1.College of Mobile Telecommunications, Chongqing University of Posts and Telecom, Chongqing 401520, China 2.School of Physics and Electronics, Qian Nan Normal College for Nationalities, Duyun 558000, China
Fund Project:Project supported by the Science and Technology Department of Guizhou Province, China (Grant No. [2020]1Y208), the Guizhou Provincial Department of Education Project, China (Grant No. KY[2020]208), the Project of Qiannan Normal College for Nationalities, China (Grant Nos. 2018XJG0530, QNSY2018002), and the Research Project of Teaching Reform in College of Mobile Telecommunications, Chongqing University of Posts and Telecom, China (Grant No. YTJG2019050)
Received Date:20 November 2020
Accepted Date:10 February 2021
Available Online:25 June 2021
Published Online:05 July 2021
Abstract:With the continuous development of nanotechnology, people have higher and higher requirements for the performances of nanomaterials. In the past few decades, researchers have used various methods to prepare nanomaterials with different dopants, and studied their optical and electrical properties. Nanomaterials with ferromagnetic properties have a wide range of applications, and there have been many reports about the ferromagnetic properties of doped magnetic elements. However, there have been few reports about Cr-doped ZnS and CdS. In order to obtain Cr-doped ZnS and CdS nanosheets with room temperature ferromagnetism, in this paper, using ethanolamine (EA) and ethylenediamine (EN) as mixed solvents, ZnS and CdS semiconductor nanostructures doped with different amounts of chromium are successfully prepared in S, ZnO and CdO sources by simple solvent thermal method. The X-ray diffraction (XRD) measurements show that the ZnS and CdS nanostructure have a wurtzite structure. Scanning electron microscopy (SEM) images show the morphologies of ZnS and CdS with different chromium content. When the content of Cr is 4.31 at% or 7.25 at%, the thickness of Cr-doped ZnS nanosheets is about 210–290 nm, and the morphology of undoped ZnS is composed of sub-morphologies of relatively thick nanosheets. The morphologies of CdS doped with different amounts of Cr are composed of sub-morphologies of snowflake like nanosheets with thickness of about 120–190 nm. Energy dispersive spectrometer (EDS) is used to observe the product composed of Cr, Zn, Cd, and S. The EDS measurement and calculation of the Cr content in Cr-doped ZnS nanosheets are 4.31 at% and 7.25 at% respectively, and those of the Cr content in Cr-doped CdS nanosheets are 1.84 at% and 2.12 at%. The vibration sample magnetometer(VSM) measurements show that ZnS doped with chromium exhibits ferromagnetism at room temperature, while the undoped ZnS exhibits diamagnetism at room temperature. The values of saturation magnetization Ms of Cr-doped ZnS nanosheets with Cr = 4.31 at% and 7.25 at% are 2.314 and 5.683 (10–3 emu/g), and the coercivity values of Hc are 54.721 and 88.441 Oe, respectively. The ferromagnetism of pure CdS is weak, while that of Cr-doped CdS is enhanced at room temperature. The saturation magnetization Ms values of Cr-doped CdS nanosheets with Cr = 0, 1.84 at% and 2.12 at% are 0.854, 2.351 and 7.525(10–3 emu/g), respectively, and the coercivity values of Hc are 74.631, 114.372 and 64.349 Oe, respectively. The values of saturation magnetization of ZnS and CdS increases with the Cr doping increasing. The ferromagnetism of Cr-doped ZnS at room temperature is confirmed by the experimental result, which is consistent with the ferromagnetism of Cr-doped ZnS calculated by the first principle. The origin of ferromagnetism of Cr-doped CdS is related to the doping of Cr in CdS lattice. Keywords:ZnS/ CdS/ Cr/ ferromagnetism
表1制备样品(A—F)的反应条件(所有实验在200 ℃下反应24 h) Table1.Reaction conditions of the prepared products (All experments are carried out 200 ℃ for 24 h).
22.2.性能测试 -->
2.2.性能测试
样品的晶体结构和化学成分用X-射线衍射(XRD)(Mac Science M18XHF22-SRA, Cu Kα靶, λ = 0.154 nm)表征; 样品的形貌由扫描电子显微镜(SEM)(Philips XL-30)表征; 通过电子能量散射谱(EDS)测量样品的化学组成, 通过振动样品磁强计(VSM, Lake 7400)表征样品的磁性能. -->
3.1.物相分析
通过XRD方法分析晶体结构和化学组成, 图1是Cr掺杂ZnS纳米片的XRD图谱, 三条曲线分别对应样本A (Cr原子百分比为4.31%, a); 样本B (Cr原子百分比为7.25%, b); 样本E (Cr原子百分比为0.00%, e). 图2是Cr掺杂CdS纳米片的XRD图谱, 三条曲线分别对应样本C (Cr原子百分比为1.84%, c); 样本D (Cr原子百分比为2.12%, d); 样本F (Cr原子百分比为0.00%, f). Cr掺杂ZnS的衍射峰位2θ是27.91°, 32.72°, 47.43°, 56.98°, 58.76°, 68.87°和76.90°, 与 (111), (200), (220), (311), (222), (400) 和(331) 六方纤锌矿ZnS晶面相对应, 这与[PDF 65-16917(ICCD, 2002), a = 0.3820 nm, c = 0.6257 nm]相一致. Cr掺杂CdS的衍射峰位2θ是24.70°, 26.32°, 28.55°, 37.14°, 43.66°, 48.28°, 52.23°和54.60°, 与(100), (002), (101), (102), (110), (103), (112) 和(201) 六方纤锌矿CdS的晶面相对应, 这与[PDF 41-1049 (ICCD, 2002), a = 0.4150 nm, c = 0.6750 nm]相一致. 图1和图2中未发现Cr2S3或任何其他第二相, 这表明Cr3+在一定程度上掺入到ZnS和CdS晶格中. 如图1所示, 在仪器分辨范围内, Cr掺杂ZnS的(111)峰位置相对于纯ZnS的(111)峰位置稍微向低角度移动了0.2°, 这证实了Cr3+掺入ZnS晶格中, 而Cr掺杂CdS的(100)峰值位置相对于未掺杂的CdS的(100)稍微向高角度移0.3°, 如图2所示. Cr掺杂ZnS的(111)特征峰峰强度和峰宽均增大, 表明纳米结构在生长. 众所周知, 晶格发生变化, 是由于半径为Cr3+ (RCr = 0.0890 nm)的离子, 有效取代半径为Zn2+或Cd2+(RZn = 0.0740 nm, RCd = 0.0970 nm)的离子效应产生的. 根据布拉格衍射公式($ 2 d{\rm{sin}}\theta =k\lambda $)可以证实有少量Cr掺入ZnS和CdS晶格中. 图 1 Cr掺杂ZnS纳米片的XRD图谱, 三条曲线分别对应样本A (Cr原子百分比为4.31%, a), 样本B (Cr原子百分比为7.25%, b)和样本E (Cr原子百分比为0.00%, e) Figure1. Some of the powder XRD patterns of Cr-doped ZnS nanosheets. Three curves correspond to sample A (atomic percentages of Cr is4.31%, a), sample B (atomic percentages of Cr is 7.25%, b), sample E (atomic percentages of Cr is 0%, e), respectively.
图 2 Cr掺杂CdS纳米片的XRD图谱, 三条曲线分别对应样本C (Cr原子百分比为1.84%, c), 样本D (Cr原子百分比为2.12%, d)和样本F (Cr原子百分比为0.00%, f) Figure2. Some of the powder XRD patterns of the Cr-doped CdS nanosheets. Three curves correspond to sample C (atomic percentages of Cr is 1.84%, c), sample D (atomic percentages of Cr is 2.12%, d) and sample F (atomic percentages of Cr is 0.00%, f), respectively.
图 8 Cr掺杂ZnS和CdS的饱和磁化强度(Ms)和矫顽力(Hc)的直方图 Figure8. Histogram of saturation magnetization (Ms) and coercivity (Hc) of Cr-doped ZnS and CdS nanosheets.
Cr content/%
Morphologies
Size/nm
Magnetic properties
Coercivity/Oe
Saturation magnetization/ (10–3 emu·g–1)
ZnS
0
Hexagonal flake
310—390
Diamagnetism
—
—
4.31
flower-like sheet
210—290
Ferromagnetism
54.721
2.314
7.25
Flower-like sheet
200—250
Ferromagnetism
88.441
5.683
CdS
0
Snowflake
110—160
Weak ferromagnetism
74.631
0.854
1.84
Snowflake
100—170
strong ferromagnetism
114.372
2.351
2.12
Snowflake
100—200
Strong ferromagnetism
64.349
7.525
表2SEM, EDS和VSM计算Cr掺杂的ZnS和CdS纳米片的Cr含量、形貌、尺寸、磁性、矫顽力和饱和磁化强度图 Table2.Measured chromium content, morphology, size, magnetic properties, coercivity and saturation magnetization of Cr doped ZnS and CdS nanosheets using SEM, EDS and VSM.