Risk Factors Associated with Ninety Day Readmission in Chronic Obstructive Pulmonary Disease Exacerbation at a Tertiary Care Hospital: A retrospective cohort study

Background Chronic obstructive pulmonary disease (COPD) exacerbation is a leading cause of frequent hospital admission. Globally, several studies have reported potential risk factors associated with COPD exacerbations which are largely unknown in Nepalese health care setting. Objective To identify the risk factors associated with hospital readmission within ninety days of discharge in acute COPD exacerbation. Method This is a hospital based retrospective cohort study conducted at Tribhuvan University Teaching Hospital. COPD patients admitted in respiratory ward from August 2019 to November 2019 were followed up till 90 days after discharge. Logistic regression analysis was performed at 95% Confidence Interval (CI) to identify risk factors for readmission in COPD exacerbation. Statistical analysis was performed using SPSS version 20.0. Result Of total 86 patients hospitalized for COPD, 42 (48.8%) had at least one subsequent readmission during post-discharge follow-up period of 90 days. Mean age of patients was 70.55±10.98 years. There were 45 (52.3%) males. Logistic regression analysis revealed preadmission domiciliary oxygen use (Odds Ratio (OR) 2.93; 95% CI 1.195- 7.202; p=0.019), admission in intensive care unit (ICU) (OR 3.060; 95% CI 1.145- 8.179; p=0.026), previous hospital admission for COPD exacerbation (OR 3.230; 95% CI 1.219-8.556; p=0.018), age (OR 0.946; 95% CI 0.905-0.988; p=0.012) and duration of hospital stay (OR 0.901; 95% CI 0.819-0.992; p=0.034) were independently associated with ninety day readmission in COPD patients. Conclusion Five clinical factors were found to be independently associated with COPD readmission in this study. Large multi-centre study at various health care levels is recommended to validate the potential risk factors in different populations and health care settings in Nepal.

Direct conversion of carbon nanofibers and nanotubes into diamond nanofibers and the subsequent growth of large-sized diamonds

We report a pulsed laser annealing method to convert carbon fibers and nanotubes into diamond fibers at ambient temperature and pressure in air. The conversion of carbon nanofibers and nanotubes into diamond nanofibers involves melting in a super undercooled state using nanosecond laser pulses, and quenching rapidly to convert into phase-pure diamond. The conversion process occurs at ambient temperature and pressure, and can be carried out in air. The structure of diamond fibers has been confirmed by selected-area electron diffraction in transmission electron microscopy, electron-back-scatter-diffraction in high-resolution scanning electron microscopy, all showing characteristic diffraction lines for the diamond structure. The bonding characteristics were determined by Raman spectroscopy with a strong peak near 1332 cm-1, and high-resolution electron-energy-loss spectroscopy in transmission electron microscopy with a characteristic peak at 292 eV for σ* for sp3 bonding and the absence of π* for sp2 bonding. The Raman peak at 1332 cm-1 downshifts to 1321 cm-1 for diamond nanofibers due to the phonon confinement in nanodiamonds. These laser-treated carbon fibers with diamond seeds are used to grow larger diamond crystallites further by using standard hot-filament chemical vapor deposition (HFCVD). We compare these results with those obtained without laser treating the carbon fibers. The details of diamond conversion and HFCVD growth are presented in this paper.

Unresolving Pneumonia with Pleural effusion: Pulmonary Paragonimiasis

Paragonimiasis is a zoonosis caused by many species of Paragonimus commonly P. westermani. Human get infected by eating raw, salted, pickled, smoked, partially cooked crustaceans (crayfish or crabs). Clinical manifestations ranges from non-specific symptoms like pain abdomen, diarrhea, urticarial rashes, fever to pleuropulmonary symptoms like cough, hemoptysis, chest pain and dyspnea. A 48 years, female presented at TUTH emergency with fever on and off for nine months, cough and shortness of breath for three months, lethargy, malaise and urticaria with history of raw crab intake one month prior to the onset of symptoms. Blood and pleural fluid analysis revealed raised total counts with eosinophilia and x-ray showed bilateral infiltration of lower lobes with pleural effusion. Diagnosis was confirmed by microscopic examination of sputum for Paragonimus. She responded well to Praziquantel. Pulmonary paragonimiasis must be considered in the differential diagnosis of unresolving pneumonia and unexplained hypereosinophilia.

Changing picture of acute kidney injury in pregnancy: Study of 259 cases over a period of 33 years

The incidence of acute kidney injury (AKI) in pregnancy is declining in developing countries but still remains a major cause of maternal and fetal morbidity and mortality. The aim of the study was to analyze the changing trends in pregnancy related AKI (PR-AKI) over a period of thirty-three years. Clinical characteristics of PR-AKI with respect to incidence, etiology and fetal and maternal outcomes were compared in three study periods, namely 1982-1991,1992-2002 and 2003-2014. The incidence of PR-AKI decreased to 10.4% in 1992-2002, from 15.2% in 1982-1991, with declining trend continuing in 2003-2014 (4.68%).Postabortal AKI decreased to 1.49% in 2003-2014 from 9.4% in 1982-1991of total AKI cases. The AKI related to puerperal sepsis increased to 1.56% of all AKI cases in 2003-2014 from 1.4% in 1982-1991. Preeclampsia/eclampsia associated AKI decreased from 3.5% of total AKI cases in 1982-1991 to 0.54% in 2003-2014. Pregnancy associated – thrombotic microangiopathy and acute fatty liver of pregnancy were uncommon causes of AKI. Hyperemesis gravidarum associated AKI was not observed in our study. Incidence of renal cortical necrosis (RCN) decreased to 1.4% in 2003-2014 from 17% in 1982-1991.Maternal mortality reduced to 5.79% from initial high value 20% in 1982-1991. The progression of PR-AKI to ESRD decreased to1.4% in 2003-2014 from 6.15% in 1982-1991. The incidence of PR-AKI has decreased over last three decades, mainly due to decrease in incidence of postabortal AKI. Puerperal sepsis and obstetric hemorrhage were the major causes of PR-AKI followed by preeclampsia in late pregnancy. Maternal mortality and incidence and severity of RCN have significantly decreased in PR-AKI. The progression to CKD and ESRD has decreased in women with AKI in pregnancy in recent decade. However, the perinatal mortality did not change throughout study period.

Pulmonary azygous lobe--an anatomical variant

Pulmonary azygous lobe is one of the common lung malformations. There is only few article about azygous lobe. Its a small accessory lobe sometimes found on the upper part of the right lung, separated from the rest of the upper lobe by a deep groove lodging the ayzygous vein. This reports decribes the presence of azygous lobe, a rare anatomical variant, encounted during chest x-ray discussion. We describe here the anatomical basis and the clinical significance of azygous lobe.

Ritual scalp shaving-a risk factor for community acquired late onset neonatal sepsis

Background Neonatal sepsis is one of the major causes of morbidity and mortality at the community and hospital levels in India. There are several community practices associated with and contributing to Neonatal sepsis, especially late onset variety.Objective To analyze whether scalp shaving is an independent risk factor associated with community acquired late onset neonatal sepsis and the causative organism responsible.Methods This was a prospective, non-interventional, observational study. The study was conducted at two tertiary teaching hospitals in Eastern India from 1st May 2010 to 30th April 2011. A total of 382 babies were diagnosed as Late Onset Neonatal Sepsis and 410 , age and sex matched controls were taken from the Well Baby and Immunization clinics. The patients were clinically screened for sepsis and "septic screen" and blood, urine and CSF cultures sent, as needed.Results History of scalp shaving was present in 46(12.04%) out of 382 cases of Late Onset Neonatal Sepsis as compared to 20(4.87%) of 410 matched community controls, the difference was statistically significant (p<0.005). Positive blood cultures were obtained in 20(43.48%) out of 46 scalp shaven babies as compared to 118(35.11%) out of 336 non scalp shaven babies. The commonest organism in babies with scalp shaving was found to be methicillin resistant Staphylococcus aureus(MRSA), whereas the most common organism in non scalp shaven babies was Klebsiella pnuemoniae.Conclusion Scalp shaving appears to be an independent variable associated with community acquired Late Onset Neonatal Sepsis.Journal of College of Medical Sciences-Nepal, 2013, Vol-9, No-3, 35-44

Prevalence and correction of near vision impairment at Kaski, Nepal

INTRODUCTION

Presbyopia is an important cause of avoidable visual disability.

OBJECTIVE

To estimate the prevalence of near vision impairment and spectacle coverage among middle and older-aged adults in rural Nepal.

MATERIALS AND METHODS

The surveys was carried out among the people of age 35 and over in randomly-selected cluster samples in rural settings of Kaski district of western Nepal, Near visual acuity, with and without presenting near correction, was measured at 40 cm using a LogMAR near vision tumbling E chart under ambient indoor lighting. Subjects with uncorrected binocular distance vision of 20/40 or worse were refracted and those with near vision of 20/40 or worse tested with plus sphere to obtain the best-corrected binocular near visual acuity.

RESULTS

A total of 2,360 persons aged 35 years and over were enumerated and 2,156 (91.3%) were examined. The age- and gender-standardized prevalence of uncorrected near visual impairment (vision of 20/40 or worse) in study population was found to be 66.1 %. Near vision could not be corrected (>20/40) even after distance and near vision correction in 6.4 % . Using the multiple logistic regression models, uncorrected visual impairment was associated with an older age (odds ratio [OR] = 1.13, P less than 0.001) and a lower educational level (OR = 1.11, P = 0.01) was less associated with female gender (OR = 0.72, P = 0.038). Over 90 % of people with near visual impairment did not have spectacles.

CONCLUSION

The prevalence of presbyopia appears to be higher with an earlier onset and over 90 % of people in need of near correction do not have spectacles in this setting.

A fatal presentation of dermatomyositis

Dermatomyositis (DM) is an autoimmune disease that mainly affects the skin, muscle, and lung. The pathogenesis of skin inflammation in DM is not well understood. We present a 40-year-old male who presented with four months history of generalized skin lesion, pain and weakness. He had elevated transaminases with detectable muscle weakness. This case highlights the need to consider dermatomyositis with skin lesion and weakness; and the use of aggressive immunosuppressive therapies due to its associated vasculopathies.

Spectrum of diseases in a medical ward of a teaching hospital in a developing country

Communicable and respiratory tract diseases especially chronic obstructive pulmonary diseases are the main reasons of admission in medical ward of low and middle income countries. This is different from the developed countries where non communicable diseases are the main reasons of hospital admission. In developing countries the data of hospital admission are still lacking. Therefore this study will help us to assess the common patterns of diseases admitted in a medical ward, the average length of hospital stay etc. The record of 1040 hospitalized patients in medical ward was analyzed for the period of six months from Jan 2010 to Jun 2010. Patient’s medical records were retrieved and data analysis was done to obtain age, sex, common diagnosis, the affected system and the duration of the hospital stay. The data was analyzed by using SPSSV 16. After reviewing the data the most common age of patients being admitted were between 46-65 years (31.5%) followed by more than 65 years (25%) between 26-45 years (21.28%) and less than 25 years (21.28%). Among the admitted patients females were more than the males except in neurolog ward. The most effected system was respiratory (31.73 %),and the most common diagnosis was Chronic obstructive pulmonary diseases (23.17%). The next common system involved was gastroenterology including liver (18.64%) ,genitourinary (12.01%), cardiovascular ( 11.34%), neurology (9.23%), endocrine (4.80%) hematology (2.30%). The cause for hospital admission by infection in different system was (30.08%) The average duration of hospital stay of the patients was less than 7 days. The respiratory diseases and the infectious disease are the most common disease in Nepal. The communicable diseases still hold a greater position, while non communicable diseases are main reasons for admission to the medical wards in developed countries. Journal of College of Medical Sciences-Nepal,2012,Vol-8,No-2, 7-11 DOI: http://dx.doi.org/10.3126/jcmsn.v8i2.6831

Study of clinical profile of megaloblastic anemia: An experience of six year at Kathmandu University Hospital, Dhulikhel

Megaloblastic anemia is not uncommon, however varied of presentation makes difficult to come to conclusion. It’s more difficult when resources are limited. In this back ground clinical features of megaloblastic anemia are very important for diagnosis and treatment. It is a retrospective analysis of data from December 2003 to September 2009. During the period, bone marrow aspiration was done for analysis of cause and type of anemia.A total of 14 cases bone marrow findings was consistent with megaloblastic anemia. These reports were taken into consideration after pathologist impression. Serum Vitamin B12 and RBC folate were not done in view of limited resources and financial constrain. In the analysis 14 (11.96%) bone marrow findings were consistent with megaloblastic anemia. Regarding clinical presentation; pallor was 13 (92.85%) followed by glossitis 5 (35.71%) and Jaundice 5 (35.71%), paresthesia 3 (21.42%), and pigmentation, ataxia, confusion each case (7.14 %). Mostly the patients were between the 21- 40 years of age. Megloblastic anemia is common clinical problem with pallor and glossitis as major presentation. However some had neurological features. This disease can be diagnosed and treated on the basis of bone marrow aspiration when resources are limited.Journal of College of Medical Sciences-Nepal, 2011, Vol-7, No-2, 41-44DOI: http://dx.doi.org/10.3126/jcmsn.v7i2.6679

Understanding of tobacco and lung cancer among medical students in Kathmandu University School of Medical Sciences (KUSMS)

BACKGROUND

Often, lung cancer is diagnosed at terminal stages. Poor awareness about the symptoms or risk factors of lung cancer among medics may be one of the factors for delayed diagnosis.

OBJECTIVE

We explored the knowledge of medical students and their behavior with the patients of lung cancer.

METHOD

Qualitative and quantitative approaches were used for data collection from 153 medical student of Kathmandu University School of Medical Sciences from December 2011 to May 2012.

RESULTS

Among the results, eighty-nine students had over 80% knowledge of the 14 cancer warning signs, among them 83% knew the nine risk factors for lung cancer. Twenty-three students told lung cancer can be hereditary. Sixty five percent of all participants believed that lung cancer can be detected at early stage; of them 81% told that it can be treated. About 24% of the total students were current or exsmokers and about half of them believed that lung cancer does not occur in light smokers. Only 10% have heard of Framework Convention on Tobacco Control in Nepal.

CONCLUSION

Study finds that all medical students who know about any cancers may not necessarily have knowledge about lung cancers. Their perception about the cause of lung cancer may be influenced by their smoking behavior and there was little knowledge of public health measures for smoking control. Awareness about national policies needs to be increased.

Spatial and temporal diversity of begomoviral complexes in papayas with leaf curl disease

Old World, monopartite begomoviruses associated with satellite DNA β were observed in papaya showing symptoms of leaf curl disease sampled randomly over five years from within a radius of 250 km in north-central India. Three groups of DNA A sequences were evident. One group resembled chili leaf curl virus infecting tomatoes (ChiLCuV). Another group resembled tomato leaf curl New Delhi virus (ToLCuNDV). The third group was novel (tentatively named papaya leaf crumple virus, PaLCrV), with less than 89% identity to known begomovirus sequences in the GenBank database. At least seven DNA A sequences were putative recombinants. The AC4-encoding regions exhibited highest numbers of non-synonymous substitutions. Most DNA β sequences resembled tomato leaf curl virus-associated DNA βs. A few DNA β sequences were similar to that of croton yellow vein mosaic virus-associated DNA β (CroYVMVβ). One DNA β sequence was novel and showed <65% similarity to its counterparts. Mixed infections and sequence diversity among 25 cloned av1 genes indicated that papayas grown in plantations, kitchen gardens and feral patches in the region are vulnerable to disease outbreak. No geographic or temporal patterns were discernable in the distribution of these viruses.

Microalbuminuria in diabetes mellitus: Association with age, sex, weight, and creatinine clearance

Studies in the Western literature show a linear relationship between degree of microalbuminuria and body mass index (BMI), blood pressure, and duration of diabetes. This study was aimed to determine the correlation of microalbuminuria with age, sex, duration of diabetes, BMI, and creatinine clearance in type-2 diabetics in Indian population. One hundred patients (59 males and 41 females) with type-2 diabetes mellitus of duration six months or more and negative for albumin in urine by albustic method were included in the study. Detailed clinical history was taken followed by a thorough physical examination that included neurological examination in the selected patients. Micral test was used for estimation of microalbuminuria. Overall prevalence of microalbuminuria in the present study was 37%. Among the patients with microalbuminuria, 20 were males and 17 were females. Pearson correlation of microalbuminuria with age showed statistically significant linear relationship. Gender-wise correlation analysis of microalbuminuria failed to show any statistical significance. Correlation of microalbuminuria with BMI was also not significant (r = 0.063, P > 0.05). Creatinine clearance negatively correlated with microalbuminuria, but this was statistically insignificant. There was a statistically significant correlation of microalbuminuria with duration of diabetes. Prevalence of microalbuminuria is around 37% in type-2 diabetes mellitus. Incidence of microalbuminuria increases with age as well as with increased duration of diabetes mellitus. There is no effect of BMI and sex on the prevalence of microalbuminuria.

Upper gastro-intestinal bleeding: aetiology and demographic profile based on endoscopic examination at Dhulikhel Hospital, Kathmandu University Hospital

BACKGROUND

The upper gastrointestinal bleeding (UGIB) is defined as bleeding within the intraluminal gastrointestinal tract from any location between the upper oesophagus to the duodenum at the ligament of Treitz. It is one of the important medical emergencies worldwide.

OBJECTIVE

The objective of this study is to study the aetiology of upper gastrointestinal bleeding based on endoscopic examination findings in patients of various demographic characteristics.

MATERIALS AND METHODS

This is a retrospective observational study. The endoscopic record book from 2007 January to 2009 October was reviewed for all the cases who underwent oesophago-gastro-duodenoscopic examination for upper GI bleeding. The clinico-epidemiological data of all the patients was reviewed and analyzed in concert with the aetiology of bleeding.

RESULTS

A total of 90 patients (58 males, 32 females; mean age 45.32+ 18.47 years) of upper gastrointestinal bleeding was studied and analyzed in terms of aetiology of bleeding and demographic profile. Among the ethnic groups, Aryan 46 (51%) was the most common ethnic group to have upper GI bleeding followed by Newars 24 (27%), Mongolians 16 (18%), Dalits 3 (3%) and others 1 (1%). Out of 90 patients, 47( 52.2%) cases was less than 45 years of age, 30(33.3%) of 46 to 65 age ; and 13(14.4 %) more than 65 years of age. Gastric ulcer 23(25.6%) was the most common endoscopic finding, followed by oesophageal varices 14 (15.6%), acute erosive/haemorrhagic gastropathy 11 (12.2%), duodenal ulcer 9(10%), growth 7(7.8%), vascular lesions 3(3.3%), Mallory-Weiss tear 1(1.1%), fundal varices 1(1.1%) and, no cause was identified in 21(23.3%) cases. The peptic ulcer bleeding was the most common finding in Aryan 22(47.9%), whereas oesophageal varices and growth were more common in Newar 7(29.2%) and 3 (12.5%) respectively.

CONCLUSION

Peptic ulcer disease is the most common cause of upper GI bleeding which was most commonly found in Aryan population; followed by oesophageal varices and growth as second and third most common causes and were more prevalent in Newar and Mongolian people.

Mercury contamination in the riparian zones along the East Fork Poplar Creek at Oak Ridge

Oak Ridge (Tennessee, USA) has a history of mercury (Hg) contamination in its aquatic and soil environment associated with past nuclear-weapons production activities at its Department of Energy (DOE) sites. Three different riparian zones along the Lower East Fork Poplar Creek were investigated in order to study Hg distribution and transformation in surface soils. The surface soil samples collected from these areas showed higher total Hg on an average (129.08 mg/kg) and higher total organic carbon (5.50%) in the upstream soils compared to the other two downstream locations that contained only 31.78 and 19.98 mg/kg total Hg and 2.88% and 1.65% of TOC on average, respectively. Further, methyl Hg concentrations were also comparatively higher in case of the upstream soils (30.10 μg/kg) than that of the downstream sites (5.69 and 4.05 μg/kg). The study showed a plume-like dispersion of Hg in the terrestrial environment along the creek, with decreasing Hg concentrations with distance from the Hg source zone. Also, the transformation of Hg in the soils was found to have been influenced by the soil TOC contents.

Mercury uptake and translocation in Impatiens walleriana plants grown in the contaminated soil from Oak Ridge

Mercury (Hg) contaminated soils from Oak Ridge, Tennessee were investigated for phytoavailability of mercury as measured by degree of Hg translocation in aboveground biomass of Impatiens walleriana plants grown in the soils. After 90 days of incubation, results revealed a higher concentration of total Hg in the leaves than in the flowers or the stems. Plants that were grown in the soils with higher Hg concentrations showed significantly higher Hg uptake and translocation in the aboveground plant-biomass, and the correlation with the initial soil-Hg was significant for the leaves and the stems in the plants that were tested. On an average, only 4.06 microg of Hg could be found in the above ground plant biomass of all the plants, compared to an average 3673.50 microg of initial total Hg concentrations in these soils. Statistical analysis revealed a greater affinity of Hg for the soil carbon, which supported the finding of this study on low soil Hg bioavailability.

Unusual site of metastasis of bronchogenic carcinoma

Metastasis of bronchogenic carcinoma to the chest wall and axillary lymphnodes is a rare occurrence. This study reports the case of a patient presenting with chest wall swelling as initial symptom which on evaluation was found to be a lymphnode metastasis. The patient also had axillary lymphnode metastasis on the same side as the chest swelling with a contralateral pleural effusion. Here, we discuss the pathways and possible mechanisms of contra lateral axillary and chest wall lymphnode involvement without ispilateral nodal involvement in bronchogenic carcinoma.

Young people's knowledge, attitude, and behaviour on STI/HIV/AIDS in the context of Nepal: a systematic review

BACKGROUND

Sexual and reproductive health of young people has become a major health problem in recent decades. Recent and rapidly increasing Human Immune Deficiency Virus (HIV) rates show an urgent need for Sexually Transmitted Infections (STIs) and HIV prevention interventions in Nepal.

OBJECTIVES

This paper attempts to assess knowledge, attitude and behaviour on STIs/HIV/AIDS in the context of young peoples of Nepal.

METHOD AND MATERIAL

A systematic review based on the available literature was carried out including both qualitative and quantitative studies.

RESULTS

Our findings indicate that the overall knowledge regarding STIs and HIV/AIDS is high although the level of knowledge seems to differ according to education, gender, and area of residence. Knowledge about condoms was also very high but practice of correct and consistent use in premarital and extramarital sexual relations with non-regular partners seems to be lower. The overall sexual behaviour among young people is unsafe.

CONCLUSION

This suggests that young people's sexual and reproductive health issues need to be further addressed and explored in order to promote safer and responsible sexual behaviour.

Lipid Profile in a Tertiary Care Center

INTRODUCTION: Lipid profile is changing with changing developmental status and lifestyle in less developed countries and coronary artery disease risk factor is rising. The aim of the study is to find the lipid pattern in Department of Medicine in tertiary care hospital. METHODS: An observational prospective study was conducted in 408 subjects from January 2009 to February 2010. Study subjects were selected irrespective of co-morbid condition and coronary risk factors. RESULTS: The mean triglycerides, cholesterol, LDL, HDL were 138.3 +/- 78.3 mg/dl, 180.2 +/- 53.7 mg/dl, 113.8 +/- 41.2 mg/dl, 40.1 +/- 10.1 mg/dl respectively. The Triglycerides (>140 mg/dl), Cholesterol (>250 mg/dl), LDL (>92 mg/dl), HDL (<45mg/dl) were 35.5%, 7.6%, 67.9%, 76% respectively. CONCLUSIONS: Lipid profile is becoming atherogenic with high triglyceride, high LDL and low HDL being the most common abnormality. An epidemiological study is recommended to understand the true burden of the disease in the community.  KEYWORDS: atherogenic, cholestrol, coronary artery diseases, lipid profile, triglyceride. 

Lipid profile in a tertiary care center

INTRODUCTION

Lipid profile is changing with changing developmental status and lifestyle in less developed countries and coronary artery disease risk factor is rising. The aim of the study is to find the lipid pattern in Department of Medicine in tertiary care hospital.

METHODS

An observational prospective study was conducted in 408 subjects from January 2009 to February 2010. Study subjects were selected irrespective of co-morbid condition and coronary risk factors.

RESULTS

The mean triglycerides, cholesterol, LDL, HDL were 138.3 +/- 78.3 mg/dl, 180.2 +/- 53.7 mg/dl, 113.8 +/- 41.2 mg/dl, 40.1 +/- 10.1 mg/dl respectively. The Triglycerides (>140 mg/dl), Cholesterol (>250 mg/dl), LDL (>92 mg/dl), HDL (<45mg/dl) were 35.5%, 7.6%, 67.9%, 76% respectively.

CONCLUSIONS

Lipid profile is becoming atherogenic with high triglyceride, high LDL and low HDL being the most common abnormality. An epidemiological study is recommended to understand the true burden of the disease in the community.

Comparative Raman and HRTEM study of nanostructured GaN nucleation layers and device layers on sapphire (0001)

Raman spectroscopy in conjunction with high-resolution transmission electron microscopy (HRTEM) has been used to study structural characteristics and strain distribution of the nanostructured GaN nucleation layer (NL) and the GaN device layer on (0001) sapphire substrates used for light-emitting diodes and lasers. Raman peaks corresponding to the cubic and the hexagonal phase of GaN are observed in the Raman spectrum from 15 nm and 45 nm NLs. A comparison of the peak intensities for the cubic and hexagonal phases of GaN in the NLs suggests that the cubic phase is dominant in the 15 nm NL and the hexagonal phase in the 45 nm NL. An increase in the density of stacking faults in the metastable cubic GaN (c-GaN) phase with increasing growth time lowers the system energy as well as locally converts c-GaN phase into hexagonal GaN (h-GaN). It also explains the observation of the more intense peaks of h-GaN in the 45 nm NL compared to c-GaN peaks. For the sample wherein an h-GaN device layer was grown at higher temperatures on the NL, narrow Raman peaks corresponding to only h-GaN were observed, confirming the high-quality of the films. The peak shift of the E2(H)(LO) mode of h-GaN in the NLs and the h-GaN film suggests the presence of a tensile stress in the NL which is attributed to defects such as stacking faults and twins, and a compressive stress in high-temperature grown h-GaN film which is attributed to the thermal-expansion mismatch between the film and the substrate. The peak shifts of the substrate also reveal that during the low temperature growth of the NL the substrate is under a compressive stress which is attributed to defects in the NL and during the high temperature growth of the device layer, there is a tensile strain in the substrate as expected from differences in coefficients of thermal expansion of the film and the substrate during the cooling cycle.

Nanostructured GaN nucleation layer for light-emitting diodes

This paper addresses the formation of nanostructured gallium nitride nucleation (NL) or initial layer (IL), which is necessary to obtain a smooth surface morphology and reduce defects in h-GaN layers for light-emitting diodes and lasers. From detailed X-ray and HR-TEM studies, researchers determined that this layer consists of nanostructured grains with average grain size of 25 nm, which are separated by small-angle grain boundaries (with misorientation approximately 1 degrees), known as subgrain boundaries. Thus NL is considered to be single-crystal layer with mosaicity of about 1 degrees. These nc grains are mostly faulted cubic GaN (c-GaN) and a small fraction of unfaulted c-GaN. This unfaulted Zinc-blende c-GaN, which is considered a nonequilibrium phase, often appears as embedded or occluded within the faulted c-GaN. The NL layer contained in-plane tensile strain, presumably arising from defects due to island coalescence during Volmer-Weber growth. The 10L X-ray scans showed c-GaN fraction to be over 63% and the rest h-GaN. The NL layer grows epitaxially with the (0001) sapphire substrate by domain matching epitaxy, and this epitaxial relationship is remarkably maintained when c-GaN converts into h-GaN during high-temperature growth.