Quantum transport in a gate-controlled p-n junction in 3-dimensional Dirac semimetal Cd3As2 nanostructures

Cd3As2, Dirac semimetal, p-n junction, quantum transportDirac semimetals such as Cd3As2 have drawn significant interest owing to their distinctive linear band structure. Several studies investigate the intriguing physical phenomena and electronic properties of these materials. In this study, Cd3As2 nanowires were synthesized using vapor transport method and transferred to a highly doped p-silicon substrate where recessed bottom gates were initially fabricated. Tuning of the bottom gates resulted to the realization of four conductance regimes forming p-n junctions in the nanowire device. Measurements at high magnetic fields show the formation of quantum dot in the bipolar regime. We find that the electrostatic potentials by the bottom gates as well as the suppression of Klein tunneling by magnetic field serves as tunnel barriers for the quantum confinement. Further investigation by performing both two-terminal and four-terminal measurements, allows the determination of contact resistance as well as electron and hole mobility. The ease in tunability of Cd3As2 makes it a practical candidate for functional quantum devices that require precise control of carrier density.open1. Theoretical Background 1 1.1 Dirac Semimetal 1 1.2 Cadmium Arsenide (Cd3As2) 3 1.3 p-n Junctions in Dirac Semimetal 4 1.4 Quantum Dot 6 1.5 Motivation and Potential Application 9 2. Suspended Nanowire Device Fabrication 10 2.1 Nanowire Growth 10 2.2 Bottom Gate Fabrication 11 2.3 Nanowire Transfer 12 2.4 Device Fabrication 13 3. Measurement Techniques 15 3.1 Initial Characterization and Sample Preparation 15 3.2 Measurement Schematic 17 3.3 Low Temperature Measurement Setup 17 3.4 He-3 Refrigeration System 19 4. Experimental Results 21 4.1 Device Specifications 21 4.2 p-n Junctions in Cd3As2 Nanostructures 22 4.3 Quantum Dot Formation 27 4.4 Suspended vs Non suspended structure 29 4.5 Contact Resistance Measurement 30 4.6 Fabry Perot Interference 31 4.7 Mobility by Four Terminal Measurement 33 5. Summary and Conclusion 35 Bibliography 36 Appendix 41 A. Fabrication Details and Recipes 41 A.1 Wafer Characteristics 41 A.2 Photopad Fabrication 41 A.3 Designing using KLayout and Layout Editor 42 A.4 Bottom Gate Fabrication 44 A.5 Device Fabrication 45 B. Pre Cooldown Sample Preparation 46 B.1 Wirebonding 46 B.2 He-3 Sample Exchange Procedure (Unloading and loading Sample) 47 Korean Summary 48 Acknowledgements 49MasterdCollectio

Responses of ‘Carabao’ Mango to 1-Methylcyclopropene in Delaying Ripening

1-methylcyclopropene (1-MCP) is widely used to extend the postharvest life of various fruits and vegetables. The effect of 1-MCP in sachets was tested on ‘Carabao’ mango to delay its ripening. Mature green mangoes of uniform quality harvested at 105 d after flower induction were sanitized with 200 μL L–1 sodium hypochlorite, air-dried, and packed inside bamboo baskets (5-kg capacity) lined with newspaper, then treated with different concentrations of 1-MCP (0, 1, 10, 140 μL L–1) in sachets. Once the 1-MCP sachet was placed in the center of the piled fruit, the bamboo basket was covered with five sheets of newspaper, secured with polypropylene twine and treated for 24 h under ambient room conditions. After treatment, the mangoes were stored in a cold room (19.0±1.2 °C, 90.7±9.3% RH) and its quality was evaluated at two-day intervals for up to ten days. Weight loss, firmness, total soluble solids (sweetness), visual quality, stem-end rot, anthracnose, and peel color (using a peel color index, L*, a*, b*, chroma, and hue angle) of the fruit were evaluated. Results showed that 140 μL L–1 1-MCP was able to maintain firmness and sweetness of the fruit, indications of delayed ripening, until 2 and 5 d after treatment, respectively. In addition, mango fruit treated with 1-MCP also had better visual quality than untreated fruit. 1-MCP was not able to slow down the peel color changes in the fruit but maintained the skin lightness (L*) until 5 d after treatment, particularly at 10 μL L–1 1-MCP. 1-MCP did not affect fruit weight loss and the onset of stem-end rot and anthracnose

Survival and Growth Rates of Rafted Sago (Metroxylon sagu Rottboell) Suckers as Influenced by Size and Trimming under Nursery Conditions

In Mindanao, the sago palms (Metroxylon sagu Rottb.) grow in the marsh as semi-wild stands. Attempts to grow suckers in garden soils showed low survival. This study aimed to determine the survival and growth rates of suckers based on stem base diameter (small, 4–9 cm, and large, 10–15 cm), trimmed or untrimmed, rafted for 0, 1, 2, and 3 months in the wild (Agusan del Sur) prior to polybagging in the nursery (Davao City). Holding suckers in bamboo rafts by floating in waterways for up to three months and trimmed of their leaves were shown to improve survival in the nursery. During rafting, a mean survival rate of 81% for trimmed suckers (both large and small) was observed when rafted for a month, but survival dropped to 40% when extended to three months. Untrimmed large and small suckers exhibited 60% mortality after a month of rafting. When extended to three months, large suckers were affected with a low 6% survival. In the nursery, rafted suckers (one or two months) did not vary with control (no rafting) in terms of survival of trimmed suckers. Rafting for three months improved survival rates to 62% for large and 74% for small samples. For untrimmed suckers, large and small suckers in rafts for three months obtained 100% and 67% survival, respectively; while 88% for small suckers for two months. Trimmed suckers rafted longest produced higher leaf count than non-rafted suckers regardless of base size

Effect of Ethanol and Perforations in Polyethylene Bags on the Postharvest and Antioxidant Quality of ‘Thai Round Green’ Eggplants

Eggplant is a horticulturally important crop that is also highly perishable. To delay the deterioration of eggplant fruit and antioxidant quality, the use of packaging with different perforations and ethanol in sachet were evaluated. Treatments included polyethylene bag (PEB, 0.04 mm) with 12 or 18 pin-prick perforations (0.5 mm) and with or without ethanol sachet (0 or 0.3 g). ‘Thai Round Green’ eggplants stored at 13 °C with average weight of 250.7+3.2 g per pack were evaluated every four days for twelve days. Antioxidants like 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, total phenolic content (TPC), and vitamin C were analyzed along with weight loss, respiration rate, and browning index. Browning increased while respiration rate decreased with storage. Ethanol was able to reduce fungal contamination only at eight days of storage. The use of PEB with 12 perforations for ‘Thai Round Green’ eggplants can maintain better fruit quality by reducing fungal contamination and weight loss. No consistent trend was shown for vitamin C. The use of PEB with 18 perforations decreased the TPC while addition of ethanol increased browning of fruit. Addition of ethanol in PEB with 12 perforations increased both the TPC of pedicel and DPPH of fruit at four days. Respiration of eggplant was initially higher in PEB with 12 perforations, but this decreased at eight days of storage. Ethanol and PEB with 12 perforations showed potential in maintaining the quality of eggplant at 13 °C for four to eight days

Effect of Delayed Heat Treatment on the Postharvest Characteristics of ‘Carabao’ Mango

Hot water treatment (HWT) controls postharvest diseases in ‘Carabao’ mango, but delays in treatment could influence fruit quality. In this study, ‘Carabao’ mango fruit were subjected to different heat treatments (Rapid Hot Water Treatment [RHWT] at 60 ºC for 35–60 sec; HWT, 52–55 ºC for 5 min; or HWT, 52–55 ºC for 10 min) within 24 or after 24 h from harvest. Fruit were initially sanitized with 200 ppm sodium hypochlorite and stored in 20 ºC after heat treatment. Visual quality, peel color, degree of decay, weight loss, total soluble solids (TSS), firmness, days to table ripe stage, days to onset of decay, and shelf life were regularly observed. HWT at 52–55 ºC for 5 or 10 min extended the shelf life of mango fruit for one and two days, respectively, due to lesser diseases and delayed expression of anthracnose. Time to heat treatment whether within 24 or after 24 h from harvest did not affect disease incidence, but fruit treated within 24 h showed a slight delay in the onset of diseases compared to treatment after 24 h. Except for RHWT, fruit ripening, indicated by color change from green to yellow and time to reach table ripe stage, was hastened by heat treatments, especially in HWT, for 10 min. Rapid ripening of fruit exposed to HWT, indicated also by lower firmness and high TSS at 6 d after treatment, resulted in higher weight loss compared to untreated fruit. HWT can translate to more available visually acceptable and disease-free mangoes in the market

Food Handling Practices for Fresh-Cut Vegetables at Wet Markets and Supermarkets in Davao City, Philippines

Fresh-cuts, either ready-to-cook (RTC) or ready-to-eat (RTE) fruits and vegetables, are becoming more popular due to consumers’ increasing demand for convenient and healthy foods. This paper aimed to document different fresh-cut vegetables available in wet markets and supermarkets in Davao City, Philippines, to differentiate fresh-cut processing practices between the two locations, and to identify some inadequacies in their practices. Overall, the fresh-cuts were available as either monotype (e.g. coconut pith, squash, and immature jackfruit) or mixed (e.g. pinakbet and chop suey). With regards to the pre- and post-cutting treatment, water was not always used since consumers were expected to wash them before cooking and/or eating. Water used for washing was also reused, which could be a source of contamination. During processing, inappropriate craft cutter blades were sometimes used in wet markets, which could lead to more produce injury that may result in more browning. Moreover, packaging was mostly used only upon purchase in the wet markets whereas supermarkets had more pre-packed options. Lastly, an evident observation was the temperature abuse (above 5°C) during storage in both locations. This poses a threat of pathogen contamination especially since visual indications of deterioration are not always obvious. Thus, interventions are recommended to educate fresh-cut processors in both wet markets and supermarkets about useful techniques in preserving the quality and safety of fresh-cut vegetables. Additional information on the degree of microbial contamination and shelf-life of these products may also aid in generating applicable food safety strategies. Keywords: fresh-cut practices · minimal processing · vegetable crop

The use of brick-walled evaporative cooler for storage of tomato

A cost-effective alternative to cold storage is the brick-walled evaporative cooler (BEC). The effects of BEC on mature green and breaker ‘Diamante Max’ tomatoes were assessed. Two trials were carried out at ambient conditions with (i) 27.13±0.78 °C and 80.89±4.47%RH; (ii) 26.93±0.87 °C and 80.05±5.20% RH and with BEC (i) 25.49±0.58 °C and 99.90±0.10% RH; (ii) 25.42±0.90 °C and 97.75±3.25% RH. BEC-stored tomatoes showed 10.36% lesser weight loss, lesser decay incidence, redder color and better visual quality compared to control fruit. The higher L* and hue of around 90 in ambient-stored tomatoes indicated a lighter color as fruit turned to yellow compared to a lower L* and hue in BEC indicating a darker red color. An increased chroma was recorded as fruit turned from green or breaker to yellow, orange, or light red while the values of a* became negative. The BEC maintained the firmness and total soluble solids, especially in mature green tomatoes. After 49 days of storage, 61.8% of the fruit stored in the BEC were marketable compared to 23.3% in ambient conditions. The BEC system showed 27.16% higher annual benefit over cost than the ambient storage conditions. Thus, the BEC system can potentially maintain the quality of ‘Diamante Max’ tomatoes

Color Changes and Quality Maintenance on Tomato (Solanum lycopersicum L. cv. Diamante Max) Using a Brick-Walled Evaporative Cooler

Postharvest quality in tomatoes is influenced by temperature and relative humidity. Though expensive, storage in low temperature is the most effective method of maintaining quality of produce longer. Evaporative cooling is a less costly alternative option. A brick-walled evaporative cooling (BEC) system converts warm air from the ambient environment into cold air as it passes through a moistened insulation between the double-walled BEC. The effects of the storage environment in the BEC were evaluated using mature green and breaker stages of tomato cultivar Diamante Max from November 2018 to January 2019. The tomatoes were stored at ambient (27.10±0.67 °C and 81.85±2.51% RH) and BEC (25.48±0.56 °C and 99.91±1.54% RH) conditions in. Tomatoes stored in BEC showed 10.36% lesser weight loss, lesser decay incidence, redder color, and better visual quality as compared to fruit stored under ambient conditions. BEC was able to maintain firmness and total soluble solids especially in mature green tomatoes. After 49 d of storage, 61.8% of the fruit stored in the BEC were marketable compared to 23.3% in ambient conditions. When used for a year, the computed benefit over cost value of the BEC storage system was 29.11% higher than the ambient storage system. Thus, the BEC storage system can help maintain the quality of Diamante Max tomatoes during storage in the temperature and relative humidity conditions as above

Yellowing and Granulation of ‘Magallanes’ Pummelo (Citrus maxima [Burm. ex Rumph] Merr) Fruit as Influenced by 1-Methylcyclopropene

The yellowing, granulation, and other physico-chemical characteristics of ‘Magallanes’ pummelo [Citrus maxima (Burm. ex Rumph) Merr] fruit treated with 1-methylcyclopene (1-MCP) for 8 h at 0, 50, or 500 nL L-1) were evaluated. L*, a*, b*, chroma and hue values gradually increased during 12 weeks of storage at ambient conditions (26.4 °C, 83.3% RH). Rind color became more vivid and yellow. Decay, juice content, and electrolyte leakage were similar among treatments. However, weight loss, visual quality, shriveling, pH, total soluble solids (TSS), titratable acidity (TA), and TSS:TA were affected by 1-MCP. Weight loss was lowered by 50 nL L-1 at 6 weeks after treatment (WAT). Treated fruit had better visual quality than control fruit at 6 and 9 WAT because of lesser shriveling. At 12 WAT, fruit treated with 500 nL L-1 exhibited highest %TA and lowest TSS:TA ratio. Granulation or vesicle drying was most frequently observed initially in the middle and stylar ends of fruit segments. Granulated samples exhibited higher pH and lower TSS than the non-granulated segments. 1-MCP but not storage period showed similar yellowing and granulation of ‘Magallanes’ pummelo as the control lot. 1-MCP maintained a good fruit visual quality longer

Short-term Evaporative Cooling Extends Shelf Life of Two Sweet Pepper Cultivars, ‘Sweet Cayene’ and ‘Sultan’

In the Philippines, postharvest losses for vegetables are estimated to reach 40%, which can be attributed to improper handling and lack of adequate storage facilities. Although refrigeration is the best storage option, it is expensive and energy extensive. An alternative short-term non-refrigerated storage option is through the use of evaporative coolers. A 60 × 40 × 29–inch wood cabinet with outer framing and three shelves made of aluminum and two layers of jute sack for walls served as evaporative cooler for this study. Water flowed from a container placed on top of the cabinet wetting the walls. Two sweet pepper cultivars (‘Sweet Cayenne’ and ‘Sultan’) at mature green stage were stored under ambient (28.74±0.94 °C, 65.68±7.43% RH) and evaporative cooling (23.91±3.85 °C, 93.84±9.33% RH) conditions to assess their effects on the physico-chemical properties of the produce. Both cultivars stored in the evaporative cooler significantly showed reduced weight loss, slower decline in moisture content, longer retention of firmness, and better visual quality rating. On the other hand, rapid changes were observed in titratable acidity, total soluble solids, and ascorbic acid in both cultivars stored at ambient condition indicating a faster rate of ripening. Very slight decay with longer shelf life were observed in both cultivars stored in the evaporative cooler as ‘Smooth Cayenne’ and ‘Sultan’ reached its end of shelf life at days 18 and 15, respectively, while this was only at days 9 and 6 for those that were stored in ambient conditions