Nanoscale mapping of noise-source-controlled hopping and tunneling conduction in domains of reduced graphene oxide

Shekhar, Shashank,Lee, Hyungwoo,Cho, Duckhyung,Yang, Myungjae,Lee, Minju,Hong, Seunghun Elsevier 2019 Carbon Vol.148 No.-

<P><B>Abstract</B></P> <P>We report a nanoscale mapping of noise-source-controlled transport characteristics in the domains of reduced graphene oxide by utilizing noise-source imaging strategies. In this method, current and noise images were measured simultaneously using a scanning noise microscopy and analyzed to map sheet−resistances (<I>R</I> <SUB>□</SUB>) and noise−source densities (<I>n</I> <SUB>eff</SUB>). The maps showed the formation of conducting and insulating domains, where the insulating domains exhibited up to three-four orders of higher <I>R</I> <SUB>□</SUB> and <I>n</I> <SUB>eff</SUB> than those of conducting domains. Interestingly, the sheet−conductance (<I>Σ</I> <SUB>□</SUB>) and <I>n</I> <SUB>eff</SUB> followed rather opposite power−law behaviors like <I>Σ</I> <SUB>□</SUB>∝ <I>n</I> <SUB>eff</SUB> <SUP>−0.5</SUP> and <I>Σ</I> <SUB>□</SUB> ∝ <I>n</I> <SUB>eff</SUB> <SUP>0.5</SUP> in <I>conducting</I> and <I>insulating</I> domains, respectively, which could be attributed to the difference in mesoscopic charge transport mechanisms controlled by <I>n</I> <SUB>eff</SUB> in domains. Notably, high biases resulted in the increased conductance (Δ<I>Σ</I> <SUB>□</SUB>) and decreased noise−source density (Δ<I>n</I> <SUB>eff</SUB>) following a relationship like Δ<I>Σ</I> <SUB>□</SUB> ∝−Δ<I>n</I> <SUB>eff</SUB> <SUP>0.5</SUP> for both conducting and insulting domains, which could be explained by the passivation of noise−sources at high biases. Furthermore, Δ<I>Σ</I> <SUB>□</SUB> <I>versus</I> Δ<I>n</I> <SUB>eff</SUB> plot on the annealing also followed a power−law dependence (Δ<I>Σ</I> <SUB>□</SUB> ∝−Δ<I>n</I> <SUB>eff</SUB> <SUP>0.5</SUP>) in conducting domains, which could be attributed to carrier generation on the annealing. Our results about mesoscopic charge transports could be significant advancements in fundamental researches and applications.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Mapping nanoscale effects of localized noise-source activities on photoconductive charge transports in polymer-blend films

Shekhar, Shashank,Cho, Duckhyung,Cho, Dong-Guk,Yang, Myungjae,Hong, Seunghun IOP 2018 Nanotechnology Vol.29 No.20

<P>We develolped a method to directly image the nanoscale effects of localized noise-source activities on photoconducting charge transports in domain structures of phase-separated polymer-blend films of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) and Poly(9,9-di<I>-n</I>-octylfluorene-<I>alt</I>-benzothiadiazole). For the imaging, current and noise maps of the polymer-blend were recorded using a conducting nanoprobe in contact with the surface, enabling the conductivity (<I>σ</I>) and noise-source density (<I>N</I> <SUB>T</SUB>) mappings under an external stimulus. The blend-films exhibited the phase-separation between the constituent polymers at domains level. Within a domain, high <I>σ</I> (low <I>N</I> <SUB>T</SUB>) and low <I>σ</I> (high <I>N</I> <SUB>T</SUB>) regions were observed, which could be associated with the ordered and disordered regions of a domain. In the <I>N</I> <SUB>T</SUB> maps, we observed that noise-sources strongly affected the conduction mechanism, resulting in a scaling behavior of <I>σ</I>?∝?<img ALIGN='MIDDLE' ALT='${{N}_{{\rm{T}}}}^{-0.5}$' SRC='http://ej.iop.org/images/0957-4484/29/20/205204/nanoaab2ddieqn1.gif'/> in both ordered and disordered regions. When a blend film was under an influence of an external stimulus such as a high bias or an illumination, an increase in the <I>σ</I> was observed, but that also resulted in increases in the <I>N</I> <SUB>T</SUB> as a trade-off. Interestingly, the Δ<I>σ </I>versus Δ<I>N</I> <SUB>T</SUB> plot exhibited an unusual scaling behavior of Δ<I>σ</I>?∝?<img ALIGN='MIDDLE' ALT='${\rm{\Delta }}{{N}_{{\rm{T}}}}^{0.5},$' SRC='http://ej.iop.org/images/0957-4484/29/20/205204/nanoaab2ddieqn2.gif'/> which is attributed to the de-trapping of carriers from deep traps by the external stimuli. In addition, we found that an external stimulus increased the conductivity at the interfaces without significantly increasing their <I>N</I> <SUB>T</SUB>, which can be the origin of the superior performances of polymer-blend based devices. These results provide valuable insight about the effects of noise-sources on nanoscale optoelectronic properties in polymer-blend films, which can be an important guideline for improving devices based on polymer-blend.</P>

Cervical Cancer Screening: Knowledge, Attitude and Practices among Nursing Staff in a Tertiary Level Teaching Institution of Rural India

Shekhar, Shashank,Sharma, Chanderdeep,Thakur, Sita,Raina, Nidhi Asian Pacific Journal of Cancer Prevention 2013 Asian Pacific journal of cancer prevention Vol.14 No.6

Background: Assessment of the nursing staff knowledge, attitude and practices about cervical cancer screening in a tertiary care teaching institute of rural India. Materials and Methods: A cross sectional, descriptive, interview-based survey was conducted with a pretested questionnaire among 262 staff nurses of a tertiary care teaching and research institute. Results: In this study 77% respondents knew that Pap smear is used for detection of cervical cancer, but less than half knew that Pap smear can detect even precancerous lesions of cervix. Only 23.4% knew human papilloma virus infection as a risk factor. Only 26.7% of the respondents were judged as having adequate knowledge based on scores allotted for questions evaluating knowledge about cervical cancer and screening. Only 17 (7%) of the staff nurses had themselves been screened by Pap smear, while 85% had never taken a Pap smear of a patient. Adequate knowledge of cervical cancer and screening, higher parity and age >30 years were significantly associated with self screening for cervical cancer. Most nurese held a view that Pap test is a doctor procedure, and nearly 90% of nurses had never referred a patient for Pap testing. Conclusions: The majority of nursing staff in rural India may have inadequate knowledge about cervical cancer screening, and their attitude and practices towards cervical cancer screening could not be termed positive.

Nanoscale Mapping of Molecular Vibrational Modes via Vibrational Noise Spectroscopy

Cho, Duckhyung,Shekhar, Shashank,Lee, Hyungwoo,Hong, Seunghun American Chemical Society 2018 NANO LETTERS Vol.18 No.2

<P>We have developed a 'vibrational noise spectroscopy (VNS)' method to identify and map vibrational modes of molecular wires on a solid substrate. In the method, electrical-noises generated in molecules on a conducting substrate were measured using a conducting atomic force microscopy (AFM) with a nanoresolution. We found that the bias voltage applied to the conducting AFM probe can stimulate specific vibrational modes of measured molecules, resulting in enhanced electrical noises. Thus, by analyzing noise-voltage spectra, we could identify various vibrational modes of the molecular wires on the substrates. Further, we could image the distribution of vibrational modes on molecule patterns on the substrates. In addition, we found that VNS imaging data could be further analyzed to quantitatively estimate the density of a specific vibrational mode in the layers of different molecular species. The VNS method allows one to measure molecular vibrational modes under ambient conditions with a nanoresolution, and thus it can be a powerful tool for nanoscale electronics and materials researches in general.</P>

Pre-COVID and COVID experience of objective structured clinical examination as a learning tool for post-graduate residents in Obstetrics & Gynecology-a quality improvement study

Charu Sharma,Pratibha Singh,Shashank Shekhar,Abhishek Bhardwaj,Manisha Jhirwal,Navdeep Kaur Ghuman,Meenakshi Gothwal,Garima Yadav,Priyanka Kathuria,Vibha Mishra 대한산부인과학회 2023 Obstetrics & Gynecology Science Vol.66 No.4

Objective Due to its comprehensive, reliable, and valid format, the objective structured clinical examination (OSCE) is the gold standard for assessing the clinical competency of medical students. In the present study, we evaluated the importance of the OSCE as a learning tool for postgraduate (PG) residents assessing their junior undergraduate students. We further aimed to analyze quality improvement during the pre-coronavirus disease (COVID) and COVID periods. Methods This quality-improvement interventional study was conducted at the Department of Obstetrics and Gynecology. The PG residents were trained to conduct the OSCE. A formal feedback form was distributed to 22 participants, and their responses were analyzed using a five-point Likert scale. Fishbone analysis was performed, and the ‘plan-do-study-act’ (PDSA) cycle was implemented to improve the OSCE. Results Most of the residents (95%) believed that this examination system was extremely fair and covered a wide range of clinical skills and knowledge. Further, 4.5% believed it was more labor- and resource intensive and time-consuming. Eighteen (81.8%) residents stated that they had learned all three domains: communication skills, time management skills, and a stepwise approach to clinical scenarios. The PDSA cycle was run eight times, resulting in a dramatic improvement (from 30% to 70%) in the knowledge and clinical skills of PGs and the standard of OSCE. Conclusion The OSCE can be used as a learning tool for young assessors who are receptive to novel tools. The involvement of PGs in the OSCE improved their communication skills and helped overcome human resource limitations while manning various OSCE stations.

Nanoscale Direct Mapping of Noise Source Activities on Graphene Domains

Lee, Hyungwoo,Cho, Duckhyung,Shekhar, Shashank,Kim, Jeongsu,Park, Jaesung,Hong, Byung Hee,Hong, Seunghun American Chemical Society 2016 ACS NANO Vol.10 No.11

<P>An electrical noise is one of the key parameters determining the performance of modern electronic devices. However, it has been extremely difficult, if not impossible, to image localized noise sources or their activities in such devices. We report a 'noise spectral imaging' strategy to map the activities of localized noise sources in graphene domains. Using this method, we could quantitatively estimate sheet resistances and noise source densities inside graphene domains, on domain boundaries and on the edge of graphene. The results show high activities of noise sources and large sheet resistance values at the domain boundary and edge of graphene. Additionally, we showed that the top layer in double layer graphene had lower noises than single-layer graphene. This work provides valuable insights about the electrical noises of graphene. Furthermore, the capability to directly map noise sources in electronic channels can be a major breakthrough in electrical noise research in general.</P>

Nanoscale reduction of resistivity and charge trap activities induced by carbon nanotubes embedded in metal thin films

Shin, Narae,Kim, Jeongsu,Shekhar, Shashank,Yang, Myungjae,Hong, Seunghun Elsevier 2019 Carbon Vol.141 No.-

<P><B>Abstract</B></P> <P>We mapped the nanoscale reduction of resistivity and noise source activities induced by metallic single walled carbon nanotubes (m-SWCNTs) embedded in gold thin films. In this method, current and noise maps of m-SWCNTs/gold hybrid thin films were recorded using a conducting probe in contact with the surface, and the maps were utilized to estimate the nanoscale variation of resistivity (<I>ρ</I>) and the density distribution of noise sources (<I>N</I> <SUB>eff</SUB>) generating electrical noises in the hybrid thin film. The m-SWCNTs/gold hybrid thin films with a 5 nm thick gold layer exhibited 300% improved conductivity compared to that of pristine gold thin films. Additionally, the regions with embedded m-SWCNTs showed significantly reduced noise source densities compared with pristine gold film regions. These results clearly show that embedded m-SWCNTs improve the conductivity and reduce electrical noises of metallic electrodes. Interestingly, we observed that the <I>ρ</I> and the <I>N</I> <SUB>eff</SUB> on both m-SWCNTs/gold hybrid and pristine gold regions exhibited a scaling behavior of <I>ρ</I> ∝ <I>N</I> <SUB>eff</SUB> <SUP>0.5</SUP>, implying the hopping charge conduction and noise characteristics of m-SWCNTs/gold hybrid films. Our works can be a useful guideline for the development of high performance electrodes based on CNTs.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Diagnostic Significance of p38 Isoforms (p38α, p38β, p38γ, p38δ) in Head and Neck Squamous Cell Carcinoma: Comparative Serum Level Evaluation and Design of Novel Peptide Inhibitor Targeting the Same

Vishal Sahu,Lokesh Nigam,Vertica Agnihotri,Abhishek Gupta,Shashank Shekhar,Naidu Subbarao,Suman Bhaskar,Sharmistha Dey 대한암학회 2019 Cancer Research and Treatment Vol.51 No.1

Purpose The p38 mitogen-activated protein kinase (MAPKs) play a crucial role in the production of pro-inflammatory cytokines and over-expression of it increase cytokines which promote cancer. Among four isoforms, p38α has been well studied in head and neck squamous cell carcinoma (HNSCC) and other cancers as a therapeutic target. p38δ has recently emerged as a potential disease-specific drug target. Elevated serum p38α level in HNSCC was reported earlier from our lab. This study aims to estimate the levels of p38 MAPK-isoforms in the serum of HNSCC and design peptide inhibitor targeting the same. Materials and Methods Levels of p38 MAPK isoforms in the serum of HNSCC and healthy controls were quantified by surface plasmon resonance technology. The peptide inhibitor for p38 MAPK was designed by molecular modeling using Grid-based Ligand Docking with Energetics tools and compared with known specific inhibitors. Results We have observed highly elevated levels of all four isoforms of p38 MAPK in serum of HNSCC patients compared to the control group. Further, serum p38α, p38β, and p38δ levels were down regulated after therapy in follow-up patients, while p38γ showed no response to the therapy. Present study screened designed peptide WFYH as a specific inhibitor against p38δ. The specific inhibitor of p38δ was found to have no effect on p38α due to great structural difference at ATP binding pocket. Conclusion In this study, first time estimated the levels of p38 MAPK isoforms in the serum of HNSCC. It can be concluded that p38 MAPK isoforms can be a diagnostic and prognostic marker for HNSCC and p38δ as a therapeutic target.