• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2761-2764
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• 2011

A new Ruddlesden-Popper phase $NdSr_2MnCrO_7$ has been prepared by the standard ceramic method. The powder X-ray diffraction studies suggest that the phase crystallizes with tetragonal unit cell in the space group I4/mmm. The electrical transport properties show that the phase is an electrical insulator and the electrical conduction in the phase occurs by a 3D variable range hopping mechanism. The magnetic studies suggest that the ferromagnetic interactions are dominant.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.2
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• pp.105-111
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• 1999

This paper presents experimental results on the electrical properties of hydrogenated amorphous carbon films(a-C:H) prepared by PECVD. DC conductance of a-C:H was measured as a function of temperatures in the range of 100 to 423K. We studied two a-C:H films: one was well explained by the Mott's Variable Range Hopping(VRH) rule, but the other sample did not follow it. However, the conduction data of second sample were well fitted to Shimakawa's Multi-Phonon Hopping(MPH) model according to which conductivity is proportional to $T^M$ with m=15-17. but, in our samples, m was 10-12. Also a-C:H showed several bias effects like relaxation of conductance, bias-dependent conductance and the change of conductance slope in 1n(${\sigma}{\sqrt{T}}$) vs. $T^{1/4}$ plot. In this study we interpret these data by bias-dependent detrapping model.

• Journal of Korean Ophthalmic Optics Society
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• v.2 no.1
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• pp.103-110
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• 1997

This work presents experimental results on the electrical properties of hydrogenated amorphous carbon films(a-C : H) prepared by PECVD. Conductance of a-C: H was measured as a function of temperatures in the range of 100 to 423K. We studied two a -C: H films: one was well explanied by the Mott's variable range hopping(VRH) rule. But the other sample did not follow it. The conduction data of second sample were well fitted to Shimakawa's multi-phonon hopping(MPH) model according to which conductivity is proportional to Tm with m= 15~17. But, in our samples, m was 10~12.

• Current Applied Physics
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• v.18 no.12
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• pp.1492-1495
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• 2018

This paper studies the influence of temperature on electrical resistivity in ${\alpha}-InAs$ thin films between 30 K-2K based on the analysis of Mott VRH model and ES VRH model. The effect of the interactions between electrons at lower temperature must be considered, therefore, ES VRH conduction will dominate mechanism, and the crossover from Mott to ES VRH conduction is observed about 7 K. Based on available experiment data and VRH conduction model, the parameters of VRH conduction are determined. And the calculated values of $T_C$ are consistent with the experimental results. In addition, $R_M/{\xi}$, ${\Delta}_M/kT$, $R_{ES}/{\xi}$ and ${\Delta}_{ES}/kT$ are satisfied with the validity of Mott and ES models. Furthermore, the temperature dependence of resistivity at low temperature obeys a universal scaling law, which well describes the overall temperature range of VRH conduction. However, the values of $T^{\prime}_M$ from the universal function are two order of magnitudes lower than $T_M$ deduced from fitting experiment.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.53-54
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• 2000

Measurements of the direct current resistivity, on multiwalled carbon nanotubes(MWNT) for field electron emitter source that had been screen printed in a thick film form were made as a function of temperature T in the range of 1.7K-390K. In this measuring temperature range, the electrical resistivity for the MWNT show that the main contribution to the conductivity comes form carries that hop directly between localized states executing variable range hopping processes. This thick-film form system for large area display showed a high bright light emission as well as very low turn-on field as like an individual MWNT system at room temperature. Furthermore, the electron emission characteristics followed well typical Fowler-Nordheim conduction under the vacuum.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.1-6
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• 1998

The influence of the order-disorder structural transition on the magnetic and mageto-optical, and transport properties of Fe-Al and Co-Al alloy films has been investigated. The disordered states in the alloy films were prepared by vapor quenching deposition on glass substrates cooled by liquid nitrogen. The experimental study of the magento-optical properties of the ordered and disordered Fe-Al and Co-Al alloy films has been carried out in 1.05-5.0 eV energy range at room temperature. The transport properties have been measured in 2-300K temperature range with and without magnetic field of 0.5T. The influence of the order-disorder structural transition on the magnetic and magneto-optical properties was discussed by using the effective medium approximation and the structural defect approach. That on the temperature dependence of the resistivity was analyzed in a framework of the partial localization of the electronic states and the variable range hopping conductivity.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1709-1711
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• 2004

3,4-ethylenedioxythiophene(EDOT)을 ferric-toluenesulfonate(FTS)로 doping하여 합성하였다. 이때 다양한 유기용매를 함께 첨가하여 합성하였고, 온도에 따른 각각의 DC 전도도를 측정하였다. FTS로 dofing된 poly(3,4-ethylenedioxythiophene) (PEDOT)는 3-D variable range hopping model을 잘 따르며, alcohol류의 용매와 함께 합성한 경우는 상온의 DC 전도도가 2 S/cm로 0.4 S/cm의 reference 보다 전기전도를 증가시키는 반면, ketone류는 약 $10^{-11}$ S/cm로 전기전도를 감소시키는 경향을 보였다. 전도도의 증감과 doping level의 관계를 규명하기 위하여 X-ray 분석을 하였다.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.966-969
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• 2003

Thin film capacitors with Al-Polymer-Al sandwich structure were fabricated. The bottom and top aluminium (Al) electrodes were deposited by vacuum evaporation and copper phthalocyanine (CuPc), polyaniline-emeraldine base (Pani-EB) and cobalt phthalocyanine/polyaniline - emeraldine base (CoPc /Pani-EB) blend films (which can be used as buffer hole injection layer in OLEDs) were deposited by spin coating technique. X-ray diffractograms indicated amorphous nature of the polymer films whose thicknesses were measured by capacitance and Rutherford Backscattering Spectrometry (RBS) methods. AC conduction studies revealed that the conduction mechanism responsible in these films is variable range hopping of polarons. From D.C conduction studies, it is observed that, the nature of conduction is ohmic in the lower fields and at higher fields the dominating D.C conduction is of Poole-Frenkel type.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.595-599
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• 2004

We investigated the structural, electrical and magnetic properties of Mn-doped $CuAlO_2$ delafossite ceramics ($CuAl_{1-x}Mn_{x}O_2,\;0\le\;x\;\le0.05$), synthesized by solid-state reaction method in an air atmosphere at a sintering temperature of $1150^{\circ}C$. The solubility limit of Mn ions in delafossite $CuAlO_2$ was found to be as low as about 3 $mol\%$. Positive Hall coefficient and the temperature dependence of conductivity established that non-doped $CuAlO_2$ ceramic is a variable-range hopping p-type semiconductor. It was found that the Mn-doping in $CuAlO_2$ rapidly reduced the hole concentration and conductivity, indicating compensation of free holes. The analysis of the magnetization data provided an evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Mn ions in $CuAl_{1-x}Mn_{x}O$ alloy, leading to an almost paramagnetic behavior in this alloy.

• Journal of the Korean Chemical Society
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• v.55 no.4
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• pp.697-702
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• 2011

The new layered perovskite manganites $La_{0.5}Sr_{1.5}Mn_{0.5}Cr_{0.5-x}Fe_xO_4$ (x=0.15, 0.3) have been prepared by standard ceramic method. The powder X-ray diffraction studies show that the phases crystallize with tetragonal unit cell in the space group I4/mmm. The electrical transport properties suggest that the phases show insulating behaviour and the electrical conduction in the phases occurs by a 3D variable range hopping mechanism. The magnetic properties suggest that both the phases are antiferromagnetic.