Electronic states at 4,4´-N,N´-dicarbazol-biphenyl (CBP)emetal (Mg, Ag, and Au) interfaces: A joint experimental and theoretical study

Bhatt Mahesh Datt,Akahasi Baba,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.3

We used ultraviolet photoelectron spectroscopy (UPS) to study the electronic structure at the interface between organic semiconductor (CBP) and metals (Mg, Ag, and Au). Controlling the injection of charges at the interface requires a better understanding of the basic mechanism of the formation of interface states. In this context, photoelectron spectroscopy and density functional theory calculations were used to investigate the interaction of CBP with metal (111) surfaces. The position of HOMO relative to the Fermi level and the magnitude of the interface dipole were measured for each interface by UPS measurement. For CBP on Au, interface state (continuous state) was observed near the Fermi level by density functional theory calculations. However, no interface state was observed for CBP on Mg and Ag. It is suggested that the interface state plays an important role in charge transport at the interface. It was analyzed by density functional theory calculations that the interface state is formed due to interaction of CBP with metals and the position of the Fermi level varies strongly with the metal work function. The mechanism of formation of interface states and electrical properties were discussed.

Characterizations of Interface-state Density between Top Silicon and Buried Oxide on Nano-SOI Substrate by using Pseudo-MOSFETs

Cho, Won-Ju The Institute of Electronics and Information Engin 2005 Journal of semiconductor technology and science Vol.5 No.2

The interface-states between the top silicon layer and buried oxide layer of nano-SOI substrate were developed. Also, the effects of thermal treatment processes on the interface-state distributions were investigated for the first time by using pseudo-MOSFETs. We found that the interface-state distributions were strongly influenced by the thermal treatment processes. The interface-states were generated by the rapid thermal annealing (RTA) process. Increasing the RTA temperature over $800^{\circ}C$, the interface-state density considerably increased. Especially, a peak of interface-states distribution that contributes a hump phenomenon of subthreshold curve in the inversion mode operation of pseudo-MOSFETs was observed at the conduction band side of the energy gap, hut it was not observed in the accumulation mode operation. On the other hand, the increased interface-state density by the RTA process was effectively reduced by the relatively low temperature annealing process in a conventional thermal annealing (CTA) process.

Development of Unified Interface for Multi-Vendors’ CNC Based on Machine State Model

윤주성(Joo Sung Yoon),박일하(Il Ha Park),손진호(Jin Ho Sohn),김헌정(Hoen Jeong Kim) Korean Society for Precision Engineering 2018 한국정밀공학회지 Vol.35 No.2

The Human Machine Interface (HMI) is dependent on the Computerized Numerical Control (CNC). As a result, the HMI software is developed according to the interface method of each CNC in duplicate. Even though the same function of HMI software module is developed using the same data item, it must be implemented separately in different development environments. This is because each CNC has a different address system and provides unique data interface method. In this study, we proposed a unified interface system that can standardize and integrate data interface method to support the development of HMI software module applicable to machine tools adopting multi-vendors’ CNCs. To clearly define this work, we developed new parameters, methods, and address system based on the machine state model, composed of data elements of machine tool structure, process, and status, provides the same interface by capsulizing existing CNC interfaces. The proposed interface system is designed to provide an API (Application Programming Interface) in the form of a library. The implementation architecture is designed and details of the operating logic within the detailed components and interfaces are elaborated. The implementation and test results are illustrated to verify an application example of the proposed unified interface system.

Chemical effects at interfaces of Fe/MgO/Fe magnetic tunnel junction

Singh, Jitendra Pal,Kaur, Baljeet,Gautam, Sanjeev,Lim, Weon Cheol,Asokan, Kandasami,Chae, Keun Hwa Elsevier 2016 Superlattices and microstructures Vol.100 No.-

<P><B>Abstract</B></P> <P>Present review focuses the investigation carried out in order to understand the interface structure of magnetic tunnel junction (MTJ) by considering Fe/MgO/Fe as prototype structure. Tunneling magnetoresistence (TMR) of MTJ is affected by the spin polarization of ferromagnetic layers. This phenomena is governed by spin dependent tunneling in perfect MTJ. In MTJ with disordered interface, resonance states through interface play an important role. Some important phenomena like perpendicular magnetic anisotropy, spin transfer torques, and electrical switching are also affected by the interface structure. Apart from disorder and lattice mismatch, interface structure is governed by several factors like oxidation, defects, vacancies as well as hybridization among Fe(3<I>d</I>)-O(2<I>p</I>) states. These effects are categorized as ‘chemical effects’. Due to these factors, contribution from interface resonance states dominates which reduces TMR and related properties. A discussion for determination of these effects are highlighted using several techniques like X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Simulation results reveal modification of TMR via chemical effects occuring at interface in these MTJ. Thus tailoring of chemical effects in controlled manner is discussed to understand the interface assisted phenomena in these structures. Modification of the chemical effects is induced by irradiation of swift heavy ions, thereby, providing an opportunity to correlate chemical effects and TMR of MTJ.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Interface structure affects spin dependent tunneling. </LI> <LI> Chemical effects are dominant at interfaces. </LI> <LI> These effects can be tailored using swift heavy ion irradiation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of doping on metal doped semiconductor

Bhatt Mahesh Datt,Shugo Suzuki,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.2

The effect of doping on position of interface states for metal doped bathocuproine (BCP) was studied with density functional theory (DFT). The doping of Ca atoms with BCP induces the formation of interface states with shift in their relative positions from Fermi level and approximately no shift in HOMO position of BCP molecule. The shift in the position of interface states towards higher binding energy was believed to be due to the presence of doping excess electrons from Ca at the interface. The analysis of modification in intensity of LUMO or EF or interface states, suggests the formation of multiply charged anions in heavily doped film. It clearly gives the direct evidence for the origin of the doping interface states in organic molecules. The effects of Ca doping on electrical properties were discussed.

A Study of the Properties of the Cu/SiOC(-H)/p-Si(100)and Cu/TaN/SiOC(-H)/p-Si(100) Interface

김창영,R. Navamathavan,Heang Seuk Lee,유영훈,우종관,최치규 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.5

Metal-insulator-semiconductor (MIS) structures based on low-dielectric-constant SiOC(-H) films with Cu (electrode) and TaN (barrier) layers are compared to study the effect of the electrode materials on the properties of the dielectric/semiconductor interface. The detailed experimental results for the C-V, G/! -V, and I-V characteristics were analyzed out in order to extract the electrical parameters, such as the interface state density, the fixed charge density, the flat band voltage, and the breakdown strength of the low- dielectric SiOC(-H) film with the stack of Cu/SiOC(-H)/p- Si(100)/Al and Cu/TaN/SiOC(-H)/p-Si(100)/Al structures. The capacitance and the conductance values were to three times higher for the 200 ˚C annealed Cu/SiOC(-H)/p-Si(100)/Al structure than they were for the as-deposited one whereas no significant change was observed with the Cu/TaN/SiOC(-H)/p-Si(100)/Al structure. The surface state density in the Cu/TaN/SiOC(-H)/p-Si(100)/Al structure was considerably lower than that in the Cu/SiOC(-H)/p-Si(100)/Al structure. Metal-insulator-semiconductor (MIS) structures based on low-dielectric-constant SiOC(-H) films with Cu (electrode) and TaN (barrier) layers are compared to study the effect of the electrode materials on the properties of the dielectric/semiconductor interface. The detailed experimental results for the C-V, G/! -V, and I-V characteristics were analyzed out in order to extract the electrical parameters, such as the interface state density, the fixed charge density, the flat band voltage, and the breakdown strength of the low- dielectric SiOC(-H) film with the stack of Cu/SiOC(-H)/p- Si(100)/Al and Cu/TaN/SiOC(-H)/p-Si(100)/Al structures. The capacitance and the conductance values were to three times higher for the 200 ˚C annealed Cu/SiOC(-H)/p-Si(100)/Al structure than they were for the as-deposited one whereas no significant change was observed with the Cu/TaN/SiOC(-H)/p-Si(100)/Al structure. The surface state density in the Cu/TaN/SiOC(-H)/p-Si(100)/Al structure was considerably lower than that in the Cu/SiOC(-H)/p-Si(100)/Al structure.

Interface characteristics of spin-on-dielectric SiO_x-buffered passivation layers for AlGaN/GaN high electron mobility transistors

Ko, Pil-Seok,Park, Kyoung-Seok,Yoon, Yeo-Chang,Sheen, Mi-Hyang,Kim, Sam-Dong Elsevier 2015 THIN SOLID FILMS - Vol.589 No.-

<P><B>Abstract</B></P> <P>To reveal the cause for significant enhancement of dc current performance of the AlGaN/GaN high electron mobility transistors (HEMTs) with the spin-on-dielectric (SOD) SiO<SUB>x</SUB>-buffered passivation structure compared to the conventional Si<SUB>3</SUB>N<SUB>4</SUB> passivation deposited by plasma-enhanced vapor deposition (PECVD), we characterized the passivation interfaces using the cross-sectional transmission electron microscopy, cathodoluminescence, capacitance–voltage (C–V) characterizations, and Hall-effect measurements. The interface state density of PECVD Si<SUB>3</SUB>N<SUB>4</SUB> passivation was in the range of 10<SUP>12</SUP>–10<SUP>13</SUP> cm<SUP>−2</SUP> eV<SUP>−1</SUP>, which is one-order higher than that of the SOD (10<SUP>11</SUP>–10<SUP>12</SUP> cm<SUP>−2</SUP> eV<SUP>−1</SUP>) as measured by C–V measurements from the metal–insulator–semiconductor capacitors. Higher density of effective oxide charge density (especially dominant contribution of ionic mobile charge) was also derived from the PECVD Si<SUB>3</SUB>N<SUB>4</SUB> passivation. A well-resolved reduction of the electron Hall mobility of the Si<SUB>3</SUB>N<SUB>4</SUB> passivation compared to that of the perhydropolysilazane SOD passivation, which can be due to the higher-density interface states and trap charges, can answer the relative dc current collapse of our HEMT devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spin-on-dielectric (SOD)-buffered passivation for AlGaN/GaN HEMTs </LI> <LI> Characterize the charge density and interface states using the C–V measurements </LI> <LI> SOD-buffered passivation minimizes surface states at the interface. </LI> <LI> DC performance of SOD-buffered structure is due to the interface characteristics. </LI> </UL> </P>

Development of Strain-softening Model for Geosynthetic-involved Interface Using Disturbed State Concept

Woo, Seo-Min,Park, Jun-Boum,Park, Inn-Joon 한국지반공학회 2003 지반 : 한국지반공학회지 Vol.19 No.5

본 연구에서는 DSC를 이용한 구성방정식을 이용하여 토목섬유 사이의 접촉전단 응력과 변위와의 관계를 모델링하였다. DSC 모델은 두 개의 기준 상태, 즉 상대적으로 손상되지 않은 RI 상태와 완전히 파괴된 FA 상태와 한가지의 교란 함수로 구성된다. 본 모델은 통합된 모델로서, RI 상태를 탄성-완전 소성 모델, 계층적 단일 항복곡면 (HiSS) 모델 등 다양한 모델을 이용하여 모사할 수 있다. 한편 본 모델은 탄성과 소성 변위를 동시에 고려할 수 있다는 장점을 가지고 있다. 4가지의 대형 직접전단 시험으로부터 측정된 자료와 측정자료로부터 도출된 모델 변수를 이용하여 재해석한 결과를 서로 비교하여, 둘 사이의 비교 결과가 상당히 일치함을 발견하였으며, 특히 표면이 매끄러운 지오멤브레인의 접촉면에서는 매우 상관관계를 보였다. 비록 표면이 거친 지오멤브레인이 포함된 접촉면에서는 예측 최대 전단강도가 실험결과와 약간의 차이를 보이기는 하였지만, 전체적으로 본 모델이 최대 전단응력이 나타나는 변위점과 대변형에서의 전단강도를 상당히 정확히 예측하였으며, 이를 통해 본 모델이 변형율 연화 현상을 보이는 접촉면 전단거동의 모델링에 유용함을 확인하였다. In this study, a constitutive model called the disturbed state concept (DSC) was modified to be applied to the interface shear stress-displacement relationship between geosynthetics. The DSC model is comprised of two reference states, namely the relative intact (RI) and the fully adjusted (FA) state, and one function, namely the disturbance function. This model is a unified approach and can allow for various models as an RI state such as elastic-perfectly plastic model, hierarchical model, and so on. In addition, by using this model, the elastic and plastic displacements can be considered simultaneously. Comparisons between the measured data and predicted results through the parameters determined from four sets of large direct shear tests showed good agreements with each other, especially for the smooth geomembrane-involved interface. Although there are slight differences at peak shear strength for textured geomembrane-involved interface, this model can still be useful to predict the position of displacement at peak strength and the large displacement (or residual) shear strength.

Dynamic Shear Behavior of Concrete-soil Interface based on Cyclic Simple Shear Test

곽창원,박인준,박준범 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.3

Complicated and difficult responses between different materials are widely observed at many sites and situations in the civil engineering field. The behavior of soil is nonlinear and shows diverse features according to the material interaction with each other. Soil and other material comprise an area which transfers load and called as the interface. Though there are various kinds of interface, the characteristics of concrete-soil interface which represent the behaviors at the perimeter of soil-tunnel has been investigated based on the experimental approach in this study. The Multi-Purpose Interface Apparatus (M-PIA) has been modified and cyclic simple shear tests for concrete-soil interface were performed to consider dynamic load such as the earthquake. The Disturbed State Concept (DSC) was employed to analyze the test results and understand physical meaning of the interface shear behaviors of soil-tunnel. Furthermore, the disturbance function was also evaluated to describe dynamic shear behaviors of concrete-soil interface quantitatively.

Observation of Interfacial States by Using Photocurrent Difference Spectroscopy for ZnSe/GaAs Heterostructures

송정훈,심은덕,장수경,백경선,이규석 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.4

Photocurrent-difference spectroscopy (PDS), performed by measuring the difference between photocurrent spectra with and without additional laser illuminations, was demonstrated. The change in the photocurrent spectra, ΔPC, caused by the illuminations had a probe-energy dependency in the heterostructures. The ΔPC spectra varied with the energy of the additional illuminating lights. Compared to the conventional photocurrent spectra, the measured spectra were proven to be very sensitive to the interfacial electronic states in ZnSe/GaAs (001). Unusual features related to the interface states were observed and the possible origins of those peaks are discussed. The mechanism for the change in PC spectra is explained in terms of existence of trap states where the Fermi level is pinned at the interface. The in uence of trap states on the photocurrent spectra was examined with above and below ZnSe-bandgap excitations.