MOCVD Growth of Thermoelectric BiSbTe3 Films on Surface-Treated Sapphire Substrates

권성도,Jin-Sang Kim 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.4

Metal organic chemical vapor deposition(MOCVD) has been used to grow BiSbTe3 films on (0001) sapphire substrates. Prior to growth, some of the substrates were subjected to chemical treatment. The impact of this process on the surface morphology and on the crystalline quality of the resulting BiSbTe3 films is investigated. We demonstrated that the surface treatment of a sapphire substrates with a potassium-containing solution has a marked effect on the surface morphology of the resulting layers. In particular, BiSbTe3 layers grown on sapphire substrates treated with a potassium-containing solution exhibited a high nucleation density during the initial growth stage, leading to a smooth mirror-like morphology. In contrast, the growth of films on sapphire substrates without treatment was found to result in randomsized island-like surface defects Untreated substrates led to multi-oriented films while films on treated substrates were close to epitaxially oriented. We believe that the formation of nanoscale defects on the substrate surface during chemical treatment may account for the observed improved surface morphology. Metal organic chemical vapor deposition(MOCVD) has been used to grow BiSbTe3 films on (0001) sapphire substrates. Prior to growth, some of the substrates were subjected to chemical treatment. The impact of this process on the surface morphology and on the crystalline quality of the resulting BiSbTe3 films is investigated. We demonstrated that the surface treatment of a sapphire substrates with a potassium-containing solution has a marked effect on the surface morphology of the resulting layers. In particular, BiSbTe3 layers grown on sapphire substrates treated with a potassium-containing solution exhibited a high nucleation density during the initial growth stage, leading to a smooth mirror-like morphology. In contrast, the growth of films on sapphire substrates without treatment was found to result in randomsized island-like surface defects Untreated substrates led to multi-oriented films while films on treated substrates were close to epitaxially oriented. We believe that the formation of nanoscale defects on the substrate surface during chemical treatment may account for the observed improved surface morphology.

Evaporation of sessile water droplet on heated surface with needle-shaped nanostructures by pre-boiling oxidation process

Kang, Dong Gu,Nam, Gang Min,In, Wang Kee,Lee, Chi Young Elsevier 2019 Experimental thermal and fluid science Vol.101 No.-

<P><B>Abstract</B></P> <P>The effects of surface morphology by oxidation and surface temperature on the behavior of an evaporating water droplet on heated surface were investigated. As the test specimen, the pre-boiled (oxidized) aluminum surface was used with non-boiled (non-treated) surface. The surface temperature conditions were 40, 57, and 73 °C, respectively. By the pre-boiling process, a lot of unique needle-shaped nanostructures were spontaneously formed on the surface, which affected significantly the behaviors of an evaporating water droplet. The variations of the important parameters (i.e., contact diameter, contact angle, height, volume, surface area, and evaporation mass flux) were measured and discussed in detail. In addition, the evaporation time, evaporation rate, and heat transfer rate were evaluated and examined. Based on this work, it was found that potentially, using the pre-boiling process which is easier, simpler, and more cost-effective as well as applicable to the large-area, the droplet evaporation on the heated surface can be controlled and the heat transfer performance also can be enhanced through the change in surface morphology.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of surface morphology and temperature on behavior of an evaporating water droplet were studied. </LI> <LI> Pre-boiled aluminum test specimen was tested with non-boiled one. </LI> <LI> Unique needle-shaped nanostructures were formed spontaneously by pre-boiling process. </LI> <LI> Needle-shaped nanostructures affected behaviors of an evaporating water droplet. </LI> <LI> Pre-boiled surface with needle-shaped nanostructures improved heat transfer performance. </LI> </UL> </P>

불규칙 패턴 에칭에 의한 표면 형상 제어와 광학적 특성

김성수,이정우,전법주 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.12

Randomly patterned and wet chemical etching processes were used to treat anti-glare of display cover glasses. The surface and optical properties of grain size and surface morphology controlled by randomly patterned etching andwet chemical solution etching were investigated. The surface morphology and roughness of the etched samples wereexamined using a spectrophotometer and a portable surface roughness (Ra) measuring instrument, respectively. The glosscaused by reflection from the glass surface was measured at 60° using a gloss meter. The surface of the sample etchedby the doctor-blade process was more uniform than that obtained from a screen pattern etching process at gel stateetching process of the first step. The surface roughness obtained from the randomly patterned etching process dependedgreatly on the mesh size, which in turn affected the grain size and pattern formation. The surface morphology and glossobtained by the etching process in the second step depended primarily on the mesh size of the gel state etching processof the first step. In our experimental range, the gloss increased on decreasing the grain size at a lower mesh size forthe first step process and for longer reaction times for the second step process. 디스플레이 글라스의 anti glare 표면처리를 위해 습식화학에칭방식을 적용한 불규칙 스크린 패턴에칭과 2차 용액표면에칭을 수행하고 grain size제어와 불규칙패턴에칭에 따른 표면 morphology의 변화인 표면특성과 광학적 특성을 비교하였다. 닥터블레이드와 스크린패턴에칭을 적용한 겔상태의 1차 에칭에 의한 표면조도는 닥터블레이드방식의 경우 표면조도가 낮게 나타났으며 유리기판의 종류를 달리할 경우 기판의 조성에 의해 표면 에칭반응 메커니즘과 생산과정에 기판의 결정도가 변하여 에칭정도는 에칭방법과 유리기판 종류에 의존성이 큼을 알 수 있었다. 1차 불규칙패턴에칭에 의한 표면조도의 변화는 부식액에 의한 패턴형성과 크기에 영향을 주는 mesh size에 크게 의존하였다. 2차 용액에칭은 에칭반응시간과 농도변화에 영향을 받았으나 1차 불규칙 패턴에칭된 조직의 크기에 영향을 주는 mesh size에 의존성이 크게 나타났다. 영상의 선명도에 영향을 주는 표면 광택도는 1차 에칭에서 mesh size가 작을수록, 2차 에칭에서 반응시간이 증가할수록 표면에 형성된 grain size가 감소하여 높게 나타났다.

Study on surface shape control of pure Ti fabricated by electron beam melting using electrolytic polishing

Jung, Jae-Hyun,Park, Hyung-Ki,Lee, Byoung Soo,Choi, Jaeho,Seo, Bosung,Kim, Hyo Kyu,Kim, Gun Hee,Kim, Hyung Giun Elsevier 2017 Surface & Coatings Technology Vol.324 No.-

<P><B>Abstract</B></P> <P>Titanium parts in special industries such as vacuum, catalyst and medical application require a variety of surface properties with a unique structure for high efficiency. In this study, the unique surface of commercially pure titanium (CP Ti) parts fabricated using Electron Beam Melting (EBM) in the process of additive manufacturing is post-treated by the electrolytic polishing process under conditions ranging from 10 to 30V and 10–600s in order to study the surface characteristics. The possibility of controlling microstructural surface shape according to electrolytic polishing process conditions is presented from the increase of surface area through the formation of micro-dimples on protruding residual powder on the surface to the flattening of entire surface.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Microstructural study on the surface of additive manufactured pure Ti part after electrolytic polishing. </LI> <LI> It is possible to maximize surface area by forming micro dimpling at the initial stage of electrolytic polishing. </LI> <LI> Identification of surface flattening mechanism of additive manufactured Ti part using electron beam melting. </LI> </UL> </P>

Shapes and morphologies of inkjet-printed nanosilver dots on glass substrates

Lee, Dong Jun,Oh, Je Hoon John Wiley Sons, Ltd. 2010 Surface and interface analysis Vol.42 No.6

<P>We investigated the effects of surface wettability, substrate temperature, and overprinting on the shapes and morphologies of dried and sintered inkjet-printed dots of nanosilver suspensions. The surface wettability was modified by two different plasma surface treatments: C<SUB>4</SUB>F<SUB>8</SUB> plasma treatment for hydrophobic surface and O<SUB>2</SUB> plasma treatment for hydrophilic surface. The substrate temperature was varied from 25 to 85 °C with an interval of 20 °C. In order to change the dot thickness, dots were overprinted up to three times after complete drying of the ones previously printed. Printed dots were sintered for 1 h at 210 °C. The shapes and morphologies of dried dots including both single and overprinted dots were strongly influenced by the surface wettability of the substrate. The cross-sectional profile was more convex on the hydrophobic surface at lower substrate temperature, but stack-like morphologies of overprinted dots were obtained on both surfaces at higher substrate temperature due to the fast evaporation of solvent and coffee ring effect. Dots on hydrophilic surfaces experienced more shrinkage after sintering, and the shrinkage ratio of sintered dots tended to decrease with an increase in the number of overprints. The microstructure of sintered dots showed that nanoparticle clusters were more closely packed on hydrophobic surfaces. Copyright © 2010 John Wiley & Sons, Ltd.</P>

Influence of multiple ultrasonic impact treatments on surface roughness and wear performance of SUS301 steel

Li, Liang,Kim, Miru,Lee, Seungjun,Bae, Munki,Lee, Deugwoo Elsevier 2016 Surface & coatings technology Vol.307 No.1

<P><B>Abstract</B></P> <P>This paper described an easy mechanical surface enhancement technique based on ultrasonic vibration, namely ultrasonic impact treatment (UIT). The effects of multiple ultrasonic impact treatments (UITs) on the surface properties of SUS301 steel were investigated using an optical microscope, a step profiler, a non-contact optical profiler, a micro hardness testing machine, X-ray diffraction (XRD), and a pin-on-disk tribotester. The results showed the effects of surface smoothing and hardening on the wear performance. An increase in the number of UITs resulted in a lower roughness and higher hardness. After three UITs, the surface roughness decreased from 0.694 to 0.112μm, and the hardness increased from 257.32 to 428.38HV. The evolution of surface morphology was also analyzed in detail over multiple UITs. Moreover, the volume fraction of plastic deformation-induced martensite increased with the number of UITs of the surface. The samples treated three passes showed better wear resistance than untreated samples under dry sliding conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An easy mechanical surface enhancement technique based on ultrasonic vibration was described. </LI> <LI> The roughness and hardness of SUS301 steel were respectively reduced and increased by this technique. </LI> <LI> The evolution of surface morphology was analyzed over multiple passes. </LI> <LI> This technique increased the wear resistance of SUS301 steel. </LI> </UL> </P>

Simplistic surface active agents mediated morphological tweaking of CdS thin films for photoelectrochemical solar cell performance

S.A. Vanalakar,M.P. Suryawanshi,S.S. Mali,A.V. Moholkar,J.Y.Kim,P.S. Patil,김진혁 한국물리학회 2014 Current Applied Physics Vol.14 No.12

This study reports on the formation of cadmium sulfide (CdS) nanostructures with controlled morphology synthesized via a simple chemical route in surface active agent environment. The effect of organic surface active agents (surfactants) as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG) and cetyltrimethylammonium bromide (CTAB) on structural, morphological, optical and photoelectrochemical properties of CdS thin films have been studied. Our results reveal that the organic surfactants play key roles in tweaking the surface morphology. A compact spongy ball like morphology was observed for the CdS samples grown without organic surfactants. The cauliflower's with nanopetals from the CTAB, whereas crowded star fish like morphology is observed in PEG-mediated growth. Water hyacinth like morphology is tweaked using SDS. Considering the importance of these nanostructures, the growth mechanism has been discussed in details. Additionally, the samples are photoelectrochemically (PEC) active and having a compact surface with a nanoporous structure twig helps in improved photoelectrochemical performance compared to that of CdS deposits from surfactant free solution. This is a simplistic way to tune the morphology using surfactants, which can be applied to other energy conversion applications.

Efficacy of UV-TiO₂ photocatalysis technology for inactivation of <i>Escherichia coli</i> K12 on the surface of blueberries and a model agar matrix and the influence of surface characteristics

Lee, Mijin,Shahbaz, Hafiz Muhammad,Kim, Jeong Un,Lee, Hyunah,Lee, Dong-Un,Park, Jiyong Elsevier 2018 FOOD MICROBIOLOGY Vol.76 No.-

<P><B>Abstract</B></P> <P>Surface disinfection of fresh blueberries is an important food safety challenge due to the delicate texture and short shelf life of these small fruits. A newly designed water-assisted photocatalytic reactor was developed for disinfection of fruits with a delicate texture and complex surface characteristics. Efficacy of UV-TiO<SUB>2</SUB> photocatalysis was evaluated in comparison with UV alone for inactivation of <I>Escherichia coli</I> K12 (as a surrogate for <I>Escherichia coli</I> O157:H7) inoculated onto the surface of the blueberry skin, calyx, and an experimentally prepared agar matrix that was used as a model matrix. Influence of surface characteristics such as surface hydrophobicity and surface free energy on bacterial adhesion were also investigated. The initial bacterial population on all surfaces was approximately 7.0 log CFU/g. UV-TiO<SUB>2</SUB> photocatalysis (4.5 mW/cm<SUP>2</SUP>) for 30 s achieved comparatively higher bacterial reductions of 5.3 log and 4.6 log CFU/g on blueberry skin and agar matrix surfaces, respectively, than 4.5 log and 3.4 log CFU/g reductions for UV alone (6.0 mW/cm<SUP>2</SUP>). Total phenolic and total anthocyanin contents of fruits were significantly increased after both UV-TiO<SUB>2</SUB> and UV treatments, compared with water washed control fruits. UV-TiO<SUB>2</SUB> photocatalysis technology is a non-chemical and residue-free method with reduced water usage for surface disinfection of fresh blueberries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photocatalysis method was developed for disinfection of fruits with a delicate texture. </LI> <LI> UV-TiO<SUB>2</SUB> photocatalysis was effective against <I>E. coli</I> K12 on blueberry fruit surface. </LI> <LI> Surface properties of blueberry skin and calyx influenced the disinfection efficiency. </LI> <LI> Photocatalysis is a non-chemical and residue-free method with reduced water usage. </LI> </UL> </P>

Simplistic surface active agents mediated morphological tweaking of CdS thin films for photoelectrochemical solar cell performance

Vanalakar, S.A.,Suryawanshi, M.P.,Mali, S.S.,Moholkar, A.V.,Kim, J.Y.,Patil, P.S.,Kim, J.H. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.12

This study reports on the formation of cadmium sulfide (CdS) nanostructures with controlled morphology synthesized via a simple chemical route in surface active agent environment. The effect of organic surface active agents (surfactants) as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG) and cetyltrimethylammonium bromide (CTAB) on structural, morphological, optical and photoelectrochemical properties of CdS thin films have been studied. Our results reveal that the organic surfactants play key roles in tweaking the surface morphology. A compact spongy ball like morphology was observed for the CdS samples grown without organic surfactants. The cauliflower's with nanopetals from the CTAB, whereas crowded star fish like morphology is observed in PEG-mediated growth. Water hyacinth like morphology is tweaked using SDS. Considering the importance of these nanostructures, the growth mechanism has been discussed in details. Additionally, the samples are photoelectrochemically (PEC) active and having a compact surface with a nanoporous structure twig helps in improved photoelectrochemical performance compared to that of CdS deposits from surfactant free solution. This is a simplistic way to tune the morphology using surfactants, which can be applied to other energy conversion applications.

Effect of annealing temperature on surface morphology and ultralow ferromagnetic resonance linewidth of yttrium iron garnet thin film grown by rf sputtering

Cao Van, Phuoc,Surabhi, Srivathsava,Dongquoc, Viet,Kuchi, Rambabu,Yoon, Soon-Gil,Jeong, Jong-Ryul Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.435 No.-

<P><B>Abstract</B></P> <P>We report high-quality yttrium–iron–garnet (YIG; Y<SUB>3</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB>) ultrathin films grown on {111} gadolinium–gallium–garnet (GGG; Gd<SUB>3</SUB>Ga<SUB>5</SUB>O<SUB>12</SUB>) substrates using RF sputtering deposition on an off-stoichiometric target and optimized thermal treatments. We measured a narrow peak-to-peak ferromagnetic resonance linewidth (<I>∆H</I>) whose minimum value was 1.9 Oe at 9.43 GHz for a 60-nm-thick YIG film. This value is comparable to the most recently published value for a YIG thin film grown by pulsed laser deposition. The temperature dependence of the <I>∆H</I> was investigated systematically, the optimal annealing condition for our growing condition was 875 °C. Structural analysis revealed that surface roughness and crystallinity played an important role in the observed <I>∆H</I> broadening. Furthermore, the thickness dependence of the <I>∆H</I>, which indicated that 60 nm thickness was optimal to obtain narrow <I>∆H</I> YIG films, was also investigated. The thickness dependence of <I>∆H</I> was understood on the basis of contributions of surface-associated magnon scattering and magnetic inhomogeneities to the <I>∆H</I> broadening. Other techniques such as transmission electron microscopy, scanning electron microscopy, and X-ray diffraction were used to study the crystalline structure of the YIG films. The high quality of the films in terms of their magnetic properties was expressed through a very low coercivity and high saturation magnetization measured using a vibration sample magnetometer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A high-quality YIG thin film with a FMR linewidth of 1.9Oe at 9.43GHz was grown by rf sputtering using an off-stoichiometric target. </LI> <LI> Precise control of surface morphology is crucial for improving the FMR characteristics of YIG films. </LI> <LI> The FMR linewidth investigation revealed the optimal annealing temperature for surface morphology and crystallinity development. </LI> <LI> Surface-associated magnon scattering and magnetic inhomogeneities contributed to the thickness dependence of the FMR linewidth. </LI> </UL> </P>