Johurul Islam | University of Rajshahi, Bangladesh (original) (raw)
Teaching Documents by Johurul Islam
DC motor, 2019
Objectives: To obtain the speed characteristics of a D.C shunt motor as a function of (i) armatur... more Objectives: To obtain the speed characteristics of a D.C shunt motor as a function of (i) armature voltage and (ii) field current. Apparatus: Theory: Any D.C. motor can be made to have smooth and effective control of speed over a wide range. The shunt motor runs at a speed defined by the expressions. Where N is the speed, V is applied voltage, í µí°¼ í µí± is the armature current, and í µí± í µí± is the armature resistance and Φ is the magnetic flux due to field current í µí°¼ í µí±. Speed control methods of shunt motor:
Papers by Johurul Islam
Australian Journal of Chemistry, 2013
Systematic studies of the thermal expansion, optical, and redox properties of a series of six squ... more Systematic studies of the thermal expansion, optical, and redox properties of a series of six squarate-based frameworks, [MII(C4O4)(H2O)2] (MII = MnII, FeII, CoII, NiII, ZnII, CdII) have revealed that five members of the series exhibit cubic structures in which the squarate ligands are configured in an ‘eclipsed’ phase, while the CdII analogue exhibits a trigonal structure with a ‘staggered’ orientation of the ligands. The ‘eclipsed’ structures are characterised by a positive coefficient of thermal expansion, while the CdII analogue exhibits zero thermal expansion. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and electrochemical measurements indicate that electron delocalisation across the dianionic squarate bridge is absent.
Nickel thin films have been prepared by using electron beam evaporation technique at a pressure o... more Nickel thin films have been prepared by using electron beam evaporation technique at a pressure of 410 mbar on silicon and glass substrates. Some of as-deposited films have been annealed at 573 K for 1.5 hours in open air. Electrical and morphological properties of both as-deposited and annealed films are investigated. The magnetic properties of as-deposited Ni films are studied by VSM at room temperature. The resistivity of Ni films on silicon substrate is higher than resistivity of Ni films found on glass substrate. T.C.R. of Ni films is found to be positive indicating metallic nature of the samples. Coercivity of Ni films increases with the increase of film thickness. The coercivity of 80 nm as-deposited Ni film on glass substrate is 9 Oe. The rms value of surface roughness of 150 nm as-deposited Ni films on glass substrate is 12 nm. It becomes 7 nm after annealing. On the other hand the coercivity of 90 nm and 160 nm as-deposited Ni films on silicon substrate is 50 Oe and 85 Oe...
Current Applied Physics, 2012
The structural, electrical and optical characteristics of porous silicon (PS) due to the impregna... more The structural, electrical and optical characteristics of porous silicon (PS) due to the impregnation of LaF 3 into PS by a novel chemical-bath deposition (CBD) technique have been investigated in this article. Without removing the PS from the anodization chamber the impregnation with LaF 3 has been done by reacting LaCl 3 with HF in the same chamber at room temperature. The impregnation of LaF 3 was confirmed by the SEM on the cross-section of the LaF 3 /PS/Si system and EDX. The modification of PS surface by LaF 3 had direct influence on the electrical and optical properties of PS. Electrical properties of Ag/LaF 3 /PS/p-Si/Ag structures were studied through the currentevoltage (IeV) and capacitanceevoltage (CeV) characteristics. Formation of metaleinsulatoresemiconductor (MIS) diode was evident whose forward current increased with annealing. A diode factor of about 2.4 has been obtained for the annealed heterostructure indicating a high density of trap states. The C À2-V curves of all samples showed negative flat band voltage of around À2 V confirming a large number of fixed positive charges in the LaF 3. The photoluminescence (PL) intensity of the LaF 3-impregnated PS showed aging for the as-deposited samples, but when annealed PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF 3 on porous silicon could enable the porous silicon to be an important material for photonic application.
Cobalt silicide layers have been grown by E-beam evaporation of Co onto Si (100) substrate and su... more Cobalt silicide layers have been grown by E-beam evaporation of Co onto Si (100) substrate and subsequent thermal treatment at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on the silicide layer (sample-1). A thin layer of 5 nm Co have been deposited on GaAs (100) substrate and annealed at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on 5 nm annealed Co buffer layer (sample-2). 100 nm Co films have been grown on glass substrate for comparison. Magnetic properties of Co thin films have been studied by Vibrating sample magnetometer (VSM). Measurements of magnetic properties show that the coercivity is 580 Oe for sample-1. The coercivity of the sample-2 is 240 Oe. The coercivity of 100 nm as-deposited Co films on glass substrate is only 50 Oe and the coercivity increases up to 100 Oe after annealing at 673K for 5 hours. Electrical measurements show that the Sample-1 is metallic in nature but the Sample-2 is semiconducting in nature. In X-ray diffraction measurement, the Co films grown on n-GaAs and Si substrates exhibited a polycrystalline hcp structure. XRD study of Co thin films grown on glass substrate show a microcrystalline hcp structure.
DC motor, 2019
Objectives: To obtain the speed characteristics of a D.C shunt motor as a function of (i) armatur... more Objectives: To obtain the speed characteristics of a D.C shunt motor as a function of (i) armature voltage and (ii) field current. Apparatus: Theory: Any D.C. motor can be made to have smooth and effective control of speed over a wide range. The shunt motor runs at a speed defined by the expressions. Where N is the speed, V is applied voltage, í µí°¼ í µí± is the armature current, and í µí± í µí± is the armature resistance and Φ is the magnetic flux due to field current í µí°¼ í µí±. Speed control methods of shunt motor:
Australian Journal of Chemistry, 2013
Systematic studies of the thermal expansion, optical, and redox properties of a series of six squ... more Systematic studies of the thermal expansion, optical, and redox properties of a series of six squarate-based frameworks, [MII(C4O4)(H2O)2] (MII = MnII, FeII, CoII, NiII, ZnII, CdII) have revealed that five members of the series exhibit cubic structures in which the squarate ligands are configured in an ‘eclipsed’ phase, while the CdII analogue exhibits a trigonal structure with a ‘staggered’ orientation of the ligands. The ‘eclipsed’ structures are characterised by a positive coefficient of thermal expansion, while the CdII analogue exhibits zero thermal expansion. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectra and electrochemical measurements indicate that electron delocalisation across the dianionic squarate bridge is absent.
Nickel thin films have been prepared by using electron beam evaporation technique at a pressure o... more Nickel thin films have been prepared by using electron beam evaporation technique at a pressure of 410 mbar on silicon and glass substrates. Some of as-deposited films have been annealed at 573 K for 1.5 hours in open air. Electrical and morphological properties of both as-deposited and annealed films are investigated. The magnetic properties of as-deposited Ni films are studied by VSM at room temperature. The resistivity of Ni films on silicon substrate is higher than resistivity of Ni films found on glass substrate. T.C.R. of Ni films is found to be positive indicating metallic nature of the samples. Coercivity of Ni films increases with the increase of film thickness. The coercivity of 80 nm as-deposited Ni film on glass substrate is 9 Oe. The rms value of surface roughness of 150 nm as-deposited Ni films on glass substrate is 12 nm. It becomes 7 nm after annealing. On the other hand the coercivity of 90 nm and 160 nm as-deposited Ni films on silicon substrate is 50 Oe and 85 Oe...
Current Applied Physics, 2012
The structural, electrical and optical characteristics of porous silicon (PS) due to the impregna... more The structural, electrical and optical characteristics of porous silicon (PS) due to the impregnation of LaF 3 into PS by a novel chemical-bath deposition (CBD) technique have been investigated in this article. Without removing the PS from the anodization chamber the impregnation with LaF 3 has been done by reacting LaCl 3 with HF in the same chamber at room temperature. The impregnation of LaF 3 was confirmed by the SEM on the cross-section of the LaF 3 /PS/Si system and EDX. The modification of PS surface by LaF 3 had direct influence on the electrical and optical properties of PS. Electrical properties of Ag/LaF 3 /PS/p-Si/Ag structures were studied through the currentevoltage (IeV) and capacitanceevoltage (CeV) characteristics. Formation of metaleinsulatoresemiconductor (MIS) diode was evident whose forward current increased with annealing. A diode factor of about 2.4 has been obtained for the annealed heterostructure indicating a high density of trap states. The C À2-V curves of all samples showed negative flat band voltage of around À2 V confirming a large number of fixed positive charges in the LaF 3. The photoluminescence (PL) intensity of the LaF 3-impregnated PS showed aging for the as-deposited samples, but when annealed PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF 3 on porous silicon could enable the porous silicon to be an important material for photonic application.
Cobalt silicide layers have been grown by E-beam evaporation of Co onto Si (100) substrate and su... more Cobalt silicide layers have been grown by E-beam evaporation of Co onto Si (100) substrate and subsequent thermal treatment at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on the silicide layer (sample-1). A thin layer of 5 nm Co have been deposited on GaAs (100) substrate and annealed at 673K for 5 hours. A fresh layer of 100 nm Co is deposited on 5 nm annealed Co buffer layer (sample-2). 100 nm Co films have been grown on glass substrate for comparison. Magnetic properties of Co thin films have been studied by Vibrating sample magnetometer (VSM). Measurements of magnetic properties show that the coercivity is 580 Oe for sample-1. The coercivity of the sample-2 is 240 Oe. The coercivity of 100 nm as-deposited Co films on glass substrate is only 50 Oe and the coercivity increases up to 100 Oe after annealing at 673K for 5 hours. Electrical measurements show that the Sample-1 is metallic in nature but the Sample-2 is semiconducting in nature. In X-ray diffraction measurement, the Co films grown on n-GaAs and Si substrates exhibited a polycrystalline hcp structure. XRD study of Co thin films grown on glass substrate show a microcrystalline hcp structure.