Kamsul Abraha’s research while affiliated with Universitas Gadjah Mada and other places

Linear response theory in quantum theory with its linear response function and its quantization process has been formulated. The relation between the linear response function with its generalized susceptibility, its symmetry properties, and its analyticity has been studied. These properties produce the dispersion relation or Kramers-Kronig relation. The explicit form of the quantum response function and generalized susceptibility also been reviewed. Applications of linear response functions have been described for three elementary processes. The process discussed is the magnetic field disturbance in the magnetic system that generates magnetic susceptibility, and the electric field disturbance in the electrical system that generates electrical conductivity tensor and the ferromagnet Heisenberg that generates its generalized susceptibility.

The electronics structure of monochalcogenide materials buckled square lattice is investigated by computation based on Density Functional Theory (DFT). The investigation shows that there is spin splitting on xy-plane at Γ point and M point as a Rashba effect. Perturbation theory k.p and symmetry group C 2v used to calculate the originates of the spin splitting. The results show that there are strong Rashba splitting for materials with center atom Pb (with Rashba parameter 5~ eVÅ). Spin orientation displayed by spin-texture and show that there is time reversal symmetry between upper band and lower band. This condition explains that monochalcogenide materials buckled square lattice as potential candidates for spintronics devices. Keywords: electronics structure, monochalcogenides, square lattice, Rashba effect, spin texture.

Nano-sized chitosan has been prepared by ball mill (High Energy Milling) with 1500 rpm to determine itsgrainz size and functional group. A nanopowder sample was prepared in the various milling time of the precusor. The milling time were 60, 120, 180, 240, 300 and 360 minutes. The Scanning Electron Microscopy (SEM)images indicated that the microstructures and grain size of as-prepared chitosan changed by increasing the milling time. The average of grain size is 15,1 nm. The Fourier Transform Infra-Red (FTIR) spectra showedthat the -OH bond shifted after milling process. The new C=O roups formedduring the milling process, because of the ordered microstructures in the nano-sized chitosan granules weredestroyed after ball millingThe surface area of the nano-sized chitosan was high, the particles tend to agglomerate since the ionic electrostatic could not prevent to form the agglomeration. The ball milling treatment was an effective method to reduce the grain size of chitosan, and functional groups will not automatically change during the milling process.

We have previously reported the surface plasmon resonance (SPR)-based biosensor ability for quantitatively differentiating bovine and porcine gelatin has been done by us before. However, it has some inaccuracies. By improving the method of detection, the results of this study shows that the difference between bovine and porcine gelatin was more distinguishable. The sensor response models acquired were nonlinear as in the previous study. However, they show different characteristics. The sensitivities of the sensor obtained are higher than those of the previous ones, i.e., 3.04 o and 4.29 o for bovine and porcine gelatin concentration change of 0.1%, respectively. And the sensor’s LOD and LOQ towards both gelatin concentrations were 0.22% and 0.74% (w/w), respectively.

A theoretical analysis and computational study of biomaterial sample detection with surface plasmon resonance (SPR) phenomenon spectroscopy are presented in this work with the objective of achieving more sensitive detection. In this paper, a Fe3O4@Au core-shell, a nanocomposite spherical nanoparticle consisting of a spherical Fe3O4 core covered by an Au shell, was used as an active material for biomaterial sample detection, such as for blood plasma, haemoglobin (Hb) cytoplasm and lecithin, with a wavelength of 632.8 nm. We present the detection amplification technique through an attenuated total reflection (ATR) spectrum in the Kretschmann configuration. The system consists of a four-layer material, i.e., prism/Ag/Fe3O4@Au + biomaterial sample/air. The effective permittivity determination of the core-shell nanoparticle (Fe3O4@Au) and the composite (Fe3O4@Au + biomaterial sample) was done by applying the effective medium theory approximation, and the calculation of the reflectivity was carried out by varying the size of the core-shell, volume fraction and biomaterial sample. In this model, the refractive index (RI) of the BK7 prism is 1.51; the RI of the Ag thin film is 0.13455 + 3.98651i with a thickness of 40 nm; and the RI of the composite is varied depending on the size of the nanoparticle core-shell and the RI of the biomaterial samples. Our results show that by varying the sizes of the core-shell, volume fraction and the RIs of the biomaterial samples, the dip in the reflectivity (ATR) spectrum is shifted to the larger angle of incident light, and the addition of a core-shell in the conventional SPR-based biosensor leads to the enhancement of the SPR biosensor sensitivity. For a core-shell with a radius a = 2.5 nm, the sensitivity increased by 10% for blood plasma detection, 47.72% for Hb cytoplasm detection and by 22.08% for lecithin detection compared to the sensitivity of the conventional SPR-based biosensor without core-shell addition.

A theoretical analysis of haemoglobin (Hb) concentration detection is presented in this work with the objective of achieving more sensitive detection and monitoring low concentrations. Surface-enhanced SPR spectroscopy on silver nanoparticles was employed for recording Hb concentrations less than 10 g/L. In this paper, Fe3O4@Au core-shell, nanocomposite spherical nanoparticle consisting of a spherical Fe3O4 core covered by Au shell, was used as an active material for biomolecules detection in the Surface Plasmon Resonance (SPR)-based biosensor in the wavelength 632.8 nm. We present the simulation of detection amplification technique through Attenuated Total Reflection (ATR) spectrum in the Kretschmann configuration. The system consists of a four-layer material i.e prism/Ag/Fe3O4@Au+Hb/air. Dielectric function determination of the core-shell nanoparticle (Fe3O4@Au) and the composite (Fe3O4@Au+Hb) was done by applying the Effective Medium Theory approximation and the calculation of the reflectivity is carried out by varying the size of core-shell (r0). In this simulation, the refractive index of the BK7 prism is 1.51; the refractive index of Ag thin film is 0.13455+3.98651i with the thickness of 40 nm, and the refractive index of the composite is varied depending on the size of nanoparticle core-shell. Our results show that by varying the radius of the core and the shell thickness, the dip of the reflectivity (ATR) spectrum is shifted to the larger angle of incident light and the addition of core-shell in the conventional SPR-based biosensor leads to enhancement of the SPR biosensor sensitivity, for the core-shell radius 10 nm, the sensitivity increased by 1.35% for F = 0.1, and by 4.89% for F =0.8 compared to the sensitivity of the conventional SPR-based biosensor without core-shell addition.

A theoretical analysis of haemoglobin (Hb) concentration detection is presented in this work with the objective of achieving more sensitive detection and monitoring low concentrations. Surface-enhanced SPR spectroscopy on silver nanoparticles was employed for recording Hb concentrations less than 10 g/L. In this paper, Fe3O4@Au core-shell, nanocomposite spherical nanoparticle consisting of a spherical Fe3O4 core covered by Au shell, was used as an active material for biomolecules detection in the Surface Plasmon Resonance (SPR)-based biosensor in the wavelength 632.8 nm. We present the simulation of detection amplification technique through Attenuated Total Reflection (ATR) spectrum in the Kretschmann configuration. The system consists of a four-layer material i.e., prism/Ag/Fe3O4@Au+Hb/air. Dielectric function determination of the core-shell nanoparticle (Fe3O4@Au) and the composite (Fe3O4@Au+Hb) was done by applying the Effective Medium Theory approximation and the calculation of the reflectivity is carried out by varying the size of core-shell (r0). In this simulation, the refractive index of the BK7 prism is 1.51; the refractive index of Ag thin film is 0.13455 + 3.98651i with the thickness of 40 nm, and the refractive index of the composite is varied depending on the size of nanoparticle core-shell. Our results show that by varying the radius of the core and the shell thickness, the dip of the reflectivity (ATR) spectrum is shifted to the larger angle of incident light and the addition of core-shell in the conventional SPR-based biosensor leads to enhancement of the SPR biosensor sensitivity, for the core-shell radius 10 nm, the sensitivity increased by 1.35% for F = 0.1, and by 4.89% for F = 0.8 compared to the sensitivity of the conventional SPR-based biosensor without core-shell addition.

The recent epitaxial growth of 1T-phase of PtSe2 monolayer (ML) has opened possibility for its novel applications, in particular for spintronic devices. However, in contrast to 2H-phase of transition-metal dichalcogenides (TMDs), the absence of the spin splitting in the PtSe2 ML may limit the functionality of spintronics. Through fully-relativistic density-functional theory calculations, we show that the large spin splitting can be induced in the PtSe2 ML by introducing a substitutional halogen impurity. Depending on the radius of the halogen dopants, we observe an enhancement of the spin splitting in the localized impurity states (LIS), which is due to the increased contribution of the p-d orbitals coupling. Importantly, we identify very large Rashba splitting in the LIS near Fermi level around the Gamma point characterized by hexagonal warping of the Fermi surface. We further clarify the properties of the Rashba splitting in the LIS by using a simplified Hamiltonian model taking into account the effect of higher order correction of wave vector k. Therefore, this work paves a possible way to induce the significant Rashba splitting in the two-dimensional TMDs, which provide useful information for the potential applications in the spintronic devices operating at room temperature.

Pergeseran sudut surface plasmon resonance (SPR) pada konfigurasi Kretschmann-perak termodifikasi oleh nanopartikel cobalt ferrite (CoFe2O4) telah dikaji secara eksperimen di bawah pengaruh medan magnet. Tiga sampel nanopartikel CoFe2O4 dengan ukuran partikel yang berbeda, yaitu 1,68 nm untuk sampel A; 1,95 nm untuk sampel B; dan 5,87 untuk sampel C, disintesis dengan metode kopresipitasi. Pendeposisian tiga sampel menggeser sudut SPR referensi (prisma/Ag) dengan nilai yang berbeda-beda, yaitu sebesar 0,10°; 0,10°; dan 0,30°, dengan ketidakpastian masing-masing sebesar ±0,05° untuk sampel A, B, dan C secara berturut-turut. Setelah dikenai medan magnet luar,sudut SPR bergeser lagi sejauh 0,30° untuk sampel A dan B, dan 0,5° untuk sampel C, dengan ketidakpastian masing-masing sebesar ±0,05°. Selain itu, perbedaan dua arah medan magnet terkonfirmasi bahwa pergeseran sudut SPR memiliki nilai yang berbeda, yaitu 0,3°±0,05° dan 0,6°±0,05°. Respon nanopartikel CoFe2O4 pada pergeseran sudut SPR memberikan potensi sebagai smart materials pada sistem SPR

Telah dilakukan kajian berkaitan dengan pengaruh nanopartikel Fe3O4 pada deteksi biosensor berbasis surface plasmon resonance (SPR). Penelitian ini bertujuan untuk melihat penyebab munculnya dip baru atau pergeseran dip ke arah kanan pada kurva ATR (AttenuatedTotalReflection) setelah adanya penambahan nanopartikel magnetik Fe3O4.Sifat magnetik nanopartikel berupa permeabilitas magnet disubstitusikan pada kurva ATR dan sudut SPR terbentuk pada sudut 51,8º; 47,3º; 46,0º dan 45,6º untuk ketebalan perak 10 nm, 20 nm, 30 nm dan 40 nm berturut-turut dengan ketebalan nanopartikel 10 nm.Untuk melihat pengaruh permeabilitas magnet, diplot kurva ATR tanpa permeabilitas magnet. Hasilnya menunjukkan bahwa sudut SPR terbentuk pada sudut yang sama. Sehingga kemunculan dip baru pada panjang gelombang sinar laser 632,8 nm bukan dikarenakan sifat magnetnya. Sifat magnet ini akan muncul pada rentang gelombang mikro. Dengan pendekatan Teori Medium Efektif (TME) Landauer dan Bruggeman untuk sistem empat lapisan prisma/perak/komposit (nanopartikel+udara)/udara, diperoleh kurva relasi dispersi surface plasmon pada angka gelombang ; ;; dan untuk variasi fraksi volume 0,1; 0,2; 0,3; 0,4 dan 0,5 berturut-turut mengalami kopling dengan gelombang evanescent. Ini menunjukkan bahwa pergeseran dip muncul dengan pendekatan teori medium efektif Landauer dan Bruggeman. Kata Kunci : Surface Plasmon Resonance (SPR), nanopartikel magnetik Fe3O4,Evanescent, , TME Landauer dan Bruggeman.