consider level of disorder and allows an
arbitrary orientation of magnetic field for the measurements. Thus, q = KF , where q is the arbitrary disorder factor of the material. According to B-K model [8–10]; 1 =1− 0 42 kF
with
1
1
(A) 2
∞ 0
dt exp cosh (ht)
s˜t (A)
1 2
F t, ,
(4)
(5)
R.U.R. Sagar et al. / Sensors and Actuators A 254 (2017) 89–94
In the B-K model, two anisotropy parameters ˛ =
1
93
D /D⊥
and = ˛ kz /k⊥ can be estimated from the fitting of resis tance 1vs. 1 (R, ) (Fig. 7(b) and (c)) [8]. The ˛ = 1.2 and = 1 c a =0.49 at 2 K, that were close to the already reported 3 literature [8]. The c and a can be obtained from HRTEM image (Fig. 3 (a)) in which diameter of one crystallite was around a ∼5 nm while c ∼0.34 nm. Thus, unique anisotropic MR phenomenon has been evidenced in a-C thin films, which can be useful in magnetic field position sensor application. 4. Conclusions Anisotropic magnetotransport has been detected in a-C thin films for the first time. We observed an unusual sign switching of MR with the variation of = 0–360◦ (i.e. is angle between applied magnetic field and normal to the surface) at low temperature without any role of (i.e. is the angle between aplied magnetic field and current), which suggests the presence of AMR phenomenon in a-C thin films. This phenomenon can be used as AMR sensor for magnetic field position sensing. Moreover, a-C thin films are nonmagnetic, suggesting non-saturated sensor even at large magnetic fields, which is technologically important in space science. Acknowledgements The authors would like to thank the National Science Foundation of China (21574086), Nanshan District Key Lab for Biopolymers and Safety Evaluation (No. KC2014ZDZJ0001A), Shenzhen Sci & Tech research grant (ZDSYS201507141105130), Shenzhen City Science and Technology Plan Project (JCYJ20140509172719311) and R. U. R. Sagar would like to thank the Postdoctoral Science Foundation of China (No. 2016M592531) for financial support. References
Fig. 7. (a) Rotation details of specimens along short and long axis of the specimen, (b) R− curves at fixed = 90 under 7 T, and (c) R− curves at variable under 7 T.
1
F t, = −1
d
1 2g3/2
0
and g=
2
du
√
Erf
2 2 tanh (ht) u − 1 + 1 2 + 1 1 h (A) 2 (A) 2
× ucos + where, s˜ =
2 2 0 ,
√ g − 2 ge−g ,
t−
1 sin sin ( ) 1 − u2 ˛
h=
tan (ht) h
2
(6)
2
2
(LB K )
√
, and A = cos2 +
(7)
1 ˛2
sin2 ,
0
is
the ratio of scattering times that explains the anisotropic transport, according to Einstein relation ,⊥ = e2 NF D,⊥ in which NF is the density of states at the Fermi surface and D,⊥ is the dynamic diffusion coefficient that can be expressed by one renormalization scattering time of d-dimensional lattice,
[1] T. Wang, M. Si, D. Yang, Z. Shi, F. Wang, Z. Yang, et al., Angular dependence of the magnetoresistance effect in a silicon based p-n junction device, Nanoscale 6 (2014) 3978–3983. [2] C. Moron, C. Cabrera, A. Moron, A. Garcia, M. Gonzalez, Magnetic sensors based on amorphous ferromagnetic materials: a review, Sensors (Basel) 15 (2015) 28340–28366. [3] C. Reig, M.D. Cubells-Beltran, D.R. Munoz, Magnetic field sensors based on giant magnetoresistance (GMR) technology: applications in electrical current sensing, Sensors (Basel) 9 (2009) 7919–7942. [4] L.C. Phillips, A. Lombardo, M. Ghidini, W. Yan, S. Kar-Narayan, S.J. Hämäläinen, et al., Tunnelling anisotropic magnetoresistance at la0. 67Sr0. 33MnO3-graphene interfaces, Appl. Phys. Lett. 108 (2016) 112405. [5] J. Velev, R.F. Sabirianov, S.S. Jaswal, E.Y. Tsymbal, Ballistic anisotropic magnetoresistance, Phys. Rev. Lett. 94 (2005). [6] S. Awais Siddique, S. Rizwan Ur Rehman, S. Rajan, L. Zhaochu, Z. Xiaozhong, Angle dependent magnetotransport in transfer-free amorphous carbon thin films, J. Phys. D: Appl. Phys. 49 (2016) 415005. [7] A.J. Fleming, A review of nanometer resolution position sensors: operation and performance, Sensor Actuat. A: Phys. 190 (2013) 106–126. [8] S. Bhattacharyya, D. Churochkin, Polarization dependent asymmetric magneto-resistance features in nanocrystalline diamond films, Appl. Phys. Lett. 105 (2014) 073111. [9] A.B. Gougam, J. Sicart, J.L. Robert, B. Etienne, Electron localization and anisotropic magnetoconductivity in GaAs-AlAs superlattices, Phys. Rev. B 59 (1999) 15308–15311. [10] V.V. Bryksin, P. Kleinert, Anderson localization in anisotropic systems at an arbitrary orientation of the magnetic field, Z Phys. B 101 (1996) 91–96. [11] R.U.R. Sagar, X.Z. Zhang, J.M. Wang, C.Y. Xiong, Negative magnetoresistance in undoped semiconducting amorphous carbon films, J. Appl. Phys. 115 (2014). [12] R.U.R. Sagar, X.Z. Zhang, C.Y. Xiong, Y. Yu, Semiconducting amorphous carbon thin films for transparent conducting electrodes, Carbon 76 (2014) 64–70. [13] R.U.R. Sagar, A.S. Saleemi, X. Zhang, Angular magnetoresistance in semiconducting undoped amorphous carbon thin films, J. Appl. Phys. 117 (2015) 174503. [14] R.U.R. Sagar, F.J. Stadler, M. Namvari, S.T. Navale, Synthesis of scalable and tunable slightly oxidized graphene via chemical vapor deposition, J. Colloid Interface Sci. (2016).
94
R.U.R. Sagar et al. / Sensors and Actuators A 254 (2017) 89–94
[15] R.R. Sagar, X. Zhang, C. Xiong, Growth of graphene on copper and nickel foils via chemical vapour deposition using ethylene, Mater. Res. Innov. 18 (2014) (S4-706-S4-10). [16] R.U.R. Sagar, N. Mahmood, F.J. Stadler, T. Anwar, S.T. Navale, K. Shehzad, et al., High capacity retention anode material for lithium ion battery, Electrochim. Acta 211 (2016) 156–163. [17] K. Shehzad, Y. Xu, C. Gao, X. Duan, Three-dimensional macro-structures of two-dimensional nanomaterials, Chem. Soc. Rev. 45 (2016) 5541–5588. [18] D. Voiry, J. Yang, J. Kupferberg, R. Fullon, C. Lee, H.Y. Jeong, et al., High-quality graphene via microwave reduction of solution-exfoliated graphene oxide, Science 353 (2016) 1413–1416.
Sachin T. Navale received his MSc (2012) and PhD (2015) degrees in Physics from the School of Physical Sciences, Solapur University, Solapur, India. Currently, he is actively involved in the synthesis of metal oxides and conducting polymer composites and nanostructures for gas sensors and energy storage applications.
Biographies
Rizwan Ur Rehman Sagar completed his MSc (2005–2008) degree in Physics from University of Sargodha, Pakistan, MPhil (2008–2010) degree in Physics from COMSATS Institute of Information & Technology, Pakistan, PhD (2010–2015) degree in Materials Science & Engineering, Tsinghua University, Beijing, China. Currently, he is serving as post doctorate fellow in College of Materials Science & Engineering and Optoelectronic Engineering, Shenzhen University, Shenzhen, China. He is actively engaged in the fabrication of low-dimensional carbon-based materials and detected interesting physical phenomena involved therein. Awais Siddique Saleemi holds Master of Science (MS) degree in 2012 from COMSATS Institute of Information and Technology, Islamabad, Pakistan. Recently, he is working as a PhD scholar in School of Materials Science and Engineering, Tsinghua University, Beijing, China.
Khurram Shehzad received his MSc and MPhil degree in Chemistry from University of the Punjab, Lahore, Pakistan, the PhD in Materials Science and Engineering from Beijing University of Chemical Technology, Beijing, China. From 2011–2013, he holds a postdoctoral research fellow at the Center for Nano and Micro Mechanics, Tsinghua University, Beijing, China. Currently, he is a postdoctoral fellow at the College of Information Science and Electronics, Zhejiang University, China. He is the recipient of several awards including International Young Scientist Fellowship from NSF China, Nanchang University Fellowship, Chinese Academy of Sciences (CAS) President Fellowship, and the Cultural Exchange Fellowship. His current research interests include synthesis of hetero-structures and the macro-assemblies of two-dimensional materials for energy, healthcare, and electronics applications.
Rajaram S. Mane is professor and international Professor at School of Physical Sciences, SRTM University, Nanded, India, and at KSU, Saudi Arabia, respectively. He has authored and co-authored more than 200 publications. His research interests include solid and liquid-based DSSCs, supercapacitors, gas sensors, biogenic activities etc.
Florian J. Stadler is a Distinguished Professor at College of Materials Science and Engineering, Shenzhen University, Shenzhen, China. He has authored and co-authored more than 100 publications. His research interests include soft matter physics, rheology, polymer chemistry, DSSCs, and chemical sensors etc.
